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Sample records for stratified galactic disks

  1. The age of the galactic disk

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    Sandage, A.

    1988-07-01

    The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc

  2. Accretion disks in active galactic nuclei

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    Shields, G.A.

    1989-01-01

    Active galactic nuclei (AGN) have taunted astrophysicists for a quarter century. How do these objects produce huge luminosities---in some cases, far outshining our galaxy---from a region perhaps no larger than the solar system? Accretion onto supermassive black holes has been widely considered the best buy in theories of AGN. Much work has gone into accretion disk theory, searches for black holes in galactic nuclei, and observational tests. These efforts have not proved the disk model, but there is progress. Evidence for black holes in the nuclei of nearby galaxies is provided by observations of stellar velocities, and radiation from the disk's hot surface may be observed in the ultraviolet (UV) and neighboring spectral bands. In the review, the author describe some of the recent work on accretion disks in AGN, with an emphasis on points of contact between theory and observation

  3. Gauging the Galactic thick disk with RR Lyrae stars

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    Cruz G.

    2012-02-01

    Full Text Available In this contribution we present results from the QUEST RR Lyrae Survey of the thick disk. The survey spans ~480 sq. deg. at low latitude |b| < 30°, with multi-epoch VRI observations, obtained with the QUEST-I camera at the 1m Jürgen Stock Schmidt telescope located at the National Astronomical Observatory of Venezuela. This constitutes the first deep RR Lyrae survey of the Galactic thick disk conducted at low galactic latitudes, covering simultaneously a large range in radial (8Galactic Plane. The spatial coverage of the survey together with the multi-band multi-epoch photometry allowed for the derivation of the thick disk structural parameters from in situ RR Lyrae stars having accurate distances (errors <7% and individual reddenings derived from each star’s color curve at minimum light. Moreover, the use of RR Lyrae stars as tracers ensures negligible contamination from the Galactic thin disk. We find a thick disk mean scale height hZ = 0.94 ± 0.11kpc and scale length hR = 3.2 ± 0.4kpc, derived from the vertical and radial mean density profiles of RR Lyrae stars. We also find evidence of thick disk flaring and results that may suggest the thick disk radial density profile shows signs of antitruncation. We discuss our findings in the context of recent thick disk formation models.

  4. Stratified Simulations of Collisionless Accretion Disks

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    Hirabayashi, Kota; Hoshino, Masahiro, E-mail: hirabayashi-k@eps.s.u-tokyo.ac.jp [Department of Earth and Planetary Science, The University of Tokyo, Tokyo, 113-0033 (Japan)

    2017-06-10

    This paper presents a series of stratified-shearing-box simulations of collisionless accretion disks in the recently developed framework of kinetic magnetohydrodynamics (MHD), which can handle finite non-gyrotropy of a pressure tensor. Although a fully kinetic simulation predicted a more efficient angular-momentum transport in collisionless disks than in the standard MHD regime, the enhanced transport has not been observed in past kinetic-MHD approaches to gyrotropic pressure anisotropy. For the purpose of investigating this missing link between the fully kinetic and MHD treatments, this paper explores the role of non-gyrotropic pressure and makes the first attempt to incorporate certain collisionless effects into disk-scale, stratified disk simulations. When the timescale of gyrotropization was longer than, or comparable to, the disk-rotation frequency of the orbit, we found that the finite non-gyrotropy selectively remaining in the vicinity of current sheets contributes to suppressing magnetic reconnection in the shearing-box system. This leads to increases both in the saturated amplitude of the MHD turbulence driven by magnetorotational instabilities and in the resultant efficiency of angular-momentum transport. Our results seem to favor the fast advection of magnetic fields toward the rotation axis of a central object, which is required to launch an ultra-relativistic jet from a black hole accretion system in, for example, a magnetically arrested disk state.

  5. ORIGIN OF CHEMICAL AND DYNAMICAL PROPERTIES OF THE GALACTIC THICK DISK

    International Nuclear Information System (INIS)

    Bekki, Kenji; Tsujimoto, Takuji

    2011-01-01

    We adopt a scenario in which the Galactic thick disk was formed by minor merging between the first generation of the Galactic thin disk (FGTD) and a dwarf galaxy about ∼9 Gyr ago and thereby investigate chemical and dynamical properties of the Galactic thick disk. In this scenario, the dynamical properties of the thick disk have long been influenced both by the mass growth of the second generation of the Galactic thin disk (i.e., the present thin disk) and by its non-axisymmetric structures. On the other hand, the early star formation history and chemical evolution of the thin disk was influenced by the remaining gas of the thick disk. Based on N-body simulations and chemical evolution models, we investigate the radial metallicity gradient, structural and kinematical properties, and detailed chemical abundance patterns of the thick disk. Our numerical simulations show that the ancient minor merger event can significantly flatten the original radial metallicity gradient of the FGTD, in particular, in the outer part, and also can be responsible for migration of inner metal-rich stars into the outer part (R > 10 kpc). The simulations show that the central region of the thick disk can develop a bar due to dynamical effects of a separate bar in the thin disk. Whether or not rotational velocities (V φ ) can correlate with metallicities ([Fe/H]) for the simulated thick disks depends on the initial metallicity gradients of the FGTDs. The simulated orbital eccentricity distributions in the thick disk for models with higher mass ratios (∼0.2) and lower orbital eccentricities (∼0.5) of minor mergers are in good agreement with the corresponding observations. The simulated V φ -|z| relation of the thick disk in models with low orbital inclination angles of mergers are also in good agreement with the latest observational results. The vertical metallicity gradient of the simulated thick disk is rather flat or very weakly negative in the solar neighborhood. Our Galactic

  6. Chemical evolution of the galactic disk

    International Nuclear Information System (INIS)

    Wyse, R.F.G.; Gilmore, G.

    1987-01-01

    The distribution of enriched material in the stars and gas of their Galaxy contains information pertaining to the chemical evolution of the Milky Way from its formation epoch to the present day, and provides general constraints on theories of galaxy formation. The separate stellar components of the Galaxy cannot readily be understood if treated in isolation, but a reasonably self-consistent model for Galactic chemical evolution may be found if one considers together the chemical properties of the extreme spheroid, thick disk and thin disk populations of the Galaxy. The three major stellar components of the Galaxy are characterized by their distinct spatial distributions, metallicity structure, and kinematics, with the newly-identified thick disk being approximately three times more massive than the classical metal-poor, non-rotating extreme spheroid. Stellar evolution in the thick disk straightforwardly provides the desired pre-enrichment for resolution of the thin disk G dwarf problem

  7. Rotation of gas above the galactic disk

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    Gvaramadze, V.V.; Lominadze, D.G.

    1988-01-01

    The galactic disk is modeled by an oblate spheroid with confocal spherodial isodensity surfaces. An explicit analytic expression is found for the angular velocity of the gas outside the disk. The parameters of a three-component model of a spiral galaxy (oblate spheroid with central hole, bulge, and massive corona) are chosen in such a way as to obtain in the disk a two-hump rotation curve (as in the Galaxy, M 31, and M 81). It is shown that at heights absolute value z ≤ 2 kpc the gas rotates in the same manner as the disk. However, at greater heights the rotation curve ceases to have two humps. Allowance for the pressure gradient of the gas slightly changes the rotation curve directly above the disk (r r/sub disk/)

  8. Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk

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    Ferguson, Deborah; Gardner, Susan [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506-0055 (United States); Yanny, Brian [Fermi National Accelerator Laboratory, Batavia, IL 60510 (United States)

    2017-07-10

    We use the number density distributions of K and M dwarf stars with vertical height from the Galactic disk, determined using observations from the Sloan Digital Sky Survey, to probe the structure of the Milky Way disk across the survey’s footprint. Using photometric parallax as a distance estimator we analyze a sample of several million disk stars in matching footprints above and below the Galactic plane, and we determine the location and extent of vertical asymmetries in the number counts in a variety of thin- and thick-disk subsamples in regions of some 200 square degrees within 2 kpc in vertical distance from the Galactic disk. These disk asymmetries present wave-like features as previously observed on other scales and at other distances from the Sun. We additionally explore the scale height of the disk and the implied offset of the Sun from the Galactic plane at different locations, noting that the scale height of the disk can differ significantly when measured using stars only above or only below the plane. Moreover, we compare the shape of the number density distribution in the north for different latitude ranges with a fixed range in longitude and find the shape to be sensitive to the selected latitude window. We explain why this may be indicative of a change in stellar populations in the latitude regions compared, possibly allowing access to the systematic metallicity difference between thin- and thick-disk populations through photometry.

  9. Wobbling The Galactic Disk with Bombardment of Satellite Galaxies

    Science.gov (United States)

    D'Onghia, Elena

    We propose to assess the effect of impacts of large visible satellite galaxies on a disk, as well as the relevance of the continuing bombardment of the Galactic disk by dark matter clumps as predicted by the current cosmological framework that can wobble the disk, heating it and eventually exciting ragged spiral structures. In particular, we make detailed predictions for observable features such as spiral arms, rings and their associated stars in galactic disks and relate them to the physical processes that drive their formation and evolution in our Milky Way galaxy and nearby spirals. To do this, we will combine analytic methods and numerical simulations that allow us to calculate observables, which we will compare to present and forthcoming observations. Our methodology utilizes a combination of state of the art hydrodynamic simulations of galaxy evolution and multi- wavelength radiative transfer simulations. Our primary goals are: (1) To identify the physical processes that are responsible for spiral structure formation observed in our Milky Way and nearby disk galaxies, from the flocculent to grand- designed spiral galaxies and to provide observable signatures to be compared with data on nearby galaxies combining maps of 24 micron emission (Spitzer) and cold gas, CO (Heracles) and HI (THINGS). (2) To explore different morphologies of spiral galaxies: from the multi-armed galaxies to the Milky Way sized galaxies with few arms. (3) For a Milky Way disk we will assess the effect of impacts of substructures passing through the disk to origin the asymmetry in the number density of stars recently discovered from SDSS and SEGUE data and confirmed from RAVE data. We will also investigate the disk heating in the vertical plane due to the formation of vertical oscillations that are produced by the impact and migration of stars in the disk as consequence of the heating as compared to the classical stellar migration mechanism. (4) We will measure the spiral pattern speed

  10. On the metallicity gradients of the Galactic disk as revealed by LSS-GAC red clump stars

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    Huang, Yang; Liu, Xiao-Wei; Zhang, Hua-Wei; Yuan, Hai-Bo; Xiang, Mao-Sheng; Chen, Bing-Qiu; Ren, Juan-Juan; Sun, Ning-Chen; Wang, Chun; Zhang, Yong; Hou, Yong-Hui; Wang, Yue-Fei; Yang, Ming

    2015-08-01

    Using a sample of over 70 000 red clump (RC) stars with 5%-10% distance accuracy selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC), we study the radial and vertical gradients of the Galactic disk(s) mainly in the anti-center direction, covering a significant volume of the disk in the range of projected Galactocentric radius 7 ≤ RGC ≤ 14 kpc and height from the Galactic midplane 0 ≤ |Z| ≤ 3 kpc. Our analysis shows that both the radial and vertical metallicity gradients are negative across much of the volume of the disk that is probed, and they exhibit significant spatial variations. Near the solar circle (7 ≤ RGC ≤ 115 kpc), the radial gradient has a moderately steep, negative slope of -0.08 dex kpc-1 near the midplane (|Z| plane, suggesting that the outer disk may have experienced an evolutionary path different from that of the inner disk. The vertical gradients are found to flatten largely with increasing RGC. However, the vertical gradient of the lower disk (0 ≤ |Z| ≤ 1 kpc) is found to flatten with RGC quicker than that of the upper disk (1 < |Z| ≤ 3 kpc). Our results should provide strong constraints on the theory of disk formation and evolution, as well as the underlying physical processes that shape the disk (e.g. gas flows, radial migration, and internal and external perturbations).

  11. THE FUTILE SEARCH FOR GALACTIC DISK DARK MATTER

    International Nuclear Information System (INIS)

    Garrido Pestana, Jose Luis; Eckhardt, Donald H.

    2010-01-01

    Several approaches have been used to search for dark matter in our galactic disk, but with mixed results: maybe yes and maybe no. The prevailing approach, integrating the Poisson-Boltzmann equation for tracer stars, has led to more definitive results: yes and no. The touchstone 'yes' analysis of Bahcall et al. has subsequently been confirmed or refuted by various other investigators. This has been our motivation for approaching the search from a different direction: applying the virial theorem to extant data. We conclude that the vertical density profile of the disk is not in a state of equilibrium and, therefore, that the Poisson-Boltzmann approach is inappropriate and it thereby leads to indefensible conclusions.

  12. THE EDGE OF THE YOUNG GALACTIC DISK

    International Nuclear Information System (INIS)

    Carraro, Giovanni; Vazquez, Ruben A.; Costa, Edgardo; Perren, Gabriel; Moitinho, Andre

    2010-01-01

    In this work, we report and discuss the detection of two distant diffuse stellar groups in the third Galactic quadrant. They are composed of young stars, with spectral types ranging from late O to late B, and lie at galactocentric distances between 15 and 20 kpc. These groups are located in the area of two cataloged open clusters (VdB-Hagen 04 and Ruprecht 30), projected toward the Vela-Puppis constellations, and within the core of the Canis Major overdensity. Their reddening and distances have been estimated by analyzing their color-color and color-magnitude diagrams, derived from deep UBV photometry. The existence of young star aggregates at such extreme distances from the Galactic center challenges the commonly accepted scenario in which the Galactic disk has a sharp cutoff at about 14 kpc from the Galactic center and indicates that it extends to much greater distances (as also supported by the recent detection of CO molecular complexes well beyond this distance). While the groups we find in the area of Ruprecht 30 are compatible with the Orion and Norma-Cygnus spiral arms, respectively, the distant group we identify in the region of VdB-Hagen 04 lies in the external regions of the Norma-Cygnus arm, at a galactocentric distance (∼20 kpc) where no young stars have been detected so far in the optical.

  13. Molecular Abundances in the Disk of AN Active Galactic Nucleus

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    Harada, N.; Thompson, T. A.; Herbst, E.

    2011-06-01

    There are galactic nuclei that emit high luminosities L˜1044-46 erg S-1 including luminosity produced by X-rays from high mass accretion onto the central black holes. These nuclei are called active galactic nuclei (AGNs), and they are accompanied by molecular disks. Observations show high abundances of CN and HCN in the disks; the molecules are proposed to be probes of X-ray dominated regions (XDRs) created by the X-rays from AGNs. We have constructed a spatially-dependent chemical-abundance model of the molecular disk in NGC 1068, a typical AGN-dominated galaxy. Recently, new observations of CN and HCN have been made at much higher spatial resolution, and there are also detections of polyatomic molecules such as HC3N, c-C3H2, and C2H. We discuss how these observations and our simulations can help us to better understand the physical conditions, the disk structure, and conditions for star formation within molecular disks, which are still uncertain. We also include a comparison with other types of galaxies such as (ultra-) luminous infrared galaxies. Usero et al.Astronomy and Astrophysics. 419 (897), 2004. Initial results were presented at the International Symposium on Molecular Spectroscopy 2010, RF05 Garcia-Burillo et al. Astronomy and Astrophysics. 519 (2), 2010. Garcia-Burillo et al. Journal of Physics Conference Series, 131 (12031), 2008. Costagliola et al. ArXiv e-print arXiv:1101.2122, 2011. Nakajima et al. Astrophysical Journal Letters 728 (L38), 2008.

  14. CO LINE EMISSION FROM COMPACT NUCLEAR STARBURST DISKS AROUND ACTIVE GALACTIC NUCLEI

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    Armour, J. N.; Ballantyne, D. R., E-mail: jarmour3@gatech.edu [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, 837 State Street, Atlanta, GA 30332-0430 (United States)

    2012-06-20

    There is substantial evidence for a connection between star formation in the nuclear region of a galaxy and growth of the central supermassive black hole. Furthermore, starburst activity in the region around an active galactic nucleus (AGN) may provide the obscuration required by the unified model of AGNs. Molecular line emission is one of the best observational avenues to detect and characterize dense, star-forming gas in galactic nuclei over a range of redshift. This paper presents predictions for the carbon monoxide (CO) line features from models of nuclear starburst disks around AGNs. These small-scale ({approx}< 100 pc), dense and hot starbursts have CO luminosities similar to scaled-down ultra-luminous infrared galaxies and quasar host galaxies. Nuclear starburst disks that exhibit a pc-scale starburst and could potentially act as the obscuring torus show more efficient CO excitation and higher brightness temperature ratios than those without such a compact starburst. In addition, the compact starburst models predict strong absorption when J{sub Upper} {approx}> 10, a unique observational signature of these objects. These findings allow for the possibility that CO spectral line energy distributions (SLEDs) could be used to determine if starburst disks are responsible for the obscuration in z {approx}< 1 AGNs. Directly isolating the nuclear CO line emission of such compact regions around AGNs from galactic-scale emission will require high-resolution imaging or selecting AGN host galaxies with weak galactic-scale star formation. Stacking individual CO SLEDs will also be useful in detecting the predicted high-J features.

  15. Stratified magnetically driven accretion-disk winds and their relations to jets

    International Nuclear Information System (INIS)

    Fukumura, Keigo; Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2014-01-01

    We explore the poloidal structure of two-dimensional magnetohydrodynamic (MHD) winds in relation to their potential association with the X-ray warm absorbers (WAs) and the highly ionized ultra-fast outflows (UFOs) in active galactic nuclei (AGNs), in a single unifying approach. We present the density n(r, θ), ionization parameter ξ(r, θ), and velocity structure v(r, θ) of such ionized winds for typical values of their fluid-to-magnetic flux ratio, F, and specific angular momentum, H, for which wind solutions become super-Alfvénic. We explore the geometrical shape of winds for different values of these parameters and delineate the values that produce the widest and narrowest opening angles of these winds, quantities necessary in the determination of the statistics of AGN obscuration. We find that winds with smaller H show a poloidal geometry of narrower opening angles with their Alfvén surface at lower inclination angles and therefore they produce the highest line of sight (LoS) velocities for observers at higher latitudes with the respect to the disk plane. We further note a physical and spatial correlation between the X-ray WAs and UFOs that form along the same LoS to the observer but at different radii, r, and distinct values of n, ξ, and v consistent with the latest spectroscopic data of radio-quiet Seyfert galaxies. We also show that, at least in the case of 3C 111, the winds' pressure is sufficient to contain the relativistic plasma responsible for its radio emission. Stratified MHD disk winds could therefore serve as a unique means to understand and unify the diverse AGN outflows.

  16. Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk.

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    Bergemann, Maria; Sesar, Branimir; Cohen, Judith G; Serenelli, Aldo M; Sheffield, Allyson; Li, Ting S; Casagrande, Luca; Johnston, Kathryn V; Laporte, Chervin F P; Price-Whelan, Adrian M; Schönrich, Ralph; Gould, Andrew

    2018-03-15

    Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo-the faint, roughly spherical component of the Galaxy-reveals rich 'fossil' evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane-locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

  17. The effect of radial migration on galactic disks

    International Nuclear Information System (INIS)

    Vera-Ciro, Carlos; D'Onghia, Elena; Navarro, Julio; Abadi, Mario

    2014-01-01

    We study the radial migration of stars driven by recurring multi-arm spiral features in an exponential disk embedded in a dark matter halo. The spiral perturbations redistribute angular momentum within the disk and lead to substantial radial displacements of individual stars, in a manner that largely preserves the circularity of their orbits and that results, after 5 Gyr (∼40 full rotations at the disk scale length), in little radial heating and no appreciable changes to the vertical or radial structure of the disk. Our results clarify a number of issues related to the spatial distribution and kinematics of migrators. In particular, we find that migrators are a heavily biased subset of stars with preferentially low vertical velocity dispersions. This 'provenance bias' for migrators is not surprising in hindsight, for stars with small vertical excursions spend more time near the disk plane, and thus respond more readily to non-axisymmetric perturbations. We also find that the vertical velocity dispersion of outward migrators always decreases, whereas the opposite holds for inward migrators. To first order, newly arrived migrators simply replace stars that have migrated off to other radii, thus inheriting the vertical bias of the latter. Extreme migrators might therefore be recognized, if present, by the unexpectedly small amplitude of their vertical excursions. Our results show that migration, understood as changes in angular momentum that preserve circularity, can strongly affect the thin disk, but cast doubts on models that envision the Galactic thick disk as a relic of radial migration.

  18. RESONANT CLUMPING AND SUBSTRUCTURE IN GALACTIC DISKS

    International Nuclear Information System (INIS)

    Molloy, Matthew; Smith, Martin C.; Shen, Juntai; Evans, N. Wyn

    2015-01-01

    We describe a method to extract resonant orbits from N-body simulations, exploiting the fact that they close in frames rotating with a constant pattern speed. Our method is applied to the N-body simulation of the Milky Way by Shen et al. This simulation hosts a massive bar, which drives strong resonances and persistent angular momentum exchange. Resonant orbits are found throughout the disk, both close to the bar and out to the very edges of the disk. Using Fourier spectrograms, we demonstrate that the bar is driving kinematic substructure even in the very outer parts of the disk. We identify two major orbit families in the outskirts of the disk, one of which makes significant contributions to the kinematic landscape, namely, the m:l = 3:−2 family, resonating with the bar. A mechanism is described that produces bimodal distributions of Galactocentric radial velocities at selected azimuths in the outer disk. It occurs as a result of the temporal coherence of particles on the 3:−2 resonant orbits, which causes them to arrive simultaneously at pericenter or apocenter. This resonant clumping, due to the in-phase motion of the particles through their epicycle, leads to both inward and outward moving groups that belong to the same orbital family and consequently produce bimodal radial velocity distributions. This is a possible explanation of the bimodal velocity distributions observed toward the Galactic anticenter by Liu et al. Another consequence is that transient overdensities appear and dissipate (in a symmetric fashion), resulting in a periodic pulsing of the disk’s surface density

  19. RESONANT CLUMPING AND SUBSTRUCTURE IN GALACTIC DISKS

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    Molloy, Matthew [Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871 (China); Smith, Martin C.; Shen, Juntai [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Evans, N. Wyn, E-mail: matthewmolloy@gmail.com, E-mail: msmith@shao.ac.cn, E-mail: jshen@shao.ac.cn, E-mail: nwe@ast.cam.ac.uk [Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA (United Kingdom)

    2015-05-10

    We describe a method to extract resonant orbits from N-body simulations, exploiting the fact that they close in frames rotating with a constant pattern speed. Our method is applied to the N-body simulation of the Milky Way by Shen et al. This simulation hosts a massive bar, which drives strong resonances and persistent angular momentum exchange. Resonant orbits are found throughout the disk, both close to the bar and out to the very edges of the disk. Using Fourier spectrograms, we demonstrate that the bar is driving kinematic substructure even in the very outer parts of the disk. We identify two major orbit families in the outskirts of the disk, one of which makes significant contributions to the kinematic landscape, namely, the m:l = 3:−2 family, resonating with the bar. A mechanism is described that produces bimodal distributions of Galactocentric radial velocities at selected azimuths in the outer disk. It occurs as a result of the temporal coherence of particles on the 3:−2 resonant orbits, which causes them to arrive simultaneously at pericenter or apocenter. This resonant clumping, due to the in-phase motion of the particles through their epicycle, leads to both inward and outward moving groups that belong to the same orbital family and consequently produce bimodal radial velocity distributions. This is a possible explanation of the bimodal velocity distributions observed toward the Galactic anticenter by Liu et al. Another consequence is that transient overdensities appear and dissipate (in a symmetric fashion), resulting in a periodic pulsing of the disk’s surface density.

  20. A SCALING RELATION BETWEEN MEGAMASER DISK RADIUS AND BLACK HOLE MASS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Wardle, Mark; Yusef-Zadeh, Farhad

    2012-01-01

    Several thin, Keplerian, sub-parsec megamaser disks have been discovered in the nuclei of active galaxies and used to precisely determine the mass of their host black holes. We show that there is an empirical linear correlation between the disk radius and the black hole mass. We demonstrate that such disks are naturally formed by the partial capture of molecular clouds passing through the galactic nucleus and temporarily engulfing the central supermassive black hole. Imperfect cancellation of the angular momenta of the cloud material colliding after passing on opposite sides of the hole leads to the formation of a compact disk. The radial extent of the disk is determined by the efficiency of this process and the Bondi-Hoyle capture radius of the black hole, and naturally produces the empirical linear correlation of the radial extent of the maser distribution with black hole mass. The disk has sufficient column density to allow X-ray irradiation from the central source to generate physical and chemical conditions conducive to the formation of 22 GHz H 2 O masers. For initial cloud column densities ∼ 23.5 cm –2 the disk is non-self-gravitating, consistent with the ordered kinematics of the edge-on megamaser disks; for higher cloud columns the disk would fragment and produce a compact stellar disk similar to that observed around Sgr A* at the galactic center.

  1. Non-linear dynamics in galactic disks: the spiral-warps connection

    International Nuclear Information System (INIS)

    Masset, Frederic

    1997-01-01

    After a recall on warp theories and on warp waves, this research thesis reports a linear study of warp waves with an assessment of the role of gas compressibility when taking the galactic disk thickness into account. Then, the author reports an analytical study of the non-linear coupling between warp waves and density waves, in order to calculate coupling efficiency, to identify areas of the galactic disk in which it is efficient, and to discuss concurrent physical processes (such as Landau absorption) and the validity of assumptions made to perform the calculations. The next part reports numerical simulations which have been performed to check the coupling mechanism. The author notably comments evolutions brought to existing codes, and finally presents the three-dimensional version of the developed code, and discusses choices made for this code (presence of gas, choice of hydrodynamics algorithms and of gas mesh geometry, and so on). Numerical results are then presented and discussed: they actually show the existence of a coupling between density waves and warp waves [fr

  2. Massachusetts Stony Brook galactic plane CO survey - disk and spiral arm molecular cloud populations

    International Nuclear Information System (INIS)

    Solomon, P.M.; Sanders, D.B.; Rivolo, A.R.; Five College Radio Astronomy Observatory, Pasadena, CA; Space Telescope Science Institute, Baltimore, MD)

    1985-01-01

    A preliminary analysis of a new high-resolution CO survey of the galactic disk is presented, which can detect and measure essentially all molecular clouds and cloud components in the inner Galaxy with size greater than 10 pc. In the region of l between 20 and 50 deg approximately 2000 emission centers are identified. Two populations which separate according to temperature are found. The disk population of cold molecular cores contains about three-quarters of the total number of cores, is not confined to any large-scale pattern in longitude-velocity space, and must be widespread in the Galaxy both in and out of spiral arms. The spiral arm population of warm molecular cores contains about one-quarter of the population with one-half of the emission and is very closely associated with radio H II regions. Between longitudes 20 and 50 deg their radial distribution shows two peaks at R = 5 and 7.5 kpc. The warm molecular cloud cores have a nonaxisymmetric galactic distribution, occur in clusters, and are confined to restricted regions and patterns in longitude-velocity space and in the galactic disk. 20 references

  3. Two chemically similar stellar overdensities on opposite sides of the plane of the Galactic disk

    Science.gov (United States)

    Bergemann, Maria; Sesar, Branimir; Cohen, Judith G.; Serenelli, Aldo M.; Sheffield, Allyson; Li, Ting S.; Casagrande, Luca; Johnston, Kathryn V.; Laporte, Chervin F. P.; Price-Whelan, Adrian M.; Schönrich, Ralph; Gould, Andrew

    2018-03-01

    Our Galaxy is thought to have an active evolutionary history, dominated over the past ten billion years or so by star formation, the accretion of cold gas and, in particular, the merging of clumps of baryonic and dark matter. The stellar halo—the faint, roughly spherical component of the Galaxy—reveals rich ‘fossil’ evidence of these interactions, in the form of stellar streams, substructures and chemically distinct stellar components. The effects of interactions with dwarf galaxies on the content and morphology of the Galactic disk are still being explored. Recent studies have identified kinematically distinct stellar substructures and moving groups of stars in our Galaxy, which may have extragalactic origins. There is also mounting evidence that stellar overdensities (regions with greater-than-average stellar density) at the interface between the outer disk and the halo could have been caused by the interaction of a dwarf galaxy with the disk. Here we report a spectroscopic analysis of 14 stars from two stellar overdensities, each lying about five kiloparsecs above or below the Galactic plane—locations suggestive of an association with the stellar halo. We find that the chemical compositions of these two groups of stars are almost identical, both within and between these overdensities, and closely match the abundance patterns of stars in the Galactic disk. We conclude that these stars came from the disk, and that the overdensities that they are part of were created by tidal interactions of the disk with passing or merging dwarf galaxies.

  4. DISCOVERY OF CANDIDATE H2O DISK MASERS IN ACTIVE GALACTIC NUCLEI AND ESTIMATIONS OF CENTRIPETAL ACCELERATIONS

    International Nuclear Information System (INIS)

    Greenhill, Lincoln J.; Moran, James M.; Tilak, Avanti; Kondratko, Paul T.

    2009-01-01

    Based on spectroscopic signatures, about one-third of known H 2 O maser sources in active galactic nuclei (AGNs) are believed to arise in highly inclined accretion disks around central engines. These 'disk maser candidates' are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC 1320, NGC 17) in a survey of 40 inclined active galaxies (v sys -1 ). The remaining three disk maser candidates were identified in monitoring of known sources: NGC 449, NGC 2979, and NGC 3735. We also confirm a previously marginal case in UGC 4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 km s -1 . Monitoring of three more rapidly rotating candidate disks (CG 211, NGC 6264, VV 340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses ((2-7) x10 7 M sun ) and mean disk radii (0.2-0.4 pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGNs are relatively distant (10,000 km s -1 sys -1 ), and fractional error in a derived Hubble constant, due to peculiar motion of the galaxies, would be small. As signposts of highly inclined geometries at galactocentric radii of ∼0.1-1 pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGNs and surrounding galactic stellar disks, even without extensive interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies. This provides independent support for conclusions that in late-type galaxies, central engine accretion disks and galactic plane orientations are not correlated.

  5. On the metallicity distribution of classical Cepheids in the Galactic inner disk

    NARCIS (Netherlands)

    Genovali, K.; Lemasle, B.; Bono, G.; Romaniello, M.; Primas, F.; Fabrizio, M.; Buonanno, R.; François, P.; Inno, L.; Laney, C.D.; Matsunaga, N.; Pedicelli, S.; Thévenin, F.

    2013-01-01

    We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R ~ 40 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk

  6. Accretion disks in active galactic nuclei

    International Nuclear Information System (INIS)

    Begelman, M.C.

    1985-01-01

    The innermost regions of the central engines in active galactic nuclei are examined, and it is shown how different modes of accretion with angular momentum may account for the diverse manifestations of activity in the nuclei of galaxies. These modes are subsequently compared with the observed properties of quasars, Type I Seyferts, and radio galaxies. It was found that the qualitative features of an accretion flow orbiting a massive black hole depend principally on the ratio of the actual accretion rate to the Eddington accretion rate. For a value of this ratio much less than one, the flow may become an ion torus supported by gas pressure; for a value much greater than one, the flow traps its radiative output and becomes an inefficient radiation torus. At intermediate values, the flow may settle into a thin accretion disk. 62 references

  7. NO EVIDENCE FOR A DARK MATTER DISK WITHIN 4 kpc FROM THE GALACTIC PLANE

    International Nuclear Information System (INIS)

    Moni Bidin, C.; Carraro, G.; Mendez, R. A.; Van Altena, W. F.

    2010-01-01

    We estimated the dynamical surface mass density (Σ) at the solar Galactocentric distance between 2 and 4 kpc from the Galactic plane, as inferred from the observed kinematics of the thick disk. We find Σ(z = 2 kpc) = 57.6 ± 5.8 M sun pc -2 , and it shows only a tiny increase in the z range considered by our investigation. We compared our results with the expectations for the visible mass, adopting the most recent estimates in the literature for contributions of the Galactic stellar disk and interstellar medium, and proposed models of the dark matter distribution. Our results match the expectation for the visible mass alone, never differing from it by more than 0.8 M sun pc -2 at any z, and thus we find little evidence for any dark component. We assume that the dark halo could be undetectable with our method, but the dark disk, recently proposed as a natural expectation of the ΛCDM models, should be detected. Given the good agreement with the visible mass alone, models including a dark disk are less likely, but within errors its existence cannot be excluded. In any case, these results put constraints on its properties: thinner models (scale height lower than 4 kpc) reconcile better with our results and, for any scale height, the lower-density models are preferred. We believe that successfully predicting the stellar thick disk properties and a dark disk in agreement with our observations could be a challenging theoretical task.

  8. PROBING THE GALACTIC POTENTIAL WITH NEXT-GENERATION OBSERVATIONS OF DISK STARS

    International Nuclear Information System (INIS)

    Sumi, T.; Johnston, K. V.; Tremaine, S.; Spergel, D. N.; Majewski, S. R.

    2009-01-01

    Our current knowledge of the rotation curve of the Milky Way is remarkably poor compared to other galaxies, limited by the combined effects of extinction and the lack of large samples of stars with good distance estimates and proper motions. Near-future surveys promise a dramatic improvement in the number and precision of astrometric, photometric, and spectroscopic measurements of stars in the Milky Way's disk. We examine the impact of such surveys on our understanding of the Galaxy by 'observing' particle realizations of nonaxisymmetric disk distributions orbiting in an axisymmetric halo with appropriate errors and then attempting to recover the underlying potential using a Markov Chain Monte Carlo approach. We demonstrate that the azimuthally averaged gravitational force field in the Galactic plane-and hence, to a lesser extent, the Galactic mass distribution-can be tightly constrained over a large range of radii using a variety of types of surveys so long as the error distribution of the measurements of the parallax, proper motion, and radial velocity are well understood and the disk is surveyed globally. One advantage of our method is that the target stars can be selected nonrandomly in real or apparent-magnitude space to ensure just such a global sample without biasing the results. Assuming that we can always measure the line-of-sight velocity of a star with at least 1 km s -1 precision, we demonstrate that the force field can be determined to better than ∼1% for Galactocentric radii in the range R = 4-20 kpc using either: (1) small samples (a few hundred stars) with very accurate trigonometric parallaxes and good proper-motion measurements (uncertainties δ p,tri ∼ μ ∼ -1 respectively); (2) modest samples (∼1000 stars) with good indirect parallax estimates (e.g., uncertainty in photometric parallax δ p,phot ∼ 10%-20%) and good proper-motion measurements (δ μ ∼ 100 μas yr -1 ); or (3) large samples (∼10 4 stars) with good indirect parallax

  9. Galactic Structure in the Outer Disk: The Field in the Line of Sight to the Intermediate-Age open Cluster Tombaugh 1

    Energy Technology Data Exchange (ETDEWEB)

    Carraro, Giovanni [Dipartimento di Fisica e Astronomia, Universitá di Padova Vicolo Osservatorio 3 I-35122, Padova (Italy); Silva, Joao Victor Sales [Observatorio Nacional/MCT Rua Gen. José Cristino 77 20291-400, Rio de Janeiro (Brazil); Bidin, Christian Moni [Instituto de Astronomia, Universidad Catolica del Norte Av. Angamos 0610, Casilla 1280 Antofagasta (Chile); Vazquez, Ruben A., E-mail: giovanni.carraro@unipd.it [Instituto de Astrofisica de La Plata CONICET/ UNLP, Paseo del Bosque s/n La Plata (Argentina)

    2017-03-01

    We employ optical photometry and high-resolution spectroscopy to study a field toward the open cluster Tombaugh 1, where we identify a complex population mixture that we describe in terms of young and old Galactic thin disks. Of particular interest is the spatial distribution of the young population, which consists of dwarfs with spectral types as early as B6 and is distributed in a blue plume feature in the color–magnitude diagram. For the first time, we confirm spectroscopically that most of these stars are early-type stars and not blue stragglers or halo/thick-disk subdwarfs. Moreover, they are not evenly distributed along the line of sight but crowd at heliocentric distances between 6.6 and 8.2 kpc. We compare these results with present-day understanding of the spiral structure of the Galaxy and suggest that they trace the outer arm. This range of distances challenges current Galactic models adopting a disk cutoff at 14 kpc from the Galactic center. The young dwarfs overlap in space with an older component, which is identified as an old Galactic thin disk. Both young and old populations are confined in space since the disk is warped at the latitude and longitude of Tombaugh 1. The main effects of the warp are that the line of sight intersects the disk and entirely crosses it at the outer arm distance and that there are no traces of the closer Perseus arm, which would then be either unimportant in this sector or located much closer to the formal Galactic plane. Finally, we analyze a group of giant stars, which turn out to be located at very different distances and to possess very different chemical properties, with no obvious relation to the other populations.

  10. SPITZER PARALLAX OF OGLE-2015-BLG-0966: A COLD NEPTUNE IN THE GALACTIC DISK

    Energy Technology Data Exchange (ETDEWEB)

    Street, R. A.; Bachelet, E. [LCOGT, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States); Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Novati, S. Calchi [NASA Exoplanet Science Institute, MS 100-22, California Institute of Technology, Pasadena, CA 91125 (United States); Hundertmark, M. P. G.; Jørgensen, U. G. [Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5, DK-1350—Copenhagen K (Denmark); Zhu, W.; Gould, A. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Yee, J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Tsapras, Y. [Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg (ZAH), D-69120 Heidelberg (Germany); Bennett, D. P. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Dominik, M. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Andersen, M. I. [Niels Bohr Institute and Dark Cosmology Centre, University of Copenhagen, Juliane Mariesvej 30, DK-2100—Copenhagen Ø (Denmark); Bozza, V. [Dipartimento di Fisica “E.R. Caianiello,” Università di Salerno, Via Giovanni Paolo II 132, I-84084, Fisciano (Italy); Bramich, D. M. [Qatar Environment and Energy Research Institute, Qatar Foundation, P.O. Box 5825, Doha (Qatar); Collaboration: RoboNet Project and MiNDSTEp Consortium; OGLE Project; Spitzer Team; MOA Collaboration; KMTNet Modeling Team; and others

    2016-03-10

    We report the detection of a cold Neptune m{sub planet} = 21 ± 2 M{sub ⊕} orbiting a 0.38 M{sub ⊙} M dwarf lying 2.5–3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near to mid-disk and are clearly not in the Galactic bulge.

  11. Water Masers and Accretion Disks in Galactic Nuclei

    Science.gov (United States)

    Greenhill, L. J.

    2005-12-01

    There are over 50 sources of H2O maser emission in type-2 active galactic nuclei, a large fraction discovered in the last two years. Interferometer maps of water masers are presently the only means by which structures ⪉ 1 pc from massive black holes can be mapped directly, which is particularly important for type-2 systems because edge-on orientation and obscuration complicate study by other means. Investigations of several sources have demonstrated convincingly that the maser emission traces warped accretion disks 0.1 to 1 pc from central engines of order 106-108 M⊙. The same may be true for almost half the known (but unmapped) sources, based on spectral characteristics consistent with emission from edge-on accretion disks. Mapping these sources is a high priority. Study of most recently discovered masers requires long baseline arrays that include 100-m class apertures and would benefit from aggregate bit rates on the order of 1 gigabit per second. The Square Kilometer Array should provide an order of magnitude boost in mapping sensitivity, but outrigger antennas will be needed to achieve necesssary angular resolutions, as may be space-borne antennas.

  12. Accretion Disk Spectra of the Ultra-Luminous X-Ray Sources in Nearby Spiral Galaxies and Galactic Superluminal Jet Sources

    Energy Technology Data Exchange (ETDEWEB)

    Mizuno, T

    2003-12-11

    Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, the standard accretion disk around the Kerr black hole might explain the observed high disk temperature, as the inner radius of the Kerr disk gets smaller and the disk temperature can be consequently higher. However, we point out that the observable Kerr disk spectra becomes significantly harder than Schwarzschild disk spectra only when the disk is highly inclined. This is because the emission from the innermost part of the accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen for a face-on disk. The Galactic superluminal jet sources are known to be highly inclined systems, thus their energy spectra may be explained with the standard Kerr disk with known black hole masses. For ULXs, on the other hand, the standard Kerr disk model seems implausible, since it is highly unlikely that their accretion disks are preferentially inclined, and, if edge-on Kerr disk model is applied, the black hole mass becomes unreasonably large (> 300 M{sub solar}). Instead, the slim disk (advection dominated optically thick disk) model is likely to explain the observed super-Eddington luminosities, hard energy spectra, and spectral variations of ULXs. We suggest that ULXs are accreting black holes with a few tens of solar mass, which is not unexpected from the standard stellar evolution scenario, and that their X-ray emission is from the slim disk shining at super-Eddington luminosities.

  13. New Classical Cepheids in the Inner Part of the Northern Galactic Disk, and Their Kinematics

    Energy Technology Data Exchange (ETDEWEB)

    Tanioka, Satoshi [Department of Astronomical Science, School of Physical Sciences, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588 (Japan); Matsunaga, Noriyuki [Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Fukue, Kei [Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan); Inno, Laura [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Bono, Giuseppe [Instituto Nazionale de Astrofisica, Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio Catone (Italy); Kobayashi, Naoto, E-mail: matsunaga@astron.s.u-tokyo.ac.jp [Laboratory of Infrared High-resolution spectroscopy (LiH), Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555 (Japan)

    2017-06-20

    The characteristics of the inner Galaxy remain obscured by significant dust extinction, hence infrared surveys are useful for finding young Cepheids whose distances and ages can be accurately determined. A near-infrared photometric and spectroscopic survey was carried out and three classical Cepheids were unveiled in the inner disk, around 20° and 30° in Galactic longitude. The targets feature small Galactocentric distances, 3–5 kpc, and their velocities are important, as they may be under the environmental influence of the Galactic bar. While one of the Cepheids has a radial velocity consistent with the Galactic rotation, the other two are moving significantly slower. We also compare their kinematics with that of high-mass star-forming regions with measured parallactic distances.

  14. H II REGION DRIVEN GALACTIC BUBBLES AND THEIR RELATIONSHIP TO THE GALACTIC MAGNETIC FIELD

    Energy Technology Data Exchange (ETDEWEB)

    Pavel, Michael D.; Clemens, D. P., E-mail: pavelmi@bu.edu, E-mail: clemens@bu.edu [Institute for Astrophysical Research, Boston University, 725 Commonwealth Ave., Boston, MA 02215 (United States)

    2012-12-01

    The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H II region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H II regions, based on hydrogen radio recombination linewidths, the subthermal H II regions showed a marginal deviation from random orientations, but the suprathermal H II regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H II regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H II regions, then the evolution of young H II regions is significantly affected by the Galactic magnetic field. As H II regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H II regions.

  15. General relativistic model for the gravitational field of active galactic nuclei surrounded by a disk

    NARCIS (Netherlands)

    Vogt, D.; Letelier, P.S.

    2005-01-01

    An exact but simple general relativistic model for the gravitational field of active galactic nuclei is constructed, based on the superposition in Weyl coordinates of a black hole, a Chazy-Curzon disk and two rods, which represent matter jets. The influence of the rods on the matter properties of

  16. White dwarf stars and the age of the Galactic disk

    Science.gov (United States)

    Wood, M. A.

    1990-01-01

    The history of the Galaxy is written in its oldest stars, the white dwarf (WD) stars. Significant limits can be placed on both the Galactic age and star formation history. A wide range of input WD model sequences is used to derive the current limits to the age estimates suggested by fitting to the observed falloff in the WD luminosity function. The results suggest that the star formation rate over the history of the Galaxy has been relatively constant, and that the disk age lies in the range 6-12 billion years, depending upon the assumed structure of WD stars, and in particular on the core composition and surface helium layer mass. Using plausible mixed C/O core input models, the estimates for the disk age range from 8-10.5 Gyr, i.e.,sustantially younger than most age estimates for the halo globular clusters. After speculating on the significance of the results, expected observational and theoretical refinements which will further enhance the reliability of the method are discussed.

  17. Population Synthesis Studies of the White Dwarfs of the Galactic Disk and Halo

    Science.gov (United States)

    Cojocaru, Elena-Ruxandra

    2016-09-01

    White dwarfs are fossil stars that can encode valuable information about the formation, evolution and other properties of the different Galactic stellar populations. They are the direct descendants of main-sequence stars with masses ranging from ∼0.8 M⊙ to ∼10 M⊙, which means that over 95% of the stars in our Galaxy will eventually become white dwarfs. This fact, correlated with the excellent quality of modern white dwarf cooling models, clearly marks their potential as cosmic clocks for estimating the ages of Galactic stellar populations, as well as place white dwarfs as privileged objects in understanding several actual astrophysical problems. Stellar population synthesis methods (Tinsley, 1968) use theoretical evolutionary sequences to reproduce luminosities, temperatures and other parameters building up to a synthetic population that can be readily compared to an observed sample of stars. Such techniques are perfect for the study of the different white dwarf populations in our Galaxy and their strength has only grown in recent years, fueled both by improved evolutionary sequences and detailed cooling tracks and also by the ever growing samples of white dwarfs identified through modern survey missions. In particular, the work presented in this thesis uses an updated population synthesis code based on previous versions of the code from our group (García-Berro et al., 1999; Torres et al., 2002; García-Berro et al., 2004; Torres et al., 2005; Camacho et al., 2014). Our synthetic population code, based on Monte Carlo statistical techniques, has been extensively used in the study of the disk (García-Berro et al., 1! 999; Torres et al., 2001; Torres & García-Berro, 2016) and halo (Torres et al., 2002; García-Berro et al., 2004) single white-dwarf population, white dwarf plus main sequence stars (Camacho et al., 2014), as well as open clusters such as NGC 6791 (García-Berro et al., 2010; García-Berro et al., 2011) or globular clusters, as 47 Tuc (Garc

  18. Molecular Gas Feeding the Circumnuclear Disk of the Galactic Center

    Energy Technology Data Exchange (ETDEWEB)

    Hsieh, Pei-Ying; Koch, Patrick M.; Ho, Paul T. P.; Tang, Ya-Wen [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China); Kim, Woong-Tae [Department of Physics and Astronomy, Seoul National University, Seoul 151-742 (Korea, Republic of); Wang, Hsiang-Hsu [Department of Physics and Institute of Theoretical Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong (China); Yen, Hsi-Wei [European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Hwang, Chorng-Yuan, E-mail: pyhsieh@asiaa.sinica.edu.tw [Institute of Astronomy, National Central University, No.300, Jhongda Road, Jhongli City, Taoyuan County 32001, Taiwan (China)

    2017-09-20

    The interaction between a supermassive black hole (SMBH) and the surrounding material is of primary importance in modern astrophysics. The detection of the molecular 2 pc circumnuclear disk (CND) immediately around the Milky Way SMBH, SgrA*, provides a unique opportunity to study SMBH accretion at subparsec scales. Our new wide-field CS( J = 2 − 1) map toward the Galactic center (GC) reveals multiple dense molecular streamers that originated from the ambient clouds 20 pc further out, and that are connected to the central 2 pc of the CND. These dense gas streamers appear to carry gas directly toward the nuclear region and might be captured by the central potential. Our phase-plot analysis indicates that these streamers show a signature of rotation and inward radial motion with progressively higher velocities as the gas approaches the CND and finally ends up corotating with the CND. Our results might suggest a possible mechanism of gas feeding the CND from 20 pc around 2 pc in the GC. In this paper, we discuss the morphology and the kinematics of these streamers. As the nearest observable Galactic nucleus, this feeding process may have implications for understanding the processes in extragalactic nuclei.

  19. An asymmetric distribution of positrons in the Galactic disk revealed by γ-rays

    International Nuclear Information System (INIS)

    Weidenspointner, G.; Skinner, G.; Jean, P.; Knoedlseder, J.; Von Ballmoos, P.; Bignami, G.; Weidenspointner, G.; Diehl, R.; Strong, A.; Weidenspointner, G.; Skinner, G.; Skinner, G.; Skinner, G.; Cordier, B.; Schanne, S.; Winkler, Ch.; Bignami, G.

    2008-01-01

    Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk (∼ 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies ≥20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10 41 positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

  20. An asymmetric distribution of positrons in the Galactic disk revealed by {gamma}-rays

    Energy Technology Data Exchange (ETDEWEB)

    Weidenspointner, G; Skinner, G; Jean, P; Knoedlseder, J; Von Ballmoos, P; Bignami, G [UPS, CNRS, Ctr Etud Spatiale Rayonnements, Toulouse 4, (France); Weidenspointner, G; Diehl, R; Strong, A [Max Planck Inst Extraterr Phys, D-85741 Garching, (Germany); Weidenspointner, G [MPI Halbleiterlab, D-81739 Munich, (Germany); Skinner, G [NASA, CRESST, Greenbelt, MD 20771 (United States); Skinner, G [NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 (United States); Skinner, G [Univ Maryland, Dept Astron, College Pk, MD 20742 (United States); Cordier, B; Schanne, S [CEA Saclay, DSM, DAPNIA, SAp, F-91191 Gif Sur Yvette, (France); Winkler, Ch [ESA, ESTEC, SCI SA, NL-2201 AZ Noordwijk, (Netherlands); Bignami, G [IUSS, I-27100 Pavia, (Italy)

    2008-07-01

    Gamma-ray line radiation at 511 keV is the signature of electron positron annihilation. Such radiation has been known for 30 years to come from the general direction of the Galactic Centre, but the origin of the positrons has remained a mystery. Stellar nucleosynthesis, accreting compact objects, and even the annihilation of exotic dark-matter particles have all been suggested. Here we report a distinct asymmetry in the 511 keV line emission coming from the inner Galactic disk ({approx} 10-50 degrees from the Galactic Centre). This asymmetry resembles an asymmetry in the distribution of low mass X-ray binaries with strong emission at photon energies {>=}20 keV ('hard' LMXBs), indicating that they may be the dominant origin of the positrons. Although it had long been suspected that electron-positron pair plasmas may exist in X-ray binaries, it was not evident that many of the positrons could escape to lose energy and ultimately annihilate with electrons in the interstellar medium and thus lead to the emission of a narrow 511 keV line. For these models, our result implies that up to a few times 10{sup 41} positrons escape per second from a typical hard LMXB. Positron production at this level from hard LMXBs in the Galactic bulge would reduce (and possibly eliminate) the need for more exotic explanations, such as those involving dark matter. (authors)

  1. INTERACTION BETWEEN DARK MATTER SUB-HALOS AND A GALACTIC GASEOUS DISK

    International Nuclear Information System (INIS)

    Kannan, Rahul; Macciò, Andrea V.; Walter, Fabian; Pasquali, Anna; Moster, Benjamin P.

    2012-01-01

    We investigate the idea that the interaction of dark matter (DM) sub-halos with the gaseous disks of galaxies can be the origin for the observed holes and shells found in their neutral hydrogen (H I) distributions. We use high-resolution hydrodynamic simulations to show that pure DM sub-halos impacting a galactic disk are not able to produce holes; on the contrary, they result in high-density regions in the disk. However, sub-halos containing a small amount of gas (a few percent of the total DM mass of the sub-halo) are able to displace the gas in the disk and form holes and shells. The sizes and lifetimes of these holes depend on the sub-halo gas mass, density, and impact velocity. A DM sub-halo, of mass 10 8 M ☉ and a gas mass fraction of ∼3%, is able to create a kiloparsec-scale hole with a lifetime similar to those observed in nearby galaxies. We also register an increase in the star formation rate at the rim of the hole, again in agreement with observations. Even though the properties of these simulated structures resemble those found in observations, we find that the number of predicted holes (based on mass and orbital distributions of DM halos derived from cosmological N-body simulations) falls short compared to the observations. Only a handful of holes are produced per gigayear. This leads us to conclude that DM halo impact is not the major channel through which these holes are formed.

  2. The Galactic magnetic fields

    International Nuclear Information System (INIS)

    Han Jinlin

    2006-01-01

    A good progress has been made on studies of Galactic magnetic fields in last 10 years. I describe what we want to know about the Galactic magnetic fields, and then review we current knowledge about magnetic fields in the Galactic disk, the Galactic halo and the field strengths. I also listed many unsolved problems on this area

  3. Relations between age, metallicity and kinematics of F-G stars of the Galactic disk

    International Nuclear Information System (INIS)

    Shevelev, Yu.G.; Marsakov, V.A.; Suchkov, A.A.

    1989-01-01

    The data for ∼ 5500 F-G stars are used to study their kinematics, metal abindance and HR diagram in terms of uvby photometry. The age-metallicity, velocity-metallicity, and age-velocity relations are derived. An estimate for the age of the galactic disk is obtained. The following is shown: 1) At[Fe/H] -0.1, turn out to be kinematically younger than these G dwarfs. The same paradox is revealed by G and K giants

  4. Galactic warps and the shape of heavy halos

    International Nuclear Information System (INIS)

    Sparke, L.S.

    1984-01-01

    The outer disks of many spiral galaxies are bent away from the plane of the inner disk; the abundance of these warps suggests that they are long-lived. Isolated galactic disks have long been thought to have no discrete modes of vertical oscillation under their own gravity, and so to be incapable of sustaining persistent warps. However, the visible disk contains only a fraction of the galactic mass; an invisible galactic halo makes up the rest. This paper presents an investigation of vertical warping modes in self-gravitating disks, in the imposed potential due to an axisymmetric unseen massive halo. If the halo matter is distributed so that the free precession rate of a test particle decreases with radius near the edge of the disk, then the disk has a discrete mode of vibration; oblate halos which become rapidly more flattened at large radii, and uniformly prolate halos, satisfy this requirement. Otherwise, the disk has no discrete modes and so cannot maintain a long-lived warp, unless the edge is sharply truncated. Computed mode shapes which resemble the observed warps can be found for halo masses consistent with those inferred from galactic rotation curves

  5. Numerical Simulations of Multiphase Winds and Fountains from Star-forming Galactic Disks. I. Solar Neighborhood TIGRESS Model

    Science.gov (United States)

    Kim, Chang-Goo; Ostriker, Eve C.

    2018-02-01

    Gas blown away from galactic disks by supernova (SN) feedback plays a key role in galaxy evolution. We investigate outflows utilizing the solar neighborhood model of our high-resolution, local galactic disk simulation suite, TIGRESS. In our numerical implementation, star formation and SN feedback are self-consistently treated and well resolved in the multiphase, turbulent, magnetized interstellar medium. Bursts of star formation produce spatially and temporally correlated SNe that drive strong outflows, consisting of hot (T> 5× {10}5 {{K}}) winds and warm (5050 {{K}} 1 {kpc} from the midplane has mass and energy fluxes nearly constant with d. The hot flow escapes our local Cartesian box barely affected by gravity, and is expected to accelerate up to terminal velocity of {v}{wind}∼ 350{--}500 {km} {{{s}}}-1. The mean mass and energy loading factors of the hot wind are 0.1 and 0.02, respectively. For warm gas, the mean outward mass flux through d=1 {kpc} is comparable to the mean star formation rate, but only a small fraction of this gas is at velocity > 50 {km} {{{s}}}-1. Thus, the warm outflows eventually fall back as inflows. The warm fountain flows are created by expanding hot superbubbles at d< 1 {kpc}; at larger d neither ram pressure acceleration nor cooling transfers significant momentum or energy flux from the hot wind to the warm outflow. The velocity distribution at launching near d∼ 1 {kpc} is a better representation of warm outflows than a single mass loading factor, potentially enabling development of subgrid models for warm galactic winds in arbitrary large-scale galactic potentials.

  6. Open Clusters as Tracers of the Galactic Disk

    Science.gov (United States)

    Cantat-Gaudin, Tristan

    2015-01-01

    Open clusters (OCs) are routinely used as reliable tracers of the properties and evolution of the galactic disk, as they can be found at all galactocentric distances and span a wide range of ages. More than 3000 OCs are listed in catalogues, although few have been studied in details. The goal of this work is to study the properties of open clusters. This work was conducted in the framework of the Gaia-ESO Survey (GES). GES is an observational campaign targeting more than 100,000 stars in all major components of the Milky Way, including stars in a hundred open clusters. It uses the FLAMES instrument at the VLT to produce high and medium-resolution spectra, which provide accurate radial velocities and individual elemental abundances. In this framework, the goals of the Thesis are: * to study the properties of OCs and of their stars from photometry and spectroscopy to derive their age, the extinction and the chemical composition of the stars, to begin to build a homogeneous data base. Looking at literature data it is clear that different authors derive substantially different chemical compositions, and in general OC parameters. * the study of OCs and their chemical homogeneity (or inhomogeneity) can cast light on what is still an open issue: the presence of multiple populations in clusters. While multiple generations of stars are now ubiquitously found in globular clusters in the Milky Way and in the Magellanic Clouds, they have not been yet detected in open clusters. What is the main driver of the self-pollution process? * to study the cluster formation process. All, or at least a significant fraction of stars form in clusters. Young clusters (a few Myr) can retain some of the properties of the molecular cloud they originate from and give us insight about the cluster assembly process. The first GES data release contains data for the young OC Gamma Velorum, in which two (dynamically different) subpopulations have been identified. This cluster can serve as a test case

  7. The Power Spectrum of the Milky Way: Velocity Fluctuations in the Galactic Disk

    Science.gov (United States)

    Bovy, Jo; Bird, Jonathan C.; García Pérez, Ana E.; Majewski, Steven R.; Nidever, David L.; Zasowski, Gail

    2015-02-01

    We investigate the kinematics of stars in the mid-plane of the Milky Way (MW) on scales between 25 pc and 10 kpc with data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the Radial Velocity Experiment (RAVE), and the Geneva-Copenhagen survey (GCS). Using red-clump (RC) stars in APOGEE, we determine the large-scale line-of-sight velocity field out to 5 kpc from the Sun in (0.75 kpc)2 bins. The solar motion V ⊙ - c with respect to the circular velocity Vc is the largest contribution to the power on large scales after subtracting an axisymmetric rotation field; we determine the solar motion by minimizing the large-scale power to be V ⊙ - c = 24 ± 1 (ran.) ± 2 (syst. [Vc ]) ± 5 (syst.[large-scale]) km s-1, where the systematic uncertainty is due to (1) a conservative 20 km s-1 uncertainty in Vc and (2) the estimated power on unobserved larger scales. Combining the APOGEE peculiar-velocity field with RC stars in RAVE out to 2 kpc from the Sun and with local GCS stars, we determine the power spectrum of residual velocity fluctuations in the MW's disk on scales between 0.2 kpc-1 plane of the Galactic disk near the Sun. Streaming motions ≈10 km s-1 on >~ 3 kpc scales in the MW are in good agreement with observations of external galaxies and directly explain why local determinations of the solar motion are inconsistent with global measurements.

  8. Stellar dynamics and galactic evolution

    International Nuclear Information System (INIS)

    Gilmore, G.; Kuijken, K.; Wyse, R.F.G.

    1989-01-01

    Solar neighbourhood observations have the unique capability of providing detailed study of the consequences of the early evolution of the Galaxy. Important examples of this capability include determination of the distribution of luminous and unseen mass in the Galaxy, and deduction of the rate of star formation and chemical evolution in the proto-Galaxy. We describe a new method to determine the distribution of mass in the Galactic disk. We reinvestigate determinations of the local volume mass density (the Oort limit) and show there to be serious internal inconsistencies in the available data. The most likely value for the local volume mass density, based on old stars and with kinematic models consistent with the age structure of the local disk is ∼ 0.1 solar mass pc -3 , though this value is still poorly determined. Thus, there is no significant evidence for any missing mass associated with the Galactic disk. We also reinvestigate observational data on the chemical abundances and kinematics of old stars in the Galaxy. The (Intermediate Population II) thick disk stars are most likely as old as the globular clusters, and kinematically distinct from the old disk. This favours models of thick disk origin involving a discrete disruptive event, such as the accretion of a satellite of the Galaxy early in the evolution of the Galactic disk. (author)

  9. Compressional heating in magnetized disks neighborhood: from the galactic center to micro-quasars

    International Nuclear Information System (INIS)

    Belmont, Renaud

    2005-01-01

    Faint, magnetized and energetic plasmas are very common media in Astrophysics. This thesis is dedicated to two specific cases characterized by a thin disk geometry: the Galactic center and the corona of micro-quasars. In both cases, observations show evidence for a faint and very hot plasma (at 100 million and 1 billion degrees) whose origin is unknown; some clues seem also to indicate a strong, large scale bipolar magnetic field. At the Galactic Center, the gas temperature is such that, if it were collisional and mostly composed by hydrogen, it would escape quickly, so that the power required to sustain the related energy losses would be huge. We however show that the specific conditions of this region can lead to form a helium plasma that is confined by the Galactic potential. In this favorable situation, we study a possible heating mechanism based on the high viscosity of the hot plasma and friction with cold molecular clouds flowing in this region. The corona of micro-quasars is a very similar issue but it is probably weakly collisional. In this regime we study a heating by magnetic pumping, by which the resonance between the periodic motion of some coronal ions and the periodic excitation by an instability in the disc itself can energize the corona. We show that this mechanism is inefficient to explain the hot temperature. (author) [fr

  10. MOA-2013-BLG-220Lb: Massive planetary companion to galactic-disk host

    Energy Technology Data Exchange (ETDEWEB)

    Yee, J. C.; Gould, A.; Gaudi, B. S. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Han, C.; Choi, J.-Y.; Hwang, K.-H.; Jung, Y. K. [Department of Physics, Chungbuk National University, Cheongju 361-763 (Korea, Republic of); Skowron, J.; Udalski, A. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland); Bond, I. A. [Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland (New Zealand); Hundertmark, M. [SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Monard, L. A. G. [Klein Karoo Observatory, Centre for Backyard Astrophysics, Calitzdorp (South Africa); Porritt, I. [Turitea Observatory, Palmerston North (New Zealand); Nelson, P. [Ellinbank Observatory, Ellinbank, Victoria (Australia); Bozza, V. [Dipartimento di Fisica " E. R. Caianiello," Università degli Studi di Salerno, Via S. Allende, I-84081 Baronissi (Italy); Albrow, M. D. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8020 (New Zealand); Christie, G. W. [Auckland Observatory, Auckland (New Zealand); DePoy, D. L. [Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843-4242 (United States); Lee, C.-U. [Korea Astronomy and Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); McCormick, J. [Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland (New Zealand); Collaboration: μFUN Collaboration),; MOA Collaboration),; OGLE Collaboration),; RoboNet Collaboration),; and others

    2014-07-20

    We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 ± 0.02 × 10{sup –3} relative to its host. The proper motion, μ = 12.5 ± 1 mas yr{sup –1}, is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within ∼7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.

  11. Kinematics of HI near the galactic center

    International Nuclear Information System (INIS)

    Sinha, R.P.

    1979-01-01

    The results of a survey of 21-cm line emission in the Milky Way Galaxy from 338. 0 5 through 360 0 to 11 0 longitude and from -2 0 to +2 0 latitude are presented. The latitude coverage is complete over this range for a given longitude. Points are observed at an interval of 15 arcmin (0.7 beamwidth). The longitude coverage is complete between 1 = 357 0 and 1 = 3 0 . Outside this range points have been observed at intervals of 0. 0 5 in longitude. The symmetry properties of the distribution of HI in the region around the galactic center have been explored. Inside a radius of 1 kpc the HI appears to be distributed in the shape of an elongated non-circular slowly rotating disk which is inclined to the galactic equator. This disk is separate from the general galactic disk of HI. In the central disk the density of HI decreases steeply as the distance from the center increases. The density of HI in the annular space between the central disk and the general galactic disk is very low. The velocity dispersion of the HI distribution in the central elongated disk is of the order of 100 km/s. The isovelocity contours on the longitude-latitude plane of the HI associated with this elongated central disk have the characteristic shape such that the angle between the minor axis and the zero-Doppler velocity contour is different than zero. Such a phenomenon has been observed in the central regions of elliptical galaxies and has been attributed to the triaxial nature of the mass distribution

  12. IRON OPACITY BUMP CHANGES THE STABILITY AND STRUCTURE OF ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Yan-Fei [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Davis, Shane W. [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904-4325 (United States); Stone, James M. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2016-08-10

    Accretion disks around supermassive black holes have regions where the Rosseland mean opacity can be larger than the electron scattering opacity due to the large number of bound–bound transitions in iron. We study the effects of this iron opacity “bump” on the thermal stability and vertical structure of radiation-pressure-dominated accretion disks, utilizing three-dimensional radiation magnetohydrodynamic (MHD) simulations in the local shearing box approximation. The simulations self-consistently calculate the heating due to MHD turbulence caused by magneto-rotational instability and radiative cooling by using the radiative transfer module based on a variable Eddington tensor in Athena. For a 5 × 10{sup 8} solar mass black hole with ∼3% of the Eddington luminosity, a model including the iron opacity bump maintains its structure for more than 10 thermal times without showing significant signs of thermal runaway. In contrast, if only electron scattering and free–free opacity are included as in the standard thin disk model, the disk collapses on the thermal timescale. The difference is caused by a combination of (1) an anti-correlation between the total optical depth and the midplane pressure, and (2) enhanced vertical advective energy transport. These results suggest that the iron opacity bump may have a strong impact on the stability and structure of active galactic nucleus (AGN) accretion disks, and may contribute to a dependence of AGN properties on metallicity. Since this opacity is relevant primarily in UV emitting regions of the flow, it may help to explain discrepancies between observation and theory that are unique to AGNs.

  13. THE DISTRIBUTION OF THE ELEMENTS IN THE GALACTIC DISK. II. AZIMUTHAL AND RADIAL VARIATION IN ABUNDANCES FROM CEPHEIDS

    International Nuclear Information System (INIS)

    Luck, R. E.; Andrievsky, S. M.; Kovtyukh, V. V.; Gieren, W.; Graczyk, D.

    2011-01-01

    This paper reports on the spectroscopic investigation of 101 Cepheids in the Carina region. These Cepheids extend previous samples by about 35% in number and increase the amount of the Galactic disk coverage especially in the direction of l ∼ 270 0 . The new Cepheids do not add much information to the radial gradient, but provide a substantial increase in azimuthal coverage. We find no azimuthal dependence in abundance over an 80 deg. angle from the Galactic center in an annulus of 1 kpc depth centered on the Sun. A simple linear fit to the Cepheid data yields a gradient d[Fe/H]/dR G = -0.055 ± 0.003 dex kpc -1 which is somewhat shallower than found from our previous, smaller Cepheid sample.

  14. The Surface Density Profile of the Galactic Disk from the Terminal Velocity Curve

    Science.gov (United States)

    McGaugh, Stacy S.

    2016-01-01

    The mass distribution of the Galactic disk is constructed from the terminal velocity curve and the mass discrepancy-acceleration relation. Mass models numerically quantifying the detailed surface density profiles are tabulated. For R0 = 8 kpc, the models have stellar mass 5 spiral galaxy that obeys scaling relations like the Tully-Fisher relation, the size-mass relation, and the disk maximality-surface brightness relation. The stellar disk is maximal, and the spiral arms are massive. The bumps and wiggles in the terminal velocity curve correspond to known spiral features (e.g., the Centaurus arm is a ˜50% overdensity). The rotation curve switches between positive and negative over scales of hundreds of parsecs. The rms amplitude { }1/2≈ 14 {km} {{{s}}}-1 {{kpc}}-1, implying that commonly neglected terms in the Jeans equations may be nonnegligible. The spherically averaged local dark matter density is ρ0,DM ≈ 0.009 {M}⊙ {{pc}}-3 (0.34 {GeV} {{cm}}-3). Adiabatic compression of the dark matter halo may help reconcile the Milky Way with the c-V200 relation expected in ΛCDM while also helping to mitigate the too-big-to-fail problem, but it remains difficult to reconcile the inner bulge/bar-dominated region with a cuspy halo. We note that NGC 3521 is a near twin to the Milky Way, having a similar luminosity, scale length, and rotation curve.

  15. Galactic winds and the hubble sequence

    International Nuclear Information System (INIS)

    Bregman, J.N.

    1978-01-01

    The conditions for maintenance of supernova-driven galactic winds have been investigated to assess their role in the morphology of disk-bulge galaxies. A fluid mechanical model with gas and stars which includes galactic rotation has been used to investigate several classes of winds. It is found that many galaxies, once their initial gas is depleted, can maintain a wind throughout the entire galaxy, a conditon most easily satisfied by systems with a small bulge-to-disk ratio. If the ratio of supernova heating to total mass loss falls below a critical value that depends on galaxy type and mass, only a partial wind exterior to a critical surface can exist, with infall occurring at interior points. Galaxies in which only the bulge was depleted of gas may support a bulge wind that does not interact with the colder and denser gas in the disk.These results indicate that if SO galaxies are a transition class between elliptical and spiral galaxies, it is probably because early galactic winds, which may initially deplete a galaxy of gas, are more prevalent in SO than in spiral galaxies. However, if SO's form a parallel sequence with spirals, the initial gas-depletion mechanism must be independent of bulge-to-disk ratio. These results are not strongly influenced by altering the galactic mass model, including electron conduction in the flow equations, or adding massive halos

  16. EVOLUTION OF WARPED ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI. I. ROLES OF FEEDING AT THE OUTER BOUNDARIES

    International Nuclear Information System (INIS)

    Li, Yan-Rong; Wang, Jian-Min; Cheng, Cheng; Qiu, Jie

    2013-01-01

    We investigate the alignment processes of spinning black holes and their surrounding warped accretion disks in a frame of two different types of feeding at the outer boundaries. We consider (1) fixed flows in which gas is continually fed with a preferred angular momentum, and (2) free flows in which there is no gas supply and the disks diffuse freely at their outer edges. As expected, we find that for the cases of fixed flows the black hole disk systems always align on timescales of several 10 6 yr, irrespective of the initial inclinations. If the initial inclination angles are larger than π/2, the black hole accretion transits from retrograde to prograde fashion, and the accreted mass onto the black holes during these two phases is comparable. On the other hand, for the cases of free flows, both alignments and anti-alignments can occur, depending on the initial inclinations and the ratios of the angular momentum of the disks to that of the black holes. In such cases, the disks will be consumed within timescales of 10 6 yr by black holes accreting at the Eddington limit. We propose that there is a close connection between the black hole spin and the lifetime for which the feeding persists, which determines the observable episodic lifetimes of active galactic nuclei. We conclude that careful inclusion of the disk feeding at the outer boundaries is crucial for modeling the evolution of the black hole spin.

  17. Angular Spectra of Polarized Galactic Foregrounds

    OpenAIRE

    Cho, Jung; Lazarian, A.

    2003-01-01

    It is believed that magnetic field lines are twisted and bend by turbulent motions in the Galaxy. Therefore, both Galactic synchrotron emission and thermal emission from dust reflects statistics of Galactic turbulence. Our simple model of Galactic turbulence, motivated by results of our simulations, predicts that Galactic disk and halo exhibit different angular power spectra. We show that observed angular spectra of synchrotron emission are compatible with our model. We also show that our mod...

  18. Impact of Distance Determinations on Galactic Structure. I. Young and Intermediate-Age Tracers

    Science.gov (United States)

    Matsunaga, Noriyuki; Bono, Giuseppe; Chen, Xiaodian; de Grijs, Richard; Inno, Laura; Nishiyama, Shogo

    2018-06-01

    Here we discuss impacts of distance determinations on the Galactic disk traced by relatively young objects. The Galactic disk, ˜40 kpc in diameter, is a cross-road of studies on the methods of measuring distances, interstellar extinction, evolution of galaxies, and other subjects of interest in astronomy. A proper treatment of interstellar extinction is, for example, crucial for estimating distances to stars in the disk outside the small range of the solar neighborhood. We'll review the current status of relevant studies and discuss some new approaches to the extinction law. When the extinction law is reasonably constrained, distance indicators found in today and future surveys are telling us stellar distribution and more throughout the Galactic disk. Among several useful distance indicators, the focus of this review is Cepheids and open clusters (especially contact binaries in clusters). These tracers are particularly useful for addressing the metallicity gradient of the Galactic disk, an important feature for which comparison between observations and theoretical models can reveal the evolution of the disk.

  19. Transport of gas from disk to halo in starforming galaxies

    Directory of Open Access Journals (Sweden)

    Shevchenko Mikhail G.

    2017-12-01

    Full Text Available Using 3-D gas dynamic simulations, we study the supernova (SNe driven transport of gas from the galactic disk. We assume that SNe are distributed randomly and uniformly in the galactic plane and we consider sufficiently high volume SNe rates that are typical for starforming galaxies: νSN = (0.3 − 3 × 10−11 pc−3 yr−1. We found that under such conditions, a major part of gas locked initially in the galactic disk is transported up to ∼ 1 − 5 stellar scale heights within several millions years. As expected gas transport is more efficient in the case of a thinner stellar disk. An decrease/increase of SN rate in the galactic disk with the same stellar scale height leads to an enlarging/shortening of time scale for gas transport. Independent of SN rate, the major fraction of the swept up gas is in the cold phase (T 106 K is elevated to larger heights than cold gas.

  20. Large-scale gas dynamical processes affecting the origin and evolution of gaseous galactic halos

    Science.gov (United States)

    Shapiro, Paul R.

    1991-01-01

    Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions ad superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

  1. Oscillations of disks

    CERN Document Server

    Kato, Shoji

    2016-01-01

    This book presents the current state of research on disk oscillation theory, focusing on relativistic disks and tidally deformed disks. Since the launch of the Rossi X-ray Timing Explorer (RXTE) in 1996, many high-frequency quasiperiodic oscillations (HFQPOs) have been observed in X-ray binaries. Subsequently, similar quasi-periodic oscillations have been found in such relativistic objects as microquasars, ultra-luminous X-ray sources, and galactic nuclei. One of the most promising explanations of their origin is based on oscillations in relativistic disks, and a new field called discoseismology is currently developing. After reviewing observational aspects, the book presents the basic characteristics of disk oscillations, especially focusing on those in relativistic disks. Relativistic disks are essentially different from Newtonian disks in terms of several basic characteristics of their disk oscillations, including the radial distributions of epicyclic frequencies. In order to understand the basic processes...

  2. PLANETESIMAL AND PROTOPLANET DYNAMICS IN A TURBULENT PROTOPLANETARY DISK: IDEAL STRATIFIED DISKS

    International Nuclear Information System (INIS)

    Yang, Chao-Chin; Mac Low, Mordecai-Mark; Menou, Kristen

    2012-01-01

    Due to the gravitational influence of density fluctuations driven by magneto-rotational instability in the gas disk, planetesimals and protoplanets undergo diffusive radial migration as well as changes in other orbital properties. The magnitude of the effect on particle orbits can have important consequences for planet formation scenarios. We use the local-shearing-box approximation to simulate an ideal, isothermal, magnetized gas disk with vertical density stratification and simultaneously evolve numerous massless particles moving under the gravitational field of the gas and the host star. We measure the evolution of the particle orbital properties, including mean radius, eccentricity, inclination, and velocity dispersion, and its dependence on the disk properties and the particle initial conditions. Although the results converge with resolution for fixed box dimensions, we find the response of the particles to the gravity of the turbulent gas correlates with the horizontal box size, up to 16 disk scale heights. This correlation indicates that caution should be exercised when interpreting local-shearing-box models involving gravitational physics of magneto-rotational turbulence. Based on heuristic arguments, nevertheless, the criterion L h /R ∼ O(1), where L h is the horizontal box size and R is the distance to the host star, is proposed to possibly circumvent this conundrum. If this criterion holds, we can still conclude that magneto-rotational turbulence seems likely to be ineffective at driving either diffusive migration or collisional erosion under most circumstances.

  3. Probing the Galactic Structure of the Milky Way with H II Regions

    Science.gov (United States)

    Red, Wesley Alexander; Wenger, Trey V.; Balser, Dana; Anderson, Loren; Bania, Thomas

    2018-01-01

    Mapping the structure of the Milky Way is challenging since we reside within the Galactic disk and distances are difficult to determine. Elemental abundances provide important constraints on theories of the formation and evolution of the Milky Way. HII regions are the brightest objects in the Galaxy at radio wavelengths and are detected across the entire Galactic disk. We use the Jansky Very Large Array (VLA) to observe the radio recombination line (RRL) and continuum emission of 120 Galactic HII regions located across the Galactic disk. In thermal equilibrium, metal abundances are expected to set the nebular electron temperature with high abundances producing low temperatures. We derive the metallicity of HII regions using an empirical relation between an HII region's radio recombination line-to-continuum ratio and nebular metallicity. Here we focus on a subset of 20 HII regions from our sample that have been well studied with the Green Bank Telescope (GBT) to test our data reduction pipeline and analysis methods. Our goal is to expand this study to the Southern skies with the Australia Telescope Compact Array and create a metallicity map of the entire Galactic disk.

  4. Galactic models

    International Nuclear Information System (INIS)

    Buchler, J.R.; Gottesman, S.T.; Hunter, J.H. Jr.

    1990-01-01

    Various papers on galactic models are presented. Individual topics addressed include: observations relating to galactic mass distributions; the structure of the Galaxy; mass distribution in spiral galaxies; rotation curves of spiral galaxies in clusters; grand design, multiple arm, and flocculent spiral galaxies; observations of barred spirals; ringed galaxies; elliptical galaxies; the modal approach to models of galaxies; self-consistent models of spiral galaxies; dynamical models of spiral galaxies; N-body models. Also discussed are: two-component models of galaxies; simulations of cloudy, gaseous galactic disks; numerical experiments on the stability of hot stellar systems; instabilities of slowly rotating galaxies; spiral structure as a recurrent instability; model gas flows in selected barred spiral galaxies; bar shapes and orbital stochasticity; three-dimensional models; polar ring galaxies; dynamical models of polar rings

  5. THE POWER SPECTRUM OF THE MILKY WAY: VELOCITY FLUCTUATIONS IN THE GALACTIC DISK

    Energy Technology Data Exchange (ETDEWEB)

    Bovy, Jo [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States); Bird, Jonathan C. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Pérez, Ana E. García; Majewski, Steven R. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Nidever, David L. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48104 (United States); Zasowski, Gail, E-mail: bovy@ias.edu [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)

    2015-02-20

    We investigate the kinematics of stars in the mid-plane of the Milky Way (MW) on scales between 25 pc and 10 kpc with data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the Radial Velocity Experiment (RAVE), and the Geneva-Copenhagen survey (GCS). Using red-clump (RC) stars in APOGEE, we determine the large-scale line-of-sight velocity field out to 5 kpc from the Sun in (0.75 kpc){sup 2} bins. The solar motion V{sub ☉} {sub –} {sub c} with respect to the circular velocity V{sub c} is the largest contribution to the power on large scales after subtracting an axisymmetric rotation field; we determine the solar motion by minimizing the large-scale power to be V{sub ☉} {sub –} {sub c} = 24 ± 1 (ran.) ± 2 (syst. [V{sub c} ]) ± 5 (syst.[large-scale]) km s{sup –1}, where the systematic uncertainty is due to (1) a conservative 20 km s{sup –1} uncertainty in V{sub c} and (2) the estimated power on unobserved larger scales. Combining the APOGEE peculiar-velocity field with RC stars in RAVE out to 2 kpc from the Sun and with local GCS stars, we determine the power spectrum of residual velocity fluctuations in the MW's disk on scales between 0.2 kpc{sup –1} ≤ k ≤ 40 kpc{sup –1}. Most of the power is contained in a broad peak between 0.2 kpc{sup –1} < k < 0.9 kpc{sup –1}. We investigate the expected power spectrum for various non-axisymmetric perturbations and demonstrate that the central bar with commonly used parameters but of relatively high mass can explain the bulk of velocity fluctuations in the plane of the Galactic disk near the Sun. Streaming motions ≈10 km s{sup –1} on ≳ 3 kpc scales in the MW are in good agreement with observations of external galaxies and directly explain why local determinations of the solar motion are inconsistent with global measurements.

  6. Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters

    Science.gov (United States)

    Richert, A. J. W.; Getman, K. V.; Feigelson, E. D.; Kuhn, M. A.; Broos, P. S.; Povich, M. S.; Bate, M. R.; Garmire, G. P.

    2018-04-01

    Photometric detections of dust circumstellar disks around pre-main sequence (PMS) stars, coupled with estimates of stellar ages, provide constraints on the time available for planet formation. Most previous studies on disk longevity, starting with Haisch, Lada & Lada (2001), use star samples from PMS clusters but do not consider datasets with homogeneous photometric sensitivities and/or ages placed on a uniform timescale. Here we conduct the largest study to date of the longevity of inner dust disks using X-ray and 1-8 {μ m} infrared photometry from the MYStIX and SFiNCs projects for 69 young clusters in 32 nearby star-forming regions with ages t ≤ 5 Myr. Cluster ages are derived by combining the empirical AgeJX method with PMS evolutionary models, which treat dynamo-generated magnetic fields in different ways. Leveraging X-ray data to identify disk-free objects, we impose similar stellar mass sensitivity limits for disk-bearing and disk-free YSOs while extending the analysis to stellar masses as low as M ˜ 0.1 M⊙. We find that the disk longevity estimates are strongly affected by the choice of PMS evolutionary model. Assuming a disk fraction of 100% at zero age, the inferred disk half-life changes significantly, from t1/2 ˜ 1.3 - 2 Myr to t1/2 ˜ 3.5 Myr when switching from non-magnetic to magnetic PMS models. In addition, we find no statistically significant evidence that disk fraction varies with stellar mass within the first few Myr of life for stars with masses <2 M⊙, but our samples may not be complete for more massive stars. The effects of initial disk fraction and star-forming environment are also explored.

  7. Chemical constraints on the formation of the Galactic thick disk

    Directory of Open Access Journals (Sweden)

    Feltzing S.

    2012-02-01

    Full Text Available We highlight some results from our detailed abundance analysis study of 703 kinematically selected F and G dwarf stars in the solar neighbourhood. The analysis is based on spectra of high-resolution (R = 45000 to 110 000 and high signal-to-noise (S/N ≈ 150 to 300. The main findings include: (1 at a given metallicity, the thick disk abundance trends are more α-enhanced than those of the thin disk; (2 the metal-rich limit of the thick disk reaches at least solar metallicities; (3 the metal-poor limit of the thin disk is around [Fe/H] ≈−0.8; (4 the thick disk shows an age-metallicity gradient; (5 the thin disk does not show an age-metallicity gradient; (6 the most metal-rich thick disk stars at [Fe/H] ≈ 0 are significantly older than the most metal-poor thin disk stars at [Fe/H] ≈−0.7; (7 based on our elemental abundances we find that kinematical criteria produce thin and thick disk stellar samples that are biased in the sense that stars from the low-velocity tail of the thick disk are classified as thin disk stars, and stars from the high-velocity tail of the thin disk are classified as thick disk stars; (8 age criteria appears to produce thin and thick disk stellar samples with less contamination.

  8. THE CHEMICAL EVOLUTION OF THE MONOCEROS RING/GALACTIC ANTICENTER STELLAR STRUCTURE

    International Nuclear Information System (INIS)

    Chou Meiyin; Majewski, Steven R.; Patterson, Richard J.; Cunha, Katia; Smith, Verne V.; MartInez-Delgado, David

    2010-01-01

    The origin of the Galactic Anticenter Stellar Structure (GASS) or 'Monoceros Ring' - a low-latitude overdensity at the edge of the Galactic disk spanning at least the second and third Galactic quadrants-remains controversial. Models for the origin of GASS generally fall into scenarios where either it is a part (e.g., warp) of the Galactic disk or it represents tidal debris from the disruption of a Milky Way (MW) satellite galaxy. To further constrain models for the origin of GASS, we derive chemical abundance patterns from high-resolution spectra for 21 M giants spatially and kinematically identified with it. The abundances of the (mostly) α-element, titanium, and s-process elements, yttrium and lanthanum, for these GASS stars are found to be lower at the same [Fe/H] than those for MW stars, but similar to those of stars in the Sagittarius stream, other dwarf spheroidal galaxies, and the Large Magellanic Cloud. This demonstrates that GASS stars have a chemical enrichment history typical of dwarf galaxies-and unlike those of typical MW stars (at least MW stars near the Sun). Nevertheless, these abundance results cannot definitively rule out the possibility that GASS was dynamically created out of a previously formed, outer MW disk because ΛCDM-based structure formation models show that galactic disks grow outward by accretion of dwarf galaxies. On the other hand, the chemical patterns seen in GASS stars do provide striking verification that accretion of dwarf galaxies has indeed happened at the edge of the MW disk.

  9. Ab Initio Simulations of a Supernova-driven Galactic Dynamo in an Isolated Disk Galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Butsky, Iryna [Astronomy Department, University of Washington, Seattle, WA 98195 (United States); Zrake, Jonathan; Kim, Ji-hoon; Yang, Hung-I; Abel, Tom [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Menlo Park, CA 94025 (United States)

    2017-07-10

    We study the magnetic field evolution of an isolated spiral galaxy, using isolated Milky Way–mass galaxy formation simulations and a novel prescription for magnetohydrodynamic (MHD) supernova feedback. Our main result is that a galactic dynamo can be seeded and driven by supernova explosions, resulting in magnetic fields whose strength and morphology are consistent with observations. In our model, supernovae supply thermal energy and a low-level magnetic field along with their ejecta. The thermal expansion drives turbulence, which serves a dual role by efficiently mixing the magnetic field into the interstellar medium and amplifying it by means of a turbulent dynamo. The computational prescription for MHD supernova feedback has been implemented within the publicly available ENZO code and is fully described in this paper. This improves upon ENZO 's existing modules for hydrodynamic feedback from stars and active galaxies. We find that the field attains microgauss levels over gigayear timescales throughout the disk. The field also develops a large-scale structure, which appears to be correlated with the disk’s spiral arm density structure. We find that seeding of the galactic dynamo by supernova ejecta predicts a persistent correlation between gas metallicity and magnetic field strength. We also generate all-sky maps of the Faraday rotation measure from the simulation-predicted magnetic field, and we present a direct comparison with observations.

  10. Cosmic Rays and Non-thermal Emission Induced by Accretion of Cool Gas onto the Galactic Disk

    Science.gov (United States)

    Inoue, Susumu; Uchiyama, Yasunobu; Arakawa, Masanori; Renaud, Matthieu; Wada, Keiichi

    2017-11-01

    On both observational and theoretical grounds, the disk of our Galaxy should be accreting cool gas with temperature ≲ {10}5 K via the halo at a rate ˜1 {{M}⊙ {yr}}-1. At least some of this accretion is mediated by high-velocity clouds (HVCs), observed to be traveling in the halo with velocities of a few 100 km s-1 and occasionally impacting the disk at such velocities, especially in the outer regions of the Galaxy. We address the possibility of particle acceleration in shocks triggered by such HVC accretion events, and the detectability of consequent non-thermal emission in the radio to gamma-ray bands and high-energy neutrinos. For plausible shock velocities ˜ 300 {km} {{{s}}}-1 and magnetic field strengths ˜ 0.3{--}10 μ {{G}}, electrons and protons may be accelerated up to ˜1-10 TeV and ˜ 30{--}{10}3 TeV, respectively, in sufficiently strong adiabatic shocks during their lifetime of ˜ {10}6 {{yr}}. The resultant pion decay and inverse Compton gamma-rays may be the origin of some unidentified Galactic GeV-TeV sources, particularly the “dark” source HESS J1503-582 that is spatially coincident with the anomalous H I structure known as “forbidden-velocity wings.” Correlation of their locations with star-forming regions may be weak, absent, or even opposite. Non-thermal radio and X-ray emission from primary and/or secondary electrons may be detectable with deeper observations. The contribution of HVC accretion to Galactic cosmic rays is subdominant, but could be non-negligible in the outer Galaxy. As the thermal emission induced by HVC accretion is likely difficult to detect, observations of such phenomena may offer a unique perspective on probing gas accretion onto the Milky Way and other galaxies.

  11. Does the Galactic Bulge Have Fewer Planets?

    Science.gov (United States)

    Kohler, Susanna

    2016-12-01

    The Milky Ways dense central bulge is a very different environment than the surrounding galactic disk in which we live. Do the differences affect the ability of planets to form in the bulge?Exploring Galactic PlanetsSchematic illustrating how gravitational microlensing by an extrasolar planet works. [NASA]Planet formation is a complex process with many aspects that we dont yet understand. Do environmental properties like host star metallicity, the density of nearby stars, or the intensity of the ambient radiation field affect the ability of planets to form? To answer these questions, we will ultimately need to search for planets around stars in a large variety of different environments in our galaxy.One way to detect recently formed, distant planets is by gravitational microlensing. In this process, light from a distant source star is bent by a lens star that is briefly located between us and the source. As the Earth moves, this momentary alignment causes a blip in the sources light curve that we can detect and planets hosted by the lens star can cause an additional observable bump.Artists impression of the Milky Way galaxy. The central bulge is much denserthan the surroundingdisk. [ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt]Relative AbundancesMost source stars reside in the galactic bulge, so microlensing events can probe planetary systems at any distance between the Earth and the galactic bulge. This means that planet detections from microlensing could potentially be used to measure the relative abundances of exoplanets in different parts of our galaxy.A team of scientists led by Matthew Penny, a Sagan postdoctoral fellow at Ohio State University, set out to do just that. The group considered a sample of 31 exoplanetary systems detected by microlensing and asked the following question: are the planet abundances in the galactic bulge and the galactic disk the same?A Paucity of PlanetsTo answer this question, Penny and collaborators derived the expected

  12. Kiloparsec-scale Simulations of Star Formation in Disk Galaxies. IV. Regulation of Galactic Star Formation Rates by Stellar Feedback

    International Nuclear Information System (INIS)

    Butler, Michael J.; Tan, Jonathan C.; Teyssier, Romain; Nickerson, Sarah; Rosdahl, Joakim; Van Loo, Sven

    2017-01-01

    Star formation from the interstellar medium of galactic disks is a basic process controlling the evolution of galaxies. Understanding the star formation rate (SFR) in a local patch of a disk with a given gas mass is thus an important challenge for theoretical models. Here we simulate a kiloparsec region of a disk, following the evolution of self-gravitating molecular clouds down to subparsec scales, as they form stars that then inject feedback energy by dissociating and ionizing UV photons and supernova explosions. We assess the relative importance of each feedback mechanism. We find that H 2 -dissociating feedback results in the largest absolute reduction in star formation compared to the run with no feedback. Subsequently adding photoionization feedback produces a more modest reduction. Our fiducial models that combine all three feedback mechanisms yield, without fine-tuning, SFRs that are in excellent agreement with observations, with H 2 -dissociating photons playing a crucial role. Models that only include supernova feedback—a common method in galaxy evolution simulations—settle to similar SFRs, but with very different temperatures and chemical states of the gas, and with very different spatial distributions of young stars.

  13. Kiloparsec-scale Simulations of Star Formation in Disk Galaxies. IV. Regulation of Galactic Star Formation Rates by Stellar Feedback

    Energy Technology Data Exchange (ETDEWEB)

    Butler, Michael J. [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Tan, Jonathan C. [Departments of Astronomy and Physics, University of Florida, Gainesville, FL 32611 (United States); Teyssier, Romain; Nickerson, Sarah [Institute for Computational Science, University of Zurich, 8049 Zurich (Switzerland); Rosdahl, Joakim [Leiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2017-06-01

    Star formation from the interstellar medium of galactic disks is a basic process controlling the evolution of galaxies. Understanding the star formation rate (SFR) in a local patch of a disk with a given gas mass is thus an important challenge for theoretical models. Here we simulate a kiloparsec region of a disk, following the evolution of self-gravitating molecular clouds down to subparsec scales, as they form stars that then inject feedback energy by dissociating and ionizing UV photons and supernova explosions. We assess the relative importance of each feedback mechanism. We find that H{sub 2}-dissociating feedback results in the largest absolute reduction in star formation compared to the run with no feedback. Subsequently adding photoionization feedback produces a more modest reduction. Our fiducial models that combine all three feedback mechanisms yield, without fine-tuning, SFRs that are in excellent agreement with observations, with H{sub 2}-dissociating photons playing a crucial role. Models that only include supernova feedback—a common method in galaxy evolution simulations—settle to similar SFRs, but with very different temperatures and chemical states of the gas, and with very different spatial distributions of young stars.

  14. No more active galactic nuclei in clumpy disks than in smooth galaxies at z ∼ 2 in CANDELS/3D-HST

    Energy Technology Data Exchange (ETDEWEB)

    Trump, Jonathan R.; Luo, Bin; Brandt, W. N. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Barro, Guillermo; Guo, Yicheng; Koo, David C.; Faber, S. M. [University of California Observatories/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Juneau, Stéphanie [Irfu/Service d' Astrophysique, CEA-Saclay, Orme des Merisiers, F-91191 Gif-sur-Yvette Cedex (France); Weiner, Benjamin J. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Brammer, Gabriel B.; Ferguson, Henry C.; Grogin, Norman A.; Kartaltepe, Jeyhan; Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Dekel, Avishai [Center for Astrophysics and Planetary Science, Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel); Hopkins, Philip F. [California Institute of Technology, MC 105-24, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Kocevski, Dale D. [Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506 (United States); McIntosh, Daniel H. [Department of Physics and Astronomy, University of Missouri-Kansas City, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Momcheva, Ivelina [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); and others

    2014-10-01

    We use CANDELS imaging, 3D-HST spectroscopy, and Chandra X-ray data to investigate if active galactic nuclei (AGNs) are preferentially fueled by violent disk instabilities funneling gas into galaxy centers at 1.3 < z < 2.4. We select galaxies undergoing gravitational instabilities using the number of clumps and degree of patchiness as proxies. The CANDELS visual classification system is used to identify 44 clumpy disk galaxies, along with mass-matched comparison samples of smooth and intermediate morphology galaxies. We note that despite being mass-matched and having similar star formation rates, the smoother galaxies tend to be smaller disks with more prominent bulges compared to the clumpy galaxies. The lack of smooth extended disks is probably a general feature of the z ∼ 2 galaxy population, and means we cannot directly compare with the clumpy and smooth extended disks observed at lower redshift. We find that z ∼ 2 clumpy galaxies have slightly enhanced AGN fractions selected by integrated line ratios (in the mass-excitation method), but the spatially resolved line ratios indicate this is likely due to extended phenomena rather than nuclear AGNs. Meanwhile, the X-ray data show that clumpy, smooth, and intermediate galaxies have nearly indistinguishable AGN fractions derived from both individual detections and stacked non-detections. The data demonstrate that AGN fueling modes at z ∼ 1.85—whether violent disk instabilities or secular processes—are as efficient in smooth galaxies as they are in clumpy galaxies.

  15. THE CONTRIBUTION OF SPIRAL ARMS TO THE THICK DISK ALONG THE HUBBLE SEQUENCE

    Energy Technology Data Exchange (ETDEWEB)

    Martinez-Medina, L. A. [Departamento de Física, Centro de Investigación y de Estudios Avanzados del IPN, A.P. 14-740, 07000 México D.F. (Mexico); Pichardo, B.; Moreno, E. [Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 70-264, 04510, México D.F. (Mexico); Pérez-Villegas, A., E-mail: lmedina@fis.cinvestav.mx, E-mail: barbara@astro.unam.mx, E-mail: mperez@astro.unam.mx [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apartado Postal 3-72, 58090 Morelia, Michoacán (Mexico)

    2015-04-01

    The first mechanism invoked to explain the existence of the thick disk in the Milky Way Galaxy was the spiral arms. Up-to-date work summons several other possibilities that together seem to better explain this component of our Galaxy. All these processes must affect distinct types of galaxies differently, but the contribution of each one has not been straightforward to quantify. In this work, we present the first comprehensive study of the effect of the spiral arms on the formation of thick disks, looking at early- to late-type disk galaxies in an attempt to characterize and quantify this specific mechanism in galactic potentials. To this purpose, we perform test particle numerical simulations in a three-dimensional spiral galactic potential (for early- to late-types spiral galaxies). By varying the parameters of the spiral arms we found that the vertical heating of the stellar disk becomes very important in some cases and strongly depends on the galactic morphology, pitch angle, arm mass, and the arm pattern speed. The later the galaxy type, the larger is the effect on the disk heating. This study shows that the physical mechanism causing the vertical heating is different from simple resonant excitation. The spiral pattern induces chaotic behavior not linked necessarily to resonances but to direct scattering of disk stars, which leads to an increase of the velocity dispersion. We applied this study to the specific example of the Milky Way Galaxy, for which we have also added an experiment that includes the Galactic bar. From this study we deduce that the effect of spiral arms of a Milky-Way-like potential on the dynamical vertical heating of the disk is negligible, unlike later galactic potentials for disks.

  16. The Fragmentation Criteria in Local Vertically Stratified Self-gravitating Disk Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Baehr, Hans; Klahr, Hubert [Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany); Kratter, Kaitlin M., E-mail: baehr@mpia.de [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2017-10-10

    Massive circumstellar disks are prone to gravitational instabilities, which trigger the formation of spiral arms that can fragment into bound clumps under the right conditions. Two-dimensional simulations of self-gravitating disks are useful starting points for studying fragmentation because they allow high-resolution simulations of thin disks. However, convergence issues can arise in 2D from various sources. One of these sources is the 2D approximation of self-gravity, which exaggerates the effect of self-gravity on small scales when the potential is not smoothed to account for the assumed vertical extent of the disk. This effect is enhanced by increased resolution, resulting in fragmentation at longer cooling timescales β . If true, it suggests that the 3D simulations of disk fragmentation may not have the same convergence problem and could be used to examine the nature of fragmentation without smoothing self-gravity on scales similar to the disk scale height. To that end, we have carried out local 3D self-gravitating disk simulations with simple β cooling with fixed background irradiation to determine if 3D is necessary to properly describe disk fragmentation. Above a resolution of ∼40 grid cells per scale height, we find that our simulations converge with respect to the cooling timescale. This result converges in agreement with analytic expectations which place a fragmentation boundary at β {sub crit} = 3.

  17. Ordinary Dark Matter versus Mysterious Dark Matter in Galactic Rotation

    Science.gov (United States)

    Gallo, C. F.; Feng, James

    2008-04-01

    To theoretically describe the measured rotational velocity curves of spiral galaxies, there are two different approaches and conclusions. (1) ORDINARY DARK MATTER. We assume Newtonian gravity/dynamics and successfully find (via computer) mass distributions in bulge/disk configurations that duplicate the measured rotational velocities. There is ordinary dark matter within the galactic disk towards the cooler periphery which has lower emissivity/opacity. There are no mysteries in this scenario based on verified physics. (2) MYSTERIOUS DARK MATTER. Others INaccurately assume the galactic mass distributions follow the measured light distributions, and then the measured rotational velocity curves are NOT duplicated. To alleviate this discrepancy, speculations are invoked re ``Massive Peripheral Spherical Halos of Mysterious Dark Matter.'' But NO matter has been detected in this UNtenable Halo configuration. Many UNverified ``Mysteries'' are invoked as necessary and convenient. CONCLUSION. The first approach utilizing Newtonian gravity/dynamics and searching for the ordinary mass distributions within the galactic disk simulates reality and agrees with data.

  18. A Discovery of a Compact High Velocity Cloud-Galactic Supershell System

    Science.gov (United States)

    Park, Geumsook; Koo, Bon-Chul; Kang, Ji-hyun; Gibson, Steven J.; Peek, Joshua Eli Goldston; Douglas, Kevin A.; Korpela, Eric J.; Heiles, Carl E.

    2017-01-01

    High velocity clouds (HVCs) are neutral hydrogen (HI) gas clouds having very different radial velocities from those of the Galactic disk material. While some large HVC complexes are known to be gas streams tidally stripped from satellite galaxies of the Milky Way, there are relatively isolated and small angular-sized HVCs, so called “compact HVCs (CHVCs)”, the origin of which remains controversial. There are about 300 known CHVCs in the Milky Way, and many of them show a head-tail structure, implying a ram pressure interaction with the diffuse Galactic halo gas. It is, however, not clear whether CHVCs are completely dissipated in the Galactic halo to feed the multi-phase circumgalactic medium or they can survive their trip through the halo and collide with the Galactic disk. The colliding CHVCs may leave a gigantic trail in the disk, and it had been suggested that some of HI supershells that require ≧ 3 x 1052 erg may be produced by the collision of such HVCs.Here we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040+01-282 (hereafter, CHVC040) at its geometrical center using the “Inner-Galaxy Arecibo L-band Feed Array” HI 21 cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud that originated from an intergalactic accreting flow, collided with the disk ˜5 Myr ago to form the supershell. Our results show that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk.

  19. CONSTRAINTS ON COMPTON-THICK WINDS FROM BLACK HOLE ACCRETION DISKS: CAN WE SEE THE INNER DISK?

    International Nuclear Information System (INIS)

    Reynolds, Christopher S.

    2012-01-01

    Strong evidence is emerging that winds can be driven from the central regions of accretion disks in both active galactic nuclei and Galactic black hole binaries. Direct evidence for highly ionized, Compton-thin inner-disk winds comes from observations of blueshifted (v ∼ 0.05-0.1c) iron-K X-ray absorption lines. However, it has been suggested that the inner regions of black hole accretion disks can also drive Compton-thick winds—such winds would enshroud the inner disk, preventing us from seeing direct signatures of the accretion disk (i.e., the photospheric thermal emission, or the Doppler/gravitationally broadened iron Kα line). Here, we show that, provided the source is sub-Eddington, the well-established wind-driving mechanisms fail to launch a Compton-thick wind from the inner disk. For the accelerated region of the wind to be Compton-thick, the momentum carried in the wind must exceed the available photon momentum by a factor of at least 2/λ, where λ is the Eddington ratio of the source, ruling out radiative acceleration unless the source is very close to the Eddington limit. Compton-thick winds also carry large mass fluxes, and a consideration of the connections between the wind and the disk shows this to be incompatible with magneto-centrifugal driving. Finally, thermal driving of the wind is ruled out on the basis of the large Compton radii that typify black hole systems. In the absence of some new acceleration mechanisms, we conclude that the inner regions of sub-Eddington accretion disks around black holes are indeed naked.

  20. ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

    Energy Technology Data Exchange (ETDEWEB)

    McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield, NSW 2122 (Australia); Lockman, F. J. [National Radio Astronomy Observatory, Green Bank, WV 24944 (United States); Dickey, J. M. [School of Physics and Mathematics, University of Tasmania, TAS 7001 (Australia); Gaensler, B. M.; Green, A. J., E-mail: naomi.mcclure-griffiths@csiro.au [Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006 (Australia)

    2013-06-10

    We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of {approx}14 km s{sup -1}, and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at {approx}200 km s{sup -1} in a Galactic wind.

  1. ATOMIC HYDROGEN IN A GALACTIC CENTER OUTFLOW

    International Nuclear Information System (INIS)

    McClure-Griffiths, N. M.; Green, J. A.; Hill, A. S.; Lockman, F. J.; Dickey, J. M.; Gaensler, B. M.; Green, A. J.

    2013-01-01

    We describe a population of small, high-velocity, atomic hydrogen clouds, loops, and filaments found above and below the disk near the Galactic center. The objects have a mean radius of 15 pc, velocity widths of ∼14 km s –1 , and are observed at |z| heights up to 700 pc. The velocity distribution of the clouds shows no signature of Galactic rotation. We propose a scenario where the clouds are associated with an outflow from a central star-forming region at the Galactic center. We discuss the clouds as entrained material traveling at ∼200 km s –1 in a Galactic wind.

  2. The ties that bind? Galactic magnetic fields and ram pressure stripping

    Energy Technology Data Exchange (ETDEWEB)

    Tonnesen, Stephanie; Stone, James, E-mail: stonnes@astro.princeton.edu, E-mail: jstone@astro.princeton.edu [Department of Astrophysics, Princeton University, Peyton Hall, Princeton, NJ 08544 (United States)

    2014-11-10

    One process affecting gas-rich cluster galaxies is ram pressure stripping (RPS), i.e., the removal of galactic gas through direct interaction with the intracluster medium (ICM). Galactic magnetic fields may have an important impact on the stripping rate and tail structure. We run the first magnetohydrodynamic (MHD) simulations of RPS that include a galactic magnetic field, using 159 pc resolution throughout our entire domain in order to resolve mixing throughout the tail. We find very little difference in the total amount of gas removed from the unmagnetized and magnetized galaxies, although a magnetic field with a radial component will initially accelerate stripped gas more quickly. In general, we find that magnetic fields in the disk lead to slower velocities in the stripped gas near the disk and faster velocities farther from the disk. We also find that magnetic fields in the galactic gas lead to larger unmixed structures in the tail. Finally, we discuss whether ram pressure stripped tails can magnetize the ICM. We find that the total magnetic energy density grows as the tail lengthens, likely through turbulence. There are μG-strength fields in the tail in all of our MHD runs, which survive to at least 100 kpc from the disk (the edge of our simulated region), indicating that the area-filling factor of magnetized tails in a cluster could be large.

  3. The Ties that Bind? Galactic Magnetic Fields and Ram Pressure Stripping

    Science.gov (United States)

    Tonnesen, Stephanie; Stone, James

    2014-11-01

    One process affecting gas-rich cluster galaxies is ram pressure stripping (RPS), i.e., the removal of galactic gas through direct interaction with the intracluster medium (ICM). Galactic magnetic fields may have an important impact on the stripping rate and tail structure. We run the first magnetohydrodynamic (MHD) simulations of RPS that include a galactic magnetic field, using 159 pc resolution throughout our entire domain in order to resolve mixing throughout the tail. We find very little difference in the total amount of gas removed from the unmagnetized and magnetized galaxies, although a magnetic field with a radial component will initially accelerate stripped gas more quickly. In general, we find that magnetic fields in the disk lead to slower velocities in the stripped gas near the disk and faster velocities farther from the disk. We also find that magnetic fields in the galactic gas lead to larger unmixed structures in the tail. Finally, we discuss whether ram pressure stripped tails can magnetize the ICM. We find that the total magnetic energy density grows as the tail lengthens, likely through turbulence. There are μG-strength fields in the tail in all of our MHD runs, which survive to at least 100 kpc from the disk (the edge of our simulated region), indicating that the area-filling factor of magnetized tails in a cluster could be large.

  4. Line-driven disk winds in active galactic nuclei: The critical importance of ionization and radiative transfer

    Energy Technology Data Exchange (ETDEWEB)

    Higginbottom, Nick; Knigge, Christian; Matthews, James H. [School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ (United Kingdom); Proga, Daniel [Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 South Maryland Parkway, Las Vegas, NV 89154-4002 (United States); Long, Knox S. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Sim, Stuart A., E-mail: nick_higginbottom@fastmail.fm [School of Mathematics and Physics, Queens University Belfast, University Road, Belfast, BT7 1NN (United Kingdom)

    2014-07-01

    Accretion disk winds are thought to produce many of the characteristic features seen in the spectra of active galactic nuclei (AGNs) and quasi-stellar objects (QSOs). These outflows also represent a natural form of feedback between the central supermassive black hole and its host galaxy. The mechanism for driving this mass loss remains unknown, although radiation pressure mediated by spectral lines is a leading candidate. Here, we calculate the ionization state of, and emergent spectra for, the hydrodynamic simulation of a line-driven disk wind previously presented by Proga and Kallman. To achieve this, we carry out a comprehensive Monte Carlo simulation of the radiative transfer through, and energy exchange within, the predicted outflow. We find that the wind is much more ionized than originally estimated. This is in part because it is much more difficult to shield any wind regions effectively when the outflow itself is allowed to reprocess and redirect ionizing photons. As a result, the calculated spectrum that would be observed from this particular outflow solution would not contain the ultraviolet spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so highly ionized that line driving would not actually be efficient. This does not necessarily mean that line-driven winds are not viable. However, our work does illustrate that in order to arrive at a self-consistent model of line-driven disk winds in AGN/QSO, it will be critical to include a more detailed treatment of radiative transfer and ionization in the next generation of hydrodynamic simulations.

  5. THE STRUCTURE AND SPECTRAL FEATURES OF A THIN DISK AND EVAPORATION-FED CORONA IN HIGH-LUMINOSITY ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Liu, J. Y.; Liu, B. F.; Qiao, E. L.; Mineshige, S.

    2012-01-01

    We investigate the accretion process in high-luminosity active galactic nuclei (HLAGNs) in the scenario of the disk evaporation model. Based on this model, the thin disk can extend down to the innermost stable circular orbit (ISCO) at accretion rates higher than 0.02 M-dot Edd while the corona is weak since part of the coronal gas is cooled by strong inverse Compton scattering of the disk photons. This implies that the corona cannot produce as strong X-ray radiation as observed in HLAGNs with large Eddington ratio. In addition to the viscous heating, other heating to the corona is necessary to interpret HLAGN. In this paper, we assume that a part of accretion energy released in the disk is transported into the corona, heating up the electrons, and is thereby radiated away. For the first time, we compute the corona structure with additional heating, fully taking into account the mass supply to the corona, and find that the corona could indeed survive at higher accretion rates and that its radiation power increases. The spectra composed of bremsstrahlung and Compton radiation are also calculated. Our calculations show that the Compton-dominated spectrum becomes harder with the increase of energy fraction (f) liberating in the corona, and the photon index for hard X-ray (2-10 keV) is 2.2 bol /L 2-10keV ) increases with increasing accretion rate for f < 8/35, which is roughly consistent with the observational results.

  6. Star formation in the outskirts of disk galaxies

    NARCIS (Netherlands)

    Ferguson, AMN

    2002-01-01

    The far outer regions of galactic disks allow an important probe of both star formation and galaxy formation. I discuss how observations of HII regions in these low gas density, low metallicity environments can shed light on the physical processes which drive galactic star formation. The history of

  7. THE ROLE OF THE ACCRETION DISK, DUST, AND JETS IN THE IR EMISSION OF LOW-LUMINOSITY ACTIVE GALACTIC NUCLEI

    Energy Technology Data Exchange (ETDEWEB)

    Mason, R. E. [Gemini Observatory, Northern Operations Center, 670 N. A' ohoku Place, Hilo, HI 96720 (United States); Ramos Almeida, C. [Instituto de Astrofísica de Canarias, C/Vía Láctea, s/n, E-38205 La Laguna, Tenerife (Spain); Levenson, N. A. [Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena (Chile); Nemmen, R. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Alonso-Herrero, A., E-mail: rmason@gemini.edu [Instituto de Física de Cantabria, CSIC-UC, Avenida de los Castros s/n, E-39005 Santander (Spain)

    2013-11-10

    We use recent high-resolution infrared (IR; 1-20 μm) photometry to examine the origin of the IR emission in low-luminosity active galactic nuclei (LLAGN). The data are compared with published model fits that describe the spectral energy distribution (SED) of LLAGN in terms of an advection-dominated accretion flow, truncated thin accretion disk, and jet. The truncated disk in these models is usually not luminous enough to explain the observed IR emission, and in all cases its spectral shape is much narrower than the broad IR peaks in the data. Synchrotron radiation from the jet appears to be important in very radio-loud nuclei, but the detection of strong silicate emission features in many objects indicates that dust must also contribute. We investigate this point by fitting the IR SED of NGC 3998 using dusty torus and optically thin (τ{sub mid-IR} ∼ 1) dust shell models. While more detailed modeling is necessary, these initial results suggest that dust may account for the nuclear mid-IR emission of many LLAGN.

  8. A Map of the Local Velocity Substructure in the Milky Way Disk

    Energy Technology Data Exchange (ETDEWEB)

    Pearl, Alan N.; Newberg, Heidi Jo; Smith, R. Fiona [Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, NY 12180 (United States); Carlin, Jeffrey L. [LSST, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2017-10-01

    We confirm, quantify, and provide a table of the coherent velocity substructure of the Milky Way disk within 2 kpc of the Sun toward the Galactic anticenter, with a 0.2 kpc resolution. We use the radial velocities of ∼340,000 F-type stars obtained with the Guoshoujing Telescope (also known as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST), and proper motions derived from the PPMXL catalog. The PPMXL proper motions have been corrected to remove systematic errors by subtracting the average proper motions of galaxies and QSOs that have been confirmed in the LAMOST spectroscopic survey, and that are within 2.°5 of the star’s position. We provide the resulting table of systematic offsets derived from the PPMXL proper motion measurements of extragalactic objects identified in the LAMOST spectroscopic survey. Using the corrected phase-space stellar sample, we find statistically significant deviations in the bulk disk velocity of 20 km s{sup −1} or more in the three-dimensional velocities of Galactic disk stars. The bulk velocity varies significantly over length scales of half a kiloparsec or less. The rotation velocity of the disk increases by 20 km s{sup −1} from the Sun’s position to 1.5 kpc outside the solar circle. Disk stars in the second quadrant, within 1 kpc of the Sun, are moving radially toward the Galactic center and vertically toward a point a few tenths of a kiloparsec above the Galactic plane; looking down on the disk, the stars appear to move in a circular streaming motion with a radius of the order of 1 kpc.

  9. A galactic disk as a two-fluid system: Consequences for the critical stellar velocity dispersion and the formation of condensations in the gas

    International Nuclear Information System (INIS)

    Jog, C.J.; Solomon, P.M.

    1984-01-01

    We examine the consequences of treating a galactic disk as a two-fluid system for the stability of the entire disk and for the stability and form of the gas in the disk. We find that the existence of even a small fraction of the total disk surface density in a cold fluid (that is, the gas) makes it much harder to stabilize the entire two-fluid disk. (C/sub s/,min)/sub 2-f/, the critical stellar velocity dispersion for a two-fluid disk in an increasing function of μ/sub g//μ/sub s/, the gas fraction, and μ/sub t//kappa, where μ/sub g/, μ/sub s/, and μ/sub t/ are the gaseous, stellar, and total disk surface densities and kappa is the epicyclic frequency. In the Galaxy, we find that (C/sub s/,min)/sub 2-f/ as a function of R peaks when μ/sub t//kappa peaks-at galactocentric radii of Rapprox.5-7 kpc; two-fluid instabilities are most likely to occur in this region. This region is coincident with the peak in the molecular cloud distribution in the Galaxy. At the higher effective gas density resulting from the growth of a two-fluid instability, the gas may become unstble, even when originally the gas by itself is stable. The wavelength of a typical (induced) gas instability in the inner galaxy is approx.400 pc, and it contains approx.10 7 M/sub sun/ of interstellar matter; these instabilities may be identified with clusters of giant molecular clouds. We suggest that many of the spiral features seen in gas-rich spiral galaxies may be material arms or arm segments resulting from sheared two-fluid gravitational instabilities. The analysis presented here is applicable to any general disk galaxy consisting of stars and gas

  10. THE MASS-INDEPENDENCE OF SPECIFIC STAR FORMATION RATES IN GALACTIC DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Abramson, Louis E.; Gladders, Michael D. [Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics, The University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Kelson, Daniel D.; Dressler, Alan; Oemler, Augustus Jr. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Poggianti, Bianca [INAF-Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Vulcani, Benedetta, E-mail: labramson@uchicago.edu [Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai Institutes for Advanced Study, University of Tokyo, Kashiwa 277-8582 (Japan)

    2014-04-20

    The slope of the star formation rate/stellar mass relation (the SFR {sup M}ain Sequence{sup ;} SFR-M {sub *}) is not quite unity: specific star formation rates (SFR/M {sub *}) are weakly but significantly anti-correlated with M {sub *}. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions—portions of a galaxy not forming stars—with M {sub *}. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFR{sub disk} ≡ SFR/M {sub *,} {sub disk}) reduces the M {sub *} dependence of SF efficiency by ∼0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log sSFR{sub disk}-log M {sub *} to have a slope β{sub disk} in [ – 0.20, 0.00] ± 0.02 (depending on the SFR estimator and Main Sequence definition) for star-forming galaxies with M {sub *} ≥ 10{sup 10} M {sub ☉} and bulge mass-fractions B/T ≲ 0.6, generally consistent with a pure-disk control sample (β{sub control} = –0.05 ± 0.04). That (SFR/M {sub *,} {sub disk}) is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any SFR-M {sub *} relation, including manifestations of ''mass quenching'' (bulge growth), factors shaping the star-forming stellar mass function (uniform dlog M {sub *}/dt for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in SFR(M {sub *}, t)). Our results emphasize the need to treat galaxies as composite systems—not integrated masses—in observational and theoretical work.

  11. Finding evolved stars in the inner Galactic disk with Gaia

    Science.gov (United States)

    Quiroga-Nuñez, L. H.; van Langevelde, H. J.; Pihlström, Y. M.; Sjouwerman, L. O.; Brown, A. G. A.

    2018-04-01

    The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey will provide positions and line-of-sight velocities of ~20, 000 evolved, maser bearing stars in the Galactic plane. Although this Galactic region is affected by optical extinction, BAaDE targets may have Gaia cross-matches, eventually providing additional stellar information. In an initial attempt to cross-match BAaDE targets with Gaia, we have found more than 5,000 candidates. Of these, we may expect half to show SiO emission, which will allow us to obtain velocity information. The cross-match is being refined to avoid false positives using different criteria based on distance analysis, flux variability, and color assessment in the mid- and near-IR. Once the cross-matches can be confirmed, we will have a unique sample to characterize the stellar population of evolved stars in the Galactic bulge, which can be considered fossils of the Milky Way formation.

  12. STAR FORMATION IN SELF-GRAVITATING DISKS IN ACTIVE GALACTIC NUCLEI. II. EPISODIC FORMATION OF BROAD-LINE REGIONS

    International Nuclear Information System (INIS)

    WangJianmin; Du Pu; Ge Junqiang; Hu Chen; Baldwin, Jack A.; Ferland, Gary J.

    2012-01-01

    This is the second in a series of papers discussing the process and effects of star formation in the self-gravitating disk around the supermassive black holes in active galactic nuclei (AGNs). We have previously suggested that warm skins are formed above the star-forming (SF) disk through the diffusion of warm gas driven by supernova explosions. Here we study the evolution of the warm skins when they are exposed to the powerful radiation from the inner part of the accretion disk. The skins initially are heated to the Compton temperature, forming a Compton atmosphere (CAS) whose subsequent evolution is divided into four phases. Phase I is the duration of pure accumulation supplied by the SF disk. During phase II clouds begin to form due to line cooling and sink to the SF disk. Phase III is a period of preventing clouds from sinking to the SF disk through dynamic interaction between clouds and the CAS because of the CAS overdensity driven by continuous injection of warm gas from the SF disk. Finally, phase IV is an inevitable collapse of the entire CAS through line cooling. This CAS evolution drives the episodic appearance of broad-line regions (BLRs). We follow the formation of cold clouds through the thermal instability of the CAS during phases II and III, using linear analysis. Since the clouds are produced inside the CAS, the initial spatial distribution of newly formed clouds and angular momentum naturally follow the CAS dynamics, producing a flattened disk of clouds. The number of clouds in phases II and III can be estimated, as well as the filling factor of clouds in the BLR. Since the cooling function depends on the metallicity, the metallicity gradients that originate in the SF disk give rise to different properties of clouds in different radial regions. We find from the instability analysis that clouds have column density N H ∼ 22 cm –2 in the metal-rich regions whereas they have N H ∼> 10 22 cm –2 in the metal-poor regions. The metal-rich clouds

  13. HERSCHEL OBSERVATIONS REVEAL ANOMALOUS MOLECULAR ABUNDANCES TOWARD THE GALACTIC CENTER

    Energy Technology Data Exchange (ETDEWEB)

    Sonnentrucker, P. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Neufeld, D. A.; Indriolo, N. [Physics and Astronomy Department, Johns Hopkins University, Baltimore, MD 21218 (United States); Gerin, M.; De Luca, M. [LERMA-LRA, UMR 8112 du CNRS, Observatoire de Paris, Ecole Normale Superieure, UPMC and UCP, 24 rue Lhomond, F-75231, Paris Cedex 05 (France); Lis, D. C. [Astronomy Department, California Institute of Technology, Pasadena, CA 91125 (United States); Goicoechea, J. R., E-mail: sonnentr@stsci.edu [Centro de Astrobiologia, CSIC/INTA, E-28850, Madrid (Spain)

    2013-01-20

    We report the Herschel detections of hydrogen fluoride (HF) and para-water (p-H{sub 2}O) in gas intercepting the sight lines to two well-studied molecular clouds in the vicinity of the Sgr A complex: G-0.02-0.07 (the {sup +}50 km s{sup -1} cloud{sup )} and G-0.13-0.08 (the {sup +}20 km s{sup -1} cloud{sup )}. Toward both sight lines, HF and water absorption components are detected over a wide range of velocities covering {approx}250 km s{sup -1}. For all velocity components with V{sub LSR} > -85 km s{sup -1}, we find that the HF and water abundances are consistent with those measured toward other sight lines probing the Galactic disk gas. The velocity components with V{sub LSR} {<=} -85 km s{sup -1}, which are known to trace gas residing within {approx}200 pc of the Galactic center, however, exhibit water vapor abundances with respect to HF at least a factor three higher than those found in the Galactic disk gas. Comparison with CH data indicates that our observations are consistent with a picture where HF and a fraction of the H{sub 2}O absorption arise in diffuse molecular clouds showing Galactic disk-like abundances while the bulk of the water absorption arises in warmer (T {>=} 400 K) diffuse molecular gas for V{sub LSR} {<=} -85 km s{sup -1}. This diffuse Interstellar Medium (ISM) phase has also been recently revealed through observations of CO, HF, H{sup +}{sub 3}, and H{sub 3}O{sup +} absorption toward other sight lines probing the Galactic center inner region.

  14. Hard X-ray emission mechanism of active galactic nuclei sources

    International Nuclear Information System (INIS)

    Liang, E.P.T.

    1979-01-01

    Within the framework of unsaturated Compton disk accretion onto a supermassive black hole as model for power-law active galactic nuclei X-ray sources (as opposed to the synchro-Compton model), we compare the hot inner disk model of Shapiro, Lightman, and Eardley and the disk corona model with balanced conduction and Compton losses. Both can generate electron temperatures > or approx. =10 9 K in the supermassive case but promise other observable distinctions. The sandwich configuration of the disk corona provides a natural explanation of why Comptonization is unsaturated

  15. Scale Length of the Galactic Thin Disk

    Indian Academy of Sciences (India)

    tribpo

    thin disk density scale length, hR, is rather short (2.7 ± 0.1 kpc). Key words. ... The 2MASS near infrared data provide, for the first time, deep star counts on a ... peaks allows to adjust the spatial extinction law in the model. ... probability that fi.

  16. Astrophysical disks Collective and Stochastic Phenomena

    CERN Document Server

    Fridman, Alexei M; Kovalenko, Ilya G

    2006-01-01

    The book deals with collective and stochastic processes in astrophysical discs involving theory, observations, and the results of modelling. Among others, it examines the spiral-vortex structure in galactic and accretion disks , stochastic and ordered structures in the developed turbulence. It also describes sources of turbulence in the accretion disks, internal structure of disk in the vicinity of a black hole, numerical modelling of Be envelopes in binaries, gaseous disks in spiral galaxies with shock waves formation, observation of accretion disks in a binary system and mass distribution of luminous matter in disk galaxies. The editors adaptly brought together collective and stochastic phenomena in the modern field of astrophysical discs, their formation, structure, and evolution involving the methodology to deal with, the results of observation and modelling, thereby advancing the study in this important branch of astrophysics and benefiting Professional Researchers, Lecturers, and Graduate Students.

  17. RINGED ACCRETION DISKS: EQUILIBRIUM CONFIGURATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: d.pugliese.physics@gmail.com, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2015-12-15

    We investigate a model of a ringed accretion disk, made up by several rings rotating around a supermassive Kerr black hole attractor. Each toroid of the ringed disk is governed by the general relativity hydrodynamic Boyer condition of equilibrium configurations of rotating perfect fluids. Properties of the tori can then be determined by an appropriately defined effective potential reflecting the background Kerr geometry and the centrifugal effects. The ringed disks could be created in various regimes during the evolution of matter configurations around supermassive black holes. Therefore, both corotating and counterrotating rings have to be considered as being a constituent of the ringed disk. We provide constraints on the model parameters for the existence and stability of various ringed configurations and discuss occurrence of accretion onto the Kerr black hole and possible launching of jets from the ringed disk. We demonstrate that various ringed disks can be characterized by a maximum number of rings. We present also a perturbation analysis based on evolution of the oscillating components of the ringed disk. The dynamics of the unstable phases of the ringed disk evolution seems to be promising in relation to high-energy phenomena demonstrated in active galactic nuclei.

  18. Properties of the disk system of globular clusters

    International Nuclear Information System (INIS)

    Armandroff, T.E.

    1989-01-01

    A large refined data sample is used to study the properties and origin of the disk system of globular clusters. A scale height for the disk cluster system of 800-1500 pc is found which is consistent with scale-height determinations for samples of field stars identified with the Galactic thick disk. A rotational velocity of 193 + or - 29 km/s and a line-of-sight velocity dispersion of 59 + or - 14 km/s have been found for the metal-rich clusters. 70 references

  19. Variable Stars Observed in the Galactic Disk by AST3-1 from Dome A, Antarctica

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Lingzhi; Ma, Bin; Hu, Yi; Liu, Qiang; Shang, Zhaohui [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China); Li, Gang; Fu, Jianning [Department of Astronomy, Beijing Normal University, Beijing, 100875 (China); Wang, Lifan; Cui, Xiangqun; Du, Fujia; Gong, Xuefei; Li, Xiaoyan; Li, Zhengyang; Yuan, Xiangyan; Zhou, Jilin [Chinese Center for Antarctic Astronomy, Nanjing 210008 (China); Ashley, Michael C. B. [School of Physics, University of New South Wales, NSW 2052 (Australia); Pennypacker, Carl R. [Center for Astrophysics, Lawrence Berkeley National Laboratory, Berkeley, CA (United States); York, Donald G., E-mail: wanglingzhi@bao.ac.cn [Department of Astronomy and Astrophysics and Enrico Fermi Institute, University of Chicago, Chicago, IL 60637 (United States)

    2017-03-01

    AST3-1 is the second-generation wide-field optical photometric telescope dedicated to time-domain astronomy at Dome A, Antarctica. Here, we present the results of an i -band images survey from AST3-1 toward one Galactic disk field. Based on time-series photometry of 92,583 stars, 560 variable stars were detected with i magnitude ≤16.5 mag during eight days of observations; 339 of these are previously unknown variables. We tentatively classify the 560 variables as 285 eclipsing binaries (EW, EB, and EA), 27 pulsating variable stars ( δ Scuti, γ Doradus, δ Cephei variable, and RR Lyrae stars), and 248 other types of variables (unclassified periodic, multiperiodic, and aperiodic variable stars). Of the eclipsing binaries, 34 show O’Connell effects. One of the aperiodic variables shows a plateau light curve and another variable shows a secondary maximum after peak brightness. We also detected a complex binary system with an RS CVn-like light-curve morphology; this object is being followed-up spectroscopically using the Gemini South telescope.

  20. Binary pulsars as probes of a Galactic dark matter disk

    Science.gov (United States)

    Caputo, Andrea; Zavala, Jesús; Blas, Diego

    2018-03-01

    As a binary pulsar moves through a wind of dark matter particles, the resulting dynamical friction modifies the binary's orbit. We study this effect for the double disk dark matter (DDDM) scenario, where a fraction of the dark matter is dissipative and settles into a thin disk. For binaries within the dark disk, this effect is enhanced due to the higher dark matter density and lower velocity dispersion of the dark disk, and due to its co-rotation with the baryonic disk. We estimate the effect and compare it with observations for two different limits in the Knudsen number (Kn). First, in the case where DDDM is effectively collisionless within the characteristic scale of the binary (Kn ≫ 1) and ignoring the possible interaction between the pair of dark matter wakes. Second, in the fully collisional case (Kn ≪ 1), where a fluid description can be adopted and the interaction of the pair of wakes is taken into account. We find that the change in the orbital period is of the same order of magnitude in both limits. A comparison with observations reveals good prospects to probe currently allowed DDDM models with timing data from binary pulsars in the near future. We finally comment on the possibility of extending the analysis to the intermediate (rarefied gas) case with Kn ∼ 1.

  1. Spin temperature and density of cold and warm H I in the Galactic disk: Hidden H I

    Science.gov (United States)

    Sofue, Yoshiaki

    2018-05-01

    We present a method to determine the spin temperature TS and volume density n of H I gas simultaneously along the tangent-point circle of Galactic rotation in the Milky Way by using the χ2 method. The best-fit TS is shown to range either in TS ˜ 100-120 K or in 1000-3000 K, indicating that the gas is in the cold H I phase with high density and large optical depth, or in warm H I with low density and small optical depth. Averaged values at 3 ≤ R ≤ 8 kpc are obtained to be TS = 106.7 ± 16.0 K and n = 1.53 ± 0.86 H cm-3 for cold H I, and 1720 ± 1060 K and 0.38 ± 0.10 H cm-3 for warm H I, where R = 8 |sinl| kpc is the galacto-centric distance along the tangent-point circle. The cold H I appears in spiral arms and rings, whereas warm H I appears in the inter-arm regions. The cold H I is denser by a factor of ˜4 than warm H I. The present analysis has revealed the hidden H I mass in the cold and optically thick phase in the Galactic disk. The total H I mass inside the solar circle is shown to be greater by a factor of 2-2.5 than the current estimation by the optically thin assumption.

  2. THE EVOLUTION OF PROTOPLANETARY DISKS IN THE ARCHES CLUSTER

    International Nuclear Information System (INIS)

    Olczak, C.; Kaczmarek, T.; Pfalzner, S.; Harfst, S.; Portegies Zwart, S.

    2012-01-01

    Most stars form in a cluster environment. These stars are initially surrounded by disks from which potentially planetary systems form. Of all cluster environments, starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favor rapid destruction of circumstellar disks via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field, we investigate the effect of stellar encounters on circumstellar disks in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic center, only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one-third of the circumstellar disks in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a weaker second pair of tidal tails that is overpopulated by disk-poor stars. Two predictions arise from our study. (1) If not destroyed by photoevaporation protoplanetary disks of massive late B- and early O-type stars represent the most likely hosts of planet formation in starburst clusters. (2) Multi-epoch K- and L-band photometry of the Arches cluster would provide the kinematically selected membership sample required to detect the additional pair of disk-poor tidal tails.

  3. The properties of the disk system of globular clusters

    Science.gov (United States)

    Armandroff, Taft E.

    1989-01-01

    A large refined data sample is used to study the properties and origin of the disk system of globular clusters. A scale height for the disk cluster system of 800-1500 pc is found which is consistent with scale-height determinations for samples of field stars identified with the Galactic thick disk. A rotational velocity of 193 + or - 29 km/s and a line-of-sight velocity dispersion of 59 + or - 14 km/s have been found for the metal-rich clusters.

  4. MAXIMALLY STAR-FORMING GALACTIC DISKS. II. VERTICALLY RESOLVED HYDRODYNAMIC SIMULATIONS OF STARBURST REGULATION

    Energy Technology Data Exchange (ETDEWEB)

    Shetty, Rahul [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); Ostriker, Eve C., E-mail: R.Shetty@.uni-heidelberg.de, E-mail: ostriker@astro.umd.edu [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

    2012-07-20

    We explore the self-regulation of star formation using a large suite of high-resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium, the total midplane pressure, dominated by turbulence, must balance the vertical weight of the interstellar medium. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a wide range of parameters, including surface density {Sigma}, momentum injected per stellar mass formed (p{sub *}/m{sub *}), and angular velocity. The simulations are two-dimensional radial-vertical slices, and include both self-gravity and an external potential that helps to confine gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate {Sigma}{sub SFR}, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with p{sub *}/m{sub *}. The efficiency of star formation per free-fall time at the midplane density, {epsilon}{sub ff}(n{sub 0}), is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure {epsilon}{sub ff}(n{sub 0}) {approx} 0.004-0.01, consistent with low and approximately constant efficiencies inferred from observations. For {Sigma} in (100-1000) M{sub Sun} pc{sup -2}, we find {Sigma}{sub SFR} in (0.1-4) M{sub Sun} kpc{sup -2} yr{sup -1}, generally following a {Sigma}{sub SFR} {proportional_to} {Sigma}{sup 2} relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed {Sigma}-{Sigma}{sub SFR} relation in high

  5. MASS TRANSPORT AND TURBULENCE IN GRAVITATIONALLY UNSTABLE DISK GALAXIES. II. THE EFFECTS OF STAR FORMATION FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Goldbaum, Nathan J. [National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 1205 W. Clark St., Urbana, IL 61801 (United States); Krumholz, Mark R. [Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2601 (Australia); Forbes, John C., E-mail: ngoldbau@illinois.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2016-08-10

    Self-gravity and stellar feedback are capable of driving turbulence and transporting mass and angular momentum in disk galaxies, but the balance between them is not well understood. In the previous paper in this series, we showed that gravity alone can drive turbulence in galactic disks, regulate their Toomre Q parameters to ∼1, and transport mass inwards at a rate sufficient to fuel star formation in the centers of present-day galaxies. In this paper we extend our models to include the effects of star formation feedback. We show that feedback suppresses galaxies’ star formation rates by a factor of ∼5 and leads to the formation of a multi-phase atomic and molecular interstellar medium. Both the star formation rate and the phase balance produced in our simulations agree well with observations of nearby spirals. After our galaxies reach steady state, we find that the inclusion of feedback actually lowers the gas velocity dispersion slightly compared to the case of pure self-gravity, and also slightly reduces the rate of inward mass transport. Nevertheless, we find that, even with feedback included, our galactic disks self-regulate to Q ∼ 1, and transport mass inwards at a rate sufficient to supply a substantial fraction of the inner disk star formation. We argue that gravitational instability is therefore likely to be the dominant source of turbulence and transport in galactic disks, and that it is responsible for fueling star formation in the inner parts of galactic disks over cosmological times.

  6. Are dSph galaxies Galactic building blocks?

    Directory of Open Access Journals (Sweden)

    Gilmore G.

    2012-02-01

    Full Text Available Dwarf spheroidal galaxies (dSph are frequently assumed to represent surviving examples of a vast now destroyed population of small systems in which many of the stars now forming the Milky Way were formed. Ongoing accretion and considerable sub-structure in the outer Galactic halo is direct evidence that there is some role for stars formed in small galaxies in populating the (outer galaxy. The evidence from stellar populations is however contradictory to this. dSph stellar populations are unlike any stars found in significant numbers in the Milky Way. The dSph are indeed small galaxies, formed over long times with low rates of star formation. Most of the stars in the Milky Way halo however seem to have formed quickly, at higher star formation rate, in gas mixed efficiently on kpc scales. The overwhelming majority of Milky Way stars, those in the Galactic thick disk and thin disk, seem to have nothing at all to do with dwarf galaxy origins.

  7. Star formation rates and abundance gradients in disk galaxies

    International Nuclear Information System (INIS)

    Wyse, R.F.G.; Silk, J.

    1989-01-01

    Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies. 67 refs

  8. THE ROLE OF COSMIC-RAY PRESSURE IN ACCELERATING GALACTIC OUTFLOWS

    Energy Technology Data Exchange (ETDEWEB)

    Simpson, Christine M.; Pakmor, Rüdiger; Pfrommer, Christoph; Springel, Volker [Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Marinacci, Federico [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Glover, Simon C. O. [Zentrum für Astronomie der Universität Heidelberg, ITA, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Clark, Paul C. [School of Physics and Astronomy, Queen’s Buildings, The Parade, Cardiff University, Cardiff CF24 3AA (United Kingdom); Smith, Rowan J., E-mail: Christine.Simpson@h-its.org [Jodrell Bank Centre for Astrophysics, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)

    2016-08-20

    We study the formation of galactic outflows from supernova (SN) explosions with the moving-mesh code AREPO in a stratified column of gas with a surface density similar to the Milky Way disk at the solar circle. We compare different simulation models for SN placement and energy feedback, including cosmic rays (CRs), and find that models that place SNe in dense gas and account for CR diffusion are able to drive outflows with similar mass loading as obtained from a random placement of SNe with no CRs. Despite this similarity, CR-driven outflows differ in several other key properties including their overall clumpiness and velocity. Moreover, the forces driving these outflows originate in different sources of pressure, with the CR diffusion model relying on non-thermal pressure gradients to create an outflow driven by internal pressure and the random-placement model depending on kinetic pressure gradients to propel a ballistic outflow. CRs therefore appear to be non-negligible physics in the formation of outflows from the interstellar medium.

  9. Island universes structure and evolution of disk galaxies

    CERN Document Server

    DE JONG, R. S

    2007-01-01

    This book contains an up-to-date review of the structure and evolution of disk galaxies from both the observational and theoretical point of view. The book is the proceedings of the "Island Universes" conference held at the island of Terschelling, The Netherlands in July 2005, which attracted about 130 experts and students in the field. The conference was organized as a tribute to Dr. Piet C. van der Kruit for receiving the honorary Jacobus C. Kapteyn Professorship in Astronomy. The eight topical themes discussed at the meeting are reflected in these proceedings: 1) Properties of Stellar Disks, 2) Kinematics and Dynamics of Disk Galaxies, 3) Bars, Spiral Structure, and Secular Evolution in Disk Galaxies, 4) The Outskirts and Environment of Disk Galaxies, 5) Interstellar Matter, 6) (Evolution of) Star Formation in Galactic Disks, 7) Disk Galaxies through Cosmic Time, and 8) Formation Models of Disk Galaxies. These proceedings are concluded with a conference summary reflecting on the most significant recent pro...

  10. Ionized Absorbers as Evidence for Supernova-driven Cooling of the Lower Galactic Corona

    NARCIS (Netherlands)

    Fraternali, Filippo; Marasco, Antonino; Marinacci, Federico; Binney, James

    2013-01-01

    We show that the ultraviolet absorption features, newly discovered in Hubble Space Telescope spectra, are consistent with being formed in a layer that extends a few kpc above the disk of the Milky Way. In this interface between the disk and the Galactic corona, high-metallicity gas ejected from the

  11. Constraints on Galactic populations from the unidentified EGRET sources

    International Nuclear Information System (INIS)

    Siegal-Gaskins, Jennifer M.; Pavlidou, Vasiliki; Brown, Carolyn; Olinto, Angela V.; Fields, Brian D.

    2007-01-01

    A significant fraction of the sources in the third EGRET catalog have not yet been identified with a low-energy counterpart. We evaluate the plausibility of a Galactic population accounting for some or all of the unidentified EGRET sources by making the simple assumption that galaxies similar to the Milky Way host comparable populations of gamma-ray emitters. Rather than focusing on the properties of a specific candidate emitter, we constrain the abundance and spatial distribution of proposed Galactic populations. We find that it is highly improbable that the unidentified EGRET sources contain more than a handful of members of a Galactic halo population, but that current observations are consistent with all of these sources being Galactic objects if they reside entirely in the disk and bulge. We discuss the additional constraints and new insights into the nature of Galactic gamma-ray emitting populations that GLAST is expected to provide

  12. The Large Scale Structure of the Galactic Magnetic Field and High Energy Cosmic Ray Anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Alvarez-Muniz, Jaime [Department de Fisica de PartIculas, University de Santiago de Compostela, 15782 Santiago, SPAIN (Spain); Stanev, Todor [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States)

    2006-10-15

    Measurements of the magnetic field in our Galaxy are complex and usually difficult to interpret. A spiral regular field in the disk is favored by observations, however the number of field reversals is still under debate. Measurements of the parity of the field across the Galactic plane are also very difficult due to the presence of the disk field itself. In this work we demonstrate that cosmic ray protons in the energy range 10{sup 18} to 10{sup 19}eV, if accelerated near the center of the Galaxy, are sensitive to the large scale structure of the Galactic Magnetic Field (GMF). In particular if the field is of even parity, and the spiral field is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.

  13. The interstellar medium and star formation of galactic disks. I. Interstellar medium and giant molecular cloud properties with diffuse far-ultraviolet and cosmic-ray backgrounds

    Science.gov (United States)

    Li, Qi; Tan, Jonathan C.; Christie, Duncan; Bisbas, Thomas G.; Wu, Benjamin

    2018-01-01

    We present a series of adaptive mesh refinement hydrodynamic simulations of flat rotation curve galactic gas disks, with a detailed treatment of the interstellar medium (ISM) physics of the atomic to molecular phase transition under the influence of diffuse far-ultraviolet (FUV) radiation fields and cosmic-ray backgrounds. We explore the effects of different FUV intensities, including a model with a radial gradient designed to mimic the Milky Way. The effects of cosmic rays, including radial gradients in their heating and ionization rates, are also explored. The final simulations in this series achieve 4 pc resolution across the ˜20 kpc global disk diameter, with heating and cooling followed down to temperatures of ˜10 K. The disks are evolved for 300 Myr, which is enough time for the ISM to achieve a quasi-statistical equilibrium. In particular, the mass fraction of molecular gas is stabilized by ˜200 Myr. Additional global ISM properties are analyzed. Giant molecular clouds (GMCs) are also identified and the statistical properties of their populations are examined. GMCs are tracked as the disks evolve. GMC collisions, which may be a means of triggering star cluster formation, are counted and their rates are compared with analytic models. Relatively frequent GMC collision rates are seen in these simulations, and their implications for understanding GMC properties, including the driving of internal turbulence, are discussed.

  14. The interstellar medium and star formation of galactic disks. I. Interstellar medium and giant molecular cloud properties with diffuse far-ultraviolet and cosmic-ray backgrounds

    Science.gov (United States)

    Li, Qi; Tan, Jonathan C.; Christie, Duncan; Bisbas, Thomas G.; Wu, Benjamin

    2018-05-01

    We present a series of adaptive mesh refinement hydrodynamic simulations of flat rotation curve galactic gas disks, with a detailed treatment of the interstellar medium (ISM) physics of the atomic to molecular phase transition under the influence of diffuse far-ultraviolet (FUV) radiation fields and cosmic-ray backgrounds. We explore the effects of different FUV intensities, including a model with a radial gradient designed to mimic the Milky Way. The effects of cosmic rays, including radial gradients in their heating and ionization rates, are also explored. The final simulations in this series achieve 4 pc resolution across the ˜20 kpc global disk diameter, with heating and cooling followed down to temperatures of ˜10 K. The disks are evolved for 300 Myr, which is enough time for the ISM to achieve a quasi-statistical equilibrium. In particular, the mass fraction of molecular gas is stabilized by ˜200 Myr. Additional global ISM properties are analyzed. Giant molecular clouds (GMCs) are also identified and the statistical properties of their populations are examined. GMCs are tracked as the disks evolve. GMC collisions, which may be a means of triggering star cluster formation, are counted and their rates are compared with analytic models. Relatively frequent GMC collision rates are seen in these simulations, and their implications for understanding GMC properties, including the driving of internal turbulence, are discussed.

  15. On Estimating the Mass of Keplerian Accretion Disks in H2O Maser Galaxies

    Science.gov (United States)

    Kuo, C. Y.; Reid, M. J.; Braatz, J. A.; Gao, F.; Impellizzeri, C. M. V.; Chien, W. T.

    2018-06-01

    H2O maser disks with Keplerian rotation in active galactic nuclei offer a clean way to determine accurate black hole mass and the Hubble constant. An important assumption made in using a Keplerian H2O maser disk for measuring black hole mass and the Hubble constant is that the disk mass is negligible compared to the black hole mass. A simple and useful model of Huré et al. can be used to test this assumption. In that work, the authors apply a linear disk model to a position–dynamical mass diagram and re-analyze position–velocity data from H2O maser disks associated with active galactic nuclei. They claim that a maser disk with nearly perfect Keplerian rotation could have a disk mass comparable to the black hole mass. This would imply that ignoring the effects of disk self-gravity can lead to large systematic errors in the measurement of black hole mass and the Hubble constant. We examine their methods and find that their large estimated disk masses of Keplerian disks are likely the result of their use of projected instead of three-dimensional position and velocity information. To place better constraints on the disk masses of Keplerian maser systems, we incorporate disk self-gravity into a three-dimensional Bayesian modeling program for maser disks and also evaluate constraints based on the physical conditions for disks that support water maser emission. We find that there is little evidence that disk masses are dynamically important at the ≲1% level compared to the black holes.

  16. The Dynamics of Truncated Black Hole Accretion Disks. I. Viscous Hydrodynamic Case

    Energy Technology Data Exchange (ETDEWEB)

    Hogg, J. Drew; Reynolds, Christopher S. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)

    2017-07-10

    Truncated accretion disks are commonly invoked to explain the spectro-temporal variability in accreting black holes in both small systems, i.e., state transitions in galactic black hole binaries (GBHBs), and large systems, i.e., low-luminosity active galactic nuclei (LLAGNs). In the canonical truncated disk model of moderately low accretion rate systems, gas in the inner region of the accretion disk occupies a hot, radiatively inefficient phase, which leads to a geometrically thick disk, while the gas in the outer region occupies a cooler, radiatively efficient phase that resides in the standard geometrically thin disk. Observationally, there is strong empirical evidence to support this phenomenological model, but a detailed understanding of the dynamics of truncated disks is lacking. We present a well-resolved viscous, hydrodynamic simulation that uses an ad hoc cooling prescription to drive a thermal instability and, hence, produce the first sustained truncated accretion disk. With this simulation, we perform a study of the dynamics, angular momentum transport, and energetics of a truncated disk. We find that the time variability introduced by the quasi-periodic transition of gas from efficient cooling to inefficient cooling impacts the evolution of the simulated disk. A consequence of the thermal instability is that an outflow is launched from the hot/cold gas interface, which drives large, sub-Keplerian convective cells into the disk atmosphere. The convective cells introduce a viscous θ − ϕ stress that is less than the generic r − ϕ viscous stress component, but greatly influences the evolution of the disk. In the truncated disk, we find that the bulk of the accreted gas is in the hot phase.

  17. METALLICITY GRADIENTS OF THICK DISK DWARF STARS

    Energy Technology Data Exchange (ETDEWEB)

    Carrell, Kenneth; Chen Yuqin; Zhao Gang, E-mail: carrell@nao.cas.cn [Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

    2012-12-01

    We examine the metallicity distribution of the Galactic thick disk using F, G, and K dwarf stars selected from the Sloan Digital Sky Survey, Data Release 8. Using the large sample of dwarf stars with proper motions and spectroscopically determined stellar parameters, metallicity gradients in the radial direction for various heights above the Galactic plane and in the vertical direction for various radial distances from the Galaxy center have been found. In particular, we find a vertical metallicity gradient of -0.113 {+-} 0.010 (-0.125 {+-} 0.008) dex kpc{sup -1} using an isochrone (photometric) distance determination in the range 1 kpc <|Z| < 3 kpc, which is the vertical height range most consistent with the thick disk of our Galaxy. In the radial direction, we find metallicity gradients between +0.02 and +0.03 dex kpc{sup -1} for bins in the vertical direction between 1 kpc <|Z| < 3 kpc. Both of these results agree with similar values determined from other populations of stars, but this is the first time a radial metallicity gradient for the thick disk has been found at these vertical heights. We are also able to separate thin and thick disk stars based on kinematic and spatial probabilities in the vertical height range where there is significant overlap of these two populations. This should aid further studies of the metallicity gradients of the disk for vertical heights lower than those studied here but above the solar neighborhood. Metallicity gradients in the thin and thick disks are important probes into possible formation scenarios for our Galaxy and a consistent picture is beginning to emerge from results using large spectroscopic surveys, such as the ones presented here.

  18. The vertical metallicity gradient of the Milky Way disk: transitions in [α/Fe] populations

    International Nuclear Information System (INIS)

    Schlesinger, Katharine J.; Johnson, Jennifer A.; Rockosi, Constance M.; Lee, Young Sun; Beers, Timothy C.; Harding, Paul; Allende Prieto, Carlos; Bird, Jonathan C.; Schönrich, Ralph; Yanny, Brian; Schneider, Donald P.; Weaver, Benjamin A.; Brinkmann, Jon

    2014-01-01

    Using G dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey, we have determined the vertical metallicity gradient in the Milky Way's disk and examined how this gradient varies for different [α/Fe] subsamples. Our sample contains over 40,000 stars with low-resolution spectroscopy over 144 lines of sight. It also covers a significant disk volume, between ∼0.3 and 1.6 kpc from the Galactic plane, and allows us to examine the disk in situ, whereas previous analyses were more limited in scope. Furthermore, this work does not presuppose a disk structure, whether composed of a single complex population or distinct thin and thick disk components. We employ the SEGUE Stellar Parameter Pipeline to obtain estimates of stellar parameters, [Fe/H], and [α/Fe] and extract multiple volume-complete subsamples of approximately 1000 stars each. Based on SEGUE's target-selection algorithm, we adjust each subsample to determine an unbiased picture of disk chemistry; consequently, each individual star represents the properties of many. The metallicity gradient is –0.243 −0.053 +0.039 dex kpc –1 for the entire sample, which we compare to various literature results. This gradient stems from the different [α/Fe] populations inhabiting different ranges of height above the Galactic plane. Each [α/Fe] subsample shows little change in median [Fe/H] with height. If we associate [α/Fe] with age, the negligible gradients of our [α/Fe] subsamples suggest that stars formed in different epochs exhibit comparable vertical structure, implying similar star formation processes and evolution.

  19. MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

    International Nuclear Information System (INIS)

    Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik

    2016-01-01

    Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R g , where R g  = 2GM/c 2 is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations

  20. A magnetic torsional wave near the Galactic Centre traced by a 'double helix' nebula.

    Science.gov (United States)

    Morris, Mark; Uchida, Keven; Do, Tuan

    2006-03-16

    The magnetic field in the central few hundred parsecs of the Milky Way has a dipolar geometry and is substantially stronger than elsewhere in the Galaxy, with estimates ranging up to a milligauss (refs 1-6). Characterization of the magnetic field at the Galactic Centre is important because it can affect the orbits of molecular clouds by exerting a drag on them, inhibit star formation, and could guide a wind of hot gas or cosmic rays away from the central region. Here we report observations of an infrared nebula having the morphology of an intertwined double helix about 100 parsecs from the Galaxy's dynamical centre, with its axis oriented perpendicular to the Galactic plane. The observed segment is about 25 parsecs in length, and contains about 1.25 full turns of each of the two continuous, helically wound strands. We interpret this feature as a torsional Alfvén wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear gas disk. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the images show a possible meandering channel that warrants further investigation.

  1. Photoionization of the diffuse interstellar medium and galactic halo by OB associtations

    Science.gov (United States)

    Dove, James B.; Shull, J. Michael

    1994-01-01

    Assuming smoothly varying H I distributions in te Galactic disk, we have calculated the geometry of diffuse II regions due to OB associations in the Galactic plane. Near the solar circle, OB associations with a Lyman continuum (Lyc) photon luminosity Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1), produce H II regions that are density bounded in the vertical direction (H II chimneys) allowing Lyc to escape the gaseous disk and penetrate into the Galactic halo. We provide analytic formulae for the Lyc escape fraction as functions of S(sub 0) O-star catalog of Garmany and a new Lyc stellar stellar Lyc stellar flux calibration, we find a production rate of Lyc photons by OB associations within 2.5 kpc of Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1). Integrating the fraction of Lyc photons that escape the disk over our adopted luminosity function of OB associations, we estimate that approximately 7% of the ionizing photons, or Phi(sub Lyc) = 2.3 x 10(exp 6) cm(exp -2) s(exp -1), escape each side of the H I disk layer and penetrate the diffuse ionized medium ('Reynolds layer'). This flux is sufficient to explain the potoionization of this, although we have not constructed a model for the observed H-alpha emission and pulsar dispersion measures that is fully consistent with the absorption rate of Lyc in the H II layer. Since our quiescent model does not account for the effects of dynamic chimneys and superbubbles, which should enhance Lyc escape, we conclude the O stars are the probable source of ionizing radiation for the Reynolds layer. For a random distribution of OB associations throughout the disk, the Lyc flux is nearly uniform for heights Z is greater than approximately 0.8 kpc above the midplane.

  2. Hydraulic jumps in ''viscous'' accretion disks

    International Nuclear Information System (INIS)

    Michel, F.C.

    1984-01-01

    We propose that the dissipative process necessary for rapid accretion disk evolution is driven by hydraulic jump waves on the surface of the disk. These waves are excited by the asymmetric nature of the central rotator (e.g., neutron star magnetosphere) and spiral out into the disk to form a pattern corotating with the central object. Disk matter in turn is slowed slightly at each encounter with the jump and spirals inward. In this process, the disk is heated by true turbulence produced in the jumps. Additional effects, such as a systematic misalignment of the magnetic moment of the neutron star until it is nearly orthogonal, and systematic distortion of the magnetosphere in such a way as to form an even more asymmetric central ''paddle wheel'' may enhance the interaction with inflowing matter. The application to X-ray sources corresponds to the ''slow'' solutions of Ghosh and Lamb, and therefore to rms magnetic fields of about 4 x 10 10 gauss. Analogous phenomena have been proposed to act in the formation of galactic spiral structure

  3. The rotation of accretion-disks and the power spectra of X-rays 'flickering'

    International Nuclear Information System (INIS)

    Zhang Xiaohe; Bao Gang

    1990-07-01

    The X-ray producing, inner region of the accretion disk in Active Galactic Nuclei (AGN) is likely to be non-stationary and non-axisymmetric. This non-stationarity and non-axisymmetry in disk surface brightness may be modeled by considering the pre-sense of many 'hot spots' on a steady, axisymmetric disk. As long as a 'spot' can survive for a few orbital periods, its orbital frequency can be introduced into the light curve either by relativistic orbital motion or by eclipsing of the spot by the disk. These rotational effects vary with the local properties of the spot population. Depending on the radial variation of spot brightness, lifetime and number density, the observed variability power spectrum may differ from that due to the intrinsic variability of spots alone, within the orbital frequency range in which these spots occur. In this paper, we explore the relation between properties assumed for the spot population and the resulting predictions for the observed variability. The implications of our results for the 'flickering' of X-ray sources powered by accretion disks (both AGN and galactic sources) are also discussed. (author). 24 refs, 6 figs

  4. Large-scale dynamo of accretion disks around supermassive nonrotating black holes

    Directory of Open Access Journals (Sweden)

    Poplavsky A.L.

    2006-01-01

    Full Text Available In this paper one presents an analytical model of accretion disk magnetosphere dynamics around supermassive nonrotating black holes in the centers of active galactic nuclei. Based on general relativistic equations of magneto hydrodynamics, the nonstationary solutions for time-dependent dynamo action in the accretion disks, spatial and temporal distribution of magnetic field are found. It is shown that there are two distinct stages of dynamo process: the transient and the steady-state regimes, the induction of magnetic field at t > 6:6665 x 1011GM/c3 s becomes stationary, magnetic field is located near the innermost stable circular orbit, and its value rises up to ~ 105 G. Applications of such systems with nonrotating black holes in real active galactic nuclei are discussed.

  5. Figuring Out Gas and Galaxies in Enzo (FOGGIE): Simulating effects of feedback on galactic outflows

    Science.gov (United States)

    Morris, Melissa Elizabeth; Corlies, Lauren; Peeples, Molly; Tumlinson, Jason; O'Shea, Brian; Smith, Britton

    2018-01-01

    The circumgalactic medium (CGM) is the region beyond the galactic disk in which gas is accreted through pristine inflows from the intergalactic medium and expelled from the galaxy by stellar feedback in large outflows that can then be recycled back onto the disk. These gas cycles connect the galactic disk with its cosmic environment, making the CGM a vital component of galaxy evolution. However, the CGM is primarily observed in absorption, which can be difficult to interpret. In this study, we use high resolution cosmological hydrodynamic simulations of a Milky Way mass halo evolved with the code Enzo to aid the interpretation of these observations. In our simulations, we vary feedback strength and observe the effect it has on galactic outflows and the evolution of the galaxy’s CGM. We compare the star formation rate of the galaxy with the velocity flux and mass outflow rate as a function of height above the plane of the galaxy in order to measure the strength of the outflows and how far they extend outside of the galaxy.This work was supported by The Space Astronomy Summer Program at STScI and NSF grant AST-1517908.

  6. Investigation of some galactic and extragalactic gravitational phenomena

    Directory of Open Access Journals (Sweden)

    Jovanović P.

    2012-01-01

    Full Text Available Here we present a short overview of the most important results of our investigations of the following galactic and extragalactic gravitational phenomena: supermassive black holes in centers of galaxies and quasars, supermassive black hole binaries, gravitational lenses and dark matter. For the purpose of these investigations, we developed a model of a relativistic accretion disk around a supermassive black hole, based on the ray-tracing method in the Kerr metric, a model of a bright spot in an accretion disk and three different models of gravitational microlenses. All these models enabled us to study physics, spacetime geometry and effects of strong gravity in the vicinity of supermassive black holes, variability of some active galaxies and quasars, different effects in the lensed quasars with multiple images, as well as the dark matter fraction in the Universe. We also found an observational evidence for the first spectroscopically resolved sub-parsec orbit of a supermassive black hole binary system in the core of active galaxy NGC 4151. Besides, we studied applications of one potential alternative to dark matter in the form of a modified theory of gravity on Galactic scales, to explain the recently observed orbital precession of some S-stars, which are orbiting around a massive black hole at the Galactic center. [Projekat Ministarstva nauke Republike Srbije, br. 176003: Gravitation and the Large Scale Structure of the Universe

  7. MIGRATION TRAPS IN DISKS AROUND SUPERMASSIVE BLACK HOLES

    Energy Technology Data Exchange (ETDEWEB)

    Bellovary, Jillian M.; Low, Mordecai-Mark Mac; McKernan, Barry; Ford, K. E. Saavik [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024 (United States)

    2016-03-10

    Accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGNs) contain stars, stellar mass black holes, and other stellar remnants, which perturb the disk gas gravitationally. The resulting density perturbations exert torques on the embedded masses causing them to migrate through the disk in a manner analogous to planets in protoplanetary disks. We determine the strength and direction of these torques using an empirical analytic description dependent on local disk gradients, applied to two different analytic, steady-state disk models of SMBH accretion disks. We find that there are radii in such disks where the gas torque changes sign, trapping migrating objects. Our analysis shows that major migration traps generally occur where the disk surface density gradient changes sign from positive to negative, around 20–300R{sub g}, where R{sub g} = 2GM/c{sup 2} is the Schwarzschild radius. At these traps, massive objects in the AGN disk can accumulate, collide, scatter, and accrete. Intermediate mass black hole formation is likely in these disk locations, which may lead to preferential gap and cavity creation at these radii. Our model thus has significant implications for SMBH growth as well as gravitational wave source populations.

  8. KINEMATICS OF CLASSICAL CEPHEIDS IN THE NUCLEAR STELLAR DISK

    International Nuclear Information System (INIS)

    Matsunaga, Noriyuki; Fukue, Kei; Yamamoto, Ryo; Kobayashi, Naoto; Hamano, Satoshi; Inno, Laura; Genovali, Katia; Bono, Giuseppe; Baba, Junichi; Fujii, Michiko S.; Aoki, Wako; Tsujimoto, Takuji; Kondo, Sohei; Ikeda, Yuji; Nishiyama, Shogo; Nagata, Tetsuya

    2015-01-01

    Classical Cepheids are useful tracers of the Galactic young stellar population because their distances and ages can be determined from their period-luminosity and period-age relations. In addition, the radial velocities and chemical abundance of the Cepheids can be derived from spectroscopic observations, providing further insights into the structure and evolution of the Galaxy. Here, we report the radial velocities of classical Cepheids near the Galactic center, three of which were reported in 2011 and a fourth being reported for the first time. The velocities of these Cepheids suggest that the stars orbit within the nuclear stellar disk, a group of stars and interstellar matter occupying a region of ∼200 pc around the center, although the three-dimensional velocities cannot be determined until the proper motions are known. According to our simulation, these four Cepheids formed within the nuclear stellar disk like younger stars and stellar clusters therein

  9. Population studies - evidence for accretion of the galactic halo

    International Nuclear Information System (INIS)

    Norris, J.E.; Ryan, S.G.

    1989-01-01

    While there are comparatively few prograde-orbit dwarf stars in advance of the sun's motion of the type of which 510, selected kinematically, are presented, it is noted that there are significant numbers of objects on retrograde orbits that move with a speed greater than the sun's, relative to a nonrotating system, in the opposite direction about the Galactic center. It is suggested that this asymmetry is explainable in terms of the Searle and Zinn (1978) and Rodgers and Paltoglou (1984) models of halo formation by accretion; in these, fragments experience dynamical friction from an already-formed Galactic disk. 21 references

  10. Active galactic nuclei. From the central engine to the host galaxy

    International Nuclear Information System (INIS)

    Gilbert, Didier

    2008-01-01

    After some recalls on galaxies, on their classification, on the Universe expansion and on the Hubble law, this academic report addresses active galactic nuclei (AGN) by describing their anatomy (central black hole, accretion disk, jets and winds, Broad Line Region, Narrow Line Region, molecular torus and dusts, radio lobes). The author also presents the unified model. In the next part, he proposes an overview of active galaxies and active galactic nuclei by distinguishing galaxies with a strong stellar activity, radio-quiet and radio-loud active galactic nuclei. Examples are presented for each of these types. In the last part, the author draws perspectives for research in cosmology, and outlines questions which are still to be answered

  11. Exploring the Local Milky Way: M Dwarfs as Tracers of Galactic Populations

    National Research Council Canada - National Science Library

    Bochanski, John J; Munn, Jeffrey A; Hawley, Suzanne L; West, Andrew A; Covey, Kevin R; Schneider, Donald P

    2007-01-01

    We have assembled a spectroscopic sample of low-mass dwarfs observed as part of the Sloan Digital Sky Survey along one Galactic sight line, designed to investigate the observable properties of the thin and thick disks. This sample...

  12. Galactic Habitable Zone and Astrobiological Complexity

    Science.gov (United States)

    Vukotic, B.

    2012-12-01

    This is a short thesis description and for the sake of brevity most things are left out. For more details, those interested are further directed to the thesis related papers in this article reference list. Thesis itself is available at the University of Belgrade library "Svetozar Markovic" (Serbian version only). In this thesis we study the astrobiological history of the Galactic habitable zone through the means of numerical modeling. First group of simulations are unidimensional (time-axis) toy models examine the influence of global regulation mechanisms (gamma-ray bursts and supernovae) on temporal evolution of Galactic astrobiological complexity. It is shown that under the assumption of global regulation classical anti SETI arguments can be undermined. Second group of simulations are more complex bidimensional probabilistic cellular automata models of the Galactic thin disk. They confirm the findings of the toy models and give some insights into the spatial clustering of astrobiological complexity. As a new emerging multidisciplinary science the basic concepts of astrobiology are poorly understood and although all the simulations present here do not include some basic physics (such as Galactic kinematics and dynamics), the input parameters are somewhat arbitrary and could use a future refinement (such as the boundaries of the Galactic habitable zone). This is the cause for low weight and high uncertainty in the output results of the simulations. However, the probabilistic cellular automata has shown as a highly adaptable modeling platform that can simulate various class of astrobiological models with great ease.

  13. Population Synthesis Models for Normal Galaxies with Dusty Disks

    Directory of Open Access Journals (Sweden)

    Kyung-Won Suh

    2003-09-01

    Full Text Available To investigate the SEDs of galaxies considering the dust extinction processes in the galactic disks, we present the population synthesis models for normal galaxies with dusty disks. We use PEGASE (Fioc & Rocca-Volmerange 1997 to model them with standard input parameters for stars and new dust parameters. We find that the model results are strongly dependent on the dust parameters as well as other parameters (e.g. star formation history. We compare the model results with the observations and discuss about the possible explanations. We find that the dust opacity functions derived from studies of asymptotic giant branch stars are useful for modeling a galaxy with a dusty disk.

  14. Widespread rotationally hot hydronium ion in the galactic interstellar medium

    International Nuclear Information System (INIS)

    Lis, D. C.; Phillips, T. G.; Schilke, P.; Comito, C.; Higgins, R.

    2014-01-01

    We present new Herschel observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ∼500 K, rotational temperatures characterizing the population of the highly excited metastable H 3 O + rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ∼380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic-ray fluxes, shocks, and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and the temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation of the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process not limited to the active environments associated with galactic nuclei.

  15. Proper Motions and Structural Parameters of the Galactic Globular Cluster M71

    Energy Technology Data Exchange (ETDEWEB)

    Cadelano, M.; Dalessandro, E.; Ferraro, F. R.; Miocchi, P.; Lanzoni, B.; Pallanca, C. [Dipartimento di Fisica e Astronomia, Università di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna (Italy); Massari, D. [INAF—Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy)

    2017-02-20

    By exploiting two ACS/ HST data sets separated by a temporal baseline of ∼7 years, we have determined the relative stellar proper motions (PMs; providing membership) and the absolute PM of the Galactic globular cluster M71. The absolute PM has been used to reconstruct the cluster orbit within a Galactic, three-component, axisymmetric potential. M71 turns out to be in a low-latitude disk-like orbit inside the Galactic disk, further supporting the scenario in which it lost a significant fraction of its initial mass. Since large differential reddening is known to affect this system, we took advantage of near-infrared, ground-based observations to re-determine the cluster center and density profile from direct star counts. The new structural parameters turn out to be significantly different from the ones quoted in the literature. In particular, M71 has a core and a half-mass radii almost 50% larger than previously thought. Finally, we estimate that the initial mass of M71 was likely one order of magnitude larger than its current value, thus helping to solve the discrepancy with the observed number of X-ray sources.

  16. The continuous rise of bulges out of galactic disks

    Science.gov (United States)

    Breda, Iris; Papaderos, Polychronis

    2018-06-01

    Context. A key subject in extragalactic astronomy concerns the chronology and driving mechanisms of bulge formation in late-type galaxies (LTGs). The standard scenario distinguishes between classical bulges and pseudo-bulges (CBs and PBs, respectively), the first thought to form monolithically prior to disks and the second gradually out of disks. These two bulge formation routes obviously yield antipodal predictions on the bulge age and bulge-to-disk age contrast, both expected to be high (low) in CBs (PBs). Aims: Our main goal is to explore whether bulges in present-day LTGs segregate into two evolutionary distinct classes, as expected from the standard scenario. Other questions motivating this study center on evolutionary relations between LTG bulges and their hosting disks, and the occurrence of accretion-powered nuclear activity as a function of bulge stellar mass ℳ⋆ and stellar surface density Σ⋆. Methods: In this study, we have combined three techniques - surface photometry, spectral modeling of integral field spectroscopy data and suppression of stellar populations younger than an adjustable age cutoff with the code REMOVEYOUNG (ℛ𝒴) - toward a systematic analysis of the physical and evolutionary properties (e.g., ℳ⋆, Σ⋆ and mass-weighted stellar age ℳ and metallicity ℳ, respectively) of a representative sample of 135 nearby (≤ 130 Mpc) LTGs from the CALIFA survey that cover a range between 108.9 M⊙ and 1011.5 M⊙ in total stellar mass ℳ⋆,T. In particular, the analysis here revolves around ⟨δμ9G⟩, a new distance- and formally extinction-independent measure of the contribution by stellar populations of age ≥ 9 Gyr to the mean r-band surface brightness of the bulge. We argue that ⟨δμ9G⟩ offers a handy semi-empirical tracer of the physical and evolutionary properties of LTG bulges and a promising means for their characterization. Results: The essential insight from this study is that LTG bulges form over 3 dex

  17. Sporadic mass loss, spin-down, and element redistribution in young disk galaxies

    International Nuclear Information System (INIS)

    Charlton, J.C.; Salpeter, E.E.

    1989-01-01

    Violent conditions in young spiral disks may be conducive to the high-velocity ejection of large blobs of material powered by the concerted action of supernovae. Using explicit numerical Monte Carlo models, treating ejected bobs as galactic cannonballs traveling with little interaction through the corona, several important consequences for galactic evolution are found. Preferential escape from the galaxy or objects with high specific angular momenta lead to a significant spin-down of the disk. In addition, this process may contribute to the production of an exponential column density distribution, and a metallicity gradient. The models predict a reversal in the sign of the metallicity gradient at large radii because the metal-rich objects that return to such a low column density region suffer relatively little dilution. 39 refs

  18. THE ODD OFFSET BETWEEN THE GALACTIC DISK AND ITS BAR IN NGC 3906

    Energy Technology Data Exchange (ETDEWEB)

    Swardt, Bonita de [South African Astronomical Observatory, Observatory, 7935 Cape Town (South Africa); Sheth, Kartik; Kim, Taehyun; Muñoz-Mateos, Juan-Carlos [National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Stephen Pardy; Elena D’ Onghia; Eric Wilcots [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States); Hinz, Joannah [MMTO, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Regan, Michael W. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Athanassoula, E.; Bosma, Albert [Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France); Buta, Ronald J. [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Cisternas, Mauricio; Erroz-Ferrer, Santiago [Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Comerón, Sébastien [Division of Astronomy, Department of Physical Sciences, University of Oulu, Oulu, FI-90014 (Finland); Gadotti, Dimitri A. [European Southern Observatory, Casilla 19001, Santiago 19 (Chile); Paz, Armando Gil de [Departamento de Astrofísica, Universidad Complutense de Madrid, Madrid E-28040 (Spain); Jarrett, Thomas H. [Astronomy Department, University of Cape Town, Rondebosch 7701 (South Africa); Elmegreen, Bruce G. [IBM Research Division, T.J. Watson Research Center, Yorktown Hts., NY 10598 (United States); Ho, Luis C. [The Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); and others

    2015-07-20

    We use mid-infrared 3.6 and 4.5 μm imaging of NGC 3906 from the Spitzer Survey of Stellar Structure in Galaxies (S{sup 4}G) to understand the nature of an unusual offset between its stellar bar and the photometric center of an otherwise regular, circular outer stellar disk. We measure an offset of ∼910 pc between the center of the stellar bar and photometric center of the stellar disk; the bar center coincides with the kinematic center of the disk determined from previous HI observations. Although the undisturbed shape of the disk suggests that NGC 3906 has not undergone a significant merger event in its recent history, the most plausible explanation for the observed offset is an interaction. Given the relatively isolated nature of NGC 3906 this interaction could be with dark matter substructure in the galaxy's halo or from a recent interaction with a fast moving neighbor that remains to be identified. Simulations aimed at reproducing the observed offset between the stellar bar/kinematic center of the system and the photometric center of the disk are necessary to confirm this hypothesis and constrain the interaction history of the galaxy.

  19. Hot stars in young massive clusters: Mapping the current Galactic metallicity

    Science.gov (United States)

    de la Fuente, Diego; Najarro, Francisco; Davies, Ben; Trombley, Christine; Figer, Donald F.; Herrero, Artemio

    2013-06-01

    Young Massive Clusters (YMCs) with ages guarantee that these objects present the same chemical composition than the surrounding environment where they are recently born. Finally, the YMCs host very massive stars whose extreme luminosities allow to accomplish detailed spectroscopic analyses even in the most distant regions of the Milky Way. Our group has carried out ISAAC/VLT spectroscopic observations of hot massive stars belonging to several YMCs in different locations around the Galactic disk. As a result, high signal-to-noise, near-infrared spectra of dozens of blue massive stars (including many OB supergiants, Wolf-Rayet stars and a B hypergiant) have been obtained. These data are fully reduced, and NLTE spherical atmosphere modeling is in process. Several line diagnostics will be combined in order to calculate metal abundances accurately for each cluster. The diverse locations of the clusters will allow us to draw a two-dimensional chemical map of the Galactic disk for the first time. The study of the radial and azimuthal variations of elemental abundances will be crucial for understanding the chemical evolution of the Milky Way. Particularly, the ratio between Fe-peak and alpha elements will constitute a powerful tool to investigate the past stellar populations that originated the current Galactic chemistry.

  20. STELLAR TRANSITS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Béky, Bence; Kocsis, Bence

    2013-01-01

    Supermassive black holes (SMBHs) are typically surrounded by a dense stellar population in galactic nuclei. Stars crossing the line of site in active galactic nuclei (AGNs) produce a characteristic transit light curve, just like extrasolar planets do when they transit their host star. We examine the possibility of finding such AGN transits in deep optical, UV, and X-ray surveys. We calculate transit light curves using the Novikov-Thorne thin accretion disk model, including general relativistic effects. Based on the expected properties of stellar cusps, we find that around 10 6 solar mass SMBHs, transits of red giants are most common for stars on close orbits with transit durations of a few weeks and orbital periods of a few years. We find that detecting AGN transits requires repeated observations of thousands of low-mass AGNs to 1% photometric accuracy in optical, or ∼10% in UV bands or soft X-ray. It may be possible to identify stellar transits in the Pan-STARRS and LSST optical and the eROSITA X-ray surveys. Such observations could be used to constrain black hole mass, spin, inclination, and accretion rate. Transit rates and durations could give valuable information on the circumnuclear stellar clusters as well. Transit light curves could be used to image accretion disks with unprecedented resolution, allowing us to resolve the SMBH silhouette in distant AGNs.

  1. Mass models for disk and halo components in spiral galaxies

    International Nuclear Information System (INIS)

    Athanassoula, E.; Bosma, A.

    1987-01-01

    The mass distribution in spiral galaxies is investigated by means of numerical simulations, summarizing the results reported by Athanassoula et al. (1986). Details of the modeling technique employed are given, including bulge-disk decomposition; computation of bulge and disk rotation curves (assuming constant mass/light ratios for each); and determination (for spherical symmetry) of the total halo mass out to the optical radius, the concentration indices, the halo-density power law, the core radius, the central density, and the velocity dispersion. Also discussed are the procedures for incorporating galactic gas and checking the spiral structure extent. It is found that structural constraints limit disk mass/light ratios to a range of 0.3 dex, and that the most likely models are maximum-disk models with m = 1 disturbances inhibited. 19 references

  2. KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD

    International Nuclear Information System (INIS)

    Moni Bidin, C.; Smith, R.; Carraro, G.; Méndez, R. A.

    2012-01-01

    We estimated the dynamical surface mass density Σ at the solar position between Z = 1.5 and 4 kpc from the Galactic plane, as inferred from the kinematics of thick disk stars. The formulation is exact within the limit of validity of a few basic assumptions. The resulting trend of Σ(Z) matches the expectations of visible mass alone, and no dark component is required to account for the observations. We extrapolate a dark matter (DM) density in the solar neighborhood of 0 ± 1 mM ☉ pc –3 , and all the current models of a spherical DM halo are excluded at a confidence level higher than 4σ. A detailed analysis reveals that a small amount of DM is allowed in the volume under study by the change of some input parameter or hypothesis, but not enough to match the expectations of the models, except under an exotic combination of non-standard assumptions. Identical results are obtained when repeating the calculation with kinematical measurements available in the literature. We demonstrate that a DM halo would be detected by our method, and therefore the results have no straightforward interpretation. Only the presence of a highly prolate (flattening q > 2) DM halo can be reconciled with the observations, but this is highly unlikely in ΛCDM models. The results challenge the current understanding of the spatial distribution and nature of the Galactic DM. In particular, our results may indicate that any direct DM detection experiment is doomed to fail if the local density of the target particles is negligible.

  3. KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD

    Energy Technology Data Exchange (ETDEWEB)

    Moni Bidin, C.; Smith, R. [Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile); Carraro, G. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Mendez, R. A., E-mail: cmbidin@astro-udec.cl [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile)

    2012-05-20

    We estimated the dynamical surface mass density {Sigma} at the solar position between Z = 1.5 and 4 kpc from the Galactic plane, as inferred from the kinematics of thick disk stars. The formulation is exact within the limit of validity of a few basic assumptions. The resulting trend of {Sigma}(Z) matches the expectations of visible mass alone, and no dark component is required to account for the observations. We extrapolate a dark matter (DM) density in the solar neighborhood of 0 {+-} 1 mM{sub Sun} pc{sup -3}, and all the current models of a spherical DM halo are excluded at a confidence level higher than 4{sigma}. A detailed analysis reveals that a small amount of DM is allowed in the volume under study by the change of some input parameter or hypothesis, but not enough to match the expectations of the models, except under an exotic combination of non-standard assumptions. Identical results are obtained when repeating the calculation with kinematical measurements available in the literature. We demonstrate that a DM halo would be detected by our method, and therefore the results have no straightforward interpretation. Only the presence of a highly prolate (flattening q > 2) DM halo can be reconciled with the observations, but this is highly unlikely in {Lambda}CDM models. The results challenge the current understanding of the spatial distribution and nature of the Galactic DM. In particular, our results may indicate that any direct DM detection experiment is doomed to fail if the local density of the target particles is negligible.

  4. RED FRACTION AMONG SATELLITE GALAXIES WITH DISK-LIKE LIGHT PROFILES: EVIDENCE FOR INFLOW IN THE H I DISK

    International Nuclear Information System (INIS)

    Hester, J. A.

    2010-01-01

    The relationships between color, characterized with respect to the g - r red sequence; stellar structure, as determined using the i-band Sersic index; and group membership are explored using the Sloan Digital Sky Survey (SDSS). The new results place novel constraints on theories of galaxy evolution, despite the strong correlation between color and stellar structure. Observed correlations are of three independent types-those based on stellar structure, on the color of disk-like galaxies, and on the color of elliptical galaxies. Of particular note, the fraction of galaxies residing on the red sequence measured among galaxies with disk-like light profiles is enhanced for satellite galaxies compared to central galaxies. This fraction increases with group mass. When these new results are considered, theoretical treatments of galaxy evolution that adopt a gas accretion model centered on the hot galactic halo cannot consistently account for all observations of disk galaxies. The hypothesis is advanced that inflow within the extended H I disk prolongs star formation in satellite galaxies. When combined with partial ram pressure stripping (RPS) of this disk, this new scenario is consistent with the observations. This is demonstrated by applying an analytical model of RPS of the extended H I disk to the SDSS groups. These results motivate incorporating more complex modes of gas accretion into models of galaxy evolution, including cold mode accretion, an improved treatment of gas dynamics within disks, and disk stripping.

  5. Is there dust in galactic haloes

    International Nuclear Information System (INIS)

    Greenberg, J.M.; Ferrini, F.; Pisa Univ.; Barsella, B.; Aiello, S.

    1987-01-01

    The ubiquitous presence of dust within the disks of spiral galaxies is well established. The authors predict that the presence of dust in these regions may be revealed in bright edge-on galaxies, especially by using the polarization of the scattered light from the symmetric lanes. The detection of scattered light above the galactic plane may be an indicator that the parent galaxy has not suffered close encounters with other galaxies at least within the timescale required to establish the dust layers. (author)

  6. A truncated accretion disk in the galactic black hole candidate source H1743-322

    International Nuclear Information System (INIS)

    Sriram, Kandulapati; Agrawal, Vivek Kumar; Rao, Arikkala Raghurama

    2009-01-01

    To investigate the geometry of the accretion disk in the source H1743-322, we have carried out a detailed X-ray temporal and spectral study using RXTE pointed observations. We have selected all data pertaining to the Steep Power Law (SPL) state during the 2003 outburst of this source. We find anti-correlated hard X-ray lags in three of the observations and the changes in the spectral and timing parameters (like the QPO frequency) confirm the idea of a truncated accretion disk in this source. Compiling data from similar observations of other sources, we find a correlation between the fractional change in the QPO frequency and the observed delay. We suggest that these observations indicate a definite size scale in the inner accretion disk (the radius of the truncated disk) and we explain the observed correlation using various disk parameters like Compton cooling time scale, viscous time scale etc. (research papers)

  7. Disk Model with Central Bulge for Galaxy M94

    International Nuclear Information System (INIS)

    Jalocha, J.; Bratek, L.; Kutschera, M.

    2010-01-01

    A global disk model for spiral galaxies is modified by adding a spherical component to the galactic center to account for the presence of a central spherical bulge. It is verified whether such modification could be substantial for predictions of total mass and of its distribution in spiral galaxy M94. (authors)

  8. OGLE-III MICROLENSING EVENTS AND THE STRUCTURE OF THE GALACTIC BULGE

    Energy Technology Data Exchange (ETDEWEB)

    Wyrzykowski, Łukasz; Rynkiewicz, Alicja E.; Skowron, Jan; Kozłowski, Szymon; Udalski, Andrzej; Szymański, Michał K.; Kubiak, Marcin; Soszyński, Igor; Pietrzyński, Grzegorz; Poleski, Radosław; Pietrukowicz, Paweł; Pawlak, Michał, E-mail: lw@astrouw.edu.pl [Warsaw University Astronomical Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland)

    2015-01-01

    We present and study the largest and most comprehensive catalog of microlensing events ever constructed. The sample of standard microlensing events comprises 3718 unique events from 2001-2009 with 1409 events that had not been detected before in real-time by the Early Warning System of the Optical Gravitational Lensing Experiment. The search pipeline uses machine learning algorithms to help find rare phenomena among 150 million objects and to derive the detection efficiency. Applications of the catalog can be numerous, from analyzing individual events to large statistical studies of the Galactic mass, kinematics distributions, and planetary abundances. We derive maps of the mean Einstein ring crossing time of events spanning 31 deg{sup 2} toward the Galactic center and compare the observed distributions with the most recent models. We find good agreement within the observed region and we see the signature of the tilt of the bar in the microlensing data. However, the asymmetry of the mean timescales seems to rise more steeply than predicted, indicating either a somewhat different orientation of the bar or a larger bar width. The map of events with sources in the Galactic bulge shows a dependence of the mean timescale on the Galactic latitude, signaling an increasing contribution from disk lenses closer to the plane relative to the height of the disk. Our data present a perfect set for comparing and enhancing new models of the central parts of the Milky Way and creating a three-dimensional picture of the Galaxy.

  9. An Alternative Explanation of the Varying Boron-to-carbon Ratio in Galactic Cosmic Rays

    Energy Technology Data Exchange (ETDEWEB)

    Eichler, David [Department of Physics, Ben-Gurion University, Be’er-Sheba 84105 (Israel)

    2017-06-10

    It is suggested that the decline with energy of the boron-to-carbon abundance ratio in Galactic cosmic rays is due, in part, to a correlation between the maximum energy attainable by shock acceleration in a given region of the Galactic disk and the grammage traversed before escape. In this case the energy dependence of the escape rate from the Galaxy may be less than previously thought and the spectrum of antiprotons becomes easier to understand.

  10. The discovery of an eccentric millisecond pulsar in the Galactic plane

    NARCIS (Netherlands)

    Champion, D.J.; Ransom, S.M.; Lazarus, P.; Camilo, F.; Kaspi, V.M.; Nice, D.J.; Freire, P.C.C.; Cordes, J.M.; Hessels, J.W.T.; Bassa, C.; Lorimer, D.R.; Stairs, I.H.; van Leeuwen, J.; Arzoumnian, Z.; Backer, D.C.; Bhat, N.D.R.; Chatterjee, S.; Crawford, F.; Deneva, J.S.; Faucher-Giguère, C.A.; Gaensler, B.M.; Han, J.; Jenet, F.A.; Kasian, L.; Kondratiev, V.I.; Kramer, M.; Lazio, J.; McLaughlin, M.A.; Stappers, B.W.; Venkataraman, A.; Vlemmings, W.

    2008-01-01

    The evolution of binary systems is governed by their orbital properties and the stellar density of the local environment. Studies of neutron stars in binary star systems offer unique insights into both these issues. In an Arecibo survey of the Galactic disk, we have found PSR J1903+0327, a radio

  11. SHOCKS AND A GIANT PLANET IN THE DISK ORBITING BP PISCIUM?

    International Nuclear Information System (INIS)

    Melis, C.; Zuckerman, B.; Gielen, C.; Chen, C. H.; Rhee, Joseph H.; Song, Inseok

    2010-01-01

    Spitzer Infrared Spectrograph data support the interpretation that BP Piscium, a gas and dust enshrouded star residing at high Galactic latitude, is a first-ascent giant rather than a classical T Tauri star. Our analysis suggests that BP Piscium's spectral energy distribution can be modeled as a disk with a gap that is opened by a giant planet. Modeling the rich mid-infrared emission line spectrum indicates that the solid-state emitting grains orbiting BP Piscium are primarily composed of ∼75 K crystalline, magnesium-rich olivine; ∼75 K crystalline, magnesium-rich pyroxene; ∼200 K amorphous, magnesium-rich pyroxene; and ∼200 K annealed silica (cristobalite). These dust grains are all sub-micron sized. The giant planet and gap model also naturally explains the location and mineralogy of the small dust grains in the disk. Disk shocks that result from disk-planet interaction generate the highly crystalline dust which is subsequently blown out of the disk mid-plane and into the disk atmosphere.

  12. THE INNER GALACTIC BULGE: EVIDENCE FOR A NUCLEAR BAR?

    International Nuclear Information System (INIS)

    Gerhard, Ortwin; Martinez-Valpuesta, Inma

    2012-01-01

    Recent data from the VVV survey have strengthened evidence for a structural change in the Galactic bulge inward of |l| ≤ 4°. Here we show with an N-body barred galaxy simulation that a boxy bulge formed through the bar and buckling instabilities effortlessly matches measured bulge longitude profiles for red clump stars. The same simulation snapshot was earlier used to clarify the apparent boxy bulge—long bar dichotomy, for the same orientation and scaling. The change in the slope of the model longitude profiles in the inner few degrees is caused by a transition from highly elongated to more nearly axisymmetric isodensity contours in the inner boxy bulge. This transition is confined to a few degrees from the Galactic plane; thus the change of slope is predicted to disappear at higher Galactic latitudes. We also show that the nuclear star count map derived from this simulation snapshot displays a longitudinal asymmetry similar to that observed in the Two Micron All Sky Survey (2MASS) data, but is less flattened to the Galactic plane than the 2MASS map. These results support the interpretation that the Galactic bulge originated from disk evolution and question the evidence advanced from star count data for the existence of a secondary nuclear bar in the Milky Way.

  13. The G-dwarf problem and the closed-box models of Galactic evolution

    International Nuclear Information System (INIS)

    Francois, P.; Vangioni-Flam, E.; Audouze, J.

    1990-01-01

    The paucity of very iron-poor stars in the Galactic disk with respect to the predictions of the simple model of Galactic chemical evolution (the notorious G-dwarf problem) is one of the most fundamental constraints of Galactic evolutionary models. This paper tests recently proposed models, with bimodal and varying star formation rates, against the G-dwarf metallicity distribution, the gas/total mass ratio in the solar vicinity, the age-metallicity relation, and the abundances of deuterium, O-16, Mg-24, Si-28, and Fe-56 at the birth of the sun. It is shown that none of these models agree entirely with the data, but that it is possible to find a combination of the two models leading to reasonable results. 35 refs

  14. Sinuous oscillations and steady warps of polytropic disks

    International Nuclear Information System (INIS)

    Balmforth, N.J.; Spiegel, E.A.

    1995-05-01

    In an asymptotic development of the equations governing the equilibria and linear stability of rapidly rotating polytropes we employed the slender aspect of these objects to reduce the three-dimensional partial differential equations to a somewhat simpler, ordinary integro-differential form. The earlier calculations dealt with isolated objects that were in centrifugal balance, that is the centrifugal acceleration of the configuration was balanced largely by self gravity with small contributions from the pressure gradient. Another interesting situation is that in which the polytrope rotates subject to externally imposed gravitational fields. In astrophysics, this is common in the theory of galactic dynamics because disks are unlikely to be isolated objects. The dark halos associated with disks also provide one possible explanation of the apparent warping of many galaxies. If the axis of the highly flattened disk is not aligned with that of the much less flattened halo, then the resultant torque of the halo gravity on the disk might provide a nonaxisymmetric distortion or disk warp. Motivated by these possibilities we shall here build models of polytropic disks of small but finite thickness which are subjected to prescribed, external gravitational fields. First we estimate how a symmetrical potential distorts the structure of the disk, then we examine its sinuous oscillations to confirm that they freely decay, hence suggesting that a warp must be externally forced. Finally, we consider steady warps of the disk plane when the axis of the disk does not coincide with that of the halo

  15. Orbit elements and kinematics of the halo stars and the old disk population: evidence for active phases in the evolution of the Galaxy

    International Nuclear Information System (INIS)

    Marsakov, V.A.; Suchkov, A.A.

    1978-01-01

    The distributions of orbits eccentricities and of angular momenta for the halo stars and for the old disk population are considered. The distributions have gaps separating the halo from the disk and diving the halo population into three groups. From the point of view of star formation during the collapse at the earliy stages of evolution the gaps evidence that threre were in the Galaxy long periods of suppression of star formation. The kinematics and the orbit elements of the halo stars and of the old disk population allow to conclude that there was no significant relaxation in the halo; the halo subsystems are not stationary, they perform radial oscillations with respect to the galactic centre; the velocity dispersion in the galactic rotation direction for the halo stars having the same age does not exceed 20-40 km/s; the dispersion of the velocity component along the galactic radius is symmetrically higher for the subsystems with a greater eccentrically and reaches 215 km/s for the stars with the greatest eccentricaities; the sing of the angular momentum in the protogalactic gas cloud probably changed at some distance form the galactic centre

  16. GRAVITATIONAL INSTABILITY OF ROTATING, PRESSURE-CONFINED, POLYTROPIC GAS DISKS WITH VERTICAL STRATIFICATION

    International Nuclear Information System (INIS)

    Kim, Jeong-Gyu; Kim, Woong-Tae; Seo, Young Min; Hong, Seung Soo

    2012-01-01

    We investigate the gravitational instability (GI) of rotating, vertically stratified, pressure-confined, polytropic gas disks using a linear stability analysis as well as analytic approximations. The disks are initially in vertical hydrostatic equilibrium and bounded by a constant external pressure. We find that the GI of a pressure-confined disk is in general a mixed mode of the conventional Jeans and distortional instabilities, and is thus an unstable version of acoustic-surface-gravity waves. The Jeans mode dominates in weakly confined disks or disks with rigid boundaries. On the other hand, when the disk has free boundaries and is strongly pressure confined, the mixed GI is dominated by the distortional mode that is surface-gravity waves driven unstable under their own gravity and thus incompressible. We demonstrate that the Jeans mode is gravity-modified acoustic waves rather than inertial waves and that inertial waves are almost unaffected by self-gravity. We derive an analytic expression for the effective sound speed c eff of acoustic-surface-gravity waves. We also find expressions for the gravity reduction factors relative to a razor-thin counterpart that are appropriate for the Jeans and distortional modes. The usual razor-thin dispersion relation, after correcting for c eff and the reduction factors, closely matches the numerical results obtained by solving a full set of linearized equations. The effective sound speed generalizes the Toomre stability parameter of the Jeans mode to allow for the mixed GI of vertically stratified, pressure-confined disks.

  17. ALMA observations of molecular absorption in four directions toward the Galactic bulge

    Science.gov (United States)

    Liszt, H.; Gerin, M.

    2018-02-01

    Context. Alma Cycle 3 observations serendipitously showed strong absorption from diffuse molecular gas in the Galactic bulge at -200 km s-1 51(3σ) for the bulge gas toward J1744 and 58 ± 9 and 64 ± 4 for the disk gas toward J1717 and J1744, respectively, all well above the value of 20-25 typical of the central molecular zone. Conclusions: The kinematics and chemistry of the bulge gas observed toward J1744 more nearly resemble that of gas in the Milky Way disk than in the central molecular zone.

  18. COBE diffuse infrared background experiment observations of the galactic bulge

    Science.gov (United States)

    Weiland, J. L.; Arendt, R. G.; Berriman, G. B.; Dwek, E.; Freudenreich, H. T.; Hauser, M. G.; Kelsall, T.; Lisse, C. M.; Mitra, M.; Moseley, S. H.

    1994-01-01

    Low angular resolution maps of the Galactic bulge at 1.25, 2.2, 3.5, and 4.9 micrometers obtained by the Diffuse Infrared Background Experiment (DIRBE) onboard NASA's Cosmic Background Explorer (COBE) are presented. After correction for extinction and subtraction of an empirical model for the Galactic disk, the surface brightness distribution of the bulge resembles a flattened ellipse with a minor-to-major axis ratio of approximately 0.6. The bulge minor axis scale height is found to be 2.1 deg +/- 0.2 deg for all four near-infrared wavelengths. Asymmetries in the longitudinal distribution of bulge brightness contours are qualitatively consistent with those expected for a triaxial bar with its near end in the first Galactic quadrant (0 deg less than l less than 90 deg). There is no evidence for an out-of-plane tilt of such a bar.

  19. Irradiation instability at the inner edges of accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Fung, Jeffrey; Artymowicz, Pawel, E-mail: fung@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada)

    2014-07-20

    An instability can potentially operate in highly irradiated disks where the disk sharply transitions from being radially transparent to opaque (the 'transition region'). Such conditions may exist at the inner edges of transitional disks around T Tauri stars and accretion disks around active galactic nuclei. We derive the criterion for this instability, which we term the 'irradiation instability', or IRI. We also present the linear growth rate as a function of β, the ratio between radiation force and gravity, and c{sub s}, the sound speed of the disk, obtained using two methods: a semi-analytic analysis of the linearized equations and a numerical simulation using the GPU-accelerated hydrodynamical code PEnGUIn. In particular, we find that IRI occurs at β ∼ 0.1 if the transition region extends as wide as ∼0.05r, and at higher β values if it is wider. This threshold value applies to c{sub s} ranging from 3% of the Keplerian orbital speed to 5%, and becomes higher if c{sub s} is lower. Furthermore, in the nonlinear evolution of the instability, disks with a large β and small c{sub s} exhibit 'clumping', extreme local surface density enhancements that can reach over 10 times the initial disk surface density.

  20. Positron Transport and Annihilation in the Galactic Bulge

    Directory of Open Access Journals (Sweden)

    Fiona Helen Panther

    2018-03-01

    Full Text Available The annihilation of positrons in the Milky Way Galaxy has been observed for ∼50 years; however, the production sites of these positrons remains hard to identify. The observed morphology of positron annihilation gamma-rays provides information on the annihilation sites of these Galactic positrons. It is understood that the positrons responsible for the annihilation signal originate at MeV energies. The majority of sources of MeV positrons occupy the star-forming thin disk of the Milky Way. If positrons propagate far from their sources, we must develop accurate models of positron propagation through all interstellar medium (ISM phases in order to reveal the currently uncertain origin of these Galactic positrons. On the other hand, if positrons annihilate close to their sources, an alternative source of MeV positrons with a distribution that matches the annihilation morphology must be identified. In this work, I discuss the various models that have been developed to understand the origin of the 511 keV line from the direction of the Galactic bulge, and the propagation of positrons in the ISM.

  1. Properties of Stellar Streams in the Galactic Disk

    Directory of Open Access Journals (Sweden)

    Marsakov V. A.

    2016-12-01

    Full Text Available Stars of the Sirius, Coma Berenices, Hyades, Pleiades, Wolf 630, Dehnen 6, Dehnen 14, HR 1614, η Cephei, γ Leo streams, the newly identified two subgroups of the Hercules stream, and the streams BB 14, BB 17, BB 20, and BB 21 are selected using the components of space velocities from three independent catalogs. The relationship between their ages, metallicities and relative abundances of α-elements are studied. The data of the three catalogs show slightly different properties for each of the streams studied. However, the general tendency shows that the dependences studied for the stars within the streams hardly differ from those found for the field stars with the corresponding velocities. The dependences found confirm the assumption that all of the streams studied could have been formed as a result of resonance effects due to the Galactic bar or spiral density waves acting on field stars.

  2. A NEW NETWORK FOR HIGHER-TEMPERATURE GAS-PHASE CHEMISTRY. I. A PRELIMINARY STUDY OF ACCRETION DISKS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Harada, Nanase; Herbst, Eric; Wakelam, Valentine

    2010-01-01

    We present a new interstellar chemical gas-phase reaction network for time-dependent kinetics that can be used for modeling high-temperature sources up to ∼800 K. This network contains an extended set of reactions based on the Ohio State University (OSU) gas-phase chemical network. The additional reactions include processes with significant activation energies, reverse reactions, proton exchange reactions, charge exchange reactions, and collisional dissociation. Rate coefficients already in the OSU network are modified for H 2 formation on grains, ion-neutral dipole reactions, and some radiative association reactions. The abundance of H 2 O is enhanced at high temperature by hydrogenation of atomic O. Much of the elemental oxygen is in the form of water at T ≥ 300 K, leading to effective carbon-rich conditions, which can efficiently produce carbon-chain species such as C 2 H 2 . At higher temperatures, HCN and NH 3 are also produced much more efficiently. We have applied the extended network to a simplified model of the accretion disk of an active galactic nucleus.

  3. Radiation pressure in galactic disks: stability, turbulence, and winds in the single-scattering limit

    Science.gov (United States)

    Wibking, Benjamin D.; Thompson, Todd A.; Krumholz, Mark R.

    2018-04-01

    The radiation force on dust grains may be dynamically important in driving turbulence and outflows in rapidly star-forming galaxies. Recent studies focus on the highly optically-thick limit relevant to the densest ultra-luminous galaxies and super star clusters, where reprocessed infrared photons provide the dominant source of electromagnetic momentum. However, even among starburst galaxies, the great majority instead lie in the so-called "single-scattering" limit, where the system is optically-thick to the incident starlight, but optically-thin to the re-radiated infrared. In this paper we present a stability analysis and multidimensional radiation-hydrodynamic simulations exploring the stability and dynamics of isothermal dusty gas columns in this regime. We describe our algorithm for full angle-dependent radiation transport based on the discontinuous Galerkin finite element method. For a range of near-Eddington fluxes, we show that the medium is unstable, producing convective-like motions in a turbulent atmosphere with a scale height significantly inflated compared to the gas pressure scale height and mass-weighted turbulent energy densities of ˜0.01 - 0.1 of the midplane radiation energy density, corresponding to mass-weighted velocity dispersions of Mach number ˜0.5 - 2. Extrapolation of our results to optical depths of 103 implies maximum turbulent Mach numbers of ˜20. Comparing our results to galaxy-averaged observations, and subject to the approximations of our calculations, we find that radiation pressure does not contribute significantly to the effective supersonic pressure support in star-forming disks, which in general are substantially sub-Eddington. We further examine the time-averaged vertical density profiles in dynamical equilibrium and comment on implications for radiation-pressure-driven galactic winds.

  4. Star formation and galactic evolution. I. General expressions and applications to our galaxy

    International Nuclear Information System (INIS)

    Kaufman, M.

    1979-01-01

    The study of galactic evolution involves three mechanisms for triggering star formation in interstellar clouds: (i) star formation triggered by a galactic spiral density wave, (ii) star formation triggered by shock waves from supernovae, and (iii) star formation triggered by an expanding H II region. Useful analytic approximations to the birthrate per unit mass are obtained by treating the efficiencies of these various mechanisms as time independent. In situations where shock waves from high-mass stars (either expanding H II regions or supernova explosions) are the only important star-forming mechanisms, the birthrate is exponential in time. This case is appropriate for the past evolution of an elliptical galaxy, nuclear bulge, or galactic halo. In the disk of a spiral galaxy where all three mechanisms operate, the birthrate consists of an exponential term plus a time-independent term. In both situations, the value of the time constant T in the exponential term is directly related to the efficiency of the shock waves from massive stars in initiating star formation.For our Galaxy, this simplified model is used to compute the radial distributions of young objects and low-mass stars in the disk, and the past and present birthrates in the solar-neighborhood shell

  5. galpy: A python LIBRARY FOR GALACTIC DYNAMICS

    International Nuclear Information System (INIS)

    Bovy, Jo

    2015-01-01

    I describe the design, implementation, and usage of galpy, a python package for galactic-dynamics calculations. At its core, galpy consists of a general framework for representing galactic potentials both in python and in C (for accelerated computations); galpy functions, objects, and methods can generally take arbitrary combinations of these as arguments. Numerical orbit integration is supported with a variety of Runge-Kutta-type and symplectic integrators. For planar orbits, integration of the phase-space volume is also possible. galpy supports the calculation of action-angle coordinates and orbital frequencies for a given phase-space point for general spherical potentials, using state-of-the-art numerical approximations for axisymmetric potentials, and making use of a recent general approximation for any static potential. A number of different distribution functions (DFs) are also included in the current release; currently, these consist of two-dimensional axisymmetric and non-axisymmetric disk DFs, a three-dimensional disk DF, and a DF framework for tidal streams. I provide several examples to illustrate the use of the code. I present a simple model for the Milky Way's gravitational potential consistent with the latest observations. I also numerically calculate the Oort functions for different tracer populations of stars and compare them to a new analytical approximation. Additionally, I characterize the response of a kinematically warm disk to an elliptical m = 2 perturbation in detail. Overall, galpy consists of about 54,000 lines, including 23,000 lines of code in the module, 11,000 lines of test code, and about 20,000 lines of documentation. The test suite covers 99.6% of the code. galpy is available at http://github.com/jobovy/galpy with extensive documentation available at http://galpy.readthedocs.org/en/latest

  6. Self-gravitating axially symmetric disks in general-relativistic rotation

    Science.gov (United States)

    Karkowski, Janusz; Kulczycki, Wojciech; Mach, Patryk; Malec, Edward; Odrzywołek, Andrzej; Piróg, Michał

    2018-05-01

    We integrate numerically axially symmetric stationary Einstein equations describing self-gravitating disks around spinless black holes. The numerical scheme is based on a method developed by Shibata, but contains important new ingredients. We derive a new general-relativistic Keplerian rotation law for self-gravitating disks around spinning black holes. Former results concerning rotation around spinless black holes emerge in the limit of a vanishing spin parameter. These rotation curves might be used for the description of rotating stars, after appropriate modification around the symmetry axis. They can be applied to the description of compact torus-black hole configurations, including active galactic nuclei or products of coalescences of two neutron stars.

  7. THE DARK DISK OF THE MILKY WAY

    International Nuclear Information System (INIS)

    Purcell, Chris W.; Bullock, James S.; Kaplinghat, Manoj

    2009-01-01

    Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. In agreement with previous results, we find that the Milky Way's merger history must have been unusually quiescent compared to median Λ cold dark matter expectations and, therefore, its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km s -1 , is enhanced by about 30% or less compared to a standard halo model. Such a dark disk could contribute dominantly to the low energy (of order keV for a dark matter particle with mass 100 GeV) nuclear recoil event rate of direct detection experiments, but it will not change the likelihood of detection significantly. These dark disks provide testable predictions of weakly interacting massive particle dark matter models and should be considered in detailed comparisons to experimental data. Our findings suggest that the dark disk of the Milky Way may provide a detectable signal for indirect detection experiments, contributing up to about 25% of the dark matter self-annihilation signal in the direction of the center of the Galaxy, lending the signal a noticeably oblate morphology.

  8. Gamma-ray bursts from fast, galactic neutron stars

    International Nuclear Information System (INIS)

    Colgate, S.A.; Leonard, P.J.

    1996-01-01

    What makes a Galactic model of gamma-ray bursts (GBs) feasible is the observation of a new population of objects, fast neutron stars, that are isotropic with respect to the galaxy following a finite period, ∼30 My, after their formation (1). Our Galactic model for the isotropic component of GBs is based upon high-velocity neutron stars (NSs) that have accretion disks. These fast NSs are formed in tidally locked binaries, producing a unique population of high velocity (approx-gt 10 3 kms -1 ) and slowly rotating (8 s) NSs. Tidal locking occurs due to the meridional circulation caused by the conservation of angular momentum of the tidal lobes. Following the collapse to a NS and the explosion, these lobes initially perturb the NS in the direction of the companion. Subsequent accretion (1 to 2 s) occurs on the rear side of the initial motion, resulting in a runaway acceleration of the NS by neutrino emission from the hot accreted matter. The recoil momentum of the relativistic neutrino emission from the localized, down flowing matter far exceeds the momentum drag of the accreted matter. The recoil of the NS is oriented towards the companion, but the NS misses because of the pre-explosion orbital motion. The near miss captures matter from the companion and forms a disk around the NS. Accretion onto the NS from this initially gaseous disk due to the ''alpha'' viscosity results in a soft gamma-ray repeater phase, which lasts ∼10 4 yr. Later, after the neutron star has moved ∼30 kpc from its birthplace, solid bodies form in the disk, and accrete to planetoid size bodies after ∼3x10 7 years. Some of these planetoid bodies, with a mass of ∼10 21 endash 10 22 g, are perturbed into an orbit inside the tidal distortion radius of approx-gt 10 5 km. Of these ∼1% are captured by the magnetic field of the NS at R 3 km to create GBs

  9. PHYSICAL CONTACT BETWEEN THE +20 km s{sup −1} CLOUD AND THE GALACTIC CIRCUMNUCLEAR DISK

    Energy Technology Data Exchange (ETDEWEB)

    Takekawa, Shunya; Oka, Tomoharu [School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223-8522 (Japan); Tanaka, Kunihiko, E-mail: shunya@aysheaia.phys.keio.ac.jp [Department of Physics, Institute of Science and Technology, Keio University, 3-14-1 Hiyoshi, Yokohama, Kanagawa 223-8522 (Japan)

    2017-01-10

    This paper reports the discovery of evidence for physical contact between the Galactic circumnuclear disk (CND) and an exterior giant molecular cloud. The central 10 pc of our Galaxy has been imaged in the HCN J  = 1–0, HCO{sup +} J  = 1–0, CS J  = 2–1, H{sup 13}CN J  = 1–0, SiO J  = 2–1, SO N{sub J}  = 2{sub 3}–1{sub 2}, and HC{sub 3}N J  = 11–10 lines using the Nobeyama Radio Observatory 45 m radio telescope. Based on our examination of the position–velocity maps of several high-density probe lines, we have found that an emission “bridge” may be connecting the +20 km s{sup −1} cloud (M–0.13–0.08) and the negative-longitude extension of the CND. Analyses of line intensity ratios imply that the chemical property of the bridge is located between the +20 km s{sup −1} cloud and the CND. We introduce a new interpretation that a part of the CND may be colliding with the 20 km s{sup −1} cloud and the collision may be responsible for the formation of the bridge. Such collisional events could promote mass accretion onto the CND or into the inner ionized cavity, which may be further tested by proper motion studies.

  10. A Heuristic Model for the Active Galactic Nucleus Based on the Planck Vacuum Theory

    Directory of Open Access Journals (Sweden)

    Daywitt W. C.

    2009-07-01

    Full Text Available The standard explanation for an active galactic nucleus (AGN is a "central engine" consisting of a hot accretion disk surrounding a supermassive black hole. Energy is generated by the gravitational infall of material which is heated to high temperatures in this dissipative accretion disk. What follows is an alternative model for the AGN based on the Planck vacuum (PV theory, where both the energy of the AGN and its variable luminosity are explained in terms of a variable photon flux emanating from the PV.

  11. ACCRETION DISKS AROUND KICKED BLACK HOLES: POST-KICK DYNAMICS

    International Nuclear Information System (INIS)

    Ponce, Marcelo; Faber, Joshua A.; Lombardi, James C.

    2012-01-01

    Numerical calculations of merging black hole binaries indicate that asymmetric emission of gravitational radiation can kick the merged black hole at up to thousands of km s –1 , and a number of systems have been observed recently whose properties are consistent with an active galactic nucleus containing a supermassive black hole moving with substantial velocity with respect to its broader accretion disk. We study here the effect of an impulsive kick delivered to a black hole on the dynamical evolution of its accretion disk using a smoothed particle hydrodynamics code, focusing attention on the role played by the kick angle with respect to the orbital angular momentum vector of the pre-kicked disk. We find that for more vertical kicks, for which the angle between the kick and the normal vector to the disk θ ∼ 45°, matter rapidly accretes toward the black hole. There is a systematic trend for higher potential luminosities for more oblique kick angles for a given black hole mass, disk mass, and kick velocity, and we find large amplitude oscillations in time in the case of a kick oriented 60° from the vertical.

  12. Metallicity in galactic clusters from high signal-to-noise spectroscopy

    International Nuclear Information System (INIS)

    Boesgaard, A.M.

    1989-01-01

    High-quality spectroscopic data on selected F dwarfs in six Galactic clusters are used to determine global (Fe/H) values for the clusters. For the two youngest clusters, Pleiades and Alpha Per, the (Fe/H) values are solar: 0.017 + or - 0.055. The Hyades and Praesepe are slightly metal-enhanced at (Fe/H) = + 0.125 + or - 0.032, even though they are an order of magnitude older than the Pleiades. Coma and the UMa Group at the age of the Hyades are slightly metal-deficient with (Fe/H) = - 0.082 + or - 0.039. The lack of an age-metallicity relationship indicates that the enrichment and mixing in the Galactic disk have not been uniform on time scales less than a billion years. 39 references

  13. A UNIVERSAL, LOCAL STAR FORMATION LAW IN GALACTIC CLOUDS, NEARBY GALAXIES, HIGH-REDSHIFT DISKS, AND STARBURSTS

    International Nuclear Information System (INIS)

    Krumholz, Mark R.; Dekel, Avishai; McKee, Christopher F.

    2012-01-01

    Star formation laws are rules that relate the rate of star formation in a particular region, either an entire galaxy or some portion of it, to the properties of the gas, or other galactic properties, in that region. While observations of Local Group galaxies show a very simple, local star formation law in which the star formation rate per unit area in each patch of a galaxy scales linearly with the molecular gas surface density in that patch, recent observations of both Milky Way molecular clouds and high-redshift galaxies apparently show a more complicated relationship in which regions of equal molecular gas surface density can form stars at quite different rates. These data have been interpreted as implying either that different star formation laws may apply in different circumstances, that the star formation law is sensitive to large-scale galaxy properties rather than local properties, or that there are high-density thresholds for star formation. Here we collate observations of the relationship between gas and star formation rate from resolved observations of Milky Way molecular clouds, from kpc-scale observations of Local Group galaxies, and from unresolved observations of both disk and starburst galaxies in the local universe and at high redshift. We show that all of these data are in fact consistent with a simple, local, volumetric star formation law. The apparent variations stem from the fact that the observed objects have a wide variety of three-dimensional size scales and degrees of internal clumping, so even at fixed gas column density the regions being observed can have wildly varying volume densities. We provide a simple theoretical framework to remove this projection effect, and we use it to show that all the data, from small solar neighborhood clouds with masses ∼10 3 M ☉ to submillimeter galaxies with masses ∼10 11 M ☉ , fall on a single star formation law in which the star formation rate is simply ∼1% of the molecular gas mass per local

  14. VERY METAL-POOR STARS IN THE OUTER GALACTIC BULGE FOUND BY THE APOGEE SURVEY

    International Nuclear Information System (INIS)

    García Pérez, Ana E.; Majewski, Steven R.; Hearty, Fred R.; Cunha, Katia; Shetrone, Matthew; Johnson, Jennifer A.; Zasowski, Gail; Smith, Verne V.; Beers, Timothy C.; Schiavon, Ricardo P.; Holtzman, Jon; Nidever, David; Allende Prieto, Carlos; Bizyaev, Dmitry; Ebelke, Garrett; Malanushenko, Elena; Malanushenko, Viktor; Eisenstein, Daniel J.; Frinchaboy, Peter M.; Girardi, Léo

    2013-01-01

    Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] ≤ –1.7), including two that are very metal-poor [Fe/H] ∼ –2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the α-elements O, Mg, and Si without significant α-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.

  15. VERY METAL-POOR STARS IN THE OUTER GALACTIC BULGE FOUND BY THE APOGEE SURVEY

    Energy Technology Data Exchange (ETDEWEB)

    Garcia Perez, Ana E.; Majewski, Steven R.; Hearty, Fred R. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Cunha, Katia [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Shetrone, Matthew [McDonald Observatory, University of Texas at Austin, Fort Davis, TX 79734 (United States); Johnson, Jennifer A.; Zasowski, Gail [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); Smith, Verne V.; Beers, Timothy C. [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States); Schiavon, Ricardo P. [Gemini Observatory, 670 N. A' Ohoku Place, Hilo, HI 96720 (United States); Holtzman, Jon [Department of Astronomy, MSC 4500, New Mexico State University, P.O. Box 30001, Las Cruces, NM 88003 (United States); Nidever, David [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Allende Prieto, Carlos [Departamento de Astrofisica, Universidad de La Laguna, E-38206 La Laguna, Tenerife (Spain); Bizyaev, Dmitry; Ebelke, Garrett; Malanushenko, Elena; Malanushenko, Viktor [Apache Point Observatory, P.O. Box 59, Sunspot, NM 88349-0059 (United States); Eisenstein, Daniel J. [Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Frinchaboy, Peter M. [Department of Physics and Astronomy, Texas Christian University, 2800 South University Drive, Fort Worth, TX 76129 (United States); Girardi, Leo [Laboratorio Interinstitucional de e-Astronomia - LIneA, Rua Gal. Jose Cristino 77, Rio de Janeiro, RJ - 20921-400 (Brazil); and others

    2013-04-10

    Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] {<=} -1.7), including two that are very metal-poor [Fe/H] {approx} -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the {alpha}-elements O, Mg, and Si without significant {alpha}-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.

  16. MAGNETOHYDRODYNAMIC ACCRETION DISK WINDS AS X-RAY ABSORBERS IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Fukumura, Keigo; Kazanas, Demosthenes; Behar, Ehud; Contopoulos, Ioannis

    2010-01-01

    We present the two-dimensional ionization structure of self-similar magnetohydrodynamic winds off accretion disks around and irradiated by a central X-ray point source. On the basis of earlier observational clues and theoretical arguments, we focus our attention on a subset of these winds, namely those with radial density dependence n(r) ∝ 1/r (r is the spherical radial coordinate). We employ the photoionization code XSTAR to compute the ionic abundances of a large number of ions of different elements and then compile their line-of-sight (LOS) absorption columns. We focus our attention on the distribution of the column density of the various ions as a function of the ionization parameter ξ (or equivalently r) and the angle θ. Particular attention is paid to the absorption measure distribution (AMD), namely their hydrogen-equivalent column per logarithmic ξ interval, dN H /dlog ξ, which provides a measure of the winds' radial density profiles. For the chosen density profile n(r) ∝ 1/r, the AMD is found to be independent of ξ, in good agreement with its behavior inferred from the X-ray spectra of several active galactic nuclei (AGNs). For the specific wind structure and X-ray spectrum, we also compute detailed absorption line profiles for a number of ions to obtain their LOS velocities, v ∼ 100-300 km s -1 (at log ξ ∼ 2-3) for Fe XVII and v ∼ 1000-4000 km s -1 (at log ξ ∼ 4-5) for Fe XXV, in good agreement with the observation. Our models describe the X-ray absorption properties of these winds with only two parameters, namely the mass-accretion rate m-dot and the LOS angle θ. The probability of obscuration of the X-ray ionizing source in these winds decreases with increasing m-dot and increases steeply with the LOS inclination angle θ. As such, we concur with previous authors that these wind configurations, viewed globally, incorporate all the requisite properties of the parsec scale 'torii' invoked in AGN unification schemes. We indicate that a

  17. Exploring the Dust Content of Galactic Winds with Herschel. II. Nearby Dwarf Galaxies*

    Science.gov (United States)

    McCormick, Alexander; Veilleux, Sylvain; Meléndez, Marcio; Martin, Crystal L.; Bland-Hawthorn, Joss; Cecil, Gerald; Heitsch, Fabian; Müller, Thomas; Rupke, David S. N.; Engelbracht, Chad

    2018-03-01

    We present results from analysis of deep Herschel Space Observatory observations of six nearby dwarf galaxies known to host galactic-scale winds. The superior far-infrared sensitivity and angular resolution of Herschel have allowed detection of cold circumgalactic dust features beyond the stellar components of the host galaxies traced by Spitzer 4.5 μm images. Comparisons of these cold dust features with ancillary data reveal an imperfect spatial correlation with the ionized gas and warm dust wind components. We find that typically ˜10-20% of the total dust mass in these galaxies resides outside of their stellar disks, but this fraction reaches ˜60% in the case of NGC 1569. This galaxy also has the largest metallicity (O/H) deficit in our sample for its stellar mass. Overall, the small number of objects in our sample precludes drawing strong conclusions on the origin of the circumgalactic dust. We detect no statistically significant trends with star formation properties of the host galaxies, as might be expected if the dust were lifted above the disk by energy inputs from on-going star formation activity. Although a case for dust entrained in a galactic wind is seen in NGC 1569, in all cases, we cannot rule out the possibility that some of the circumgalactic dust might be associated instead with gas accreted or removed from the disk by recent galaxy interaction events, or that it is part of the outer gas-rich portion of the disk that lies below the sensitivity limit of the Spitzer 4.5 μm data.

  18. The response of relativistic outflowing gas to the inner accretion disk of a black hole.

    Science.gov (United States)

    Parker, Michael L; Pinto, Ciro; Fabian, Andrew C; Lohfink, Anne; Buisson, Douglas J K; Alston, William N; Kara, Erin; Cackett, Edward M; Chiang, Chia-Ying; Dauser, Thomas; De Marco, Barbara; Gallo, Luigi C; Garcia, Javier; Harrison, Fiona A; King, Ashley L; Middleton, Matthew J; Miller, Jon M; Miniutti, Giovanni; Reynolds, Christopher S; Uttley, Phil; Vasudevan, Ranjan; Walton, Dominic J; Wilkins, Daniel R; Zoghbi, Abderahmen

    2017-03-01

    The brightness of an active galactic nucleus is set by the gas falling onto it from the galaxy, and the gas infall rate is regulated by the brightness of the active galactic nucleus; this feedback loop is the process by which supermassive black holes in the centres of galaxies may moderate the growth of their hosts. Gas outflows (in the form of disk winds) release huge quantities of energy into the interstellar medium, potentially clearing the surrounding gas. The most extreme (in terms of speed and energy) of these-the ultrafast outflows-are the subset of X-ray-detected outflows with velocities higher than 10,000 kilometres per second, believed to originate in relativistic (that is, near the speed of light) disk winds a few hundred gravitational radii from the black hole. The absorption features produced by these outflows are variable, but no clear link has been found between the behaviour of the X-ray continuum and the velocity or optical depth of the outflows, owing to the long timescales of quasar variability. Here we report the observation of multiple absorption lines from an extreme ultrafast gas flow in the X-ray spectrum of the active galactic nucleus IRAS 13224-3809, at 0.236 ± 0.006 times the speed of light (71,000 kilometres per second), where the absorption is strongly anti-correlated with the emission of X-rays from the inner regions of the accretion disk. If the gas flow is identified as a genuine outflow then it is in the fastest five per cent of such winds, and its variability is hundreds of times faster than in other variable winds, allowing us to observe in hours what would take months in a quasar. We find X-ray spectral signatures of the wind simultaneously in both low- and high-energy detectors, suggesting a single ionized outflow, linking the low- and high-energy absorption lines. That this disk wind is responding to the emission from the inner accretion disk demonstrates a connection between accretion processes occurring on very different

  19. Galactic abundance gradients from Cepheids : α and heavy elements in the outer disk

    NARCIS (Netherlands)

    Lemasle, B.; Francois, P.; Genovali, K.; Kovtyukh, V. V.; Bono, G.; Inno, L.; Laney, C. D.; Kaper, L.; Bergemann, M.; Fabrizio, M.; Matsunaga, N.; Pedicelli, S.; Primas, F.; Romaniello, M.

    2013-01-01

    Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients.

  20. Compton-heated winds and coronae above accretion disks. II. Instability and oscillations

    International Nuclear Information System (INIS)

    Shields, G.A.; Mckee, C.F.; Lin, D.N.C.; Begelman, M.C.; California Univ., Berkeley; California Univ., Santa Cruz; Colorado Univ., Boulder)

    1986-01-01

    The stability and evolution of windy accretion disks is investigated in detail. The basic disk evolution equations are briefly recapitulated, and an idealized analytic treatment of the wind and viscosity is used to show that steady disk flow is indeed unstable for sufficiently large ratio of the mass loss rate in the wind to the central accretion rate. Numerical solutions for a more realistic and appropriate expression for the mass loss rate and the standard ad hoc alpha model prescription for the viscosity are presented. The application of these results to real systems with Compton-heated winds is discussed, and a general formula for the oscillation period is given. The prediction is compared with observed periodic behavior of Galactic X-ray sources and AGNs. 17 references

  1. Evolution of heavy-element abundances in the galactic halo and disk

    International Nuclear Information System (INIS)

    Mathews, G.J.; Cowan, J.J.; Schramm, D.N.

    1988-05-01

    The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is described in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies

  2. GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

    International Nuclear Information System (INIS)

    Hanasz, Michal; Woltanski, Dominik; Kowalik, Kacper

    2009-01-01

    We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.

  3. Consistency between the luminosity function of resolved millisecond pulsars and the galactic center excess

    Energy Technology Data Exchange (ETDEWEB)

    Ploeg, Harrison; Gordon, Chris [Department of Physics and Astronomy, Rutherford Building, University of Canterbury, Private Bag 4800, Christchurch 8140 (New Zealand); Crocker, Roland [Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston Creek (Australia); Macias, Oscar, E-mail: harrison.ploeg@pg.canterbury.ac.nz, E-mail: chris.gordon@canterbury.ac.nz, E-mail: Roland.Crocker@anu.edu.au, E-mail: oscar.macias@vt.edu [Center for Neutrino Physics, Department of Physics, Virginia Tech, 850 West Campus Drive, Blacksburg, VA 24061 (United States)

    2017-08-01

    Fermi Large Area Telescope data reveal an excess of GeV gamma rays from the direction of the Galactic Center and bulge. Several explanations have been proposed for this excess including an unresolved population of millisecond pulsars (MSPs) and self-annihilating dark matter. It has been claimed that a key discriminant for or against the MSP explanation can be extracted from the properties of the luminosity function describing this source population. Specifically, is the luminosity function of the putative MSPs in the Galactic Center consistent with that characterizing the resolved MSPs in the Galactic disk? To investigate this we have used a Bayesian Markov Chain Monte Carlo to evaluate the posterior distribution of the parameters of the MSP luminosity function describing both resolved MSPs and the Galactic Center excess. At variance with some other claims, our analysis reveals that, within current uncertainties, both data sets can be well fit with the same luminosity function.

  4. Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays

    Science.gov (United States)

    Roth, Antoine S. G.; Metzler, Knut; Baumgartner, Lukas P.; Hofmann, Beda A.; Leya, Ingo

    2017-10-01

    Renazzo-type carbonaceous (CR) chondrites are accretionary breccias that formed last. As such they are ideal samples to study precompaction exposures to cosmic rays. Here, we present noble gas data for 24 chondrules and 3 dark inclusion samples (DIs) from Shişr 033 (CR2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DIs; the oxygen isotopes match those in CV3 and CO3 chondrites. Our samples contain variable mixtures of galactic cosmic ray (GCR)-produced cosmogenic noble gases and trapped noble gases of presolar origin. Remarkably, all chondrules have cosmogenic 3He and 21Ne concentrations up to 4.3 and 7.1 times higher than the DIs, respectively. We derived an average 3He-21Ne cosmic ray exposure (CRE) age for Shişr 033 of 2.03 ± 0.20 Ma (2 SD) and excesses in cosmogenic 3He and 21Ne in chondrules (relative to the DIs) in the range (in 10-8 cm3STP/g) 3.99-7.76 and 0.94-1.71, respectively. Assuming present-day GCR flux density, the excesses translate into average precompaction 3He-21Ne CRE ages of 3.1-27.3 Ma depending on the exposure geometry. The data can be interpreted assuming a protracted storage of a single chondrule generation prior to the final assembly of the Shişr 033 parent body in a region of the disk transparent to GCRs.

  5. Study of MRI in stratified viscous plasma configuration

    Science.gov (United States)

    Carlevaro, Nakia; Montani, Giovanni; Renzi, Fabrizio

    2017-02-01

    We analyze the morphology of the magneto-rotational instability (MRI) for a stratified viscous plasma disk configuration in differential rotation, taking into account the so-called corotation theorem for the background profile. In order to select the intrinsic Alfvénic nature of MRI, we deal with an incompressible plasma and we adopt a formulation of the local perturbation analysis based on the use of the magnetic flux function as a dynamical variable. Our study outlines, as consequence of the corotation condition, a marked asymmetry of the MRI with respect to the equatorial plane, particularly evident in a complete damping of the instability over a positive critical height on the equatorial plane. We also emphasize how such a feature is already present (although less pronounced) even in the ideal case, restoring a dependence of the MRI on the stratified morphology of the gravitational field.

  6. An Extreme X-ray Disk Wind in the Black Hole Candidate IGR J17091-3624

    Science.gov (United States)

    King, A. L.; Miller, J. M.; Raymond, J.; Fabian, A. C.; Reynolds, C. S.; Kallman, T. R.; Maitra, D.; Cackett, E. M.; Rupen, M. P.

    2012-01-01

    Chandra spectroscopy of transient stellar-mass black holes in outburst has clearly revealed accretion disk winds in soft, disk-dominated states, in apparent anti-correlation with relativistic jets in low/hard states. These disk winds are observed to be highly ionized. dense. and to have typical velocities of approx 1000 km/s or less projected along our line of sight. Here. we present an analysis of two Chandra High Energy Transmission Grating spectra of the Galactic black hole candidate IGR J17091-3624 and contemporaneous EVLA radio observations. obtained in 2011. The second Chandra observation reveals an absorption line at 6.91+/-0.01 keV; associating this line with He-like Fe XXV requires a blue-shift of 9300(+500/-400) km/ s (0.03c. or the escape velocity at 1000 R(sub schw)). This projected outflow velocity is an order of magnitude higher than has previously been observed in stellar-mass black holes, and is broadly consistent with some of the fastest winds detected in active galactic nuclei. A potential feature at 7.32 keV, if due to Fe XXVI, would imply a velocity of approx 14600 km/s (0.05c), but this putative feature is marginal. Photoionization modeling suggests that the accretion disk wind in IGR J17091-3624 may originate within 43,300 Schwarzschild radii of the black hole, and may be expelling more gas than accretes. The contemporaneous EVLA observations strongly indicate that jet activity was indeed quenched at the time of our Chandra observations. We discuss the results in the context of disk winds, jets, and basic accretion disk physics in accreting black hole systems

  7. Generalized Langevin equation with colored noise description of the stochastic oscillations of accretion disks

    International Nuclear Information System (INIS)

    Harko, Tiberiu; Leung, Chun Sing; Mocanu, Gabriela

    2014-01-01

    We consider a description of the stochastic oscillations of the general relativistic accretion disks around compact astrophysical objects interacting with their external medium based on a generalized Langevin equation with colored noise and on the fluctuation-dissipation theorems. The former accounts for the general memory and retarded effects of the frictional force. The presence of the memory effects influences the response of the disk to external random interactions, and it modifies the dynamical behavior of the disk, as well as the energy dissipation processes. The generalized Langevin equation of the motion of the disk in the vertical direction is studied numerically, and the vertical displacements, velocities, and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases. The power spectral distribution of the disk luminosity is also obtained. As a possible astrophysical application of the formalism we investigate the possibility that the intra-day variability of the active galactic nuclei may be due to the stochastic disk instabilities. The perturbations due to colored/nontrivially correlated noise induce a complicated disk dynamics, which could explain some astrophysical observational features related to disk variability. (orig.)

  8. Generalized Langevin equation with colored noise description of the stochastic oscillations of accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Harko, Tiberiu [University College London, Department of Mathematics, London (United Kingdom); Leung, Chun Sing [Polytechnic University, Department of Applied Mathematics, Hong Kong (China); Mocanu, Gabriela [Babes-Bolyai University, Faculty of Physics, Cluj-Napoca (Romania)

    2014-05-15

    We consider a description of the stochastic oscillations of the general relativistic accretion disks around compact astrophysical objects interacting with their external medium based on a generalized Langevin equation with colored noise and on the fluctuation-dissipation theorems. The former accounts for the general memory and retarded effects of the frictional force. The presence of the memory effects influences the response of the disk to external random interactions, and it modifies the dynamical behavior of the disk, as well as the energy dissipation processes. The generalized Langevin equation of the motion of the disk in the vertical direction is studied numerically, and the vertical displacements, velocities, and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases. The power spectral distribution of the disk luminosity is also obtained. As a possible astrophysical application of the formalism we investigate the possibility that the intra-day variability of the active galactic nuclei may be due to the stochastic disk instabilities. The perturbations due to colored/nontrivially correlated noise induce a complicated disk dynamics, which could explain some astrophysical observational features related to disk variability. (orig.)

  9. Generalized Langevin equation with colored noise description of the stochastic oscillations of accretion disks

    Science.gov (United States)

    Harko, Tiberiu; Leung, Chun Sing; Mocanu, Gabriela

    2014-05-01

    We consider a description of the stochastic oscillations of the general relativistic accretion disks around compact astrophysical objects interacting with their external medium based on a generalized Langevin equation with colored noise and on the fluctuation-dissipation theorems. The former accounts for the general memory and retarded effects of the frictional force. The presence of the memory effects influences the response of the disk to external random interactions, and it modifies the dynamical behavior of the disk, as well as the energy dissipation processes. The generalized Langevin equation of the motion of the disk in the vertical direction is studied numerically, and the vertical displacements, velocities, and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases. The power spectral distribution of the disk luminosity is also obtained. As a possible astrophysical application of the formalism we investigate the possibility that the intra-day variability of the active galactic nuclei may be due to the stochastic disk instabilities. The perturbations due to colored/nontrivially correlated noise induce a complicated disk dynamics, which could explain some astrophysical observational features related to disk variability.

  10. THE APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT: FIRST DETECTION OF HIGH-VELOCITY MILKY WAY BAR STARS

    Energy Technology Data Exchange (ETDEWEB)

    Nidever, David L.; Zasowski, Gail; Majewski, Steven R.; Beaton, Rachael L.; Wilson, John C.; Skrutskie, Michael F.; O' Connell, Robert W. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Bird, Jonathan; Schoenrich, Ralph; Johnson, Jennifer A.; Sellgren, Kris [Department of Astronomy and the Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States); Robin, Annie C.; Schultheis, Mathias [Institut Utinam, CNRS UMR 6213, OSU THETA, Universite de Franche-Comte, 41bis avenue de l' Observatoire, F-25000 Besancon (France); Martinez-Valpuesta, Inma; Gerhard, Ortwin [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Shetrone, Matthew [McDonald Observatory, University of Texas at Austin, Fort Davis, TX 79734 (United States); Schiavon, Ricardo P. [Gemini Observatory, 670 North A' Ohoku Place, Hilo, HI 96720 (United States); Weiner, Benjamin [Steward Observatory, 933 North Cherry Street, University of Arizona, Tucson, AZ 85721 (United States); Schneider, Donald P. [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Allende Prieto, Carlos, E-mail: dln5q@virginia.edu [Instituto de Astrofisica de Canarias, E-38205 La Laguna, Tenerife (Spain); and others

    2012-08-20

    Commissioning observations with the Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have produced radial velocities (RVs) for {approx}4700 K/M-giant stars in the Milky Way (MW) bulge. These high-resolution (R {approx} 22, 500), high-S/N (>100 per resolution element), near-infrared (NIR; 1.51-1.70 {mu}m) spectra provide accurate RVs ({epsilon}{sub V} {approx} 0.2 km s{sup -1}) for the sample of stars in 18 Galactic bulge fields spanning -1 Degree-Sign -32 Degree-Sign . This represents the largest NIR high-resolution spectroscopic sample of giant stars ever assembled in this region of the Galaxy. A cold ({sigma}{sub V} {approx} 30 km s{sup -1}), high-velocity peak (V{sub GSR} Almost-Equal-To +200 km s{sup -1}) is found to comprise a significant fraction ({approx}10%) of stars in many of these fields. These high RVs have not been detected in previous MW surveys and are not expected for a simple, circularly rotating disk. Preliminary distance estimates rule out an origin from the background Sagittarius tidal stream or a new stream in the MW disk. Comparison to various Galactic models suggests that these high RVs are best explained by stars in orbits of the Galactic bar potential, although some observational features remain unexplained.

  11. Comparison between UBV- and RGU-photometrically determined density functions for the photometric disk and halo and between the corresponding mean isodensity behaviour in the halo close to the galactic north-pole (SA 57)

    Science.gov (United States)

    Fenkart, R.; Esin-Yilmaz, F.

    1985-10-01

    SA 57, RG U-photometrically treated by Fenkart (1967), is the third field of the Basle Halo Program (BHP) we investigate by applying the RG U-methods for the separation of the (photometric) populations disk and halo and for the determination of their space densities analogously in UBV in order to compare the results independently obtained in both systems. Figures 1 and 2 give the V- and G-fractioned two-colour diagrams of the same 1179 stars treated in UBV and RG U, respectively. On their basis, the logarithmic space density functions of both populations have been calculated for the overall (3m to 8m ) and for the 1m -intervals absolute magnitudes M(V) and M(G). They are tabulated in tables II and III and plotted in figures 3 and 4, respectively (a : disk, b : halo). The overall density functions for the disk and for the halo are compared between the systems in figures Sa and b, respectively. The mean misidentification-rate per system (MMRS) is 7.3 %, lying between the ones for SA 54(9.2 %) and for SA 82(4.5 %) (Fenkart and Esin-Yilmaz, 1983 and 1984, respectively) and close to the mean for all three investigations (7.0 ± 2.4 %) The direction to SA 57 lies almost in the middle of the sector of the northern galactic meridian which is limited by the directions to SA 54 and to SA 82. Our results permit, together with the ones obtained in these limiting directions, the comparison of the mean isodensity-patterns obtained in both systems within this sector. They are completely parallel and blend in perfectly with the mean (RG U-) isodensity-pattern of the - partly overlapping - sector between SA 51 and SA 57 obtained by Fenkart and Karaall (1984) (Fig. 6). The appendices describe shortly the involved methods (A) and refer to related work by other authors in the direction to the galactic north-pole (B).

  12. Gemini spectroscopy of the outer disk star cluster BH176

    Science.gov (United States)

    Sharina, M. E.; Donzelli, C. J.; Davoust, E.; Shimansky, V. V.; Charbonnel, C.

    2014-10-01

    Context. BH176 is an old metal-rich star cluster. It is spatially and kinematically consistent with belonging to the Monoceros Ring. It is larger in size and more distant from the Galactic plane than typical open clusters, and it does not belong to the Galactic bulge. Aims: Our aim is to determine the origin of this unique object by accurately determining its distance, metallicity, and age. The best way to reach this goal is to combine spectroscopic and photometric methods. Methods: We present medium-resolution observations of red clump and red giant branch stars in BH176 obtained with the Gemini South Multi-Object Spectrograph. We derive radial velocities, metallicities, effective temperatures, and surface gravities of the observed stars and use these parameters to distinguish member stars from field objects. Results: We determine the following parameters for BH176: Vh = 0 ± 15 km s-1, [Fe/H] = -0.1 ± 0.1, age 7 ± 0.5 Gyr, E(V - I) = 0.79 ± 0.03, distance 15.2 ± 0.2 kpc, α-element abundance [α/Fe] ~ 0.25 dex (the mean of [Mg/Fe], and [Ca/Fe]). Conclusions: BH176 is a member of old Galactic open clusters that presumably belong to the thick disk. It may have originated as a massive star cluster after the encounter of the forming thin disk with a high-velocity gas cloud or as a satellite dwarf galaxy. Appendix A is available in electronic form at http://www.aanda.org

  13. Ringed Accretion Disks: Evolution of Double Toroidal Configurations

    Energy Technology Data Exchange (ETDEWEB)

    Pugliese, D.; Stuchlík, Z., E-mail: daniela.pugliese@fpf.slu.cz, E-mail: zdenek.stuchlik@physics.cz [Institute of Physics and Research Centre of Theoretical Physics and Astrophysics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo náměstí 13, CZ-74601 Opava (Czech Republic)

    2017-04-01

    We investigate ringed accretion disks composed of two tori (rings) orbiting on the equatorial plane of a central supermassive Kerr black hole. We discuss the emergence of the instability phases of each ring of the macro-configuration (ringed disk) according to the Paczynski violation of mechanical equilibrium. In the full general relativistic treatment, we consider the effects of the geometry of the Kerr spacetimes relevant to the characterization of the evolution of these configurations. The discussion of ring stability in different spacetimes enables us to identify particular classes of central Kerr attractors depending on their dimensionless spin. As a result of this analysis, we set constraints on the evolutionary schemes of the ringed disks relative to the torus morphology and on their rotation relative to the central black hole and to each other. The dynamics of the unstable phases of this system is significant for the high-energy phenomena related to accretion onto supermassive black holes in active galactic nuclei and the extremely energetic phenomena in quasars, which could be observed in their X-ray emission.

  14. Visualization periodic flows in a continuously stratified fluid.

    Science.gov (United States)

    Bardakov, R.; Vasiliev, A.

    2012-04-01

    To visualize the flow pattern of viscous continuously stratified fluid both experimental and computational methods were developed. Computational procedures were based on exact solutions of set of the fundamental equations. Solutions of the problems of flows producing by periodically oscillating disk (linear and torsion oscillations) were visualized with a high resolutions to distinguish small-scale the singular components on the background of strong internal waves. Numerical algorithm of visualization allows to represent both the scalar and vector fields, such as velocity, density, pressure, vorticity, stream function. The size of the source, buoyancy and oscillation frequency, kinematic viscosity of the medium effects were traced in 2D an 3D posing problems. Precision schlieren instrument was used to visualize the flow pattern produced by linear and torsion oscillations of strip and disk in a continuously stratified fluid. Uniform stratification was created by the continuous displacement method. The buoyancy period ranged from 7.5 to 14 s. In the experiments disks with diameters from 9 to 30 cm and a thickness of 1 mm to 10 mm were used. Different schlieren methods that are conventional vertical slit - Foucault knife, vertical slit - filament (Maksoutov's method) and horizontal slit - horizontal grating (natural "rainbow" schlieren method) help to produce supplementing flow patterns. Both internal wave beams and fine flow components were visualized in vicinity and far from the source. Intensity of high gradient envelopes increased proportionally the amplitude of the source. In domains of envelopes convergence isolated small scale vortices and extended mushroom like jets were formed. Experiments have shown that in the case of torsion oscillations pattern of currents is more complicated than in case of forced linear oscillations. Comparison with known theoretical model shows that nonlinear interactions between the regular and singular flow components must be taken

  15. Star Formation at the Galactic Center

    Science.gov (United States)

    Kohler, Susanna

    2015-08-01

    Could stars be forming in the inhospitable environment near Sagittarius A* in the heart of the Milky Way? A possible signature of low-mass star formation has recently been found just two light-years from the black hole at the center of our galaxy — a region that was previously thought to be too hostile for such activity. Searching for Signatures: Previous observations of the central few light-years of the Milky Way had focused on a population of about 200 massive, young and very bright stars in tight orbits around Sgr A*. These stars are only a few million years old and prompted scientists to wonder: have they somehow managed to form in situ, in spite of their close proximity to the black hole, or did they form further out and then migrate in? Motivated by this mystery, Farhad Yusef-Zadeh of Northwestern University and collaborators looked for evidence of even younger stars close to Sagittarius A*, which would demonstrate that star formation in the area is an ongoing process. Using the Very Large Array (VLA), the collaboration discovered several small sources in one arm of activity near Sgr A*. This 34-GHz image provides a close-up view of two protoplanetary disk candidates (labeled P26 and P8) located near Sgr A*. These objects are outlined on the right side by a bow shock caused by impacting stellar wind that streams from the young, hot stars closer to the Galactic center. The disks are thought to contain recently-formed, low-mass stars. (Credit: Yusef-Zadeh et al., 2015) Heated Disks: The team identified these sources as candidate photoevaporative protoplanetary disks, or “proplyds” — areas of dense, ionized gas and dust surrounding young, newly formed stars. The proplyd candidates are between 10,000 and 100,000 years old, and they lie along the edge of a large molecular cloud. It is likely that this cloud produced the disks by providing a reservoir of gas to feed the star-formation activity. The region surrounding these proplyds is blasted with harsh

  16. The Gaia-ESO Survey: Separating disk chemical substructures with cluster models. Evidence of a separate evolution in the metal-poor thin disk

    Science.gov (United States)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Schultheis, M.; Guiglion, G.; Mikolaitis, Š.; Kordopatis, G.; Hill, V.; Gilmore, G.; Randich, S.; Alfaro, E. J.; Bensby, T.; Koposov, S. E.; Costado, M. T.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Monaco, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.; Chiappini, C.

    2016-02-01

    Context. Recent spectroscopic surveys have begun to explore the Galactic disk system on the basis of large data samples, with spatial distributions sampling regions well outside the solar neighborhood. In this way, they provide valuable information for testing spatial and temporal variations of disk structure kinematics and chemical evolution. Aims: The main purposes of this study are to demonstrate the usefulness of a rigorous mathematical approach to separate substructures of a stellar sample in the abundance-metallicity plane, and provide new evidence with which to characterize the nature of the metal-poor end of the thin disk sequence. Methods: We used a Gaussian mixture model algorithm to separate in the [Mg/Fe] vs. [Fe/H] plane a clean disk star subsample (essentially at RGC -0.25 dex) highlight a change in the slope at solar metallicity. This holds true at different radial regions of the Milky Way. The distribution of Galactocentric radial distances of the metal-poor part of the thin disk ([Fe/H] Cambridge Astronomy Survey Unit (CASU) at the Institute of Astronomy, University of Cambridge, and by the FLAMES/UVES reduction team at INAF/Osservatorio Astrofisico di Arcetri. These data have been obtained from the Gaia-ESO Survey Data Archive, prepared and hosted by the Wide Field Astronomy Unit, Institute for Astronomy, University of Edinburgh, which is funded by the UK Science and Technology Facilities Council.

  17. Non-LTE effects on the strength of the Lyman edge in quasar accretion disks

    Science.gov (United States)

    Stoerzer, H.; Hauschildt, P. H.; Allard, F.

    1994-01-01

    We have calculated UV/EUV (300 A which is less than or equal to lambda which is less than or equal to 1500 A) continuous energy distributions of accretion disks in the centers of active galactic nuclei (AGNs) for disk luminosities in the range 0.1 L(sub Edd) less than or equal to L(sub acc) less than 1.0 L(sub Edd) and central masses ranging from 10(exp 8) solar mass to 10(exp 9) solar mass. The vertical gas pressure structure of the disk and the disk height are obtained analytically; the temperature stratification and the resulting continuum radiation fields are calculated numerically. We have included non-Local Thermodynamic Equilibrium (LTE) effects of both the ionization equilibrium and the level populations of hydrogen and helium. We show that these non-LTE effects reduce the strength of the Lyman edge when comapred to the LTE case. In non-LTE we find that the edge can be weakly in emission or absorption for disks seen face-on, depending on the disk parameters.

  18. Galactic-scale Feedback Observed in the 3C 298 Quasar Host Galaxy

    Science.gov (United States)

    Vayner, Andrey; Wright, Shelley A.; Murray, Norman; Armus, Lee; Larkin, James E.; Mieda, Etsuko

    2017-12-01

    We present high angular resolution multiwavelength data of the 3C 298 radio-loud quasar host galaxy (z = 1.439) taken using the W.M. Keck Observatory OSIRIS integral field spectrograph (IFS) with adaptive optics, the Atacama Large Millimeter/submillimeter Array (ALMA), the Hubble Space Telescope (HST) WFC3, and the Very Large Array (VLA). Extended emission is detected in the rest-frame optical nebular emission lines Hβ, [O III], Hα, [N II], and [S II], as well as in the molecular lines CO (J = 3‑2) and (J = 5‑4). Along the path of the relativistic jets of 3C 298, we detect conical outflows in ionized gas emission with velocities of up to 1700 {km} {{{s}}}-1 and an outflow rate of 450–1500 {M}ȯ {{yr}}-1 extended over 12 kpc. Near the spatial center of the conical outflow, CO (J = 3‑2) emission shows a molecular gas disk with a rotational velocity of ±150 {km} {{{s}}}-1 and total molecular mass ({M}{{{H}}2}) of 6.6+/- 0.36× {10}9 {M}ȯ . On the blueshifted side of the molecular disk, we observe broad extended emission that is due to a molecular outflow with a rate of 2300 {M}ȯ {{yr}}-1 and depletion timescale of 3 Myr. We detect no narrow Hα emission in the outflow regions, suggesting a limit on star formation of 0.3 {M}ȯ {{yr}}-1 {{kpc}}-2. Quasar-driven winds are evacuating the molecular gas reservoir, thereby directly impacting star formation in the host galaxy. The observed mass of the supermassive black hole is {10}9.37{--9.56} {M}ȯ , and we determine a dynamical bulge mass of {M}{bulge}=1{--}1.7× {10}10\\tfrac{R}{1.6 {kpc}} {M}ȯ . The bulge mass of 3C 298 lies 2–2.5 orders of magnitude below the expected value from the local galactic bulge—supermassive black hole mass ({M}{bulge}{--}{M}{BH}) relationship. A second galactic disk observed in nebular emission is offset from the quasar by 9 kpc, suggesting that the system is an intermediate-stage merger. These results show that galactic-scale negative feedback is occurring early in the merger

  19. NEW CONSTRAINTS ON THE GALACTIC HALO MAGNETIC FIELD USING ROTATION MEASURES OF EXTRAGALACTIC SOURCES TOWARD THE OUTER GALAXY

    International Nuclear Information System (INIS)

    Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown, J. C.; Van Eck, C. L.; Stil, J. M.; Taylor, A. R.; Haverkorn, M.; Kronberg, P. P.; Shukurov, A.

    2012-01-01

    We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100°-117°, within 30° of the Galactic plane. For |b| –2 and –62 ± 5 rad m –2 in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2 μG (7 μG) at a height 0.8-2 kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.

  20. HYDROCARBON EMISSION RINGS IN PROTOPLANETARY DISKS INDUCED BY DUST EVOLUTION

    Energy Technology Data Exchange (ETDEWEB)

    Bergin, Edwin A.; Du, Fujun; Schwarz, K.; Zhang, K. [Department of Astronomy, University of Michigan, 311 West Hall, 1085 S. University Ave, Ann Arbor, MI 48109 (United States); Cleeves, L. Ilsedore [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Blake, G. A. [Division of Geological and Planetary Sciences, MC 150-21, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125 (United States); Visser, R. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching (Germany)

    2016-11-01

    We report observations of resolved C{sub 2}H emission rings within the gas-rich protoplanetary disks of TW Hya and DM Tau using the Atacama Large Millimeter Array. In each case the emission ring is found to arise at the edge of the observable disk of millimeter-sized grains (pebbles) traced by submillimeter-wave continuum emission. In addition, we detect a C{sub 3}H{sub 2} emission ring with an identical spatial distribution to C{sub 2}H in the TW Hya disk. This suggests that these are hydrocarbon rings (i.e., not limited to C{sub 2}H). Using a detailed thermo-chemical model we show that reproducing the emission from C{sub 2}H requires a strong UV field and C/O > 1 in the upper disk atmosphere and outer disk, beyond the edge of the pebble disk. This naturally arises in a disk where the ice-coated dust mass is spatially stratified due to the combined effects of coagulation, gravitational settling and drift. This stratification causes the disk surface and outer disk to have a greater permeability to UV photons. Furthermore the concentration of ices that transport key volatile carriers of oxygen and carbon in the midplane, along with photochemical erosion of CO, leads to an elemental C/O ratio that exceeds unity in the UV-dominated disk. Thus the motions of the grains, and not the gas, lead to a rich hydrocarbon chemistry in disk surface layers and in the outer disk midplane.

  1. THE ARECIBO METHANOL MASER GALACTIC PLANE SURVEY. III. DISTANCES AND LUMINOSITIES

    International Nuclear Information System (INIS)

    Pandian, J. D.; Menten, K. M.; Goldsmith, P. F.

    2009-01-01

    We derive kinematic distances to the 86 6.7 GHz methanol masers discovered in the Arecibo Methanol Maser Galactic Plane Survey. The systemic velocities of the sources were derived from 13 CO (J = 2-1), CS (J = 5-4), and NH 3 observations made with the ARO Submillimeter Telescope, the APEX telescope, and the Effelsberg 100 m telescope, respectively. Kinematic distance ambiguities were resolved using H I self-absorption with H I data from the VLA Galactic Plane Survey. We observe roughly three times as many sources at the far distance compared to the near distance. The vertical distribution of the sources has a scale height of ∼ 30 pc, and is much lower than that of the Galactic thin disk. We use the distances derived in this work to determine the luminosity function of 6.7 GHz maser emission. The luminosity function has a peak at approximately 10 -6 L sun . Assuming that this luminosity function applies, the methanol maser population in the Large Magellanic Cloud and M33 is at least 4 and 14 times smaller, respectively, than in our Galaxy.

  2. Tully-Fisher relation, galactic rotation curves and dissipative mirror dark matter

    Energy Technology Data Exchange (ETDEWEB)

    Foot, R., E-mail: rfoot@unimelb.edu.au [ARC Centre of Excellence for Particle Physics at the Terascale, School of Physics, University of Melbourne, Victoria 3010 Australia (Australia)

    2014-12-01

    If dark matter is dissipative then the distribution of dark matter within galactic halos can be governed by dissipation, heating and hydrostatic equilibrium. Previous work has shown that a specific model, in the framework of mirror dark matter, can explain several empirical galactic scaling relations. It is shown here that this dynamical halo model implies a quasi-isothermal dark matter density, ρ(r) ≅ ρ{sub 0}r{sub 0}{sup 2}/(r{sup 2}+r{sub 0}{sup 2}), where the core radius, r{sub 0}, scales with disk scale length, r{sub D}, via r{sub 0}/kpc ≈ 1.4(r{sub D}/kpc). Additionally, the product ρ{sub 0}r{sub 0} is roughly constant, i.e. independent of galaxy size (the constant is set by the parameters of the model). The derived dark matter density profile implies that the galactic rotation velocity satisfies the Tully-Fisher relation, L{sub B}∝v{sup 3}{sub max}, where v{sub max} is the maximal rotational velocity. Examples of rotation curves resulting from this dynamics are given.

  3. Complex organic molecules in the Galactic Centre: the N-bearing family

    Science.gov (United States)

    Zeng, S.; Jiménez-Serra, I.; Rivilla, V. M.; Martín, S.; Martín-Pintado, J.; Requena-Torres, M. A.; Armijos-Abendaño, J.; Riquelme, D.; Aladro, R.

    2018-05-01

    We present an unbiased spectral line survey toward the Galactic Centre (GC) quiescent giant molecular cloud (QGMC), G+0.693 using the GBT and IRAM 30 telescopes. Our study highlights an extremely rich organic inventory of abundant amounts of nitrogen (N)-bearing species in a source without signatures of star formation. We report the detection of 17 N-bearing species in this source, of which 8 are complex organic molecules (COMs). A comparison of the derived abundances relative to H2 is made across various galactic and extragalactic environments. We conclude that the unique chemistry in this source is likely to be dominated by low-velocity shocks with X-rays/cosmic rays also playing an important role in the chemistry. Like previous findings obtained for O-bearing molecules, our results for N-bearing species suggest a more efficient hydrogenation of these species on dust grains in G+0.693 than in hot cores in the Galactic disk, as a consequence of the low dust temperatures coupled with energetic processing by X-ray/cosmic ray radiation in the GC.

  4. A Near-infrared RR Lyrae Census along the Southern Galactic Plane: The Milky Way’s Stellar Fossil Brought to Light

    Science.gov (United States)

    Dékány, István; Hajdu, Gergely; Grebel, Eva K.; Catelan, Márcio; Elorrieta, Felipe; Eyheramendy, Susana; Majaess, Daniel; Jordán, Andrés

    2018-04-01

    RR Lyrae stars (RRLs) are tracers of the Milky Way’s fossil record, holding valuable information on its formation and early evolution. Owing to the high interstellar extinction endemic to the Galactic plane, distant RRLs lying at low Galactic latitudes have been elusive. We attained a census of 1892 high-confidence RRLs by exploiting the near-infrared photometric database of the VVV survey’s disk footprint spanning ∼70° of Galactic longitude, using a machine-learned classifier. Novel data-driven methods were employed to accurately characterize their spatial distribution using sparsely sampled multi-band photometry. The RRL metallicity distribution function (MDF) was derived from their K s -band light-curve parameters using machine-learning methods. The MDF shows remarkable structural similarities to both the spectroscopic MDF of red clump giants and the MDF of bulge RRLs. We model the MDF with a multi-component density distribution and find that the number density of stars associated with the different model components systematically changes with both the Galactocentric radius and vertical distance from the Galactic plane, equivalent to weak metallicity gradients. Based on the consistency with results from the ARGOS survey, three MDF modes are attributed to the old disk populations, while the most metal-poor RRLs are probably halo interlopers. We propose that the dominant [Fe/H] component with a mean of ‑1 dex might correspond to the outskirts of an ancient Galactic spheroid or classical bulge component residing in the central Milky Way. The physical origins of the RRLs in this study need to be verified by kinematical information.

  5. Astero-archaeology: Reading the galactic history recorded in the white dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Wood, M.A.

    1990-01-01

    Galactic history is written in its oldest stars, the white dwarfs. Although still some years away from reading the details of that history, significant limits can already be placed on both the Galactic age and star formation history. The following is a complete analysis of the problem, starting with a fresh exploration of the physics of white dwarf stars. An extensive grid of numerical model sequences is presented and these are used to describe in detail the behavior of the white dwarf stars as a function of mass, core composition, surface layer masses and compositions, and uncertainties in the constitutive physics. These model sequences are used to decode the information contained in the white dwarf luminosity function. A theoretical context is established for current and future observations by presenting luminosity functions computed with differing choices for the input white dwarf evolutionary sequences, the assumed age of the local disk, the star formation rate as a function of time, and the possibility of scale height inflation of the disk with time. Finally, white dwarf cosmochronology is discussed within the context of other, conflicting, methods of cosmochronology. How this work can help resolve these conflicts and shed light on fundamental problems in galaxy formation and cosmology.

  6. Astero-archaeology: Reading the galactic history recorded in the white dwarf stars

    International Nuclear Information System (INIS)

    Wood, M.A.

    1990-01-01

    Galactic history is written in its oldest stars, the white dwarfs. Although still some years away from reading the details of that history, significant limits can already be placed on both the Galactic age and star formation history. The following is a complete analysis of the problem, starting with a fresh exploration of the physics of white dwarf stars. An extensive grid of numerical model sequences is presented and these are used to describe in detail the behavior of the white dwarf stars as a function of mass, core composition, surface layer masses and compositions, and uncertainties in the constitutive physics. These model sequences are used to decode the information contained in the white dwarf luminosity function. A theoretical context is established for current and future observations by presenting luminosity functions computed with differing choices for the input white dwarf evolutionary sequences, the assumed age of the local disk, the star formation rate as a function of time, and the possibility of scale height inflation of the disk with time. Finally, white dwarf cosmochronology is discussed within the context of other, conflicting, methods of cosmochronology. How this work can help resolve these conflicts and shed light on fundamental problems in galaxy formation and cosmology

  7. Stellar population samples at the galactic poles. III. UBVRI observations of proper motion stars near the south pole and the luminosity laws for the halo and old disk populations

    International Nuclear Information System (INIS)

    Eggen, O.J.

    1976-01-01

    Some 1200 UBV and 650 R, I observations of 1050 stars, mostly with annual proper motion greater than 0.096'', brighter than visual magnitude 15, and within 10 0 of the south galactic pole, are presented and discussed. The M-type stars (B -- V greater than + 1.15 mag) in the sample are discussed in a current article in The Astrophysical Journal, Part I. The bluer stars indicate that the slopes of the luminosity laws for old disk and halo stars are fairly similar to M/sub v/ near +6 mag, the old-disk-population law has an inflection point near M/sub v/ = +7 mag, the halo-population law may peak near M/sub v/ = +9 mag on a broad plateau that continues to beyond +10 mag and drops to zero near +13 mag, and the upper limit for the mass density of the halo population near the Sun is near 9 x 10 -4 M/sub mass/ pc -3 . Many stars of particular interest in the sample are briefly discussed. These include several possible red subluminous stars, one of which may be a very close solar neighbor; some halo-population giants; and one unique flare star with an amplitude near 0.5 mag in R

  8. PATCHY ACCRETION DISKS IN ULTRA-LUMINOUS X-RAY SOURCES

    Energy Technology Data Exchange (ETDEWEB)

    Miller, J. M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042 (United States); Bachetti, M.; Barret, D.; Webb, N. A. [Universite de Toulouse, UPS-OMP, IRAP, F- 31100 Toulouse (France); Harrison, F. A.; Walton, D. J.; Rana, V. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Fabian, A. C., E-mail: jonmm@umich.edu [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)

    2014-04-10

    The X-ray spectra of the most extreme ultra-luminous X-ray sources—those with L ≥ 10{sup 40} erg s{sup –1}—remain something of a mystery. Spectral roll-over in the 5-10 keV band was originally detected in the deepest XMM-Newton observations of the brightest sources; this is confirmed in subsequent NuSTAR spectra. This emission can be modeled via Comptonization, but with low electron temperatures (kT{sub e} ≅ 2 keV) and high optical depths (τ ≅ 10) that pose numerous difficulties. Moreover, evidence of cooler thermal emission that can be fit with thin disk models persists, even in fits to joint XMM-Newton and NuSTAR observations. Using NGC 1313 X-1 as a test case, we show that a patchy disk with a multiple temperature profile may provide an excellent description of such spectra. In principle, a number of patches within a cool disk might emit over a range of temperatures, but the data only require a two-temperature profile plus standard Comptonization, or three distinct blackbody components. A mechanism such as the photon bubble instability may naturally give rise to a patchy disk profile, and could give rise to super-Eddington luminosities. It is possible, then, that a patchy disk (rather than a disk with a standard single-temperature profile) might be a hallmark of accretion disks close to or above the Eddington limit. We discuss further tests of this picture and potential implications for sources such as narrow-line Seyfert-1 galaxies and other low-mass active galactic nuclei.

  9. The outflows accelerated by the magnetic fields and radiation force of accretion disks

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Xinwu, E-mail: cxw@shao.ac.cn [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai, 200030 (China)

    2014-03-01

    The inner region of a luminous accretion disk is radiation-pressure-dominated. We estimate the surface temperature of a radiation-pressure-dominated accretion disk, Θ=c{sub s}{sup 2}/r{sup 2}Ω{sub K}{sup 2}≪(H/r){sup 2}, which is significantly lower than that of a gas-pressure-dominated disk, Θ ∼ (H/r){sup 2}. This means that the outflow can be launched magnetically from the photosphere of the radiation-pressure-dominated disk only if the effective potential barrier along the magnetic field line is extremely shallow or no potential barrier is present. For the latter case, the slow sonic point in the outflow will probably be in the disk, which leads to a slow circular dense flow above the disk. This implies that hot gas (probably in the corona) is necessary for launching an outflow from the radiation-pressure-dominated disk, which provides a natural explanation for the observational evidence that the relativistic jets are related to hot plasma in some X-ray binaries and active galactic nuclei. We investigate the outflows accelerated from the hot corona above the disk by the magnetic field and radiation force of the accretion disk. We find that with the help of the radiation force, the mass loss rate in the outflow is high, which leads to a slow outflow. This may be why the jets in radio-loud narrow-line Seyfert galaxies are in general mildly relativistic compared with those in blazars.

  10. MAGNETICALLY DRIVEN ACCRETION DISK WINDS AND ULTRA-FAST OUTFLOWS IN PG 1211+143

    International Nuclear Information System (INIS)

    Fukumura, Keigo; Tombesi, Francesco; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Contopoulos, Ioannis

    2015-01-01

    We present a study of X-ray ionization of MHD accretion-disk winds in an effort to constrain the physics underlying the highly ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption-line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an XMM-Newton/EPIC spectrum of the narrow-line Seyfert, PG 1211+143. We find, through identifying the detected features with Fe Kα transitions, that the absorber has a characteristic ionization parameter of log (ξ c [erg cm s −1 ]) ≃ 5–6 and a column density on the order of N H ≃ 10 23 cm −2 outflowing at a characteristic velocity of v c /c ≃ 0.1–0.2 (where c is the speed of light). The best-fit model favors its radial location at r c ≃ 200 R o (R o is the black hole’s innermost stable circular orbit), with an inner wind truncation radius at R t ≃ 30 R o . The overall K-shell feature in the data is suggested to be dominated by Fe xxv with very little contribution from Fe xxvi and weakly ionized iron, which is in good agreement with a series of earlier analyses of the UFOs in various AGNs, including PG 1211+143

  11. Galactic chemical evolution with main-sequence mass loss and the distribution of F and G dwarfs

    International Nuclear Information System (INIS)

    Guzik, J.A.; Struck-Marcell, C.

    1988-01-01

    Simple closed galactic chemical-evolution models incorporating early main-sequence stellar mass loss have been developed for disk ages of 5, 10, and 15 Gyr. Relative to models without stellar mass loss, the models are shown to produce a 30-60 percent increase in the present mass ratio of dwarfs to dwarfs plus remnants, and a 200-250 percent increase in the total mass of late F dwarfs remaining on the main sequence at the current disk age. For present disk ages 5 and 10 Gyr, the total mass of mid-F dwarfs remaining on the main sequence is also shown to increase by 90-120 percent. It is concluded that models with main-sequence mass loss have a slightly reduced gas metallicity and slightly increased gas fraction midway through the evolution. 30 references

  12. STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

    Energy Technology Data Exchange (ETDEWEB)

    Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

    2015-03-01

    Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear.

  13. STAR FORMATION IN DISK GALAXIES. III. DOES STELLAR FEEDBACK RESULT IN CLOUD DEATH?

    International Nuclear Information System (INIS)

    Tasker, Elizabeth J.; Wadsley, James; Pudritz, Ralph

    2015-01-01

    Stellar feedback, star formation, and gravitational interactions are major controlling forces in the evolution of giant molecular clouds (GMCs). To explore their relative roles, we examine the properties and evolution of GMCs forming in an isolated galactic disk simulation that includes both localized thermal feedback and photoelectric heating. The results are compared with the three previous simulations in this series, which consists of a model with no star formation, star formation but no form of feedback, and star formation with photoelectric heating in a set with steadily increasing physical effects. We find that the addition of localized thermal feedback greatly suppresses star formation but does not destroy the surrounding GMC, giving cloud properties closely resembling the run in which no stellar physics is included. The outflows from the feedback reduce the mass of the cloud but do not destroy it, allowing the cloud to survive its stellar children. This suggests that weak thermal feedback such as the lower bound expected for a supernova may play a relatively minor role in the galactic structure of quiescent Milky-Way-type galaxies, compared to gravitational interactions and disk shear

  14. Role of Turbulent Damping in Cosmic Ray Galactic Winds

    Science.gov (United States)

    Holguin, Francisco; Ruszkowski, Mateusz; Lazarian, Alex; Yang, H. Y. Karen

    2018-06-01

    Large-scale galactic winds driven by stellar feedback are one phenomenon that influences the dynamical and chemical evolution of a galaxy, pushing and redistributing material throughout the interstellar medium (ISM) and galactic halo. A detailed understanding of the exact physical mechanisms responsible for these winds is lacking. Non-thermal feedback from galactic cosmic rays (CR), high-energy charged particles accelerated in supernovae and young stars, can impact the efficiency in accelerating the wind. In the self-confinement model, CR stream along magnetic field lines at the Alfven speed due to scattering off self-excited Aflv{é}n waves. However, magneto-hydrodynamic (MHD) turbulence stirred up by stellar feedback dissipates these confining waves, allowing CR to be super Aflvenic. Previous simulations relying on a simplified model of transport have shown that super-Alfv{é}nic streaming of CRs can launch a stronger wind. We perform three-dimensional MHD simulations of a section of a galactic disk, including CR streaming dependent on the local environment, using a realistic model of turbulent dissipation of Alfven waves presented in Lazarian (2016). In this implementation, the CR streaming speed can be super Alfv{é}nic depending on local conditions. We compare results for Alfv{é}nic and locally determined streaming, and find that gas/CR distributions and instantaneous mass loading factor of the wind are different depending on the level of turbulence.Lazarian, A. “Damping of Alfven waves by turbulence and its consequences: from cosmic-ray streaming to launching winds.” ApJ. Vol. 833, Num. 2. (2016).

  15. THE EVOLUTION OF GAS CLOUDS FALLING IN THE MAGNETIZED GALACTIC HALO: HIGH-VELOCITY CLOUDS (HVCs) ORIGINATED IN THE GALACTIC FOUNTAIN

    International Nuclear Information System (INIS)

    Kwak, Kyujin; Shelton, Robin L.; Raley, Elizabeth A.

    2009-01-01

    In the Galactic fountain scenario, supernovae and/or stellar winds propel material into the Galactic halo. As the material cools, it condenses into clouds. By using FLASH three-dimensional magnetohydrodynamic simulations, we model and study the dynamical evolution of these gas clouds after they form and begin to fall toward the Galactic plane. In our simulations, we assume that the gas clouds form at a height of z = 5 kpc above the Galactic midplane, then begin to fall from rest. We investigate how the cloud's evolution, dynamics, and interaction with the interstellar medium (ISM) are affected by the initial mass of the cloud. We find that clouds with sufficiently large initial densities (n ≥ 0.1 H atoms cm -3 ) accelerate sufficiently and maintain sufficiently large column densities as to be observed and identified as high-velocity clouds (HVCs) even if the ISM is weakly magnetized (1.3 μG). However, the ISM can provide noticeable resistance to the motion of a low-density cloud (n ≤ 0.01 H atoms cm -3 ) thus making it more probable that a low-density cloud will attain the speed of an intermediate-velocity cloud rather than the speed of an HVC. We also investigate the effects of various possible magnetic field configurations. As expected, the ISM's resistance is greatest when the magnetic field is strong and perpendicular to the motion of the cloud. The trajectory of the cloud is guided by the magnetic field lines in cases where the magnetic field is oriented diagonal to the Galactic plane. The model cloud simulations show that the interactions between the cloud and the ISM can be understood via analogy to the shock tube problem which involves shock and rarefaction waves. We also discuss accelerated ambient gas, streamers of material ablated from the clouds, and the cloud's evolution from a sphere-shaped to a disk- or cigar-shaped object.

  16. Self-consistent Bulge/Disk/Halo Galaxy Dynamical Modeling Using Integral Field Kinematics

    Science.gov (United States)

    Taranu, D. S.; Obreschkow, D.; Dubinski, J. J.; Fogarty, L. M. R.; van de Sande, J.; Catinella, B.; Cortese, L.; Moffett, A.; Robotham, A. S. G.; Allen, J. T.; Bland-Hawthorn, J.; Bryant, J. J.; Colless, M.; Croom, S. M.; D'Eugenio, F.; Davies, R. L.; Drinkwater, M. J.; Driver, S. P.; Goodwin, M.; Konstantopoulos, I. S.; Lawrence, J. S.; López-Sánchez, Á. R.; Lorente, N. P. F.; Medling, A. M.; Mould, J. R.; Owers, M. S.; Power, C.; Richards, S. N.; Tonini, C.

    2017-11-01

    We introduce a method for modeling disk galaxies designed to take full advantage of data from integral field spectroscopy (IFS). The method fits equilibrium models to simultaneously reproduce the surface brightness, rotation, and velocity dispersion profiles of a galaxy. The models are fully self-consistent 6D distribution functions for a galaxy with a Sérsic profile stellar bulge, exponential disk, and parametric dark-matter halo, generated by an updated version of GalactICS. By creating realistic flux-weighted maps of the kinematic moments (flux, mean velocity, and dispersion), we simultaneously fit photometric and spectroscopic data using both maximum-likelihood and Bayesian (MCMC) techniques. We apply the method to a GAMA spiral galaxy (G79635) with kinematics from the SAMI Galaxy Survey and deep g- and r-band photometry from the VST-KiDS survey, comparing parameter constraints with those from traditional 2D bulge-disk decomposition. Our method returns broadly consistent results for shared parameters while constraining the mass-to-light ratios of stellar components and reproducing the H I-inferred circular velocity well beyond the limits of the SAMI data. Although the method is tailored for fitting integral field kinematic data, it can use other dynamical constraints like central fiber dispersions and H I circular velocities, and is well-suited for modeling galaxies with a combination of deep imaging and H I and/or optical spectra (resolved or otherwise). Our implementation (MagRite) is computationally efficient and can generate well-resolved models and kinematic maps in under a minute on modern processors.

  17. Dust-enshrouded star near supermassive black hole: predictions for high-eccentricity passages near low-luminosity galactic nuclei

    Czech Academy of Sciences Publication Activity Database

    Zajaček, Michal; Karas, Vladimír; Eckart, A.

    2014-01-01

    Roč. 565, May (2014), A17/1-A17/15 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GC13-00070J Grant - others:UK(CZ) SVV-26089 Institutional support: RVO:67985815 Keywords : galactic centre * black holes * accretion disks Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  18. Chemical composition of stars in kinematical substructures of the galactic disk

    Directory of Open Access Journals (Sweden)

    Gorbaneva T.I.

    2012-02-01

    Full Text Available The Y, Zr, La, Ce, Nd , Sm and Eu abundances were found in LTE approach, and the abundance of Ba was computed in NLTE approximation for 280 FGK dwarfs in the region of metallicity of − 1<[Fe]< + 0.3. The selection of stars belonging to thin and thick disks and the stream Hercules was made on kinematic criteria. The analysis of enrichment of the different substructures of the Galaxy with α-element (Mg, Si, the iron peak (Ni and neutron-capture elements was carried out.

  19. DCOMP Award Lecture (Metropolis): A 3D Spectral Anelastic Hydrodynamic Code for Shearing, Stratified Flows

    Science.gov (United States)

    Barranco, Joseph

    2006-03-01

    We have developed a three-dimensional (3D) spectral hydrodynamic code to study vortex dynamics in rotating, shearing, stratified systems (eg, the atmosphere of gas giant planets, protoplanetary disks around newly forming protostars). The time-independent background state is stably stratified in the vertical direction and has a unidirectional linear shear flow aligned with one horizontal axis. Superposed on this background state is an unsteady, subsonic flow that is evolved with the Euler equations subject to the anelastic approximation to filter acoustic phenomena. A Fourier-Fourier basis in a set of quasi-Lagrangian coordinates that advect with the background shear is used for spectral expansions in the two horizontal directions. For the vertical direction, two different sets of basis functions have been implemented: (1) Chebyshev polynomials on a truncated, finite domain, and (2) rational Chebyshev functions on an infinite domain. Use of this latter set is equivalent to transforming the infinite domain to a finite one with a cotangent mapping, and using cosine and sine expansions in the mapped coordinate. The nonlinear advection terms are time integrated explicitly, whereas the Coriolis force, buoyancy terms, and pressure/enthalpy gradient are integrated semi- implicitly. We show that internal gravity waves can be damped by adding new terms to the Euler equations. The code exhibits excellent parallel performance with the Message Passing Interface (MPI). As a demonstration of the code, we simulate vortex dynamics in protoplanetary disks and the Kelvin-Helmholtz instability in the dusty midplanes of protoplanetary disks.

  20. Radiation magnetohydrodynamic simulations of the formation of hot accretion disk coronae

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Yan-Fei [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Stone, James M. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Davis, Shane W. [Canadian Institute for Theoretical Astrophysics. Toronto, ON M5S3H4 (Canada)

    2014-04-01

    A new mechanism to form a magnetic pressure supported, high temperature corona above the photosphere of an accretion disk is explored using three dimensional radiation magnetohydrodynamic (MHD) simulations. The thermal properties of the disk are calculated self-consistently by balancing radiative cooling through the surfaces of the disk with heating due to dissipation of turbulence driven by magneto-rotational instability (MRI). As has been noted in previous work, we find the dissipation rate per unit mass increases dramatically with height above the mid-plane, in stark contrast to the α-disk model which assumes this quantity is a constant. Thus, we find that in simulations with a low surface density (and therefore a shallow photosphere), the fraction of energy dissipated above the photosphere is significant (about 3.4% in our lowest surface density model), and this fraction increases as surface density decreases. When a significant fraction of the accretion energy is dissipated in the optically thin photosphere, the gas temperature increases substantially and a high temperature, magnetic pressure supported corona is formed. The volume-averaged temperature in the disk corona is more than 10 times larger than at the disk mid-plane. Moreover, gas temperature in the corona is strongly anti-correlated with gas density, which implies the corona formed by MRI turbulence is patchy. This mechanism to form an accretion disk corona may help explain the observed relation between the spectral index and luminosity from active galactic nucleus (AGNs), and the soft X-ray excess from some AGNs. It may also be relevant to spectral state changes in X-ray binaries.

  1. General relativistic razor-thin disks with magnetically polarized matter

    Science.gov (United States)

    Navarro-Noguera, Anamaría; Lora-Clavijo, F. D.; González, Guillermo A.

    2018-06-01

    The origin of magnetic fields in the universe still remains unknown and constitutes one of the most intriguing questions in astronomy and astrophysics. Their significance is enormous since they have a strong influence on many astrophysical phenomena. In regards of this motivation, theoretical models of galactic disks with sources of magnetic field may contribute to understand the physics behind them. Inspired by this, we present a new family of analytical models for thin disks composed by magnetized material. The solutions are axially symmetric, conformastatic and are obtained by solving the Einstein-Maxwell Field Equations for continuum media without the test field approximation, and assuming that the sources are razor-thin disk of magnetically polarized matter. We find analytical expressions for the surface energy density, the pressure, the polarization vector, the electromagnetic fields, the mass and the rotational velocity for circular orbits, for two particular solutions. In each case, the energy-momentum tensor agrees with the energy conditions and also the convergence of the mass for all the solutions is proved. Since the solutions are well-behaved, they may be used to model astrophysical thin disks, and also may contribute as initial data in numerical simulations. In addition, the process to obtain the solutions is described in detail, which may be used as a guide to find solutions with magnetized material in General Relativity.

  2. Diffuse γ-ray emission from galactic pulsars

    International Nuclear Information System (INIS)

    Calore, F.; Di Mauro, M.; Donato, F.

    2014-01-01

    galactic center, we expect them to contribute significantly to the γ-ray diffuse emission at low latitudes. Because, along the galactic disk, the population of young pulsars overcomes in number that of MSPs, we compute the γ-ray emission from the whole population of unresolved pulsars, both young and millisecond, in two low-latitude regions: the inner Galaxy and the galactic center.

  3. Galactic Angular Momentum in Cosmological Zoom-in Simulations. I. Disk and Bulge Components and the Galaxy-Halo Connection

    Science.gov (United States)

    Sokołowska, Aleksandra; Capelo, Pedro R.; Fall, S. Michael; Mayer, Lucio; Shen, Sijing; Bonoli, Silvia

    2017-02-01

    We investigate the angular momentum evolution of four disk galaxies residing in Milky-Way-sized halos formed in cosmological zoom-in simulations with various sub-grid physics and merging histories. We decompose these galaxies, kinematically and photometrically, into their disk and bulge components. The simulated galaxies and their components lie on the observed sequences in the j *-M * diagram, relating the specific angular momentum and mass of the stellar component. We find that galaxies in low-density environments follow the relation {j}* \\propto {M}* α past major mergers, with α ˜ 0.6 in the case of strong feedback, when bulge-to-disk ratios are relatively constant, and α ˜ 1.4 in the other cases, when secular processes operate on shorter timescales. We compute the retention factors (I.e., the ratio of the specific angular momenta of stars and dark matter) for both disks and bulges and show that they vary relatively slowly after averaging over numerous but brief fluctuations. For disks, the retention factors are usually close to unity, while for bulges, they are a few times smaller. Our simulations therefore indicate that galaxies and their halos grow in a quasi-homologous way.

  4. Chemo-orbital evidence from SDSS/SEGUE G dwarf stars for a mixed origin of the Galactic thick disk

    Directory of Open Access Journals (Sweden)

    van de Ven G.

    2012-02-01

    Full Text Available About 13,000 G dwarf within 7disk. Combining [α/Fe] and [Fe/H] measurements with six-dimensional position-velocity parameters, we find that the sample is composed of two distinct stellar populations. The metal-rich population encompasses the thin disk with α-deficient stars and smoothly extends into a thick disk with α-enhanced stars, consistent with an in-situ formation through radial migration. On the other hand, the metal-poor population with enhanced α-abundance, higher scale height, and disperse kinematical properties, is difficult to explain with radial migration but might have originated from gas-rich mergers. The thick disk of the Milky Way seems to have a mixed origin.

  5. THE BOLOCAM GALACTIC PLANE SURVEY. VIII. A MID-INFRARED KINEMATIC DISTANCE DISCRIMINATION METHOD

    Energy Technology Data Exchange (ETDEWEB)

    Ellsworth-Bowers, Timothy P.; Glenn, Jason; Battersby, Cara; Ginsburg, Adam; Bally, John [CASA, University of Colorado, UCB 389, University of Colorado, Boulder, CO 80309 (United States); Rosolowsky, Erik [Department of Physics and Astronomy, University of British Columbia Okanagan, 3333 University Way, Kelowna, BC V1V 1V7 (Canada); Mairs, Steven [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC V8P 1A1 (Canada); Evans, Neal J. II [Department of Astronomy, University of Texas, 1 University Station C1400, Austin, TX 78712 (United States); Shirley, Yancy L., E-mail: timothy.ellsworthbowers@colorado.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2013-06-10

    We present a new distance estimation method for dust-continuum-identified molecular cloud clumps. Recent (sub-)millimeter Galactic plane surveys have cataloged tens of thousands of these objects, plausible precursors to stellar clusters, but detailed study of their physical properties requires robust distance determinations. We derive Bayesian distance probability density functions (DPDFs) for 770 objects from the Bolocam Galactic Plane Survey in the Galactic longitude range 7. Degree-Sign 5 {<=} l {<=} 65 Degree-Sign . The DPDF formalism is based on kinematic distances, and uses any number of external data sets to place prior distance probabilities to resolve the kinematic distance ambiguity (KDA) for objects in the inner Galaxy. We present here priors related to the mid-infrared absorption of dust in dense molecular regions and the distribution of molecular gas in the Galactic disk. By assuming a numerical model of Galactic mid-infrared emission and simple radiative transfer, we match the morphology of (sub-)millimeter thermal dust emission with mid-infrared absorption to compute a prior DPDF for distance discrimination. Selecting objects first from (sub-)millimeter source catalogs avoids a bias towards the darkest infrared dark clouds (IRDCs) and extends the range of heliocentric distance probed by mid-infrared extinction and includes lower-contrast sources. We derive well-constrained KDA resolutions for 618 molecular cloud clumps, with approximately 15% placed at or beyond the tangent distance. Objects with mid-infrared contrast sufficient to be cataloged as IRDCs are generally placed at the near kinematic distance. Distance comparisons with Galactic Ring Survey KDA resolutions yield a 92% agreement. A face-on view of the Milky Way using resolved distances reveals sections of the Sagittarius and Scutum-Centaurus Arms. This KDA-resolution method for large catalogs of sources through the combination of (sub-)millimeter and mid-infrared observations of molecular

  6. Unusual Metals in Galactic Center Stars

    Science.gov (United States)

    Hensley, Kerry

    2018-03-01

    while one star is only slightly above solar metallicity, the other is likely more than four times as metal-rich as the Sun.The features in the observed and synthetic spectra generally matched well, but the absorption lines of scandium, vanadium, and yttrium were consistently stronger in the observed spectra than in the synthetic spectra. This led the authors to conclude that these galactic center stars are unusually rich in these metals trace elements that could reveal the formation history of the galactic nucleus.Old Stars, New Trends?Scandium to iron ratio versusiron abundance for stars in the disk of the Milky Way (blue) and the stars in this sample (orange). The value reported for this sample is a 95% lower limit. [Do et al. 2018]For stars in the disk of the Milky Way, the abundance of scandium relative to iron tends to decrease as the overall metallicity increases, but the stars investigated in this study are both iron-rich and anomalously high in scandium. This hints that the nuclear star cluster might represent a distinct stellar population with different metallicity trends.However, its not yet clear what could cause the elevated abundances of scandium, vanadium, and yttrium relative to other metals. Each of these elements is linked to a different source; scandium and vanadium are mainly produced in Type II and Type Ia supernovae, respectively, while yttrium is likely synthesized in asymptotic giant branch stars. Future observations of stars near the center of the Milky Way may help answer this question and further constrain the origin of our galaxys nuclear star cluster.CitationTuan Do et al 2018 ApJL 855 L5. doi:10.3847/2041-8213/aaaec3

  7. Sagittarius A* as an origin of the Galactic PeV cosmic rays?

    Energy Technology Data Exchange (ETDEWEB)

    Fujita, Yutaka [Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Murase, Kohta; Kimura, Shigeo S., E-mail: fujita@vega.ess.sci.osaka-u.ac.jp, E-mail: murase@psu.edu, E-mail: szk323@psu.edu [Center for Particle and Gravitational Astrophysics, Department of Physics, Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States)

    2017-04-01

    Supernova remnants (SNRs) have commonly been considered as a source of the observed PeV cosmic rays (CRs) or a Galactic PeV particle accelerator ('Pevatron'). In this work, we study Sagittarius A* (Sgr A*), which is the low-luminosity active galactic nucleus of the Milky Way Galaxy, as another possible canditate of the Pevatron, because it sometimes became very active in the past. We assume that a large number of PeV CRs were injected by Sgr A* at the outburst about 10{sup 7} yr ago when the Fermi bubbles were created. We constrain the diffusion coefficient for the CRs in the Galactic halo on the condition that the CRs have arrived on the Earth by now, while a fairly large fraction of them have escaped from the halo. Based on a diffusion-halo model, we solve a diffusion equation for the CRs and compare the results with the CR spectrum on the Earth. The observed small anisotropy of the arrival directions of CRs may be explained if the diffusion coefficient in the Galactic disk is smaller than that in the halo. Our model predicts that a boron-to-carbon ratio should be energy-independent around the knee, where the CRs from Sgr A* become dominant. It is unlikely that the spectrum of the CRs accelerated at the outburst is represented by a power-law similar to the one for those responsible for the gamma-ray emission from the central molecular zone (CMZ) around the Galactic center.

  8. Thick Disks in the Hubble Space Telescope Frontier Fields

    Energy Technology Data Exchange (ETDEWEB)

    Elmegreen, Bruce G. [IBM Research Division, T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, NY 10598 (United States); Elmegreen, Debra Meloy; Tompkins, Brittany; Jenks, Leah G., E-mail: bge@us.ibm.com, E-mail: elmegreen@vassar.edu [Department of Physics and Astronomy, Vassar College, Poughkeepsie, NY 12604 (United States)

    2017-09-20

    Thick disk evolution is studied using edge-on galaxies in two Hubble Space Telescope Frontier Field Parallels. The galaxies were separated into 72 clumpy types and 35 spiral types with bulges. Perpendicular light profiles in F435W, F606W, and F814W ( B , V , and I ) passbands were measured at 1 pixel intervals along the major axes and fitted to sech{sup 2} functions convolved with the instrument line spread function (LSF). The LSF was determined from the average point spread function of ∼20 stars in each passband and field, convolved with a line of uniform brightness to simulate disk blurring. A spread function for a clumpy disk was also used for comparison. The resulting scale heights were found to be proportional to galactic mass, with the average height for a 10{sup 10±0.5} M {sub ⊙} galaxy at z = 2 ± 0.5 equal to 0.63 ± 0.24 kpc. This value is probably the result of a blend between thin and thick disk components that cannot be resolved. Evidence for such two-component structure is present in an inverse correlation between height and midplane surface brightness. Models suggest that the thick disk is observed best between the clumps, and there the average scale height is 1.06 ± 0.43 kpc for the same mass and redshift. A 0.63 ± 0.68 mag V − I color differential with height is also evidence for a mixture of thin and thick components.

  9. Confirmation of the Galactic Thick Disk Component by the Basle RGU-and UBV-photometric space densities. II. (Synopsis of 25 years Basle Halo Program; II: Plaut I, NGC 6171, SA 158, M 13)

    International Nuclear Information System (INIS)

    Fenkart, R.

    1989-01-01

    This contribution treats four fields, all with directions pointing into the galactic centre hemisphere (270 0 0 ). The purpose of the comparison-phase of the BHP is to homogeneously compare the three-colour photometrically determined space densities for different luminosity groups of the combined (photometric) populations I and II with the gradients predicted for the involved direction by a representative set of current standard multi-component models for the stellar space distribution in the Galaxy and to evaluate a best-fitting model by a simple quantitative procedure. In no case the existence of a Thick Disk component is ruled out by the findings; in the safer directions it is even slightly indicated, though much less compellingly than in all previous investigations of the model-comparison phase

  10. SIMULATING THE TIMESCALE-DEPENDENT COLOR VARIATION IN QUASARS WITH A REVISED INHOMOGENEOUS DISK MODEL

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Zhen-Yi; Wang, Jun-Xian; Sun, Yu-Han; Wu, Mao-Chun; Huang, Xing-Xing; Chen, Xiao-Yang [CAS Key Laboratory for Researches in Galaxies and Cosmology, University of Science and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China); Gu, Wei-Min, E-mail: zcai@ustc.edu.cn, E-mail: jxw@ustc.edu.cn [Department of Astronomy and Institute of Theoretical Physics and Astrophysics, Xiamen University, Xiamen, Fujian 361005 (China)

    2016-07-20

    The UV–optical variability of active galactic nuclei and quasars is useful for understanding the physics of the accretion disk and is gradually being attributed to stochastic fluctuations over the accretion disk. Quasars generally appear bluer when they brighten in the UV–optical bands; the nature of this phenomenon remains controversial. Recently, Sun et al. discovered that the color variation of quasars is timescale-dependent, in the way that faster variations are even bluer than longer term ones. While this discovery can directly rule out models that simply attribute the color variation to contamination from the host galaxies, or to changes in the global accretion rates, it favors the stochastic disk fluctuation model as fluctuations in the inner-most hotter disk could dominate the short-term variations. In this work, we show that a revised inhomogeneous disk model, where the characteristic timescales of thermal fluctuations in the disk are radius-dependent (i.e., τ ∼ r ; based on that originally proposed by Dexter and Agol), can reproduce well a timescale-dependent color variation pattern, similar to the observed one and unaffected by the uneven sampling and photometric error. This demonstrates that one may statistically use variation emission at different timescales to spatially resolve the accretion disk in quasars, thus opening a new window with which to probe and test the accretion disk physics in the era of time domain astronomy. Caveats of the current model, which ought to be addressed in future simulations, are discussed.

  11. Galactic structure

    International Nuclear Information System (INIS)

    1989-01-01

    The occurrence of hot, apparently normal, massive stars far from the galactic plane has been a major puzzle in an understanding of galactic structure and evolution. Such stars have been discovered and studied at the South African Astronomical Observatory (SAAO) over a number of years. During 1989 further evidence has been obtained indicating that these stars are normal, massive objects. Other studies of galactic structure conducted by the SAAO have included research on: the central bulge region of our galaxy; populations of M giants in the galaxy; a faint blue object survey; a survey of the galactic plane for distant Cepheid variables; interstellar reddening, and K-type dwarfs as tracers for the gravitational force perpendicular to the galactic plane. 1 fig

  12. Globular Clusters: Absolute Proper Motions and Galactic Orbits

    Science.gov (United States)

    Chemel, A. A.; Glushkova, E. V.; Dambis, A. K.; Rastorguev, A. S.; Yalyalieva, L. N.; Klinichev, A. D.

    2018-04-01

    We cross-match objects from several different astronomical catalogs to determine the absolute proper motions of stars within the 30-arcmin radius fields of 115 Milky-Way globular clusters with the accuracy of 1-2 mas yr-1. The proper motions are based on positional data recovered from the USNO-B1, 2MASS, URAT1, ALLWISE, UCAC5, and Gaia DR1 surveys with up to ten positions spanning an epoch difference of up to about 65 years, and reduced to Gaia DR1 TGAS frame using UCAC5 as the reference catalog. Cluster members are photometrically identified by selecting horizontal- and red-giant branch stars on color-magnitude diagrams, and the mean absolute proper motions of the clusters with a typical formal error of about 0.4 mas yr-1 are computed by averaging the proper motions of selected members. The inferred absolute proper motions of clusters are combined with available radial-velocity data and heliocentric distance estimates to compute the cluster orbits in terms of the Galactic potential models based on Miyamoto and Nagai disk, Hernquist spheroid, and modified isothermal dark-matter halo (axisymmetric model without a bar) and the same model + rotating Ferre's bar (non-axisymmetric). Five distant clusters have higher-than-escape velocities, most likely due to large errors of computed transversal velocities, whereas the computed orbits of all other clusters remain bound to the Galaxy. Unlike previously published results, we find the bar to affect substantially the orbits of most of the clusters, even those at large Galactocentric distances, bringing appreciable chaotization, especially in the portions of the orbits close to the Galactic center, and stretching out the orbits of some of the thick-disk clusters.

  13. Galactoseismology: From The Milky Way To XUV Disks

    Science.gov (United States)

    Chakrabarti, Sukanya

    The variety of discrepancies between observations and simulations on galactic scales, from the anisotropic distribution of dwarf galaxies to the "too big to fail" problem (where massive satellites in simulations are too dense relative to observations), suggests that we may not yet fully understand galaxy formation. If these satellites exist, they would leave traces of their passage in extended HI disks. Extended HI disks of galaxies reach to several times the optical radius, presenting the largest possible cross-section for interaction with sub-halos at large distances (where theoretical models expect them to be). We will provide definitive constraints on the distribution of dark matter in spiral galaxies by building on our ongoing work in characterizing galactic satellites from analysis of disturbances in extended HI disks with respect to hydrodynamical simulations. Spiral galaxies in the Local Volume (from the Milky Way to the XUV disks discovered by GALEX) exhibit a wealth of unexplained morphology, but these morphological signatures have not yet been used to place constraints on the evolution of HI disks and the dark matter distribution. We are now poised to make significant progress in Galactoseismology, i.e. connect morphological disturbances with the mass distribution. By using the FIRE model for explicit star formation and feedback, we will also develop a better understanding for the star formation history of our Galaxy and XUV Disks. Our Milky Way models will be informed by the HST proper motions, and will match the observed planar disturbances, the warp, and vertical waves recently discovered by the RAVE and LAMOST surveys. We are also carrying high resolution simulations with the Gizmo code that incorporates the FIRE model to develop a comprehensive understanding of the star formation history and star formation rate (that matches Spitzer observations) of the Milky Way. These models will provide a much needed interpretative framework for JWST and WFIRST

  14. Disk-Wind Connection During the Heartbeats of GRS 1915+105

    Science.gov (United States)

    Zoghbi, Abderahmen; Miller, J. M.; King, A. L.; Miller, M. C.; Proga, D.; Kallman, T.; Fabian, A. C.; Harrison, F. A.; Kaastra, J.; Raymond, J.; hide

    2016-01-01

    Disk and wind signatures are seen in the soft state of Galactic black holes, while the jet is seen in the hard state. Here we study the disk-wind connection in the Rho class of variability in GRS 1915+105 using a joint NuSTAR-Chandra observation. The source shows 50 s limit cycle oscillations. By including new information provided by the reflection spectrum and using phase-resolved spectroscopy, we find that the change in the inner disk inferred from the blackbody emission is not matched by reflection measurements. The latter is almost constant, independent of the continuum model. The two radii are comparable only if the disk temperature color correction factor changes, an effect that could be due to the changing opacity of the disk caused by changes in metal abundances. The disk inclination is similar to that inferred from the jet axis, and oscillates by approx.10 deg. The simultaneous Chandra data show the presence of two wind components with velocities between 500 and 5000 km s(exp. -1), and possibly two more with velocities reaching 20,000 km s(exp. -1) (approx. 0.06 c). The column densities are approx. 5 × 10(exp. 22) cm(exp. -2). An upper limit to the wind response time of 2 s is measured, implying a launch radius of less than 6 × 10(exp. 10) cm. The changes in wind velocity and absorbed flux require the geometry of the wind to change during the oscillations, constraining the wind to be launched from a distance of 290-1300 r (sub g) from the black hole. Both data sets support fundamental model predictions in which a bulge originates in the inner disk and moves outward as the instability progresses.

  15. The Gaia-ESO Survey: Exploring the complex nature and origins of the Galactic bulge populations

    Science.gov (United States)

    Rojas-Arriagada, A.; Recio-Blanco, A.; de Laverny, P.; Mikolaitis, Š.; Matteucci, F.; Spitoni, E.; Schultheis, M.; Hayden, M.; Hill, V.; Zoccali, M.; Minniti, D.; Gonzalez, O. A.; Gilmore, G.; Randich, S.; Feltzing, S.; Alfaro, E. J.; Babusiaux, C.; Bensby, T.; Bragaglia, A.; Flaccomio, E.; Koposov, S. E.; Pancino, E.; Bayo, A.; Carraro, G.; Casey, A. R.; Costado, M. T.; Damiani, F.; Donati, P.; Franciosini, E.; Hourihane, A.; Jofré, P.; Lardo, C.; Lewis, J.; Lind, K.; Magrini, L.; Morbidelli, L.; Sacco, G. G.; Worley, C. C.; Zaggia, S.

    2017-05-01

    Context. As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge - and especially of the metal-poor bulge - and their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data samples. Aims: We used the fourth internal data release of the Gaia-ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous sampling of the different Galactic populations provided by the Gaia-ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg/Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities. Methods: We obtained spectroscopic data for 2500 red clump stars in 11 bulge fields, sampling the area -10° ≤ l ≤ + 8° and -10° ≤ b ≤ -4° from the fourth internal data release of the Gaia-ESO survey. A sample of 6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a sample of stars likely located in the bulge region. Results: From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole sampled area. The relative ratio between the two modes of the MDF changes as a function of b, with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe] vs. [Fe/H] plane. On the other hand, metal-poor bulge stars have a more isotropic hot kinematics and do

  16. LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) — The survey's science plan

    International Nuclear Information System (INIS)

    Deng Licai; Liu Chao; Chen Yuqin; Li Jing; Newberg Heidi Jo; Carlin, Jeffrey L.; Beers, Timothy C.; Chen Li; Hou Jinliang; Christlieb, Norbert; Grillmair, Carl J.; Guhathakurta, Puragra; Han Zhanwen; Wang Bo; Lee, Hsu-Tai; Lépine, Sébastien; Liu Xiaowei; Pan Kaike; Sellwood, J. A.; Wang Hongchi

    2012-01-01

    We describe the current plans for a spectroscopic survey of millions of stars in the Milky Way galaxy using the Guo Shou Jing Telescope (GSJT, formerly called the Large sky Area Multi-Object fiber Spectroscopic Telescope — LAMOST). The survey will obtain spectra for 2.5 million stars brighter than r < 19 during dark/grey time, and 5 million stars brighter than r < 17 or J < 16 on nights that are moonlit or have low transparency. The survey will begin in the fall of 2012, and will run for at least four years. The telescope's design constrains the optimal declination range for observations to 10° < δ < 50°, and site conditions lead to an emphasis on stars in the direction of the Galactic anticenter. The survey is divided into three parts with different target selection strategies: disk, anticenter, and spheroid. The resulting dataset will be used to study the merger history of the Milky Way, the substructure and evolution of the disks, the nature of the first generation of stars through identification of the lowest metallicity stars, and star formation through study of open clusters and OB associations. Detailed design of the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey will be completed in summer 2012, after a review of the results of the pilot survey.

  17. DYNAMICS OF TIDALLY CAPTURED PLANETS IN THE GALACTIC CENTER

    International Nuclear Information System (INIS)

    Trani, Alessandro A.; Bressan, Alessandro; Mapelli, Michela; Spera, Mario

    2016-01-01

    Recent observations suggest ongoing planet formation in the innermost parsec of the Galactic center. The supermassive black hole (SMBH) might strip planets or planetary embryos from their parent star, bringing them close enough to be tidally disrupted. Photoevaporation by the ultraviolet field of young stars, combined with ongoing tidal disruption, could enhance the near-infrared luminosity of such starless planets, making their detection possible even with current facilities. In this paper, we investigate the chance of planet tidal captures by means of high-accuracy N -body simulations exploiting Mikkola's algorithmic regularization. We consider both planets lying in the clockwise (CW) disk and planets initially bound to the S-stars. We show that tidally captured planets remain on orbits close to those of their parent star. Moreover, the semimajor axis of the planetary orbit can be predicted by simple analytic assumptions in the case of prograde orbits. We find that starless planets that were initially bound to CW disk stars have mild eccentricities and tend to remain in the CW disk. However, we speculate that angular momentum diffusion and scattering by other young stars in the CW disk might bring starless planets into orbits with low angular momentum. In contrast, planets initially bound to S-stars are captured by the SMBH on highly eccentric orbits, matching the orbital properties of the clouds G1 and G2. Our predictions apply not only to planets but also to low-mass stars initially bound to the S-stars and tidally captured by the SMBH.

  18. Strong magnetic fields, galaxy formation, and the Galactic engine

    International Nuclear Information System (INIS)

    Greyber, H.D.

    1989-01-01

    The strong-magnetic-field model proposed as an energy source for AGN and quasars by Greyber (1961, 1962, 1964, 1967, 1984, 1988, and 1989) is discussed. The basic principles of the model are reviewed; its advantages (in explaining the observed features of AGN and quasars) over models based on a rotating accretion disk are indicated in a table; and its implications for galaxy and quasar formation are explored. The gravitationally bound current loops detected in nearby spiral galaxies are interpreted as weak remnants of the current loops present during their formation. An observational search for a similar loop near the Galactic center is proposed. 27 refs

  19. GIANT MOLECULAR CLOUD FORMATION IN DISK GALAXIES: CHARACTERIZING SIMULATED VERSUS OBSERVED CLOUD CATALOGS

    Energy Technology Data Exchange (ETDEWEB)

    Benincasa, Samantha M.; Pudritz, Ralph E.; Wadsley, James [Department of Physics and Astronomy, McMaster University, Hamilton, ON L8S 4M1 (Canada); Tasker, Elizabeth J. [Department of Physics, Faculty of Science, Hokkaido University, Kita-ku, Sapporo 060-0810 (Japan)

    2013-10-10

    We present the results of a study of simulated giant molecular clouds (GMCs) formed in a Milky Way-type galactic disk with a flat rotation curve. This simulation, which does not include star formation or feedback, produces clouds with masses ranging between 10{sup 4} M{sub ☉} and 10{sup 7} M{sub ☉}. We compare our simulated cloud population to two observational surveys: the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey and the BIMA All-Disk Survey of M33. An analysis of the global cloud properties as well as a comparison of Larson's scaling relations is carried out. We find that simulated cloud properties agree well with the observed cloud properties, with the closest agreement occurring between the clouds at comparable resolution in M33. Our clouds are highly filamentary—a property that derives both from their formation due to gravitational instability in the sheared galactic environment, as well as to cloud-cloud gravitational encounters. We also find that the rate at which potentially star-forming gas accumulates within dense regions—wherein n{sub thresh} ≥ 10{sup 4} cm{sup –3}—is 3% per 10 Myr, in clouds of roughly 10{sup 6} M{sub ☉}. This suggests that star formation rates in observed clouds are related to the rates at which gas can be accumulated into dense subregions within GMCs via filamentary flows. The most internally well-resolved clouds are chosen for listing in a catalog of simulated GMCs—the first of its kind. The cataloged clouds are available as an extracted data set from the global simulation.

  20. Planetesimal Formation by the Streaming Instability in a Photoevaporating Disk

    Energy Technology Data Exchange (ETDEWEB)

    Carrera, Daniel; Johansen, Anders; Davies, Melvyn B. [Lund Observatory, Dept. of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund (Sweden); Gorti, Uma [NASA Ames Research Center, Moffett Field, CA (United States)

    2017-04-10

    Recent years have seen growing interest in the streaming instability as a candidate mechanism to produce planetesimals. However, these investigations have been limited to small-scale simulations. We now present the results of a global protoplanetary disk evolution model that incorporates planetesimal formation by the streaming instability, along with viscous accretion, photoevaporation by EUV, FUV, and X-ray photons, dust evolution, the water ice line, and stratified turbulence. Our simulations produce massive (60–130 M {sub ⊕}) planetesimal belts beyond 100 au and up to ∼20 M {sub ⊕} of planetesimals in the middle regions (3–100 au). Our most comprehensive model forms 8 M {sub ⊕} of planetesimals inside 3 au, where they can give rise to terrestrial planets. The planetesimal mass formed in the inner disk depends critically on the timing of the formation of an inner cavity in the disk by high-energy photons. Our results show that the combination of photoevaporation and the streaming instability are efficient at converting the solid component of protoplanetary disks into planetesimals. Our model, however, does not form enough early planetesimals in the inner and middle regions of the disk to give rise to giant planets and super-Earths with gaseous envelopes. Additional processes such as particle pileups and mass loss driven by MHD winds may be needed to drive the formation of early planetesimal generations in the planet-forming regions of protoplanetary disks.

  1. HIGH ENERGY NEUTRINOS PRODUCED IN THE ACCRETION DISKS BY NEUTRONS FROM NUCLEI DISINTEGRATED IN THE AGN JETS

    Energy Technology Data Exchange (ETDEWEB)

    Bednarek, W., E-mail: bednar@uni.lodz.pl [Department of Astrophysics, The University of Lodz, 90-236 Lodz, ul. Pomorska 149/153 (Poland)

    2016-12-20

    We investigate the consequences of acceleration of nuclei in jets of active galaxies not far from the surface of an accretion disk. The nuclei can be accelerated in the re-connection regions in the jet and/or at the jet boundary, between the relativistic jet and its cocoon. It is shown that the relativistic nuclei can efficiently fragment onto specific nucleons in collisions with the disk radiation. Neutrons, directed toward the accretion disk, take a significant part of energy from the relativistic nuclei. These neutrons develop a cascade in the dense accretion disk. We calculate the neutrino spectra produced in such a hadronic cascade within the accretion disk. We propose that the neutrinos produced in such a scenario, from the whole population of super-massive black holes in active galaxies, can explain the extragalactic neutrino background recently measured by the IceCube neutrino detector, provided that a 5% fraction of galaxies have an active galactic nucleus and a few percent of neutrons reach the accretion disk. We predict that the neutrino signals in the present neutrino detectors, produced in terms of such a model, will not be detectable even from the nearby radio galaxies similar to M87.

  2. Galactic radio astronomy

    CERN Document Server

    Sofue, Yoshiaki

    2017-01-01

    This book is a concise primer on galactic radio astronomy for undergraduate and graduate students, and provides wide coverage of galactic astronomy and astrophysics such as the physics of interstellar matter and the dynamics and structure of the Milky Way Galaxy and galaxies. Radio astronomy and its technological development have led to significant progress in galactic astronomy and contributed to understanding interstellar matter and galactic structures. The book begins with the fundamental physics of radio-wave radiation, i.e., black body radiation, thermal emission, synchrotron radiation, and HI and molecular line emissions. The author then gives overviews of ingredients of galactic physics, including interstellar matter such as the neutral (HI), molecular hydrogen, and ionized gases, as well as magnetic fields in galaxies. In addition, more advanced topics relevant to the Galaxy and galaxies are also contained here: star formation, supernova remnants, the Galactic Center and black holes, galactic dynamics...

  3. Millisecond Pulsars and the Galactic Center Excess

    Science.gov (United States)

    Gonthier, Peter L.; Koh, Yew-Meng; Kust Harding, Alice; Ferrara, Elizabeth C.

    2017-08-01

    Various groups including the Fermi team have confirmed the spectrum of the gamma- ray excess in the Galactic Center (GCE). While some authors interpret the GCE as evidence for the annihilation of dark matter (DM), others have pointed out that the GCE spectrum is nearly identical to the average spectrum of Fermi millisecond pul- sars (MSP). Assuming the Galactic Center (GC) is populated by a yet unobserved source of MSPs that has similar properties to that of MSPs in the Galactic Disk (GD), we present results of a population synthesis of MSPs from the GC. We establish parameters of various models implemented in the simulation code by matching characteristics of 54 detected Fermi MSPs in the first point source catalog and 92 detected radio MSPs in a select group of thirteen radio surveys and targeting a birth rate of 45 MSPs per mega-year. As a check of our simulation, we find excellent agreement with the estimated numbers of MSPs in eight globular clusters. In order to reproduce the gamma-ray spectrum of the GCE, we need to populate the GC with 10,000 MSPs having a Navarro-Frenk-White distribution suggested by the halo density of DM. It may be possible for Fermi to detect some of these MSPs in the near future; the simulation also predicts that many GC MSPs have radio fluxes S1400above 10 �μJy observable by future pointed radio observations. We express our gratitude for the generous support of the National Science Foundation (RUI: AST-1009731), Fermi Guest Investigator Program and the NASA Astrophysics Theory and Fundamental Program (NNX09AQ71G).

  4. A ∼ 3.8 hr PERIODICITY FROM AN ULTRASOFT ACTIVE GALACTIC NUCLEUS CANDIDATE

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Dacheng; Irwin, Jimmy A. [Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, AL 35487 (United States); Godet, Olivier; Webb, Natalie A.; Barret, Didier, E-mail: dlin@ua.edu [CNRS, IRAP, 9 avenue du Colonel Roche, BP 44346, F-31028 Toulouse Cedex 4 (France)

    2013-10-10

    Very few galactic nuclei are found to show significant X-ray quasi-periodic oscillations (QPOs). After carefully modeling the noise continuum, we find that the ∼3.8 hr QPO in the ultrasoft active galactic nucleus candidate 2XMM J123103.2+110648 was significantly detected (∼5σ) in two XMM-Newton observations in 2005, but not in the one in 2003. The QPO root mean square (rms) is very high and increases from ∼25% in 0.2-0.5 keV to ∼50% in 1-2 keV. The QPO probably corresponds to the low-frequency type in Galactic black hole X-ray binaries, considering its large rms and the probably low mass (∼10{sup 5} M {sub ☉}) of the black hole in the nucleus. We also fit the soft X-ray spectra from the three XMM-Newton observations and find that they can be described with either pure thermal disk emission or optically thick low-temperature Comptonization. We see no clear X-ray emission from the two Swift observations in 2013, indicating lower source fluxes than those in XMM-Newton observations.

  5. Transition from galactic to extra-galactic cosmic rays

    International Nuclear Information System (INIS)

    Aloisio, Roberto

    2006-01-01

    In this paper we review the main features of the observed Cosmic Rays spectrum in the energy range 10 17 eV to 10 20 eV. We present a theoretical model that explains the main observed features of the spectrum, namely the second Knee and Dip, and implies a transition from Galactic to Extra-Galactic cosmic rays at energy E ≅ 10 18 eV, with a proton dominated Extra-Galactic spectrum

  6. Disk Heating, Galactoseismology, and the Formation of Stellar Halos

    Directory of Open Access Journals (Sweden)

    Kathryn V. Johnston

    2017-08-01

    Full Text Available Deep photometric surveys of the Milky Way have revealed diffuse structures encircling our Galaxy far beyond the “classical” limits of the stellar disk. This paper reviews results from our own and other observational programs, which together suggest that, despite their extreme positions, the stars in these structures were formed in our Galactic disk. Mounting evidence from recent observations and simulations implies kinematic connections between several of these distinct structures. This suggests the existence of collective disk oscillations that can plausibly be traced all the way to asymmetries seen in the stellar velocity distribution around the Sun. There are multiple interesting implications of these findings: they promise new perspectives on the process of disk heating; they provide direct evidence for a stellar halo formation mechanism in addition to the accretion and disruption of satellite galaxies; and, they motivate searches of current and near-future surveys to trace these oscillations across the Galaxy. Such maps could be used as dynamical diagnostics in the emerging field of “Galactoseismology”, which promises to model the history of interactions between the Milky Way and its entourage of satellites, as well examine the density of our dark matter halo. As sensitivity to very low surface brightness features around external galaxies increases, many more examples of such disk oscillations will likely be identified. Statistical samples of such features not only encode detailed information about interaction rates and mergers, but also about long sought-after dark matter halo densities and shapes. Models for the Milky Way’s own Galactoseismic history will therefore serve as a critical foundation for studying the weak dynamical interactions of galaxies across the universe.

  7. Consequences of Relativistic Neutron Outflow beyond the Accretion Disks of Active Galaxies

    Science.gov (United States)

    Ekejiuba, I. E.; Okeke, P. N.

    1993-05-01

    Three channels of relativistic electron injection in the jets of extragalactic radio sources (EGRSs) are discussed. With the assumption that an active galactic nucleus (AGN) is powered by a spinning supermassive black hole of mass ~ 10(8) M_⊙ which sits at the center of the nucleus and ingests matter and energy through an accretion disk, a model for extracting relativistic neutrons from the AGN is forged. In this model, the inelastic proton--proton and proton--photon interactions within the accretion disk, of relativistic protons with background thermal protons and photons, respectively, produce copious amounts of relativistic neutrons. These neutrons travel ballistically for ~ 10(3gamma_n ) seconds and escape from the disk before they decay. The secondary particles produced from the neutron decays then interact with the ambient magnetic field and/or other particles to produce the radio emissions observed in the jets of EGRSs. IEE acknowledges the support of the World Bank and the Federal University of Technology, Yola, Nigeria as well as the hospitality of Georgia State University.

  8. A 3D spectral anelastic hydrodynamic code for shearing, stratified flows

    Science.gov (United States)

    Barranco, Joseph A.; Marcus, Philip S.

    2006-11-01

    We have developed a three-dimensional (3D) spectral hydrodynamic code to study vortex dynamics in rotating, shearing, stratified systems (e.g., the atmosphere of gas giant planets, protoplanetary disks around newly forming protostars). The time-independent background state is stably stratified in the vertical direction and has a unidirectional linear shear flow aligned with one horizontal axis. Superposed on this background state is an unsteady, subsonic flow that is evolved with the Euler equations subject to the anelastic approximation to filter acoustic phenomena. A Fourier Fourier basis in a set of quasi-Lagrangian coordinates that advect with the background shear is used for spectral expansions in the two horizontal directions. For the vertical direction, two different sets of basis functions have been implemented: (1) Chebyshev polynomials on a truncated, finite domain, and (2) rational Chebyshev functions on an infinite domain. Use of this latter set is equivalent to transforming the infinite domain to a finite one with a cotangent mapping, and using cosine and sine expansions in the mapped coordinate. The nonlinear advection terms are time-integrated explicitly, the pressure/enthalpy terms are integrated semi-implicitly, and the Coriolis force and buoyancy terms are treated semi-analytically. We show that internal gravity waves can be damped by adding new terms to the Euler equations. The code exhibits excellent parallel performance with the message passing interface (MPI). As a demonstration of the code, we simulate the merger of two 3D vortices in the midplane of a protoplanetary disk.

  9. NO EVIDENCE FOR CLASSICAL CEPHEIDS AND A NEW DWARF GALAXY BEHIND THE GALACTIC DISK

    Energy Technology Data Exchange (ETDEWEB)

    Pietrukowicz, P.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Pietrzyński, G.; Wyrzykowski, Ł.; Poleski, R.; Ulaczyk, K.; Skowron, J.; Mróz, P.; Pawlak, M.; Kozłowski, S. [Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa (Poland)

    2015-11-10

    Based on data from the ongoing OGLE Galaxy Variability Survey (OGLE GVS), we have verified observed properties of stars detected by the near-infrared VVV survey in a direction near the Galactic plane at longitude l ≈ −27° and recently tentatively classified as classical Cepheids belonging to, hence claimed, a dwarf galaxy at a distance of about 90 kpc from the Galactic Center. Three of four stars are detected in the OGLE GVS I-band images. We show that two of the objects are not variable at all, and the third one with a period of 5.695 days and a nearly sinusoidal light curve of an amplitude of 0.5 mag cannot be a classical Cepheid and is very likely a spotted object. These results together with a very unusual shape of the K{sub s}-band light curve of the fourth star indicate that it is very likely that none of them is a Cepheid and, thus there is no evidence for a background dwarf galaxy. Our observations show that great care must be taken when classifying objects by their low-amplitude close-to-sinusoidal near-infrared light curves, especially with a small number of measurements. We also provide a sample of high-amplitude spotted stars with periods of a few days that can mimic pulsations and even eclipses.

  10. The Growth of Central Black Hole and the Ionization Instability of Quasar Disk

    Science.gov (United States)

    Lu, Ye; Cheng, K. S.; Zhang, S. N.

    2003-01-01

    A possible accretion model associated with the ionization instability of quasar disks is proposed to address the growth of the central black hole harbored in the host galaxy. The evolution of quasars in cosmic time is assumed to change from a highly active state to a quiescent state triggered by the S-shaped ionization instability of the quasar accretion disk. For a given external mass transfer rate supplied by the quasar host galaxy, ionization instability can modify accretion rate in the disk and separates the accretion flows of the disk into three different phases, like a S-shape. We suggest that the bright quasars observed today are those quasars with disks in the upper branch of S-shaped instability, and the faint or 'dormant' quasars are simply the system in the lower branch. The middle branch is the transition state which is unstable. We assume the quasar disk evolves according to the advection-dominated inflow-outflow solutions (ADIOS) configuration in the stable lower branch of S-shaped instability, and Eddington accretion rate is used to constrain the accretion rate in each phase. The mass ratio between black hole and its host galactic bulge is a nature consequence of ADIOS. Our model also demonstrates that a seed black hole (BH) similar to those found in spiral galaxies today is needed to produce a BH with a final mass 2 x 10(exp 8) solar mases.

  11. PROBING THE ROLE OF CARBON IN ULTRAVIOLET EXTINCTION ALONG GALACTIC SIGHT LINES

    Energy Technology Data Exchange (ETDEWEB)

    Parvathi, V. S.; Babu, B. R. S. [Department of Physics, University of Calicut, Kerala 673635 (India); Sofia, U. J. [Department of Physics, American University, 4400 Massachusetts Avenue, NW, Washington, DC 20016 (United States); Murthy, J., E-mail: veena.makesh@gmail.com, E-mail: brsbabu@gmail.com, E-mail: sofia@american.edu, E-mail: jmurthy@yahoo.com [Indian Institute of Astrophysics, II Block, Koramangala, Bangalore 560034 (India)

    2012-11-20

    We report previously undetermined interstellar gas and dust-phase carbon abundances along 15 Galactic sight lines based on archival data of the strong 1334.5323 A transition observed with the Space Telescope Imaging Spectrograph. These are combined with previously reported carbon measurements along six sight lines to produce a complete sample of interstellar C II measurements determined with the 1334 A transition. Our data set includes a variety of Galactic disk environments characterized by different extinctions and samples paths ranging over three orders of magnitude in average density of hydrogen ((n(H))). Our data support the idea that dust, specifically carbon-based grains, are processed in the neutral interstellar medium. We, however, do not find that the abundance of carbon in dust or the grain-size distribution is related to the strength of the 2175 A bump. This is surprising, given that many current models have polycyclic aromatic hydrocarbons as the bump-producing dust.

  12. THE VVV SURVEY REVEALS CLASSICAL CEPHEIDS TRACING A YOUNG AND THIN STELLAR DISK ACROSS THE GALAXY’S BULGE

    Energy Technology Data Exchange (ETDEWEB)

    Dékány, I. [Instituto Milenio de Astrofísica, Santiago (Chile); Minniti, D. [Departamento de Física, Facultad de Ciencias Exactas, Universidad Andres Bello, República 220, Santiago (Chile); Majaess, D. [Saint Mary’s University, Halifax, Nova Scotia (Canada); Zoccali, M.; Hajdu, G.; Catelan, M. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago (Chile); Alonso-García, J. [Unidad de Astronomía, Fac. Cs. Básicas, Universidad de Antofagasta, Avda. U. de Antofagasta 02800, Antofagasta (Chile); Gieren, W. [Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile); Borissova, J., E-mail: idekany@astro.puc.cl [Instituto de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaso (Chile)

    2015-10-20

    Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy’s evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years.

  13. Disk

    NARCIS (Netherlands)

    P.A. Boncz (Peter); L. Liu (Lei); M. Tamer Özsu

    2008-01-01

    htmlabstractIn disk storage, data is recorded on planar, round and rotating surfaces (disks, discs, or platters). A disk drive is a peripheral device of a computer system, connected by some communication medium to a disk controller. The disk controller is a chip, typically connected to the CPU of

  14. LSS-GAC - A LAMOST Spectroscopic Survey of the Galactic Anti-center

    Science.gov (United States)

    Liu, X.-W.; Yuan, H.-B.; Huo, Z.-Y.; Deng, L.-C.; Hou, J.-L.; Zhao, Y.-H.; Zhao, G.; Shi, J.-R.; Luo, A.-L.; Xiang, M.-S.; Zhang, H.-H.; Huang, Y.; Zhang, H.-W.

    2014-01-01

    As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~3,400 sq.deg., centered on the Galactic anti-center (|b| ~ 3 M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~5,400 sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity (V r) and stellar parameters (effective temperature (T eff), surface gravity (log g) and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique data set to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties. The survey was initiated in the fall of 2012 and expected to complete in the spring of 2017. Hitherto, about 0.4 M spectra of S/N(λ7450) >= 10 per pixel have been accumulated. In addition, bright nights have been used to target stars brighter than 14 mag and have so far generated over 0.4 M spectra, yielding an excellent sample of local stars to probe the solar neighborhood. LSP3, a set of pipelines tailored to the need of LSS-GAC, for spectral flux-calibration, and radial velocity and stellar

  15. Unsteady Plasma Ejections from Hollow Accretion Columns of Galactic Neutron Stars as a Trigger for Gamma-Ray Bursts

    Science.gov (United States)

    Gvaramadze, V. V.

    1995-09-01

    We propose a model of gamma-ray bursts (GRBs) based on close Galactic neutron stars with accretion disks. We outline a simple mechanism of unsteady plasma ejections during episodic accretion events. The relative kinetic energy of ejected blobs can be converted into gamma-rays by internal shocks. The beaming of gamma-ray emission can be responsible for the observed isotropic angular distribution of GRBs.

  16. Does SEGUE/SDSS indicate a dual galactic halo?

    International Nuclear Information System (INIS)

    Schönrich, Ralph; Asplund, Martin; Casagrande, Luca

    2014-01-01

    We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment and neglect of selection effects. In particular, the detection of a vertical abundance gradient in the halo can be explained as a metallicity bias in distance. A similar bias and the impact of disk contamination affect the sample of blue horizontal branch stars. These examples highlight why non-volume complete samples require forward modeling from theoretical models or extensive bias-corrections. We also show how observational uncertainties produce the specific non-Gaussianity in the observed azimuthal velocity distribution of halo stars, which can be erroneously identified as two Gaussian components. A single kinematic component yields an excellent fit to the observed data, when we model the measurement process including distance uncertainties. Furthermore, we show that sample differences in proper motion space are the direct consequence of kinematic cuts and are enhanced when distance estimates are less accurate. Thus, their presence is neither proof of a separate population nor a measure of reliability for the applied distances. We conclude that currently there is no evidence from SEGUE/SDSS that would favor a dual Galactic halo over a single halo that is full of substructure.

  17. Impact of Cosmic-Ray Transport on Galactic Winds

    Science.gov (United States)

    Farber, R.; Ruszkowski, M.; Yang, H.-Y. K.; Zweibel, E. G.

    2018-04-01

    The role of cosmic rays generated by supernovae and young stars has very recently begun to receive significant attention in studies of galaxy formation and evolution due to the realization that cosmic rays can efficiently accelerate galactic winds. Microscopic cosmic-ray transport processes are fundamental for determining the efficiency of cosmic-ray wind driving. Previous studies modeled cosmic-ray transport either via a constant diffusion coefficient or via streaming proportional to the Alfvén speed. However, in predominantly cold, neutral gas, cosmic rays can propagate faster than in the ionized medium, and the effective transport can be substantially larger; i.e., cosmic rays can decouple from the gas. We perform three-dimensional magnetohydrodynamical simulations of patches of galactic disks including the effects of cosmic rays. Our simulations include the decoupling of cosmic rays in the cold, neutral interstellar medium. We find that, compared to the ordinary diffusive cosmic-ray transport case, accounting for the decoupling leads to significantly different wind properties, such as the gas density and temperature, significantly broader spatial distribution of cosmic rays, and higher wind speed. These results have implications for X-ray, γ-ray, and radio emission, and for the magnetization and pollution of the circumgalactic medium by cosmic rays.

  18. Convection Enhances Magnetic Turbulence in AM CVn Accretion Disks

    Science.gov (United States)

    Coleman, Matthew S. B.; Blaes, Omer; Hirose, Shigenobu; Hauschildt, Peter H.

    2018-04-01

    We present the results of local, vertically stratified, radiation magnetohydrodynamic shearing-box simulations of magnetorotational instability (MRI) turbulence for a (hydrogen poor) composition applicable to accretion disks in AM CVn type systems. Many of these accreting white dwarf systems are helium analogs of dwarf novae (DNe). We utilize frequency-integrated opacity and equation-of-state tables appropriate for this regime to accurately portray the relevant thermodynamics. We find bistability of thermal equilibria in the effective-temperature, surface-mass-density plane typically associated with disk instabilities. Along this equilibrium curve (i.e., the S-curve), we find that the stress to thermal pressure ratio α varied with peak values of ∼0.15 near the tip of the upper branch. Similar to DNe, we found enhancement of α near the tip of the upper branch caused by convection; this increase in α occurred despite our choice of zero net vertical magnetic flux. Two notable differences we find between DN and AM CVn accretion disk simulations are that AM CVn disks are capable of exhibiting persistent convection in outburst, and ideal MHD is valid throughout quiescence for AM CVns. In contrast, DNe simulations only show intermittent convection, and nonideal MHD effects are likely important in quiescence. By combining our previous work with these new results, we also find that convective enhancement of the MRI is anticorrelated with mean molecular weight.

  19. Asymmetric mass models of disk galaxies. I. Messier 99

    Science.gov (United States)

    Chemin, Laurent; Huré, Jean-Marc; Soubiran, Caroline; Zibetti, Stefano; Charlot, Stéphane; Kawata, Daisuke

    2016-04-01

    Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M 99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M 99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M 99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.

  20. Development of dark disk model of positron anomaly origin

    Science.gov (United States)

    Belotsky, K. M.; Kirillov, A. A.; Solovyov, M. L.

    Dark disk model could be a remedy for dark matter (DM) explanation of positron anomaly (PA) in cosmic rays (CR). The main difficulty in PA explanation relates to cosmic gamma-radiation which is inevitably produced in DM annihilation or decay leading to tension with respective observation data. Introduction of “active” (producing CR) DM component concentrating in galactic disk alleviates this tension. Earlier, we considered 2-lepton modes, with branching ratios being chosen to fit in the best way all the observation data. Here we considered, in the framework of the same dark disk model, two cases: 2-body final state annihilation and 4-body one, and in each case a quark mode is added to the leptonic ones. It is shown that 4-body mode case is a little better than 2-body one from viewpoint of quality of observation data description at the fixed all other parameters (of CR propagation, background, disk height). The values of DM particle mass around 350GeV and 500GeV are more favorable for 2- and 4-body modes, respectively. Higher values would improve description of data on positrons only but accounting for data on gamma-radiation prevents it because of unwanted more abundant high-energy gamma production. Inclusion of the quark modes improves a little fitting data in both 4- and 2-body mode cases, contrary to naive expectations. In fact, quark mode has a bigger gammas yield than that of most gamma-productive leptonic mode — tau, but they are softer due to bigger final state hadron multiplicity.

  1. Searching for ghosts in the galactic halo: What can we learn about the formation of the Galaxy from the stellar halo?

    Science.gov (United States)

    Aguilar, L. A.; Brown, A. G. A.; Velázquez, H.

    2006-06-01

    We study the feasibility of recovering information of remnants of tidally disrupted satellite galaxies in the halo of our Galaxy, using space astrometry from Gaia. This mission will provide a very large data set ( ˜ 10^9 stars) with an unprecedent level of detail in phase space (tens of μs). However, before recovering useful information, sampling biases, observational errors and the stellar galactic background must be taken into account. We present a Monte Carlo simulation of the Gaia catalogue that excludes the galactic disk (|b|criteria must be used. The numerical tool here developed can be employed to test the feasibility of other search criteria.

  2. On the Dynamical Structure of the Jet System in the Disk with the Keplerian Rotation

    Directory of Open Access Journals (Sweden)

    Kyung-Sook Jeong

    1989-06-01

    Full Text Available The classical sloar wind theory proposed by Parker(1963 explains well the dynamics of the wind pheonomena such as stellar wind accretion disk. While the stellar wind system like the solar wind has the spherically symmetric wind structure, there are various jet phenomena which collimate the system into the narrow space. We can find these dynamical structures in SS433, in the optical jet of M87, and around the active galactic nulei. We present the dynamical structure of the jet system in disks, which conserves the angular momentum, with the Keplerian rotation and the strong relation between the geometrical cross section and the physical change of the jet stream on the basis of the hydrodynamic equations.

  3. The Galactic Distribution of Planets via Spitzer Microlensing Parallax

    Science.gov (United States)

    Gould, Andrew; Yee, Jennifer; Carey, Sean; Shvartzvald, Yossi

    2018-05-01

    We will measure the Galactic distribution of planets by obtaining 'microlens parallaxes' of about 200 events, including 3 planetary events, from the comparison of microlens lightcurves observed from Spitzer and Earth, which are separated by >1.5 AU in projection. The proposed observations are part of a campaign that we have conducted with Spitzer since 2014. The planets expected to be identified in this campaign when combined with previous work will yield a first statistically significant measurement of the frequency of planets in the Galactic bulge versus the Galactic disk. As we have demonstrated in three previous programs, the difference in these lightcurves yields both the 'microlens parallax' (ratio of the lens-source relative parallax) to the Einstein radius, and the direction of lens-source relative motion. For planetary events, this measurement directly yields the mass and distance of the planet. This proposal is significantly more sensitive to planets than previous work because it takes advantage of the KMTNet observing strategy that covers >85 sq.deg t >0.4/hr cadence, 24/7 from 3 southern observatories and a alert system KMTNet is implementing for 2019. This same observing program also provides a unique probe of dark objects. It will yield an improved measurement of the isolated-brown-dwarf mass function. Thirteen percent of the observations will specifically target binaries, which will probe systems with dark components (brown dwarfs, neutron stars, black holes) that are difficult or impossible to investigate by other methods. The observations and methods from this work are a test bed for WFIRST microlensing.

  4. CONNECTION BETWEEN THE ACCRETION DISK AND JET IN THE RADIO GALAXY 3C 111

    International Nuclear Information System (INIS)

    Chatterjee, Ritaban; Marscher, Alan P.; Jorstad, Svetlana G.; Harrison, Brandon; Agudo, Ivan; Taylor, Brian W.; Markowitz, Alex; Rivers, Elizabeth; Rothschild, Richard E.; McHardy, Ian M.; Aller, Margo F.; Aller, Hugh D.; Laehteenmaeki, Anne; Tornikoski, Merja; Gomez, Jose L.; Gurwell, Mark

    2011-01-01

    We present the results of extensive multi-frequency monitoring of the radio galaxy 3C 111 between 2004 and 2010 at X-ray (2.4-10 keV), optical (R band), and radio (14.5, 37, and 230 GHz) wave bands, as well as multi-epoch imaging with the Very Long Baseline Array (VLBA) at 43 GHz. Over the six years of observation, significant dips in the X-ray light curve are followed by ejections of bright superluminal knots in the VLBA images. This shows a clear connection between the radiative state near the black hole, where the X-rays are produced, and events in the jet. The X-ray continuum flux and Fe line intensity are strongly correlated, with a time lag shorter than 90 days and consistent with zero. This implies that the Fe line is generated within 90 lt-day of the source of the X-ray continuum. The power spectral density function of X-ray variations contains a break, with a steeper slope at shorter timescales. The break timescale of 13 +12 -6 days is commensurate with scaling according to the mass of the central black hole based on observations of Seyfert galaxies and black hole X-ray binaries (BHXRBs). The data are consistent with the standard paradigm, in which the X-rays are predominantly produced by inverse Compton scattering of thermal optical/UV seed photons from the accretion disk by a distribution of hot electrons-the corona-situated near the disk. Most of the optical emission is generated in the accretion disk due to reprocessing of the X-ray emission. The relationships that we have uncovered between the accretion disk and the jet in 3C 111, as well as in the Fanaroff-Riley class I radio galaxy 3C 120 in a previous paper, support the paradigm that active galactic nuclei and Galactic BHXRBs are fundamentally similar, with characteristic time and size scales proportional to the mass of the central black hole.

  5. A Pulsar and a Disk

    Science.gov (United States)

    Kohler, Susanna

    2016-07-01

    Recent, unusual X-ray observations from our galactic neighbor, the Small Magellanic Cloud, have led to an interesting model for SXP 214, a pulsar in a binary star system.Artists illustration of the magnetic field lines of a pulsar, a highly magnetized, rotating neutron star. [NASA]An Intriguing BinaryAn X-ray pulsar is a magnetized, rotating neutron star in a binary system with a stellar companion. Material is fed from the companion onto the neutron star, channeled by the objects magnetic fields onto a hotspot thats millions of degrees. This hotspot rotating past our line of sight is what produces the pulsations that we observe from X-ray pulsars.Located in the Small Magellanic Cloud, SXP 214 is a transient X-ray pulsar in a binary with a Be-type star. This star is spinning so quickly that material is thrown off of it to form a circumstellar disk.Recently, a team of authors led by JaeSub Hong (Harvard-Smithsonian Center for Astrophysics) have presented new Chandra X-ray observations of SXP 214, tracking it for 50 ks (~14 hours) in January 2013. These observations reveal some very unexpected behavior for this pulsar.X-ray PuzzleThe energy distribution of the X-ray emission from SXP 214 over time. Dark shades or blue colors indicate high counts, and light shades or yellow colors indicate low counts. Lower-energy X-ray emission appeared only later, after about 20 ks. [Hong et al. 2016]Three interesting pieces of information came from the Chandra observations:SXP 214s rotation period was measured to be 211.5 s an increase in the spin rate since the discovery measurement of a 214-second period. Pulsars usually spin down as they lose angular momentum over time so what caused this one to spin up?Its overall X-ray luminosity steadily increased over the 50 ks of observations.Its spectrum became gradually softer (lower energy) over time; in the first 20 ks, the spectrum only consisted of hard X-ray photons above 3 keV, but after 20 ks, softer X-ray photons below 2 ke

  6. Abundances of Copper and Zinc in Stars of the Galactic Thin and Thick Disks

    Science.gov (United States)

    Gorbaneva, T. I.; Mishenina, T. V.; Basak, N. Yu.; Soubiran, C.; Kovtyukh, V. V.

    The spectra of studied stars were obtained with the ELODIE spectrograph at the 1.93-m telescope of the Observatoire de Haute Provence (France). The determination of Cu and Zn abundances was carried out in LTE assumption by model atmosphere method, for Cu the hyperfine structure was taken into account. Cu and Zn abundance trends for thin and thick disk's stars are presented.

  7. Galactic dynamics

    CERN Document Server

    Binney, James

    2008-01-01

    Since it was first published in 1987, Galactic Dynamics has become the most widely used advanced textbook on the structure and dynamics of galaxies and one of the most cited references in astrophysics. Now, in this extensively revised and updated edition, James Binney and Scott Tremaine describe the dramatic recent advances in this subject, making Galactic Dynamics the most authoritative introduction to galactic astrophysics available to advanced undergraduate students, graduate students, and researchers. Every part of the book has been thoroughly overhauled, and many section

  8. C II forbidden-line 158 micron mapping in Sagittarius A Rotation curve and mass distribution in the galactic center

    Science.gov (United States)

    Lugten, J. B.; Genzel, R.; Crawford, M. K.; Townes, C. H.

    1986-01-01

    Based on data obtained with the NASA Kuiper Airborne Observatory 91.4 cm telescope, the 158-micron fine structure line emission of C(+) is mapped near the galactic center. The strongest emission comes from a 10-pc FWHM diameter disk centered on Sgr A West whose dominant motion is rotation. Extended C(+) emission is also found from the +50 km/s galactic center molecular cloud, and a second cloud at v(LSR) of about -35 km/s. The rotation curve and mass distribution within 10 pc of the galactic center are derived, and the C(+) profiles show a drop-off of rotation velocity between 2 and 10 pc. A mass model is suggested with 2-4 million solar masses in a central point mass, and a M/L ratio of the central stellar cluster of 0.5 solar masses/solar luminosities, suggesting a large abundance of giants and relatively recent star formation in the center.

  9. The evoluation of the galactic globular clusters; I Metal abundance calibrations

    International Nuclear Information System (INIS)

    Lee, S.W.; Park, N.K.

    1984-01-01

    Five different calibrations of metal abundances of globular clusters are examined and these are compared with metallicity ranking parameters such as (Sp)sub(c), , Q39 and IR-indices. Except for the calibration *(Fe/H*)sub(H) by the high dispersion echelle analysis, the other calibration scales are correlated with the morphological parameters of red giant branch. In the *(Fe/H*)sub(Hsup(-))scale, the clusters later than approx.F8 have nearly a constant metal abundance, *(Fe/H*)sub(H)approx.-1.05, regardless of morphological characteristics of horizontal branch and red giant branch. By the two fundamental calibration scales of *(Fe/H*)sub(L) (derived by the low dispersion analysis), and *(Fe/H*)sub(delta S) (derived by the spectral analysis of RR Lyrae stars), the globular clusters are divided into the halo clusters with *(Fe/H*)<-1.0 and the disk clusters confined within the galactocentric distance rsub(G)=10 kpc and galactic plane distance absolute z=3 kpc. In this case the abundance gradient is given by d*(Fe/H*)/drsub(G)approx.-0.05kpcsup(-1) and d*(Fe/H*)/d absolute z approx. -0.08 kpcsup(-1) within rsub(G)=20 kpc and absolute z=10 kpc, respectively. According to these characteristics of the spatial distribution of globular clusters, the chemical evolution of the galactic globular clusters can be accounted for by the two-zone (disk-halo) slow collapse model when the *(Fe/H*)sub(Lsup(-)) or *(Fe/H*)sub(DELTA Ssup(-))scale is applied. In the case of *(Fe/H*)sub(Hsup(-))scale, the one-zone fast collapse model is preferred for the evolution of globular clusters. (Author)

  10. Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

    Energy Technology Data Exchange (ETDEWEB)

    Asahina, Yuta; Ohsuga, Ken [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan); Nomura, Mariko, E-mail: asahina@cfca.jp [Keio University, Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522 (Japan)

    2017-05-01

    By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tension force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.

  11. Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

    International Nuclear Information System (INIS)

    Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko

    2017-01-01

    By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tension force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.

  12. Exploring Black Hole Accretion in Active Galactic Nuclei with Simbol-X

    Science.gov (United States)

    Goosmann, R. W.; Dovčiak, M.; Mouchet, M.; Czerny, B.; Karas, V.; Gonçalves, A.

    2009-05-01

    A major goal of the Simbol-X mission is to improve our knowledge about black hole accretion. By opening up the X-ray window above 10 keV with unprecedented sensitivity and resolution we obtain new constraints on the X-ray spectral and variability properties of active galactic nuclei. To interpret the future data, detailed X-ray modeling of the dynamics and radiation processes in the black hole vicinity is required. Relativistic effects must be taken into account, which then allow to constrain the fundamental black hole parameters and the emission pattern of the accretion disk from the spectra that will be obtained with Simbol-X.

  13. On a simple model for self-regulating star formation in the galactic disk

    International Nuclear Information System (INIS)

    Meusinger, H.

    1989-01-01

    Star formation in galaxies is a process with feedback to the interstellar medium (ISM) and possibly it is part of a self-regulating cycle. Dopita (1985) proposed a model in which star formation in spiral and irregular galaxies is self-regulated by the pressure in the ISM. In the present paper it is shown that available data for radial distributions of gas, total mass and the flux of Lyman continuum photons in the disk of our galaxy do not support such a simple model. Several possible causes are discussed. (author)

  14. An observational study of disk-population globular clusters

    International Nuclear Information System (INIS)

    Armandroff, T.E.

    1988-01-01

    Integrated-light spectroscopy was obtained for twenty-seven globular clusters at the Ca II infrared triplet. Line strengths and radial velocities were measured from the spectra. For the well-studied clusters in the sample, the strength of the CA II lines is very well correlated with previous metallicity estimates obtained using a variety of techniques. The greatly reduced effect of interstellar extinction at these wavelengths compared to the blue region of the spectrum has permitted observations of some of the most heavily reddened clusters in the Galaxy. For several such clusters, the Ca II triplet metallicities are in poor agreement with metallicity estimates from infrared photometry by Malkan. Color-magnitude diagrams were constructed for six previously unstudied metal-rich globular clusters and for the well-studied cluster 47 Tuc. The V magnitudes of the horizontal branch stars in the six clusters are in poor agreement with previous estimates based on secondary methods. The horizontal branch morphologies and reddenings of the program clusters were also determined. Using the improved set of metallicities, radial velocities, and distance moduli, the spatial distribution, kinematics, and metallicity distribution of the Galactic globulars were analyzed. The revised data supports Zinn's conclusion that the metal-rich clusters form a highly flattened, rapidly rotating disk system, while the metal-poor clusters make up the familiar, spherically distributed, slowly rotating halo population. The scale height, metallicity distribution, and kinematics of the metal-rich globulars are in good agreement with those of the stellar thick disk. Luminosity functions were constructed, and no significant difference is found between disk and halo samples. Metallicity gradients seem to be present in the disk cluster system. The implications of these results for the formation and evol

  15. Effects of thermal plasma on self-absorbed synchrotron sources in active galactic nuclei

    International Nuclear Information System (INIS)

    De Kool, M.; Begelman, M.C.

    1989-01-01

    The observable effects of a thermal background plasma in a self-absorbed synchrotron source are reviewed, in the context of a model for the central engine of an active galactic nucleus (AGN). Considering the effects of free-free absorption and emission, Thomson and Compton scattering, and spatial stratification, it is found that the observations set an upper limit on the thermal electron scattering optical depth in the central synchrotron-emitting region of an AGN. The upper limit, tau(max) about 1, results mainly from the apparent absence of induced Compton scattering and inverse thermal Comptonization effects. The low value of tau(max) poses some problems for nonthermal models of the AGN continuum that can be partly resolved by assuming a thin disk or layer-like geometry for the source, with (h/R) less than about 0.01. A likely site for the synchrotron-producing region seems to be the surface of an accretion disk or torus. 20 refs

  16. Unveiling the Role of Galactic Rotation on Star Formation

    Science.gov (United States)

    Utreras, José; Becerra, Fernando; Escala, Andrés

    2016-12-01

    We study the star formation process at galactic scales and the role of rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS) and Silk-Elmegreen (SE) laws, and the dimensionally homogeneous equation proposed by Escala {{{Σ }}}{SFR}\\propto \\sqrt{G/L}{{{Σ }}}{gas}1.5. We show that using the last we take into account the effects of the integration along the line of sight and find a unique regime of star formation for both types of galaxies, suppressing the observed bi-modality of the KS law. We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk Ω for the three laws studied in this work. Finally, we show that the dimensionless efficiency of star formation is well represented by an exponentially decreasing function of -1.9{{Ω }}{t}{ff}{ini}, where {t}{ff}{ini} is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala relations by 43%, 43%, and 35%, respectively.

  17. ELEMENTAL ABUNDANCE RATIOS IN STARS OF THE OUTER GALACTIC DISK. IV. A NEW SAMPLE OF OPEN CLUSTERS

    International Nuclear Information System (INIS)

    Yong, David; Carney, Bruce W.; Friel, Eileen D.

    2012-01-01

    We present radial velocities and chemical abundances for nine stars in the old, distant open clusters Be18, Be21, Be22, Be32, and PWM4. For Be18 and PWM4, these are the first chemical abundance measurements. Combining our data with literature results produces a compilation of some 68 chemical abundance measurements in 49 unique clusters. For this combined sample, we study the chemical abundances of open clusters as a function of distance, age, and metallicity. We confirm that the metallicity gradient in the outer disk is flatter than the gradient in the vicinity of the solar neighborhood. We also confirm that the open clusters in the outer disk are metal-poor with enhancements in the ratios [α/Fe] and perhaps [Eu/Fe]. All elements show negligible or small trends between [X/Fe] and distance ( –1 ), but for some elements, there is a hint that the local (R GC GC > 13 kpc) samples may have different trends with distance. There is no evidence for significant abundance trends versus age ( –1 ). We measure the linear relation between [X/Fe] and metallicity, [Fe/H], and find that the scatter about the mean trend is comparable to the measurement uncertainties. Comparison with solar neighborhood field giants shows that the open clusters share similar abundance ratios [X/Fe] at a given metallicity. While the flattening of the metallicity gradient and enhanced [α/Fe] ratios in the outer disk suggest a chemical enrichment history different from that of the solar neighborhood, we echo the sentiments expressed by Friel et al. that definitive conclusions await homogeneous analyses of larger samples of stars in larger numbers of clusters. Arguably, our understanding of the evolution of the outer disk from open clusters is currently limited by systematic abundance differences between various studies.

  18. Magnetized Disk Winds in NGC 3783

    Science.gov (United States)

    Fukumura, Keigo; Kazanas, Demosthenes; Shrader, Chris; Behar, Ehud; Tombesi, Francesco; Contopoulos, Ioannis

    2018-01-01

    We analyze a 900 ks stacked Chandra/HETG spectrum of NGC 3783 in the context of magnetically driven accretion-disk wind models in an effort to provide tight constraints on the global conditions of the underlying absorbers. Motivated by the earlier measurements of its absorption measure distribution (AMD) indicating X-ray-absorbing ionic columns that decrease slowly with decreasing ionization parameter, we employ 2D magnetohydrodynamic (MHD) disk wind models to describe the global outflow. We compute its photoionization structure along with the wind kinematic properties, allowing us to further calculate in a self-consistent fashion the shapes of the major X-ray absorption lines. With the wind radial density profile determined by the AMD, the profiles of the ensemble of the observed absorption features are determined by the two global parameters of the MHD wind; i.e., disk inclination {θ }{obs} and wind density normalization n o . Considering the most significant absorption features in the ∼1.8–20 Å range, we show that the MHD wind is best described by n{(r)∼ 6.9× {10}11(r/{r}o)}-1.15 cm‑3 and {θ }{obs}=44^\\circ . We argue that winds launched by X-ray heating or radiation pressure, or even MHD winds but with steeper radial density profiles, are strongly disfavored by data. Considering the properties of Fe K-band absorption features (i.e., Fe XXV and Fe XXVI), while typically prominent in the active galactic nucleus X-ray spectra, they appear to be weak in NGC 3783. For the specific parameters of our model obtained by fitting the AMD and the rest of the absorption features, these features are found to be weak, in agreement with observations.

  19. Mass Flux and Terminal Velocities of Magnetically Driven Jets from Accretion Disks

    Science.gov (United States)

    Kudoh, Takahiro; Shibata, Kazunari

    1995-10-01

    In order to investigate astrophysical jets from accretion disks, we solve 1.5-dimensional steady MHD equations for a wide range of parameters, assuming the shape of poloidal magnetic field lines. We include a thermal effect to obtain the relation between the mass flux of the jet and the magnetic energy at the disk, although the jet is mainly accelerated by the magnetic force. It is found that the mass flux of the jets ( M dot ) is dependent on the magnetic energy at the disk surface, i.e., M dot ~ (rho Aa|Bp/B|)_{{slow}} ~ (rho Aa|Bp/Bphi|)_{{slow}} ~ Ealpha_{{mg}} [where rho is the density, a is the sound velocity, A is the cross section of the magnetic flux, B = (B2p + B2phi)^{1/2} , Bp and B phi are the poloidal and toroidal magnetic field strength, respectively, Emg is the magnetic energy in unit of the gravitational energy at the disk surface, and the suffix "slow" denotes the value at a slow point], when the magnetic energy is not too large. The parameter alpha increases from 0 to 0.5 with decreasing magnetic energy. Since the scaling law of Michel's minimum energy solution nearly holds in the magnetically driven flows, the dependence of the terminal velocity on the magnetic energy becomes weaker than had been expected, i.e., v_∞ ~ E^{(1-alpha)/3}_{{mg}} . It is shown that the terminal velocity of the jet is an order of Keplerian velocity at the footpoint of the jets for a wide range of values of Emg expected for accretion disks in star-forming regions and active galactic nuclei. We argue that the mass-loss rates observed in the star-forming regions would constrain the magnetic energies at the disk surfaces.

  20. Galactic sprinklers

    International Nuclear Information System (INIS)

    Vandeusen, W.

    1984-01-01

    It is believed by many astronomers that gravitation is responsible for holding a strong whirlpool of hot, dense material together at the center of the Milky Way galaxy. However, the galactic-sprinkler model suggests that the whirlpool is not being held together, and that the stars, gas and dust within the spirals are being thrown outward. It is also suggested that much of the ejected material eventually returns to the galactic center, as do stars within our stellar neighborhood. The material is believed to be subjected to extreme changes in the gravitational time rate which may cause it to follow an inbound spiral that is basically similar to the outbound spiral. Radio studies also indicate that the galactic arms on either side of the galactic center move at different velocities and in different directions with respect to our location and that the whole group of stars in the vicinity of the solar system may be moving outward from the galactic center at a velocity of about 40 kps. Through the use of velocity data in kps, and distance data in light years, the radial component of the sun's trajectory can be estimated with respect to time by a parabola. The spiral trajectory of the sun can be calculated and plotted on polar coordinates by combining both the radial component and tangential component (230 kps)

  1. THE MULTIPHASE STRUCTURE AND POWER SOURCES OF GALACTIC WINDS IN MAJOR MERGERS

    International Nuclear Information System (INIS)

    Rupke, David S. N.; Veilleux, Sylvain

    2013-01-01

    Massive, galaxy-scale outflows are known to be ubiquitous in major mergers of disk galaxies in the local universe. In this paper, we explore the multiphase structure and power sources of galactic winds in six ultraluminous infrared galaxies (ULIRGs) at z –1 , and the highest velocities (2000-3000 km s –1 ) are seen only in ionized gas. The outflow energy and momentum in the QSOs are difficult to produce from a starburst alone, but are consistent with the QSO contributing significantly to the driving of the flow. Finally, when all gas phases are accounted for, the outflows are massive enough to provide negative feedback to star formation.

  2. Chemical Evolution and Star Formation History of the Disks of Spirals in Local Group

    Science.gov (United States)

    Yin, J.

    2011-05-01

    Milky Way (MW), M31 and M33 are the only three spiral galaxies in our Local group. MW and M31 have similar mass, luminosity and morphology, while M33 is only about one tenth of MW in terms of its baryonic mass. Detailed theoretical researches on these three spirals will help us to understand the formation and evolution history of both spiral galaxies and Local group. Referring to the phenomenological chemical evolution model adopted in MW disk, a similar model is established to investigate the star formation and chemical enrichment history of these three local spirals. Firstly, the properties of M31 disk are studied by building a similar chemical evolution model which is able to successfully describe the MW disk. It is expected that a simple unified phenomenological chemical evolution model could successfully describe the radial and global properties of both disks. Comparing with the former work, we adopt an extensive data set as model constraints, including the star formation profile of M31 disk derived from the recent UV data of GALEX. The comparison among the observed properties of these two disks displays very interesting similarities in their radial profiles when the distance from the galactic center is expressed in terms of the corresponding scale length. This implies some common processes in their formation and evolution history. Based on the observed data of the gas mass surface density and SFR surface density, the SFR radial profile of MW can be well described by Kennicutt-Schmidt star formation law (K-S law) or modified K-S law (SFR is inversely proportional to the distance from the galactic center), but this is not applicable to the M31 disk. Detailed calculations show that our unified model describes fairly well all the main properties of the MW disk and most properties of M31 disk, provided that the star formation efficiency of M31 disk is adjusted to be twice as large as that of MW disk (as anticipated from the lower gas fraction of M31). However, the

  3. THE EFFICIENCY AND WAVELENGTH DEPENDENCE OF NEAR-INFRARED INTERSTELLAR POLARIZATION TOWARD THE GALACTIC CENTER

    Energy Technology Data Exchange (ETDEWEB)

    Hatano, Hirofumi; Kurita, Mikio; Kanai, Saori; Sato, Shuji [Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Nishiyama, Shogo; Nakajima, Yasushi; Tamura, Motohide; Kandori, Ryo [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8858 (Japan); Nagata, Tetsuya; Yoshikawa, Tatsuhito [Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan); Kato, Daisuke [Department of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan); Sato, Yaeko; Suenaga, Takuya, E-mail: hattan@z.phys.nagoya-u.ac.jp, E-mail: shogo.nishiyama@nao.ac.jp [Department of Astronomical Sciences, Graduate University for Advanced Studies (Sokendai), Mitaka, Tokyo 181-8858 (Japan)

    2013-04-15

    Near-infrared polarimetric imaging observations toward the Galactic center (GC) have been carried out to examine the efficiency and wavelength dependence of interstellar polarization. A total area of about 5.7 deg{sup 2} is covered in the J, H, and K{sub S} bands. We examined the polarization efficiency, defined as the ratio of the degree of polarization to color excess. The interstellar medium between the GC and us shows a polarization efficiency lower than that in the Galactic disk by a factor of three. Moreover we investigated the spatial variation of the polarization efficiency by comparing it with that of the color excess, degree of polarization, and position angle. The spatial variations of color excess and degree of polarization depend on the Galactic latitude, while the polarization efficiency varies independently of the Galactic structure. Position angles are nearly parallel to the Galactic plane, indicating a longitudinal magnetic field configuration between the GC and us. The polarization efficiency anticorrelates with dispersions of position angles. The low polarization efficiency and its spatial variation can be explained by the differences in the magnetic field directions along the line of sight. From the lower polarization efficiency, we suggest a higher strength of a random component relative to a uniform component of the magnetic field between the GC and us. We also derived the ratios of degree of polarization p{sub H} /p{sub J} = 0.581 {+-} 0.004 and p{sub K{sub S}}/p{sub H} = 0.620 {+-} 0.002. The power-law indices of the wavelength dependence of polarization are {beta}{sub JH} = 2.08 {+-} 0.02 and {beta}{sub HK{sub S}} = 1.76 {+-} 0.01. Therefore, the wavelength dependence of interstellar polarization exhibits flattening toward longer wavelengths in the range of 1.25-2.14 {mu}m. The flattening would be caused by aligned large-size dust grains.

  4. The evolution of stellar metallicity gradients of the Milky Way disk from LSS-GAC main sequence turn-off stars: a two-phase disk formation history?

    International Nuclear Information System (INIS)

    Xiang, Mao-Sheng; Liu, Xiao-Wei; Huang, Yang; Wang, Chun; Ren, Juan-Juan; Chen, Bing-Qiu; Sun, Ning-Chen; Zhang, Hua-Wei; Yuan, Hai-Bo; Rebassa-Mansergas, Alberto; Huo, Zhi-Ying

    2015-01-01

    Accurate measurements of stellar metallicity gradients in the radial and vertical directions of the disk and their temporal variations provide important constraints on the formation and evolution of the Milky Way disk. We use 297 042 main sequence turn-off stars selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) to determine the radial and vertical gradients of stellar metallicity, Δ[Fe/H]/ΔR and Δ[Fe/H]/Δ|Z| of the Milky Way disk in the direction of the anticenter. We determine ages of those turn-off stars by isochrone fitting and measure the temporal variations of metallicity gradients. We have carried out a detailed analysis of the selection effects resulting from the selection, observation and data reduction of LSS-GAC targets and the potential biases of a magnitude limited sample on the determinations of metallicity gradients. Our results show that the gradients, both in the radial and vertical directions, exhibit significant spatial and temporal variations. The radial gradients yielded by stars with the oldest ages (≳ 11 Gyr) are essentially zero at all heights from the disk midplane, while those given by younger stars are always negative. The vertical gradients deduced from stars with the oldest ages (≳ 11 Gyr) are negative and only show very weak variations with Galactocentric distance in the disk plane, R, while those yielded by younger stars show strong variations with R. After being essentially flat at the earliest epochs of disk formation, the radial gradients steepen as age decreases, reaching a maximum (steepest) at age 7–8 Gyr, and then they flatten again. Similar temporal trends are also found for the vertical gradients. We infer that the assembly of the Milky Way disk may have experienced at least two distinct phases. The earlier phase is probably related to a slow, pressure-supported collapse of gas, when the gas settles down to the disk mainly in the vertical direction. In the later phase, there are

  5. Possible Accretion Disk Origin of the Emission Variability of a Blazar Jet

    Science.gov (United States)

    Chatterjee, Ritaban; Roychowdhury, Agniva; Chandra, Sunil; Sinha, Atreyee

    2018-06-01

    We analyze X-ray light curves of the blazar Mrk 421 obtained from the Soft X-ray Imaging Telescope (SXT) and the Large Area X-ray Proportional Counter (LAXPC) instrument on board the Indian space telescope AstroSat and archival observations from Swift. We show that the X-ray power spectral density (PSD) is a piece-wise power-law with a break; i.e., the index becomes more negative below a characteristic “break timescale.” Galactic black hole (BH) X-ray binaries and Seyfert galaxies exhibit a similar characteristic timescale in their X-ray variability that is proportional to their respective BH mass. X-rays in these objects are produced in the accretion disk or corona. Hence, such a timescale is believed to be linked to the properties of the accretion flow. Any relation observed between events in the accretion disk and those in the jet can be used to characterize the disk–jet connection. However, evidence of such a link has been scarce and indirect. Mrk 421 is a BL Lac object that has a prominent jet pointed toward us and a weak disk emission, and it is assumed that most of its X-rays are generated in the jet. Hence, the existence of the break in its X-ray PSD may indicate that changes in the accretion disk, which may be the source of the break timescale, are translating into the jet where the X-rays are produced.

  6. NUSTAR and Suzaku x-ray spectroscopy of NGC 4151: Evidence for reflection from the inner accretion disk

    Energy Technology Data Exchange (ETDEWEB)

    Keck, M. L.; Brenneman, L. W.; Ballantyne, D. R.; Bauer, F.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Dauser, T.; Elvis, M.; Fabian, A. C.; Fuerst, F.; García, J.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Madejski, G.; Marinucci, A.; Matt, G.; Reynolds, C. S.; Stern, D.; Walton, D. J.; Zoghbi, A.

    2015-06-15

    We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin $a\\gt 0.9$ accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features.

  7. How does the Mass Transport in Disk Galaxy Models Influence the Character of Orbits?

    Directory of Open Access Journals (Sweden)

    Zotos Euaggelos E.

    2014-12-01

    Full Text Available We explore the regular or chaotic nature of orbits of stars moving in the meridional (R, z plane of an axially symmetric time-dependent disk galaxy model with a central, spherically symmetric nucleus. In particular, mass is linearly transported from the disk to the galactic nucleus, in order to mimic, in a way, the case of self-consistent interactions of an actual N-body simulation. We thus try to unveil the influence of this mass transportation on the different families of orbits of stars by monitoring how the percentage of chaotic orbits, as well as the percentages of orbits of the main regular resonant families, evolve as the galaxy develops a dense and massive nucleus in its core. The SALI method is applied to samples of orbits in order to distinguish safely between ordered and chaotic motion. In addition, a method based on the concept of spectral dynamics is used for identifying the various families of regular orbits and also for recognizing the secondary resonances that bifurcate from them. Our computations strongly suggest that the amount of the observed chaos is substantially increased as the nucleus becomes more massive. Furthermore, extensive numerical calculations indicate that there are orbits which change their nature from regular to chaotic and vice versa and also orbits which maintain their orbital character during the galactic evolution. The present outcomes are compared to earlier related work.

  8. Galactic bulge preferred over dark matter for the Galactic centre gamma-ray excess

    Science.gov (United States)

    Macias, Oscar; Gordon, Chris; Crocker, Roland M.; Coleman, Brendan; Paterson, Dylan; Horiuchi, Shunsaku; Pohl, Martin

    2018-05-01

    An anomalous gamma-ray excess emission has been found in the Fermi Large Area Telescope data1 covering the centre of the Galaxy2,3. Several theories have been proposed for this `Galactic centre excess'. They include self-annihilation of dark-matter particles4, an unresolved population of millisecond pulsars5, an unresolved population of young pulsars6, or a series of burst events7. Here, we report on an analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic centre excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic centre excess is not a dark-matter phenomenon but rather associated with the stellar population of the Galactic bulge and the nuclear bulge.

  9. Supergiants and the Galactic metallicity gradient. II. Spectroscopic abundances for 64 distant F- to M-type supergiants

    International Nuclear Information System (INIS)

    Luck, R.E.; Bond, H.E.

    1989-01-01

    The metallicity gradient in the Galactic disk from in situ stars with visual magnitude ranging from 6 to 10 is analyzed. Atmospheric parameters and detailed chemical abundances for 64 Population I supergiants of spectral types F through M and luminosity classes Ia through II have been determined. The derived Fe/H ratios ranging from -0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertainty of + or - 0.2. A subset of 25 supergiants fainter than 7th magnitude lying in the direction of the Galactic center shows a Fe/H mean of +0.18 + or - 0.04, while a similar sample of 15 faint supergiants lying in the direction of the Galactic anticenter shows a lower Fe/H mean of +0.07 + or - 0.06. For a sample of bright supergiants analyzed by Luck and Lambert (1985), the mean abundance pattern for all 64 stars showed the following: deficient C and O along with enhancement of N, indicating mixing of CNO-cycled material to the stellar surfaces; an apparent Sr enhancement attributed to departures from LTE; and an essentially solar pattern of other chemical elements. 50 refs

  10. Relativistic Outflows from Advection-dominated Accretion Disks around Black Holes

    Science.gov (United States)

    Becker, Peter A.; Subramanian, Prasad; Kazanas, Demosthenes

    2001-05-01

    Advection-dominated accretion flows (ADAFs) have a positive Bernoulli parameter and are therefore gravitationally unbound. The Newtonian ADAF model has been generalized recently to obtain the ADIOS model that includes outflows of energy and angular momentum, thereby allowing accretion to proceed self-consistently. However, the utilization of a Newtonian gravitational potential limits the ability of this model to describe the inner region of the disk, where any relativistic outflows are likely to originate. In this paper we modify the ADIOS scenario to incorporate a pseudo-Newtonian potential, which approximates the effects of general relativity. The analysis yields a unique, self-similar solution for the structure of the coupled disk/wind system. Interesting features of the new solution include the relativistic character of the outflow in the vicinity of the radius of marginal stability, which represents the inner edge of the quasi-Keplerian disk in our model. Hence, our self-similar solution may help to explain the origin of relativistic jets in active galaxies. At large distances the radial dependence of the accretion rate approaches the unique form M~r1/2, with an associated density variation given by ρ~r-1. This density variation agrees with that implied by the dependence of the hard X-ray time lags on the Fourier frequency for a number of accreting galactic black hole candidates. While intriguing, the predictions made using our self-similar solution need to be confirmed in the future using a detailed model that includes a physical description of the energization mechanism that drives the outflow, which is likely to be powered by the shear of the underlying accretion disk.

  11. MISALIGNED DISKS AS OBSCURERS IN ACTIVE GALAXIES

    International Nuclear Information System (INIS)

    Lawrence, Andy; Elvis, Martin

    2010-01-01

    We critically review the evidence concerning the fraction of active galactic nuclei (AGNs) that appear as Type 2 AGNs, carefully distinguishing strict Type 2 AGNs from both more lightly reddened Type 1 AGNs, and from low excitation narrow line AGNs, which may represent a different mode of activity. Low-excitation AGNs occur predominantly at low luminosities; after removing these, true Type 2 AGNs represent 58% ± 5% of all AGNs, and lightly reddened Type 1 AGNs a further ∼15%. Radio, IR, and volume-limited samples all agree in showing no change of Type 2 fraction with luminosity. X-ray samples do show a change with luminosity; we discuss possible reasons for this discrepancy. We test a very simple picture which produces this Type 2 fraction with minimal assumptions. In this picture, infall from large scales occurs in random directions, but must eventually align with the inner accretion flow, producing a severely warped disk on parsec scales. If the re-alignment is dominated by tilt, with minimal twist, a wide range of covering factors is predicted in individual objects, but with an expected mean fraction of Type 2 AGNs of exactly 50%. This 'tilted disk' picture predicts reasonable alignment of observed nuclear structures on average, but with distinct misalignments in individual cases. Initial case studies of the few well-resolved objects show that such misalignments are indeed present.

  12. Measures of gamma rays between 0,3 MeV and 3,0 MeV and of the 0,511 MeV annihilation line coming from Galactic Center Region

    International Nuclear Information System (INIS)

    Jardim, M.V.A.

    1982-04-01

    The detection of the flux of the electron-positron annihilation line coming from the Galactic Center direction allows one to estimate the rate of positrons production and the corresponding luminosity. The results of measurements of the annihilation line flux intensity at 0.511 MeV, obtained with a balloon borne experiment to measure gamma rays in the energy interval 0.3 to 3 MeV are presented. The detector looked at the galactic disk in the longitude interval -31 0 0 and observed a flux intensity of (6.70 +- 0.85) x 10 -3 photons cm -2 s -1 , which is in good agreement with the flux value estimated assuming that the Galactic Center is a line source emitting uniformly. Some likely sources of positrons and annhilation regions are also discussed. The results for the continuum spectrum emitted from the Galactic Center in the energy interval 0.3 to 0.67 MeV are presented and compared with measurements had already made. (Author) [pt

  13. Simulating the Growth of a Disk Galaxy and its Supermassive Black Hole in a Cosmological Simulating the Growth of a Disk Galaxy and its Supermassive Black Hole in a Cosmological Context

    International Nuclear Information System (INIS)

    Levine, Robyn Deborah; JILA, Boulder

    2008-01-01

    Supermassive black holes (SMBHs) are ubiquitous in the centers of galaxies. Their formation and subsequent evolution is inextricably linked to that of their host galaxies, and the study of galaxy formation is incomplete without the inclusion of SMBHs. The present work seeks to understand the growth and evolution of SMBHs through their interaction with the host galaxy and its environment. In the first part of the thesis (Chap. 2 and 3), we combine a simple semi-analytic model of outflows from active galactic nuclei (AGN) with a simulated dark matter density distribution to study the impact of SMBH feedback on cosmological scales. We find that constraints can be placed on the kinetic efficiency of such feedback using observations of the filling fraction of the Lyα forest. We also find that AGN feedback is energetic enough to redistribute baryons over cosmological distances, having potentially significant effects on the interpretation of cosmological data which are sensitive to the total matter density distribution (e.g. weak lensing). However, truly assessing the impact of AGN feedback in the universe necessitates large-dynamic range simulations with extensive treatment of baryonic physics to first model the fueling of SMBHs. In the second part of the thesis (Chap. 4-6) we use a hydrodynamic adaptive mesh refinement simulation to follow the growth and evolution of a typical disk galaxy hosting a SMBH, in a cosmological context. The simulation covers a dynamical range of 10 million allowing us to study the transport of matter and angular momentum from super-galactic scales all the way down to the outer edge of the accretion disk around the SMBH. Focusing our attention on the central few hundred parsecs of the galaxy, we find the presence of a cold, self-gravitating, molecular gas disk which is globally unstable. The global instabilities drive super-sonic turbulence, which maintains local stability and allows gas to fuel a SMBH without first fragmenting completely

  14. A possible origin of viscosity in Keplerian accretion disks due to secondary perturbation: Turbulent transport without magnetic fields

    International Nuclear Information System (INIS)

    Mukhopadhyay, Banibrata; Saha, Kanak

    2011-01-01

    The origin of hydrodynamic turbulence in rotating shear flow is a long standing puzzle. Resolving it is especially important in astrophysics when the flow's angular momentum profile is Keplerian which forms an accretion disk having negligible molecular viscosity. Hence, any viscosity in such systems must be due to turbulence, arguably governed by magnetorotational instability, especially when temperature T > or approx. 10 5 . However, such disks around quiescent cataclysmic variables, protoplanetary and star-forming disks, and the outer regions of disks in active galactic nuclei are practically neutral in charge because of their low temperature, and thus are not expected to be coupled with magnetic fields enough to generate any transport due to the magnetorotational instability. This flow is similar to plane Couette flow including the Coriolis force, at least locally. What drives their turbulence and then transport, when such flows do not exhibit any unstable mode under linear hydrodynamic perturbation? We demonstrate that the three-dimensional secondary disturbance to the primarily perturbed flow that triggers elliptical instability may generate significant turbulent viscosity in the range 0.0001 ∼ t ∼< 0.1, which can explain transport in accretion flows.

  15. Revisiting galactic black hole binary GX 339-4 by using 2007 – 2014 Swift XRT observations

    International Nuclear Information System (INIS)

    Azizi, Febrie Ahmad; Vierdayanti, Kiki; Putra, Mahasena

    2015-01-01

    This work aims to study the X-ray properties of the galactic black hole binary GX 339-4. Focus of the study is on exploration of data from Swift-XRT in exclusively photon-counting mode. We use data from 2007 up to August 2014, which contain about 40 pointing observations with level 1 data. The flux of GX 339-4 varies in a factor of 100 during this period of observations. For the purpose of this work, we also try to develop a system to conduct standard SWIFT XRT data reduction automatically, in order to greatly reduce time when working with data bulk, which produces images, lightcurves as well as spectra. We also develop another system to conduct fitting of bulk spectral data with a two-component model, disk blackbody and power-law. The fitting results show that no data have a reduced chi-squared > 2. The fraction of the disk to total flux and the power-law to total flux range from 0.00389 – 0.994 and 0.00605 – 0.996, respectively. From the analysis of the disk component, we obtain the value of the innermost disk radius that does not show any large scale truncation which is in a good agreement with a previous study that used 2007 – 2011 Swift-XRT data, indicating that the systems we developed work properly

  16. THE DATA REDUCTION PIPELINE FOR THE APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT

    International Nuclear Information System (INIS)

    Nidever, David L.; Holtzman, Jon A.; Prieto, Carlos Allende; Mészáros, Szabolcs; Beland, Stephane; Bender, Chad; Desphande, Rohit; Bizyaev, Dmitry; Burton, Adam; García Pérez, Ana E.; Hearty, Fred R.; Majewski, Steven R.; Skrutskie, Michael F.; Sobeck, Jennifer S.; Wilson, John C.; Fleming, Scott W.; Muna, Demitri; Nguyen, Duy; Schiavon, Ricardo P.; Shetrone, Matthew

    2015-01-01

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, explores the stellar populations of the Milky Way using the Sloan 2.5-m telescope linked to a high resolution (R ∼ 22,500), near-infrared (1.51–1.70 μm) spectrograph with 300 optical fibers. For over 150,000 predominantly red giant branch stars that APOGEE targeted across the Galactic bulge, disks and halo, the collected high signal-to-noise ratio (>100 per half-resolution element) spectra provide accurate (∼0.1 km s −1 ) RVs, stellar atmospheric parameters, and precise (≲0.1 dex) chemical abundances for about 15 chemical species. Here we describe the basic APOGEE data reduction software that reduces multiple 3D raw data cubes into calibrated, well-sampled, combined 1D spectra, as implemented for the SDSS-III/APOGEE data releases (DR10, DR11 and DR12). The processing of the near-IR spectral data of APOGEE presents some challenges for reduction, including automated sky subtraction and telluric correction over a 3°-diameter field and the combination of spectrally dithered spectra. We also discuss areas for future improvement

  17. THE DATA REDUCTION PIPELINE FOR THE APACHE POINT OBSERVATORY GALACTIC EVOLUTION EXPERIMENT

    Energy Technology Data Exchange (ETDEWEB)

    Nidever, David L. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Holtzman, Jon A. [New Mexico State University, Las Cruces, NM 88003 (United States); Prieto, Carlos Allende; Mészáros, Szabolcs [Instituto de Astrofísica de Canarias, Via Láctea s/n, E-38205 La Laguna, Tenerife (Spain); Beland, Stephane [Laboratory for Atmospheric and Space Sciences, University of Colorado at Boulder, Boulder, CO (United States); Bender, Chad; Desphande, Rohit [Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802 (United States); Bizyaev, Dmitry [Apache Point Observatory and New Mexico State University, P.O. Box 59, sunspot, NM 88349-0059 (United States); Burton, Adam; García Pérez, Ana E.; Hearty, Fred R.; Majewski, Steven R.; Skrutskie, Michael F.; Sobeck, Jennifer S.; Wilson, John C. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Fleming, Scott W. [Computer Sciences Corporation, 3700 San Martin Dr, Baltimore, MD 21218 (United States); Muna, Demitri [Department of Astronomy and the Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States); Nguyen, Duy [Department of Astronomy and Astrophysics, University of Toronto, Toronto, Ontario, M5S 3H4 (Canada); Schiavon, Ricardo P. [Gemini Observatory, 670 N. A’Ohoku Place, Hilo, HI 96720 (United States); Shetrone, Matthew, E-mail: dnidever@umich.edu [University of Texas at Austin, McDonald Observatory, Fort Davis, TX 79734 (United States)

    2015-12-15

    The Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, explores the stellar populations of the Milky Way using the Sloan 2.5-m telescope linked to a high resolution (R ∼ 22,500), near-infrared (1.51–1.70 μm) spectrograph with 300 optical fibers. For over 150,000 predominantly red giant branch stars that APOGEE targeted across the Galactic bulge, disks and halo, the collected high signal-to-noise ratio (>100 per half-resolution element) spectra provide accurate (∼0.1 km s{sup −1}) RVs, stellar atmospheric parameters, and precise (≲0.1 dex) chemical abundances for about 15 chemical species. Here we describe the basic APOGEE data reduction software that reduces multiple 3D raw data cubes into calibrated, well-sampled, combined 1D spectra, as implemented for the SDSS-III/APOGEE data releases (DR10, DR11 and DR12). The processing of the near-IR spectral data of APOGEE presents some challenges for reduction, including automated sky subtraction and telluric correction over a 3°-diameter field and the combination of spectrally dithered spectra. We also discuss areas for future improvement.

  18. NEAR-INFRARED REVERBERATION BY DUSTY CLUMPY TORI IN ACTIVE GALACTIC NUCLEI

    International Nuclear Information System (INIS)

    Kawaguchi, Toshihiro; Mori, Masao

    2011-01-01

    According to recent models, the accretion disk and black hole in active galactic nuclei (AGNs) are surrounded by a clumpy torus. We investigate the NIR flux variation of the torus in response to a UV flash for various geometries. Anisotropic illumination by the disk and the torus self-occultation contrast our study with earlier works. Both the waning effect of each clump and the torus self-occultation selectively reduce the emission from the region with a short delay. Therefore, the NIR delay depends on the viewing angle (where a more inclined angle leads to a longer delay), and the time response shows an asymmetric profile with negative skewness, opposing the results for optically thin tori. The range of the computed delay coincides with the observed one, suggesting that the viewing angle is primarily responsible for the scatter of the observed delay. We also propose that the red NIR-to-optical color of type 1.8/1.9 objects is caused not only by the dust extinction but also the intrinsically red color. Compared with the modest torus thickness, both a thick and a thin tori display weaker NIR emission. A selection bias is thus expected such that NIR-selected AGNs tend to possess moderately thick tori. A thicker torus shows a narrower and more heavily skewed time profile, while a thin torus produces a rapid response. A super-Eddington accretion rate leads to much weaker NIR emission due to the disk self-occultation and the disk truncation by self-gravity. A long delay is expected from an optically thin and/or a largely misaligned torus. Very weak NIR emission, such as in hot-dust-poor active nuclei, can arise from a geometrically thin torus, a super-Eddington accretion rate, or a slightly misaligned torus.

  19. Strong Support for the Millisecond Pulsar Origin of the Galactic Center GeV Excess.

    Science.gov (United States)

    Bartels, Richard; Krishnamurthy, Suraj; Weniger, Christoph

    2016-02-05

    Using γ-ray data from the Fermi Large Area Telescope, various groups have identified a clear excess emission in the Inner Galaxy, at energies around a few GeV. This excess resembles remarkably well a signal from dark-matter annihilation. One of the most compelling astrophysical interpretations is that the excess is caused by the combined effect of a previously undetected population of dim γ-ray sources. Because of their spectral similarity, the best candidates are millisecond pulsars. Here, we search for this hypothetical source population, using a novel approach based on wavelet decomposition of the γ-ray sky and the statistics of Gaussian random fields. Using almost seven years of Fermi-LAT data, we detect a clustering of photons as predicted for the hypothetical population of millisecond pulsar, with a statistical significance of 10.0σ. For plausible values of the luminosity function, this population explains 100% of the observed excess emission. We argue that other extragalactic or Galactic sources, a mismodeling of Galactic diffuse emission, or the thick-disk population of pulsars are unlikely to account for this observation.

  20. Identifying Likely Disk-hosting M dwarfs with Disk Detective

    Science.gov (United States)

    Silverberg, Steven; Wisniewski, John; Kuchner, Marc J.; Disk Detective Collaboration

    2018-01-01

    M dwarfs are critical targets for exoplanet searches. Debris disks often provide key information as to the formation and evolution of planetary systems around higher-mass stars, alongside the planet themselves. However, less than 300 M dwarf debris disks are known, despite M dwarfs making up 70% of the local neighborhood. The Disk Detective citizen science project has identified over 6000 new potential disk host stars from the AllWISE catalog over the past three years. Here, we present preliminary results of our search for new disk-hosting M dwarfs in the survey. Based on near-infrared color cuts and fitting stellar models to photometry, we have identified over 500 potential new M dwarf disk hosts, nearly doubling the known number of such systems. In this talk, we present our methodology, and outline our ongoing work to confirm systems as M dwarf disks.

  1. ALMA Survey of Lupus Protoplanetary Disks. II. Gas Disk Radii

    Science.gov (United States)

    Ansdell, M.; Williams, J. P.; Trapman, L.; van Terwisga, S. E.; Facchini, S.; Manara, C. F.; van der Marel, N.; Miotello, A.; Tazzari, M.; Hogerheijde, M.; Guidi, G.; Testi, L.; van Dishoeck, E. F.

    2018-05-01

    We present Atacama Large Millimeter/Sub-Millimeter Array (ALMA) Band 6 observations of a complete sample of protoplanetary disks in the young (∼1–3 Myr) Lupus star-forming region, covering the 1.33 mm continuum and the 12CO, 13CO, and C18O J = 2–1 lines. The spatial resolution is ∼0.″25 with a medium 3σ continuum sensitivity of 0.30 mJy, corresponding to M dust ∼ 0.2 M ⊕. We apply Keplerian masking to enhance the signal-to-noise ratios of our 12CO zero-moment maps, enabling measurements of gas disk radii for 22 Lupus disks; we find that gas disks are universally larger than millimeter dust disks by a factor of two on average, likely due to a combination of the optically thick gas emission and the growth and inward drift of the dust. Using the gas disk radii, we calculate the dimensionless viscosity parameter, α visc, finding a broad distribution and no correlations with other disk or stellar parameters, suggesting that viscous processes have not yet established quasi-steady states in Lupus disks. By combining our 1.33 mm continuum fluxes with our previous 890 μm continuum observations, we also calculate the millimeter spectral index, α mm, for 70 Lupus disks; we find an anticorrelation between α mm and millimeter flux for low-mass disks (M dust ≲ 5), followed by a flattening as disks approach α mm ≈ 2, which could indicate faster grain growth in higher-mass disks, but may also reflect their larger optically thick components. In sum, this work demonstrates the continuous stream of new insights into disk evolution and planet formation that can be gleaned from unbiased ALMA disk surveys.

  2. Review of the fermionic dark matter model applied to galactic structures

    Science.gov (United States)

    Krut, A.; Argüelles, C. R.; Rueda, J.; Ruffini, R.

    2015-12-01

    Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion) is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.

  3. Review of the fermionic dark matter model applied to galactic structures

    Energy Technology Data Exchange (ETDEWEB)

    Krut, A. [Dipartimento di Fisica, Sapienza Università di Roma, P.le Aldo Moro 5, I–00185 Rome (Italy); Argüelles, C. R. [ICRANet, P.zza della Repubblica 10, I-65122 Pescara (Italy); Rueda, J.; Ruffini, R. [Dipartimento di Fisica, Sapienza Università di Roma, P.le Aldo Moro 5, I–00185 Rome (Italy); ICRANet, P.zza della Repubblica 10, I-65122 Pescara (Italy)

    2015-12-17

    Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion) is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.

  4. THICK-DISK EVOLUTION INDUCED BY THE GROWTH OF AN EMBEDDED THIN DISK

    International Nuclear Information System (INIS)

    Villalobos, Alvaro; Helmi, Amina; Kazantzidis, Stelios

    2010-01-01

    We perform collisionless N-body simulations to investigate the evolution of the structural and kinematical properties of simulated thick disks induced by the growth of an embedded thin disk. The thick disks used in the present study originate from cosmologically common 5:1 encounters between initially thin primary disk galaxies and infalling satellites. The growing thin disks are modeled as static gravitational potentials and we explore a variety of growing-disk parameters that are likely to influence the response of thick disks. We find that the final thick-disk properties depend strongly on the total mass and radial scale length of the growing thin disk, and much less sensitively on its growth timescale and vertical scale height as well as the initial sense of thick-disk rotation. Overall, the growth of an embedded thin disk can cause a substantial contraction in both the radial and vertical direction, resulting in a significant decrease in the scale lengths and scale heights of thick disks. Kinematically, a growing thin disk can induce a notable increase in the mean rotation and velocity dispersions of thick-disk stars. We conclude that the reformation of a thin disk via gas accretion may play a significant role in setting the structure and kinematics of thick disks, and thus it is an important ingredient in models of thick-disk formation.

  5. The galactic distribution of pulsars

    International Nuclear Information System (INIS)

    Lyne, A.G.

    1981-01-01

    The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the galactic plane due to high space velocities imparted to the pulsars at birth. The evidence for this model is described and the various factors involved in estimating the total galactic population and the galactic birthrate of pulsars are discussed. The various estimates of the galactic population which cluster around 5 x 10 5 are seen to be critically dependent upon the cut-off at low luminosities and upon the value of the mean electron density within 500 pc of the Earth. Estimates of the lifetimes of pulsars are available from both the characteristic ages and proper motion measurements and both give values of about 5 million years. The implied birthrate of one in every 10 years is barely compatible with most estimates of the galactic supernova rate. (Auth.)

  6. THE CHEMICAL ABUNDANCES IN THE GALACTIC CENTER FROM THE ATMOSPHERES OF RED SUPERGIANTS

    International Nuclear Information System (INIS)

    Davies, Ben; Figer, Don F.; Origlia, Livia; Kudritzki, Rolf-Peter; Rich, R. Michael; Najarro, Francisco

    2009-01-01

    The Galactic center (GC) has experienced a high degree of recent star-forming activity, as evidenced by the large number of massive stars currently residing there. The relative abundances of chemical elements in the GC may provide insights into the origins of this activity. Here, we present high-resolution H-band spectra of two red supergiants (RSGs) in the GC (IRS 7 and VR 5-7), and in combination with spectral synthesis we derive abundances for Fe and C, as well as other α-elements Ca, Si, Mg Ti, and O. We find that the C depletion in VR 5-7 is consistent with the predictions of evolutionary models of RSGs, while the heavy depletion of C and O in IRS 7's atmosphere is indicative of deep mixing, possibly due to fast initial rotation and/or enhanced mass loss. Our results indicate that the current surface Fe/H content of each star is slightly above solar. However, comparisons to evolutionary models indicate that the initial Fe-to-H ratio was likely closer to solar, and has been driven higher by H depletion at the stars' surface. Overall, we find α-to-Fe ratios for both stars, which are consistent with the thin Galactic disk. These results are consistent with other chemical studies of the GC, given the precision to which abundances can currently be determined. We argue that the GC abundances are consistent with a scenario in which the recent star-forming activity in the GC was fueled by either material traveling down the Bar from the inner disk, or from the winds of stars in the inner bulge-with no need to invoke top-heavy stellar initial mass functions to explain anomalous abundance ratios.

  7. Analysis Of Ultra Compact Ionized Hydrogen Regions Within The Northern Half Of The Galactic Disk

    Science.gov (United States)

    Bruce, John

    2011-01-01

    From a catalog of 199 candidate ultra compact (UC) HII regions 123 sources included in the the intersection of the GLIMPSE (8 μm),Cornish (6 cm), and Bolocam ( 1.1 mm) galactic plane surveys (BGPS) were analyzed. The sources were sorted based on 6 cm morphology and coincidence with 8 μm bubbles. The 1.1 mm flux attributes were measured and calculations were performed to determine the ionized hydrogen contributions to the 1.1 mm flux. The category averages and frequencies were obtained as well. Significant differences in HII percentages were present among the morphology groups but ranged widely, without apparent distinction, between the bubble forming and triggered source categories.

  8. ISOTROPIC HEATING OF GALAXY CLUSTER CORES VIA RAPIDLY REORIENTING ACTIVE GALACTIC NUCLEUS JETS

    International Nuclear Information System (INIS)

    Babul, Arif; Sharma, Prateek; Reynolds, Christopher S.

    2013-01-01

    Active galactic nucleus (AGN) jets carry more than sufficient energy to stave off catastrophic cooling of the intracluster medium (ICM) in the cores of cool-core clusters. However, in order to prevent catastrophic cooling, the ICM must be heated in a near-isotropic fashion and narrow bipolar jets with P jet = 10 44–45 erg s –1 , typical of radio AGNs at cluster centers, are inefficient in heating the gas in the transverse direction to the jets. We argue that due to existent conditions in cluster cores, the supermassive black holes (SMBHs) will, in addition to accreting gas via radiatively inefficient flows, experience short stochastic episodes of enhanced accretion via thin disks. In general, the orientation of these accretion disks will be misaligned with the spin axis of the black holes (BHs) and the ensuing torques will cause the BH's spin axis (and therefore the jet axis) to slew and rapidly change direction. This model not only explains recent observations showing successive generations of jet-lobes-bubbles in individual cool-core clusters that are offset from each other in the angular direction with respect to the cluster center, but also shows that AGN jets can heat the cluster core nearly isotropically on the gas cooling timescale. Our model does require that the SMBHs at the centers of cool-core clusters be spinning relatively slowly. Torques from individual misaligned disks are ineffective at tilting rapidly spinning BHs by more than a few degrees. Additionally, since SMBHs that host thin accretion disks will manifest as quasars, we predict that roughly 1-2 rich clusters within z < 0.5 should have quasars at their centers.

  9. The Mass-dependent Star Formation Histories of Disk Galaxies: Infall Model Versus Observations

    Science.gov (United States)

    Chang, R. X.; Hou, J. L.; Shen, S. Y.; Shu, C. G.

    2010-10-01

    We introduce a simple model to explore the star formation histories of disk galaxies. We assume that the disk originate and grows by continuous gas infall. The gas infall rate is parameterized by the Gaussian formula with one free parameter: the infall-peak time tp . The Kennicutt star formation law is adopted to describe how much cold gas turns into stars. The gas outflow process is also considered in our model. We find that, at a given galactic stellar mass M *, the model adopting a late infall-peak time tp results in blue colors, low-metallicity, high specific star formation rate (SFR), and high gas fraction, while the gas outflow rate mainly influences the gas-phase metallicity and star formation efficiency mainly influences the gas fraction. Motivated by the local observed scaling relations, we "construct" a mass-dependent model by assuming that the low-mass galaxy has a later infall-peak time tp and a larger gas outflow rate than massive systems. It is shown that this model can be in agreement with not only the local observations, but also with the observed correlations between specific SFR and galactic stellar mass SFR/M * ~ M * at intermediate redshifts z < 1. Comparison between the Gaussian-infall model and the exponential-infall model is also presented. It shows that the exponential-infall model predicts a higher SFR at early stage and a lower SFR later than that of Gaussian infall. Our results suggest that the Gaussian infall rate may be more reasonable in describing the gas cooling process than the exponential infall rate, especially for low-mass systems.

  10. HERSCHEL SURVEY OF GALACTIC OH{sup +}, H{sub 2}O{sup +}, AND H{sub 3}O{sup +}: PROBING THE MOLECULAR HYDROGEN FRACTION AND COSMIC-RAY IONIZATION RATE

    Energy Technology Data Exchange (ETDEWEB)

    Indriolo, Nick; Neufeld, D. A. [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Gerin, M.; Falgarone, E. [LERMA, Observatoire de Paris, Ecole Normale Supérieure, PSL Research University, CNRS, UMR8112, F-75014 Paris (France); Schilke, P.; Chambers, E. T.; Ossenkopf, V. [I. Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln (Germany); Benz, A. O. [Institute of Astronomy, ETH Zürich (Switzerland); Winkel, B.; Menten, K. M. [MPI für Radioastronomie, Bonn (Germany); Black, John H.; Persson, C. M. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala (Sweden); Bruderer, S.; Van Dishoeck, E. F. [Max Planck Institut für Extraterrestrische Physik, Garching (Germany); Godard, B.; Lis, D. C. [Sorbonne Universités, UPMC Univ. Paris 06, UMR8112, LERMA, F-75005 Paris (France); Goicoechea, J. R. [Instituto de Ciencias de Materiales de Madrid (CSIC), E-28049 Cantoblanco, Madrid (Spain); Gupta, H. [California Institute of Technology, Pasadena, CA 91125 (United States); Sonnentrucker, P. [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Van der Tak, F. F. S. [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen (Netherlands); and others

    2015-02-10

    In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH{sup +}, H{sub 2}O{sup +}, and H{sub 3}O{sup +} begins with the ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H{sub 2}. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray ionization rate of atomic hydrogen (ζ{sub H}) and molecular hydrogen fraction (f{sub H{sub 2}}). We present observations targeting transitions of OH{sup +}, H{sub 2}O{sup +}, and H{sub 3}O{sup +} made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH{sup +} and H{sub 2}O{sup +} are detected in absorption in multiple velocity components along every sight line, but H{sub 3}O{sup +} is only detected along 7 sight lines. From the molecular abundances we compute f{sub H{sub 2}} in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH{sup +} and H{sub 2}O{sup +} primarily reside in gas with low H{sub 2} fractions. We also infer ζ{sub H} throughout our sample, and find a lognormal distribution with mean log (ζ{sub H}) = –15.75 (ζ{sub H} = 1.78 × 10{sup –16} s{sup –1}) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray ionization rates previously inferred from H{sub 3}{sup +} observations. Ionization rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.

  11. Mass Distribution in Rotating Thin-Disk Galaxies According to Newtonian Dynamics

    Directory of Open Access Journals (Sweden)

    James Q. Feng

    2014-04-01

    Full Text Available An accurate computational method is presented for determining the mass distribution in a mature spiral galaxy from a given rotation curve by applying Newtonian dynamics for an axisymmetrically rotating thin disk of finite size with or without a central spherical bulge. The governing integral equation for mass distribution is transformed via a boundary-element method into a linear algebra matrix equation that can be solved numerically for rotation curves with a wide range of shapes. To illustrate the effectiveness of this computational method, mass distributions in several mature spiral galaxies are determined from their measured rotation curves. All the surface mass density profiles predicted by our model exhibit approximately a common exponential law of decay, quantitatively consistent with the observed surface brightness distributions. When a central spherical bulge is present, the mass distribution in the galaxy is altered in such a way that the periphery mass density is reduced, while more mass appears toward the galactic center. By extending the computational domain beyond the galactic edge, we can determine the rotation velocity outside the cut-off radius, which appears to continuously decrease and to gradually approach the Keplerian rotation velocity out over twice the cut-off radius. An examination of circular orbit stability suggests that galaxies with flat or rising rotation velocities are more stable than those with declining rotation velocities especially in the region near the galactic edge. Our results demonstrate the fact that Newtonian dynamics can be adequate for describing the observed rotation behavior of mature spiral galaxies.

  12. Investigating SLIM Disk Solutions FOR HLX-1 IN ESO 243-49

    Science.gov (United States)

    Godet, O.; Plazolles, B.; Kawaguchi, T.; Lasota, J.-P; Barret, d.; Farrell, S. A.; Braito, V.; Servillat, M.; Webb, N.; Gehrels, N.

    2012-01-01

    The hyperluminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate-mass blackhole (BH) candidate, displays spectral transitions similar to those observed in Galactic BH binaries, but with aluminosity 100-1000 times higher. We investigated the X-ray properties of this unique source by fitting multiepochdata collected by Swift, XMM-Newton, and Chandra with a disk model computing spectra for a wide rangeof sub- and super-Eddington accretion rates assuming a non-spinning BH and a face-on disk (i=0 deg.). Under theseassumptions we find that the BH in HLX-1 is in the intermediate-mass range (approximately 2 x 10(exp 4) solar mass) and the accretionflow is in the sub-Eddington regime. The disk radiation efficiency is eta = 0.11 plus or minus 0.03. We also show that the source does follow the LX is proportional to T(exp 4) relation for our mass estimate. At the outburst peaks, the source radiates near the Eddington limit. The accretion rate then stays constant around 4 x 10(exp 4) solar mass yr (sup -1) for several days and then decreases exponentially. Such plateaus in the accretion rate could be evidence that enhanced mass-transfer rateis the driving outburst mechanism in HLX-1. We also report on the new outburst observed in 2011 August by theSwift X-Ray Telescope. The time of this new outburst further strengthens the approximately 1 year recurrence timescale.

  13. VERITAS Galactic Observations

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, Gareth

    2013-06-15

    We report on recent Galactic results and discoveries made by the VERITAS collaboration. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based gamma-ray observatory, located in southern Arizona, able to detect gamma rays of energies from 100 GeV up to 30 TeV. VERITAS has been fully operational since 2007 and its current sensitivity enables the detection of a 1% Crab Nebula flux at 5 sigma in under 30 hours. The observatory is well placed to view large parts of the galactic plane including its center, resulting in a strong galactic program. Objects routinely observed include Pulsars, Pulsar Wind Nebula, X-ray binaries and sources with unidentified counterparts in other wavelengths.

  14. SDP_wlanger_3: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

    Science.gov (United States)

    Langer, W.

    2011-09-01

    Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

  15. KPOT_wlanger_1: State of the Diffuse ISM: Galactic Observations of the Terahertz CII Line (GOT CPlus)

    Science.gov (United States)

    Langer, W.

    2007-10-01

    Star formation activity throughout the Galactic disk depends on the thermal and dynamical state of the interstellar gas, which in turn depends on heating and cooling rates, modulated by the gravitational potential and shock and turbulent pressures. Molecular cloud formation, and thus the star formation, may be regulated by pressures in the interstellar medium (ISM). To understand these processes we need information about the properties of the diffuse atomic and diffuse molecular gas clouds, and Photon Dominated Regions (PDR). An important tracer of these regions is the CII line at 158 microns (1900.5 GHz). We propose a "pencil-beam" survey of CII with HIFI band 7b, based on deep integrations and systematic sparse sampling of the Galactic disk plus selected targets, totaling over 900 lines of sight. We will detect both emission and, against the bright inner Galaxy and selected continuum sources, absorption lines. These spectra will provide the astronomical community with a large rich statistical database of the diffuse cloud properties throughout the Galaxy for understanding the Milky Way ISM and, by extension, other galaxies. It will be extremely valuable for determining the properties of the atomic gas, the role of barometric pressure and turbulence in cloud evolution, and the properties of the interface between the atomic and molecular clouds. The CII line is one of the major ISM cooling lines and is present throughout the Galactic plane. It is the strongest far-IR emission line in the Galaxy, with a total luminosity about a 1000 times that of the CO J=1-0 line. Combined with other data, it can be used to determine density, pressure, and radiation environment in gas clouds, and PDRs, and their dynamics via velocity fields. HSO is the best opportunity over the next several years to probe the ISM in this tracer and will provide a template for large-scale surveys with dedicated small telescopes and future surveys of other important ISM tracers.

  16. Particle Dark Matter constraints: the effect of Galactic uncertainties

    Energy Technology Data Exchange (ETDEWEB)

    Benito, Maria; Bernal, Nicolás; Iocco, Fabio [ICTP South American Institute for Fundamental Research Instituto de Física Teórica - Universidade Estadual Paulista (UNESP) Rua Dr. Bento Teobaldo Ferraz 271, 01140-070 São Paulo, SP Brazil (Brazil); Bozorgnia, Nassim; Calore, Francesca, E-mail: mariabenitocst@gmail.com, E-mail: nicolas.bernal@uan.edu.co, E-mail: n.bozorgnia@uva.nl, E-mail: calore@lapth.cnrs.fr, E-mail: fabio.iocco.astro@gmail.com [GRAPPA Institute, Institute for Theoretical Physics Amsterdam and Delta Institute for Theoretical Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)

    2017-02-01

    Collider, space, and Earth based experiments are now able to probe several extensions of the Standard Model of particle physics which provide viable dark matter candidates. Direct and indirect dark matter searches rely on inputs of astrophysical nature, such as the local dark matter density or the shape of the dark matter density profile in the target in object. The determination of these quantities is highly affected by astrophysical uncertainties. The latter, especially those for our own Galaxy, are ill-known, and often not fully accounted for when analyzing the phenomenology of particle physics models. In this paper we present a systematic, quantitative estimate of how astrophysical uncertainties on Galactic quantities (such as the local galactocentric distance, circular velocity, or the morphology of the stellar disk and bulge) propagate to the determination of the phenomenology of particle physics models, thus eventually affecting the determination of new physics parameters. We present results in the context of two specific extensions of the Standard Model (the Singlet Scalar and the Inert Doublet) that we adopt as case studies for their simplicity in illustrating the magnitude and impact of such uncertainties on the parameter space of the particle physics model itself. Our findings point toward very relevant effects of current Galactic uncertainties on the determination of particle physics parameters, and urge a systematic estimate of such uncertainties in more complex scenarios, in order to achieve constraints on the determination of new physics that realistically include all known uncertainties.

  17. DUST TRANSPORT IN PROTOSTELLAR DISKS THROUGH TURBULENCE AND SETTLING

    International Nuclear Information System (INIS)

    Turner, N. J.; Carballido, A.; Sano, T.

    2010-01-01

    We apply ionization balance and magnetohydrodynamical (MHD) calculations to investigate whether magnetic activity moderated by recombination on dust grains can account for the mass accretion rates and the mid-infrared spectra and variability of protostellar disks. The MHD calculations use the stratified shearing-box approach and include grain settling and the feedback from the changing dust abundance on the resistivity of the gas. The two-decade spread in accretion rates among solar-mass T Tauri stars is too large to result solely from variations in the grain size and stellar X-ray luminosity, but can plausibly be produced by varying these parameters together with the disk magnetic flux. The diverse shapes and strengths of the mid-infrared silicate bands can come from the coupling of grain settling to the distribution of the magnetorotational turbulence, through the following three effects. First, recombination on grains 1 μm or smaller yields a magnetically inactive dead zone extending more than two scale heights from the midplane, while turbulent motions in the magnetically active disk atmosphere overshoot the dead zone boundary by only about one scale height. Second, grains deep in the dead zone oscillate vertically in wave motions driven by the turbulent layer above, but on average settle at the rates found in laminar flow, so that the interior of the dead zone is a particle sink and the disk atmosphere will become dust-depleted unless resupplied from elsewhere. Third, with sufficient depletion, the dead zone is thinner and mixing dredges grains off the midplane. The last of these processes enables evolutionary signatures such as the degree of settling to sometimes decrease with age. The MHD results also show that the magnetic activity intermittently lifts clouds of small grains into the atmosphere. Consequently the photosphere height changes by up to one-third over timescales of a few orbits, while the extinction along lines of sight grazing the disk surface

  18. Magnetically Induced Disk Winds and Transport in the HL Tau Disk

    International Nuclear Information System (INIS)

    Hasegawa, Yasuhiro; Flock, Mario; Turner, Neal J.; Okuzumi, Satoshi

    2017-01-01

    The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β 0 ≃ 2 × 10 4 under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

  19. Magnetically Induced Disk Winds and Transport in the HL Tau Disk

    Energy Technology Data Exchange (ETDEWEB)

    Hasegawa, Yasuhiro; Flock, Mario; Turner, Neal J. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Okuzumi, Satoshi, E-mail: yasuhiro@caltech.edu [Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551 (Japan)

    2017-08-10

    The mechanism of angular momentum transport in protoplanetary disks is fundamental to understanding the distributions of gas and dust in the disks. The unprecedented ALMA observations taken toward HL Tau at high spatial resolution and subsequent radiative transfer modeling reveal that a high degree of dust settling is currently achieved in the outer part of the HL Tau disk. Previous observations, however, suggest a high disk accretion rate onto the central star. This configuration is not necessarily intuitive in the framework of the conventional viscous disk model, since efficient accretion generally requires a high level of turbulence, which can suppress dust settling considerably. We develop a simplified, semi-analytical disk model to examine under what condition these two properties can be realized in a single model. Recent, non-ideal MHD simulations are utilized to realistically model the angular momentum transport both radially via MHD turbulence and vertically via magnetically induced disk winds. We find that the HL Tau disk configuration can be reproduced well when disk winds are properly taken into account. While the resulting disk properties are likely consistent with other observational results, such an ideal situation can be established only if the plasma β at the disk midplane is β {sub 0} ≃ 2 × 10{sup 4} under the assumption of steady accretion. Equivalently, the vertical magnetic flux at 100 au is about 0.2 mG. More detailed modeling is needed to fully identify the origin of the disk accretion and quantitatively examine plausible mechanisms behind the observed gap structures in the HL Tau disk.

  20. EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS

    International Nuclear Information System (INIS)

    Cleeves, L. Ilsedore; Adams, Fred C.; Bergin, Edwin A.

    2013-01-01

    Cosmic rays (CRs) are thought to provide an important source of ionization in the outermost and densest regions of protoplanetary disks; however, it is unknown to what degree they are physically present. As is observed in the solar system, stellar winds can inhibit the propagation of CRs within the circumstellar environment and subsequently into the disk. In this work, we explore the hitherto neglected effects of CR modulation by both stellar winds and magnetic field structures and study how these processes act to reduce disk ionization rates. We construct a two-dimensional protoplanetary disk model of a T-Tauri star system, focusing on ionization from stellar and interstellar FUV, stellar X-ray photons, and CRs. We show that stellar winds can power a heliosphere-like analog, i.e., a ''T-Tauriosphere,'' diminishing CR ionization rates by several orders of magnitude at low to moderate CR energies (E CR ≤ 1 GeV). We explore models of both the observed solar wind CR modulation and a highly simplified estimate for ''elevated'' CR modulation as would be expected from a young T-Tauri star. In the former (solar analog) case, we estimate the ionization rate from galactic CRs to be ζ CR ∼ (0.23-1.4) × 10 –18 s –1 . This range of values, which we consider to be the maximum CR ionization rate for the disk, is more than an order of magnitude lower than what is generally assumed in current models for disk chemistry and physics. In the latter elevated case, i.e., for a ''T-Tauriosphere,'' the ionization rate by CRs is ζ CR ∼ –20 s –1 , which is 1000 times smaller than the interstellar value. We discuss the implications of a diminished CR ionization rate on the gas physics by estimating the size of the resulting magnetorotational instability dead zones. Indeed, if winds are as efficient at CR modulation as predicted here, short-lived radionuclides (now extinct) would have provided the major source of ionization (ζ RN ∼ 7.3 × 10 –19 s –1 ) in the planet

  1. EXTENDED X-RAY EMISSION IN THE H I CAVITY OF NGC 4151: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK?

    International Nuclear Information System (INIS)

    Wang Junfeng; Fabbiano, Giuseppina; Risaliti, Guido; Elvis, Martin; Zezas, Andreas; Mundell, Carole G.; Dumas, Gaelle; Schinnerer, Eva

    2010-01-01

    We present the Chandra discovery of soft diffuse X-ray emission in NGC 4151 (L 0.5-2 k eV ∼ 10 39 erg s -1 ), extending ∼2 kpc from the active nucleus and filling in the cavity of the H I material. The best fit to the X-ray spectrum requires either a kT ∼ 0.25 keV thermal plasma or a photoionized component. In the thermal scenario, hot gas heated by the nuclear outflow would be confined by the thermal pressure of the H I gas and the dynamic pressure of inflowing neutral material in the galactic disk. In the case of photoionization, the nucleus must have experienced an Eddington limit outburst. For both scenarios, the active galactic nucleus (AGN)-host interaction in NGC 4151 must have occurred relatively recently (some 10 4 yr ago). This very short timescale to the last episode of high activity phase may imply such outbursts occupy ∼>1% of AGN lifetime.

  2. Chemical evolution of the solar neighborhood. II. The age-metallicity relation and the history of star formation in the galactic disk

    International Nuclear Information System (INIS)

    Twarog, B.A.

    1980-01-01

    The age-metallicty relation for the disk in the neighborhood of the Sun is derived from four-color and Hβ photometry of a large sample of southern F dwarfs, analyzed in combination with theoretical isochrones. It is found that the mean metallicity of the disk increased by about a factor of 5 between 12 and 5 billion years ago and has increased only slightly since then; this conclusion is independent of the helium abundance assumed for the models

  3. Strongly baryon-dominated disk galaxies at the peak of galaxy formation ten billion years ago.

    Science.gov (United States)

    Genzel, R; Schreiber, N M Förster; Übler, H; Lang, P; Naab, T; Bender, R; Tacconi, L J; Wisnioski, E; Wuyts, S; Alexander, T; Beifiori, A; Belli, S; Brammer, G; Burkert, A; Carollo, C M; Chan, J; Davies, R; Fossati, M; Galametz, A; Genel, S; Gerhard, O; Lutz, D; Mendel, J T; Momcheva, I; Nelson, E J; Renzini, A; Saglia, R; Sternberg, A; Tacchella, S; Tadaki, K; Wilman, D

    2017-03-15

    In the cold dark matter cosmology, the baryonic components of galaxies-stars and gas-are thought to be mixed with and embedded in non-baryonic and non-relativistic dark matter, which dominates the total mass of the galaxy and its dark-matter halo. In the local (low-redshift) Universe, the mass of dark matter within a galactic disk increases with disk radius, becoming appreciable and then dominant in the outer, baryonic regions of the disks of star-forming galaxies. This results in rotation velocities of the visible matter within the disk that are constant or increasing with disk radius-a hallmark of the dark-matter model. Comparisons between the dynamical mass, inferred from these velocities in rotational equilibrium, and the sum of the stellar and cold-gas mass at the peak epoch of galaxy formation ten billion years ago, inferred from ancillary data, suggest high baryon fractions in the inner, star-forming regions of the disks. Although this implied baryon fraction may be larger than in the local Universe, the systematic uncertainties (owing to the chosen stellar initial-mass function and the calibration of gas masses) render such comparisons inconclusive in terms of the mass of dark matter. Here we report rotation curves (showing rotation velocity as a function of disk radius) for the outer disks of six massive star-forming galaxies, and find that the rotation velocities are not constant, but decrease with radius. We propose that this trend arises because of a combination of two main factors: first, a large fraction of the massive high-redshift galaxy population was strongly baryon-dominated, with dark matter playing a smaller part than in the local Universe; and second, the large velocity dispersion in high-redshift disks introduces a substantial pressure term that leads to a decrease in rotation velocity with increasing radius. The effect of both factors appears to increase with redshift. Qualitatively, the observations suggest that baryons in the early (high

  4. A DISTINCTIVE DISK-JET COUPLING IN THE SEYFERT-1 ACTIVE GALACTIC NUCLEUS NGC 4051

    International Nuclear Information System (INIS)

    King, A. L.; Miller, J. M.; Gueltekin, K.; Reynolds, M. T.; Cackett, E. M.; Fabian, A. C.; Markoff, S.; Nowak, M. A.; Rupen, M.

    2011-01-01

    We report on the results of a simultaneous monitoring campaign employing eight Chandra X-ray (0.5-10 keV) and six Very Large Array/Extended Very Large Array (8.4 GHz) radio observations of NGC 4051 over seven months. Evidence for compact jets is observed in the 8.4 GHz radio band; this builds on mounting evidence that jet production may be prevalent even in radio-quiet Seyferts. Assuming comparatively negligible local diffuse emission in the nucleus, the results also demonstrate an inverse correlation of L radio ∝ L -0.72±0.04 X-ray . If the A configuration is excluded in the case where diffuse emission plays a significant role, the relation is still L radio ∝ L X-ray -0.12±0.05 . Current research linking the mass of supermassive black holes and stellar-mass black holes in the 'low/hard' state to X-ray luminosities and radio luminosities suggests a 'fundamental plane of accretion onto black holes' that has a positive correlation of L radio ∝ L 0.67±0.12 X-ray . Our simultaneous results differ from this relation by more than 11σ (6σ excluding the A configuration), indicating that a separate mode of accretion and ejection may operate in this system. A review of the literature shows that the inverse correlation seen in NGC 4051 is seen in three other black hole systems, all of which accrete at near 10% of their Eddington luminosity, perhaps suggesting a distinct mode of disk-jet coupling at high Eddington fractions. We discuss our results in the context of disks and jets in black holes and accretion across the black hole mass scale.

  5. Feedback by AGN Jets and Wide-angle Winds on a Galactic Scale

    Energy Technology Data Exchange (ETDEWEB)

    Dugan, Zachary; Silk, Joseph [The Johns Hopkins University Department of Physics and Astronomy, Bloomberg Center for Physics and Astronomy, Room 366, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Gaibler, Volker [Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)

    2017-07-20

    To investigate the differences in mechanical feedback from radio-loud and radio-quiet active galactic nuclei on the host galaxy, we perform 3D AMR hydrodynamic simulations of wide-angle, radio-quiet winds with different inclinations on a single, massive, gas-rich disk galaxy at a redshift of 2–3. We compare our results to hydrodynamic simulations of the same galaxy but with a jet. The jet has an inclination of 0° (perpendicular to the galactic plane), and the winds have inclinations of 0°, 45°, and 90°. We analyze the impact on the host’s gas, star formation, and circumgalactic medium. We find that jet feedback is energy-driven and wind feedback is momentum-driven. In all the simulations, the jet or wind creates a cavity mostly devoid of dense gas in the nuclear region where star formation is then quenched, but we find strong positive feedback in all the simulations at radii greater than 3 kpc. All four simulations have similar SFRs and stellar velocities with large radial and vertical components. However, the wind at an inclination of 90° creates the highest density regions through ram pressure and generates the highest rates of star formation due to its ongoing strong interaction with the dense gas of the galactic plane. With increased wind inclination, we find greater asymmetry in gas distribution and resulting star formation. Our model generates an expanding ring of triggered star formation with typical velocities of the order of 1/3 of the circular velocity, superimposed on the older stellar population. This should result in a potentially detectable blue asymmetry in stellar absorption features at kiloparsec scales.

  6. Formation of Tidally Induced Bars in Galactic Flybys: Prograde versus Retrograde Encounters

    Science.gov (United States)

    Łokas, Ewa L.

    2018-04-01

    Bars in disk galaxies can be formed by interactions with other systems, including those of comparable mass. It has long been established that the effect of such interactions on galaxy morphology depends strongly on the orbital configuration, in particular the orientation of the intrinsic spin of the galactic disk with respect to its orbital angular momentum. Prograde encounters modify the morphology strongly, including the formation of tidally induced bars, while retrograde flybys should have little effect on morphology. Recent works on the subject reached conflicting conclusions, one using the impulse approximation and claiming no dependence on this angle in the properties of tidal bars. To resolve the controversy, we performed self-consistent N-body simulations of hyperbolic encounters between two identical Milky Way-like galaxies assuming different velocities and impact parameters, with one of the galaxies on a prograde and the other on a retrograde orbit. The galaxies were initially composed of an exponential stellar disk and an NFW dark halo, and they were stable against bar formation in isolation for 3 Gyr. We find that strong tidally induced bars form only in galaxies on prograde orbits. For smaller impact parameters and lower relative velocities, the bars are stronger and have lower pattern speeds. Stronger bars undergo extended periods of buckling instability that thicken their vertical structure. The encounters also lead to the formation of two-armed spirals with strength inversely proportional to the strength of the bars. We conclude that proper modeling of prograde and retrograde encounters cannot rely on the simplest impulse approximation.

  7. Contact statuses between functionally graded brake disk and pure pad disk

    International Nuclear Information System (INIS)

    Shahzamanian, M.M.; Sahari, B.B.; Bayat, M.; Mustapha, F.; Ismarrubie, Z.N.; Shahrjerdi, A.

    2009-01-01

    Full text: The contact statuses between functionally graded (FG) brake disks and pure pad disk are investigated by using finite element method (FEM). Two types of variation is considered for FG brake disk, the variation of materials are considered change in radial and thickness direction of disk. The material properties of these two types of FG brake disks are assumed to be represented by power-law distributions in the radius and thickness direction. The results are obtained and then compared. For the radial FG brake disk, the inner and outer surfaces are considered metal and ceramic respectively, and friction coefficient between metal surface and ceramic surface of FG brake dick with pad are considered 1.4 and 0.75 respectively. For the thickness FG brake disk the contact surface with pure pad brake disk is ceramic and the free surface is metal and friction coefficient between ceramic (contact) surface and pure pad brake disk is considered 0.75. In both types of FG brake disks the Coulomb contact friction is applied. Mechanical response of FG brake disks are compared and verified with the known results in the literatures. Three types of contact statuses are introduced as Sticking, Contact and Near Contact. The contact status between pad and disk for different values for pad thickness, grading index,n , and percentage of friction coefficient (λ) is shown. It can be seen that for all values of percentage of friction coefficient,λ , and grading indices, n, by increasing the thickness of pad cause the contact status changes from sticking to contact and then to near contact. (author)

  8. CHEMICAL COMPOSITIONS OF THIN-DISK, HIGH-METALLICITY RED HORIZONTAL-BRANCH FIELD STARS

    International Nuclear Information System (INIS)

    Afşar, M.; Sneden, C.; For, B.-Q.

    2012-01-01

    We present a detailed abundance analysis and atmospheric parameters of 76 stars from a survey to identify field Galactic red horizontal-branch (RHB) stars. High-resolution echelle spectra (R ≅ 60,000, S/N ≥ 100) were obtained with the 2.7 m Harlan J. Smith Telescope at McDonald Observatory. The target stars were selected only by color and parallax information. Overall metallicities and relative abundances of proton-capture elements (C, N, O, Li), α-elements (Ca and Si), and neutron-capture elements (Eu and La) were determined by either equivalent width or synthetic spectrum analyses. We used CN features at the λλ7995-8040 region in order to determine the 12 C/ 13 C ratios of our targets. Investigation of the evolutionary stages, using spectroscopic T eff and log g values along with derived 12 C/ 13 C ratios, revealed the presence of 18 probable RHB stars in our sample. We also derived kinematics of the stars with available distance information. Taking into account both the kinematics and probable evolutionary stages, we conclude that our sample contains 5 thick-disk and 13 thin-disk RHB stars. Up until now, RHB stars have been considered as members of the thick disk, and were expected to have large space velocities and sub-solar metallicities. However, our sample is dominated by low-velocity solar-metallicity RHB stars; their existence cannot be easily explained with standard stellar evolution.

  9. GIANT PLANET MIGRATION, DISK EVOLUTION, AND THE ORIGIN OF TRANSITIONAL DISKS

    International Nuclear Information System (INIS)

    Alexander, Richard D.; Armitage, Philip J.

    2009-01-01

    We present models of giant planet migration in evolving protoplanetary disks. Our disks evolve subject to viscous transport of angular momentum and photoevaporation, while planets undergo Type II migration. We use a Monte Carlo approach, running large numbers of models with a range in initial conditions. We find that relatively simple models can reproduce both the observed radial distribution of extrasolar giant planets, and the lifetimes and accretion histories of protoplanetary disks. The use of state-of-the-art photoevaporation models results in a degree of coupling between planet formation and disk clearing, which has not been found previously. Some accretion across planetary orbits is necessary if planets are to survive at radii ∼<1.5 AU, and if planets of Jupiter mass or greater are to survive in our models they must be able to form at late times, when the disk surface density in the formation region is low. Our model forms two different types of 'transitional' disks, embedded planets and clearing disks, which show markedly different properties. We find that the observable properties of these systems are broadly consistent with current observations, and highlight useful observational diagnostics. We predict that young transition disks are more likely to contain embedded giant planets, while older transition disks are more likely to be undergoing disk clearing.

  10. KILOPARSEC-SCALE SIMULATIONS OF STAR FORMATION IN DISK GALAXIES. I. THE UNMAGNETIZED AND ZERO-FEEDBACK LIMIT

    International Nuclear Information System (INIS)

    Van Loo, Sven; Butler, Michael J.; Tan, Jonathan C.

    2013-01-01

    We present hydrodynamic simulations of the evolution of self-gravitating dense gas on scales of 1 kpc down to ∼< parsec in a galactic disk, designed to study dense clump formation from giant molecular clouds (GMCs). These structures are expected to be the precursors to star clusters and this process may be the rate limiting step controlling star formation rates in galactic systems as described by the Kennicutt-Schmidt relation. We follow the thermal evolution of the gas down to ∼5 K using extinction-dependent heating and cooling functions. We do not yet include magnetic fields or localized stellar feedback, so the evolution of the GMCs and clumps is determined solely by self-gravity balanced by thermal and turbulent pressure support and the large-scale galactic shear. While cloud structures and densities change significantly during the simulation, GMC virial parameters remain mostly above unity for timescales exceeding the free-fall time of GMCs indicating that energy from galactic shear and large-scale cloud motions continuously cascades down to and within the GMCs. We implement star formation at a slow, inefficient rate of 2% per local free-fall time, but even this yields global star formation rates that are about two orders of magnitude larger than the observed Kennicutt-Schmidt relation due to overproduction of dense gas clumps. We expect a combination of magnetic support and localized stellar feedback is required to inhibit dense clump formation to ∼1% of the rate that results from the nonmagnetic, zero-feedback limit.

  11. DISCOVERY OF SiO BAND EMISSION FROM GALACTIC B[e] SUPERGIANTS

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, M. [Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov (Czech Republic); Oksala, M. E. [LESIA, Observatoire de Paris, CNRS UMR 8109, UPMC, Université Paris Diderot, 5 place Jules Janssen, F-92190, Meudon (France); Cidale, L. S.; Arias, M. L.; Torres, A. F. [Departamento de Espectroscopía Estelar, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata (Argentina); Fernandes, M. Borges, E-mail: michaela.kraus@asu.cas.cz [Observatório Nacional, Rua General José Cristino 77, 20921-400 São Cristovão, Rio de Janeiro (Brazil)

    2015-02-20

    B[e] supergiants (B[e]SGs) are evolved massive stars in a short-lived transition phase. During this phase, these objects eject large amounts of material, which accumulate in a circumstellar disk-like structure. The expelled material is typically dense and cool, providing the cradle for molecule and dust condensation and for a rich, ongoing chemistry. Very little is known about the chemical composition of these disks, beyond the emission from dust and CO revolving around the star on Keplerian orbits. As massive stars preserve an oxygen-rich surface composition throughout their life, other oxygen-based molecules can be expected to form. As SiO is the second most stable oxygen compound, we initiated an observing campaign to search for first-overtone SiO emission bands. We obtained high-resolution near-infrared L-band spectra for a sample of Galactic B[e]SGs with reported CO band emission. We clearly detect emission from the SiO first-overtone bands in CPD-52 9243 and indications for faint emission in HD 62623, HD 327083, and CPD-57 2874. From model fits, we find that in all these stars the SiO bands are rotationally broadened with a velocity lower than observed in the CO band forming regions, suggesting that SiO forms at larger distances from the star. Hence, searching for and analyzing these bands is crucial for studying the structure and kinematics of circumstellar disks, because they trace complementary regions to the CO band formation zone. Moreover, since SiO molecules are the building blocks for silicate dust, their study might provide insight in the early stage of dust formation.

  12. A self-consistent model of the three-phase interstellar medium in disk galaxies

    International Nuclear Information System (INIS)

    Wang, Z.

    1989-01-01

    In the present study the author analyzes a number of physical processes concerning velocity and spatial distributions, ionization structure, pressure variation, mass and energy balance, and equation of state of the diffuse interstellar gas in a three phase model. He also considers the effects of this model on the formation of molecular clouds and the evolution of disk galaxies. The primary purpose is to incorporate self-consistently the interstellar conditions in a typical late-type galaxy, and to relate these to various observed large-scale phenomena. He models idealized situations both analytically and numerically, and compares the results with observational data of the Milky Way Galaxy and other nearby disk galaxies. Several main conclusions of this study are: (1) the highly ionized gas found in the lower Galactic halo is shown to be consistent with a model in which the gas is photoionized by the diffuse ultraviolet radiation; (2) in a quasi-static and self-regulatory configuration, the photoelectric effects of interstellar grains are primarily responsible for heating the cold (T ≅ 100K) gas; the warm (T ≅ 8,000K) gas may be heated by supernova remnants and other mechanisms; (3) the large-scale atomic and molecular gas distributions in a sample of 15 disk galaxies can be well explained if molecular cloud formation and star formation follow a modified Schmidt Law; a scaling law for the radial gas profiles is proposed based on this model, and it is shown to be applicable to the nearby late-type galaxies where radio mapping data is available; for disk galaxies of earlier type, the effect of their massive central bulges may have to be taken into account

  13. Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge

    International Nuclear Information System (INIS)

    Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

    2015-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  14. A Comparison of the Characteristics of Planar and Axisymmetric Bluff-Body Combustors Operated under Stratified Inlet Mixture Conditions

    Directory of Open Access Journals (Sweden)

    G. Paterakis

    2013-01-01

    Full Text Available The work presents comparisons of the flame stabilization characteristics of axisymmetric disk and 2D slender bluff-body burner configurations, operating with inlet mixture stratification, under ultralean conditions. A double cavity propane air premixer formed along three concentric disks, supplied with a radial equivalence ratio gradient the afterbody disk recirculation, where the first flame configuration is stabilized. Planar fuel injection along the center plane of the leading face of a slender square cylinder against the approach cross-flow results in a stratified flame configuration stabilized alongside the wake formation region in the second setup. Measurements of velocities, temperatures, OH∗ and CH∗ chemiluminescence, local extinction criteria, and large-eddy simulations are employed to examine a range of ultralean and close to extinction flame conditions. The variations of the reacting front disposition within these diverse reacting wake topologies, the effect of the successive suppression of heat release on the near flame region characteristics, and the reemergence of large-scale vortical activity on approach to lean blowoff (LBO are investigated. The cross-correlation of the performance of these two popular flame holders that are at the opposite ends of current applications might offer helpful insights into more effective control measures for expanding the operational margin of a wider range of stabilization configurations.

  15. The LEGUE disk targets for LAMOST's pilot survey

    International Nuclear Information System (INIS)

    Chen Li; Hou Jinliang; Yu Jincheng; Shen Shiyin; Liu Chao; Deng Licai; Yang Fan; Zhang Yueyang; Zhang Haotong; Chen Jianjun; Chen Yuqin; Shi Jianrong; Newberg, Heidi Jo; Carlin, Jeffrey L.; Christlieb, Norbert; Han Zhanwen; Lee, Hsu-Tai; Liu Xiaowei; Pan Kaike; Wang Hongchi

    2012-01-01

    We describe the target selection algorithm for the low latitude disk portion of the LAMOST Pilot Survey, which aims to test systems in preparation for the LAMOST spectroscopic survey. We use the PPMXL astrometric catalog, which provides positions, proper motions, B/R/I magnitudes (mostly) from USNO-B and J/H/Ks from the Two Micron All Sky Survey (2MASS) as well. We chose eight plates along the Galactic plane, in the region 0° th magnitude. For each plate, we create an input catalog in the magnitude range 11.3 mag mag available from PPMXL. The stars are selected to satisfy the requirements of the fiber positioning system and have a uniform distribution in the I vs. B — I color-magnitude diagram. Our final input catalog consists of 12 000 objects on each of eight plates that are observable during the winter observing season from the Xinglong Station of the National Astronomical Observatory of China.

  16. CT-guided percutaneous laser disk decompression for cervical and lumbar disk hernia

    International Nuclear Information System (INIS)

    Shimizu, Kanichiro; Koyama, Tutomu; Harada, Junta; Abe, Toshiaki

    2008-01-01

    Percutaneous laser disk decompression under X-ray fluoroscopy was first reported in 1987 for minimally invasive therapy of lumbar disk hernia. In patients with disk hernia, laser vaporizes a small portion of the intervertebral disk thereby reducing the volume and pressure of the affected disk. We present the efficacy and safety of this procedure, and analysis of fair or poor response cases. In our study, 226 cases of lumbar disk hernia and 7 cases of cervical disk hernia were treated under CT guided PLDD. Japan Orthopedic Association (JOA) score and Mac-Nab criteria were investigated to evaluate the response to treatment. Improvement ratio based on the JOA score was calculated as follows. Overall success rate was 91.6% in cases lumber disk hernia, and 100% in cases of cervical disk hernia. We experienced two cases with two cases with postoperative complication. Both cases were treated conservatively. The majority of acute cases and post operative cases were reported to be 'good' on Mac-Nab criteria. Cases of fair or poor response on Mac-Nab criteria were lateral type, foraminal stenosis or large disk hernia. CT-guided PLDD is a safe and accurate procedure. The overall success rate can be increased by carefully selecting patients. (author)

  17. Disk Storage Server

    CERN Multimedia

    This model was a disk storage server used in the Data Centre up until 2012. Each tray contains a hard disk drive (see the 5TB hard disk drive on the main disk display section - this actually fits into one of the trays). There are 16 trays in all per server. There are hundreds of these servers mounted on racks in the Data Centre, as can be seen.

  18. Prediction of the whirl gas motion between galactic spiral arms from the laboratory modelling

    International Nuclear Information System (INIS)

    Nezlin, M.V.; Polyachenko, V.L.; Snezhkin, E.N.; Trubnikov, A.S.; Fridman, A.M.; AN SSSR, Moscow. Astronomicheskij Sovet)

    1986-01-01

    The shallow water laboratory modelling of the spiral structure generation in galaxies with a discontinuity of the rotation velocity has revealed the banana-like anticyclone whirls with the surface density minima between the spiral waves. The particles trapped by the whirls flow into the spiral arms and move there with considerable radial velocities in the vicinity of the corotation (near the location of discontinuity). This puts in new light the problem of relative motion of the arms and a galactic disk's material. Self-consistent spiral-whirl structure is observed even for so fast rotation of the periphery when the Rossby-Obukhov radius is the order of magnitude less than arms' length. The results obtained are compared with observation data for NGC 1566 galaxy. It is also noted that in some SB galaxies the bar-phenomenon may by a consequence of the spiral-whirl structure of gaseous disk. The results of observations and laboratory experiment initiate the hypothesis that, in galaxies with nearby satellite oppositely rotating, the generation of spiral arms which are leading in the wave meaning is possible, that is with their ends rotating forwards (oppositely to the direction of the galaxy rotation)

  19. Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

    Science.gov (United States)

    Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

    2018-05-01

    Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

  20. HNC IN PROTOPLANETARY DISKS

    International Nuclear Information System (INIS)

    Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua; Kastner, Joel

    2015-01-01

    The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling

  1. HNC IN PROTOPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Graninger, Dawn; Öberg, Karin I.; Qi, Chunhua [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kastner, Joel, E-mail: dgraninger@cfa.harvard.edu [Center for Imaging Science, School of Physics and Astronomy, and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623 (United States)

    2015-07-01

    The distributions and abundances of small organics in protoplanetary disks are potentially powerful probes of disk physics and chemistry. HNC is a common probe of dense interstellar regions and the target of this study. We use the Submillimeter Array (SMA) to observe HNC 3–2 toward the protoplanetary disks around the T Tauri star TW Hya and the Herbig Ae star HD 163296. HNC is detected toward both disks, constituting the first spatially resolved observations of HNC in disks. We also present SMA observations of HCN 3–2 and IRAM 30 m observations of HCN and HNC 1–0 toward HD 163296. The disk-averaged HNC/HCN emission ratio is 0.1–0.2 toward both disks. Toward TW Hya, the HNC emission is confined to a ring. The varying HNC abundance in the TW Hya disk demonstrates that HNC chemistry is strongly linked to the disk physical structure. In particular, the inner rim of the HNC ring can be explained by efficient destruction of HNC at elevated temperatures, similar to what is observed in the ISM. However, to realize the full potential of HNC as a disk tracer requires a combination of high SNR spatially resolved observations of HNC and HCN and disk-specific HNC chemical modeling.

  2. Stochastic self-propagating star formation in three-dimensional disk galaxy simulations

    International Nuclear Information System (INIS)

    Statler, T.; Comins, N.; Smith, B.F.

    1983-01-01

    Stochastic self-propagating star formation (SSPSF) is a process of forming new stars through the compression of the interstellar medium by supernova shock waves. Coupling this activity with galactic differential rotation produces spiral structure in two-dimensional disk galaxy simulations. In this paper the first results of a three-dimensional SSPSF simulation of disk galaxies are reported. Our model generates less impressive spirals than do the two-dimensional simulations. Although some spirals do appear in equilibrium, more frequently we observe spirals as non-equilibrium states of the models: as the spiral arms evolve, they widen until the spiral structure is no longer discernible. The two free parameters that we vary in this study are the probability of star formation due to a recent, nearby explosion, and the relaxation time for the interstellar medium to return to a condition of maximum star formation after it has been cleared out by an explosion and subsequent star formation. We find that equilibrium spiral structure is formed over a much smaller range of these parameters in our three-dimensional SSPSF models than in similar two-dimensional models. We discuss possible reasons for these results as well as improvements on the model which are being explored

  3. A SOUTHERN SKY AND GALACTIC PLANE SURVEY FOR BRIGHT KUIPER BELT OBJECTS

    International Nuclear Information System (INIS)

    Sheppard, Scott S.; Udalski, Andrzej; Kubiak, Marcin; Pietrzynski, Grzegorz; Poleski, Radoslaw; Soszynski, Igor; Szymanski, Michal K.; Ulaczyk, Krzysztof; Trujillo, Chadwick

    2011-01-01

    About 2500 deg 2 of sky south of declination -25 0 and/or near the Galactic Plane were surveyed for bright outer solar system objects. This survey is one of the first large-scale southern sky and Galactic Plane surveys to detect dwarf planets and other bright Kuiper Belt Objects in the trans-Neptunian region. The survey was able to obtain a limiting R-band magnitude of 21.6. In all, 18 outer solar system objects were detected, including Pluto which was detected near the Galactic center using optimal image subtraction techniques to remove the high stellar density background. Fourteen of the detections were previously unknown trans-Neptunian objects, demonstrating that the southern sky had not been well searched to date for bright outer solar system objects. Assuming moderate albedos, several of the new discoveries from this survey could be in hydrostatic equilibrium and thus could be considered dwarf planets. Combining this survey with previous surveys from the northern hemisphere suggests that the Kuiper Belt is nearly complete to around 21st magnitude in the R band. All the main dynamical classes in the Kuiper Belt are occupied by at least one dwarf-planet-sized object. The 3:2 Neptune resonance, which is the innermost well-populated Neptune resonance, has several large objects while the main outer Neptune resonances such as the 5:3, 7:4, 2:1, and 5:2 do not appear to have any large objects. This indicates that the outer resonances are either significantly depleted in objects relative to the 3:2 resonance or have a significantly different assortment of objects than the 3:2 resonance. For the largest objects (H < 4.5 mag), the scattered disk population appears to have a few times more objects than the main Kuiper Belt (MKB) population, while the Sedna population could be several times more than that of the MKB.

  4. Development of Disk Rover, wall-climbing robot using permanent magnet disk

    International Nuclear Information System (INIS)

    Hirose, Shigeo; Tsutsumitake; Hiroshi; Toyama, Ryousei; Kobayashi, Kengo.

    1992-01-01

    A new type of wall climbing robot, named Disk Rover, using permanent magnet disks are developed. The newly introduced permanent magnet disk is to rotate the magnet disk on the surface of wall with partly contacted posture. It allows to produce high magnetic attraction force compared with conventional permanent wheel which utilizes only a small portion of the magnet installed around the wheel. The optimum design of the magnetic wheel is done by using finit element method and it is shown that the magnetic attraction force vs. weight ratio can be designed about three times higher than conventional type magnet wheel. The developed Disk Rover is 25 kg in weight including controller and battery, about 685 mm in diameter, 239 mm in height and has a pair of permanent magnet disks. It is demonstrated by the experiments that the Disk Rover can move around on the surface of the wall quite smoothly by radio control and has payload of about its own weight. Several considerations are also done in order to surmount bead weld. (author)

  5. GOT C+: Galactic Plane Survey of the 1.9 THz [CII] Line

    Science.gov (United States)

    Langer, William

    2012-01-01

    The ionized carbon [CII] 1.9 THz fine structure line is a major gas coolant in the interstellar medium (ISM) and controls the thermal conditions in diffuse gas clouds and Photodissociation Regions (PDRs). The [CII] line is also an important tracer of the atomic gas and atomic to molecular transition in diffuse clouds throughout the Galaxy. I will review some of the results from the recently completed Galactic Observations of Terahertz C+ (GOT C+) survey. This Herschel Open Time Key Project is a sparse, but uniform volume sample survey of [CII] line emission throughout the Galactic disk using the HIFI heterodyne receiver. HIFI observations, with their high spectral resolution, isolate and locate individual clouds in the Galaxy and provide excitation information on the gas. I will present [CII] position-velocity maps that reveal the distribution and motion of the clouds in the inner Galaxy and discuss results on the physical properties of the gas using spectral observations of [CII] and ancillary HI and 12CO, 13CO, and C18O J=1-0 data. The [CII] emission is also a useful tracer of the "Dark H2 Gas", and I will discuss its distribution in a sample of interstellar clouds. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration.

  6. Dark Matter Annihilation in The Galactic Center As Seen by the Fermi Gamma Ray Space Telescope

    Energy Technology Data Exchange (ETDEWEB)

    Hooper, Dan; /Fermilab /Chicago U., Astron. Astrophys. Ctr.; Goodenough, Lisa; /New York U.

    2010-10-01

    We analyze the first two years of data from the Fermi Gamma Ray Space Telescope from the direction of the inner 10{sup o} around the Galactic Center with the intention of constraining, or finding evidence of, annihilating dark matter. We find that the morphology and spectrum of the emission between 1.25{sup o} and 10{sup o} from the Galactic Center is well described by a the processes of decaying pions produced in cosmic ray collisions with gas, and the inverse Compton scattering of cosmic ray electrons in both the disk and bulge of the Inner Galaxy, along with gamma rays from known points sources in the region. The observed spectrum and morphology of the emission within approximately 1.25{sup o} ({approx}175 parsecs) of the Galactic Center, in contrast, cannot be accounted for by these processes or known sources. We find that an additional component of gamma ray emission is clearly present which is highly concentrated around the Galactic Center, but is not point-like in nature. The observed morphology of this component is consistent with that predicted from annihilating dark matter with a cusped (and possibly adiabatically contracted) halo distribution ({rho} {proportional_to} r{sup -1.34{+-}0.04}). The observed spectrum of this component, which peaks at energies between 2-4 GeV (in E{sup 2} units), is well fit by that predicted for a 7.3-9.2 GeV dark matter particle annihilating primarily to tau leptons with a cross section in the range of <{sigma}{nu}> = 3.3 x 10{sup -27} to 1.5 x 10{sup -26} cm{sup 3}/s, depending on how the dark matter distribution is normalized. We discuss other possible sources for this component, but argue that they are unlikely to account for the observed emission.

  7. Radiative Hydrodynamic Simulations of In Situ Star Formation in the Galactic Center

    Science.gov (United States)

    Frazer, Chris; Heitsch, Fabian

    2018-01-01

    Many stars observed in the Galactic Center (GC) orbit the supermassive black hole (SMBH), Sagittarius A*, in a region where the extreme gravitational field is expected to inhibit star formation. Yet, many of these stars are young which favors an in situ formation scenario. Previous numerical work on this topic has focused on two possible solutions. First, the tidal capture of a > 10^4 Msun infalling molecular cloud by an SMBH may result in the formation of a surrounding gas disk which then rapidly cools and forms stars. This process results in stellar populations that are consistent with the observed stellar disk in the GC. Second, dense gas clumps of approximately 100 Msun on highly eccentric orbits about an SMBH can experience sparks of star formation via orbital compressions occurring during pericenter passage. In my dissertation, I build upon these models using a series of grid-based radiative hydrodynamic simulations, including the effects of both ionizing ultraviolet light from existing stars as well as X-ray radiation emanating from the central black hole. Radiation is treated with an adaptive ray-tracing routine, including appropriate heating and cooling for both neutral and ionized gas. These models show that ultraviolet radiation is sufficiently strong to heat low mass gas clouds, thus suppressing star formation from clump compression. Gas disks that form from cloud capture become sufficiently dense to provide shielding from the radiation of existing central stars, thus allowing star formation to continue. Conversely, X-rays easily penetrate and heat the potentially star forming gas. For sufficiently high radiation fields, this provides a mechanism to disrupt star formation for both scenarios considered above.

  8. HERSCHEL's ''COLD DEBRIS DISKS'': BACKGROUND GALAXIES OR QUIESCENT RIMS OF PLANETARY SYSTEMS?

    Energy Technology Data Exchange (ETDEWEB)

    Krivov, A. V.; Loehne, T.; Mutschke, H.; Neuhaeuser, R. [Astrophysikalisches Institut und Universitaetssternwarte, Friedrich-Schiller-Universitaet Jena, Schillergaesschen 2-3, D-07745 Jena (Germany); Eiroa, C.; Marshall, J. P.; Mustill, A. J. [Departamento de Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Montesinos, B. [Departamento de Astrofisica, Centro de Astrobiologia (CAB, CSIC-INTA), ESAC Campus, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Del Burgo, C. [Instituto Nacional de Astrofisica, Optica y Electronica (INAOE), Apartado Postal 51 y 216, 72000 Puebla, Pue. (Mexico); Absil, O. [Institut d' Astrophysique et de Geophysique, Universite de Liege, Allee du 6 Aout 17, B-4000 Liege (Belgium); Ardila, D. [NASA Herschel Science Center, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Augereau, J.-C.; Ertel, S.; Lebreton, J. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG), UMR 5274, F-38041 Grenoble (France); Bayo, A. [European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago (Chile); Bryden, G. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Danchi, W. [NASA Goddard Space Flight Center, Exoplanets and Stellar Astrophysics, Code 667, Greenbelt, MD 20771 (United States); Liseau, R. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992, Onsala (Sweden); Mora, A. [ESA-ESAC Gaia SOC, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Pilbratt, G. L., E-mail: krivov@astro.uni-jena.de [ESA Astrophysics and Fundamental Physics Missions Division, ESTEC/SRE-SA, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands); and others

    2013-07-20

    Infrared excesses associated with debris disk host stars detected so far peak at wavelengths around {approx}100 {mu}m or shorter. However, 6 out of 31 excess sources studied in the Herschel Open Time Key Programme, DUNES, have been seen to show significant-and in some cases extended-excess emission at 160 {mu}m, which is larger than the 100 {mu}m excess. This excess emission has been attributed to circumstellar dust and has been suggested to stem from debris disks colder than those known previously. Since the excess emission of the cold disk candidates is extremely weak, challenging even the unrivaled sensitivity of Herschel, it is prudent to carefully consider whether some or even all of them may represent unrelated galactic or extragalactic emission, or even instrumental noise. We re-address these issues using several distinct methods and conclude that it is highly unlikely that none of the candidates represents a true circumstellar disk. For true disks, both the dust temperatures inferred from the spectral energy distributions and the disk radii estimated from the images suggest that the dust is nearly as cold as a blackbody. This requires the grains to be larger than {approx}100 {mu}m, even if they are rich in ices or are composed of any other material with a low absorption in the visible. The dearth of small grains is puzzling, since collisional models of debris disks predict that grains of all sizes down to several times the radiation pressure blowout limit should be present. We explore several conceivable scenarios: transport-dominated disks, disks of low dynamical excitation, and disks of unstirred primordial macroscopic grains. Our qualitative analysis and collisional simulations rule out the first two of these scenarios, but show the feasibility of the third one. We show that such disks can indeed survive for gigayears, largely preserving the primordial size distribution. They should be composed of macroscopic solids larger than millimeters, but smaller

  9. A New Determination of the Luminosity Function of the Galactic Halo.

    Science.gov (United States)

    Dawson, Peter Charles

    The luminosity function of the galactic halo is determined by subtracting from the observed numbers of proper motion stars in the LHS Catalogue the expected numbers of main-sequence, degenerate, and giant stars of the disk population. Selection effects are accounted for by Monte Carlo simulations based upon realistic colour-luminosity relations and kinematic models. The catalogue is shown to be highly complete, and a calibration of the magnitude estimates therein is presented. It is found that, locally, the ratio of disk to halo material is close to 950, and that the mass density in main sequence and subgiant halo stars with 3 account the possibility of a moderate rate of halo rotation, it is argued that the total density does not much exceed 5 x 10('-5) M(,o) pc('-3), in which case the total mass interior to the sun is of the order of 5 x 10('8) M(,o) for a density distribution which projects to a de Vaucouleurs r(' 1/4) law. It is demonstrated that if the Wielen luminosity function is a faithful representation of the stellar distribution in the solar neighbourhood, then the observed numbers of large proper motion stars are inconsistent with the presence of an intermediate popula- tion at the level, and with the kinematics advocated recently by Gilmore and Reid. The initial mass function (IMF) of the halo is considered, and weak evidence is presented that its slope is at least not shallower than that of the disk population IMF. A crude estimate of the halo's age, based on a comparison of the main sequence turnoff in the reduced proper motion diagram with theoretical models is obtained; a tentative lower limit is 15 Gyr with a best estimate of between 15 and 18 Gyr. Finally, the luminosity function obtained here is compared with those determined in other investigations.

  10. STAR FORMATION IN DISK GALAXIES. I. FORMATION AND EVOLUTION OF GIANT MOLECULAR CLOUDS VIA GRAVITATIONAL INSTABILITY AND CLOUD COLLISIONS

    International Nuclear Information System (INIS)

    Tasker, Elizabeth J.; Tan, Jonathan C.

    2009-01-01

    We investigate the formation and evolution of giant molecular clouds (GMCs) in a Milky-Way-like disk galaxy with a flat rotation curve. We perform a series of three-dimensional adaptive mesh refinement numerical simulations that follow both the global evolution on scales of ∼20 kpc and resolve down to scales ∼ H ≥ 100 cm -3 and track the evolution of individual clouds as they orbit through the galaxy from their birth to their eventual destruction via merger or via destructive collision with another cloud. After ∼140 Myr a large fraction of the gas in the disk has fragmented into clouds with masses ∼10 6 M sun and a mass spectrum similar to that of Galactic GMCs. The disk settles into a quasi-steady-state in which gravitational scattering of clouds keeps the disk near the threshold of global gravitational instability. The cloud collision time is found to be a small fraction, ∼1/5, of the orbital time, and this is an efficient mechanism to inject turbulence into the clouds. This helps to keep clouds only moderately gravitationally bound, with virial parameters of order unity. Many other observed GMC properties, such as mass surface density, angular momentum, velocity dispersion, and vertical distribution, can be accounted for in this simple model with no stellar feedback.

  11. The Mass and Absorption Columns of Galactic Gaseous Halos

    Science.gov (United States)

    Qu, Zhijie; Bregman, Joel N.

    2018-01-01

    The gaseous halo surrounding the galaxy is a reservoir for the gas on the galaxy disk, supplying materials for the star formation. We developed a gaseous halo model connecting the galactic disk and the gaseous halo by assuming the star formation rate is equal to the radiative cooling rate. Besides the single-phase collisional gaseous halo, we also consider the photoionization effect and a time-independent cooling model that assumes the mass cooling rate is constant over all temperatures. The photoionization dominates the low mass galaxy and the outskirts of the massive galaxy due to the low-temperature or low-density nature. The multi-phase cooling model dominates the denser region within the cooling radius, where the efficient radiative cooling must be included. Applying these two improvements, our model can reproduce the most of observed high ionization state ions (i.e., O VI, O VII, Ne VIII and Mg X). Our models show that the O VI column density is almost a constant of around 10^14 cm^-2 over a wide stellar mass from M_\\star ~10^8 M_Sun to 10^11 M_Sun, which is constant with current observations. This model also implies the O VI is photoionized for the galaxy with a halo mass fraction function of the EAGLE simulation. Finally, our model predicts plateaus of the Ne VIII and the Mg X column densities above the sub-L^* galaxy, and the possibly detectable O VII and O VIII column densities for low-mass galaxies, which help to determine the required detection limit for the future observations and missions.

  12. Galactic diffusion and the antiproton signal of supersymmetric dark matter

    CERN Document Server

    Chardonnet, P; Salati, Pierre; Taillet, R

    1996-01-01

    The leaky box model is now ruled out by measurements of a cosmic ray gradient throughout the galactic disk. It needs to be replaced by a more refined treatment which takes into account the diffusion of cosmic rays in the magnetic fields of the Galaxy. We have estimated the flux of antiprotons on the Earth in the framework of a two-zone diffusion model. Those species are created by the spallation reactions of high-energy nuclei with the interstellar gas. Another potential source of antiprotons is the annihilation of supersymmetric particles in the dark halo that surrounds our Galaxy. In this letter, we investigate both processes. Special emphasis is given to the antiproton signature of supersymmetric dark matter. The corresponding signal exceeds the conventional spallation flux below 300 MeV, a domain that will be thoroughly explored by the Antimatter Spectrometer experiment. The propagation of the antiprotons produced in the remote regions of the halo back to the Earth plays a crucial role. Depending on the e...

  13. Understanding Floppy Disks.

    Science.gov (United States)

    Valentine, Pamela

    1980-01-01

    The author describes the floppy disk with an analogy to the phonograph record, and discusses the advantages, disadvantages, and capabilities of hard-sectored and soft-sectored floppy disks. She concludes that, at present, the floppy disk will continue to be the primary choice of personal computer manufacturers and their customers. (KC)

  14. OT1_ipascucc_1: Understanding the Origin of Transition Disks via Disk Mass Measurements

    Science.gov (United States)

    Pascucci, I.

    2010-07-01

    Transition disks are a distinguished group of few Myr-old systems caught in the phase of dispersing their inner dust disk. Three different processes have been proposed to explain this inside-out clearing: grain growth, photoevaporation driven by the central star, and dynamical clearing by a forming giant planet. Which of these processes lead to a transition disk? Distinguishing between them requires the combined knowledge of stellar accretion rates and disk masses. We propose here to use 43.8 hours of PACS spectroscopy to detect the [OI] 63 micron emission line from a sample of 21 well-known transition disks with measured mass accretion rates. We will use this line, in combination with ancillary CO millimeter lines, to measure their gas disk mass. Because gas dominates the mass of protoplanetary disks our approach and choice of lines will enable us to trace the bulk of the disk mass that resides beyond tens of AU from young stars. Our program will quadruple the number of transition disks currently observed with Herschel in this setting and for which disk masses can be measured. We will then place the transition and the ~100 classical/non-transition disks of similar age (from the Herschel KP "Gas in Protoplanetary Systems") in the mass accretion rate-disk mass diagram with two main goals: 1) reveal which gaps have been created by grain growth, photoevaporation, or giant planet formation and 2) from the statistics, determine the main disk dispersal mechanism leading to a transition disk.

  15. Exploring Disks Around Planets

    Science.gov (United States)

    Kohler, Susanna

    2017-07-01

    Giant planets are thought to form in circumstellar disks surrounding young stars, but material may also accrete into a smaller disk around the planet. Weve never detected one of these circumplanetary disks before but thanks to new simulations, we now have a better idea of what to look for.Image from previous work simulating a Jupiter-mass planet forming inside a circumstellar disk. The planet has its own circumplanetary disk of accreted material. [Frdric Masset]Elusive DisksIn the formation of giant planets, we think the final phase consists of accretion onto the planet from a disk that surrounds it. This circumplanetary disk is important to understand, since it both regulates the late gas accretion and forms the birthplace of future satellites of the planet.Weve yet to detect a circumplanetary disk thus far, because the resolution needed to spot one has been out of reach. Now, however, were entering an era where the disk and its kinematics may be observable with high-powered telescopes (like the Atacama Large Millimeter Array).To prepare for such observations, we need models that predict the basic characteristics of these disks like the mass, temperature, and kinematic properties. Now a researcher at the ETH Zrich Institute for Astronomy in Switzerland, Judit Szulgyi, has worked toward this goal.Simulating CoolingSzulgyi performs a series of 3D global radiative hydrodynamic simulations of 1, 3, 5, and 10 Jupiter-mass (MJ) giant planets and their surrounding circumplanetary disks, embedded within the larger circumstellar disk around the central star.Density (left column), temperature (center), and normalized angular momentum (right) for a 1 MJ planet over temperatures cooling from 10,000 K (top) to 1,000 K (bottom). At high temperatures, a spherical circumplanetary envelope surrounds the planet, but as the planet cools, the envelope transitions around 64,000 K to a flattened disk. [Szulgyi 2017]This work explores the effects of different planet temperatures and

  16. Accretion Disk Reverberation with Hubble Space Telescope Observations of NGC 4593: Evidence for Diffuse Continuum Lags

    Science.gov (United States)

    Cackett, Edward M.; Chiang, Chia-Ying; McHardy, Ian; Edelson, Rick; Goad, Michael R.; Horne, Keith; Korista, Kirk T.

    2018-04-01

    The Seyfert 1 galaxy NGC 4593 was monitored spectroscopically with the Hubble Space Telescope as part of a reverberation mapping campaign that also included Swift, Kepler, and ground-based photometric monitoring. During 2016 July 12–August 6, we obtained 26 spectra across a nearly continuous wavelength range of ∼1150–10000 Å. These were combined with Swift data to produce a UV/optical “lag spectrum,” which shows the interband lag relative to the Swift UVW2 band as a function of wavelength. The broad shape of the lag spectrum appears to follow the τ ∝ λ 4/3 relation seen previously in photometric interband lag measurements of other active galactic nuclei (AGNs). This shape is consistent with the standard thin disk model, but the magnitude of the lags implies a disk that is a factor of ∼3 larger than predicted, again consistent with what has been previously seen in other AGNs. In all cases these large disk sizes, which are also implied by independent gravitational microlensing of higher-mass AGNs, cannot be simply reconciled with the standard model. However, the most striking feature in this higher-resolution lag spectrum is a clear excess around the 3646 Å Balmer jump. This strongly suggests that diffuse emission from gas in the much larger broad-line region (BLR) must also contribute significantly to the interband lags. While the relative contributions of the disk and BLR cannot be uniquely determined in these initial measurements, it is clear that both will need to be considered to comprehensively model and understand AGN lag spectra.

  17. Effect of increasing helium content and disk dwarfs evolution on the chemical enrichment of the galaxy

    Energy Technology Data Exchange (ETDEWEB)

    Caimmi, R [Padua Univ. (Italy). Ist. di Astronomia

    1979-07-01

    The author deals with two main effects: First the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighbourhood, and second, the theoretical possibility of (i) an increased helium content as the Galaxy evolves, and (ii) the presence of evolutionary effects in disk dwarfs (i.e., the age of some or all stars considered up to the subgiant phase is not necessarily longer than the age of the galactic disk). Account is taken of a linear increase of helium content with metal content, and some constraints are imposed relative to initial, solar and present-day observed values of Y and Z, and to observed relative helium to heavy element enrichment, ..delta..Y/..delta..Z. In this way, little influence is found on the empirical metal abundance distribution in the range 0<=..delta..Y/..delta..Z<=3, while larger values of ..delta..Y/..delta..Zwould lead to a more significant influence. 'Evolved' and 'unevolved' theoretical metal abundance distributions are derived by accounting for a two-phase model of chemical evolution of galaxies and for a linear mass dependence of star lifetimes in the spectral range G2V-G8V and are compared with the empirical distribution. All are in satisfactory agreement due to systematic shift data by different observations; several values of collapse time Tsub(c) and age of the Galaxy T are also considered. Finally, models of chemical evolution invoking homogeneous collapse without infall and inhomogeneous collapse with infall, are briefly discussed relative to the empirical metal abundance distribution in Main Sequence disk dwarfs of the solar neighbourhood.

  18. Accretion States of the Galactic Micro Quasar GRS 1758-258

    Science.gov (United States)

    Soria, Roberto; Mehdipour, Missagh; Broderick, Jess W.; Hao, JingFang; Hannikainen, Diana C.; Pottschmidt, Katja; Zhang, Shuang-Nan

    2011-01-01

    We present the results of a radio and X-ray study of the Galactic micro quasar GRS 1758-258, using unpublished archival data and new observations. We focus in particular on the 2000-2002 state transitions, and on its more quiet behaviour in 2008-2009. Our spectral and timing analysis of the XMM-Newton data shows that the source was in the canonical intermediate, soft and hard states in 2000 September 19,2001 March 22 and 2002 September 28, respectively. We estimate the disk size, luminosity and temperature, which are consistent with a black hole mass approx.10 Solar Mass, There is much overlap between the range of total X-ray luminosities (on average approx. 0.02L(sub Edd)) in the hard and soft states, and probably between the corresponding mass accretion rates; in fact, the hard state is often more luminous. The extended radio lobes seen in 1992 and 1997 are still present in 2008-2009. The 5-GHz radio core flux density has shown variability between approx. 0.1-0.5 mJy over the last two decades. This firmly places GRS 1758-258 in the radio-quiet sequence of Galactic black holes, in the radio/X-ray plane. We note that this dichotomy is similar to the dichotomy between the radio/X-ray sequences of Seyfert and radio galaxies. We propose that the different radio efficiency of the two sequences is due to relativistic electron/positron jets in radio-loud black holes, and sub-relativistic, thermally dominated outflows in radio-quiet sources.

  19. Cosmic-ray electrons and galactic radio emission - a conflict

    International Nuclear Information System (INIS)

    Badhwar, G.D.; Daniel, R.R.; Stephens, S.A.

    1977-01-01

    Reference is made to attempts in the past to deduce information of astrophysical importance from a study of the galactic non-thermal continuum in relation to cosmic ray electrons observed in the neighbourhood of the Earth. Such investigations were carried out using the cosmic ray electron data obtained from a single experiment or by making use of an average spectrum derived from world data, although it was known that the flux values observed by different investigators in any energy band differed by as much as a factor of 4. This has led to conflicting conclusions being drawn from the analysis of data of different observers. The present authors used a different approach for analysing the observational data, based on arguments of internal consistency between each measured electron spectrum and the magnetic field strength and the dimension of the radio-emitting region required to explain the radio observations. Such an approach makes it possible to highlight the inconsistencies associated with some of the electron measurements and permits certain inferences of cosmic ray and astrophysical interest. From the discussion it is concluded that the observed spectral index of the radio continuum in the Galaxy is in conflict with some of the cosmic ray electron measurements; also that the absolute intensities of cosmic ray electrons as measured in some experiments are so low that they cannot be reconciled either with the interstellar magnetic field limits or with the extent of the galactic disk, and it is likely that the field strength derived from Faraday rotation measurements gives only a lower limit to the local magnetic field in the Galaxy. (U.K.)

  20. Indications of M-Dwarf Deficits in the Halo and Thick Disk of the Galaxy

    Science.gov (United States)

    Konishi, Mihoko; Shibai, Hiroshi; Sumi, Takahiro; Fukagawa, Misato; Matsuo, Taro; Samland, Matthias S.; Yamamoto, Kodai; Sudo, Jun; Itoh, Yoichi; Arimoto, Nobuo; hide

    2014-01-01

    We compared the number of faint stars detected in deep survey fields with the current stellar distribution model of the Galaxy and found that the detected number in the H band is significantly smaller than the predicted number. This indicates that M-dwarfs, the major component, are fewer in the halo and the thick disk. We used archived data of several surveys in both the north and south field of GOODS (Great Observatories Origins Deep Survey), MODS in GOODS-N, and ERS and CANDELS in GOODS-S. The number density of M-dwarfs in the halo has to be 20+/-13% relative to that in the solar vicinity, in order for the detected number of stars fainter than 20.5 mag in the H band to match with the predicted value from the model. In the thick disk, the number density of M-dwarfs must be reduced (52+/-13%) or the scale height must be decreased ( approx. 600 pc). Alternatively, overall fractions of the halo and thick disks can be significantly reduced to achieve the same effect, because our sample mainly consists of faint M-dwarfs. Our results imply that the M-dwarf population in regions distant from the Galactic plane is significantly smaller than previously thought. We then discussed the implications this has on the suitability of the model predictions for the prediction of non-companion faint stars in direct imaging extrasolar planet surveys by using the best-fit number densities.

  1. Parsec-scale Obscuring Accretion Disk with Large-scale Magnetic Field in AGNs

    Energy Technology Data Exchange (ETDEWEB)

    Dorodnitsyn, A.; Kallman, T. [Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD, 20771 (United States)

    2017-06-10

    A magnetic field dragged from the galactic disk, along with inflowing gas, can provide vertical support to the geometrically and optically thick pc-scale torus in AGNs. Using the Soloviev solution initially developed for Tokamaks, we derive an analytical model for a rotating torus that is supported and confined by a magnetic field. We further perform three-dimensional magneto-hydrodynamic simulations of X-ray irradiated, pc-scale, magnetized tori. We follow the time evolution and compare models that adopt initial conditions derived from our analytic model with simulations in which the initial magnetic flux is entirely contained within the gas torus. Numerical simulations demonstrate that the initial conditions based on the analytic solution produce a longer-lived torus that produces obscuration that is generally consistent with observed constraints.

  2. Equilibrium configuration of a stratus floating above accretion disks: Full-disk calculation

    Science.gov (United States)

    Itanishi, Yusuke; Fukue, Jun

    2017-06-01

    We examine floating strati above a luminous accretion disk, supported by the radiative force from the entire disk, and calculate the equilibrium locus, which depends on the disk luminosity and the optical depth of the stratus. Due to the radiative transfer effect (albedo effect), the floating height of the stratus with a finite optical depth generally becomes high, compared with the particle case. In contrast to the case of the near-disk approximation, moreover, the floating height becomes yet higher in the present full-disk calculation, since the intense radiation from the inner disk is taken into account. As a result, when the disk luminosity normalized by the Eddington luminosity is ˜0.3 and the stratus optical depth is around unity, the stable configuration disappears at around r ˜ 50 rg, rg being the Schwarzschild radius, and the stratus would be blown off as a cloudy wind consisting of many strati with appropriate conditions. This luminosity is sufficiently smaller than the Eddington one, and the present results suggest that the radiation-driven cloudy wind can be easily blown off from the sub-Eddington disk, and this can explain various outflows observed in ultra-fast outflow objects as well as in broad-absorption-line quasars.

  3. The Fine Transverse Structure of a Vortex Flow Beyond the Edge of a Disc Rotating in a Stratified Fluid

    Science.gov (United States)

    Chashechkin, Yu. D.; Bardakov, R. N.

    2018-02-01

    By the methods of schlieren visualization, the evolution of elements of the fine structure of transverse vortex loops formed in the circular vortex behind the edge of a disk rotating in a continuously stratified fluid is traced for the first time. An inhomogeneous distribution of the density of a table-salt solution in a basin was formed by the continuous-squeezing method. The development of periodic perturbations at the outer boundary of the circular vortex and their transformation at the vortex-loop vertex are traced. A slow change in the angular size of the structural elements in the supercritical-flow mode is noted.

  4. Magnetic braking in galactic flows

    International Nuclear Information System (INIS)

    Sparke, L.S.

    1982-01-01

    The nuclear fireworks of active galaxies are believed to derive their power from the kinetic energy of gas falling onto a massive central objects; mass shed from evolving galactic stars is an obvious source of fuel for this process. But this ejected material shares the galactic rotation, and a centrifugal barrier will prevent it from reaching the nucleus, if its angular momentum is not removed. This paper shows that, if the large-scale galactic magnetic field has a strong enough radial component, magnetic torques can act to spin down the infalling matter. Rotation of the interstellar gas induces a toroidal magnetic field, and Maxwell stresses remove angular momentum from the flow; gas can then fall inward to the galactic center. In this way, the monster in the nucleus can be fed on gas from a galaxy's own stars. The magnetic fields in M87 and NGC 1275, giant elliptical galaxies which are accreting from an intracluster medium, appear to be strong enough to allow magnetic braking

  5. Light, Alpha, and Fe-peak Element Abundances in the Galactic Bulge

    Science.gov (United States)

    Johnson, Christian I.; Rich, R. Michael; Kobayashi, Chiaki; Kunder, Andrea; Koch, Andreas

    2014-10-01

    We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l, b) = (+5.25,-3.02) and (0,-12). The (+5.25,-3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high-resolution (R ~ 20,000), high signal-to-noise ration (S/N >~ 70) FLAMES-GIRAFFE spectra obtained through the European Southern Observatory archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analyses of this data set beyond Fe and the α-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H] >~ -0.5. In particular, the bulge [α/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk, and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high-velocity populations. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae may be required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40 M ⊙ are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field stars. However, the

  6. Light, alpha, and Fe-peak element abundances in the galactic bulge

    International Nuclear Information System (INIS)

    Johnson, Christian I.; Rich, R. Michael; Kobayashi, Chiaki; Kunder, Andrea; Koch, Andreas

    2014-01-01

    We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l, b) = (+5.25,–3.02) and (0,–12). The (+5.25,–3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high-resolution (R ∼ 20,000), high signal-to-noise ration (S/N ≳ 70) FLAMES-GIRAFFE spectra obtained through the European Southern Observatory archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analyses of this data set beyond Fe and the α-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H] ≳ –0.5. In particular, the bulge [α/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk, and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high-velocity populations. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae may be required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40 M ☉ are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field stars

  7. Light, alpha, and Fe-peak element abundances in the galactic bulge

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Christian I. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-15, Cambridge, MA 02138 (United States); Rich, R. Michael [Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States); Kobayashi, Chiaki [Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Kunder, Andrea [Leibniz-Institute für Astrophysik Potsdam (AIP), Ander Sternwarte 16, D-14482, Potsdam (Germany); Koch, Andreas, E-mail: cjohnson@cfa.harvard.edu, E-mail: rmr@astro.ucla.edu, E-mail: c.kobayashi@herts.ac.uk, E-mail: akunder@aip.de, E-mail: akoch@lsw.uni-heidelberg.de [Zentrum für Astronomie der Universität Heidelberg, Landessternwarte, Königstuhl 12, Heidelberg (Germany)

    2014-10-01

    We present radial velocities and chemical abundances of O, Na, Mg, Al, Si, Ca, Cr, Fe, Co, Ni, and Cu for a sample of 156 red giant branch stars in two Galactic bulge fields centered near (l, b) = (+5.25,–3.02) and (0,–12). The (+5.25,–3.02) field also includes observations of the bulge globular cluster NGC 6553. The results are based on high-resolution (R ∼ 20,000), high signal-to-noise ration (S/N ≳ 70) FLAMES-GIRAFFE spectra obtained through the European Southern Observatory archive. However, we only selected a subset of the original observations that included spectra with both high S/N and that did not show strong TiO absorption bands. This work extends previous analyses of this data set beyond Fe and the α-elements Mg, Si, Ca, and Ti. While we find reasonable agreement with past work, the data presented here indicate that the bulge may exhibit a different chemical composition than the local thick disk, especially at [Fe/H] ≳ –0.5. In particular, the bulge [α/Fe] ratios may remain enhanced to a slightly higher [Fe/H] than the thick disk, and the Fe-peak elements Co, Ni, and Cu appear enhanced compared to the disk. There is also some evidence that the [Na/Fe] (but not [Al/Fe]) trends between the bulge and local disk may be different at low and high metallicity. We also find that the velocity dispersion decreases as a function of increasing [Fe/H] for both fields, and do not detect any significant cold, high-velocity populations. A comparison with chemical enrichment models indicates that a significant fraction of hypernovae may be required to explain the bulge abundance trends, and that initial mass functions that are steep, top-heavy (and do not include strong outflow), or truncated to avoid including contributions from stars >40 M {sub ☉} are ruled out, in particular because of disagreement with the Fe-peak abundance data. For most elements, the NGC 6553 stars exhibit abundance trends nearly identical to comparable metallicity bulge field

  8. COLLIMATION AND SCATTERING OF THE ACTIVE GALACTIC NUCLEUS EMISSION IN THE SOMBRERO GALAXY

    International Nuclear Information System (INIS)

    Menezes, R. B.; Steiner, J. E.; Ricci, T. V.

    2013-01-01

    We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the Hα emission line. The collimation and scattering of this broad Hα component was also revealed by fitting the [N II] λλ6548, 6583 and Hα emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = –18° ± 13° and P.A. = 162° ± 13°) along a direction perpendicular to the torus/disk (P.A. = 72° ± 14°) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the unified model and explains why only a weak broad component of the Hα emission line is visible and also why many previous studies detected no broad Hα. The technique used here proved to be an efficient method not only for detecting scattered light, but also for testing the unified model in low-luminosity AGNs.

  9. First results from the INTEGRAL galactic plane scans

    DEFF Research Database (Denmark)

    Winkler, C.; Gehrels, N.; Schonfelder, V.

    2003-01-01

    Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time observations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved mapp...... mapping of the Galactic plane in continuum and diffuse line emission. This paper describes first results obtained from the Galactic plane scans executed so far during the early phase (Dec. 2002-May 2003) of the nominal mission.......Scans of the Galactic plane performed at regular intervals constitute a key element of the guaranteed time observations of the INTEGRAL observing programme. These scans are done for two reasons: frequent monitoring of the Galactic plane in order to detect transient sources, and time resolved...

  10. Cosmic ray acceleration by large scale galactic shocks

    International Nuclear Information System (INIS)

    Cesarsky, C.J.; Lagage, P.O.

    1987-01-01

    The mechanism of diffusive shock acceleration may account for the existence of galactic cosmic rays detailed application to stellar wind shocks and especially to supernova shocks have been developed. Existing models can usually deal with the energetics or the spectral slope, but the observed energy range of cosmic rays is not explained. Therefore it seems worthwhile to examine the effect that large scale, long-lived galactic shocks may have on galactic cosmic rays, in the frame of the diffusive shock acceleration mechanism. Large scale fast shocks can only be expected to exist in the galactic halo. We consider three situations where they may arise: expansion of a supernova shock in the halo, galactic wind, galactic infall; and discuss the possible existence of these shocks and their role in accelerating cosmic rays

  11. Dynamo dominated accretion and energy flow: The mechanism of active galactic nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Colgate, S.A.; Li, H.

    1998-12-31

    An explanation of the magnetic fields of the universe, the central mass concentration of galaxies, the massive black hole of every galaxy, and the AGN phenomena has been an elusive goal. The authors suggest here the outlines of such a theoretical understanding and point out where the physical understanding is missing. They believe there is an imperative to the sequence of mass flow and hence energy flow in the collapse of a galactic mass starting from the first non-linearity appearing in structure formation following decoupling. This first non-linearity of a two to one density fluctuation, the Lyman-{alpha} clouds, ultimately leads to the emission spectra of the phenomenon of AGN, quasars, blazars, etc. The over-arching physical principle is the various mechanisms for the transport of angular momentum. They believe they have now understood the new physics of two of these mechanisms that have previously been illusive and as a consequence they impose strong constraints on the initial conditions of the mechanisms for the subsequent emission of the gravitational binding energy. The new phenomena described are: (1) the Rossby vortex mechanism of the accretion disk {alpha}-viscosity, and (2) the mechanism of the {alpha}-{Omega} dynamo in the accretion disk. The Rossby vortex mechanism leads to a prediction of the black hole mass and rate of energy release and the {alpha}-{Omega} dynamo leads to the generation of the magnetic flux of the galaxy (and the far greater magnetic flux of clusters) and separately explains the primary flux of energy emission as force-free magnetic energy density. This magnetic flux and magnetic energy density separately are the necessary consequence of the saturation of a dynamo created by the accretion disk with a gain greater than unity.

  12. Structure and content of the galaxy and galactic gamma rays

    International Nuclear Information System (INIS)

    1976-01-01

    The conference included papers on γ-ray pulsars, galactic diffuse flux and surveys, radio surveys of external galaxies, galactic distribution of pulsars, and galactic gamma emission. Galactic structure drawing on all branches of galactic astronomy is discussed. New and unpublished material is included

  13. THE LONG-TERM DYNAMICAL EVOLUTION OF DISK-FRAGMENTED MULTIPLE SYSTEMS IN THE SOLAR NEIGHBORHOOD

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yun [Department of Astronomy, School of Physics, Peking University, Yiheyuan Lu 5, Haidian Qu, Beijing 100871 (China); Kouwenhoven, M. B. N. [Department of Mathematical Sciences, Xi’an Jiaotong-Liverpool University, 111 Ren’ai Road, Suzhou Dushu Lake Science and Education Innovation District, Suzhou Industrial Park, Suzhou 215123 (China); Stamatellos, D. [Jeremiah Horrocks Institute for Mathematics, Physics and Astronomy, University of Central Lancashire, Preston PR1 2HE (United Kingdom); Goodwin, Simon P., E-mail: t.kouwenhoven@xjtlu.edu.cn [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom)

    2016-11-10

    The origin of very low-mass hydrogen-burning stars, brown dwarfs (BDs), and planetary-mass objects (PMOs) at the low-mass end of the initial mass function is not yet fully understood. Gravitational fragmentation of circumstellar disks provides a possible mechanism for the formation of such low-mass objects. The kinematic and binary properties of very low-mass objects formed through disk fragmentation at early times (<10 Myr) were discussed in our previous paper. In this paper we extend the analysis by following the long-term evolution of disk-fragmented systems up to an age of 10 Gyr, covering the ages of the stellar and substellar populations in the Galactic field. We find that the systems continue to decay, although the rates at which companions escape or collide with each other are substantially lower than during the first 10 Myr, and that dynamical evolution is limited beyond 1 Gyr. By t = 10 Gyr, about one third of the host stars are single, and more than half have only one companion left. Most of the other systems have two companions left that orbit their host star in widely separated orbits. A small fraction of companions have formed binaries that orbit the host star in a hierarchical triple configuration. The majority of such double-companion systems have internal orbits that are retrograde with respect to their orbits around their host stars. Our simulations allow a comparison between the predicted outcomes of disk fragmentation with the observed low-mass hydrogen-burning stars, BDs, and PMOs in the solar neighborhood. Imaging and radial velocity surveys for faint binary companions among nearby stars are necessary for verification or rejection of the formation mechanism proposed in this paper.

  14. 2TB hard disk drive

    CERN Multimedia

    This particular object was used up until 2012 in the Data Centre. It slots into one of the Disk Server trays. Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes (link is external). They were originally called "fixed disks" or "Winchesters" (a code name used for a popular IBM product). They later became known as "hard disks" to distinguish them from "floppy disks (link is external)." Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

  15. Structure and content of the galaxy and galactic gamma rays

    Energy Technology Data Exchange (ETDEWEB)

    1976-01-01

    The conference included papers on ..gamma..-ray pulsars, galactic diffuse flux and surveys, radio surveys of external galaxies, galactic distribution of pulsars, and galactic gamma emission. Galactic structure drawing on all branches of galactic astronomy is discussed. New and unpublished material is included. (JFP)

  16. DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

    Energy Technology Data Exchange (ETDEWEB)

    Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L. [NASA Goddard Space Flight Center Exoplanets and Stellar Astrophysics Laboratory, Code 667 Greenbelt, MD 21230 (United States); Silverberg, Steven M.; Wisniewski, John P. [Homer L. Dodge Department of Physics and Astronomy The University of Oklahoma 440 W. Brooks St. Norman, OK 73019 (United States); Bans, Alissa S. [Valparaiso University, Department of Physics and Astronomy, Neils Science Center, 1610 Campus Drive East, Valparaiso, IN 46383 (United States); Bhattacharjee, Shambo [International Space University 1 Rue Jean-Dominique Cassini F-67400 Illkirch-Graffenstaden (France); Kenyon, Scott J. [Smithsonian Astrophysical Observatory 60 Garden Street Cambridge, MA 02138 (United States); Debes, John H. [Space Telescope Science Institute 3700 San Martin Dr. Baltimore, MD 21218 (United States); Currie, Thayne [National Astronomical Observatory of Japan 650 N A’ohokhu Place Hilo, HI 96720 (United States); García, Luciano [Observatorio Astronómico de Córdoba Universidad Nacional de Córdoba Laprida 854, X5000BGR, Córdoba (Argentina); Jung, Dawoon [Korea Aerospace Research Institute Lunar Exploration Program Office 169-84 Gwahak-ro, Yuseong-gu, Daejeon 34133 (Korea, Republic of); Lintott, Chris [Denys Wilkinson Building Keble Road Oxford, OX1 3RH (United Kingdom); Rebull, Luisa M. [Infrared Processing and Analaysis Center Caltech M/S 314-6 1200 E. California Blvd. Pasadena, CA 91125 (United States); Nesvold, Erika, E-mail: Marc.Kuchner@nasa.gov, E-mail: michael.w.mcelwain@nasa.gov, E-mail: deborah.l.padgett@nasa.gov, E-mail: carol.a.grady@nasa.gov, E-mail: silverberg@ou.edu, E-mail: wisniewski@ou.edu [Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, DC 20015-1305 (United States); Collaboration: Disk Detective Collaboration; and others

    2016-10-20

    The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

  17. DISK DETECTIVE: DISCOVERY OF NEW CIRCUMSTELLAR DISK CANDIDATES THROUGH CITIZEN SCIENCE

    International Nuclear Information System (INIS)

    Kuchner, Marc J.; McElwain, Michael; Padgett, Deborah L.; Silverberg, Steven M.; Wisniewski, John P.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; García, Luciano; Jung, Dawoon; Lintott, Chris; Rebull, Luisa M.; Nesvold, Erika

    2016-01-01

    The Disk Detective citizen science project aims to find new stars with 22 μ m excess emission from circumstellar dust using data from NASA’s Wide-field Infrared Survey Explorer ( WISE ) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10 different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and protoplanetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137, and HD 218546) and a new detection of 22 μ m excess around the previously known debris disk host star HD 22128.

  18. Disk Detective: Discovery of New Circumstellar Disk Candidates Through Citizen Science

    Science.gov (United States)

    Kuchner, Marc J.; Silverberg, Steven M.; Bans, Alissa S.; Bhattacharjee, Shambo; Kenyon, Scott J.; Debes, John H.; Currie, Thayne; Garcia, Luciano; Jung, Dawoon; Lintott, Chris; hide

    2016-01-01

    The Disk Detective citizen science project aims to find new stars with 22 micron excess emission from circumstellar dust using data from NASAs Wide-field Infrared Survey Explorer (WISE) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and proto planetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137,and HD 218546) and a new detection of 22 micron excess around the previously known debris disk host star HD 22128.

  19. Magnetohydrodynamics of accretion disks

    International Nuclear Information System (INIS)

    Torkelsson, U.

    1994-04-01

    The thesis consists of an introduction and summary, and five research papers. The introduction and summary provides the background in accretion disk physics and magnetohydrodynamics. The research papers describe numerical studies of magnetohydrodynamical processes in accretion disks. Paper 1 is a one-dimensional study of the effect of magnetic buoyancy on a flux tube in an accretion disk. The stabilizing influence of an accretion disk corona on the flux tube is demonstrated. Paper 2-4 present numerical simulations of mean-field dynamos in accretion disks. Paper 11 verifies the correctness of the numerical code by comparing linear models to previous work by other groups. The results are also extended to somewhat modified disk models. A transition from an oscillatory mode of negative parity for thick disks to a steady mode of even parity for thin disks is found. Preliminary results for nonlinear dynamos at very high dynamo numbers are also presented. Paper 3 describes the bifurcation behaviour of the nonlinear dynamos. For positive dynamo numbers it is found that the initial steady solution is replaced by an oscillatory solution of odd parity. For negative dynamo numbers the solution becomes chaotic at sufficiently high dynamo numbers. Paper 4 continues the studies of nonlinear dynamos, and it is demonstrated that a chaotic solution appears even for positive dynamo numbers, but that it returns to a steady solution of mixed parity at very high dynamo numbers. Paper 5 describes a first attempt at simulating the small-scale turbulence of an accretion disk in three dimensions. There is only find cases of decaying turbulence, but this is rather due to limitations of the simulations than that turbulence is really absent in accretion disks

  20. Preparation of thin actinide metal disks using a multiple disk casting technique

    International Nuclear Information System (INIS)

    Conner, W.V.

    1975-01-01

    A casting technique has been developed for preparing multiple actinide metal disks which have a minimum thickness of 0.006 inch. This technique was based on an injection casting procedure which utilizes the weight of a tantalum metal rod to force the molten metal into the mold cavity. Using the proper mold design and casting parameters, it has been possible to prepare ten 1/2 inch diameter neptunium or plutonium metal disks in a single casting, This casting technique is capable of producing disks which are very uniform. The average thickness of the disks from a typical casting will vary no more than 0.001 inch and the variation in the thickness of the individual disks will range from 0.0001 to 0.0005 inch. (Auth.)

  1. Preparation of thin actinide metal disks using a multiple disk casting technique

    International Nuclear Information System (INIS)

    Conner, W.V.

    1976-01-01

    A casting technique has been developed for preparing multiple actinide metal disks which have a minimum thickness of 0.006 inch. This technique was based on an injection casting procedure which utilizes the weight of a tantalum metal rod to force the molten metal into the mold cavity. Using the proper mold design and casting parameters, it has been possible to prepare ten 1/2 inch diameter neptunium or plutonium metal disks in a single casting. This casting technique is capable of producing disks which are very uniform. The average thickness of the disks from a typical casting will vary no more than 0.001 inch and the variation in the thickness of the individual disks will range from 0.0001 to 0.0005 inch. (author)

  2. Galactic structure and gamma radiation

    International Nuclear Information System (INIS)

    Casse, Michel; Cesarsky, Catherine; Paul Jacques

    1977-01-01

    A model of spiral structure of the Galaxy is outlined from radiosynchrotron and gamma observations. The most interesting observations in the galactic context, obtained by the SAS II American satellite are concerned with the distribution of the γ photoemission at energies higher than 10 8 eV, along the galactic equator. The model proposed is in quantitative agreement with the present ideas on the spiral structure of the Galaxy, the galactic magnetic field, and the confinement of cosmic rays by the magnetic field and of the magnetic field by matter. Following the American era, the European COS-B satellite opens the European phase towards an identification of the discrete gamma radiation sources [fr

  3. Ultrafast Outflows: Galaxy-scale Active Galactic Nucleus Feedback

    Science.gov (United States)

    Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

    2013-01-01

    We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

  4. ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, A. Y.; Umemura, M. [Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8577 (Japan); Bicknell, G. V., E-mail: ayw@ccs.tsukuba.ac.jp [Research School of Astronomy and Astrophysics, Australian National University, ACT 2611 (Australia)

    2013-01-20

    We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

  5. ULTRAFAST OUTFLOWS: GALAXY-SCALE ACTIVE GALACTIC NUCLEUS FEEDBACK

    International Nuclear Information System (INIS)

    Wagner, A. Y.; Umemura, M.; Bicknell, G. V.

    2013-01-01

    We show, using global three-dimensional grid-based hydrodynamical simulations, that ultrafast outflows (UFOs) from active galactic nuclei (AGNs) result in considerable feedback of energy and momentum into the interstellar medium (ISM) of the host galaxy. The AGN wind interacts strongly with the inhomogeneous, two-phase ISM consisting of dense clouds embedded in a tenuous, hot, hydrostatic medium. The outflow floods through the intercloud channels, sweeps up the hot ISM, and ablates and disperses the dense clouds. The momentum of the UFO is primarily transferred to the dense clouds via the ram pressure in the channel flow, and the wind-blown bubble evolves in the energy-driven regime. Any dependence on UFO opening angle disappears after the first interaction with obstructing clouds. On kpc scales, therefore, feedback by UFOs operates similarly to feedback by relativistic AGN jets. Negative feedback is significantly stronger if clouds are distributed spherically rather than in a disk. In the latter case, the turbulent backflow of the wind drives mass inflow toward the central black hole. Considering the common occurrence of UFOs in AGNs, they are likely to be important in the cosmological feedback cycles of galaxy formation.

  6. ON THE TRANSITIONAL DISK CLASS: LINKING OBSERVATIONS OF T TAURI STARS AND PHYSICAL DISK MODELS

    International Nuclear Information System (INIS)

    Espaillat, C.; Andrews, S.; Qi, C.; Wilner, D.; Ingleby, L.; Calvet, N.; Hernández, J.; Furlan, E.; D'Alessio, P.; Muzerolle, J.

    2012-01-01

    Two decades ago 'transitional disks' (TDs) described spectral energy distributions (SEDs) of T Tauri stars with small near-IR excesses, but significant mid- and far-IR excesses. Many inferred this indicated dust-free holes in disks possibly cleared by planets. Recently, this term has been applied disparately to objects whose Spitzer SEDs diverge from the expectations for a typical full disk (FD). Here, we use irradiated accretion disk models to fit the SEDs of 15 such disks in NGC 2068 and IC 348. One group has a 'dip' in infrared emission while the others' continuum emission decreases steadily at all wavelengths. We find that the former have an inner disk hole or gap at intermediate radii in the disk and we call these objects 'transitional disks' and 'pre-transitional disks' (PTDs), respectively. For the latter group, we can fit these SEDs with FD models and find that millimeter data are necessary to break the degeneracy between dust settling and disk mass. We suggest that the term 'transitional' only be applied to objects that display evidence for a radical change in the disk's radial structure. Using this definition, we find that TDs and PTDs tend to have lower mass accretion rates than FDs and that TDs have lower accretion rates than PTDs. These reduced accretion rates onto the star could be linked to forming planets. Future observations of TDs and PTDs will allow us to better quantify the signatures of planet formation in young disks.

  7. Lithium abundances for 185 main-sequence stars: Galactic evolution and stellar depletion of lithium

    Science.gov (United States)

    Chen, Y. Q.; Nissen, P. E.; Benoni, T.; Zhao, G.

    2001-06-01

    We present a survey of lithium abundances in 185 main-sequence field stars with 5600 interesting result from this study is the presence of a large gap in the log varepsilon (Li) - Teff plane, which distinguishes ``Li-dip'' stars like those first identified in the Hyades cluster by Boesgaard & Tripicco (\\cite{Boesgaard86}) from other stars with a much higher Li abundance. The Li-dip stars concentrate on a certain mass, which decreases with metallicity from about 1.4 Msun at solar metallicity to 1.1 Msun at [Fe/H] =~ -1.0. Excluding the Li-dip stars and a small group of lower mass stars with Teff rate of angular momentum loss. It cannot be excluded, however, that a cosmic scatter of the Li abundance in the Galaxy at a given metallicity contributes to the dispersion in Li abundance. These problems make it difficult to determine the Galactic evolution of Li from the data, but a comparison of the upper envelope of the distribution of stars in the log varepsilon (Li) - [Fe/H] plane with recent Galactic evolutionary models by Romano et al. (\\cite{Romano99}) suggests that novae are a major source for the Li production in the Galactic disk; their occurrence seems to be the explanation for the steep increase of Li abundance at [Fe/H] =~ -0.4. Based on observations carried out at Beijing Astronomical Observatory (Xinglong, PR China) and European Southern Observatory, La Silla, Chile. Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/371/943 and at http://www.edpsciences.org

  8. AN XMM-NEWTON SURVEY OF THE SOFT X-RAY BACKGROUND. III. THE GALACTIC HALO X-RAY EMISSION

    International Nuclear Information System (INIS)

    Henley, David B.; Shelton, Robin L.

    2013-01-01

    We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on ∼4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 × 10 6 K, interquartile range = 0.63 × 10 6 K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude (∼(0.4-7) × 10 –3 cm –6 pc and ∼(0.5-7) × 10 –12 erg cm –2 s –1 deg –2 , respectively, with median detections of 1.9 × 10 –3 cm –6 pc and 1.5 × 10 –12 erg cm –2 s –1 deg –2 , respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper

  9. THE SPITZER INFRARED SPECTROGRAPH SURVEY OF PROTOPLANETARY DISKS IN ORION A. I. DISK PROPERTIES

    Energy Technology Data Exchange (ETDEWEB)

    Kim, K. H. [Korea Astronomy and Space Science Institute (KASI), 776, Daedeokdae-ro, Yuseong-gu, Daejeon 305-348 (Korea, Republic of); Watson, Dan M.; Manoj, P.; Forrest, W. J. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Furlan, Elise [Infrared Processing and Analysis Center, Caltech, 770 S. Wilson Avenue, Pasadena, CA 91125 (United States); Najita, Joan [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Sargent, Benjamin [Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Dr., Rochester, NY 14623 (United States); Hernández, Jesús [Centro de Investigaciones de Astronomía, Apdo. Postal 264, Mérida 5101-A (Venezuela, Bolivarian Republic of); Calvet, Nuria [Department of Astronomy, University of Michigan, 830 Dennison Building, 500 Church Street, Ann Arbor, MI 48109 (United States); Adame, Lucía [Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, Av. Universidad S/N, San Nicolás de los Garza, Nuevo León, C.P. 66451, México (Mexico); Espaillat, Catherine [Department of Astronomy, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Megeath, S. T. [Ritter Astrophysical Research Center, Department of Physics and Astronomy, University of Toledo, 2801 W. Bancroft St., Toledo, OH 43606 (United States); Muzerolle, James, E-mail: quarkosmos@kasi.re.kr [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2016-09-01

    We present our investigation of 319 Class II objects in Orion A observed by Spitzer /IRS. We also present the follow-up observations of 120 of these Class II objects in Orion A from the Infrared Telescope Facility/SpeX. We measure continuum spectral indices, equivalent widths, and integrated fluxes that pertain to disk structure and dust composition from IRS spectra of Class II objects in Orion A. We estimate mass accretion rates using hydrogen recombination lines in the SpeX spectra of our targets. Utilizing these properties, we compare the distributions of the disk and dust properties of Orion A disks with those of Taurus disks with respect to position within Orion A (Orion Nebular Cluster [ONC] and L1641) and with the subgroups by the inferred radial structures, such as transitional disks (TDs) versus radially continuous full disks (FDs). Our main findings are as follows. (1) Inner disks evolve faster than the outer disks. (2) The mass accretion rates of TDs and those of radially continuous FDs are statistically significantly displaced from each other. The median mass accretion rate of radially continuous disks in the ONC and L1641 is not very different from that in Taurus. (3) Less grain processing has occurred in the disks in the ONC compared to those in Taurus, based on analysis of the shape index of the 10 μ m silicate feature ( F {sub 11.3}/ F {sub 9.8}). (4) The 20–31 μ m continuum spectral index tracks the projected distance from the most luminous Trapezium star, θ {sup 1} Ori C. A possible explanation is UV ablation of the outer parts of disks.

  10. Brown dwarf disks with ALMA

    Energy Technology Data Exchange (ETDEWEB)

    Ricci, L.; Isella, A. [Department of Astronomy, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Testi, L.; De Gregorio-Monsalvo, I. [European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching (Germany); Natta, A. [INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Scholz, A., E-mail: lricci@astro.caltech.edu [School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2 (Ireland)

    2014-08-10

    We present Atacama Large Millimeter/submillimeter Array continuum and spectral line data at 0.89 mm and 3.2 mm for three disks surrounding young brown dwarfs and very low mass stars in the Taurus star forming region. Dust thermal emission is detected and spatially resolved for all the three disks, while CO(J = 3-2) emission is seen in two disks. We analyze the continuum visibilities and constrain the disks' physical structure in dust. The results of our analysis show that the disks are relatively large; the smallest one has an outer radius of about 70 AU. The inferred disk radii, radial profiles of the dust surface density, and disk to central object mass ratios lie within the ranges found for disks around more massive young stars. We derive from our observations the wavelength dependence of the millimeter dust opacity. In all the three disks, data are consistent with the presence of grains with at least millimeter sizes, as also found for disks around young stars, and confirm that the early stages of the solid growth toward planetesimals occur also around very low-mass objects. We discuss the implications of our findings on models of solids evolution in protoplanetary disks, the main mechanisms proposed for the formation of brown dwarfs and very low-mass stars, as well as the potential of finding rocky and giant planets around very low-mass objects.

  11. PLANETESIMAL DISK MICROLENSING

    International Nuclear Information System (INIS)

    Heng, Kevin; Keeton, Charles R.

    2009-01-01

    Motivated by debris disk studies, we investigate the gravitational microlensing of background starlight by a planetesimal disk around a foreground star. We use dynamical survival models to construct a plausible example of a planetesimal disk and study its microlensing properties using established ideas of microlensing by small bodies. When a solar-type source star passes behind a planetesimal disk, the microlensing light curve may exhibit short-term, low-amplitude residuals caused by planetesimals several orders of magnitude below Earth mass. The minimum planetesimal mass probed depends on the photometric sensitivity and the size of the source star, and is lower when the planetesimal lens is located closer to us. Planetesimal lenses may be found more nearby than stellar lenses because the steepness of the planetesimal mass distribution changes how the microlensing signal depends on the lens/source distance ratio. Microlensing searches for planetesimals require essentially continuous monitoring programs that are already feasible and can potentially set constraints on models of debris disks, the progeny of the supposed extrasolar analogues of Kuiper Belts.

  12. A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

    Energy Technology Data Exchange (ETDEWEB)

    Yao, J. M.; Wang, N. [Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150, Science 1-Street, Urumqi, Xinjiang 830011 (China); Manchester, R. N. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping NSW 1710 (Australia)

    2017-01-20

    We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

  13. A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES

    International Nuclear Information System (INIS)

    Yao, J. M.; Wang, N.; Manchester, R. N.

    2017-01-01

    We present a new model for the distribution of free electrons in the Galaxy, the Magellanic Clouds, and the intergalactic medium (IGM) that can be used to estimate distances to real or simulated pulsars and fast radio bursts (FRBs) based on their dispersion measure (DM). The Galactic model has an extended thick disk representing the so-called warm interstellar medium, a thin disk representing the Galactic molecular ring, spiral arms based on a recent fit to Galactic H ii regions, a Galactic Center disk, and seven local features including the Gum Nebula, Galactic Loop I, and the Local Bubble. An offset of the Sun from the Galactic plane and a warp of the outer Galactic disk are included in the model. Parameters of the Galactic model are determined by fitting to 189 pulsars with independently determined distances and DMs. Simple models are used for the Magellanic Clouds and the IGM. Galactic model distances are within the uncertainty range for 86 of the 189 independently determined distances and within 20% of the nearest limit for a further 38 pulsars. We estimate that 95% of predicted Galactic pulsar distances will have a relative error of less than a factor of 0.9. The predictions of YMW16 are compared to those of the TC93 and NE2001 models showing that YMW16 performs significantly better on all measures. Timescales for pulse broadening due to interstellar scattering are estimated for (real or simulated) Galactic and Magellanic Cloud pulsars and FRBs.

  14. Dusty disks around young stars

    NARCIS (Netherlands)

    Verhoeff, A.

    2009-01-01

    Stars are formed through the collapse of giant molecular clouds. During this contraction the matter spins up and naturally forms a circumstellar disk. Once accretion comes to a halt, these disks are relatively stable. Some disks are known to last up to 10 Myrs. Most disks however, dissipate on

  15. The galactic distribution of pulsars

    International Nuclear Information System (INIS)

    Lyne, A.G.

    1982-01-01

    The galactic distribution of pulsars follows the general form of many population I objects in galactocentric radius, but has a wide distribution above and below the plane due to high space velocities imparted to the pulsars at birth. Statistical studies of the properties of large numbers of pulsars and proper motion measurements demonstrate that the effective magnetic dipole moments decay on a timescale of about 8 million years. This work provides a better knowledge of pulsar evolution and ages and shows that a birthrate of one pulsar every 20 to 50 years is required to sustain the observed galactic population of 300,000. This rate is comparable with most recent estimates of the galactic supernova rate, but requires nearly all supernovae to produce active pulsars. (orig.)

  16. Debris Disks: Probing Planet Formation

    OpenAIRE

    Wyatt, Mark C.

    2018-01-01

    Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km i...

  17. Fast, Capacious Disk Memory Device

    Science.gov (United States)

    Muller, Ronald M.

    1990-01-01

    Device for recording digital data on, and playing back data from, memory disks has high recording or playback rate and utilizes available recording area more fully. Two disks, each with own reading/writing head, used to record data at same time. Head on disk A operates on one of tracks numbered from outside in; head on disk B operates on track of same number in sequence from inside out. Underlying concept of device applicable to magnetic or optical disks.

  18. THE MAGELLANIC STREAM: BREAK-UP AND ACCRETION ONTO THE HOT GALACTIC CORONA

    Energy Technology Data Exchange (ETDEWEB)

    Tepper-García, Thor; Bland-Hawthorn, Joss [Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW 2006 (Australia); Sutherland, Ralph S. [Mount Stromlo Observatory, Australia National University, Woden, ACT 2611 (Australia)

    2015-11-10

    The Magellanic H i Stream (≈2 × 10{sup 9} M{sub ⊙} [d/55 kpc]{sup 2}) encircling the Galaxy at a distance d is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent observations reveal that the Stream’s mass is in fact dominated (3:1) by its ionized component. Here we revisit the origin of the mysterious Hα recombination emission observed along much of its length that is overly bright (∼150–200 mR) for the known Galactic ultraviolet (UV) background (≈20–40 mR [d/55 kpc]{sup −2}). In an earlier model, we proposed that a slow shock cascade was operating along the Stream due to its interaction with the extended Galactic hot corona. We find that for a smooth coronal density profile, this model can explain the bright Hα emission if the coronal density satisfies 2 × 10{sup −4} < (n/cm{sup −3}) < 4 × 10{sup −4} at d = 55 kpc. But in view of updated parameters for the Galactic halo and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d > 55 kpc), we revisit the shock cascade model in detail. At lower densities, the H i gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. At higher densities, the hot coronal mass (including the other baryonic components) exceeds the baryon budget of the Galaxy. If the Hα emission arises from the shock cascade, the upper limit on the smooth coronal density constrains the Stream’s mean distance to ≲75 kpc. If, as some models indicate, the Stream is even further out, either the shock cascade is operating in a regime where the corona is substantially mass-loaded with recent gas debris, or an entirely different ionization mechanism is responsible.

  19. Mass distributions in disk galaxies

    NARCIS (Netherlands)

    Martinsson, Thomas; Verheijen, Marc; Bershady, Matthew; Westfall, Kyle; Andersen, David; Swaters, Rob

    We present results on luminous and dark matter mass distributions in disk galaxies from the DiskMass Survey. As expected for normal disk galaxies, stars dominate the baryonic mass budget in the inner region of the disk; however, at about four optical scale lengths (hR ) the atomic gas starts to

  20. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    International Nuclear Information System (INIS)

    Perets, Hagai B.; Kenyon, Scott J.

    2013-01-01

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10 –5 -10 –3 M ☉ , with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M ☉ . When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  1. A High-mass Protobinary System with Spatially Resolved Circumstellar Accretion Disks and Circumbinary Disk

    Energy Technology Data Exchange (ETDEWEB)

    Kraus, S.; Kluska, J.; Kreplin, A.; Bate, M.; Harries, T. J.; Hone, E.; Anugu, A. [School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom); Hofmann, K.-H.; Weigelt, G. [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Monnier, J. D. [Department of Astronomy, University of Michigan, 311 West Hall, 1085 South University Avenue, Ann Arbor, MI 48109 (United States); De Wit, W. J. [ESO, Alonso de Cordova 3107, Vitacura, Santiago 19 (Chile); Wittkowski, M., E-mail: skraus@astro.ex.ac.uk [ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München (Germany)

    2017-01-20

    High-mass multiples might form via fragmentation of self-gravitational disks or alternative scenarios such as disk-assisted capture. However, only a few observational constraints exist on the architecture and disk structure of high-mass protobinaries and their accretion properties. Here, we report the discovery of a close (57.9 ± 0.2 mas = 170 au) high-mass protobinary, IRAS17216-3801, where our VLTI/GRAVITY+AMBER near-infrared interferometry allows us to image the circumstellar disks around the individual components with ∼3 mas resolution. We estimate the component masses to ∼20 and ∼18 M {sub ⊙} and find that the radial intensity profiles can be reproduced with an irradiated disk model, where the inner regions are excavated of dust, likely tracing the dust sublimation region in these disks. The circumstellar disks are strongly misaligned with respect to the binary separation vector, which indicates that the tidal forces did not have time to realign the disks, pointing toward a young dynamical age of the system. We constrain the distribution of the Br γ and CO-emitting gas using VLTI/GRAVITY spectro-interferometry and VLT/CRIRES spectro-astrometry and find that the secondary is accreting at a higher rate than the primary. VLT/NACO imaging shows L ′-band emission on (3–4)× larger scales than the binary separation, matching the expected dynamical truncation radius for the circumbinary disk. The IRAS17216-3801 system is ∼3× more massive and ∼5× more compact than other high-mass multiplies imaged at infrared wavelength and the first high-mass protobinary system where circumstellar and circumbinary dust disks could be spatially resolved. This opens exciting new opportunities for studying star–disk interactions and the role of multiplicity in high-mass star formation.

  2. COLLIMATION AND SCATTERING OF THE ACTIVE GALACTIC NUCLEUS EMISSION IN THE SOMBRERO GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Menezes, R. B.; Steiner, J. E.; Ricci, T. V., E-mail: robertobm@astro.iag.usp.br [Instituto de Astronomia Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo, SP CEP 05508-090 (Brazil)

    2013-03-10

    We present an analysis of a data cube of the central region of M104, the Sombrero galaxy, obtained with the GMOS-IFU of the Gemini-South telescope, and report the discovery of collimation and scattering of the active galactic nucleus (AGN) emission in the circumnuclear region of this galaxy. Analysis with PCA Tomography and spectral synthesis revealed the existence of collimation and scattering of the AGN featureless continuum and also of a broad component of the H{alpha} emission line. The collimation and scattering of this broad H{alpha} component was also revealed by fitting the [N II] {lambda}{lambda}6548, 6583 and H{alpha} emission lines as a sum of Gaussian functions. The spectral synthesis, together with a V-I image obtained with the Hubble Space Telescope, showed the existence of circumnuclear dust, which may cause the light scattering. We also identify a dusty feature that may be interpreted as a torus/disk structure. The existence of two opposite regions with featureless continuum (P.A. = -18 Degree-Sign {+-} 13 Degree-Sign and P.A. = 162 Degree-Sign {+-} 13 Degree-Sign ) along a direction perpendicular to the torus/disk (P.A. = 72 Degree-Sign {+-} 14 Degree-Sign ) suggests that this structure is approximately edge-on and collimates the AGN emission. The edge-on torus/disk also hides the broad-line region. The proposed scenario is compatible with the unified model and explains why only a weak broad component of the H{alpha} emission line is visible and also why many previous studies detected no broad H{alpha}. The technique used here proved to be an efficient method not only for detecting scattered light, but also for testing the unified model in low-luminosity AGNs.

  3. Observation of galactic gamma radiation

    International Nuclear Information System (INIS)

    Paul, J.A.

    1982-09-01

    A complete and deep survey of the galactic high-energy gamma radiation is now available, thanks to the gamma-ray telescopes on board of the SAS-2 and COS-B spacecrafts. A comparison of the COS-B gamma-ray survey with a fully sampled CO survey together with an Hsub(I) survey is used to show that a simple model, in which uniformly distributed cosmic rays interact with the interstellar gas, can account for almost all the gamma-ray emission observed in the first galactic quadrant. At medium galactic latitudes, it is shown that a relationship exists between the gamma radiation and the interstellar absorption derived from galaxy counts. Therefore gamma rays from the local galactic environment can be used as a valuable probe of the content and structure of the local interstellar medium. The large scale features of the local interstellar gas are revealed, in particular wide concentrations of nearby molecular hydrogen. On a smaller scale, the detection of numerous localized gamma-ray sources focuses the attention on some particular phases of clusters of young and massive stars where diffuse processes of gamma-ray emission may also be at work

  4. Source to Accretion Disk Tilt

    OpenAIRE

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source to cause and maintain disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through...

  5. Evolution of magnetic disk subsystems

    Science.gov (United States)

    Kaneko, Satoru

    1994-06-01

    The higher recording density of magnetic disk realized today has brought larger storage capacity per unit and smaller form factors. If the required access performance per MB is constant, the performance of large subsystems has to be several times better. This article describes mainly the technology for improving the performance of the magnetic disk subsystems and the prospects of their future evolution. Also considered are 'crosscall pathing' which makes the data transfer channel more effective, 'disk cache' which improves performance coupling with solid state memory technology, and 'RAID' which improves the availability and integrity of disk subsystems by organizing multiple disk drives in a subsystem. As a result, it is concluded that since the performance of the subsystem is dominated by that of the disk cache, maximation of the performance of the disk cache subsystems is very important.

  6. STELLAR MASS DEPENDENT DISK DISPERSAL

    International Nuclear Information System (INIS)

    Kennedy, Grant M.; Kenyon, Scott J.

    2009-01-01

    We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

  7. WIND-DRIVEN ACCRETION IN PROTOPLANETARY DISKS. I. SUPPRESSION OF THE MAGNETOROTATIONAL INSTABILITY AND LAUNCHING OF THE MAGNETOCENTRIFUGAL WIND

    International Nuclear Information System (INIS)

    Bai Xuening; Stone, James M.

    2013-01-01

    We perform local, vertically stratified shearing-box MHD simulations of protoplanetary disks (PPDs) at a fiducial radius of 1 AU that take into account the effects of both Ohmic resistivity and ambipolar diffusion (AD). The magnetic diffusion coefficients are evaluated self-consistently from a look-up table based on equilibrium chemistry. We first show that the inclusion of AD dramatically changes the conventional picture of layered accretion. Without net vertical magnetic field, the system evolves into a toroidal field dominated configuration with extremely weak turbulence in the far-UV ionization layer that is far too inefficient to drive rapid accretion. In the presence of a weak net vertical field (plasma β ∼ 10 5 at midplane), we find that the magnetorotational instability (MRI) is completely suppressed, resulting in a fully laminar flow throughout the vertical extent of the disk. A strong magnetocentrifugal wind is launched that efficiently carries away disk angular momentum and easily accounts for the observed accretion rate in PPDs. Moreover, under a physical disk wind geometry, all the accretion flow proceeds through a strong current layer with a thickness of ∼0.3H that is offset from disk midplane with radial velocity of up to 0.4 times the sound speed. Both Ohmic resistivity and AD are essential for the suppression of the MRI and wind launching. The efficiency of wind transport increases with increasing net vertical magnetic flux and the penetration depth of the FUV ionization. Our laminar wind solution has important implications on planet formation and global evolution of PPDs.

  8. Manipulation of magnetic vortex parameters in disk-on-disk nanostructures with various geometry

    Directory of Open Access Journals (Sweden)

    Maxim E. Stebliy

    2015-03-01

    Full Text Available Magnetic nanostructures in the form of a sandwich consisting of two permalloy (Py disks with diameters of 600 and 200 nm separated by a nonmagnetic interlayer are studied. Magnetization reversal of the disk-on-disk nanostructures depends on the distance between centers of the small and big disks and on orientation of an external magnetic field applied during measurements. It is found that manipulation of the magnetic vortex chirality and the trajectory of the vortex core in the big disk is only possible in asymmetric nanostructures. Experimentally studied peculiarities of a motion path of the vortex core and vortex parameters by the magneto-optical Kerr effect (MOKE magnetometer are supported by the magnetic force microscopy imaging and micromagnetic simulations.

  9. Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

    2017-08-10

    The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (∼1–20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

  10. Global Simulations of the Inner Regions of Protoplanetary Disks with Comprehensive Disk Microphysics

    Science.gov (United States)

    Bai, Xue-Ning

    2017-08-01

    The gas dynamics of weakly ionized protoplanetary disks (PPDs) are largely governed by the coupling between gas and magnetic fields, described by three non-ideal magnetohydrodynamical (MHD) effects (Ohmic, Hall, ambipolar). Previous local simulations incorporating these processes have revealed that the inner regions of PPDs are largely laminar and accompanied by wind-driven accretion. We conduct 2D axisymmetric, fully global MHD simulations of these regions (˜1-20 au), taking into account all non-ideal MHD effects, with tabulated diffusion coefficients and approximate treatment of external ionization and heating. With the net vertical field aligned with disk rotation, the Hall-shear instability strongly amplifies horizontal magnetic field, making the overall dynamics dependent on initial field configuration. Following disk formation, the disk likely relaxes into an inner zone characterized by asymmetric field configuration across the midplane, which smoothly transitions to a more symmetric outer zone. Angular momentum transport is driven by both MHD winds and laminar Maxwell stress, with both accretion and decretion flows present at different heights, and modestly asymmetric winds from the two disk sides. With anti-aligned field polarity, weakly magnetized disks settle into an asymmetric field configuration with supersonic accretion flow concentrated at one side of the disk surface, and highly asymmetric winds between the two disk sides. In all cases, the wind is magneto-thermal in nature, characterized by a mass loss rate exceeding the accretion rate. More strongly magnetized disks give more symmetric field configuration and flow structures. Deeper far-UV penetration leads to stronger and less stable outflows. Implications for observations and planet formation are also discussed.

  11. A fluid dynamical flow model for the central peak in the rotation curve of disk galaxies

    International Nuclear Information System (INIS)

    Bhattacharyya, T.; Basu, B.

    1980-01-01

    The rotation curve of the central region in some disk galaxies shows a linear rise, terminating at a peak (primary peak) which is then vollowed by a deep minimum. The curve then again rises to another peak at more or less half-way across the galactic radius. This latter peak is considered as the peak of the rotation curve in all large-scale analysis of galactic structure. The primary peak is usually ignored for the purpose. In this work an attempt has been made to look at the primary peak as the manifestation of the post-explosion flow pattern of gas in the deep central region of galaxies. Solving hydrodynamical equations of motion, a flow model has been derived which imitates very closely the actually observed linear rotational velocity, followed by the falling branch of the curve to minimum. The theoretical flow model has been compared with observed results for nine galaxies. The agreement obtained is extremely encouraging. The distance of the primary peak from the galactic centre has been shown to be correlated with the angular velocity in the linear part of the rotation curve. Here also, agreement is very good between theoretical and observed results. It is concluded that the distance of the primary peak from the centre not only speaks of the time that has elapsed since the explosion occurred in the nucleus, it also speaks of the potential capability of the nucleus of the galaxy for repeating explosions through some efficient process of mass replenishment at the core. (orig.)

  12. The impact of galaxy geometry and mass evolution on the survival of star clusters

    International Nuclear Information System (INIS)

    Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

    2014-01-01

    Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10 10 M ☉ to 10 × 10 10 M ☉ halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk of identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.

  13. WIND-ACCRETION DISKS IN WIDE BINARIES, SECOND-GENERATION PROTOPLANETARY DISKS, AND ACCRETION ONTO WHITE DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Perets, Hagai B. [Technion-Israel Institute of Technology, Haifa (Israel); Kenyon, Scott J., E-mail: hperets@physics.technion.ac.il [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

    2013-02-20

    Mass transfer from an evolved donor star to its binary companion is a standard feature of stellar evolution in binaries. In wide binaries, the companion star captures some of the mass ejected in a wind by the primary star. The captured material forms an accretion disk. Here, we study the evolution of wind-accretion disks, using a numerical approach which allows us to follow the long-term evolution. For a broad range of initial conditions, we derive the radial density and temperature profiles of the disk. In most cases, wind accretion leads to long-lived stable disks over the lifetime of the asymptotic giant branch donor star. The disks have masses of a few times 10{sup -5}-10{sup -3} M {sub Sun }, with surface density and temperature profiles that follow broken power laws. The total mass in the disk scales approximately linearly with the viscosity parameter used. Roughly, 50%-80% of the mass falling into the disk accretes onto the central star; the rest flows out through the outer edge of the disk into the stellar wind of the primary. For systems with large accretion rates, the secondary accretes as much as 0.1 M {sub Sun }. When the secondary is a white dwarf, accretion naturally leads to nova and supernova eruptions. For all types of secondary star, the surface density and temperature profiles of massive disks resemble structures observed in protoplanetary disks, suggesting that coordinated observational programs might improve our understanding of uncertain disk physics.

  14. Design of dry sand soil stratified sampler

    Science.gov (United States)

    Li, Erkang; Chen, Wei; Feng, Xiao; Liao, Hongbo; Liang, Xiaodong

    2018-04-01

    This paper presents a design of a stratified sampler for dry sand soil, which can be used for stratified sampling of loose sand under certain conditions. Our group designed the mechanical structure of a portable, single - person, dry sandy soil stratified sampler. We have set up a mathematical model for the sampler. It lays the foundation for further development of design research.

  15. Numerical simulations with a FSI-calibrated actuator disk model of wind turbines operating in stratified ABLs

    Science.gov (United States)

    Gohari, S. M. Iman; Sarkar, Sutanu; Korobenko, Artem; Bazilevs, Yuri

    2017-11-01

    Numerical simulations of wind turbines operating under different regimes of stability are performed using LES. A reduced model, based on the generalized actuator disk model (ADM), is implemented to represent the wind turbines within the ABL. Data from the fluid-solid interaction (FSI) simulations of wind turbines have been used to calibrate and validate the reduced model. The computational cost of this method to include wind turbines is affordable and incurs an overhead as low as 1.45%. Using this reduced model, we study the coupling of unsteady turbulent flow with the wind turbine under different ABL conditions: (i) A neutral ABL with zero heat-flux and inversion layer at 350m, in which the incoming wind has the maximum mean shear between the heights of upper-tip and lower-tip; (2) A shallow ABL with surface cooling rate of -1 K/hr wherein the low level jet occurs at the wind turbine hub height. We will discuss how the differences in the unsteady flow between the two ABL regimes impact the wind turbine performance.

  16. A high spatial resolution X-ray and Hα study of hot gas in the halos of star-forming disk galaxies -- testing feedback models

    Science.gov (United States)

    Strickland, D. K.; Heckman, T. M.; Colbert, E. J. M.; Hoopes, C. G.; Weaver, K. A.

    2002-12-01

    We present arcsecond resolution Chandra X-ray and ground-based optical Hα imaging of a sample of ten edge-on star-forming disk galaxies (seven starburst and three ``normal'' spiral galaxies), a sample which covers the full range of star-formation intensity found in disk galaxies. The X-ray observations make use of the unprecented spatial resolution of the Chandra X-ray observatory to robustly remove X-ray emission from point sources, and hence obtain the X-ray properties of the diffuse thermal emission alone. This data has been combined with existing, comparable-resolution, ground-based Hα imaging. We compare these empirically-derived diffuse X-ray properties with various models for the generation of hot gas in the halos of star-forming galaxies: supernova feedback-based models (starburst-driven winds, galactic fountains), cosmologically-motivated accretion of the IGM and AGN-driven winds. SN feedback models best explain the observed diffuse X-ray emission. We then use the data to test basic, but fundamental, aspects of wind and fountain theories, e.g. the critical energy required for disk "break-out." DKS is supported by NASA through Chandra Postdoctoral Fellowship Award Number PF0-10012.

  17. Interpretation of astrophysical neutrinos observed by IceCube experiment by setting Galactic and extra-Galactic spectral components

    CERN Document Server

    Marinelli, Antonio; Grasso, Dario; Urbano, Alfredo; Valli, Mauro

    2016-01-01

    The last IceCube catalog of High Energy Starting Events (HESE) obtained with a livetime of 1347 days comprises 54 neutrino events equally-distributed between the three families with energies between 25 TeV and few PeVs. Considering the homogeneous flavors distribution (1:1:1) and the spectral features of these neutrinos the IceCube collaboration claims the astrophysical origin of these events with more than $5\\sigma$. The spatial distribution of cited events does not show a clear correlation with known astrophysical accelerators leaving opened both the Galactic and the extra-Galactic origin interpretations. Here, we compute the neutrino diffuse emission of our Galaxy on the basis of a recently proposed phenomenological model characterized by radially-dependent cosmic-ray (CR) transport properties. We show that the astrophysical spectrum measured by IceCube experiment can be well explained adding to the diffuse Galactic neutrino flux (obtained with this new model) a extra-Galactic component derived from the as...

  18. Vibration of imperfect rotating disk

    Directory of Open Access Journals (Sweden)

    Půst L.

    2011-12-01

    Full Text Available This study is concerned with the theoretical and numerical calculations of the flexural vibrations of a bladed disk. The main focus of this study is to elaborate the basic background for diagnostic and identification methods for ascertaining the main properties of the real structure or an experimental model of turbine disks. The reduction of undesirable vibrations of blades is proposed by using damping heads, which on the experimental model of turbine disk are applied only on a limited number of blades. This partial setting of damping heads introduces imperfection in mass, stiffness and damping distribution on the periphery and leads to more complicated dynamic properties than those of a perfect disk. Calculation of FEM model and analytic—numerical solution of disk behaviour in the limited (two modes frequency range shows the splitting of resonance with an increasing speed of disk rotation. The spectrum of resonance is twice denser than that of a perfect disk.

  19. CN rings in full protoplanetary disks around young stars as probes of disk structure

    Science.gov (United States)

    Cazzoletti, P.; van Dishoeck, E. F.; Visser, R.; Facchini, S.; Bruderer, S.

    2018-01-01

    Aims: Bright ring-like structure emission of the CN molecule has been observed in protoplanetary disks. We investigate whether such structures are due to the morphology of the disk itself or if they are instead an intrinsic feature of CN emission. With the intention of using CN as a diagnostic, we also address to which physical and chemical parameters CN is most sensitive. Methods: A set of disk models were run for different stellar spectra, masses, and physical structures via the 2D thermochemical code DALI. An updated chemical network that accounts for the most relevant CN reactions was adopted. Results: Ring-shaped emission is found to be a common feature of all adopted models; the highest abundance is found in the upper outer regions of the disk, and the column density peaks at 30-100 AU for T Tauri stars with standard accretion rates. Higher mass disks generally show brighter CN. Higher UV fields, such as those appropriate for T Tauri stars with high accretion rates or for Herbig Ae stars or for higher disk flaring, generally result in brighter and larger rings. These trends are due to the main formation paths of CN, which all start with vibrationally excited H_2^* molecules, that are produced through far ultraviolet (FUV) pumping of H2. The model results compare well with observed disk-integrated CN fluxes and the observed location of the CN ring for the TW Hya disk. Conclusions: CN rings are produced naturally in protoplanetary disks and do not require a specific underlying disk structure such as a dust cavity or gap. The strong link between FUV flux and CN emission can provide critical information regarding the vertical structure of the disk and the distribution of dust grains which affects the UV penetration, and could help to break some degeneracies in the SED fitting. In contrast with C2H or c-C3H2, the CN flux is not very sensitive to carbon and oxygen depletion.

  20. HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

    International Nuclear Information System (INIS)

    Cieza, Lucas A.; Olofsson, Johan; Henning, Thomas; Harvey, Paul M.; Evans II, Neal J.; Pinte, Christophe; Augereau, Jean-Charles; Ménard, Francois; Merín, Bruno; Najita, Joan

    2011-01-01

    T Cha is a nearby (d ∼ 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huélamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 μm) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 μm without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond ∼40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

  1. HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

    Energy Technology Data Exchange (ETDEWEB)

    Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Olofsson, Johan; Henning, Thomas [Max Planck Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg (Germany); Harvey, Paul M.; Evans II, Neal J. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Pinte, Christophe; Augereau, Jean-Charles; Menard, Francois [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041 (France); Merin, Bruno [Herschel Science Centre, European Space Agency (ESAC), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Najita, Joan, E-mail: lcieza@ifa.hawaii.edu [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 86719 (United States)

    2011-11-10

    T Cha is a nearby (d {approx} 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 {mu}m) of T Cha from the 'Dust, Ice, and Gas in Time' Key Program, which bridges the wavelength range between existing Spitzer and millimeter data and provide important constraints on the outer disk properties of this extraordinary system. We model the entire optical to millimeter wavelength spectral energy distribution (SED) of T Cha (19 data points between 0.36 and 3300 {mu}m without any major gaps in wavelength coverage). T Cha shows a steep spectral slope in the far-IR, which we find clearly favors models with outer disks containing little or no dust beyond {approx}40 AU. The full SED can be modeled equally well with either an outer disk that is very compact (only a few AU wide) or a much larger one that has a very steep surface density profile. That is, T Cha's outer disk seems to be either very small or very tenuous. Both scenarios suggest a highly unusual outer disk and have important but different implications for the nature of T Cha. Spatially resolved images are needed to distinguish between the two scenarios.

  2. Power spectrum analysis of polarized emission from the Canadian galactic plane survey

    Energy Technology Data Exchange (ETDEWEB)

    Stutz, R. A.; Rosolowsky, E. W. [University of British Columbia Okanagan, 3333 University Way, Kelowna BC, V1V 1V7 (Canada); Kothes, R.; Landecker, T. L. [National Research Council Canada, Dominion Radio Astrophysical Observatory, Box 248, Penticton, BC, V2A 6J9 (Canada)

    2014-05-20

    Angular power spectra are calculated and presented for the entirety of the Canadian Galactic Plane Survey polarization data set at 1.4 GHz covering an area of 1060 deg{sup 2}. The data analyzed are a combination of data from the 100 m Effelsberg Telescope, the 26 m Telescope at the Dominion Radio Astrophysical Observatory, and the Synthesis Telescope at the Dominion Radio Astrophysical Observatory, allowing all scales to be sampled down to arcminute resolution. The resulting power spectra cover multipoles from ℓ ≈ 60 to ℓ ≈ 10{sup 4} and display both a power-law component at low multipoles and a flattening at high multipoles from point sources. We fit the power spectrum with a model that accounts for these components and instrumental effects. The resulting power-law indices are found to have a mode of 2.3, similar to previous results. However, there are significant regional variations in the index, defying attempts to characterize the emission with a single value. The power-law index is found to increase away from the Galactic plane. A transition from small-scale to large-scale structure is evident at b = 9°, associated with the disk-halo transition in a 15° region around l = 108°. Localized variations in the index are found toward H II regions and supernova remnants, but the interpretation of these variations is inconclusive. The power in the polarized emission is anticorrelated with bright thermal emission (traced by Hα emission) indicating that the thermal emission depolarizes background synchrotron emission.

  3. Boundary layer circulation in disk-halo galaxies. III. The dispersion relation for local disturbances and large-scale spiral waves

    International Nuclear Information System (INIS)

    Waxman, A.M.

    1980-01-01

    This paper concerns the geometry and physical properties of waves which arise from a shear-flow (i.e. inflection point) instability of the galactic boundary layer circulation. This circulation was shown to exist in the meridional plane of a model galaxy containing a gaseous disk embedded in a rotating gaseous halo. Previously derived equations describe the local effects of Boussinesq perturbations, in the form of spiral waves with aribitrary pitch angle, on the model disk-halo system. The equations are solved asymptotically for large values of the local Reynolds number. In passing to the limit of inviscid waves, it is possible to derive a locally valid dispersion relation. A perturbation technique is developed whereby the inviscid wave eigenvalues can be corrected for the effects of small but finite viscosity. In this way the roles of the buoyancy force, Coriolis acceleration, viscous stresses, and their interactions can be studied. It is found that, locally, the most unstable inviscid waves are leading and open with large azimuthal wavenumbers. However, these waves display little or no coherence over the face of the disk and so would not emerge as modes in a global analysis.The geometry of the dominant inviscid waves is found to be leading, tightly wound spirals. Viscous corrections shift the dominant wave form to trailing, tightly wound spirals with small azimuthal wavenumbers. These waves grow on a time scale of about 10 7 years. It is suggested that these waves can initiate spiral structure in galaxies during disk formation and that a subsequent transition to a self-gravitating acoustical mode with the same spiral geometry may occur. This transition becomes possible once the contrast in gas densities between the disk and surrounding halo becomes sufficiently large

  4. The galactic distribution of Wolf-Rayet stars

    International Nuclear Information System (INIS)

    Hidayat, B.; Supelli, K.; Hucht, K.A. van der

    1982-01-01

    On the basis of the most recent compilation of narrow-band photometry and absolute visual magnitudes of Wolf-Rayet stars, and adopting a normal interstellar extinction law in all directions, the galactic distribution of 132 of the 159 known galactic WR stars is presented and discussed. The spiral structure is found to be more clearly pronounced than in earlier studies. Furthermore the authors find an indication of two spiral arms at r=4 and 6 kpc. There appears to be an asymmetry of the z-distribution of single stars with respect to galactic longitude. The location of the WC8.5 and WC9 stars between 4.5 and 9 kpc from the galactic center is discussed in the context of Maeder's red supergiant to WR star scenario. (Auth.)

  5. Audit: Automated Disk Investigation Toolkit

    Directory of Open Access Journals (Sweden)

    Umit Karabiyik

    2014-09-01

    Full Text Available Software tools designed for disk analysis play a critical role today in forensics investigations. However, these digital forensics tools are often difficult to use, usually task specific, and generally require professionally trained users with IT backgrounds. The relevant tools are also often open source requiring additional technical knowledge and proper configuration. This makes it difficult for investigators without some computer science background to easily conduct the needed disk analysis. In this paper, we present AUDIT, a novel automated disk investigation toolkit that supports investigations conducted by non-expert (in IT and disk technology and expert investigators. Our proof of concept design and implementation of AUDIT intelligently integrates open source tools and guides non-IT professionals while requiring minimal technical knowledge about the disk structures and file systems of the target disk image.

  6. THE STRUCTURE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI. I. RECONSTRUCTED VELOCITY-DELAY MAPS

    International Nuclear Information System (INIS)

    Grier, C. J.; Peterson, B. M.; Pogge, R. W.; De Rosa, G.; Martini, Paul; Kochanek, C. S.; Zu, Y.; Shappee, B.; Beatty, T. G.; Salvo, C. Araya; Bird, J. C.; Horne, Keith; Bentz, M. C.; Denney, K. D.; Siverd, R.; Sergeev, S. G.; Borman, G. A.; Kaspi, S.; Bord, D. J.; Che, X.

    2013-01-01

    We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the Hβ emission line. The four velocity-delay maps show unique dynamical signatures for each object. For 3C 120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the He II λ4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the He II emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocity-binned analysis of Mrk 6. The maps for 3C 120 and Mrk 335 are two of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements.

  7. THE STRUCTURE OF THE BROAD-LINE REGION IN ACTIVE GALACTIC NUCLEI. I. RECONSTRUCTED VELOCITY-DELAY MAPS

    Energy Technology Data Exchange (ETDEWEB)

    Grier, C. J.; Peterson, B. M.; Pogge, R. W.; De Rosa, G.; Martini, Paul; Kochanek, C. S.; Zu, Y.; Shappee, B.; Beatty, T. G.; Salvo, C. Araya; Bird, J. C. [Department of Astronomy, The Ohio State University, 140 W 18th Ave, Columbus, OH 43210 (United States); Horne, Keith [SUPA Physics and Astronomy, University of St. Andrews, Fife, KY16 9SS Scotland (United Kingdom); Bentz, M. C. [Department of Physics and Astronomy, Georgia State University, Astronomy Offices, One Park Place South SE, Suite 700, Atlanta, GA 30303 (United States); Denney, K. D. [Marie Curie Fellow at the Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen (Denmark); Siverd, R. [Department of Physics and Astronomy, Vanderbilt University, 5301 Stevenson Center, Nashville, TN 37235 (United States); Sergeev, S. G.; Borman, G. A. [Crimean Astrophysical Observatory, P/O Nauchny Crimea 98409 (Ukraine); Kaspi, S. [School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Bord, D. J. [Department of Natural Sciences, The University of Michigan - Dearborn, 4901 Evergreen Rd, Dearborn, MI 48128 (United States); Che, X. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 41809 (United States); and others

    2013-02-10

    We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the H{beta} emission line. The four velocity-delay maps show unique dynamical signatures for each object. For 3C 120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the He II {lambda}4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the He II emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocity-binned analysis of Mrk 6. The maps for 3C 120 and Mrk 335 are two of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements.

  8. YottaYotta announces new world record set for TCP disk-to-disk bulk transfer

    CERN Document Server

    2002-01-01

    The Yottabyte NetStorage(TM) Company, today announced a new world record for TCP disk-to-disk data transfer using the company's NetStorager(R) System. The record-breaking demonstration transferred 5 terabytes of data between Chicago, Il. to Vancouver, BC and Ottawa, ON, at a sustained average throughput of 11.1 gigabits per second. Peak throughput exceeded 11.6 gigabits per second, more than 15-times faster than previous records for TCP transfer from disk-to-disk (1 page).

  9. Disk-to-Disk network transfers at 100 Gb/s

    Science.gov (United States)

    Barczyk, Artur; Gable, Ian; Hay, Marilyn; Leavett-Brown, Colin; Legrand, Iosif; Lewall, Kim; McKee, Shawn; McWilliam, Donald; Mughal, Azher; Newman, Harvey; Rozsa, Sandor; Savard, Yvan; Sobie, Randall J.; Tam, Thomas; Voicu, Ramiro

    2012-12-01

    A 100 Gbps network was established between the California Institute of Technology conference booth at the Super Computing 2011 conference in Seattle, Washington and the computing center at the University of Victoria in Canada. A circuit was established over the BCNET, CANARIE and Super Computing (SCInet) networks using dedicated equipment. The small set of servers at the endpoints used a combination of 10GE and 40GE technologies, and SSD drives for data storage. The configuration of the network and the server configuration are discussed. We will show that the system was able to achieve disk-to-disk transfer rates of 60 Gbps and memory-to-memory rates in excess of 180 Gbps across the WAN. We will discuss the transfer tools, disk configurations, and monitoring tools used in the demonstration.

  10. Disk-to-Disk network transfers at 100 Gb/s

    International Nuclear Information System (INIS)

    Barczyk, Artur; Legrand, Iosif; Mughal, Azher; Newman, Harvey; Rozsa, Sandor; Voicu, Ramiro; Gable, Ian; Leavett-Brown, Colin; Lewall, Kim; Savard, Yvan; Sobie, Randall J; Hay, Marilyn; McWilliam, Donald; McKee, Shawn; Tam, Thomas

    2012-01-01

    A 100 Gbps network was established between the California Institute of Technology conference booth at the Super Computing 2011 conference in Seattle, Washington and the computing center at the University of Victoria in Canada. A circuit was established over the BCNET, CANARIE and Super Computing (SCInet) networks using dedicated equipment. The small set of servers at the endpoints used a combination of 10GE and 40GE technologies, and SSD drives for data storage. The configuration of the network and the server configuration are discussed. We will show that the system was able to achieve disk-to-disk transfer rates of 60 Gbps and memory-to-memory rates in excess of 180 Gbps across the WAN. We will discuss the transfer tools, disk configurations, and monitoring tools used in the demonstration.

  11. Probing disk wind and other properties of 4U 1630-47

    Science.gov (United States)

    Bhattacharyya, Sudip

    2015-09-01

    The accreting Galactic black hole transient 4U 1630-47, which is currently in outburst, is an ideal source to probe two types of accreted matter ejection: (1) via disk wind and (2) via jet, both using the observed narrow spectral lines (Diaz Trigo et al., 2013, Nature, 504, 206; Neilsen et al. 2014; Diaz Trigo et al. 2014). Chandra gratings are ideal to study such lines. The source also showed indications of high-frequency (HF) quasi-periodic oscillations (QPOs) in a rather high (150-450 Hz) frequency range, which can be extremely useful to probe the strong gravity regime. The AstroSat satellite, because of its large area and high timing resolution in a broad energy band, can potentially detect and measure HF QPOs and probe the source broadband spectrum and state. Hence, our proposed 30 ks Chandra exposure, nearly contemporaneous with complementary AstroSat observations, will provide an excellent way to probe the accretion and ejection mechanism in the strong gravity regime.

  12. Galactic Winds and the Role Played by Massive Stars

    Science.gov (United States)

    Heckman, Timothy M.; Thompson, Todd A.

    Galactic winds from star-forming galaxies play at key role in the evolution of galaxies and the intergalactic medium. They transport metals out of galaxies, chemically enriching the intergalactic medium and modifying the chemical evolution of galaxies. They affect the surrounding interstellar and circumgalactic media, thereby influencing the growth of galaxies though gas accretion and star formation. In this contribution we first summarize the physical mechanisms by which the momentum and energy output from a population of massive stars and associated supernovae can drive galactic winds. We use the prototypical example of M 82 to illustrate the multiphase nature of galactic winds. We then describe how the basic properties of galactic winds are derived from the data, and summarize how the properties of galactic winds vary systematically with the properties of the galaxies that launch them. We conclude with a brief discussion of the broad implications of galactic winds.

  13. MODELING DUST EMISSION OF HL TAU DISK BASED ON PLANET–DISK INTERACTIONS

    International Nuclear Information System (INIS)

    Jin, Sheng; Ji, Jianghui; Li, Shengtai; Li, Hui; Isella, Andrea

    2016-01-01

    We use extensive global two-dimensional hydrodynamic disk gas+dust simulations with embedded planets, coupled with three-dimensional radiative transfer calculations, to model the dust ring and gap structures in the HL Tau protoplanetary disk observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We include the self-gravity of disk gas and dust components and make reasonable choices of disk parameters, assuming an already settled dust distribution and no planet migration. We can obtain quite adequate fits to the observed dust emission using three planets with masses of 0.35, 0.17, and 0.26 M Jup at 13.1, 33.0, and 68.6 AU, respectively. Implications for the planet formation as well as the limitations of this scenario are discussed

  14. Fast disk array for image storage

    Science.gov (United States)

    Feng, Dan; Zhu, Zhichun; Jin, Hai; Zhang, Jiangling

    1997-01-01

    A fast disk array is designed for the large continuous image storage. It includes a high speed data architecture and the technology of data striping and organization on the disk array. The high speed data path which is constructed by two dual port RAM and some control circuit is configured to transfer data between a host system and a plurality of disk drives. The bandwidth can be more than 100 MB/s if the data path based on PCI (peripheral component interconnect). The organization of data stored on the disk array is similar to RAID 4. Data are striped on a plurality of disk, and each striping unit is equal to a track. I/O instructions are performed in parallel on the disk drives. An independent disk is used to store the parity information in the fast disk array architecture. By placing the parity generation circuit directly on the SCSI (or SCSI 2) bus, the parity information can be generated on the fly. It will affect little on the data writing in parallel on the other disks. The fast disk array architecture designed in the paper can meet the demands of the image storage.

  15. MODIFIED GRAVITY SPINS UP GALACTIC HALOS

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jounghun [Astronomy Program, Department of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-747 (Korea, Republic of); Zhao, Gong-Bo [National Astronomy Observatories, Chinese Academy of Science, Beijing 100012 (China); Li, Baojiu [Institute of Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Koyama, Kazuya, E-mail: jounghun@astro.snu.ac.kr [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom)

    2013-01-20

    We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

  16. Galactic Observations of Terahertz C+ (GOT C+): Inner Galaxy Survey

    Science.gov (United States)

    Yorke, Harold; Langer, William; Velusamy, T.; Pineda, J. L.; Goldsmith, P. F.; Li, D.

    To understand the lifecycle of the interstellar gas and star formation we need detailed information about the diffuse atomic and diffuse molecular gas cloud properties. The ionized carbon [CII] 1.9 THz fine structure line is an important tracer of the atomic gas in the diffuse regions and the interface regions of atomic gas to molecular clouds. Furthermore, C+ is a major ISM coolant and among the Galaxy's strongest far-IR emission lines, and thus controls the thermal conditions throughout large parts of the Galaxy. Until now our knowledge of interstellar gas has been limited to the diffuse atomic phase traced by HI and to the dense molecular H2 phase traced by CO. However, we are missing an important phase of the ISM, called "dark gas" in which there is no or little, HI, and mostly molecular hydrogen but with insufficient shielding of UV to allow CO to form. C+ emission and absorption lines at 1.9 THz have the potential to trace such cloud transitions and evolution. Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory Open Time Key Program to study the diffuse interstellar medium by sampling [CII] 1.9 THz line emission throughout the Galactic disk. We discuss the broader perspective of this survey and the first results of GOT C+ obtained during the Science Demonstration Phase (SDP) and Priority Science Phase (PSP) of HIFI, which focus on approximately 100 lines of sight in the inner galaxy. These observations are being carried out with the Herschel Space Observatory, which is an ESA cornerstone mission, with contributions from NASA. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. JLP is a Caltech-JPL Postdoctoral Associate.

  17. Origins of galactic spiral structures

    International Nuclear Information System (INIS)

    Piddington, J.H.

    1978-01-01

    Theories of galactic structure are reviewed briefly before comparing them with recent observations. Also reviewed is the evidence for an intergalactic magnetic field and its possible effects on gas concentrations and patterns of star creation, including spiral arms. It is then shown that normal spiral galaxies may be divided into the M51-type and others. The rare M51-type have H I gas arms coincident with unusually filamentary and luminous optical arms; they also have a companion galaxy. The remaining great majority of spirals have no well-defined gas arms and their optical arms are irregular, broader and less luminous; they have no companion galaxy. It appears that without exception the half-dozen or so galaxies whose structures appear to support the density-wave theory show one or more of the characteristics of the rare type of spiral, and that 'the three principal confirmations of the spiral-wave idea' (M51, M81, M101) have companions which may account for their arms. Toomre has rejected this idea on the grounds that his models do not agree with the observed structures. It is shown that these models are inadequate in two major respects, and when replaced by magneto-tidal models using non-uniform gas disks one might expect agreement. The original hydromagnetic model of spiral arms is now reserved for non-interacting galaxies, of which M33 might be taken as a prototype. The model predicts broad or 'massive' optical arms and no corresponding arms of neutral hydrogen, as observed. (Auth.)

  18. The distances of the Galactic Novae

    Science.gov (United States)

    Ozdonmez, Aykut; Guver, Tolga; Cabrera-Lavers, Antonio; Ak, Tansel

    2016-07-01

    Using location of the RC stars on the CMDs obtained from the UKIDSS, VISTA and 2MASS photometry, we have derived the reddening-distance relations towards each Galactic nova for which at least one independent reddening measurement exists. We were able to determine the distances of 72 Galactic novae and set lower limits on the distances of 45 systems. The reddening curves of the systems are presented. These curves can be also used to estimate reddening or the distance of any source, whose location is close to the position of the nova in our sample. The distance measurement method in our study can be easily applicable to any source, especially for ones that concentrated along the Galactic plane.

  19. Debris Disks in Aggregate: Using Hubble Space Telescope Coronagraphic Imagery to Understand the Scattered-Light Disk Detection Rate

    Science.gov (United States)

    Grady, Carol A.

    2011-01-01

    Despite more than a decade of coronagraphic imaging of debris disk candidate stars, only 16 have been imaged in scattered light. Since imaged disks provide our best insight into processes which sculpt disks, and can provide signposts of the presence of giant planets at distances which would elude radial velocity and transit surveys, we need to understand under what conditions we detect the disks in scattered light, how these disks differ from the majority of debris disks, and how to increase the yield of disks which are imaged with 0.1" angular resolution. In this talk, I will review what we have learned from a shallow HSTINICMOS NIR survey of debris disks, and present first results from our on-going HST /STIS optical imaging of bright scattered-light disks.

  20. Coevolution of Binaries and Circumbinary Gaseous Disks

    Science.gov (United States)

    Fleming, David; Quinn, Thomas R.

    2018-04-01

    The recent discoveries of circumbinary planets by Kepler raise questions for contemporary planet formation models. Understanding how these planets form requires characterizing their formation environment, the circumbinary protoplanetary disk, and how the disk and binary interact. The central binary excites resonances in the surrounding protoplanetary disk that drive evolution in both the binary orbital elements and in the disk. To probe how these interactions impact both binary eccentricity and disk structure evolution, we ran N-body smooth particle hydrodynamics (SPH) simulations of gaseous protoplanetary disks surrounding binaries based on Kepler 38 for 10^4 binary orbital periods for several initial binary eccentricities. We find that nearly circular binaries weakly couple to the disk via a parametric instability and excite disk eccentricity growth. Eccentric binaries strongly couple to the disk causing eccentricity growth for both the disk and binary. Disks around sufficiently eccentric binaries strongly couple to the disk and develop an m = 1 spiral wave launched from the 1:3 eccentric outer Lindblad resonance (EOLR). This wave corresponds to an alignment of gas particle longitude of periastrons. We find that in all simulations, the binary semi-major axis decays due to dissipation from the viscous disk.

  1. The Galactic Club or Galactic Cliques? Exploring the limits of interstellar hegemony and the Zoo Hypothesis

    Science.gov (United States)

    Forgan, Duncan H.

    2017-10-01

    The Zoo solution to Fermi's Paradox proposes that extraterrestrial intelligences (ETIs) have agreed to not contact the Earth. The strength of this solution depends on the ability for ETIs to come to agreement, and establish/police treaties as part of a so-called `Galactic Club'. These activities are principally limited by the causal connectivity of a civilization to its neighbours at its inception, i.e. whether it comes to prominence being aware of other ETIs and any treaties or agreements in place. If even one civilization is not causally connected to the other members of a treaty, then they are free to operate beyond it and contact the Earth if wished, which makes the Zoo solution `soft'. We should therefore consider how likely this scenario is, as this will give us a sense of the Zoo solution's softness, or general validity. We implement a simple toy model of ETIs arising in a Galactic Habitable Zone, and calculate the properties of the groups of culturally connected civilizations established therein. We show that for most choices of civilization parameters, the number of culturally connected groups is >1, meaning that the Galaxy is composed of multiple Galactic Cliques rather than a single Galactic Club. We find in our models for a single Galactic Club to establish interstellar hegemony, the number of civilizations must be relatively large, the mean civilization lifetime must be several millions of years, and the inter-arrival time between civilizations must be a few million years or less.

  2. Particle simulation of 3D galactic hydrodynamics on the ICL DAP

    International Nuclear Information System (INIS)

    Johns, T.C.; Nelson, A.H.

    1985-01-01

    A non-self-gravitating galactic hydrodynamics code based on a quasi-particle technique and making use of a mesh for force evaluation and sorting purposes is described. The short-range nature of the interparticle pressure forces, coupled with the use of a mesh allows a particularly fast algorithm. The 3D representation of the galaxy is mapped onto the ''3D'' main store of ICL DAP in a natural way, the 2 spatial dimensions in the plane of the galaxy becoming the 2 dimensions of the processor plane on the DAP and the third dimension varying within individual processor storage elements. This leads to a fairly straightforward implementation and a high degree of parallelism in the crucial parts of the code. The particle shuffling which is necessary after each timestep is facilitated by the use of a parallel variant of the bitonic sorting algorithm. Some results of simulations using a 63x63x16 mesh and about 50,000 particles to follow the evolution of a model disk galaxy are presented

  3. On the Calculation of the Fe K-alpha Line Emissivity of Black Hole Accretion Disks

    Energy Technology Data Exchange (ETDEWEB)

    Krawczynski, H.; Beheshtipour, B., E-mail: krawcz@wustl.edu [Physics Department and McDonnell Center for the Space Sciences, Washington University in St. Louis, 1 Brookings Drive, CB 1105, St. Louis, MO 63130 (United States)

    2017-11-01

    Observations of the fluorescent Fe K α emission line from the inner accretion flows of stellar mass black holes in X-ray binaries and supermassive black holes in active galactic nuclei have become an important tool to study the magnitude and inclination of the black hole spin, and the structure of the accretion flow close to the event horizon of the black hole. Modeling spectral, timing, and soon also X-ray polarimetric observations of the Fe K α emission requires the calculation of the specific intensity in the rest frame of the emitting plasma. We revisit the derivation of the equation used for calculating the illumination of the accretion disk by the corona. We present an alternative derivation leading to a simpler equation, and discuss the relation to previously published results.

  4. MOLECULAR GAS IN YOUNG DEBRIS DISKS

    International Nuclear Information System (INIS)

    Moor, A.; Abraham, P.; Kiss, Cs.; Juhasz, A.; Kospal, A.; Pascucci, I.; Apai, D.; Henning, Th.; Csengeri, T.; Grady, C.

    2011-01-01

    Gas-rich primordial disks and tenuous gas-poor debris disks are usually considered as two distinct evolutionary phases of the circumstellar matter. Interestingly, the debris disk around the young main-sequence star 49 Ceti possesses a substantial amount of molecular gas and possibly represents the missing link between the two phases. Motivated to understand the evolution of the gas component in circumstellar disks via finding more 49 Ceti-like systems, we carried out a CO J = 3-2 survey with the Atacama Pathfinder EXperiment, targeting 20 infrared-luminous debris disks. These systems fill the gap between primordial and old tenuous debris disks in terms of fractional luminosity. Here we report on the discovery of a second 49 Ceti-like disk around the 30 Myr old A3-type star HD21997, a member of the Columba Association. This system was also detected in the CO(2-1) transition, and the reliable age determination makes it an even clearer example of an old gas-bearing disk than 49 Ceti. While the fractional luminosities of HD21997 and 49 Ceti are not particularly high, these objects seem to harbor the most extended disks within our sample. The double-peaked profiles of HD21997 were reproduced by a Keplerian disk model combined with the LIME radiative transfer code. Based on their similarities, 49 Ceti and HD21997 may be the first representatives of a so far undefined new class of relatively old (∼>8 Myr), gaseous dust disks. From our results, neither primordial origin nor steady secondary production from icy planetesimals can unequivocally explain the presence of CO gas in the disk of HD21997.

  5. PREFACE: Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei

    Science.gov (United States)

    Iserlohe, Christof; Karas, Vladimir; Krips, Melanie; Eckart, Andreas; Britzen, Silke; Fischer, Sebastian

    2012-07-01

    We are pleased to present the proceedings from the Astronomy at High Angular Resolution 2011: The central kiloparsec in galactic nuclei conference. The conference took place in the Physikzentrum of the Deutsche Physikalische Gesellschaft (DPG), Bad Honnef, Germany, from 28 August to 2 September 2011. It was the second conference of this kind, following the Astronomy at High Angular Resolution conference held in Bad Honnef, three years earlier in 2008. The main objective of the conference was to frame the discussion of the broad range of physical processes that occur in the central 100pc of galactic nuclei. In most cases, this domain is difficult to probe through observations. This is mainly because of the lack of angular resolution, the brightness of the central engine and possible obscurations through dust and gas, which play together in the central regions of host galaxies of galactic nuclei within a broad range of activity. The presence of large amounts of molecular and atomic (both neutral and ionized) gas, dust and central engines with outflows and jets implies that the conditions for star formation in these regions are very special, and probably different from those in the disks of host galaxies. Numerous presentations covering a broad range of topics, both theoretical and experimental, those related to research on Active Galactic Nuclei and on a wide range of observed wavelengths were submitted to the Scientific Organizing Committee. Presentations have been grouped into six sessions: The nuclei of active galaxies The Galactic Center The immediate environment of Super Massive Black Holes The physics of nuclear jets and the interaction of the interstellar medium The central 100pc of the nuclear environment Star formation in that region The editors thank all participants of the AHAR 2011 conference for their enthusiasm and their numerous and vivid contributions to this conference. We would especially like to thank John Hugh Seiradakis from the Aristotle

  6. The MACHO Project Sample of Galactic Bulge High-Amplitude Scuti Stars: Pulsation Behavior and Stellar Properties

    International Nuclear Information System (INIS)

    Bennett, D.P.; Cook, K.H.; Freeman, K.C.; Geha, M.; Griest, K.; Lehner, M.J.; Marshall, S.L.; McNamara, B.J.; Minniti, D.; Nelson, C.; Peterson, B.A.; Popowski, P.; Pratt, M.R.; Quinn, P.J.; Rodgers, A.W.; Sutherland, W.; Templeton, M.R.; Vandehei, T.; Welch, D.L.

    1999-01-01

    We have detected 90 objects with periods and lightcurve structure similar to those of field(delta) Scuti stars, using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude(delta) Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground(delta) Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population(delta) Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field(delta) Scuti stars and the(delta) Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude(delta) Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles d(sup -1)) and the observed period ratios of(approx)0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes

  7. Galactic Archaeology with TESS: Prospects for Testing the Star Formation History in the Solar Neighbourhood

    Science.gov (United States)

    Thomas, Alexandra; Stevenson, Emma; Gittins, Fabian W. R.; Miglio, Andrea; Davies, Guy; Girardi, Léo; Campante, Tiago L.; Schofield, Mathew

    2017-10-01

    A period of quenching between the formation of the thick and thin disks of the Milky Way has been recently proposed to explain the observed age-[α/Fe] distribution of stars in the solar neighbourhood. However, robust constraints on stellar ages are currently available for only a limited number of stars. The all-sky survey TESS (Transiting Exoplanet Survey Satellite) will observe the brightest stars in the sky and thus can be used to investigate the age distributions of stars in these components of the Galaxy via asteroseismology, where previously this has been diffcult using other techniques. The aim of this preliminary study was to determine whether TESS will be able to provide evidence for quenching periods during the star formation history of the Milky Way. Using a population synthesis code, we produced populations based on various stellar formation history models and limited the analysis to red-giant-branch stars. We investigated the mass-Galactic-disk-height distributions, where stellar mass was used as an age proxy, to test for whether periods of quenching can be observed by TESS. We found that even with the addition of 15% noise to the inferred masses, it will be possible for TESS to find evidence for/against quenching periods suggested in the literature (e.g. between 7 and 9 Gyr ago), therefore providing stringent constraints on the formation and evolution of the Milky Way.

  8. Galactic binaries with eLISA

    OpenAIRE

    Nelemans, G.

    2013-01-01

    I review what eLISA will see from Galactic binaries -- double stars with orbital periods less than a few hours and white dwarf (or neutron star/black hole) components. I discuss the currently known binaries that are guaranteed (or verification) sources and explain why the expected total number of eLISA Galactic binaries is several thousand, even though there are large uncertainties in our knowledge of this population, in particular that of the interacting AM CVn systems. I very briefly sketch...

  9. Deformation and Life Analysis of Composite Flywheel Disk and Multi-disk Systems

    Science.gov (United States)

    Arnold, S. M.; Saleeb, A. F.; AlZoubi, N. R.

    2001-01-01

    In this study an attempt is made to put into perspective the problem of a rotating disk, be it a single disk or a number of concentric disks forming a unit. An analytical model capable of performing an elastic stress analysis for single/multiple, annular/solid, anisotropic/isotropic disk systems, subjected to both pressure surface tractions, body forces (in the form of temperature-changes and rotation fields) and interfacial misfits is derived and discussed. Results of an extensive parametric study are presented to clearly define the key design variables and their associated influence. In general the important parameters were identified as misfit, mean radius, thickness, material property and/or load gradation, and speed; all of which must be simultaneously optimized to achieve the "best" and most reliable design. Also, the important issue of defining proper performance/merit indices (based on the specific stored energy), in the presence of multiaxiality and material anisotropy is addressed. These merit indices are then utilized to discuss the difference between flywheels made from PMC and TMC materials with either an annular or solid geometry. Finally two major aspects of failure analysis, that is the static and cyclic limit (burst) speeds are addressed. In the case of static limit loads, upper, lower, and out-of-plane bounds for disks with constant thickness are presented for both the case of internal pressure loading (as one would see in a hydroburst test) and pure rotation (as in the case of a free spinning disk). The results (interaction diagrams) are displayed graphically in designer friendly format. For the case of fatigue, a representative fatigue/life master curve is illustrated in which the normalized limit speed versus number of applied cycles is given for a cladded TMC disk application.

  10. Spectral evolution of active galactic nuclei: A unified description of the X-ray and gamma-ray backgrounds

    International Nuclear Information System (INIS)

    Letter, D.; Boldt, E.

    1982-01-01

    A model for spectral evolution is presented whereby active galactic nuclei (AGN) of the type observed individually have emerged from an earlier stage at zroughly-equal4 in which they are the thermal X-ray sources responsible for most of the comic X-ray background (CXB). We pursue the conjecture that these precursor objects are initially supermassive Schwarzschild black holes with accretion disks radiating near the Eddington luminosity limit. It is noted that after approx.10 8 years these central black holes are spun up to a ''canonical'' Kerr equilibriuim state (a/M = 0.998) and shown how they can lead to spectral evolution involving nonthermal emission extending to gamma-rays, at the expense of reduced thermal disk radiation. A superposition of sources in the precursor stage can thereby account for that major portion of the CXB remaining after the contributions of usual AGN are considered, while a superposition of AGN sources at z<1 can account for the gamima-ray background. Extensive X-ray measurements carried out with the HEAO 1 and HEAO 2 missions, as well as gamma-ray and optical data, are shown to compare favorably with principal features of this model. Several further observational tests are suggested for establishing the validity of this scenario for AGN spectral evolution

  11. FOMALHAUT'S DEBRIS DISK AND PLANET: CONSTRAINING THE MASS OF FOMALHAUT B FROM DISK MORPHOLOGY

    International Nuclear Information System (INIS)

    Chiang, E.; Kalas, P.; Graham, J. R.; Kite, E.; Clampin, M.

    2009-01-01

    Following the optical imaging of exoplanet candidate Fomalhaut b (Fom b), we present a numerical model of how Fomalhaut's debris disk is gravitationally shaped by a single interior planet. The model is simple, adaptable to other debris disks, and can be extended to accommodate multiple planets. If Fom b is the dominant perturber of the belt, then to produce the observed disk morphology it must have a mass M pl J , an orbital semimajor axis a pl > 101.5 AU, and an orbital eccentricity e pl = 0.11-0.13. These conclusions are independent of Fom b's photometry. To not disrupt the disk, a greater mass for Fom b demands a smaller orbit farther removed from the disk; thus, future astrometric measurement of Fom b's orbit, combined with our model of planet-disk interaction, can be used to determine the mass more precisely. The inner edge of the debris disk at a ∼ 133 AU lies at the periphery of Fom b's chaotic zone, and the mean disk eccentricity of e ∼ 0.11 is secularly forced by the planet, supporting predictions made prior to the discovery of Fom b. However, previous mass constraints based on disk morphology rely on several oversimplifications. We explain why our constraint is more reliable. It is based on a global model of the disk that is not restricted to the planet's chaotic zone boundary. Moreover, we screen disk parent bodies for dynamical stability over the system age of ∼ 100 Myr, and model them separately from their dust grain progeny; the latter's orbits are strongly affected by radiation pressure and their lifetimes are limited to ∼ 0.1 Myr by destructive grain-grain collisions. The single planet model predicts that planet and disk orbits be apsidally aligned. Fomalhaut b's nominal space velocity does not bear this out, but the astrometric uncertainties may be large. If the apsidal misalignment proves real, our calculated upper mass limit of 3M J still holds. If the orbits are aligned, our model predicts M pl = 0.5M J , a pl = 115 AU, and e pl = 0

  12. X-ray Reflected Spectra from Accretion Disk Models. III. A Complete Grid of Ionized Reflection Calculations

    Science.gov (United States)

    Garcia, J.; Dauser, T.; Reynolds, C. S.; Kallman, T. R.; McClintock, J. E.; Wilms, J.; Ekmann, W.

    2013-01-01

    We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code xillver that incorporates new routines and a richer atomic data base. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index Gamma of the illuminating radiation, the ionization parameter zeta at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A(sub Fe) relative to the solar value. The ranges of the parameters covered are: 1.2 <= Gamma <= 3.4, 1 <= zeta <= 104, and 0.5 <= A(sub Fe) <= 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file suitable for the analysis of X-ray observations via the atable model in xspec. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of xillver.

  13. DISCOVERY OF AN EDGE-ON DEBRIS DISK WITH A DUST RING AND AN OUTER DISK WING-TILT ASYMMETRY

    International Nuclear Information System (INIS)

    Kasper, Markus; Apai, Dániel; Wagner, Kevin; Robberto, Massimo

    2015-01-01

    Using Very Large Telescope/SPHERE near-infrared dual-band imaging and integral field spectroscopy, we discovered an edge-on debris disk around the 17 Myr old A-type member of the Scorpius–Centaurus OB association HD 110058. The edge-on disk can be traced to about 0.″6 or 65 AU projected separation. In its northern and southern wings, the disk shows at all wavelengths two prominent, bright, and symmetrically placed knots at 0.″3 or 32 AU from the star. We interpret these knots as a ring of planetesimals whose collisions may produce most of the dust observed in the disk. We find no evidence for a bow in the disk, but we identify a pair of symmetric, hooklike features in both wings. Based on similar features in the Beta Pictoris disk, we propose that this wing-tilt asymmetry traces either an outer planetesimal belt that is inclined with respect to the disk midplane or radiation-pressure-driven dust blown out from a yet unseen inner belt that is inclined with respect to the disk midplane. The misaligned inner or outer disk may be a result of interaction with a yet unseen planet. Overall, the disk geometry resembles the nearby disk around Beta Pictoris, albeit seen at smaller radial scales

  14. CIRCUMSTELLAR DEBRIS DISKS: DIAGNOSING THE UNSEEN PERTURBER

    Energy Technology Data Exchange (ETDEWEB)

    Nesvold, Erika R. [Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd., Washington, DC 20015 (United States); Naoz, Smadar; Vican, Laura [Department of Physics and Astronomy, UCLA, 475 Portola Plaza, Los Angeles, CA 90095 (United States); Farr, Will M. [School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT (United Kingdom)

    2016-07-20

    The first indication of the presence of a circumstellar debris disk is usually the detection of excess infrared emission from the population of small dust grains orbiting the star. This dust is short-lived, requiring continual replenishment, and indicating that the disk must be excited by an unseen perturber. Previous theoretical studies have demonstrated that an eccentric planet orbiting interior to the disk will stir the larger bodies in the belt and produce dust via interparticle collisions. However, motivated by recent observations, we explore another possible mechanism for heating a debris disk: a stellar-mass perturber orbiting exterior to and inclined to the disk and exciting the disk particles’ eccentricities and inclinations via the Kozai–Lidov mechanism. We explore the consequences of an exterior perturber on the evolution of a debris disk using secular analysis and collisional N -body simulations. We demonstrate that a Kozai–Lidov excited disk can generate a dust disk via collisions and we compare the results of the Kozai–Lidov excited disk with a simulated disk perturbed by an interior eccentric planet. Finally, we propose two observational tests of a dust disk that can distinguish whether the dust was produced by an exterior brown dwarf or stellar companion or an interior eccentric planet.

  15. AN ABSENCE OF FAST RADIO BURSTS AT INTERMEDIATE GALACTIC LATITUDES

    Energy Technology Data Exchange (ETDEWEB)

    Petroff, E.; Van Straten, W.; Bailes, M.; Barr, E. D.; Coster, P.; Flynn, C.; Keane, E. F. [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, VIC 3122 (Australia); Johnston, S. [CSIRO Astronomy and Space Science, Australia Telescope National Facility, P.O. Box 76, Epping, NSW 1710 (Australia); Bates, S. D.; Keith, M. J.; Kramer, M.; Stappers, B. W. [Jodrell Bank Centre for Astrophysics, University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL (United Kingdom); Bhat, N. D. R. [ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), 44 Rosehill Street, Redfern, NSW 2016 (Australia); Burgay, M.; Possenti, A.; Tiburzi, C. [INAF—Osservatorio Astronomico di Cagliari, Via della Scienza, I-09047 Selargius (Italy); Burke-Spolaor, S. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91104 (United States); Champion, D.; Ng, C. [Max Planck Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Levin, L., E-mail: epetroff@astro.swin.edu.au [Department of Physics, West Virginia University, Morgantown, WV 26506 (United States); and others

    2014-07-10

    Fast radio bursts (FRBs) are an emerging class of bright, highly dispersed radio pulses. Recent work by Thornton et al. has revealed a population of FRBs in the High Time Resolution Universe (HTRU) survey at high Galactic latitudes. A variety of progenitors have been proposed, including cataclysmic events at cosmological distances, Galactic flare stars, and terrestrial radio frequency interference. Here we report on a search for FRBs at intermediate Galactic latitudes (–15° Galactic models—must be included to ease the discrepancy between the detection rates at high and low Galactic latitudes. A revised rate estimate or another strong and heretofore unknown selection effect in Galactic latitude would provide closer agreement between the surveys' detection rates. The dearth of detections at low Galactic latitude disfavors a Galactic origin for these bursts.

  16. AN ABSENCE OF FAST RADIO BURSTS AT INTERMEDIATE GALACTIC LATITUDES

    International Nuclear Information System (INIS)

    Petroff, E.; Van Straten, W.; Bailes, M.; Barr, E. D.; Coster, P.; Flynn, C.; Keane, E. F.; Johnston, S.; Bates, S. D.; Keith, M. J.; Kramer, M.; Stappers, B. W.; Bhat, N. D. R.; Burgay, M.; Possenti, A.; Tiburzi, C.; Burke-Spolaor, S.; Champion, D.; Ng, C.; Levin, L.

    2014-01-01

    Fast radio bursts (FRBs) are an emerging class of bright, highly dispersed radio pulses. Recent work by Thornton et al. has revealed a population of FRBs in the High Time Resolution Universe (HTRU) survey at high Galactic latitudes. A variety of progenitors have been proposed, including cataclysmic events at cosmological distances, Galactic flare stars, and terrestrial radio frequency interference. Here we report on a search for FRBs at intermediate Galactic latitudes (–15° Galactic models—must be included to ease the discrepancy between the detection rates at high and low Galactic latitudes. A revised rate estimate or another strong and heretofore unknown selection effect in Galactic latitude would provide closer agreement between the surveys' detection rates. The dearth of detections at low Galactic latitude disfavors a Galactic origin for these bursts

  17. The effect of surfactant on stratified and stratifying gas-liquid flows

    Science.gov (United States)

    Heiles, Baptiste; Zadrazil, Ivan; Matar, Omar

    2013-11-01

    We consider the dynamics of a stratified/stratifying gas-liquid flow in horizontal tubes. This flow regime is characterised by the thin liquid films that drain under gravity along the pipe interior, forming a pool at the bottom of the tube, and the formation of large-amplitude waves at the gas-liquid interface. This regime is also accompanied by the detachment of droplets from the interface and their entrainment into the gas phase. We carry out an experimental study involving axial- and radial-view photography of the flow, in the presence and absence of surfactant. We show that the effect of surfactant is to reduce significantly the average diameter of the entrained droplets, through a tip-streaming mechanism. We also highlight the influence of surfactant on the characteristics of the interfacial waves, and the pressure gradient that drives the flow. EPSRC Programme Grant EP/K003976/1.

  18. Molecular diagnostics of Galactic star-formation regions

    Science.gov (United States)

    Loenen, Edo; Baan, Willem; Spaans, Marco

    2007-10-01

    We propose a sensitive spectral survey of Galactic star-formation regions. Using the broadband correlator at two different frequencies, we expect to detect the (1-0) transition of CO, CN, HNC, HCN, HCO+, and HCO and various of their isotopes lines, as well as the (12-11) and (10-9) transitions of HC3N. The purpose of these observations is to create a consistent (public) database of molecular emission from galactic star-formation regions. The data will be interpreted using extensive physical and chemical modeling of the whole ensemble of lines, in order to get an accurate description of the molecular environment of these regions. In particular, this diagnostic approach will describe the optical depths, the densities, and the radiation fields in the medium and will allow the establishment of dominant temperature gradients. These observations are part of a program to study molecular emission on all scales, going from individual Galactic star-formation regions, through resolved nearby galaxies, to unresolved extra-galactic emission.

  19. Circumstellar and circumplanetary disks

    Science.gov (United States)

    Chiang, Eugene

    2000-11-01

    This thesis studies disks in three astrophysical contexts: (1)protoplanetary disks; (2)the Edgeworth-Kuiper Belt; and (3)planetary rings. We derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 μm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on. We present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, Σ(surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2 M⊕ and 1 × 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU. We propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self- gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1)velocity dispersions are enhanced by resonant satellite perturbations, and (2)the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with

  20. A synoptic view of galactic processes

    Science.gov (United States)

    Stecker, F. W.

    1981-01-01

    The power of using synoptic galactic surveys in many wavelength bands in order to obtain a more complete picture and a better understanding of the dynamics of the interstellar medium and to study galactic structure and evolution on a large scale is discussed. The implications of the picture presented by mm wave CO, far infrared and X ray surveys of the Galaxy are emphasized.

  1. A RAPIDLY EVOLVING REGION IN THE GALACTIC CENTER: WHY S-STARS THERMALIZE AND MORE MASSIVE STARS ARE MISSING

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xian; Amaro-Seoane, Pau, E-mail: Xian.Chen@aei.mpg.de, E-mail: Pau.Amaro-Seoane@aei.mpg.de [Max Planck Institut für Gravitationsphysik (Albert-Einstein-Institut), D-14476 Potsdam (Germany)

    2014-05-10

    The existence of ''S-stars'' within a distance of 1'' from Sgr A* contradicts our understanding of star formation, due to Sgr A* 's forbiddingly violent environment. A suggested possibility is that they form far away and were brought in by some fast dynamical process, since they are young. Nonetheless, all conjectured mechanisms either fail to reproduce their eccentricities—without violating their young age—or cannot explain the problem of {sup i}nverse mass segregation{sup :} the fact that lighter stars (the S-stars) are closer to Sgr A* and more massive ones, Wolf-Rayet (WR) and O-stars, are farther out. In this Letter we propose that the mechanism responsible for both the distribution of the eccentricities and the paucity of massive stars is the Kozai-Lidov-like resonance induced by a sub-parsec disk recently discovered in the Galactic center. Considering that the disk probably extended to a smaller radius in the past, we show that in as short as (a few) 10{sup 6} yr, the stars populating the innermost 1'' region would redistribute in angular-momentum space and recover the observed ''super-thermal'' distribution. Meanwhile, WR and O-stars in the same region intermittently attain ample eccentricities that will lead to their tidal disruptions by the central massive black hole. Our results provide new evidences that Sgr A* was powered several millions years ago by an accretion disk as well as by tidal stellar disruptions.

  2. Electromagnetic waves in stratified media

    CERN Document Server

    Wait, James R; Fock, V A; Wait, J R

    2013-01-01

    International Series of Monographs in Electromagnetic Waves, Volume 3: Electromagnetic Waves in Stratified Media provides information pertinent to the electromagnetic waves in media whose properties differ in one particular direction. This book discusses the important feature of the waves that enables communications at global distances. Organized into 13 chapters, this volume begins with an overview of the general analysis for the electromagnetic response of a plane stratified medium comprising of any number of parallel homogeneous layers. This text then explains the reflection of electromagne

  3. Head-Disk Interface Technology: Challenges and Approaches

    Science.gov (United States)

    Liu, Bo

    Magnetic hard disk drive (HDD) technology is believed to be one of the most successful examples of modern mechatronics systems. The mechanical beauty of magnetic HDD includes simple but super high accuracy positioning head, positioning technology, high speed and stability spindle motor technology, and head-disk interface technology which keeps the millimeter sized slider flying over a disk surface at nanometer level slider-disk spacing. This paper addresses the challenges and possible approaches on how to further reduce the slider disk spacing whilst retaining the stability and robustness level of head-disk systems for future advanced magnetic disk drives.

  4. Observation of galactic far-infrared ray

    International Nuclear Information System (INIS)

    Maihara, Toshinori; Oda, Naoki; Okuda, Haruyuki; Sugiyama, Takuya; Sakai, Kiyomi.

    1978-01-01

    Galactic far-infrared was observed to study the spatial distribution of interstellar dust. Far-infrared is emitted by interstellar dust distributing throughout the galactic plane. The observation of far-infrared is very important to study the overall structure of the galaxy, that is the structure of the galactic arm and gas distribution. The balloon experiment was conducted on May 25, 1978. The detector was a germanium bolometer cooled by liquid helium. The size of the detector is 1.6 mm in diameter. The geometrical factor was 4 x 10 3 cm 2 sr. The result showed that the longitude distribution of far-infrared at 150 μm correlated with H 166 α recombination line. This indicates that the observed far-infrared is emitted by interstellar dust heated by photons of Lyman continuum. (Yoshimori, M.)

  5. Imprint of Galactic dynamics on Earth's climate

    DEFF Research Database (Denmark)

    Svensmark, Henrik

    2006-01-01

    A connection between climate and the Solar system's motion perpendicular to the Galactic plane during the last 200 Myr years is studied. An imprint of galactic dynamics is found in a long-term record of the Earth's climate that is consistent with variations in the Solar system oscillation around...

  6. An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Gao Hua [Department of Astronomy, School of Physics, Peking University, Beijing 100871 (China); Ho, Luis C. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

    2017-08-20

    The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R -band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.

  7. An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

    Science.gov (United States)

    Gao, Hua; Ho, Luis C.

    2017-08-01

    The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R-band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.

  8. An Optimal Strategy for Accurate Bulge-to-disk Decomposition of Disk Galaxies

    International Nuclear Information System (INIS)

    Gao Hua; Ho, Luis C.

    2017-01-01

    The development of two-dimensional (2D) bulge-to-disk decomposition techniques has shown their advantages over traditional one-dimensional (1D) techniques, especially for galaxies with non-axisymmetric features. However, the full potential of 2D techniques has yet to be fully exploited. Secondary morphological features in nearby disk galaxies, such as bars, lenses, rings, disk breaks, and spiral arms, are seldom accounted for in 2D image decompositions, even though some image-fitting codes, such as GALFIT, are capable of handling them. We present detailed, 2D multi-model and multi-component decomposition of high-quality R -band images of a representative sample of nearby disk galaxies selected from the Carnegie-Irvine Galaxy Survey, using the latest version of GALFIT. The sample consists of five barred and five unbarred galaxies, spanning Hubble types from S0 to Sc. Traditional 1D decomposition is also presented for comparison. In detailed case studies of the 10 galaxies, we successfully model the secondary morphological features. Through a comparison of best-fit parameters obtained from different input surface brightness models, we identify morphological features that significantly impact bulge measurements. We show that nuclear and inner lenses/rings and disk breaks must be properly taken into account to obtain accurate bulge parameters, whereas outer lenses/rings and spiral arms have a negligible effect. We provide an optimal strategy to measure bulge parameters of typical disk galaxies, as well as prescriptions to estimate realistic uncertainties of them, which will benefit subsequent decomposition of a larger galaxy sample.

  9. First detection of the white dwarf cooling sequence of the galactic bulge

    Energy Technology Data Exchange (ETDEWEB)

    Calamida, A.; Sahu, K. C.; Anderson, J.; Casertano, S.; Brown, T.; Sokol, J.; Bond, H. E.; Ferguson, H.; Livio, M.; Valenti, J. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Cassisi, S.; Buonanno, R.; Pietrinferni, A. [Osservatorio Astronomico di Teramo—INAF, Via M. Maggini, I-64100 Teramo (Italy); Salaris, M. [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Ferraro, I. [Osservatorio Astronomico di Roma—INAF, Via Frascati 33, I-00040 Monte Porzio Catone (Italy); Clarkson, W., E-mail: calamida@stsci.edu [University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI 48128 (United States)

    2014-08-01

    We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr{sup –1} (≈4 km s{sup –1}) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr{sup –1} (≈20 km s{sup –1}) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.

  10. First detection of the white dwarf cooling sequence of the galactic bulge

    International Nuclear Information System (INIS)

    Calamida, A.; Sahu, K. C.; Anderson, J.; Casertano, S.; Brown, T.; Sokol, J.; Bond, H. E.; Ferguson, H.; Livio, M.; Valenti, J.; Cassisi, S.; Buonanno, R.; Pietrinferni, A.; Salaris, M.; Ferraro, I.; Clarkson, W.

    2014-01-01

    We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr –1 (≈4 km s –1 ) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr –1 (≈20 km s –1 ) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.

  11. Galactic Observations of Terahertz C+ (GOT C+): First Results: Inner Galaxy Survey

    Science.gov (United States)

    Langer, William; Velusamy, T.; Pineda, J. L.; Goldsmith, P. F.; Li, D.; Yorke, H. W.

    2010-05-01

    To understand the lifecycle of the interstellar gas and star formation we need detailed information about the diffuse atomic and diffuse molecular gas cloud properties. The ionized carbon [CII] 1.9 THz fine structure line is an important tracer of the atomic gas in the diffuse regions and the interface regions of atomic gas to molecular clouds. Furthermore, C+ is a major ISM coolant and among the Galaxy's strongest far-IR emission lines, and thus controls the thermal conditions throughout large parts of the Galaxy. Until now our knowledge of interstellar gas has been limited to the diffuse atomic phase traced by HI and to the dense molecular H2 phase traced by CO. However, we are missing an important phase of the ISM called "dark gas” in which there is no or little, HI, and mostly molecular hydrogen but with insufficient shielding of UV to allow CO to form. C+ emission and absorption lines at 1.9 THz have the potential to trace this gas. Galactic Observations of the Terahertz C+ Line (GOT C+) is a Herschel Space Observatory Open Time Key Program to study the diffuse interstellar medium by sampling [CII] 1.9 THz line emission throughout the Galactic disk. We discuss the broader perspective of this survey and the first results of GOT C+ obtained during the Science Demonstration Phase (SDP) and Priority Science Phase (PSP) of HIFI, which focus on approximately 100 lines of sight in the inner galaxy. This research was conducted at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration.

  12. Foundations of Black Hole Accretion Disk Theory

    Directory of Open Access Journals (Sweden)

    Marek A. Abramowicz

    2013-01-01

    Full Text Available This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks, Shakura-Sunyaev (thin disks, slim disks, and advection-dominated accretion flows (ADAFs. After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs.

  13. Foundations of Black Hole Accretion Disk Theory.

    Science.gov (United States)

    Abramowicz, Marek A; Fragile, P Chris

    2013-01-01

    This review covers the main aspects of black hole accretion disk theory. We begin with the view that one of the main goals of the theory is to better understand the nature of black holes themselves. In this light we discuss how accretion disks might reveal some of the unique signatures of strong gravity: the event horizon, the innermost stable circular orbit, and the ergosphere. We then review, from a first-principles perspective, the physical processes at play in accretion disks. This leads us to the four primary accretion disk models that we review: Polish doughnuts (thick disks), Shakura-Sunyaev (thin) disks, slim disks, and advection-dominated accretion flows (ADAFs). After presenting the models we discuss issues of stability, oscillations, and jets. Following our review of the analytic work, we take a parallel approach in reviewing numerical studies of black hole accretion disks. We finish with a few select applications that highlight particular astrophysical applications: measurements of black hole mass and spin, black hole vs. neutron star accretion disks, black hole accretion disk spectral states, and quasi-periodic oscillations (QPOs).

  14. Reverberation Mapping of the Continuum Source in Active Galactic Nuclei

    Science.gov (United States)

    Fausnaugh, Michael Martin

    I present results from a monitoring campaign of 11 active galactic nuclei (AGN) conducted in Spring of 2014. I use the reverberation mapping method to probe the interior structures of the AGN, specifically the broad line regions (BLRs) and accretion disks. One of these AGN, NGC 5548, was also subject to multi-wavelength (X-ray, UV, optical, and near-IR) monitoring using 25 ground-based telescopes and four space-based facilities. For NGC 5548, I detect lags between the continuum emission at different wavelengths that follow a trend consistent with the prediction for continuum reprocessing by an accretion disk with temperature profile T ∝ R -3/4. However, the lags imply a disk radius that is 3 times larger than the prediction from standard thin-disk models. The lags at wavelengths longer than the Vband are also equal to or greater than the lags of high-ionization-state emission lines (such as HeII lambda1640 and lambda4686), suggesting that the continuum-emitting source is of a physical size comparable to the inner broad-line region. Using optical spectra from the Large Binocular Telescope, I estimate the bias of the interband continuum lags due to BLR emission observed in the filters, and I find that the bias for filters with high levels of BLR contamination (˜20%) can be important for the shortest continuum lags. This likely has a significant impact on the u and U bands owing to Balmer continuum emission. I then develop a new procedure for the internal (night-to-night) calibration of time series spectra that can reach precisions of ˜1 millimagnitude and improves traditional techniques by up to a factor of 5. At this level, other systematic issues (e.g., the nightly sensitivity functions and Fe II contamination) limit the final precision of the observed light curves. Using the new calibration method, I next present the data and first results from the optical spectroscopic monitoring component of the reverberation mapping campaign. Five AGN were sufficiently

  15. Dynamics and evolution of galactic nuclei (princeton series in astrophysics)

    CERN Document Server

    Merritt, David

    2013-01-01

    Deep within galaxies like the Milky Way, astronomers have found a fascinating legacy of Einstein's general theory of relativity: supermassive black holes. Connected to the evolution of the galaxies that contain these black holes, galactic nuclei are the sites of uniquely energetic events, including quasars, stellar tidal disruptions, and the generation of gravitational waves. This textbook is the first comprehensive introduction to dynamical processes occurring in the vicinity of supermassive black holes in their galactic environment. Filling a critical gap, it is an authoritative resource for astrophysics and physics graduate students, and researchers focusing on galactic nuclei, the astrophysics of massive black holes, galactic dynamics, and gravitational wave detection. It is an ideal text for an advanced graduate-level course on galactic nuclei and as supplementary reading in graduate-level courses on high-energy astrophysics and galactic dynamics. David Merritt summarizes the theoretical work of the las...

  16. Galactic synchrotron emission from WIMPs at radio frequencies

    International Nuclear Information System (INIS)

    Fornengo, Nicolao; Regis, Marco; Lineros, Roberto A.; Taoso, Marco

    2012-01-01

    Dark matter annihilations in the Galactic halo inject relativistic electrons and positrons which in turn generate a synchrotron radiation when interacting with the galactic magnetic field. We calculate the synchrotron flux for various dark matter annihilation channels, masses, and astrophysical assumptions in the low-frequency range and compare our results with radio surveys from 22 MHz to 1420 MHz. We find that current observations are able to constrain particle dark matter with ''thermal'' annihilation cross-sections, i.e. (σv) = 3 × 10 −26 cm 3 s −1 , and masses M DM ∼<10 GeV. We discuss the dependence of these bounds on the astrophysical assumptions, namely galactic dark matter distribution, cosmic rays propagation parameters, and structure of the galactic magnetic field. Prospects for detection in future radio surveys are outlined

  17. Planck 2013 results. XIII. Galactic CO emission

    DEFF Research Database (Denmark)

    Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.

    2014-01-01

    Rotational transition lines of CO play a major role in molecular radio astronomy as a mass tracer and in particular in the study of star formation and Galactic structure. Although a wealth of data exists for the Galactic plane and some well-known molecular clouds, there is no available high sensi...

  18. Relativistic, accreting disks

    International Nuclear Information System (INIS)

    Abramowicz, M.A; Jaroszynski, M.; Sikora, M.

    1978-01-01

    An analytic theory of the hydrodynamical structure of accreting disks (without self-gravitation but with pressure) orbiting around and axially symmetric, stationary, compact body (e.g. black hole) is presented. The inner edge of the marginally stable accreting disk (i.e. disk with constant angular momentum density) has a sharp cusp located on the equatorial plane between rsub(ms) and rsub(mb). The existence of the cusp is also typical for any angular momentum distribution. The physical importance of the cusp follows from the close analogy with the case of a close binary system (L 1 Lagrange point on the Roche lobe). The existence of the cusp is thus a crucial phenomenon in such problems as boundary condition for the viscous stresses, accretion rate etc. (orig.) [de

  19. CT recognition of lateral lumbar disk herniation

    International Nuclear Information System (INIS)

    Williams, A.L.; Haughton, V.M.; Daniels, D.L.; Thornton, R.S.

    1982-01-01

    Although computed tomography (CT) has been shown to be useful in diagnosing posterolateral and central lumbar disk herniations, its effectiveness in demonstrating lateral herniated disks has not been emphasized. The myelographic recognition of those herniations may be difficult because root sheaths or dural sacs may not be deformed. A total of 274 CT scans interpreted as showing lumbar disk herniation was reviewed. Fourteen (5%) showed a lateral disk herniation. The CT features of a lateral herniated disk included: (1) focal protrusion of the disk margin within or lateral to the intervertebral foramen: (2) displacement of epidural fat within the intervertebral foramen; (3) absence of dural sac deformity; and (4) soft-tissue mass within or lateral to the intervertebral foramen. Because it can image the disk margin and free disk fragments irrespective of dural sac or root sheath deformity, CT may be more effective than myelography for demonstrating the presence and extent of lateral disk herniation

  20. Comment on "Characterizing the population of pulsars in the Galactic bulge with the Fermi large area telescope" [arXiv:1705.00009v1

    Science.gov (United States)

    Bartels, Richard; Hooper, Dan; Linden, Tim; Mishra-Sharma, Siddharth; Rodd, Nicholas L.; Safdi, Benjamin R.; Slatyer, Tracy R.

    2018-06-01

    The Fermi-LAT Collaboration recently presented a new catalog of gamma-ray sources located within the 40 ° × 40 ° region around the Galactic Center Ajello et al. (2017) - the Second Fermi Inner Galaxy (2FIG) catalog. Utilizing this catalog, they analyzed models for the spatial distribution and luminosity function of sources with a pulsar-like gamma-ray spectrum. Ajello et al. (2017) v1 also claimed to detect, in addition to a disk-like population of pulsar-like sources, an approximately 7 σ preference for an additional centrally concentrated population of pulsar-like sources, which they referred to as a "Galactic Bulge" population. Such a population would be of great interest, as it would support a pulsar interpretation of the gamma-ray excess that has long been observed in this region. In an effort to further explore the implications of this new source catalog, we attempted to reproduce the results presented by the Fermi-LAT Collaboration, but failed to do so. Mimicking as closely as possible the analysis techniques undertaken in Ajello et al. (2017), we instead find that our likelihood analysis favors a very different spatial distribution and luminosity function for these sources. Most notably, our results do not exhibit a strong preference for a "Galactic Bulge" population of pulsars. Furthermore, we find that masking the regions immediately surrounding each of the 2FIG pulsar candidates does not significantly impact the spectrum or intensity of the Galactic Center gamma-ray excess. Although these results refute the claim of strong evidence for a centrally concentrated pulsar population presented in Ajello et al. (2017), they neither rule out nor provide support for the possibility that the Galactic Center excess is generated by a population of low-luminosity and currently largely unobserved pulsars. In a spirit of maximal openness and transparency, we have made our analysis code available at https://github.com/bsafdi/GCE-2FIG.

  1. PREFACE: Galactic Center Workshop 2006

    Science.gov (United States)

    Schödel, Rainer; Bower, Geoffrey C.; Muno, Michael P.; Nayakshin, Sergei; Ott, Thomas

    2006-12-01

    We are pleased to present the proceedings from the Galactic Center Workshop 2006—From the Center of the Milky Way to Nearby Low-Luminosity Galactic Nuclei. The conference took place in the Physikzentrum, Bad Honnef, Germany, on 18 to 22 April 2006. It is the third workshop of this kind, following the Galactic Center Workshops held 1998 in Tucson, Arizona, and 2002 in Kona, Hawaii. The center of the Milky Way is the only galactic nucleus of a fairly common spiral galaxy that can be observed in great detail. With a distance of roughly 8 kpc, the resolution that can currently be achieved is of the order 40 mpc/8000 AU in the X-ray domain, 2 mpc/400 AU in the near-infrared, and 0.01 mpc/1 AU with VLBI in the millimeter domain. This is two to three orders of magnitude better than for any comparable nearby galaxy, making thus the center of the Milky Way thetemplate object for the general physical interpretation of the phenomena that can be observed in galactic nuclei. We recommend the summary article News from the year 2006 Galactic Centre workshopby Mark Morris and Sergei Nayakshin—who also gave the summary talk of the conference—to the reader in order to obtain a first, concise overview of the results presented at the workshop and some of the currently most exciting—and debated—developments in recent GC research. While the workshops held in 1998 and 2002 were dedicated solely to the center of the Milky Way, the field of view was widened in Bad Honnef to include nearby low-luminosity nuclei. This new feature followed the realization that not only the GC serves as a template for understanding extragalactic nuclei, but that the latter can also provide the context and broader statistical base for understanding the center of our Milky Way. This concerns especially the accretion and emission processes related to the Sagittarius A*, the manifestation of the super massive black hole in the GC, but also the surprising observation of great numbers of massive, young

  2. Grain surface chemistry in protoplanetary disks

    International Nuclear Information System (INIS)

    Reboussin, Laura

    2015-01-01

    Planetary formation occurs in the protoplanetary disks of gas and dust. Although dust represents only 1% of the total disk mass, it plays a fundamental role in disk chemical evolution since it acts as a catalyst for the formation of molecules. Understanding this chemistry is therefore essential to determine the initial conditions from which planets form. During my thesis, I studied grain-surface chemistry and its impact on the chemical evolution of molecular cloud, initial condition for disk formation, and protoplanetary disk. Thanks to numerical simulations, using the gas-grain code Nautilus, I showed the importance of diffusion reactions and gas-grain interactions for the abundances of gas-phase species. Model results combined with observations also showed the effects of the physical structure (in temperature, density, AV) on the molecular distribution in disks. (author)

  3. Disk Disruptions and X-ray Intensity Excursions in Cyg X-2, LMC X-3 and Cyg X-3

    Science.gov (United States)

    Boyd, P. T.; Smale, A. P.

    2001-05-01

    The RXTE All Sky Monitor soft X-ray light curves of many X-ray binaries show long-term intensity variations (a.k.a "superorbital periodicities") that have been ascribed to precession of a warped, tilted accretion disk around the X-ray source. We have found that the excursion times between X-ray minima in Cyg X-2 can be characterized as a series of integer multiples of the 9.8 binary orbital period, (as opposed to the previously reported stable 77.7 day single periodicity, or a single modulation whose period changes slowly with time). While the data set is too short for a proper statistical analysis, it is clear that the length of any given intensity excursion cannot be used to predict the next (integer) excursion length in the series. In the black hole candidate system LMC X-3, the excursion times are shown to be related to each other by rational fractions. We find that the long term light curve of the unusual galactic X-ray jet source Cyg X-3 can also be described as a series of intensity excursions related to each other by integer multiples of a fundamental underlying clock. In the latter cases, the clock is apparently not related to the known binary periods. A unified physical model, involving both an inclined accretion disk and a fixed-probability disk disruption mechanism is presented, and compared with three-body scattering results. Each time the disk passes through the orbital plane it experiences a fixed probability P that it will disrupt. This model has testable predictions---the distribution of integers should resemble that of an atomic process with a characteristic half life. Further analysis can support or refute the model, and shed light on what system parameters effectively set the value of P.

  4. The DiskMass Survey. II. Error Budget

    Science.gov (United States)

    Bershady, Matthew A.; Verheijen, Marc A. W.; Westfall, Kyle B.; Andersen, David R.; Swaters, Rob A.; Martinsson, Thomas

    2010-06-01

    We present a performance analysis of the DiskMass Survey. The survey uses collisionless tracers in the form of disk stars to measure the surface density of spiral disks, to provide an absolute calibration of the stellar mass-to-light ratio (Υ_{*}), and to yield robust estimates of the dark-matter halo density profile in the inner regions of galaxies. We find that a disk inclination range of 25°-35° is optimal for our measurements, consistent with our survey design to select nearly face-on galaxies. Uncertainties in disk scale heights are significant, but can be estimated from radial scale lengths to 25% now, and more precisely in the future. We detail the spectroscopic analysis used to derive line-of-sight velocity dispersions, precise at low surface-brightness, and accurate in the presence of composite stellar populations. Our methods take full advantage of large-grasp integral-field spectroscopy and an extensive library of observed stars. We show that the baryon-to-total mass fraction ({F}_bar) is not a well-defined observational quantity because it is coupled to the halo mass model. This remains true even when the disk mass is known and spatially extended rotation curves are available. In contrast, the fraction of the rotation speed supplied by the disk at 2.2 scale lengths (disk maximality) is a robust observational indicator of the baryonic disk contribution to the potential. We construct the error budget for the key quantities: dynamical disk mass surface density (Σdyn), disk stellar mass-to-light ratio (Υ^disk_{*}), and disk maximality ({F}_{*,max}^disk≡ V^disk_{*,max}/ V_c). Random and systematic errors in these quantities for individual galaxies will be ~25%, while survey precision for sample quartiles are reduced to 10%, largely devoid of systematic errors outside of distance uncertainties.

  5. Possible existence of wormholes in the galactic halo region

    Energy Technology Data Exchange (ETDEWEB)

    Rahaman, Farook [Jadavpur University, Department of Mathematics, Kolkata, West Bengal (India); Kuhfittig, P.K.F. [Milwaukee School of Engineering, Department of Mathematics, Milwaukee, WI (United States); Ray, Saibal [Government College of Engineering and Ceramic Technology, Department of Physics, Kolkata, West Bengal (India); Islam, Nasarul [Danga High Madrasah, Department of Mathematics, Kolkata, West Bengal (India)

    2014-02-15

    Two observational results, the density profile from simulations performed in the ΛCDM scenario and the observed flat galactic rotation curves, are taken as input with the aim of showing that the galactic halo possesses some of the characteristics needed to support traversable wormholes. This result should be sufficient to provide an incentive for scientists to seek observational evidence for wormholes in the galactic halo region. (orig.)

  6. A COMMON SOURCE OF ACCRETION DISK TILT

    International Nuclear Information System (INIS)

    Montgomery, M. M.; Martin, E. L.

    2010-01-01

    Many different system types retrogradely precess, and retrograde precession could be from a tidal torque by the secondary on a misaligned accretion disk. However, a source that causes and maintains disk tilt is unknown. In this work, we show that accretion disks can tilt due to a force called lift. Lift results from differing gas stream supersonic speeds over and under an accretion disk. Because lift acts at the disk's center of pressure, a torque is applied around a rotation axis passing through the disk's center of mass. The disk responds to lift by pitching around the disk's line of nodes. If the gas stream flow ebbs, then lift also ebbs and the disk attempts to return to its original orientation. To first approximation, lift does not depend on magnetic fields or radiation sources but does depend on the mass and the surface area of the disk. Also, for disk tilt to be initiated, a minimum mass transfer rate must be exceeded. For example, a 10 -11 M sun disk around a 0.8 M sun compact central object requires a mass transfer rate greater than ∼ 8 x 10 -11 M sun yr -1 , a value well below the known mass transfer rates in cataclysmic variable dwarf novae systems that retrogradely precess and exhibit negative superhumps in their light curves and a value well below mass transfer rates in protostellar-forming systems.

  7. Galactic absorption line coronae

    International Nuclear Information System (INIS)

    Bregman, J.N.

    1981-01-01

    We have investigated whether gaseous coronae around galaxies rise to the absorption systems seen in quasar spectra. In our model, gas originally located in the disk is heated to the million degree range and rises to surround the galaxy; the gas remains bound to the galaxy. Optically thin radiative cooling drives a thermal instability in the hot gas which causes cool clouds (T 4 K) to condense out of the corona. These clouds, which follow ballistic trajectories back to the disk, are the absorption sites. A two-dimensional hydrodynamic code with radiative cooling was used to study the dynamics and thermodynamics of the corona as well as the position rate at which clouds form. Coupled to the code is a galaxy with two mass components, a disk (approx.10 11 M/sub sun/) and a dark halo (approx.10 12 M/sub sun/). In a model where the temperature at the base of the corona (in the disk) is 3 x 10 6 K, absorbing gas of column density NL> or approx. =10 18 cm 2 extends radially to 100 kpc (face-on orientation) and vertically to 60 Kpc (edge-on orientation). The total mass of gas required here (coronal plus cloud gas) is 1.4 x 10 10 M/sub sun/, while the minimum supernova heating rate is one supernova per 27 years. In two other models (base coronal temperatures of 0.50 x 10 6 K and 1 x 10 6 K), coronal gas rises from an extended gaseous disk (in the previous model, the gas comes from a typical gaseous disk approximately 15 kpc in extent). Here, column densities of 10 19 cm -2 out to a radius of 70 kpc (face-on orientation) are achieved with a total gas mass of 1.7 x 10 9 M/sub direct-product/ and 2.0 x 10 9 M/sub sun/ and minimum heating rates of approximately one supernova per 170 years and one supernova per 60 years

  8. The Open Cluster Chemical Abundances and Mapping (OCCAM) Survey: Galactic Neutron CaptureAbundance Gradients

    Science.gov (United States)

    O'Connell, Julia; Frinchaboy, Peter M.; Shetrone, Matthew D.; Melendez, Matthew; Cunha, Katia; Majewski, Steven R.; Zasowski, Gail; APOGEE Team

    2017-06-01

    The evolution of elements, as a function or age, throughout the Milky Way disk provides a key constraint for galaxy evolution models. In an effort to provide these constraints, we have conducted an investigation into the r- and s- process elemental abundances for a large sample of open clusters as part of an optical follow-up to the SDSS-III/APOGEE-1 survey. Stars were identified as cluster members by the Open Cluster Chemical Abundance & Mapping (OCCAM) survey, which culls member candidates by radial velocity, metallicity and proper motion from the observed APOGEE sample. To obtain data for neutron capture elements in these clusters, we conducted a long-term observing campaign covering three years (2013-2016) using the McDonald Observatory Otto Struve 2.1-m telescope and Sandiford Cass Echelle Spectrograph (R ~ 60,000). We present Galactic neutron capture abundance gradients using 30+ clusters, within 6 kpc of the Sun, covering a range of ages from ~80 Myr to ~10 Gyr .

  9. MODERATE-LUMINOSITY GROWING BLACK HOLES FROM 1.25 < z < 2.7: VARIED ACCRETION IN DISK-DOMINATED HOSTS

    Energy Technology Data Exchange (ETDEWEB)

    Simmons, B. D.; Glikman, E. [Astronomy Department, Yale University, New Haven, CT 06511 (United States); Urry, C. M.; Schawinski, K. [Yale Center for Astronomy and Astrophysics, Physics Department, Yale University, New Haven, CT 06511 (United States); Cardamone, C., E-mail: brooke.simmons@astro.ox.ac.uk [Sheridan Center for Teaching and Learning, Brown University, 96 Waterman St., Providence RI 02912 (United States)

    2012-12-10

    We compute black hole masses and bolometric luminosities for 57 active galactic nuclei (AGNs) in the redshift range 1.25 {<=} z {<=} 2.67, selected from the GOODS-South deep multi-wavelength survey field via their X-ray emission. We determine host galaxy morphological parameters by separating the galaxies from their central point sources in deep Hubble Space Telescope images, and host stellar masses and colors by multi-wavelength spectral energy distribution fitting. Of GOODS AGNs at these redshifts, 90% have detected rest-frame optical nuclear point sources; bolometric luminosities range from 2 Multiplication-Sign 10{sup 43} to 2 Multiplication-Sign 10{sup 46} erg s{sup -1}. The black holes are growing at a range of accretion rates, with {approx}> 50% of the sample having L/L{sub Edd} < 0.1. Of the host galaxies, 70% have stellar masses M{sub *} > 10{sup 10} M{sub Sun }, with a range of colors suggesting a complex star formation history. We find no evolution of AGN bolometric luminosity within the sample, and no correlation between AGN bolometric luminosity and host stellar mass, color, or morphology. Fully half the sample of host galaxies are disk-dominated, with another 25% having strong disk components. Fewer than 15% of the systems appear to be at some stage of a major merger. These moderate-luminosity AGN hosts are therefore inconsistent with a dynamical history dominated by mergers strong enough to destroy disks, indicating that minor mergers or secular processes dominate the coevolution of galaxies and their central black holes at z {approx} 2.

  10. Superluminous Transients at AGN Centers from Interaction between Black Hole Disk Winds and Broad-line Region Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Moriya, Takashi J.; Tanaka, Masaomi; Ohsuga, Ken [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Morokuma, Tomoki, E-mail: takashi.moriya@nao.ac.jp [Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)

    2017-07-10

    We propose that superluminous transients that appear at central regions of active galactic nuclei (AGNs) such as CSS100217:102913+404220 (CSS100217) and PS16dtm, which reach near- or super-Eddington luminosities of the central black holes, are powered by the interaction between accretion-disk winds and clouds in broad-line regions (BLRs) surrounding them. If the disk luminosity temporarily increases by, e.g., limit–cycle oscillations, leading to a powerful radiatively driven wind, strong shock waves propagate in the BLR. Because the dense clouds in the AGN BLRs typically have similar densities to those found in SNe IIn, strong radiative shocks emerge and efficiently convert the ejecta kinetic energy to radiation. As a result, transients similar to SNe IIn can be observed at AGN central regions. Since a typical black hole disk-wind velocity is ≃0.1 c , where c is the speed of light, the ejecta kinetic energy is expected to be ≃10{sup 52} erg when ≃1 M {sub ⊙} is ejected. This kinetic energy is transformed to radiation energy in a timescale for the wind to sweep up a similar mass to itself in the BLR, which is a few hundred days. Therefore, both luminosities (∼10{sup 44} erg s{sup −1}) and timescales (∼100 days) of the superluminous transients from AGN central regions match those expected in our interaction model. If CSS100217 and PS16dtm are related to the AGN activities triggered by limit–cycle oscillations, they become bright again in coming years or decades.

  11. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap; Kim, Sangsub; Knauer, Christian; Schlipf, Lena; Shin, Chansu; Vigneron, Antoine E.

    2013-01-01

    We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

  12. Covering and piercing disks with two centers

    KAUST Repository

    Ahn, Heekap

    2013-04-01

    We give exact and approximation algorithms for two-center problems when the input is a set D of disks in the plane. We first study the problem of finding two smallest congruent disks such that each disk in D intersects one of these two disks. Then we study the problem of covering the set D by two smallest congruent disks. © 2012 Elsevier B.V.

  13. Optical spectral properties of active galactic nuclei and quasars

    International Nuclear Information System (INIS)

    Yee, H.K.C.

    1981-01-01

    Four separate investigations dealing with the properties of optical continuum and emission-lines of active galactic nuclei (AGN) and quasars are presented. Multichannel scans of 3CR radio galaxies are decomposed by using a two-component model-an elliptical galaxy and a power-law nonthermal component. It is found that there is a strong correlation between the luminosity of the power-law component and the strength of the Balmer emission-lines. In most cases, by extrapolating to the Lyman continuum, the power-law models derived provide enough ionizing radiation to account for the Balmer line strengths. Extending the study of radio galaxies to include Seyfert galaxies and quasars, it is found that there is a strong continuity between broad-line AGN's and quasars in terms of similarities in the correlations between line luminosities and nonthermal continuum luminosity. Next, a study of the variability of absolute optical energy distribution and emission-lines of the N-galaxies 3C382 and 3C390.3 is made. Lastly, a preliminary study of surface photometry of Markarian Seyfert galaxies are presented. It is found that the properties of the underlying galaxies such as scale-length and surface brightness of the disk, color, and total brightness, do not depart systematically from those of luminous normal spiral galaxies

  14. Supermassive black holes with high accretion rates in active galactic nuclei. I. First results from a new reverberation mapping campaign

    International Nuclear Information System (INIS)

    Du, Pu; Hu, Chen; Qiu, Jie; Li, Yan-Rong; Wang, Jian-Min; Lu, Kai-Xing; Wang, Fang; Bai, Jin-Ming; Kaspi, Shai; Netzer, Hagai

    2014-01-01

    We report first results from a large project to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). Such objects may be different from other AGNs in being powered by slim accretion disks and showing saturated accretion luminosities, but both are not yet fully understood. The results are part of a large reverberation mapping (RM) campaign using the 2.4 m Shangri-La telescope at the Yunnan Observatory in China. The goals are to investigate the gas distribution near the BH and the properties of the central accretion disks, to measure BH mass and Eddington ratios, and to test the feasibility of using such objects as a new type of cosmological candles. The paper presents results for three objects, Mrk 335, Mrk 142, and IRAS F12397+3333, with Hβ time lags relative to the 5100 Å continuum of 10.6 −2.9 +1.7 , 6.4 −2.2 +0.8 and 11.4 −1.9 +2.9 days, respectively. The corresponding BH masses are (8.3 −3.2 +2.6 )×10 6 M ⊙ , (3.4 −1.2 +0.5 )×10 6 M ⊙ , and (7.5 −4.1 +4.3 )×10 6 M ⊙ , and the lower limits on the Eddington ratios are 0.6, 2.3, and 4.6 for the minimal radiative efficiency of 0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from the currently known relation between Hβ lag and continuum luminosity. The three Eddington ratios are beyond the values expected in thin accretion disks and two of them are the largest measured so far among objects with RM-based BH masses. We briefly discuss implications for slim disks, BH growth, and cosmology.

  15. Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. I. First Results from a New Reverberation Mapping Campaign

    Science.gov (United States)

    Du, Pu; Hu, Chen; Lu, Kai-Xing; Wang, Fang; Qiu, Jie; Li, Yan-Rong; Bai, Jin-Ming; Kaspi, Shai; Netzer, Hagai; Wang, Jian-Min; SEAMBH Collaboration

    2014-02-01

    We report first results from a large project to measure black hole (BH) mass in high accretion rate active galactic nuclei (AGNs). Such objects may be different from other AGNs in being powered by slim accretion disks and showing saturated accretion luminosities, but both are not yet fully understood. The results are part of a large reverberation mapping (RM) campaign using the 2.4 m Shangri-La telescope at the Yunnan Observatory in China. The goals are to investigate the gas distribution near the BH and the properties of the central accretion disks, to measure BH mass and Eddington ratios, and to test the feasibility of using such objects as a new type of cosmological candles. The paper presents results for three objects, Mrk 335, Mrk 142, and IRAS F12397+3333, with Hβ time lags relative to the 5100 Å continuum of 10.6^{+1.7}_{-2.9}, 6.4^{+0.8}_{-2.2} and 11.4^{+2.9}_{-1.9} days, respectively. The corresponding BH masses are (8.3_{-3.2}^{+2.6})\\times 10^6\\,M_{\\odot }, (3.4_{-1.2}^{+0.5})\\times 10^6\\,M_{\\odot }, and (7.5_{-4.1}^{+4.3})\\times 10^6\\,M_{\\odot }, and the lower limits on the Eddington ratios are 0.6, 2.3, and 4.6 for the minimal radiative efficiency of 0.038. Mrk 142 and IRAS F12397+333 (extinction corrected) clearly deviate from the currently known relation between Hβ lag and continuum luminosity. The three Eddington ratios are beyond the values expected in thin accretion disks and two of them are the largest measured so far among objects with RM-based BH masses. We briefly discuss implications for slim disks, BH growth, and cosmology.

  16. Galactic synchrotron emission from WIMPs at radio frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Fornengo, Nicolao; Regis, Marco [Dipartimento di Fisica Teorica, Università di Torino, Istituto Nazionale di Fisica Nucleare, via P. Giuria 1, I-10125 Torino (Italy); Lineros, Roberto A.; Taoso, Marco, E-mail: fornengo@to.infn.it, E-mail: rlineros@ific.uv.es, E-mail: regis@to.infn.it, E-mail: taoso@ific.uv.es [IFIC, CSIC-Universidad de Valencia, Ed. Institutos, Apdo. Correos 22085, E-46071 Valencia (Spain)

    2012-01-01

    Dark matter annihilations in the Galactic halo inject relativistic electrons and positrons which in turn generate a synchrotron radiation when interacting with the galactic magnetic field. We calculate the synchrotron flux for various dark matter annihilation channels, masses, and astrophysical assumptions in the low-frequency range and compare our results with radio surveys from 22 MHz to 1420 MHz. We find that current observations are able to constrain particle dark matter with ''thermal'' annihilation cross-sections, i.e. (σv) = 3 × 10{sup −26} cm{sup 3} s{sup −1}, and masses M{sub DM}∼<10 GeV. We discuss the dependence of these bounds on the astrophysical assumptions, namely galactic dark matter distribution, cosmic rays propagation parameters, and structure of the galactic magnetic field. Prospects for detection in future radio surveys are outlined.

  17. HERSCHEL OBSERVATIONS OF THE T CHA TRANSITION DISK: CONSTRAINING THE OUTER DISK PROPERTIES

    OpenAIRE

    Cieza, Lucas A.; Olofsson, Johan; Harvey, Paul M.; Pinte, Christophe; Merin, Bruno; Augereau, Jean-Charles; Evans, Neal J., II; Najita, Joan; Henning, Thomas; Menard, Francois

    2011-01-01

    T Cha is a nearby (d = 100 pc) transition disk known to have an optically thin gap separating optically thick inner and outer disk components. Huelamo et al. (2011) recently reported the presence of a low-mass object candidate within the gap of the T Cha disk, giving credence to the suspected planetary origin of this gap. Here we present the Herschel photometry (70, 160, 250, 350, and 500 micron) of T Cha from the "Dust, Ice, and Gas in Time" (DIGIT) Key Program, which bridges the wavelength ...

  18. Analysis of Turbulent Combustion in Simplified Stratified Charge Conditions

    Science.gov (United States)

    Moriyoshi, Yasuo; Morikawa, Hideaki; Komatsu, Eiji

    The stratified charge combustion system has been widely studied due to the significant potentials for low fuel consumption rate and low exhaust gas emissions. The fuel-air mixture formation process in a direct-injection stratified charge engine is influenced by various parameters, such as atomization, evaporation, and in-cylinder gas motion at high temperature and high pressure conditions. It is difficult to observe the in-cylinder phenomena in such conditions and also challenging to analyze the following stratified charge combustion. Therefore, the combustion phenomena in simplified stratified charge conditions aiming to analyze the fundamental stratified charge combustion are examined. That is, an experimental apparatus which can control the mixture distribution and the gas motion at ignition timing was developed, and the effects of turbulence intensity, mixture concentration distribution, and mixture composition on stratified charge combustion were examined. As a result, the effects of fuel, charge stratification, and turbulence on combustion characteristics were clarified.

  19. EMBEDDED PROTOSTELLAR DISKS AROUND (SUB-)SOLAR STARS. II. DISK MASSES, SIZES, DENSITIES, TEMPERATURES, AND THE PLANET FORMATION PERSPECTIVE

    International Nuclear Information System (INIS)

    Vorobyov, Eduard I.

    2011-01-01

    We present basic properties of protostellar disks in the embedded phase of star formation (EPSF), which is difficult to probe observationally using available observational facilities. We use numerical hydrodynamics simulations of cloud core collapse and focus on disks formed around stars in the 0.03-1.0 M sun mass range. Our obtained disk masses scale near-linearly with the stellar mass. The mean and median disk masses in the Class 0 and I phases (M mean d,C0 = 0.12 M sun , M mdn d,C0 = 0.09 M sun and M mean d,CI = 0.18 M sun , M mdn d,CI = 0.15 M sun , respectively) are greater than those inferred from observations by (at least) a factor of 2-3. We demonstrate that this disagreement may (in part) be caused by the optically thick inner regions of protostellar disks, which do not contribute to millimeter dust flux. We find that disk masses and surface densities start to systematically exceed that of the minimum mass solar nebular for objects with stellar mass as low as M * = 0.05-0.1 M sun . Concurrently, disk radii start to grow beyond 100 AU, making gravitational fragmentation in the disk outer regions possible. Large disk masses, surface densities, and sizes suggest that giant planets may start forming as early as in the EPSF, either by means of core accretion (inner disk regions) or direct gravitational instability (outer disk regions), thus breaking a longstanding stereotype that the planet formation process begins in the Class II phase.

  20. TOWARD A GLOBAL EVOLUTIONARY MODEL OF PROTOPLANETARY DISKS

    Energy Technology Data Exchange (ETDEWEB)

    Bai, Xue-Ning, E-mail: xbai@cfa.harvard.edu [Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS-51, Cambridge, MA 02138 (United States)

    2016-04-20

    A global picture of the evolution  of protoplanetary disks (PPDs) is key to understanding almost every aspect of planet formation, where standard α-disk models have been continually employed for their simplicity. In the meantime, disk mass loss has been conventionally attributed to photoevaporation, which controls disk dispersal. However, a paradigm shift toward accretion driven by magnetized disk winds has taken place in recent years, thanks to studies of non-ideal magnetohydrodynamic effects in PPDs. I present a framework of global PPD evolution aiming to incorporate these advances, highlighting the role of wind-driven accretion and wind mass loss. Disk evolution is found to be largely dominated by wind-driven processes, and viscous spreading is suppressed. The timescale of disk evolution is controlled primarily by the amount of external magnetic flux threading the disks, and how rapidly the disk loses the flux. Rapid disk dispersal can be achieved if the disk is able to hold most of its magnetic flux during the evolution. In addition, because wind launching requires a sufficient level of ionization at the disk surface (mainly via external far-UV (FUV) radiation), wind kinematics is also affected by the FUV penetration depth and disk geometry. For a typical disk lifetime of a few million years, the disk loses approximately the same amount of mass through the wind as through accretion onto the protostar, and most of the wind mass loss proceeds from the outer disk via a slow wind. Fractional wind mass loss increases with increasing disk lifetime. Significant wind mass loss likely substantially enhances the dust-to-gas mass ratio and promotes planet formation.