WorldWideScience

Sample records for molecular clouds predictions

  1. Interstellar molecular clouds

    Science.gov (United States)

    Bally, J.

    1986-04-01

    The physical properties of the molecular phase of the interstellar medium are studied with regard to star formation and the structure of the Galaxy. Most observations of molecular clouds are made with single-dish, high-surface precision radio telescopes, with the best resolution attainable at 0.2 to 1 arcmin; the smallest structures that can be resolved are of order 10 to the 17th cm in diameter. It is now believed that: (1) most of the mass of the Galaxy is in the form of giant molecular clouds; (2) the largest clouds and those responsible for most massive star formation are concentrated in spiral arms; (3) the molecular clouds are the sites of perpetual star formation, and are significant in the chemical evolution of the Galaxy; (4) giant molecular clouds determine the evolution of the kinematic properties of galactic disk stars; (5) the total gas content is diminishing with time; and (6) most clouds have supersonic internal motions and do not form stars on a free-fall time scale. It is concluded that though progress has been made, more advanced instruments are needed to inspect the processes operating within stellar nurseries and to study the distribution of the molecular clouds in more distant galaxies. Instruments presently under construction which are designed to meet these ends are presented.

  2. The California Molecular Cloud

    CERN Document Server

    Lada, Charles J; Alves, Joao F

    2009-01-01

    We present an analysis of wide-field infrared extinction maps of a region in Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis we have identified a massive, nearby, but previously unrecognized, giant molecular cloud (GMC). From comparison of foreground star counts with Galactic models we derive a distance of 450 +/- 23 parsecs to the cloud. At this distance the cloud extends over roughly 80 pc and has a mass of approximately 10^5 solar masses, rivaling the Orion (A) Molecular Cloud as the largest and most massive GMC in the solar neighborhood. Although surprisingly similar in mass and size to the more famous Orion Molecular Cloud (OMC) the newly recognized cloud displays significantly less star formation activity with more than an order of magnitude fewer young stellar objects than found in the OMC, suggesting that both the level of star formation and perhaps the star formation rate in this cloud are an order of magnitude or more lower than in the OMC. Analysis of extinction maps ...

  3. Molecular Cloud Evolution

    CERN Document Server

    Vazquez-Semadeni, Enrique

    2010-01-01

    I describe the scenario of molecular cloud (MC) evolution that has emerged over the past decade or so. MCs can start out as cold atomic clouds formed by compressive motions in the warm neutral medium (WNM) of galaxies. Such motions can be driven by large-scale instabilities, or by local turbulence. The compressions induce a phase transition to the cold neutral medium (CNM) to form growing cold atomic clouds, which in their early stages may constitute thin CNM sheets. Several dynamical instabilities soon destabilize a cloud, rendering it turbulent. For solar neighborhood conditions, a cloud is coincidentally expected to become molecular, magnetically supercritical, and gravitationally dominated at roughly the same column density, $N \\sim 1.5 \\times 10^21 \\psc \\approx 10 \\Msun$ pc$^{-2}$. At this point, the cloud begins to contract gravitationally. However, before its global collapse is completed ($\\sim 10^7$ yr later), the nonlinear density fluctuations within the cloud, which have shorter local free-fall time...

  4. Fragmentation in filamentary molecular clouds

    CERN Document Server

    Contreras, Yanett; Rathborne, Jill M; Sanhueza, Patricio

    2015-01-01

    Recent surveys of dust continuum emission at sub-mm wavelengths have shown that filamentary molecular clouds are ubiquitous along the Galactic plane. These structures are inhomogeneous, with over-densities that are sometimes associated with infrared emission and active of star formation. To investigate the connection between filaments and star formation, requires an understanding of the processes that lead to the fragmentation of filaments and a determination of the physical properties of the over-densities (clumps). In this paper, we present a multi-wavelength study of five filamentary molecular clouds, containing several clumps in different evolutionary stages of star formation. We analyse the fragmentation of the filaments and derive the physical properties of their clumps. We find that the clumps in all filaments have a characteristic spacing consistent with the prediction of the `sausage' instability theory, regardless of the complex morphology of the filaments or their evolutionary stage. We also find t...

  5. Reviewing Molecular Clouds

    Science.gov (United States)

    Fernandez Lopez, Manuel

    2017-07-01

    The star formation process involves a wide range of spatial scales, densities and temperatures. Herschel observations of the cold and low density molecular gas extending tens of parsecs, that constitutes the bulk of the molecular clouds of the Milky Way, have shown a network of dense structures in the shape of filaments. These filaments supposedly condense into higher density clumps to form individual stars or stellar clusters. The study of the kinematics of the filaments through single-dish observations suggests the presence of gas flows along the filaments, oscillatory motions due to gravity infall, and the existence of substructure inside filaments that may be threaded by twisted fibers. A few molecular clouds have been mapped with interferometric resolutions bringing more insight into the filament structure. Compression due to large-scale supersonic flows is the preferred mechanism to explain filament formation although the exact nature of the filaments, their origin and evolution are still not well understood. Determining the turbulence drivers behind the origin of the filaments, the relative importance of turbulence, gravity and magnetic fields on regulating the filament structure and evolution, and providing detailed insight on the substructure inside the filaments are among the current open questions in this research area.

  6. Chemical evolution of molecular clouds

    Science.gov (United States)

    Prasad, Sheo S.; Tarafdar, Sankar P.; Villere, Karen R.; Huntress, Wesley T., Jr.

    1987-01-01

    The principles behind the coupled chemical-dynamical evolution of molecular clouds are described. Particular attention is given to current problems involving the simplest species (i.e., C. CO, O2, and H2) in quiescent clouds. The results of a comparison made between the molecular abundances in the Orion ridge and the hot core (Blake, 1986) are presented.

  7. Evolution of molecular clouds

    Science.gov (United States)

    Sevenster, M.

    1993-01-01

    The evolution of interstellar molecular hydrogen was studied, with a special interest for the formation and evolution of molecular clouds and star formation within them, by a two-dimensional hydrodynamical simulation performed on a rectangular grid of physical sizes on the order of 100 pc. It is filled with an initial density of approx. 1 cm(exp -3), except for one cell (approx. 1 pc(exp 2)) at the center of the grid where an accretion core of 1-10(exp 3) solar masses is placed. The grid is co-moving with the gridcenter that is on a circular orbit around the Galactic center and that also is the guiding center of epicyclic approximation of orbits of the matter surrounding it. The initial radial velocity is zero; to account for differential rotation the initial tangential velocity (i.e. the movement around the galactic center) is proportional to the radial distance to the grid center. The rate is comparable to the rotation rate at the Local Standard of Rest. The influence of galactic rotation is noticed by spiral or elliptical forms, but on much longer time scales than self gravitation and cooling processes. Density and temperature are kept constant at the boundaries and no inflow is allowed along the tangential boundaries.

  8. Molecular clouds without detectable CO

    Science.gov (United States)

    Blitz, Leo; Bazell, David; Desert, F. Xavier

    1990-03-01

    The clouds identified by Desert, Bazell, and Boulanger (DBB clouds) in their search for high-latitude molecular clouds were observed in the CO (J = 1-0) line, but only 13 percent of the sample was detected. The remaining 87 percent are diffuse molecular clouds with CO abundances of about 10 to the -6th, a typical value for diffuse clouds. This hypothesis is shown to be consistent with Copernicus data. The DBB clouds are shown to ben an essentially complete catalog of diffuse molecular clouds in the solar vicinity. The total molecular surface density in the vicinity of the sun is then only about 20 percent greater than the 1.3 solar masses/sq pc determined by Dame et al. (1987). Analysis of the CO detections indicates that there is a sharp threshold in extinction of 0.25 mag before CO is detectable and is derived from the IRAS I(100) micron threshold of 4 MJy/sr. This threshold is presumably where the CO abundance exhibits a sharp increase

  9. The Serpens Molecular Cloud

    CERN Document Server

    Eiroa, C; Casali, M M

    2008-01-01

    The Serpens cloud has received considerable attention in the last years, in particular the small region known as the Serpens cloud core where a plethora of star formation related phenomena are found. This review summarizes our current observational knowledge of the cloud, with emphasis on the core. Recent results are converging to a distance for the cloud of ~ 230 +- 20 pc, an issue which has been controversial over the years. We present the gas and dust properties of the cloud core and describe its structure and appearance at different wavelengths. The core contains a dense, very young, low mass stellar cluster with more than 300 objects in all evolutionary phases, from collapsing gaseous condensations to pre-main sequence stars. We describe the behaviour and spatial distribution of the different stellar populations (mm cores, Classes 0, I and II sources). The spatial concentration and the fraction number of Class 0/Class I/Class II sources is considerably larger in the Serpens core than in any other low mas...

  10. Cosmic rays and molecular clouds

    OpenAIRE

    2012-01-01

    This paper deals with the cosmic-ray penetration into molecular clouds and with the related gamma--ray emission. High energy cosmic rays interact with the dense gas and produce neutral pions which in turn decay into two gamma rays. This makes molecular clouds potential sources of gamma rays, especially if they are located in the vicinity of a powerful accelerator that injects cosmic rays in the interstellar medium. The amplitude and duration in time of the cosmic--ray overdensity around a giv...

  11. The evolution of molecular clouds

    Science.gov (United States)

    Shu, Frank H.; Lizano, Susana

    1988-01-01

    The problem of the structure and evolution of molecular clouds is reviewed, with particular emphasis given to the relationship with star formation. The basic hypothesis is that magnetic fields are the primary agents for supporting molecular clouds, although damped Alfven waves may play an important role in the direction parallel to the field lines. This picture naturally leads to a conception of 'bimodal star formation'. It is proposed that high-mass stars form from the overall gravitational collapse of a supercritical cloud, whereas low-mass stars form from small individual cores that slowly condense by ambipolar diffusion from a more extended envelope until they pass the brink of graviational instability and begin to collapse dynamically from 'inside-out'. The evidence that the infall stage of protostellar evolution is terminated by the development of a powerful stellar wind is reviewed.

  12. Fractal Structure of Molecular Clouds

    OpenAIRE

    Datta, Srabani

    2001-01-01

    Compelling evidence exists to show that the structure of molecular clouds is fractal in nature. In this paper, the author reiterates this view and, in addition, asserts that not only is cloud geometry fractal, but that they also have a common characteristic - they are similar in shape to the Horsehead nebula in Orion. This shape can be described by the Julia function f(x)= z^2 + c,where both z and c are complex quantities and c = -0.745429 + 0.113008i. The dynamical processes responsible for ...

  13. OH+ in Diffuse Molecular Clouds

    CERN Document Server

    Porras, A J; Welty, D E; Ritchey, A M

    2013-01-01

    Near ultraviolet observations of OH+ and OH in diffuse molecular clouds reveal a preference for different environments. The dominant absorption feature in OH+ arises from a main component seen in CH+ (that with the highest CH+/CH column density ratio), while OH follows CN absorption. This distinction provides new constraints on OH chemistry in these clouds. Since CH+ detections favor low-density gas with small fractions of molecular hydrogen, this must be true for OH+ as well, confirming OH+ and H2O+ observations with the Herschel Space Telescope. Our observed correspondence indicates that the cosmic ray ionization rate derived from these measurements pertains to mainly atomic gas. The association of OH absorption with gas rich in CN is attributed to the need for high enough density and molecular fraction before detectable amounts are seen. Thus, while OH+ leads to OH production, chemical arguments suggest that their abundances are controlled by different sets of conditions and that they coexist with differen...

  14. OH+ in Diffuse Molecular Clouds

    Science.gov (United States)

    Porras, A. J.; Federman, S. R.; Welty, D. E.; Ritchey, A. M.

    2014-01-01

    Near ultraviolet observations of OH+ and OH in diffuse molecular clouds reveal a preference for different environments. The dominant absorption feature in OH+ arises from a main component seen in CH+ (that with the highest CH+/CH column density ratio), while OH follows CN absorption. This distinction provides new constraints on OH chemistry in these clouds. Since CH+ detections favor low-density gas with small fractions of molecular hydrogen, this must be true for OH+ as well, confirming OH+ and H2O+ observations with the Herschel Space Telescope. Our observed correspondence indicates that the cosmic ray ionization rate derived from these measurements pertains to mainly atomic gas. The association of OH absorption with gas rich in CN is attributed to the need for a high enough density and molecular fraction before detectable amounts are seen. Thus, while OH+ leads to OH production, chemical arguments suggest that their abundances are controlled by different sets of conditions and that they coexist with different sets of observed species. Of particular note is that non-thermal chemistry appears to play a limited role in the synthesis of OH in diffuse molecular clouds.

  15. Molecular Clouds: Observation to Experiment

    Energy Technology Data Exchange (ETDEWEB)

    Kane, J O; Ryutov, D D; Mizuta, A; Remington, B A; Pound, M W

    2004-05-06

    Our ongoing investigation of how 'Pillars' and other structure form in molecular clouds irradiated by ultraviolet (UV) stars has revealed that the Rayleigh-Taylor instability is strongly suppressed by recombination in the photoevaporated outflow, that clumps and filaments may be key, that the evolution of structure is well-modeled by compressible hydrodynamics, and that directionality of the UV radiation may have significant effects. We discuss a generic, flexible set of laboratory experiments that can address these issues.

  16. TURBULENCE DECAY AND CLOUD CORE RELAXATION IN MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Yang; Law, Chung K. [Center for Combustion Energy, Tsinghua University, Beijing 100084 (China); Xu, Haitao, E-mail: gaoyang-00@mails.tsinghua.edu.cn [Max Planck Institute for Dynamics and Self-Organization (MPIDS), D-37077 Göttingen (Germany)

    2015-02-01

    The turbulent motion within molecular clouds is a key factor controlling star formation. Turbulence supports molecular cloud cores from evolving to gravitational collapse and hence sets a lower bound on the size of molecular cloud cores in which star formation can occur. On the other hand, without a continuous external energy source maintaining the turbulence, such as in molecular clouds, the turbulence decays with an energy dissipation time comparable to the dynamic timescale of clouds, which could change the size limits obtained from Jean's criterion by assuming constant turbulence intensities. Here we adopt scaling relations of physical variables in decaying turbulence to analyze its specific effects on the formation of stars. We find that the decay of turbulence provides an additional approach for Jeans' criterion to be achieved, after which gravitational infall governs the motion of the cloud core. This epoch of turbulence decay is defined as cloud core relaxation. The existence of cloud core relaxation provides a more complete understanding of the effect of the competition between turbulence and gravity on the dynamics of molecular cloud cores and star formation.

  17. Molecular cloud evolution and star formation

    Science.gov (United States)

    Silk, J.

    1985-01-01

    The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.

  18. Structures in Molecular Clouds: Modeling

    Energy Technology Data Exchange (ETDEWEB)

    Kane, J O; Mizuta, A; Pound, M W; Remington, B A; Ryutov, D D

    2006-04-20

    We attempt to predict the observed morphology, column density and velocity gradient of Pillar II of the Eagle Nebula, using Rayleigh Taylor (RT) models in which growth is seeded by an initial perturbation in density or in shape of the illuminated surface, and cometary models in which structure is arises from a initially spherical cloud with a dense core. Attempting to mitigate suppression of RT growth by recombination, we use a large cylindrical model volume containing the illuminating source and the self-consistently evolving ablated outflow and the photon flux field, and use initial clouds with finite lateral extent. An RT model shows no growth, while a cometary model appears to be more successful at reproducing observations.

  19. Observations of chemical differentiation in clumpy molecular clouds

    CERN Document Server

    Buckle, J V; Wirström, E S; Charnley, S B; Markwick-Kemper, A J; Butner, H M; Takakuwa, S

    2006-01-01

    We have extensively mapped a sample of dense molecular clouds (L1512, TMC-1C, L1262, Per 7, L1389, L1251E) in lines of HC3N, CH3OH, SO and C^{18}O. We demonstrate that a high degree of chemical differentiation is present in all of the observed clouds. We analyse the molecular maps for each cloud, demonstrating a systematic chemical differentiation across the sample, which we relate to the evolutionary state of the cloud. We relate our observations to the cloud physical, kinematical and evolutionary properties, and also compare them to the predictions of simple chemical models. The implications of this work for understanding the origin of the clumpy structures and chemical differentiation observed in dense clouds are discussed.

  20. Synthetic Observations of the Evolution of Starless Cores in a Molecular Cloud Simulation: Comparisons with JCMT Data and Predictions for ALMA

    CERN Document Server

    Mairs, Steve; Offner, Stella S R; Schnee, Scott

    2014-01-01

    Interpreting the nature of starless cores has been a prominent goal in star formation for many years. In order to characterise the evolutionary stages of these objects, we perform synthetic observations of a numerical simulation of a turbulent molecular cloud. We find that nearly all cores that we detect are associated with filaments and eventually form protostars. We conclude that observed starless cores which appear Jeans unstable are only marginally larger than their respective Jeans masses (within a factor of 3). We note single dish observations such as those performed with the JCMT appear to miss significant core structure on small scales due to beam averaging. Finally, we predict that interferometric observations with ALMA Cycle 1 will resolve the important small scale structure, which has so far been missed by mm-wavelength observations.

  1. Modelling [CI] emission from turbulent molecular clouds

    CERN Document Server

    Glover, Simon C O; Micic, Milica; Molina, Faviola

    2014-01-01

    We use detailed numerical simulations of the coupled chemical, thermal and dynamical evolution of the gas in a turbulent molecular cloud to study the usefulness of the [CI] 609 micron and 370 micron fine structure emission lines as tracers of cloud structure. Emission from these lines is observed throughout molecular clouds, and yet the question of what we can learn from them about the physics of the clouds remains largely unexplored. We show that the fact that [CI] emission is widespread within molecular clouds is a simple consequence of the fact that the clouds are dominated by turbulent motions. Turbulence creates large density inhomogeneities, allowing radiation to penetrate deeply into the clouds. As a result, [CI] emitting gas is found throughout the cloud, rather than being concentrated at the edges. We examine how well we can use [CI] emission to trace the structure of the cloud, and show that the integrated intensity of the 609 micron line traces column density accurately over a wide range of visual ...

  2. Anchoring Magnetic Field in Turbulent Molecular Clouds

    CERN Document Server

    Li, Hua-bai; Goodman, Alyssa; Hildebrand, Roger; Novak, Giles

    2009-01-01

    One of the key problems in star formation research is to determine the role of magnetic fields. Starting from the atomic inter-cloud medium (ICM) which has density nH ~ 1 per cubic cm, gas must accumulate from a volume several hundred pc across in order to form a typical molecular cloud. Star formation usually occurs in cloud cores, which have linear sizes below 1 pc and densities nH2 > 10^5 per cubic cm. With current technologies, it is hard to probe magnetic fields at scales lying between the accumulation length and the size of cloud cores, a range corresponds to many levels of turbulent eddy cascade, and many orders of magnitude of density amplification. For field directions detected from the two extremes, however, we show here that a significant correlation is found. Comparing this result with molecular cloud simulations, only the sub-Alfvenic cases result in field orientations consistent with our observations.

  3. Molecular clouds photoevaporation and FIR line emission

    Science.gov (United States)

    Vallini, L.; Ferrara, A.; Pallottini, A.; Gallerani, S.

    2017-01-01

    With the aim of improving predictions on far infrared (FIR) line emission from Giant Molecular Clouds (GMC), we study the effects of photoevaporation (PE) produced by external far-ultraviolet (FUV) and ionizing (extreme-ultraviolet, EUV) radiation on GMC structure. We consider three different GMCs with mass in the range M_GMC = 10^{3-6} {M_{⊙}}. Our model includes: (i) an observationally-based inhomogeneous GMC density field, and (ii) its time evolution during the PE process. In the fiducial case (MGMC ≈ 105M⊙), the photoevaporation time (tpe) increases from 1 Myr to 30 Myr for gas metallicity Z=0.05-1 Z_{⊙}, respectively. Next, we compute the time-dependent luminosity of key FIR lines tracing the neutral and ionized gas layers of the GMCs, ([C II] at 158 {μ m}, [O III] at 88 μ m) as a function of G0, and Z until complete photoevaporation at tpe. We find that the specific [C II] luminosity is almost independent on the GMC model within the survival time of the cloud. Stronger FUV fluxes produce higher [C II] and [O III] luminosities, however lasting for progressively shorter times. At Z = Z⊙ the [C II] emission is maximized (L_CII≈ 10^4 {L_{⊙}} for the fiducial model) for tpopulations.

  4. Molecular clouds photoevaporation and FIR line emission

    CERN Document Server

    Vallini, L; Pallottini, A; Gallerani, S

    2016-01-01

    With the aim of improving predictions on the far infrared (FIR) line emission from Giant Molecular Clouds (GMC), we have studied the effects of photoevaporation (PE) produced by external far-ultraviolet (FUV) and ionizing (extreme-ultraviolet, EUV) radiation on the GMC structure. Our model includes: (i) an observationally-based inhomogeneous GMC density field, and (ii) its time evolution during the PE process. We find that the photoevaporation timescale, $t_{pe}$, of a typical GMC ($M_{\\rm GMC}=9 \\times 10^{4}\\,\\rm{M_{\\odot}}$) is in the range $1-30$ Myr, for gas metallicity $Z=0.05-1\\,\\rm Z_{\\odot}$, respectively. At fixed metallicity, $t_{pe}$ decreases for higher FUV fluxes, $G_0$, due to the larger temperature of the photodissociation region (PDR). The presence of EUV radiation is important at $Z<0.2\\,\\rm{Z_{\\odot}}$, when the size of the HII layer becomes comparable to the cloud radius. We then compute the time-dependent luminosity (for which we give fitting formulae) of several key FIR lines ([CII], ...

  5. Temperature Evolution of Molecular Clouds in the Central Molecular Zone

    CERN Document Server

    Krieger, Nico; Walter, Fabian; Kruijssen, J M Diederik; Beuther, Henrik

    2016-01-01

    We infer the absolute time dependence of kinematic gas temperature along a proposed orbit of molecular clouds in the Central Molecular Zone (CMZ) of the Galactic Center (GC). Ammonia gas temperature maps are one of the results of the "Survey of Water and Ammonia in the Galactic Center" (SWAG, PI: J. Ott); the dynamical model of molecular clouds in the CMZ was taken from Kruijssen et al. (2015). We find that gas temperatures increase as a function of time in both regimes before and after the cloud passes pericenter on its orbit in the GC potential. This is consistent with the recent proposal that pericenter passage triggers gravitational collapse. Other investigated quantities (line width, column density, opacity) show no strong sign of time dependence but are likely dominated by cloud-to-cloud variations.

  6. Carbon Isotope Chemistry in Molecular Clouds

    Science.gov (United States)

    Robertson, Amy N.; Willacy, Karen

    2012-01-01

    Few details of carbon isotope chemistry are known, especially the chemical processes that occur in astronomical environments like molecular clouds. Observational evidence shows that the C-12/C-13 abundance ratios vary due to the location of the C-13 atom within the molecular structure. The different abundances are a result of the diverse formation pathways that can occur. Modeling can be used to explore the production pathways of carbon molecules in an effort to understand and explain the chemical evolution of molecular clouds.

  7. Molecular Tracers of Turbulent Shocks in Giant Molecular Clouds

    CERN Document Server

    Pon, A; Kaufman, M J

    2012-01-01

    Giant molecular clouds contain supersonic turbulence and simulations of MHD turbulence show that these supersonic motions decay in roughly a crossing time, which is less than the estimated lifetimes of molecular clouds. Such a situation requires a significant release of energy. We run models of C-type shocks propagating into gas with densities around 10^3 cm^(-3) at velocities of a few km / s, appropriate for the ambient conditions inside of a molecular cloud, to determine which species and transitions dominate the cooling and radiative energy release associated with shock cooling of turbulent molecular clouds. We find that these shocks dissipate their energy primarily through CO rotational transitions and by compressing pre-existing magnetic fields. We present model spectra for these shocks and by combining these models with estimates for the rate of turbulent energy dissipation, we show that shock emission should dominate over emission from unshocked gas for mid to high rotational transitions (J >5) of CO. ...

  8. Molecular cloud complex associated with ON 1

    Energy Technology Data Exchange (ETDEWEB)

    Israel, F.P.; Wooten, H.A.

    1983-03-15

    Observations of CO with different resolutions near the compact H ii region/maser source ON 1 are presented, as well as new H/sub 2/CO and HCO/sup +/ observations. ON 1 is part of an extended molecular cloud complex with overall dimensions of 25 x 60 pc at a distance of 1.4 kpc; it appears to be the only site of star formation in at least the western part of the complex. ON 1 coincides with a compact and dense molecular cloud core (size 0.8 pc) that shows little sign of disruption indicating that ON 1 has only recently turned on. The isolation and apparent youth of ON 1 suggest that we observe here the very beginning of the star formation phase of a molecular cloud complex.

  9. Molecular Clouds as Cosmic-Ray Barometers

    CERN Document Server

    Casanova, S; Fukui, Y; Gabici, S; Jones, D I; Kawamura, A; Onishi, T; Rowell, G; Torii, K; Yamamoto, H

    2009-01-01

    It is generally assumed that the flux of cosmic-rays observed at the top of the Earth's atmosphere is representative of the flux in the Galaxy at large. The advent of high sensitivity, high resolution gamma-ray detectors, together with a knowledge of the distribution of the atomic hydrogen and especially of the molecular hydrogen in the Galaxy on sub-degree scales, as provided by the NANTEN survey, creates a unique opportunity to explore the flux of cosmic rays in the Galaxy. We present a methodology which aims to provide a test bed for current and future gamma-ray observatories to explore the cosmic ray flux at various positions in our Galaxy. In particular, for a distribution of molecular clouds and local cosmic ray density as measured at the Earth, we estimate the expected GeV to TeV gamma-ray signal, which can then be compared with observations. An observed gamma-ray flux less than predicted would imply a CR density in specific regions of the Galaxy less than that observed at Earth, and vice versa. The me...

  10. Dispersion of Magnetic Fields in Molecular Clouds

    CERN Document Server

    Hildebrand, Roger H; Dotson, Jessie L; Houde, Martin; Vaillancourt, John E

    2008-01-01

    We describe a method for determining the dispersion of magnetic field vectors about local mean fields in turbulent molecular clouds. The method is designed to avoid inaccurate estimates of MHD or turbulent dispersion - and hence to avoid inaccurate estimates of field strengths - due to large-scale, non-turbulent field structure when using the well-known method of Chandrasekhar and Fermi. Our method also provides accurate, independent estimates of the turbulent to mean magnetic field strength ratio. We discuss applications to the molecular clouds Orion, M17, and DR21.

  11. Carbon chemistry in dense molecular clouds: Theory and observational constraints

    Science.gov (United States)

    Blake, Geoffrey A.

    1990-01-01

    For the most part, gas phase models of the chemistry of dense molecular clouds predict the abundances of simple species rather well. However, for larger molecules and even for small systems rich in carbon these models often fail spectacularly. Researchers present a brief review of the basic assumptions and results of large scale modeling of the carbon chemistry in dense molecular clouds. Particular attention is to the influence of the gas phase C/O ratio in molecular clouds, and the likely role grains play in maintaining this ratio as clouds evolve from initially diffuse objects to denser cores with associated stellar and planetary formation. Recent spectral line surveys at centimeter and millimeter wavelengths along with selected observations in the submillimeter have now produced an accurate inventory of the gas phase carbon budget in several different types of molecular clouds, though gaps in our knowledge clearly remain. The constraints these observations place on theoretical models of interstellar chemistry can be used to gain insights into why the models fail, and show also which neglected processes must be included in more complete analyses. Looking toward the future, larger molecules are especially difficult to study both experimentally and theoretically in such dense, cold regions, and some new methods are therefore outlined which may ultimately push the detectability of small carbon chains and rings to much heavier species.

  12. Kinematics of molecular clouds. II. New data on nearby giant molecular clouds

    Energy Technology Data Exchange (ETDEWEB)

    Stark, A.A.; Brand, J.

    1989-04-01

    The best currently available data on positions, distances, and velocities of giant molecular clouds within 3 kpc of the sun are analyzed to yield a one-dimensional rms cloud-to-cloud velocity dispersion of 7.8 +0.6, -0.5. Velocity dispersion is defined here as the root mean square of cloud peculiar velocities, a quantity which includes small-scale streaming. It is argued that this value for the velocity dispersion is pausible, based on examples of clouds whose velocities cannot be explained purely by galactic rotation. The mean motion of nearby molecular clouds is drifting by about 4 km/s with respect to the LSR. 21 refs.

  13. Distribution of Water Vapor in Molecular Clouds

    CERN Document Server

    Melnick, Gary J; Snell, Ronald L; Bergin, Edwin A; Hollenbach, David J; Kaufman, Michael J; Li, Di; Neufeld, David A

    2010-01-01

    We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C2H, 13CO J =5-4, and HCN, and less well with the volume tracer N2H+. Moreover, at total column densities corresponding to Av < 15 mag., the ratio of H2O to C18O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large Av. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations...

  14. Star Formation in Molecular Clouds

    CERN Document Server

    Krumholz, Mark R

    2011-01-01

    Star formation is one of the least understood processes in cosmic evolution. It is difficult to formulate a general theory for star formation in part because of the wide range of physical processes involved. The interstellar gas out of which stars form is a supersonically turbulent plasma governed by magnetohydrodynamics. This is hard enough by itself, since we do not understand even subsonic hydrodynamic turbulence very well, let alone supersonic non-ideal MHD turbulence. However, the behavior of star-forming clouds in the ISM is also obviously influenced by gravity, which adds complexity, and by both continuum and line radiative processes. Finally, the behavior of star-forming clouds is influenced by a wide variety of chemical processes, including formation and destruction of molecules and dust grains (which changes the thermodynamic behavior of the gas) and changes in ionization state (which alter how strongly the gas couples to magnetic fields). As a result of these complexities, there is nothing like a g...

  15. The Search for Primordial Molecular Cloud Matter

    DEFF Research Database (Denmark)

    van Kooten, Elishevah M M E

    evolution. Some of the least altered, most primitive meteorites can give us clues to the original make-up of the interstellar molecular cloud from which the Sun and its surrounding planets formed, thus, permitting us to trace Solar System formation from its most early conditions. Using state-of-the-art...

  16. Mutual influence of supernovae and molecular clouds

    CERN Document Server

    Iffrig, Olivier

    2014-01-01

    Context. Molecular clouds are known to be turbulent and strongly affected by stellar feedback. Moreover, stellar feedback is believed to be driving turbulence at large scales in galaxies. Aims. We study the role played by supernovae in molecular clouds and the influence of the magnetic field on this process. Methods. We perform three-dimensional numerical simulations of supernova explosions, in and near turbulent self-gravitating molecular clouds. In order to study the influence of the magnetic field, we perform both hydrodynamical and MHD simulations. We also run a series of simple uniform density medium simulations and develop a simple analytical model. Results. We find that the total amount of momentum that is delivered during supernova explosions typically varies by a factor of about 2 even when the gas density changes by 3 orders of magnitude. However, the amount of momentum delivered to the dense gas varies by almost a factor 10 if the supernova explodes within or outside the molecular cloud. The magnet...

  17. Molecular clouds. [significance in stellar evolution

    Science.gov (United States)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  18. Molecular cloud evolution - V. Cloud destruction by stellar feedback

    Science.gov (United States)

    Colín, Pedro; Vázquez-Semadeni, Enrique; Gómez, Gilberto C.

    2013-10-01

    We present a numerical study of the evolution of molecular clouds, from their formation by converging flows in the warm interstellar medium, to their destruction by the ionizing feedback of the massive stars they form. We improve with respect to our previous simulations by including a different stellar-particle formation algorithm, which allows them to have masses corresponding to single stars rather than to small clusters, and with a mass distribution following a near-Salpeter stellar initial mass function. We also employ a simplified radiative-transfer algorithm that allows the stellar particles to feedback on the medium at a rate that depends on their mass and the local density. Our results are as follows: (a) contrary to the results from our previous study, where all stellar particles injected energy at a rate corresponding to a star of ˜10 M⊙, the dense gas is now completely evacuated from 10 pc regions around the stars within 10-20 Myr, suggesting that this feat is accomplished essentially by the most massive stars. (b) At the scale of the whole numerical simulations, the dense gas mass is reduced by up to an order of magnitude, although star formation (SF) never shuts off completely, indicating that the feedback terminates SF locally, but new SF events continue to occur elsewhere in the clouds. (c) The SF efficiency (SFE) is maintained globally at the ˜10 per cent level, although locally, the cloud with largest degree of focusing of its accretion flow reaches SFE ˜30 per cent. (d) The virial parameter of the clouds approaches unity before the stellar feedback begins to dominate the dynamics, becoming much larger once feedback dominates, suggesting that clouds become unbound as a consequence of the stellar feedback, rather than unboundness being the cause of a low SFE. (e) The erosion of the filaments that feed the star-forming clumps produces chains of isolated dense blobs reminiscent of those observed in the vicinity of the dark globule B68.

  19. Molecular Cloud Formation Behind Shock Waves

    CERN Document Server

    Bergin, E A; Raymond, J C; Ballesteros-Paredes, J

    2004-01-01

    We examine the formation of molecular gas behind shocks in atomic gas using a chemical/dynamical model, particular emphasis is given to constraints the chemistry places on the dynamical evolution. The most important result of this study is to stress the importance of shielding the molecular gas from the destructive effects of UV radiation. For shock ram pressures comparable to or exceeding typical local ISM pressures, self-shielding controls the formation time of H2 but CO formation requires shielding of the interstellar radiation field by dust grains. We find that the molecular hydrogen fractional abundance can become significant well before CO forms. The timescale for (CO) molecular cloud formation is not set by H2 formation, but rather by the timescale for accumulating a sufficient column density or extinction, A_V > 0.7. The local ratio of atomic to molecular gas (4:1), coupled with short estimates for cloud lifetimes (3-5 Myr), suggests that the timescales for accumulating molecular clouds from atomic ma...

  20. What can simulated molecular clouds tell us about real molecular clouds?

    Science.gov (United States)

    Duarte-Cabral, A.; Dobbs, C. L.

    2016-06-01

    We study the properties of giant molecular clouds (GMCs) from a smoothed particle hydrodynamics simulation of a portion of a spiral galaxy, modelled at high resolution, with robust representations of the physics of the interstellar medium. We examine the global molecular gas content of clouds, and investigate the effect of using CO or H2 densities to define the GMCs. We find that CO can reliably trace the high-density H2 gas, but misses less dense H2 clouds. We also investigate the effect of using 3D CO densities versus CO emission with an observer's perspective, and find that CO-emission clouds trace well the peaks of the actual GMCs in 3D, but can miss the lower density molecular gas between density peaks which is often CO-dark. Thus, the CO emission typically traces smaller clouds within larger GMC complexes. We also investigate the effect of the galactic environment (in particular the presence of spiral arms), on the distribution of GMC properties, and we find that the mean properties are similar between arm and inter-arm clouds, but the tails of some distributions are indicative of intrinsic differences in the environment. We find highly filamentary clouds (similar to the giant molecular filaments of our Galaxy) exclusively in the inter-arm region, formed by galactic shear. We also find that the most massive GMC complexes are located in the arm, and that as a consequence of more frequent cloud interactions/mergers in the arm, arm clouds are more sub-structured and have higher velocity dispersions than inter-arm clouds.

  1. Modeling of the continuum and molecular line emission from the Sagittarius B2 molecular cloud

    Energy Technology Data Exchange (ETDEWEB)

    Lis, D.C.; Goldsmith, P.F. (Massachusetts Univ., Amherst (USA))

    1990-06-01

    The continuum and molecular line emission from the Sagittarius B2 molecular cloud are modeled in order to determine the conditions in the core and the envelope of the cloud. The continuum models suggest that the total luminosity of the middle source Sgr B2(M) is an order of magnitude higher than that of the northern source Sgr B2(N). The microturbulent models of the molecular line emission predict the correct spatial intensity distribution of the J = 1 - 0 transitions of C(O-18) and (C-13)O. They have difficulties, however, reproducing the observed intensities of the higher transitions of these molecules. This may indicate that the envelope has a clumpy structure. Sgr B2 differs significantly from typical disk giant molecular clouds in that it has higher mass and luminosity of the continuum sources, much greater H2 column density and mean volume density, and different fractional abundances of many interstellar molecules. 43 refs.

  2. Molecular abundances in the Sagittarius A molecular cloud

    Science.gov (United States)

    Minh, Y. C.; Irvine, W. M.; Friberg, P.

    1992-01-01

    We have obtained column densities for HCO(+), HCO, HCS(+), C3H2, HC5N, SiO, OCS, HCOOH, CH3CH2OH, and CH3CCH toward Sgr A. The fractional abundance of SiO relative to molecular hydrogen in Sgr A is comparable to that for the Orion plateau, about 10 exp-7 to 10 exp -8, which may be a typical value for hot clouds. The abundances of HCO, CH3CH2OH, and CH3CCH all appear to be enhanced relative to other molecular clouds such as Sgr B2.

  3. OH{sup +} IN DIFFUSE MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Porras, A. J.; Federman, S. R. [Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606 (United States); Welty, D. E. [Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Ritchey, A. M., E-mail: steven.federman@utoledo.edu, E-mail: aporras@live.unc.edu, E-mail: dwelty@oddjob.uchicago.edu, E-mail: aritchey@astro.washington.edu [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States)

    2014-01-20

    Near ultraviolet observations of OH{sup +} and OH in diffuse molecular clouds reveal a preference for different environments. The dominant absorption feature in OH{sup +} arises from a main component seen in CH{sup +} (that with the highest CH{sup +}/CH column density ratio), while OH follows CN absorption. This distinction provides new constraints on OH chemistry in these clouds. Since CH{sup +} detections favor low-density gas with small fractions of molecular hydrogen, this must be true for OH{sup +} as well, confirming OH{sup +} and H{sub 2}O{sup +} observations with the Herschel Space Telescope. Our observed correspondence indicates that the cosmic ray ionization rate derived from these measurements pertains to mainly atomic gas. The association of OH absorption with gas rich in CN is attributed to the need for a high enough density and molecular fraction before detectable amounts are seen. Thus, while OH{sup +} leads to OH production, chemical arguments suggest that their abundances are controlled by different sets of conditions and that they coexist with different sets of observed species. Of particular note is that non-thermal chemistry appears to play a limited role in the synthesis of OH in diffuse molecular clouds.

  4. The Giant Molecular Cloud Environments of Infrared Dark Clouds

    CERN Document Server

    Hernandez, Audra K

    2015-01-01

    We study the GMC environments surrounding 10 IRDCs, based on 13CO molecular line emission from the Galactic Ring Survey. Using a range of physical scales, we measure the physical properties of the IRDCs and their surrounding molecular material extending out to radii, R, of 30pc. By comparing different methods for defining cloud boundaries and for deriving mass surface densities, Sigma, and velocity dispersions, sigma, we settled on a preferred "CE,tau,G" method of "Connected Extraction" in position-velocity space along with Gaussian fitting to opacity-corrected line profiles for velocity dispersion and mass estimation. We examine how cloud definition affects measurements of the magnitude and direction of line of sight velocity gradients and velocity dispersions, including the associated dependencies on size scale. CE,tau,G-defined IRDCs and GMCs show velocity gradient versus size relations that scale approximately as dv_0/ds~s^(-1/2) and velocity dispersion versus size relations sigma~s^(1/2), which are consi...

  5. Molecular cloud regulated star formation in galaxies

    CERN Document Server

    Booth, C M; Okamoto, T

    2007-01-01

    We describe a numerical implementation of star formation in disk galaxies, in which the conversion of cooling gas to stars in the multiphase interstellar medium is governed by the rate at which molecular clouds are formed and destroyed. In the model, clouds form from thermally unstable ambient gas and get destroyed by feedback from massive stars and thermal conduction. Feedback in the ambient phase cycles gas into a hot galactic fountain or wind. We model the ambient gas hydrodynamically using smoothed particle hydrodynamics (SPH). However, we cannot resolve the Jeans mass in the cold and dense molecular gas and, therefore, represent the cloud phase with ballistic particles that coagulate when colliding. We show that this naturally produces a multiphase medium with cold clouds, a warm disk, hot supernova bubbles and a hot, tenuous halo. Our implementation of this model is based on the Gadget N-Body code. We illustrate the model by evolving an isolated Milky Way-like galaxy and study the properties of a disk f...

  6. Photoevaporating transitional discs and molecular cloud cores

    Science.gov (United States)

    Li, Min; Sui, Ning

    2017-04-01

    We investigate the evolution of photoevaporating protoplanetary discs including mass influx from molecular cloud cores. We examine the influence of cloud core properties on the formation and evolution of transitional discs. We use one-dimensional thin disc assumption and calculate the evolution of the protoplanetary disc. The effects of X-ray photoevaporation are also included. Our calculations suggest that most discs should experience the transitional disc phase within 10 Myr. The formation time of a gap and its initial location are functions of the properties of the cloud cores. In some circumstances, discs can open two gaps by photoevaporation alone. The two gaps form when the gas in the disc can expand to large radius and if the mass at large radius is sufficiently small. The surface density profile of the disc determines whether the two gaps can form. Since the structure of a disc is determined by the properties of a molecular cloud core, the core properties determine the formation of two gaps in the disc. We further find that even when the photoevaporation rate is reduced to 10 per cent of the standard value, two gaps can still form in the disc. The only difference is that the formation time is delayed.

  7. Water Abundance in Molecular Cloud Cores

    CERN Document Server

    Snell, R L; Ashby, M L N; Bergin, E A; Chin, G; Erickson, N R; Goldsmith, P F; Harwit, M; Kleiner, S C; Koch, D G; Neufeld, D A; Patten, B M; Plume, R; Schieder, R; Stauffer, J R; Tolls, V; Wang, Z; Winnewisser, G; Zhang, Y F; Melnick, G J

    2000-01-01

    We present Submillimeter Wave Astronomy Satellite (SWAS) observations of the 1_{10}-1_{01} transition of ortho-water at 557 GHz toward 12 molecular cloud cores. The water emission was detected in NGC 7538, Rho Oph A, NGC 2024, CRL 2591, W3, W3(OH), Mon R2, and W33, and was not detected in TMC-1, L134N, and B335. We also present a small map of the water emission in S140. Observations of the H_2^{18}O line were obtained toward S140 and NGC 7538, but no emission was detected. The abundance of ortho-water relative to H_2 in the giant molecular cloud cores was found to vary between 6x10^{-10} and 1x10^{-8}. Five of the cloud cores in our sample have previous water detections; however, in all cases the emission is thought to arise from hot cores with small angular extents. The water abundance estimated for the hot core gas is at least 100 times larger than in the gas probed by SWAS. The most stringent upper limit on the ortho-water abundance in dark clouds is provided in TMC-1, where the 3-sigma upper limit on the ...

  8. The Search for Primordial Molecular Cloud Matter

    DEFF Research Database (Denmark)

    van Kooten, Elishevah M M E

    Our Solar System today presents a somewhat static picture compared to the turbulent start of its existence. Meteorites are the left-over building blocks of planet formation and allow us to probe the chemical and physical processes that occurred during the first few million years of Solar System...... evolution. Some of the least altered, most primitive meteorites can give us clues to the original make-up of the interstellar molecular cloud from which the Sun and its surrounding planets formed, thus, permitting us to trace Solar System formation from its most early conditions. Using state......-of-the-art magnesium and chromium isotope techniques, we can distinguish a class of metal-rich meteorites with primordial molecular cloud signatures that show these objects formed in accretion regions akin to comets. As comets are proposed to have delivered some of the prerequisites of life to Earth, for example...

  9. Ambipolar Drift Heating in Turbulent Molecular Clouds

    CERN Document Server

    Padoan, P; Nordlund, A A; Padoan, Paolo

    1999-01-01

    Although thermal pressure is unimportant dynamically in most molecular gas, the temperature is an important diagnostic of dynamical processes and physical conditions. This is the first of two papers on thermal equilibrium in molecular clouds. We present calculations of frictional heating by ion-neutral (or ambipolar) drift in three-dimensional simulations of turbulent, magnetized molecular clouds. We show that ambipolar drift heating is a strong function of position in a turbulent cloud, and its average value can be significantly larger than the average cosmic ray heating rate. The volume averaged heating rate per unit volume due to ambipolar drift, H_AD ~ |JxB|^2 ~ B^4/L_B^2, is found to depend on the rms Alfvenic Mach number, M_A, and on the average field strength, as H_AD ~ M_A^2^4. This implies that the typical scale of variation of the magnetic field, L_B, is inversely proportional to M_A, which we also demonstrate.

  10. The chemical evolution of molecular clouds

    Science.gov (United States)

    Iglesias, E.

    1977-01-01

    The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.

  11. The Formation of Molecular Clouds: Insights from Numerical Models

    Science.gov (United States)

    Heitsch, Fabian

    2010-10-01

    Galactic star formation occurs at a surprisingly low rate. Yet, recent large-scale surveys of dark clouds in the Galaxy show that one rarely finds molecular clouds without young stellar objects, suggesting that star formation should occur rapidly upon molecular cloud formation. This rapid onset challenges the traditional concept of ``slow'' star formation in long-lived molecular clouds. It also imposes strong constraints on the physical properties of the parental clouds, mandating that a cloud's structure and dynamics controlling stellar birth must arise during its formation. This requires a new approach to study initial conditions of star formation, namely addressing the formation of molecular clouds. Taking into account the observational constraints, I will outline the physics of flow-driven molecular cloud formation. I will discuss the relevance and the limitations of this scenario for setting the star formation efficiency in our Galaxy and beyond.

  12. Turbulence in high latitude molecular clouds

    Science.gov (United States)

    Shore, S. N.; Larosa, T. N.; Magnani, L.; Chastain, R. J.; Costagliola, F.

    We summarize a continuing investigation of turbulence in high-latitude translucent molecular clouds. These low mass (~ 50 M(solar), nearby (~ 100 pc), non-star forming clouds appear to be condensing out of the atomic cirrus and must be forced by external dynamical processes, since they lack internal sources, for which we can distinguish the injection scale for the turbulence. We have now mapped three clouds -- MBM 3, MBM 16, and MBM 40 -- with high spatial (0.03 pc) and velocity resolution (<0.08 km/s) in 12CO(1-0) 13CO(1-0) (NRAO 12m and FCRAO). All three clouds show evidence for large-shear flows and we propose that the turbulent motions are powered by shear-flow instability. The densest gas is structured into filaments but the velocity profiles do not change in going across a filament indicating that shocks are not compressing the gas. The density field is more likely the result of thermal instability. The velocity-size relationship, a commonly used diagnostic of ISM turbulence, does not hold in these clouds: the linewidth does not increase with region size. The centroid velocity probability distribution function (PDF) is a more precise measure of turbulence. In these clouds the PDFs exhibit broad wings, consistent with a Lorentzian distribution and showing evidence non-Gaussian correlated processes. This is a clear signature of intermittency. We have also begun a mapping survey of CS (1-0), CS (2-1), H2CO, and HCO+ at Arecibo and OSO and willdiscuss results for the Polaris flare and L1512. We will also discusssome implications of these studies for the turbulent dissipation in these systems.

  13. What can simulated molecular clouds tell us about real molecular clouds?

    CERN Document Server

    Duarte-Cabral, A

    2016-01-01

    We study the properties of giant molecular clouds (GMCs) from an SPH simulation of a portion of a spiral galaxy, modelled at high resolution, with robust representations of the physics of the interstellar medium. We examine the global molecular gas content of clouds, and investigate the effect of using CO or H2 densities to define the GMCs. We find that CO can reliably trace the high-density H2 gas, but misses less dense H2 clouds. We also investigate the effect of using 3D CO densities versus CO emission with an observer's perspective, and find that CO-emission clouds trace well the peaks of the actual GMCs in 3D, but can miss the lower density molecular gas between density peaks which is often CO-dark. Thus the CO emission typically traces smaller clouds within larger GMC complexes. We also investigate the effect of the galactic environment (in particular the presence of spiral arms), on the distribution of GMC properties, and we find that the mean properties are similar between arm and inter-arm clouds, bu...

  14. The Sagittarius B2 molecular cloud: An extreme case of a galactic center giant molecular cloud

    Energy Technology Data Exchange (ETDEWEB)

    Lis, D.C.

    1989-01-01

    A model was developed of the Sagittarius B2 molecular cloud based on the J = 1 yields 0 and 2 yields 1 transitions of (13)CO and C(18)O, as well as on the far infrared and submillimeter continuum emission from the dust, in order to determine the physical conditions in this source. The total mass of the cloud is dominated by an envelope which consists of a constant density component and a power law component with a radial exponent of -2. The virial mass of the cloud is a factor of approx. 2 higher than the molecular mass, suggesting that Sgr B2 is close to virial equilibrium. The Sgr B2(M) and (N) continuum sources are situated inside small dense cores embedded in the extended clouds. The middle source is much more luminous than the northern source. The observed change in the middle-to-north peak flux ratio between 350 mu and 1300 mu is primarily a result of the difference in luminosity. In order to compare Sgr B2 with other Galactic Center clouds, the J = 1 yields 0 transition of (13)CO was observed in two selected Galactic Center fields centered on the G1.1 to 0.1 and G359.4 to 0.1 continuum sources. The molecular clouds observed there seem to be distinctively different from Sgr B2.

  15. Cosmic-ray propagation in molecular clouds

    CERN Document Server

    Padovani, Marco

    2013-01-01

    Cosmic-rays constitute the main ionising and heating agent in dense, starless, molecular cloud cores. We reexamine the physical quantities necessary to determine the cosmic-ray ionisation rate (especially the cosmic ray spectrum at E < 1 GeV and the ionisation cross sections), and calculate the ionisation rate as a function of the column density of molecular hydrogen. Available data support the existence of a low-energy component (below about 100 MeV) of cosmic-ray electrons or protons responsible for the ionisation of diffuse and dense clouds. We also compute the attenuation of the cosmic-ray flux rate in a cloud core taking into account magnetic focusing and magnetic mirroring, following the propagation of cosmic rays along flux tubes enclosing different amount of mass and mass-to-flux ratios. We find that mirroring always dominates over focusing, implying a reduction of the cosmic-ray ionisation rate by a factor of 3-4 depending on the position inside the core and the magnetisation of the core.

  16. CO Abundance Variations in the Orion Molecular Cloud

    CERN Document Server

    Ripple, F; Gutermuth, R; Snell, R L; Brunt, C M

    2013-01-01

    Infrared stellar photometry from 2MASS and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the FCRAO 14m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100% with a peak value located near regions of enhanced star formation activity. The effect of CO depletion onto the ice mantles of dust grains is limited to regions with AV > 10 mag and gas temperatures less than 20 K as predicted by chemical models that consider thermal-evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from...

  17. 13CO Cores in Taurus Molecular Cloud

    CERN Document Server

    Qian, Lei; Goldsmith, Paul

    2012-01-01

    Young stars form in molecular cores, which are dense condensations within molecular clouds. We have searched for $^{13}$CO $J=1\\to 0$ cores in the Taurus molecular cloud and studied their properties. Our data set has a spatial dynamic range (the ratio of linear map size to the pixel size) of about 1000 and spectrally resolved velocity information. We use empirical fit to the CO and CO$_2$ ice to correct the depletion. The core mass function (CMF) can be fitted better with a log-normal function than with a power law function. We also extract cores and calculate the CMF based on the integrated intensity of $^{13}$CO and the extinction from 2MASS. We demonstrate that there exists core blending, i.e. combined structures that are incoherent in velocity but continuous in column density. The resulting core samples based on 2D and 3D data thus differ significantly from each other. In particular, the cores derived from 2MASS extinction can be fitted with a power-law function, but not a log-normal function. The core ve...

  18. Prediction of cloud droplet number in a general circulation model

    Energy Technology Data Exchange (ETDEWEB)

    Ghan, S.J.; Leung, L.R. [Pacific Northwest National Lab., Richland, WA (United States)

    1996-04-01

    We have applied the Colorado State University Regional Atmospheric Modeling System (RAMS) bulk cloud microphysics parameterization to the treatment of stratiform clouds in the National Center for Atmospheric Research Community Climate Model (CCM2). The RAMS predicts mass concentrations of cloud water, cloud ice, rain and snow, and number concnetration of ice. We have introduced the droplet number conservation equation to predict droplet number and it`s dependence on aerosols.

  19. CO abundance variations in the Orion Molecular Cloud

    Science.gov (United States)

    Ripple, F.; Heyer, M. H.; Gutermuth, R.; Snell, R. L.; Brunt, C. M.

    2013-05-01

    Infrared stellar photometry from the Two Micron All-Sky Survey (2MASS) and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the Five College Radio Astronomy Observatory (FCRAO) 14-m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon-dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100 per cent with a peak value located near regions of enhanced star formation activity. The effect of CO depletion on to the ice mantles of dust grains is limited to regions with Av > 10 mag and gas temperatures less than ˜20 K as predicted by chemical models that consider thermal evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from the distributions of Av and 13CO column densities with a constant 13CO-to-H2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (Av> 3 mag), 13CO provides a reliable tracer of H2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13CO does not trace the H2 mass that resides in the extended cloud envelope, which comprises 40-50 per cent of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/LCO, are 3.2 and 2.9 for Orion A and Orion B, respectively, which are comparable to the value (2.9), derived from γ-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H2 column densities.

  20. A Far-Infrared Survey of Molecular Cloud Cores

    CERN Document Server

    Jessop, N E

    1999-01-01

    We present a catalogue of molecular cloud cores drawn from high latitude, medium opacity clouds, using the all-sky IRAS Sky Survey Atlas (ISSA) images at 60 and 100~$\\mu$m. The typical column densities of the cores are $ N(H_2)\\sim 3.8 \\times 10^{21} $cm$^{-2}$ and the typical volume densities are $ n(H_2) many other samples obtained in other ways. Those cloud cores with IRAS point sources are seen to be already forming stars, but this is found to be only a small fraction of the total number of cores. The fraction of the cores in the protostellar stage is used to estimate the prestellar timescale - the time until the formation of a hydrostatically supported protostellar object. We argue, on the basis of a comparison with other samples, that a trend exists for the prestellar lifetime of a cloud core to decrease with the mean column density and number density of the core. We compare this with model predictions and show that the data are consistent with star formation regulated by the ionisation fraction.

  1. On the massive star-forming capacity of molecular clouds

    Science.gov (United States)

    Franco, Jose; Shore, Steven N.; Tenorio-Tagle, Guillermo

    1994-01-01

    Assuming that photoionization is the self-limiting process for continued star formation, we estimate the maximum number of massive (OB) stars that can form within a molecular cloud. The most efficient cloud destruction mechanism in the early stages of H II region evolution is the evaporation of the cloud by stars located near the cloud boundary. The maximum number of OB stars is of order 1 per 10(exp 4) solar mass of average molecular gas, or 10 per 10(exp 4) solar mass of dense molecular gas. The resulting star-forming efficiencies within cloud complexes range from 2% to 16% depending on both the location of the stars in the cloud and the details of the initial mass function, with an overall value of about 5% for average molecular gas.

  2. Revealing a spiral-shaped molecular cloud in our galaxy: Cloud fragmentation under rotation and gravity

    Science.gov (United States)

    Li, Guang-Xing; Wyrowski, Friedrich; Menten, Karl

    2017-02-01

    The dynamical processes that control star formation in molecular clouds are not well understood, and in particular, it is unclear if rotation plays a major role in cloud evolution. We investigate the importance of rotation in cloud evolution by studying the kinematic structure of a spiral-shaped Galactic molecular cloud G052.24+00.74. The cloud belongs to a large filament, and is stretching over 100 pc above the Galactic disk midplane. The spiral-shaped morphology of the cloud suggests that the cloud is rotating. We have analysed the kinematic structure of the cloud, and study the fragmentation and star formation. We find that the cloud exhibits a regular velocity pattern along west-east direction - a velocity shift of 10km s-1 at a scale of 30 pc. The kinematic structure of the cloud can be reasonably explained by a model that assumes rotational support. Similarly to our Galaxy, the cloud rotates with a prograde motion. We use the formalism of Toomre (1964) to study the cloud's stability, and find that it is unstable and should fragment. The separation of clumps can be consistently reproduced assuming gravitational instability, suggesting that fragmentation is determined by the interplay between rotation and gravity. Star formation occurs in massive, gravitational bound clumps. Our analysis provides a first example in which the fragmentation of a cloud is regulated by the interplay between rotation and gravity.

  3. Giant Molecular Cloud Structure and Evolution

    Science.gov (United States)

    Hollenbach, David (Technical Monitor); Bodenheimer, P. H.

    2003-01-01

    Bodenheimer and Burkert extended earlier calculations of cloud core models to study collapse and fragmentation. The initial condition for an SPH collapse calculation is the density distribution of a Bonnor-Ebert sphere, with near balance between turbulent plus thermal energy and gravitational energy. The main parameter is the turbulent Mach number. For each Mach number several runs are made, each with a different random realization of the initial turbulent velocity field. The turbulence decays on a dynamical time scale, leading the cloud into collapse. The collapse proceeds isothermally until the density has increased to about 10(exp 13) g cm(exp -3). Then heating is included in the dense regions. The nature of the fragmentation is investigated. About 15 different runs have been performed with Mach numbers ranging from 0.3 to 3.5 (the typical value observed in molecular cloud cores is 0.7). The results show a definite trend of increasing multiplicity with increasing Mach number (M), with the number of fragments approximately proportional to (1 + M). In general, this result agrees with that of Fisher, Klein, and McKee who published three cases with an AMR grid code. However our results show that there is a large spread about this curve. For example, for M=0.3 one case resulted in no fragmentation while a second produced three fragments. Thus it is not only the value of M but also the details of the superposition of the various velocity modes that play a critical role in the formation of binaries. Also, the simulations produce a wide range of separations (10-1000 AU) for the multiple systems, in rough agreement with observations. These results are discussed in two conference proceedings.

  4. Centroid Velocity Statistics of Molecular Clouds

    CERN Document Server

    Bertram, Erik; Shetty, Rahul; Glover, Simon C O; Klessen, Ralf S

    2014-01-01

    We compute structure functions and Fourier spectra of 2D centroid velocity (CV) maps in order to study the gas dynamics of typical molecular clouds (MCs) in numerical simulations. We account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas and use a 3D radiative transfer tool to model the CO line emission in a post-processing step. We perform simulations using three different initial mean number densities of n_0 = 30, 100 and 300 cm^{-3} to span a range of typical values for dense gas clouds in the solar neighbourhood. We compute slopes of the centroid velocity increment structure functions (CVISF) and of Fourier spectra for different chemical components: the total density, H2 number density, 12CO number density as well as the integrated intensity of 12CO (J=1-0) and 13CO (J=1-0). We show that optical depth effects can significantly affect the slopes derived for the CVISF, which also leads to different scaling properties for the Fourier spectra. The slopes of CVI...

  5. Centroid velocity statistics of molecular clouds

    Science.gov (United States)

    Bertram, Erik; Konstandin, Lukas; Shetty, Rahul; Glover, Simon C. O.; Klessen, Ralf S.

    2015-02-01

    We compute structure functions and Fourier spectra of 2D centroid velocity maps in order to study the gas dynamics of typical molecular clouds in numerical simulations. We account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas and use a 3D radiative transfer tool to model the CO line emission in a post-processing step. We perform simulations using three different initial mean number densities of n0 = 30, 100 and 300 cm-3 to span a range of typical values for dense gas clouds in the solar neighbourhood. We compute slopes of the centroid velocity increment structure functions (CVISF) and of Fourier spectra for different chemical components: the total density, H2 number density, 12CO number density as well as the integrated intensity of 12CO (J = 1 → 0) and 13CO (J = 1 → 0). We show that optical depth effects can significantly affect the slopes derived for the CVISF, which also leads to different scaling properties for the Fourier spectra. The slopes of CVISF and Fourier spectra for H2 are significantly steeper than those for the different CO tracers, independent of the density and the numerical resolution. This is due to the larger space-filling factor of H2 as it is better able to self-shield in diffuse regions, leading to a larger fractal co-dimension compared to CO.

  6. Filaments in the Lupus molecular clouds

    CERN Document Server

    Benedettini, M; Pezzuto, S; Elia, D; André, P; Könyves, V; Schneider, N; Tremblin, P; Arzoumanian, D; di Giorgio, A M; Di Francesco, J; Hill, T; Molinari, S; Motte, F; Nguyen-Luong, Q; Palmeirim, P; Rivera-Ingraham, A; Roy, A; Rygl, K L J; Spinoglio, L; Ward-Thompson, D; White, G J

    2015-01-01

    We have studied the filaments extracted from the column density maps of the nearby Lupus 1, 3, and 4 molecular clouds, derived from photometric maps observed with the Herschel satellite. Filaments in the Lupus clouds have quite low column densities, with a median value of $\\sim$1.5$\\times$10$^{21}$ cm$^{-2}$ and most have masses per unit length lower than the maximum critical value for radial gravitational collapse. Indeed, no evidence of filament contraction has been seen in the gas kinematics. We find that some filaments, that on average are thermally subcritical, contain dense cores that may eventually form stars. This is an indication that in the low column density regime, the critical condition for the formation of stars may be reached only locally and this condition is not a global property of the filament. Finally, in Lupus we find multiple observational evidences of the key role that the magnetic field plays in forming filaments, and determining their confinement and dynamical evolution.

  7. Inverse Hubble Flows in Molecular Clouds

    CERN Document Server

    Toalá, Jesús A; Colín, Pedro; Gómez, Gilberto C

    2014-01-01

    Motivated by recent numerical simulations of molecular cloud (MC)evolution, in which the clouds engage in global gravitational contraction, and local collapse events culminate significantly earlier than the global collapse, we investigate the growth of density perturbations embedded in a collapsing background, to which we refer as an Inverse Hubble Flow (IHF). We use the standard procedure for the growth of perturbations in a universe that first expands (the usual Hubble Flow) and then recollapses (the IHF). We find that linear density perturbations immersed in an IHF grow faster than perturbations evolving in a static background (the standard Jeans analysis). A fundamental distinction between the two regimes is that, in the Jeans case, the time $\\tau_\\mathrm{nl}$ for a density fluctuation to become nonlinear increases without limit as its initial value approaches zero, while in the IHF case $\\tau_\\mathrm{nl} \\le \\tau_\\mathrm{ff}$ always, where $\\tau_\\mathrm{ff}$ is the free-fall time of the background densit...

  8. Filaments in the Lupus molecular clouds

    Science.gov (United States)

    Benedettini, M.; Schisano, E.; Pezzuto, S.; Elia, D.; André, P.; Könyves, V.; Schneider, N.; Tremblin, P.; Arzoumanian, D.; di Giorgio, A. M.; Di Francesco, J.; Hill, T.; Molinari, S.; Motte, F.; Nguyen-Luong, Q.; Palmeirim, P.; Rivera-Ingraham, A.; Roy, A.; Rygl, K. L. J.; Spinoglio, L.; Ward-Thompson, D.; White, G. J.

    2015-10-01

    We have studied the filaments extracted from the column density maps of the nearby Lupus 1, 3, and 4 molecular clouds, derived from photometric maps observed with the Herschel satellite. Filaments in the Lupus clouds have quite low column densities, with a median value of ˜1.5 × 1021 cm-2 and most have masses per unit length lower than the maximum critical value for radial gravitational collapse. Indeed, no evidence of filament contraction has been seen in the gas kinematics. We find that some filaments, that on average are thermally subcritical, contain dense cores that may eventually form stars. This is an indication that in the low column density regime, the critical condition for the formation of stars may be reached only locally and this condition is not a global property of the filament. Finally, in Lupus we find multiple observational evidences of the key role that the magnetic field plays in forming filaments, and determining their confinement and dynamical evolution.

  9. Predictive Control of Networked Multiagent Systems via Cloud Computing.

    Science.gov (United States)

    Liu, Guo-Ping

    2017-01-18

    This paper studies the design and analysis of networked multiagent predictive control systems via cloud computing. A cloud predictive control scheme for networked multiagent systems (NMASs) is proposed to achieve consensus and stability simultaneously and to compensate for network delays actively. The design of the cloud predictive controller for NMASs is detailed. The analysis of the cloud predictive control scheme gives the necessary and sufficient conditions of stability and consensus of closed-loop networked multiagent control systems. The proposed scheme is verified to characterize the dynamical behavior and control performance of NMASs through simulations. The outcome provides a foundation for the development of cooperative and coordinative control of NMASs and its applications.

  10. Turbulent Velocity Structure in Molecular Clouds

    CERN Document Server

    Ossenkopf, V; Ossenkopf, Volker; Low, Mordecai-Mark Mac

    2002-01-01

    We compare velocity structure observed in the Polaris Flare molecular cloud at scales ranging from 0.015 pc to 20 pc to the velocity structure of a suite of simulations of supersonic hydrodynamic and MHD turbulence computed with the ZEUS MHD code. We examine different methods of characterising the structure, including a scanning-beam size-linewidth relation, structure functions, velocity and velocity difference probability distribution functions (PDFs), and the Delta-variance wavelet transform, and use them to compare models and observations. The Delta-variance is most sensitive in detecting characteristic scales and varying scaling laws, but is limited in the observational application by its lack of intensity weighting. We compare the true velocity PDF in our models to simulated observations of velocity centroids and average line profiles in optically thin lines, and find that the line profiles reflect the true PDF better. The observed velocity structure is consistent with supersonic turbulence showing a com...

  11. Tidally-disrupted Molecular Clouds falling to the Galactic Center

    CERN Document Server

    Tsuboi, Masato; Uehara, Kenta; Miyawaki, Ryosuke; Miyazaki, Atsushi

    2016-01-01

    We found a molecular cloud connecting from the outer region to the "Galactic Center Mini-spiral (GCMS)" which is a bundle of the ionized gas streams adjacent to Sgr A*. The molecular cloud has a filamentary appearance which is prominent in the CS J=2-1 emission line and is continuously connected with the GCMS. The velocity of the molecular cloud is also continuously connected with that of the ionized gas in the GCMS observed in the H42alpha recombination line. The morphological and kinematic relations suggest that the molecular cloud is falling from the outer region to the vicinity of Sgr A*, being disrupted by the tidal shear of Sgr A* and ionized by UV emission from the Central Cluster. We also found the SiO J=2-1 emission in the boundary area between the filamentary molecular cloud and the GCMS. There seems to exist shocked gas in the boundary area.

  12. The formation of molecular clouds in spiral galaxies

    CERN Document Server

    Dobbs, C L

    2006-01-01

    We present Smoothed Particle Hydrodynamics (SPH) simulations of molecular cloud formation in spiral galaxies. These simulations model the response of a non-self-gravitating gaseous disk to a galactic potential. The formation of molecular gas occurs when cold ($T \\le 100$ K) gas is compressed during the passage of a spiral arm. The spiral arms display considerable structure and the molecular gas accumulates into dense clouds. We identify the formation of these structures as due to the dynamics of clumpy shocks, which perturb the orbits of particles passing through the spiral arm. In addition, the spiral shocks induce a large velocity dispersion in the spiral arms, comparable with the magnitude of the velocity dispersion observed in molecular clouds. The molecular clouds are largely confined to the spiral arms, since most molecular gas is photodissociated to atomic hydrogen upon leaving the arms. However a low photodissociation rate increases the amount of interarm molecular gas, and the possibility of molecula...

  13. Revealing a spiral-shaped molecular cloud in our galaxy - Cloud fragmentation under rotation and gravity

    CERN Document Server

    Li, Guang-Xing; Menten, Karl

    2016-01-01

    The dynamical processes that control star formation in molecular clouds are not well understood, and in particular, it is unclear if rotation plays a major role in cloud evolution. We investigate the importance of rotation in cloud evolution by studying the kinematic structure of a spiral-shaped Galactic molecular cloud G052.24+00.74. The cloud belongs to a large filament, and is stretching over ~ 100 pc above the Galactic disk midplane. The spiral-shaped morphology of the cloud suggests that the cloud is rotating. We have analysed the kinematic structure of the cloud, and study the fragmentation and star formation. We find that the cloud exhibits a regular velocity pattern along west-east direction - a velocity shift of ~ 10 km/s at a scale of ~ 30 pc. The kinematic structure of the cloud can be reasonably explained by a model that assumes rotational support. Similarly to our Galaxy, the cloud rotates with a prograde motion. We use the formalism of Toomre (1964) to study the cloud's stability, and find that ...

  14. Imprints of Molecular Clouds in Radio Continuum Images

    CERN Document Server

    Yusef-Zadeh, F

    2012-01-01

    We show radio continuum images of several molecular complexes in the inner Galaxy and report the presence of dark features that coincide with dense molecular clouds. Unlike infrared dark clouds, these features which we call "radio dark clouds" are produced by a deficiency in radio continuum emission from molecular clouds that are embedded in a bath of UV radiation field or synchrotron emitting cosmic ray particles. The contribution of the continuum emission along different pathlengths results in dark features that trace embedded molecular clouds. The new technique of identifying cold clouds can place constraints on the depth and the magnetic field of molecular clouds when compared to those of the surrounding hot plasma radiating at radio wavelengths. The study of five molecular complexes in the inner Galaxy, Sgr A, Sgr B2, radio Arc, the snake filament and G359.75-0.13 demonstrate an anti--correlation between the distributions of radio continuum and molecular line and dust emission. Radio dark clouds are iden...

  15. Supernova Driving. III. Synthetic Molecular Cloud Observations

    Science.gov (United States)

    Padoan, Paolo; Juvela, Mika; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-08-01

    We present a comparison of molecular clouds (MCs) from a simulation of supernova (SN) driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming that the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, T B,min = 1.4 K, of the J = 1 - 0 12CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity-size and mass-size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity-size relation is slightly too steep for some of the models, while the mass-size relation is a bit too shallow for all models only at a spatial resolution dx ≈ 1 pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity-size normalization suggests that the SN rate in the Perseus arm is approximately 70% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that SN-driven turbulence can explain the origin and dynamics of MCs.

  16. Structure and radial equilibrium of filamentary molecular clouds

    CERN Document Server

    Contreras, Yanett; Garay, Guido

    2013-01-01

    Recent dust continuum surveys have shown that filamentary structures are ubiquitous along the Galactic plane. While the study of their global properties has gained momentum recently, we are still far from fully understanding their origin and stability. Theories invoking magnetic field have been formulated to help explain the stability of filaments; however, observations are needed to test their predictions. In this paper, we investigate the structure and radial equilibrium of five filamentary molecular clouds with the aim of determining the role that magnetic field may play. To do this, we use continuum and molecular line observations to obtain their physical properties (e.g. mass, temperature and pressure). We find that the filaments have lower lineal masses compared to their lineal virial masses. Their virial parameters and shape of their dust continuum emission suggests that these filaments may be confined by a toroidal dominated magnetic field.

  17. Temperature Rise at the Edges of Dark Molecular Clouds

    Institute of Scientific and Technical Information of China (English)

    MAO Xin-Jie

    2000-01-01

    Two-fluid magnetohydrodynanic equations are applied to dark molecular clouds that are composed of neutrals mixed with minor charged particles, weakly ionized gas systems. The result shows the temperatures are higher at the cloud edges than at their inner regions, the cause of which is that the cloud potential, released as clouds contract particularly at their edges, along with some dissipated rotational kinetic energy is converted into thermal.The cloud contracting is due to the loss of the magnetic field that threads it through ambipolar diffusion.Nevertheless, without the support of the magnetic and the centrifugal forces in the direction of the magnetic field assumed to be parallel to the cloud rotating axis, the cloud collapses in that direction when its mass is over the Jeans mass.

  18. On the masses of giant molecular cloud complexes

    Science.gov (United States)

    Stark, A. A.; Blitz, L.

    1978-01-01

    A method of mass estimation for molecular clouds is presented which is based on approximate balance in the outer cloud layers between the cloud's gravitation, the galactic tide, and internal pressure. The largest observed clouds, which have greatest linear extents of 100 pc, are found to have masses of at least 200,000 solar masses. The cloud masses cannot exceed this lower limit by more than a factor of 3, or the velocity distributions of disk stars would be more relaxed than is actually observed. This implied upper limit to cloud masses combined with the galactic tide may be related to the absence of clouds at galactocentric radii less than 4 kpc. If Sagittarius B2 is bound, its mass must be more than 50 million solar masses.

  19. Gravity Assist and Scattering off AGB Stars off Molecular Clouds

    Directory of Open Access Journals (Sweden)

    Ahmad H. Abdelhadi

    2009-01-01

    Full Text Available The scattering of stellar orbits by galactic molecular clouds is studied in hope of explaining isotopic peculiarities of presolar grains from Asymptotic Giant Branch (AGB stars. Silicon isotopic anomalies found in the mainstream Silicon Carbide (SiC grains are observed to have heavy isotopes enriched. To explain the isotopic heaviness I propose that AGB stars that formed in the interior region of the galaxy, with metallicity higher than solar, change their orbits during close encounters with molecular clouds. The AGB stars give up their SiC grains in winds deposited in the solar neighborhood prior to the birth of the Sun. I model the dynamics by superposing on a standard axisymmetric galactic potential the discrete potentials of thousands of molecular clouds moving in constant circular orbits. Gravity assist occurs when a star scattered into a crossing orbit by one cloud experiences forward scattering from a second cloud.

  20. Polytropes Implications for Molecular Clouds and Dark Matter

    CERN Document Server

    McKee, C F

    2000-01-01

    Polytropic models are reasonably successful in acounting for the observed features of molecular clouds. Multi-pressure polytropes include the various pressure components that are important in molecular clouds, whereas composite polytropes provide a representation for the core halo structure. Small, very dense (n~10^{11} cm^{-3}) molecular clouds have been proposed as models for both dark matter and for extreme scattering events. Insofar as the equation of state in these clouds can be represented by a single polytropic relation (pressure varies as a power of the density), such models conflict with observation. It is possible to contrive composite polytropes that do not conflict with observation, but whether the thermal properties of the clouds are consistent with such structure remains to be determined.

  1. The emerging role of cloud computing in molecular modelling.

    Science.gov (United States)

    Ebejer, Jean-Paul; Fulle, Simone; Morris, Garrett M; Finn, Paul W

    2013-07-01

    There is a growing recognition of the importance of cloud computing for large-scale and data-intensive applications. The distinguishing features of cloud computing and their relationship to other distributed computing paradigms are described, as are the strengths and weaknesses of the approach. We review the use made to date of cloud computing for molecular modelling projects and the availability of front ends for molecular modelling applications. Although the use of cloud computing technologies for molecular modelling is still in its infancy, we demonstrate its potential by presenting several case studies. Rapid growth can be expected as more applications become available and costs continue to fall; cloud computing can make a major contribution not just in terms of the availability of on-demand computing power, but could also spur innovation in the development of novel approaches that utilize that capacity in more effective ways. Copyright © 2013 Elsevier Inc. All rights reserved.

  2. Dynamical Simulations of Molecular Clouds in the Galactic Center

    Science.gov (United States)

    Salas, Jesus; Morris, Mark

    2016-06-01

    The formation of the central massive cluster of young stars orbiting the Galactic black hole, Sgr A*, has been modeled by several groups by invoking an almost radially infalling molecular cloud that interacts with the black hole and creates a dense, gaseous disk in which stars can then form. However, the dynamical origin of such a cloud remains an open question. We present simulations of the central 30-100 pc of the Milky Way, starting from a population of molecular clouds located in a disk with scale height of ~30 pc, using the N-body/smoothed-particle hydrodynamics code, Gadget2. We followed the dynamical evolution of clouds in a galactic potential that includes a bar to explore whether cloud collisions or a succession of cloud scatterings can remove sufficient angular momentum from a massive cloud to endow it with a predominantly radial orbit. Initial results illustrate the importance of tidal shear; while dense cloud cores remain identifiable for extended periods of time, much of the molecular mass ends up in tidal streams, so cannot be deflected onto low angular momentum orbits by their mutual interactions. At the completion of our ongoing computations, we will report on whether the cloud cores can undergo sufficient scattering to achieve low-angular-momentum orbits.

  3. Deuterium Fractionation in the Ophiuchus Molecular Cloud

    CERN Document Server

    Punanova, A; Pon, A; Belloche, A; André, Ph

    2015-01-01

    Aims. We measure the deuterium fraction, RD, and the CO-depletion factor, fd, toward a number of starless and protostellar cores in the L1688 region of the Ophiuchus molecular cloud complex and search for variations based upon environmental differences across L1688. The kinematic properties of the dense gas traced by the N2H+ and N2D+ (1-0) lines are also discussed. Methods. RD has been measured via observations of the J=1-0 transition of N2H+ and N2D+ toward 33 dense cores in different regions of L1688. fd estimates have been done using C17O(1-0) and 850 micron dust continuum emission from the SCUBA survey. All line observations were carried out with the IRAM 30 meter antenna. Results. The dense cores show large (2-40%) deuterium fractions, with significant variations between the sub-regions of L1688. The CO-depletion factor also varies from one region to another (1-7). Two different correlations are found between deuterium fraction and CO-depletion factor: cores in regions A, B2 and I show increasing RD wit...

  4. Supernova Driving. III. Synthetic Molecular Cloud Observations

    CERN Document Server

    Padoan, Paolo; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-01-01

    We present a comparison of molecular clouds (MCs) from a simulation of supernova-driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, $T_{\\rm B,min}=1.4$ K, of the $J=1-0$ $^{12}$CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity-size and mass-size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity-size relation is sl...

  5. The Origin of Molecular Cloud Turbulence

    CERN Document Server

    Padoan, Paolo; Haugboelle, Troels; Nordlund, Ake

    2015-01-01

    Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. It has been shown that interstellar medium (ISM) turbulence is likely driven by SN explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc)^3, specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes velocity scaling consistent with the usual scaling laws of supersonic turbulence. This also means that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find the same scaling laws extend to the interior of MCs, and their normal...

  6. A quantitative analysis of IRAS maps of molecular clouds

    Science.gov (United States)

    Wiseman, Jennifer J.; Adams, Fred C.

    1994-01-01

    We present an analysis of IRAS maps of five molecular clouds: Orion, Ophiuchus, Perseus, Taurus, and Lupus. For the classification and description of these astrophysical maps, we use a newly developed technique which considers all maps of a given type to be elements of a pseudometric space. For each physical characteristic of interest, this formal system assigns a distance function (a pseudometric) to the space of all maps: this procedure allows us to measure quantitatively the difference between any two maps and to order the space of all maps. We thus obtain a quantitative classification scheme for molecular clouds. In this present study we use the IRAS continuum maps at 100 and 60 micrometer(s) to produce column density (or optical depth) maps for the five molecular cloud regions given above. For this sample of clouds, we compute the 'output' functions which measure the distribution of density, the distribution of topological components, the self-gravity, and the filamentary nature of the clouds. The results of this work provide a quantitative description of the structure in these molecular cloud regions. We then order the clouds according to the overall environmental 'complexity' of these star-forming regions. Finally, we compare our results with the observed populations of young stellar objects in these clouds and discuss the possible environmental effects on the star-formation process. Our results are consistent with the recently stated conjecture that more massive stars tend to form in more 'complex' environments.

  7. Giant Molecular Cloud Formation in Disk Galaxies: Characterizing Simulated versus Observed Cloud Catalogs

    Science.gov (United States)

    Benincasa, Samantha M.; Tasker, Elizabeth J.; Pudritz, Ralph E.; Wadsley, James

    2013-10-01

    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 104 M ⊙ and 107 M ⊙. 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 thresh >= 104 cm-3—is 3% per 10 Myr, in clouds of roughly 106 M ⊙. 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.

  8. 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.

  9. OH 18 cm TRANSITION AS A THERMOMETER FOR MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Ebisawa, Yuji; Inokuma, Hiroshi; Yamamoto, Satoshi [Department of Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan); Sakai, Nami [RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Menten, Karl M. [Max-Planck-Institut für Radioastronome, Auf dem Hügel 69, D-53121 Bonn (Germany); Maezawa, Hiroyuki [Department of Physical Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531 (Japan)

    2015-12-10

    We have observed the four hyperfine components of the 18 cm OH transition toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark cloud L134N, and the photodissociation region of the ρ-Ophiuchi molecular cloud with the Effelsberg 100 m telescope. We have found intensity anomalies among the hyperfine components in all three regions. In particular, an absorption feature of the 1612 MHz satellite line against the cosmic microwave background has been detected toward HCL2E and two positions of the ρ-Ophiuchi molecular cloud. On the basis of statistical equilibrium calculations, we find that the hyperfine anomalies originate from the non-LTE population of the hyperfine levels, and can be used to determine the kinetic temperature of the gas over a wide range of H{sub 2} densities (10{sup 2}–10{sup 7} cm{sup −3}). Toward the center of HCL2E, the gas kinetic temperature is determined to be 53 ± 1 K, and it increases toward the cloud peripheries (∼60 K). The ortho-to-para ratio of H{sub 2} is determined to be 3.5 ± 0.9 from the averaged spectrum for the eight positions. In L134N, a similar increase of the temperature is also seen toward the periphery. In the ρ-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a function of the distance from the exciting star HD 147889. These results demonstrate a new aspect of the OH 18 cm line that can be used as a good thermometer of molecular cloud envelopes. The OH 18 cm line can be used to trace a new class of warm molecular gas surrounding a molecular cloud, which is not well traced by the emission of CO and its isotopologues.

  10. The large system of molecular clouds in Orion and Monoceros

    Science.gov (United States)

    Maddalena, R. J.; Moscowitz, J.; Thaddeus, P.; Morris, M.

    1986-01-01

    Emission is noted over about one-eighth of an 850-sq deg region centered on Orion and Monoceros that has been surveyed in the J = 1 to 0 line of CO; most of the emission arises from giant molecular clouds associated with Orion A and B, and Mon R2. A much smaller area was surveyed for C-13O emission. A comparison of cloud masses obtained by three independent methods indicates that CO luminosity is as accurate a measure of cloud mass as other indicators. The possible relationships among clouds in the survey are discussed, including the conjecture that the overall Orion complex of clouds is a much larger system than previously considered, incorporating most of the clouds in the present survey.

  11. Giant Molecular Cloud Formation in Disk Galaxies: Characterizing Simulated versus Observed Cloud Catalogues

    CERN Document Server

    Benincasa, Samantha M; Pudritz, Ralph E; Wadsley, James

    2013-01-01

    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 10^4 Msun and 10^7 Msun. 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 s...

  12. Properties of Diffuse Molecular Gas in the Magellanic Clouds

    Science.gov (United States)

    Welty, Daniel

    2012-10-01

    Studies of the interstellar medium in the lower-metallicity Magellanic Clouds explore somewhat different environmental conditions from those typically probed in our own Galactic ISM. Recent studies based on optical/UV spectra of SMC and LMC targets, for example, have revealed unexpected differences in gas-phase abundance patterns {for various atomic and molecular species} and have begun to explore the effects of differences in metallicity on the atomic-to-molecular transition and resulting molecular fraction f{H_2} - a key aspect in the formation of molecular clouds. We propose a more detailed study of the abundances, depletions, and local physical conditions characterizing diffuse molecular material in the Magellanic Clouds, using STIS E140H and E230M spectra of two sight lines with N{H_2} > 10^20 cm^-2 {both probing the outskirts of molecular clouds seen in CO emission}. The two STIS settings will include lines from various neutral and ionized species {with a range in depletion behavior}, several C I multiplets, and several bands of CO and C_2. By probing and characterizing the atomic-to-molecular transition in the Magellanic Clouds, we will address key issues regarding the effects of differences in metallicity on the relationship between the atomic and molecular gas in galaxies; on cloud structure, physical conditions, and diffuse cloud chemistry; and on the composition and properties of interstellar dust. The results of this project should thus aid in the interpretation of observations of atomic and molecular material in more distant low-metallicity systems.

  13. Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

    Science.gov (United States)

    Goicoechea, Javier R.; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

    2016-09-01

    The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth-Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution.

  14. Submillimeter Polarization Spectrum in the Vela C Molecular Cloud

    CERN Document Server

    Gandilo, Natalie N; Angilè, Francesco E; Ashton, Peter; Benton, Steven J; Devlin, Mark J; Dober, Bradley; Fissel, Laura M; Fukui, Yasuo; Galitzki, Nicholas; Klein, Jeffrey; Korotkov, Andrei L; Li, Zhi-Yun; Martin, Peter G; Matthews, Tristan G; Moncelsi, Lorenzo; Nakamura, Fumitaka; Netterfield, Calvin B; Novak, Giles; Pascale, Enzo; Poidevin, Frédérick; Santos, Fabio P; Savini, Giorgio; Scott, Douglas; Shariff, Jamil A; Soler, Juan Diego; Thomas, Nicholas E; Tucker, Carole E; Tucker, Gregory S; Ward-Thompson, Derek

    2015-01-01

    Polarization maps of the Vela C molecular cloud were obtained at 250um, 350um, and 500um during the 2012 flight of the balloon-borne telescope BLASTPol. These measurements are used in conjunction with 850um data from Planck to study the submillimeter spectrum of the polarization fraction for this cloud. The spectrum is relatively flat and does not exhibit the minimum at \\lambda ~350um observed in previous measurements of other molecular clouds. The shape of the spectrum does not depend strongly on the radiative environment of the dust, as quantified by the column density or the dust temperature obtained from Herschel data. The polarization ratios observed in Vela C are consistent with a model of a porous clumpy molecular cloud being uniformly heated by the interstellar radiation field.

  15. Supernova Feedback in Molecular Clouds: Global Evolution and Dynamics

    CERN Document Server

    Körtgen, Bastian; Banerjee, Robi; Vázquez-Semadeni, Enrique; Zamora-Avilés, Manuel

    2016-01-01

    We use magnetohydrodynamical simulations of converging warm neutral medium flows to analyse the formation and global evolution of magnetised and turbulent molecular clouds subject to supernova feedback from massive stars. We show that supernova feedback alone fails to disrupt entire, gravitationally bound, molecular clouds, but is able to disperse small--sized (~10 pc) regions on timescales of less than 1 Myr. Efficient radiative cooling of the supernova remnant as well as strong compression of the surrounding gas result in non-persistent energy and momentum input from the supernovae. However, if the time between subsequent supernovae is short and they are clustered, large hot bubbles form that disperse larger regions of the parental cloud. On longer timescales, supernova feedback increases the amount of gas with moderate temperatures (T~300-3000 K). Despite its inability to disrupt molecular clouds, supernova feedback leaves a strong imprint on the star formation process. We find an overall reduction of the ...

  16. Connecting diverse molecular cloud environments with nascent protostars in Orion

    Science.gov (United States)

    Stutz, Amelia M.; Megeath, S.; Fischer, W. J.; Ali, B.; Furlan, E.; Tobin, J. J.; Stanke, T.; Henning, T.; Krause, O.; Manoj, P.; Osorio, M.; Robitaille, T.; HOPS Team

    2014-01-01

    Understanding how the gas environment within molecular clouds influences the properties of protostars is a key step towards understanding the physical factors that control star formation. We report on an analysis of the connection between molecular cloud environment and protostellar properties using the Herschel Orion Protostar Survey (HOPS), a large multi-observatory survey of protostars in the Orion molecular clouds. HOPS has produced well sampled 1 um to 870 um SEDs of over 300 protostars in the Orion molecular clouds using images and spectra from 2MASS, Spitzer, Herschel and APEX. Furthermore, the combination of APEX 870 um continuum observations with the HOPS/PACS 160 um data over the same area allows for a determination of the temperatures and column densities in the often filamentary dense gas surrounding the Orion protostars. Based on these data, we link the protostellar properties with their environmental properties. Utilizing the diverse environments present within the Orion molecular clouds, we show how the luminosity and spacing of protostars in Orion depends on the local gas column density. Furthermore, we report an unusual concentration of the youngest known protostars (the Herschel identified PBRS, PACS Bright Red Sources) in the Orion B cloud, and we discuss possible reasons for this concentration.

  17. The chemistry of interstellar argonium and other probes of the molecular fraction in diffuse clouds

    CERN Document Server

    Neufeld, David A

    2016-01-01

    We present a general parameter study, in which the abundance of interstellar argonium (ArH$^+$) is predicted using a model for the physics and chemistry of diffuse interstellar gas clouds. Results have been obtained as a function of UV radiation field, cosmic-ray ionization rate, and cloud extinction. No single set of cloud parameters provides an acceptable fit to the typical ArH$^+$, OH$^+$ and $\\rm H_2O^+$ abundances observed in diffuse clouds within the Galactic disk. Instead, the observed abundances suggest that ArH$^+$ resides primarily in a separate population of small clouds of total visual extinction of at most 0.02 mag per cloud, within which the column-averaged molecular fraction is in the range $10^{-5} - 10^{-2}$, while OH$^+$ and $\\rm H_2O^+$ reside primarily in somewhat larger clouds with a column-averaged molecular fraction $\\sim 0.2$. This analysis confirms our previous suggestion that the argonium molecular ion is a unique tracer of almost purely atomic gas.

  18. Linking numerical simulations of molecular cloud structure with observations.

    Science.gov (United States)

    Kainulainen, Jouni

    2015-08-01

    Understanding the physical processes that control the life-cycle of the cold interstellar medium (ISM) is one of the key themes in the astrophysics of galaxies today. This importance derives from the role of the cold ISM as the birthplace of new stars, and consequently, as an indivisible constituent of galaxy evolution. In the current paradigm of turbulence-regulated ISM, star formation is controlled by the internal structure of individual molecular clouds, which in turn is set by a complex interplay of turbulence, gravity, and magnetic fields in the clouds. It is in the very focus of the field to determine how these processes give rise to the observed structure of molecular clouds. In this talk, I will review our current efforts to confront this paradigm with the goal of observationally constraining how different processes regulate molecular cloud structure and star formation. At the heart of these efforts lies the use of numerical simulations of gravo-turbulent media to A) define physically meaningful characteristics that are sensitive to the different cloud-shaping processes, and B) determine if and how such characteristics can be recovered by observations. I will show in my talk how this approach has recently led to new constraints for some fundamental measures of the molecular cloud structure. Such constraints allow us to assess the roles of turbulence and gravity in controlling the ISM structure and star formation. I will also highlight specific recent results, focusing on the nature of filamentary structures within molecular clouds. These results may provide a novel set of observational constraints with which to challenge the turbulence-regulated ISM paradigm. Finally, I will discuss the current challenges and open questions in understanding the link between molecular cloud structure and star formation, and speculate on key directions to aim the near-future studies.

  19. THE MAGELLANIC MOPRA ASSESSMENT (MAGMA). I. THE MOLECULAR CLOUD POPULATION OF THE LARGE MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Tony; Chu, You-Hua; Gruendl, Robert A.; Looney, Leslie W.; Seale, Jonathan; Welty, Daniel E. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, Annie; Maddison, Sarah [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, VIC 3122 (Australia); Ott, Juergen [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Muller, Erik; Fukui, Yasuo; Kawamura, Akiko; Mizuno, Yoji [Department of Astrophysics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602 (Japan); Pineda, Jorge L. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099 (United States); Bernard, Jean-Philippe; Paradis, Deborah [CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France); Henkel, Christian [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Klein, Ulrich, E-mail: wongt@astro.illinois.edu [Argelander Institut fuer Astronomie, Universitaet Bonn, Auf dem Huegel 71, D-53121 Bonn (Germany)

    2011-12-01

    We present the properties of an extensive sample of molecular clouds in the Large Magellanic Cloud (LMC) mapped at 11 pc resolution in the CO(1-0) line. Targets were chosen based on a limiting CO flux and peak brightness as measured by the NANTEN survey. The observations were conducted with the ATNF Mopra Telescope as part of the Magellanic Mopra Assessment. We identify clouds as regions of connected CO emission and find that the distributions of cloud sizes, fluxes, and masses are sensitive to the choice of decomposition parameters. In all cases, however, the luminosity function of CO clouds is steeper than dN/dL{proportional_to}L{sup -2}, suggesting that a substantial fraction of mass is in low-mass clouds. A correlation between size and linewidth, while apparent for the largest emission structures, breaks down when those structures are decomposed into smaller structures. We argue that the correlation between virial mass and CO luminosity is the result of comparing two covariant quantities, with the correlation appearing tighter on larger scales where a size-linewidth relation holds. The virial parameter (the ratio of a cloud's kinetic to self-gravitational energy) shows a wide range of values and exhibits no clear trends with the CO luminosity or the likelihood of hosting young stellar object (YSO) candidates, casting further doubt on the assumption of virialization for molecular clouds in the LMC. Higher CO luminosity increases the likelihood of a cloud harboring a YSO candidate, and more luminous YSOs are more likely to be coincident with detectable CO emission, confirming the close link between giant molecular clouds and massive star formation.

  20. The Resolved Properties of Extragalactic Giant Molecular Clouds

    CERN Document Server

    Bolatto, Alberto D; Rosolowsky, Erik; Walter, Fabian; Blitz, Leo

    2008-01-01

    We use high spatial resolution observations of CO to systematically measure the resolved size-line width, luminosity-line width, luminosity-size, and the mass-luminosity relations of Giant Molecular Clouds (GMCs) in a variety of extragalactic systems. Although the data are heterogeneous we analyze them in a consistent manner to remove the biases introduced by limited sensitivity and resolution, thus obtaining reliable sizes, velocity dispersions, and luminosities. We compare the results obtained in dwarf galaxies with those from the Local Group spiral galaxies. We find that extragalactic GMC properties measured across a wide range of environments are very much compatible with those in the Galaxy. We use these results to investigate metallicity trends in the cloud average column density and virial CO-to-H2 factor. We find that these measurements do not accord with simple predictions from photoionization-regulated star formation theory, although this could be due to the fact that we do not sample small enough s...

  1. Dynamical evolution of supernova remnants breaking through molecular clouds

    CERN Document Server

    Cho, Wankee; Koo, Bon-Chul

    2015-01-01

    We carry out three-dimensional hydrodynamic simulations of the supernova remnants (SNRs) produced inside molecular clouds (MCs) near their surface using the HLL code (Harten et al. 1983). We explore the dynamical evolution and the X-ray morphology of SNRs after breaking through the MC surface for ranges of the explosion depths below the surface and the density ratios of the clouds to the intercloud media (ICM). We find that if an SNR breaks out through an MC surface in its Sedov stage, the outermost dense shell of the remnant is divided into several layers. The divided layers are subject to the Rayleigh-Taylor instability and fragmented. On the other hand, if an SNR breaks through an MC after the remnant enters the snowplow phase, the radiative shell is not divided to layers. We also compare the predictions of previous analytic solutions for the expansion of SNRs in stratified media with our onedimensional simulations. Moreover, we produce synthetic X-ray surface brightness in order to research the center-bri...

  2. Spectral Line Survey toward a Molecular Cloud in IC10

    CERN Document Server

    Nishimura, Yuri; Watanabe, Yoshimasa; Sakai, Nami; Aikawa, Yuri; Kawamura, Akiko; Yamamoto, Satoshi

    2016-01-01

    We have conducted a spectral line survey observation in the 3 mm band toward the low-metallicity dwarf galaxy IC10 with the 45 m radio telescope of Nobeyama Radio Observatory to explore its chemical composition at a molecular-cloud scale (~80 pc). The CS, SO, CCH, HCN, HCO+, and HNC lines are detected for the first time in this galaxy in addition to the CO and 13CO lines, while c-C3H2, CH3OH, CN, C18O, and N2H+ lines are not detected. The spectral intensity pattern is found to be similar to those observed toward molecular clouds in the Large Magellanic Cloud, whose metallicity is as low as IC10. Nitrogen-bearing species are deficient in comparison with the Galactic molecular clouds due to a lower elemental abundance of nitrogen. CCH is abundant in comparison with Galactic translucent clouds, whereas CH3OH may be deficient. These characteristic trends for CCH and CH3OH are also seen in the LMC, and seem to originate from photodissociation regions more extended in peripheries of molecular clouds due to the lowe...

  3. Star Formation and Molecular Clouds at High Galactic Latitude

    CERN Document Server

    McGehee, Peregrine M

    2008-01-01

    In this chapter we review the young stars and molecular clouds found at high Galactic latitudes $(|b| \\ge 30^\\circ)$. These are mostly associated with two large-scale structures on the sky, the Gould Belt and the Taurus star formation region, and a handful of molecular clouds including MBM 12 and MBM 20 which, as a population, consist of the nearest star formation sites to our Sun. There are also a few young stars that are found in apparent isolation far from any molecular cloud. The high latitude clouds are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. We review the processes that result in star formation within these low density and extraplanar environments as well as the mechanisms for production of isolated T Tauri stars. We present and discuss the k...

  4. Star Formation and Molecular Clouds at High Galactic Latitude

    Science.gov (United States)

    McGehee, P. M.

    2008-12-01

    In this chapter we review the young stars and molecular clouds found at high Galactic latitudes (|b| ≥ 30°). These are mostly associated with two large-scale structures on the sky, the Gould Belt and the Taurus star formation region, and a handful of molecular clouds including MBM 12 and MBM 20 which, as a population, consist of the nearest star formation sites to our Sun. There are also a few young stars that are found in apparent isolation far from any molecular cloud. The high latitude clouds are primarily translucent molecular clouds and diffuse Galactic cirrus with the majority of them seen at high latitude simply due to their proximity to the Sun. The rare exceptions are those, like the Draco and other intermediate or high velocity clouds, found significantly above or below the Galactic plane. We review the processes that result in star formation within these low density and extraplanar environments as well as the mechanisms for production of isolated T Tauri stars. We present and discuss the known high-latitude stellar nurseries and young stellar objects.

  5. SUPERGIANT SHELLS AND MOLECULAR CLOUD FORMATION IN THE LARGE MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J. R.; Dickey, John M. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); McClure-Griffiths, N. M. [Australia Telescope National Facility, CSIRO Astronomy and Space Science, Marsfield NSW 2122 (Australia); Wong, T. [Astronomy Department, University of Illinois, Urbana, IL 61801 (United States); Hughes, A. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117, Heidelberg (Germany); Fukui, Y. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan); Kawamura, A., E-mail: joanne.dawson@utas.edu.au [National Astronomical Observatory of Japan, Tokyo 181-8588 (Japan)

    2013-01-20

    We investigate the influence of large-scale stellar feedback on the formation of molecular clouds in the Large Magellanic Cloud (LMC). Examining the relationship between H I and {sup 12}CO(J = 1-0) in supergiant shells (SGSs), we find that the molecular fraction in the total volume occupied by SGSs is not enhanced with respect to the rest of the LMC disk. However, the majority of objects ({approx}70% by mass) are more molecular than their local surroundings, implying that the presence of a supergiant shell does on average have a positive effect on the molecular gas fraction. Averaged over the full SGS sample, our results suggest that {approx}12%-25% of the molecular mass in supergiant shell systems was formed as a direct result of the stellar feedback that created the shells. This corresponds to {approx}4%-11% of the total molecular mass of the galaxy. These figures are an approximate lower limit to the total contribution of stellar feedback to molecular cloud formation in the LMC, and constitute one of the first quantitative measurements of feedback-triggered molecular cloud formation in a galactic system.

  6. Molecular Cloud Evolution III. Accretion vs. stellar feedback

    CERN Document Server

    Vazquez-Semadeni, Enrique; Gomez, Gilberto C; Watson, Alan

    2010-01-01

    We numerically investigate the effect of feedback from the ionizing radiation heating from massive stars on the evolution of giant molecular clouds (GMCs) and their star formation efficiency (SFE). We find that the star-forming regions within the GMCs are invariably formed by gravitational contraction. After an initial period of contraction, the collapsing clouds begin forming stars, whose feedback evaporates part of the clouds' mass, opposing the continuing accretion from the infalling gas. The competition of accretion against dense gas consumption by star formation (SF) and evaporation by the feedback, regulates the clouds' mass and energy balance, as well as their SFE. We find that, in the presence of feedback, the clouds attain levels of the SFE that are consistent at all times with observational determinations for regions of comparable SF rates (SFRs). However, we observe that the dense gas mass is larger in general in the presence of feedback, while the total (dense gas + stars) is nearly insensitive to...

  7. Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

    Science.gov (United States)

    Goicoechea, Javier R.; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

    2016-01-01

    The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Owing to the close distance to Orion (about 1,350 light-year), the effects of stellar feedback on the parental cloud can be studied in detail. Visible-light observations of the Bar1 show that the transition between the hot ionised gas and the warm neutral atomic gas (the ionisation front) is spatially well separated from the transition from atomic to molecular gas (the dissociation front): about 15 arcseconds or 6,200 astronomical units. (One astronomical unit is the Earth-Sun distance.) Static equilibrium models2,3 used to interpret previous far-infrared and radio observations of the neutral gas in the Bar4,5,6 (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure consisting of dense clumps embedded in a lower density extended gas component. Here we report 1 arcsecond resolution millimetre-wave images that allow us to resolve the molecular cloud surface and constrain the gas density and temperature structures at small spatial scales. In contrast to stationary model predictions7,8,9, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. These observations reveal a fragmented ridge of high-density substructures, photo-ablative gas flows and instabilities at the molecular cloud surface. They suggest that the cloud edge has been compressed by a high-pressure wave that currently moves into the molecular cloud. The images demonstrate that dynamical and nonequilibrium effects are important. Thus, they should be included in any realistic description of irradiated interstellar matter. PMID:27509859

  8. Giant molecular cloud scaling relations: the role of the cloud definition

    Science.gov (United States)

    Khoperskov, S. A.; Vasiliev, E. O.; Ladeyschikov, D. A.; Sobolev, A. M.; Khoperskov, A. V.

    2016-01-01

    We investigate the physical properties of molecular clouds in disc galaxies with different morphologies: a galaxy without prominent structure, a spiral barred galaxy and a galaxy with flocculent structure. Our N-body/hydrodynamical simulations take into account non-equilibrium H2 and CO chemical kinetics, self-gravity, star formation and feedback processes. For the simulated galaxies, the scaling relations of giant molecular clouds, or so-called Larson's relations, are studied for two types of cloud definition (or extraction method): the first is based on total column density position-position (PP) data sets and the second is indicated by the CO (1-0) line emission used in position-position-velocity (PPV) data. We find that the cloud populations obtained using both cloud extraction methods generally have similar physical parameters, except that for the CO data the mass spectrum of clouds has a tail with low-mass objects M ˜ 103-104 M⊙. Owing toa varying column density threshold, the power-law indices in the scaling relations are significantly changed. In contrast, the relations are invariant to the CO brightness temperature threshold. Finally, we find that the mass spectra of clouds for PPV data are almost insensitive to the galactic morphology, whereas the spectra for PP data demonstrate significant variation.

  9. Modeling of molecular clouds with formation of prestellar cores

    CERN Document Server

    Donkov, Sava; Veltchev, Todor V

    2012-01-01

    We develop a statistical approach for description of dense structures (cores) in molecular clouds that might be progenitors of stars. Our basic assumptions are a core mass-density relationship and a power-law density distribution of these objects as testified by numerical simulations and observations. The core mass function (CMF) was derived and its slope in the high-mass regime was obtained analytically. Comparisons with observational CMFs in several Galactic clouds are briefly presented.

  10. On the Star Formation Rates in Molecular Clouds

    CERN Document Server

    Lada, Charles J; Alves, João F

    2010-01-01

    In this paper we investigate the level of star formation activity within nearby molecular clouds. We employ a uniform set of infrared extinction maps to provide accurate assessments of cloud mass and structure and compare these with inventories of young stellar objects within the clouds. We present evidence indicating that both the yield and rate of star formation can vary considerably in local clouds, independent of their mass and size. We find that the surface density structure of such clouds appears to be important in controlling both these factors. In particular, we find that the star formation rate (SFR) in molecular clouds is linearly proportional to the cloud mass (M_{0.8}) above an extinction threshold of A_K approximately equal to 0.8 magnitudes, corresponding to a gas surface density threshold of approximaely 116 solar masses per square pc. We argue that this surface density threshold corresponds to a gas volume density threshold which we estimate to be n(H_2) approximately equal to 10^4\\cc. Specifi...

  11. THE PROGRESSION OF STAR FORMATION IN THE ROSETTE MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Ybarra, Jason E.; Lada, Elizabeth A. [Department of Astronomy, University of Florida, Gainesville, FL 32605 (United States); Roman-Zuniga, Carlos G. [Instituto de Astronomia, Universidad Nacional Autonoma de Mexico, Unidad Academica de Ensenada, Apdo. Postal 22860, Ensenada, B. C. (Mexico); Balog, Zoltan [Max-Planck-Institut fuer Astronomie, Heidelberg (Germany); Wang Junfeng [Department of Physics and Astronomy and Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Northwestern University, 2131 Tech Dr, Evanston, IL 60208 (United States); Feigelson, Eric D., E-mail: jybarra@astro.ufl.edu [Pennsylvania State University, University Park, PA 16802 (United States)

    2013-06-01

    Using Spitzer Space Telescope and Chandra X-Ray Observatory data, we identify young stellar objects (YSOs) in the Rosette Molecular Cloud (RMC). By being able to select cluster members and classify them into YSO types, we are able to track the progression of star formation locally within the cluster environments and globally within the cloud. We employ the nearest neighbor method analysis to explore the density structure of the clusters and YSO ratio mapping to study age progressions in the cloud. We find a relationship between the YSO ratios and extinction that suggests star formation occurs preferentially in the densest parts of the cloud and that the column density of gas rapidly decreases as the region evolves. This suggests rapid removal of gas may account for the low star formation efficiencies observed in molecular clouds. We find that the overall age spread across the RMC is small. Our analysis suggests that star formation started throughout the complex around the same time. Age gradients in the cloud appear to be localized and any effect the H II region has on the star formation history is secondary to that of the primordial collapse of the cloud.

  12. Relationship between molecular cloud structure and density PDFs

    CERN Document Server

    Stanchev, Orlin; Veltchev, Todor V; Shetty, Rahul

    2013-01-01

    Volume and column density PDFs in molecular clouds are important diagnostics for understanding their general structure. We developed a novel approach to trace the cloud structure by varying the lower PDF cut-off and exploring a suggested mass-density relationship with a power-law index $x^\\prime$. The correspondence of x' as a function of spatial scale to the slope of the high-density PDF tail is studied. To validate the proposed model, we use results from hydrodynamical simulations of a turbulent self-gravitating cloud and recent data on dust continuum emission from the Planck mission.

  13. Filaments in Simulations of Molecular Cloud Formation

    CERN Document Server

    Gomez, Gilberto C

    2013-01-01

    We report on the filaments that develop self-consistently in a new numerical simulation of cloud formation by colliding flows. As in previous studies, the forming cloud begins to undergo gravitational collapse because it rapidly acquires a mass much larger than the average Jeans mass. Thus, the collapse is hierarchical in nature, proceeding along its shortest dimension first. This naturally produces filaments in cloud, and clumps within the filaments. The filaments are not in equilibrium at any time, but instead are long-lived flow features, through which the gas flows from the cloud to the clumps. The filaments are long-lived because they accrete from their environment while simultaneously accreting onto the clumps within them; they are essentially the locus where the flow changes from accreting in two dimensions to accreting in one dimension. Moreover, the clumps also exhibit a hierarchical nature: the gas in a filament flows onto a main, central clump, but other, smaller-scale clumps form along the infalli...

  14. Molecular Clouds, Star Formation and Galactic Structure.

    Science.gov (United States)

    Scoville, Nick; Young, Judith S.

    1984-01-01

    Radio observations show that the gigantic clouds of molecules where stars are born are distributed in various ways in spiral galaxies, perhaps accounting for the variation in their optical appearance. Research studies and findings in this area are reported and discussed. (JN)

  15. Super-Sonic Turbulence in the Perseus Molecular Cloud

    CERN Document Server

    Padoan, P; Billawala, Y N; Juvela, M; Nordlund, A A; Padoan, Paolo; Bally, John; Billawala, Youssef; Juvela, Mika; Nordlund, AAke

    1999-01-01

    We compare the statistical properties of J=1-0 13CO spectra observed in the Perseus Molecular Cloud with synthetic J=1-0 13CO spectra, computed solving the non-LTE radiative transfer problem for a model cloud obtained as solutions of the three dimensional magneto-hydrodynamic (MHD) equations. The model cloud is a randomly forced super-Alfvenic and highly super-sonic turbulent isothermal flow. The purpose of the present work is to test if idealized turbulent flows, without self-gravity, stellar radiation, stellar outflows, or any other effect of star formation, are inconsistent or not with statistical properties of star forming molecular clouds. We present several statistical results that demonstrate remarkable similarity between real data and the synthetic cloud. Statistical properties of molecular clouds like Perseus are appropriately described by random super-sonic and super-Alfvenic MHD flows. Although the description of gravity and stellar radiation are essential to understand the formation of single prot...

  16. Do Giant Molecular Clouds Care About the Galactic Structure?

    CERN Document Server

    Fujimoto, Yusuke; Wakayama, Mariko; Habe, Asao

    2014-01-01

    We investigate the impact of galactic environment on the properties of simulated giant molecular clouds formed in a M83-type barred spiral galaxy. Our simulation uses a rotating stellar potential to create the grand design features and resolves down to 1.5 pc. From the comparison of clouds found in the bar, spiral and disc regions, we find that the typical GMC is environment independent, with a mass of 5e+5 Msun and radius 11 pc. However, the fraction of clouds in the property distribution tails varies between regions, with larger, more massive clouds with a higher velocity dispersion being found in greatest proportions in the bar, spiral and then disc. The bar clouds also show a bimodality that is not reflected in the spiral and disc clouds except in the surface density, where all three regions show two distinct peaks. We identify these features as being due to the relative proportion of three cloud types, classified via the mass-radius scaling relation, which we label A, B and C. Type A clouds have the typi...

  17. Prediction of molecular crystal structures

    CERN Document Server

    Beyer, T

    2001-01-01

    The ab initio prediction of molecular crystal structures is a scientific challenge. Reliability of first-principle prediction calculations would show a fundamental understanding of crystallisation. Crystal structure prediction is also of considerable practical importance as different crystalline arrangements of the same molecule in the solid state (polymorphs)are likely to have different physical properties. A method of crystal structure prediction based on lattice energy minimisation has been developed in this work. The choice of the intermolecular potential and of the molecular model is crucial for the results of such studies and both of these criteria have been investigated. An empirical atom-atom repulsion-dispersion potential for carboxylic acids has been derived and applied in a crystal structure prediction study of formic, benzoic and the polymorphic system of tetrolic acid. As many experimental crystal structure determinations at different temperatures are available for the polymorphic system of parac...

  18. Waves on the surface of the Orion molecular cloud.

    Science.gov (United States)

    Berné, Olivier; Marcelino, Núria; Cernicharo, José

    2010-08-19

    Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the 'pillars of creation') and other shapes arise because of instabilities, but alternative explanations are available. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of 'waves' at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin-Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas.

  19. Chemistry in Magnetohydrodynamic Shock Waves in Diffuse Molecular Clouds

    Science.gov (United States)

    Peimbert, Antonio

    1998-09-01

    Absorption observations of the CH+ molecule with column densities of up to 1014 cm-2 in diffuse molecular clouds in many lines of sight are reviewed, and compared to the reddening and to abundances and velocity shifts of molecules like CH. Special attention is placed on the observations of the line of sight towards ς Ophiuchi where high quality observations of many chemical species are available. The problem of the required CH+ is described, and many formation mechanisms from the literature are reviewed, finding that none of them is particularly apt at describing the observations towards ς-Oph. Two fluid J-type shock models are studied as an alternative. The necessary conditions for their formation are discussed, and it is shown how they are expected to be present widely in the interstellar medium. Plane parallel numerical integrations, for the particular case in which the magnetic field is perpendicular to the shock velocity, are employed to study the region of phase-space of initial conditions that will produce 2 fluid shocks. A chemical network is developed and formation of key molecules like CH+, CH and OH, along with the excited roto-vibrational levels of H2, are studied under the shock dynamics. These models are then compared to the observations of the different lines of sight, showing they are capable of reproducing the features of the observations towards most of those clouds. An attempt to model the line of sight towards ς-Oph is done, finding that a shock with a shock speed vs = 9.0km/s going through a cloud with a density of nH = 14cm-3 with a magnetic field of B = 4.7μG does a reasonable job at satisfying most of the observations with the exception of the highest rotational excited states of molecular hydrogen for which observations are available. There is a small family of solutions capable of explaining the observed results which make specific predictions for the velocity profiles of the H2 lines of various excited levels. New observations with

  20. CHaMP: From Molecular Clouds to Massive Young Clusters

    Science.gov (United States)

    Barnes, Peter J.

    2017-03-01

    I review the major science outcomes to date of the Galactic Census of High- and Medium-mass Protostars (CHaMP), and also report the latest observational results on this unbiased, uniform sample of massive, cluster-forming molecular clumps, based on new mm-wave and IR data. These clouds represent the vast, subthermally-excited population of clumps predicted by Narayanan et al. (2008) to dominate the molecular mass of disk galaxies. Besides confirming their existence, we have presented evidence that these massive clumps probably spend a large fraction (90-95%) of their long lives (possibly up to 100 Myr) in a mostly quiescent, low star formation rate (SFR) state. This is likely ended when a density or internal pressure threshold is crossed, after which vigorous, massive cluster formation consumes the densest gas with a high SFR, dispersing the embedding envelope. New results presented in two other posters at this Symposium include (1) the first analysis of HCN emission from the dense gas (Schap et al. 2015), and (2) the first deep photometry of clusters in this sample based on NIR AAT & CTIO data, and on MIR Warm Spitzer IRAC data (Dallilar et al. 2015).

  1. A Fusion Model for CPU Load Prediction in Cloud Computing

    Directory of Open Access Journals (Sweden)

    Dayu Xu

    2013-11-01

    Full Text Available Load prediction plays a key role in cost-optimal resource allocation and datacenter energy saving. In this paper, we use real-world traces from Cloud platform and propose a fusion model to forecast the future CPU loads. First, long CPU load time series data are divided into short sequences with same length from the historical data on the basis of cloud control cycle. Then we use kernel fuzzy c-means clustering algorithm to put the subsequences into different clusters. For each cluster, with current load sequence, a genetic algorithm optimized wavelet Elman neural network prediction model is exploited to predict the CPU load in next time interval. Finally, we obtain the optimal cloud computing CPU load prediction results from the cluster and its corresponding predictor with minimum forecasting error. Experimental results show that our algorithm performs better than other models reported in previous works.

  2. OH 18 cm Transition as a Thermometer for Molecular Clouds

    CERN Document Server

    Ebisawa, Yuji; Sakai, Nami; Menten, Karl M; Maezawa, Hiroyuki; Yamamoto, Satoshi

    2016-01-01

    We have observed the four hyperfine components of the 18 cm OH transition toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark cloud L134N, and the photodissociation region of the $\\rho$-Ophiuchi molecular cloud with the Effelsberg 100 m telescope. We have found intensity anomalies amongst the hyperfine components in all three regions. In particular, an absorption feature of the 1612 MHz satellite line against the cosmic microwave background has been detected toward HCL2E and two positions of the $\\rho$-Ophiuchi molecular cloud. On the basis of statistical equilibrium calculations, we find that the hyperfine anomalies originate from the non-LTE population of the hyperfine levels, and can be used to determine the kinetic temperature of the gas over a wide range of H$_2$ density (10$^2$ - 10$^7$ cm$^{-3}$). Toward the center of HCL2E, the gas kinetic temperature is determined to be 53$\\pm$1 K, and it increases toward the cloud peripheries ($\\sim$ 60 K). The ortho-to-para ratio of H$_2$...

  3. The Magellanic Mopra Assessment (MAGMA). I. The Molecular Cloud Population of the Large Magellanic Cloud

    CERN Document Server

    Wong, Tony; Ott, Jürgen; Muller, Erik; Pineda, Jorge L; Bernard, Jean-Philippe; Chu, You-Hua; Fukui, Yasuo; Gruendl, Robert A; Henkel, Christian; Kawamura, Akiko; Klein, Ulrich; Looney, Leslie W; Maddison, Sarah; Mizuno, Yoji; Paradis, Deborah; Seale, Jonathan; Welty, Daniel E

    2011-01-01

    We present the properties of an extensive sample of molecular clouds in the Large Magellanic Cloud (LMC) mapped at 11 pc resolution in the CO(1-0) line. We identify clouds as regions of connected CO emission, and find that the distributions of cloud sizes, fluxes and masses are sensitive to the choice of decomposition parameters. In all cases, however, the luminosity function of CO clouds is steeper than dN/dL \\propto L^{-2}, suggesting that a substantial fraction of mass is in low-mass clouds. A correlation between size and linewidth, while apparent for the largest emission structures, breaks down when those structures are decomposed into smaller structures. We argue that the correlation between virial mass and CO luminosity is the result of comparing two covariant quantities, with the correlation appearing tighter on larger scales where a size-linewidth relation holds. The virial parameter (the ratio of a cloud's kinetic to self-gravitational energy) shows a wide range of values and exhibits no clear trends...

  4. Neutral atomic carbon in dense molecular clouds

    Science.gov (United States)

    Zmuidzinas, J.; Betz, A. L.; Boreiko, R. T.; Goldhaber, D. M.

    1988-01-01

    The 370 micron 3P2-3P1 fine-structure line of neutral carbon was detected in seven sources: OMC 1, NGC 2024, S140, W3, DR 21, M17, and W51. Simultaneous analysis of J = 2-1 data and available observations of the J = 1-0 line make it possible to deduce optical depths and excitation temperatures for these lines. These data indicate that both C I lines are likely to be optically thin, and that the ratio of C I to CO column densities in these clouds is typically about 0.1.

  5. From the warm magnetized atomic medium to molecular clouds

    CERN Document Server

    Hennebelle, P; Vázquez-Semadeni, E; Klessen, R; Audit, E

    2008-01-01

    {It has recently been proposed that giant molecular complexes form at the sites where streams of diffuse warm atomic gas collide at transonic velocities.} {We study the global statistics of molecular clouds formed by large scale colliding flows of warm neutral atomic interstellar gas under ideal MHD conditions. The flows deliver material as well as kinetic energy and trigger thermal instability leading eventually to gravitational collapse.} {We perform adaptive mesh refinement MHD simulations which, for the first time in this context, treat self-consistently cooling and self-gravity.} {The clouds formed in the simulations develop a highly inhomogeneous density and temperature structure, with cold dense filaments and clumps condensing from converging flows of warm atomic gas. In the clouds, the column density probability density distribution (PDF) peaks at $\\sim 2 \\times 10^{21} \\psc$ and decays rapidly at higher values; the magnetic intensity correlates weakly with density from $n \\sim 0.1$ to $10^4 \\pcc$, an...

  6. Dispersion of Magnetic Fields in Molecular Clouds. II

    CERN Document Server

    Houde, Martin; Hildebrand, Roger H; Chitsazzadeh, Shadi; Kirby, Larry

    2009-01-01

    We expand our study on the dispersion of polarization angles in molecular clouds. We show how the effect of signal integration through the thickness of the cloud as well as across the area subtended by the telescope beam inherent to dust continuum measurements can be incorporated in our analysis to correctly account for its effect on the measured angular dispersion and inferred turbulent to large-scale magnetic field strength ratio. We further show how to evaluate the turbulent magnetic field correlation scale from polarization data of sufficient spatial resolution and high enough spatial sampling rate. We apply our results to the molecular cloud OMC-1, where we find a turbulent correlation length of approximately 16 mpc, a turbulent to large-scale magnetic field strength ratio of approximately 0.5, and a plane-of-the-sky large-scale magnetic field strength of approximately 0.76 mG.

  7. Prediction of molecular crystal structures

    Energy Technology Data Exchange (ETDEWEB)

    Beyer, Theresa

    2001-07-01

    The ab initio prediction of molecular crystal structures is a scientific challenge. Reliability of first-principle prediction calculations would show a fundamental understanding of crystallisation. Crystal structure prediction is also of considerable practical importance as different crystalline arrangements of the same molecule in the solid state (polymorphs)are likely to have different physical properties. A method of crystal structure prediction based on lattice energy minimisation has been developed in this work. The choice of the intermolecular potential and of the molecular model is crucial for the results of such studies and both of these criteria have been investigated. An empirical atom-atom repulsion-dispersion potential for carboxylic acids has been derived and applied in a crystal structure prediction study of formic, benzoic and the polymorphic system of tetrolic acid. As many experimental crystal structure determinations at different temperatures are available for the polymorphic system of paracetamol (acetaminophen), the influence of the variations of the molecular model on the crystal structure lattice energy minima, has also been studied. The general problem of prediction methods based on the assumption that the experimental thermodynamically stable polymorph corresponds to the global lattice energy minimum, is that more hypothetical low lattice energy structures are found within a few kJ mol{sup -1} of the global minimum than are likely to be experimentally observed polymorphs. This is illustrated by the results for molecule I, 3-oxabicyclo(3.2.0)hepta-1,4-diene, studied for the first international blindtest for small organic crystal structures organised by the Cambridge Crystallographic Data Centre (CCDC) in May 1999. To reduce the number of predicted polymorphs, additional factors to thermodynamic criteria have to be considered. Therefore the elastic constants and vapour growth morphologies have been calculated for the lowest lattice energy

  8. Impact of Winds from Intermediate-Mass Stars on Molecular Cloud Structure and Turbulence

    CERN Document Server

    Offner, S S R

    2015-01-01

    Observations of nearby molecular clouds detect "shells", which are likely caused by winds from young main sequence stars. However, the progenitors of these observed features are not well characterized and the mass-loss rates inferred from the gas kinematics are several orders of magnitude greater than those predicted by atomic line-driven stellar wind models. We use magnetohydrodynamic simulations to model winds launching within turbulent molecular clouds and explore the impact of wind properties on cloud morphology and turbulence. We find that winds do not produce clear features in turbulent statistics such as the Fourier spectra of density and momentum but do impact the Fourier velocity spectrum. The density and velocity distribution functions, especially as probed by CO spectral lines, strongly indicate the presence and influence of winds. We show that stellar mass-loss rates for individual stars must be $\\dot m_w \\gtrsim 10^{-7}$ Msun yr$^{-1}$, similar to those estimated from observations, to reproduce s...

  9. SPECTRAL LINE SURVEY TOWARD MOLECULAR CLOUDS IN THE LARGE MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Nishimura, Yuri; Watanabe, Yoshimasa; Yamamoto, Satoshi [Department of Physics, the University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033 (Japan); Shimonishi, Takashi [Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Aramakiazaaoba 6-3, Aoba-ku, Sendai, Miyagi, 980-8578 (Japan); Sakai, Nami [RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 (Japan); Aikawa, Yuri [Center for Computational Sciences, The University of Tsukuba, 1-1-1, Tennodai, Tsukuba, Ibaraki 305-8577 (Japan); Kawamura, Akiko [National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo, 181-8588 (Japan)

    2016-02-20

    Spectral line survey observations of seven molecular clouds in the Large Magellanic Cloud (LMC) have been conducted in the 3 mm band with the Mopra 22 m telescope to reveal chemical compositions in low metallicity conditions. Spectral lines of fundamental species such as CS, SO, CCH, HCN, HCO{sup +}, and HNC are detected in addition to those of CO and {sup 13}CO, while CH{sub 3}OH is not detected in any source and N{sub 2}H{sup +} is marginally detected in two sources. The molecular-cloud scale (10 pc scale) chemical composition is found to be similar among the seven sources regardless of different star formation activities, and hence, it represents the chemical composition characteristic of the LMC without influences by star formation activities. In comparison with chemical compositions of Galactic sources, the characteristic features are (1) deficient N-bearing molecules, (2) abundant CCH, and (3) deficient CH{sub 3}OH. Feature (1) is due to a lower elemental abundance of nitrogen in the LMC, whereas features (2) and (3) seem to originate from extended photodissociation regions and warmer temperature in cloud peripheries due to a lower abundance of dust grains in the low metallicity condition. In spite of general resemblance of chemical abundances among the seven sources, the CS/HCO{sup +} and SO/HCO{sup +} ratios are found to be slightly higher in a quiescent molecular cloud. An origin of this trend is discussed in relation to possible depletion of sulfur along the molecular cloud formation.

  10. Scaling predictive modeling in drug development with cloud computing.

    Science.gov (United States)

    Moghadam, Behrooz Torabi; Alvarsson, Jonathan; Holm, Marcus; Eklund, Martin; Carlsson, Lars; Spjuth, Ola

    2015-01-26

    Growing data sets with increased time for analysis is hampering predictive modeling in drug discovery. Model building can be carried out on high-performance computer clusters, but these can be expensive to purchase and maintain. We have evaluated ligand-based modeling on cloud computing resources where computations are parallelized and run on the Amazon Elastic Cloud. We trained models on open data sets of varying sizes for the end points logP and Ames mutagenicity and compare with model building parallelized on a traditional high-performance computing cluster. We show that while high-performance computing results in faster model building, the use of cloud computing resources is feasible for large data sets and scales well within cloud instances. An additional advantage of cloud computing is that the costs of predictive models can be easily quantified, and a choice can be made between speed and economy. The easy access to computational resources with no up-front investments makes cloud computing an attractive alternative for scientists, especially for those without access to a supercomputer, and our study shows that it enables cost-efficient modeling of large data sets on demand within reasonable time.

  11. Two Populations of Molecular Clouds in the Antennae Galaxies

    CERN Document Server

    Wei, Lisa H; Ho, Luis C

    2012-01-01

    Super star clusters --- extremely massive clusters found predominately in starburst environments --- are essential building blocks in the formation of galaxies and thought to dominate star formation in the high-redshift universe. However, the transformation from molecular gas into these ultra-compact star clusters is not well understood. To study this process, we used the Submillimeter Array and the Plateau de Bure Interferometer to obtain high angular resolution (~1.5" or 160 pc) images of the Antennae overlap region in CO(2--1) to search for the molecular progenitors of the super star clusters. We resolve the molecular gas distribution into a large number of clouds, extending the differential cloud mass function down to a 5\\sigma completeness limit of 3.8x10^5 M_sun. We identify a distinct break in the mass function around log M_mol/M_sun ~ 6.5, which separates the molecular clouds into two distinct populations. The smaller, less massive clouds reside in more quiescent areas in the region, while the larger,...

  12. Primordial Molecular Cloud Material in Metal-Rich Carbonaceous Chondrites

    Science.gov (United States)

    Taylor, G. J.

    2016-03-01

    The menagerie of objects that make up our Solar System reflects the composition of the huge molecular cloud in which the Sun formed, a late addition of short-lived isotopes from an exploding supernova or stellar winds from a neighboring massive star, heating and/or alteration by water in growing planetesimals that modified and segregated the primordial components, and mixing throughout the Solar System. Outer Solar System objects, such as comets, have always been cold, hence minimizing the changes experienced by more processed objects. They are thought to preserve information about the molecular cloud. Elishevah Van Kooten (Natural History Museum of Denmark and the University of Copenhagen) and co-authors in Denmark and at the University of Hawai'i, measured the isotopic compositions of magnesium and chromium in metal-rich carbonaceous chondrites. They found that the meteorites preserve an isotopic signature of primordial molecular cloud materials, providing a potentially detailed record of the molecular cloud's composition and of materials that formed in the outer Solar System.

  13. Protostellar clusters in the Rosette Molecular Cloud

    Science.gov (United States)

    Henneman, Martin

    The HOBYS Herschel observations of Rosette reveal a population of about 50 very compact far-infrared sources. We find a dense cluster toward the cloud centre and others in the imme-diate vicinity of high-mass young stellar objects or distributed. A fraction of them lack Spitzer counterparts which indicates a very early evolutionary stage. We extract the spectral energy dis-tributions of this new population of protostars to constrain their basic properties, in particular envelope masses and bolometric luminosities. These key characteristics of the Rosette protostar population are used to build an evolutionary diagram (Me nvvsLb ol)tocompletethatmadef orlow- massstar-f ormingregions.T hecomparisontoevolutionarytracksshowsthatRosettef ormslow- tohigh-massstars.W ealsoassesstheapparentmasssegregationof theseprotostarswithrespecttothecloudde massyoungstellarobjects.

  14. Chemical evolution of giant molecular clouds in simulations of galaxies

    CERN Document Server

    Richings, Alexander J

    2016-01-01

    We present an analysis of Giant Molecular Clouds (GMCs) identified in hydrodynamic simulations of isolated, low-mass (M* ~ 10^9 M_sol) disc galaxies, with a particular focus on the evolution of molecular abundances and the implications for CO emission and the X_CO conversion factor in individual clouds. We define clouds either as regions above a density threshold n_H,min = 10 cm^-3, or using an observationally motivated velocity-integrated CO line intensity threshold of 0.25 K km s^-1. Our simulations include a non-equilibrium treatment for the chemistry of 157 species, including 20 molecules. We use a suite of runs to carefully investigate the effects of numerical resolution and pressure floors (i.e. Jeans mass limiters). We find cloud lifetimes up to ~40 Myr, with a median of 13 Myr, in agreement with observations. At ten per cent solar metallicity, young clouds (<10-15 Myr) tend to be underabundant in H2 and CO compared to chemical equilibrium, by factors of ~3 and 1-2 orders of magnitude, respectively....

  15. Molecular cores of the high-latitude cloud MBM 40

    Science.gov (United States)

    Chol Minh, Y. C. Young; Kim, Hyun-Goo; Lee, Youngung; Park, Hyeran; Kim, Kwang-Tae; Park, Yong-Sun; Joon Kim, Sang

    2003-11-01

    Towards the high-latitude cloud MBM 40, we identify 3 dense molecular cores of M˜0.2-0.5 M ⊙, and sizes of ˜0.2 pc in diameter embedded in the H I cloud of ˜8 M ⊙ which is observed to be extended along the northeast-southwest direction. The molecular cloud is located almost perpendicularly to the H I emission. We confirm the previous result of Magnani et al. that MBM 40 is not a site for new star formations. We found a very poor correlation between the H I and the IRAS 100 μm emissions, but the CO (1-0) and 100 μm emissions show a better correlation of WCO/ I100=1±0.2 K km s -1 (MJy sr -1) -1. This ratio is larger by a factor of ≥5 than in dense dark clouds, which may indicate that the CO is less depleted in MBM 40 than in dense dark clouds.

  16. Sandqvist 187 - A dense molecular cloud in Norma

    Science.gov (United States)

    Alvarez, H.; Bronfman, L.; Cohen, R.; Garay, G.; Graham, J.; Thaddeus, P.

    1986-01-01

    Observations of Sandqvist 187, an elongated dust cloud in the southern constellation Norma are presented and discussed. The cloud contains two Herbig-Haro objects, HH 56 and HH 57. HH 57 currently displays on its NE edge a 17th mag variable star of the FU Ori type. Using the Columbia University 1.2 m millimeter-wave telescope at Cerro Tololo, the region is mapped and an extended CO cloud which envelops and is elongated along the optical dust cloud is found. The position of maximum CO emission coincides with HH 56 and HH 57. Assuming a distance of 0.7 kpc, the total mass of the cloud is found to be close to 500 solar masses. The CO spectra show evidence of a molecular flow. Photographs and CCD images obtained mostly with the CTIO 4 m telescope show the detailed optical structure of the dark cloud's core region. The Herbig-Haro object HH 56 appears to be related to an emission-line star embedded in the small nebula Reipurth 13, not to the FU Ori star in HH 57.

  17. Sandqvist 187 - A dense molecular cloud in Norma

    Science.gov (United States)

    Alvarez, H.; Bronfman, L.; Cohen, R.; Garay, G.; Graham, J.; Thaddeus, P.

    1986-01-01

    Observations of Sandqvist 187, an elongated dust cloud in the southern constellation Norma are presented and discussed. The cloud contains two Herbig-Haro objects, HH 56 and HH 57. HH 57 currently displays on its NE edge a 17th mag variable star of the FU Ori type. Using the Columbia University 1.2 m millimeter-wave telescope at Cerro Tololo, the region is mapped and an extended CO cloud which envelops and is elongated along the optical dust cloud is found. The position of maximum CO emission coincides with HH 56 and HH 57. Assuming a distance of 0.7 kpc, the total mass of the cloud is found to be close to 500 solar masses. The CO spectra show evidence of a molecular flow. Photographs and CCD images obtained mostly with the CTIO 4 m telescope show the detailed optical structure of the dark cloud's core region. The Herbig-Haro object HH 56 appears to be related to an emission-line star embedded in the small nebula Reipurth 13, not to the FU Ori star in HH 57.

  18. Chemical evolution of giant molecular clouds in simulations of galaxies

    Science.gov (United States)

    Richings, Alexander J.; Schaye, Joop

    2016-08-01

    We present an analysis of giant molecular clouds (GMCs) within hydrodynamic simulations of isolated, low-mass (M* ˜ 109 M⊙) disc galaxies. We study the evolution of molecular abundances and the implications for CO emission and the XCO conversion factor in individual clouds. We define clouds either as regions above a density threshold n_{H, min} = 10 {cm}^{-3}, or using an observationally motivated CO intensity threshold of 0.25 {K} {km} {s}^{-1}. Our simulations include a non-equilibrium chemical model with 157 species, including 20 molecules. We also investigate the effects of resolution and pressure floors (i.e. Jeans limiters). We find cloud lifetimes up to ≈ 40 Myr, with a median of 13 Myr, in agreement with observations. At one-tenth solar metallicity, young clouds ( ≲ 10-15 Myr) are underabundant in H2 and CO compared to chemical equilibrium, by factors of ≈3 and one to two orders of magnitude, respectively. At solar metallicity, GMCs reach chemical equilibrium faster (within ≈ 1 Myr). We also compute CO emission from individual clouds. The mean CO intensity, ICO, is strongly suppressed at low dust extinction, Av, and possibly saturates towards high Av, in agreement with observations. The ICO-Av relation shifts towards higher Av for higher metallicities and, to a lesser extent, for stronger UV radiation. At one-tenth solar metallicity, CO emission is weaker in young clouds ( ≲ 10-15 Myr), consistent with the underabundance of CO. Consequently, XCO decreases by an order of magnitude from 0 to 15 Myr, albeit with a large scatter.

  19. Three attempts of earthquake prediction with satellite cloud images

    Directory of Open Access Journals (Sweden)

    G. Guangmeng

    2013-01-01

    Full Text Available Thermal anomalies detected from satellite data are widely reported. Nearly all the anomalies are reported after the quake. Here we report three earthquake predictions in Italy and Iran according to satellite cloud anomalies. These cloud anomalies usually show a linear pattern, stay there for hours and do not move with winds. According to these anomalies, we can give a rough estimation about impending earthquake activities. All the estimated dates and magnitudes are in good agreement with the earthquake facts, and the only unsatisfactory point is that the distance error is 100–300 km. Because the cloud anomaly is long, we can not reduce the distance error further. A possible way is to combine geophysical data and satellite data together to estimate the epicenter and this will increase the prediction accuracy.

  20. Giant Molecular Clouds in NGC5128 (Centaurus A)

    Science.gov (United States)

    Bialetski, Y.; Bender, R.; Alves, J.

    2005-12-01

    The physics of the formation of Giant Molecular Clouds (GMC) is one of the major unsolved problems of the interstellar medium. A study of GMCs in external galaxies can address the fundamental questions of whether the molecular ISM in external galaxies is organized differently than in the Milky Way and whether GMCs play the same central role in massive star formation as in the Milky Way, and are then responsible for galaxy evolution. We report the results of our study of 436 giant molecular clouds in NGC5128 using dust extinction. The proposed technique allows us to probe the extinction up to 10m in this galaxy. The clump mass spectrum, derived by a clumpfind algorithm, is consistent with a power law with the index of 2.3.

  1. Improved prediction and tracking of volcanic ash clouds

    Science.gov (United States)

    Webley, P.; Mastin, L.

    2009-01-01

    During the past 30??years, more than 100 airplanes have inadvertently flown through clouds of volcanic ash from erupting volcanoes. Such encounters have caused millions of dollars in damage to the aircraft and have endangered the lives of tens of thousands of passengers. In a few severe cases, total engine failure resulted when ash was ingested into turbines and coating turbine blades. These incidents have prompted the establishment of cooperative efforts by the International Civil Aviation Organization and the volcanological community to provide rapid notification of eruptive activity, and to monitor and forecast the trajectories of ash clouds so that they can be avoided by air traffic. Ash-cloud properties such as plume height, ash concentration, and three-dimensional ash distribution have been monitored through non-conventional remote sensing techniques that are under active development. Forecasting the trajectories of ash clouds has required the development of volcanic ash transport and dispersion models that can calculate the path of an ash cloud over the scale of a continent or a hemisphere. Volcanological inputs to these models, such as plume height, mass eruption rate, eruption duration, ash distribution with altitude, and grain-size distribution, must be assigned in real time during an event, often with limited observations. Databases and protocols are currently being developed that allow for rapid assignment of such source parameters. In this paper, we summarize how an interdisciplinary working group on eruption source parameters has been instigating research to improve upon the current understanding of volcanic ash cloud characterization and predictions. Improved predictions of ash cloud movement and air fall will aid in making better hazard assessments for aviation and for public health and air quality. ?? 2008 Elsevier B.V.

  2. Structural Analysis of Molecular Clouds: Dendrograms

    CERN Document Server

    Rosolowsky, E W; Kauffmann, J; Goodman, A A

    2008-01-01

    We demonstrate the utility of dendrograms at representing the essential features of the hierarchical structure of the isosurfaces for molecular line data cubes. The dendrogram of a data cube is an abstraction of the changing topology of the isosurfaces as a function of contour level. The ability to track hierarchical structure over a range of scales makes this analysis philosophically different from local segmentation algorithms like CLUMPFIND. Points in the dendrogram structure correspond to specific volumes in data cubes defined by their bounding isosurfaces. We further refine the technique by measuring the properties associated with each isosurface in the analysis allowing for a multiscale calculation of molecular gas properties. Using COMPLETE 13CO(1-0) data from the L1448 region in Perseus and mock observations of a simulated data cube, we identify regions that have a significant contribution by self-gravity to their energetics on a range of scales. We find evidence for self-gravitation on all spatial sc...

  3. Photometric investigation of the MBM 12 molecular cloud area in Aries. II. Cloud distance

    CERN Document Server

    Straizys, V; Kazlauskas, A; Laugalys, V

    2002-01-01

    Photoelectric magnitudes and color indices in the Vilnius seven-color system for 152 stars are used to investigate the interstellar extinction in the area of the Aries molecular cloud MBM 12, coinciding with the L1454 and L1457 dust clouds. Spectral types, absolute magnitudes, color excesses, interstellar extinctions and distances of the stars are determined. The plot of interstellar extinction Av versus distance shows that the dust cloud is situated at a distance of 325 pc, at 180 pc from the Galactic plane, and its true diameter is about 11 pc. The interstellar extinction law in the area is found to be normal, typical for the diffuse dust. Ten peculiar or unresolved binary stars and some heavily reddened stars are detected.

  4. Two Models of Magnetic Support for Photoevaporated Molecular Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Ryutov, D; Kane, J; Mizuta, A; Pound, M; Remington, B

    2004-05-05

    The thermal pressure inside molecular clouds is insufficient for maintaining the pressure balance at an ablation front at the cloud surface illuminated by nearby UV stars. Most probably, the required stiffness is provided by the magnetic pressure. After surveying existing models of this type, we concentrate on two of them: the model of a quasi-homogeneous magnetic field and the recently proposed model of a ''magnetostatic turbulence''. We discuss observational consequences of the two models, in particular, the structure and the strength of the magnetic field inside the cloud and in the ionized outflow. We comment on the possible role of reconnection events and their observational signatures. We mention laboratory experiments where the most significant features of the models can be tested.

  5. Cloud Based Metalearning System for Predictive Modeling of Biomedical Data

    Directory of Open Access Journals (Sweden)

    Milan Vukićević

    2014-01-01

    Full Text Available Rapid growth and storage of biomedical data enabled many opportunities for predictive modeling and improvement of healthcare processes. On the other side analysis of such large amounts of data is a difficult and computationally intensive task for most existing data mining algorithms. This problem is addressed by proposing a cloud based system that integrates metalearning framework for ranking and selection of best predictive algorithms for data at hand and open source big data technologies for analysis of biomedical data.

  6. Rapid formation of molecular clouds from turbulent atomic gas

    Science.gov (United States)

    Glover, S. C. O.; Mac Low, M.-M.

    The characteristic lifetimes of molecular clouds remain uncertain and a topic of frequent debate, with arguments having recently been advanced both in support of short-lived clouds, with lifetimes of a few Myr or less (see e.g. Elmegreen 2000; Hartmann et al. 2001) and in support of much longer-lived clouds, with lifetimes of the order of 10 Myr or more (see e.g. Tassis & Mouschovias, 2004; Goldsmith & Li, 2005). An argument that has previously been advanced in favour of longer lived clouds is the apparent difficulty involved in converting sufficient atomic hydrogen to molecular hydrogen within the short timescale required by the rapid cloud formation scenario. However, previous estimates of the time required for this conversion to occur have not taken into account the effects of the supersonic turbulence which is inferred to be present in the atomic gas. In this contribution, we present results from a set of high resolution three-dimensional simulations of turbulence in gravitationally unstable atomic gas. These simulations were performed using a modified version of the ZEUS-MP hydrodynamical code (Norman 2000), and include a detailed treatment of the thermal balance of the gas and of the formation of molecular hydrogen. The effects of photodissociation of H2 by the Galactic UV field are also included, with a simple local approximation used to compute the effects of H2 self-shielding. The results of our simulations demonstrate that H2 formation occurs rapidly in turbulent atomic gas. Starting from purely atomic gas, large quantities of molecular gas can be produced on timescales of less than a Myr, given turbulent velocity dispersions and magnetic field strengths consistent with observations. Moreover, as our simulations underestimate the effectiveness of H2 self-shielding and dust absorption, we can be confident that the molecular fractions which we compute are strong lower limits on the true values. The formation of large quantities of molecular gas on the

  7. Parameters of Warm Molecular Clouds from Methyl Acetylene Observations

    CERN Document Server

    Alakoz, A V; Promislov, V G; Johansson, L E B; Winnberg, A

    2002-01-01

    The results of a survey of 63 galactic star-forming regions in the 6_K-5_K and 5_K-4_K methyl acetylene lines at 102 and 85 GHz, respectively, are presented. Fourty-three sources were detected at 102 GHz, and twenty-five at 85 GHz. Emission was detected towards molecular clouds with kinetic temperatures 20-60 K (so-called ``warm clouds''). The CH3CCH abundances in these clouds appeared to be about several units X 10^(-9). Five mapped sources were analyzed using the maximum entropy method. The sizes of the mapped clouds fall within the range between 0.1 and 1.7 pc, virial masses - between 90-6200 Msun, and densities - between 6 X 10^4 and 6 X 10^5 cm^(-3). The CH3CCH sources spatially coincide with the CO and CS sources. Chemical evolution simulations showed that the typical methyl acetylene abundance in the observed clouds corresponds to an age of ~ 6 X 10^4 years.

  8. High-Resolution CH Observations of Two Translucent Molecular Clouds

    Science.gov (United States)

    Chastain, Raymond J.; Cotten, David; Magnani, Loris

    2010-01-01

    We present high-resolution (1farcm3 × 1farcm6) observations of the CH 2Π1/2 (F = 1-1) emission line at 3335 MHz in two high-latitude translucent clouds, MBM 3 and 40. At the assumed cloud distances, the angular resolution corresponds to ~0.05 pc, nearly an order of magnitude better than previous studies. Comparisons of the CH emission with previously obtained CO(1-0) data are difficult to interpret: the CO and CH line emission correlates in MBM 40 but not in MBM 3. In both clouds, there is a spatial offset in the peak emission, and perhaps in velocity for MBM 40. The difference in emission characteristics for the two tracers are noticeable in these two nearby clouds because of the high spatial resolution. Since both CH and CO are deemed to be reliable tracers of H2, our results indicate that more care should be taken when using one of these tracers to determine the mass of a nearby molecular cloud.

  9. LABOCA observations of giant molecular clouds in the south west region of the Small Magellanic Cloud

    CERN Document Server

    Bot, Caroline; Boulanger, Francois; Albrecht, Marcus; Leroy, Adam; Bolatto, Alberto D; Bertoldi, Frank; Gordon, Karl; Engelbracht, Chad; Block, Miwa; Misselt, Karl

    2010-01-01

    The amount of molecular gas is a key for understanding the future star formation in a galaxy. Because H2 is difficult to observe directly in dense and cold clouds, tracers like CO are used. However, at low metallicities especially, CO only traces the shielded interiors of the clouds. mm dust emission can be used as a tracer to unveil the total dense gas masses. The comparison of masses deduced from the continuum SIMBA 1.2 mm emission and virial masses in a sample of giant molecular clouds (GMCs), in the SW region of the Small Magellanic Cloud (SMC), showed a discrepancy that is in need of an explanation. This study aims at better assessing possible uncertainties on the dust emission observed in the sample of GMCs from the SMC and focuses on the densest parts of the GMCs where CO is detected. New observations were obtained with the LABOCA camera on the APEX telescope. All GMCs previously observed in CO are detected and their emission at 870microns is compared to ancillary data. The different contributions to t...

  10. How long does it take to form a molecular cloud?

    CERN Document Server

    Clark, Paul C; Klessen, Ralf S; Bonnell, Ian A

    2012-01-01

    We present the first numerical simulations that self-consistently follow the formation of dense molecular clouds in colliding flows. Our calculations include a time-dependent model for the H2 and CO chemistry that runs alongside a detailed treatment of the dominant heating and cooling processes in the ISM. We adopt initial conditions characteristic of the warm neutral medium and study two different flow velocities - a slow flow with v = 6.8 km/s and a fast flow with v = 13.6 km/s. The clouds formed by the collision of these flows form stars, with star formation beginning after 16 Myr in the case of the slower flow, but after only 4.4 Myr in the case of the faster flow. In both flows, the formation of CO-dominated regions occurs only around 2 Myr before the onset of star formation. Prior to this, the clouds produce very little emission in the J = 1 -> 0 transition line of CO, and would probably not be identified as molecular clouds in observational surveys. In contrast, our models show that H2-dominated region...

  11. Dust properties inside molecular clouds from coreshine modeling and observations

    CERN Document Server

    Lefèvre, Charlène; Juvela, Mika; Paladini, Roberta; Lallement, Rosine; Marshall, D J; Andersen, Morten; Bacmann, Aurore; Mcgee, Peregrine M; Montier, Ludovic; Noriega-Crespo, Alberto; Pelkonen, V -M; Ristorcelli, Isabelle; Steinacker, Jürgen

    2014-01-01

    Context. Using observations to deduce dust properties, grain size distribution, and physical conditions in molecular clouds is a highly degenerate problem. Aims. The coreshine phenomenon, a scattering process at 3.6 and 4.5 $\\mu$m that dominates absorption, has revealed its ability to explore the densest parts of clouds. We want to use this effect to constrain the dust parameters. The goal is to investigate to what extent grain growth (at constant dust mass) inside molecular clouds is able to explain the coreshine observations. We aim to find dust models that can explain a sample of Spitzer coreshine data. We also look at the consistency with near-infrared data we obtained for a few clouds. Methods. We selected four regions with a very high occurrence of coreshine cases: Taurus-Perseus, Cepheus, Chameleon and L183/L134. We built a grid of dust models and investigated the key parameters to reproduce the general trend of surface bright- nesses and intensity ratios of both coreshine and near-infrared observation...

  12. COLD WATER VAPOR IN THE BARNARD 5 MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Wirström, E. S.; Persson, C. M. [Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala (Sweden); Charnley, S. B.; Cordiner, M. A. [Astrochemistry Laboratory and The Goddard Center for Astrobiology, Mailstop 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20770 (United States); Buckle, J. V. [Astrophysics Group, Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Takakuwa, S., E-mail: eva.wirstrom@chalmers.se [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan (China)

    2014-06-20

    After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold (∼10 K) water vapor has been detected—L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work—likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H{sub 2}O (J = 1{sub 10}-1{sub 01}) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal.

  13. Cluster-formation in the Rosette molecular cloud at the junctions of filaments

    CERN Document Server

    Schneider, N; Hennemann, M; Motte, F; Didelon, P; Federrath, C; Bontemps, S; Di Francesco, J; Arzoumanian, D; Minier, V; André, Ph; Hill, T; Zavagno, A; Nguyen-Luong, Q; Attard, M; Bernard, J -Ph; Elia, D; Fallscheer, C; Griffin, M; Kirk, J; Klessen, R; Könyves, V; Martin, P; Men'shchikov, A; Palmeirim, P; Peretto, N; Pestalozzi, M; Russeil, D; Sadavoy, S; Sousbie, T; Testi, L; Tremblin, P; Ward-Thompson, D; White, G

    2012-01-01

    For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. The Rosette molecular cloud, irradiated by the NGC2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peak...

  14. ALMA view of the Galactic Center 50km/s molecular cloud

    CERN Document Server

    Uehara, Kenta; Kitamura, Yoshimi; Miyawaki, Ryosuke; Miyazaki, Atsushi

    2016-01-01

    We have observed the Galactic Center 50km/s molecular cloud (50MC) with ALMA to search for filamentary structures. In the CS J=2-1 emission line channel maps, we succeeded in identifying 27 molecular cloud filaments using the DisPerSE algorithm. This is the first attempt of "filament-finding" in the Galactic Center Region. These molecular cloud filaments strongly suggest that the molecular cloud filaments are also ubiquitous in the molecular clouds of the Galactic Center Region.

  15. ALMA view of the Galactic Center 50km/s molecular cloud

    Science.gov (United States)

    Uehara, Kenta; Tsuboi, Masato; Kitamura, Yoshimi; Miyawaki, Ryosuke; Miyazaki, Atsushi

    2017-01-01

    We have observed the Galactic Center 50km/s molecular cloud (50MC) with ALMA to search for filamentary structures. In the CS J=2-1 emission line channel maps, we succeeded in identifying 27 molecular cloud filaments using the DisPerSE algorithm. This is the first attempt of filament-finding in the Galactic Center Region. These molecular cloud filaments strongly suggest that the molecular cloud filaments are also ubiquitous in the molecular clouds of the Galactic Center Region.

  16. Draco Nebula, a molecular cloud associated with a high velocity cloud

    Energy Technology Data Exchange (ETDEWEB)

    Mebold, U.; Kalberla, P.W.M.

    1984-11-01

    Extended and very faint bright nebulae are found in high galactic latitudes at the Palomar Observatory Sky Survey. Such a nebula, located in the constellation Draco and called Draco Nebula or Dracula, was found to be in detailed positional coincidence with a 21 cm emission line feature. Estimates of the minimum visual extinction from star counts ON and OFF Dracula and an estimated visual surface brightness indicate that Dracula fits the relation SBV 24.2 - 2.5 log AV for dust clouds located above the galactic plane and reflecting the integrated starlight of the galactic disk. Hence Dracula is probably a reflection nebula. Indicators of molecular hydrogen in Dracula, molecules such as CO, were searched for by using a 2.5-m mm-telescope. Molecular hydrogen column densities were estimated. The dynamics of CO clumps was studied. Dracula has a close positional and possibly even astrophysical relationship to the high velocity cloud phenomenon.

  17. The Draco Nebula, a Molecular Cloud Associated with a High Velocity Cloud?

    Science.gov (United States)

    Mebold, U.; Kalberla, P. W. M.

    1984-01-01

    Extended and very faint bright nebulae are found in high galactic latitudes at the Palomar Observatory Sky Survey. Such a nebula, located in the constellation Draco and called Draco Nebula or Dracula, was found to be in detailed positional coincidence with a 21 cm emission line feature. Estimates of the minimum visual extinction from star counts ON and OFF Dracula and an estimated visual surface brightness indicate that Dracula fits the relation SBV = 24.2 - 2.5 log AV for dust clouds located above the galactic plane and reflecting the integrated starlight of the galactic disk. Hence Dracula is probably a reflection nebula. Indicators of molecular hydrogen in Dracula, molecules such as CO, were searched for by using a 2.5-m mm-telescope. Molecular hydrogen column densities were estimated. The dynamics of CO clumps was studied. Dracula has a close positional and possibly even astrophysical relationship to the high velocity cloud phenomenon.

  18. Gravitational acceleration and edge effects in molecular clouds

    CERN Document Server

    Li, Guang-Xing; Megeath, Tom; Wyrowski, Friedrich

    2016-01-01

    Gravity plays important roles in the evolution of molecular clouds. We present an acceleration mapping method to estimate the acceleration induced by gravitational interactions in molecular clouds based on observational data. We find that the geometry of a region has a significant impact on the behavior of gravity. In the Pipe nebula which can be approximated as a gas filament, we find that gravitational acceleration can effectively compress the end of this filament, which may have triggered star formation. We identify this as the "gravitational focusing" effect proposed by Burkert & Hartman (2004). In the sheet-like IC348-B3 region, gravity can lead to collapse at its edge, while in the centrally condensed NGC1333 cluster-forming region gravity can drive accretion towards the center. In general, gravitational acceleration tends to be enhanced in the localized regions around the ends of the filaments and the edges of sheet-like structures. Neglecting magnetic fields, these "gravitational focusing" and "ed...

  19. Ammonia observations of the nearby molecular cloud MBM 12

    CERN Document Server

    Gomes, J F; Pascual, S; Patel, N; Morales, C; Torrelles, J M; Gomez, Jose F.; Trapero, Joaquin; Pascual, Sergio; Patel, Nimesh; Morales, Carmen; Torrelles, Jose M.

    2000-01-01

    We present NH3(1,1) and NH3(2,2) observations of MBM 12, the closest known molecular cloud (65 pc distance), aimed to find evidence for on-going star formation processes. No local temperature (with a T_rot upper limit of 12 K) nor linewidth enhancement is found, which suggests that the area of the cloud we mapped (~ 15' size) is not currently forming stars. Therefore, this close ``starless'' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation. A radio continuum source was found in Very Large Array archive data, close but outside the NH3 emission. This source is likely to be a background object.

  20. High-Latitude Molecular Clouds as (Gamma)-ray Sources for GLAST

    Energy Technology Data Exchange (ETDEWEB)

    Torres, D F; Dame, T M; Digel, S W

    2005-01-05

    For about two decades, a population of relative small and nearby molecular clouds has been known to exist at high Galactic latitudes. Lying more than 10{sup o} from the Galactic plane, these clouds have typical distances of {approx}150 pc, angular sizes of {approx}1{sup o}, and masses of order tens of solar masses. These objects are passive sources of high-energy {gamma}-rays through cosmic ray-gas interactions. Using a new wide-angle CO survey of the northern sky, we show that typical high-latitude clouds are not bright enough in {gamma}-rays to have been detected by EGRET, but that of order 100 of them will be detectable by the Large Area Telescope (LAT) on GLAST. Thus, we predict a new steady population of {gamma}-ray sources at high Galactic latitudes, perhaps the most numerous after active galactic nuclei.

  1. FUSE Team Project on Molecular Hydrogen in Translucent Clouds

    Science.gov (United States)

    Snow, Theodore P.

    This Cycle 2 program plans observations of 11 stars (in addition to the original list) as an add-on to our medium project to study molecular hydrogen in translucent clouds. The new stars have been selected on the basis of reddening, known extinction and interstellar line parameters, and inclusion in the comprehensive survey of diffuse interstellar bands being carried out by group member Don York and collaborators (e.g. Snow, Welty et al.).

  2. DIFFUSE MOLECULAR CLOUD DENSITIES FROM UV MEASUREMENTS OF CO ABSORPTION

    Energy Technology Data Exchange (ETDEWEB)

    Goldsmith, Paul F. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)

    2013-09-10

    We use UV measurements of interstellar CO toward nearby stars to calculate the density in the diffuse molecular clouds containing the molecules responsible for the observed absorption. Chemical models and recent calculations of the excitation rate coefficients indicate that the regions in which CO is found have hydrogen predominantly in molecular form and that collisional excitation is by collisions with H{sub 2} molecules. We carry out statistical equilibrium calculations using CO-H{sub 2} collision rates to solve for the H{sub 2} density in the observed sources without including effects of radiative trapping. We have assumed kinetic temperatures of 50 K and 100 K, finding this choice to make relatively little difference to the lowest transition. For the sources having T{sup ex}{sub 10} only for which we could determine upper and lower density limits, we find (n(H{sub 2})) = 49 cm{sup -3}. While we can find a consistent density range for a good fraction of the sources having either two or three values of the excitation temperature, there is a suggestion that the higher-J transitions are sampling clouds or regions within diffuse molecular cloud material that have higher densities than the material sampled by the J = 1-0 transition. The assumed kinetic temperature and derived H{sub 2} density are anticorrelated when the J = 2-1 transition data, the J = 3-2 transition data, or both are included. For sources with either two or three values of the excitation temperature, we find average values of the midpoint of the density range that is consistent with all of the observations equal to 68 cm{sup -3} for T{sup k} = 100 K and 92 cm{sup -3} for T{sup k} = 50 K. The data for this set of sources imply that diffuse molecular clouds are characterized by an average thermal pressure between 4600 and 6800 K cm{sup -3}.

  3. The System of Molecular Clouds in the Gould Belt

    CERN Document Server

    Bobylev, V V

    2016-01-01

    Based on high-latitude molecular clouds with highly accurate distance estimates taken from the literature, we have redetermined the parameters of their spatial orientation. This system can be approximated by a 350x235x140 pc ellipsoid inclined by the angle i=17+/-2 degrees to the Galactic plane with the longitude of the ascending node l{\\Omega}=337+/-1 degrees. Based on the radial velocities of the clouds, we have found their group velocity relative to the Sun to be (u0,v0,w0) = (10.6,18.2,6.8)+/-(0.9,1.7,1.5) km/s. The trajectory of the center of the molecular cloud system in the past in a time interval of ~60 Myr has been constructed. Using data on masers associated with low-mass protostars, we have calculated the space velocities of the molecular complexes in Orion, Taurus, Perseus, and Ophiuchus. Their motion in the past is shown to be not random.

  4. Collapse and Fragmentation of Molecular Cloud Cores. IX. Magnetic Braking of Initially Filamentary Clouds

    Science.gov (United States)

    Boss, Alan P.

    2007-04-01

    The collapse and fragmentation of initially filamentary, magnetic molecular clouds are calculated in three dimensions with a gravitational, radiative hydrodynamics code. The code includes magnetic field effects in an approximate manner: magnetic pressure, tension, braking, and ambipolar diffusion are all modeled. The parameters varied are the ratio of the ambipolar diffusion time to the free-fall time at the center of the filamentary cloud (tad/tff=10, 20, or 106~∞), the cloud's reference magnetic field strength (Boi=0, 200, or 300 μG-the latter two values leading to magnetically subcritical clouds), the ratio of rotational to gravitational energy of the filament (10-4 or 10-2), and the efficiency of magnetic braking (represented by a factor fmb=0, 10-4, or 10-3). Three types of outcomes are observed: direct collapse and fragmentation into a multiple protostar system (models with Boi=0), periodic contraction and expansion without collapse (models with tad/tff=106), or periodic contraction and expansion leading eventually to collapse on a timescale of ~6tff-12tff (all other models). Because the computational grid is a finite-volume sphere, the expanding clouds bounce off the spherical boundary and recollapse toward the center of the spherical grid, leading to the periodic formation of shocked regions where the infalling gas collides with itself, forming dense layers susceptible to sustained collapse and eventual fragmentation. The models develop weakly supersonic velocity fields as a result of rebounding prior to collapse. The models show that magnetically supported clouds subject to magnetic braking can undergo dynamic collapse leading to protostellar fragmentation on scales of 10-100 AU, consistent with typical binary star separations.

  5. Cosmic rays as regulators of molecular cloud properties

    CERN Document Server

    Padovani, Marco; Galli, Daniele

    2014-01-01

    Cosmic rays are the main agents in controlling the chemical evolution and setting the ambipolar diffusion time of a molecular cloud. We summarise the processes causing the energy degradation of cosmic rays due to their interaction with molecular hydrogen, focusing on the magnetic effects that influence their propagation. Making use of magnetic field configurations generated by numerical simulations, we show that the increase of the field line density in the collapse region results in a reduction of the cosmic-ray ionisation rate. As a consequence the ionisation fraction decreases, facilitating the decoupling between the gas and the magnetic field.

  6. Subparsec clumping in the nearby molecular cloud MBM 12

    Energy Technology Data Exchange (ETDEWEB)

    Pound, M.W.; Wilson, R.W.; Bania, T.M. (AT T Bell Laboratories, Holmdel, NJ (USA) Boston Univ., MA (USA))

    1990-03-01

    At a distance of 65 pc, the molecular cloud MBM 12 is the nearest molecular complex known. Results of extensive molecular and preliminary atomic spectral mapping of the MBM 12 complex are reported. The total H2 mass of the cloud is estimated to be about 30 solar masses. Although there are over 50 distinct emission clumps and the (C-13)O (J = 1-0) maps show structure within the MBM 12 complex down to the resolution limit of about 6500 AU. The large line widths may reflect either the evaporation of the clumps by the ambient hot gas or the presence of an ensemble of blended emission clumps that are smaller than the resolution limit. Preliminary results show H I envelopes about the molecular cores with column densities consistent with that expected for atomic to molecular transition regions. The kinematics of the MBM 12 complex imply kinetic energies of about 10 to the 45th ergs. This energy is typical of that produced by a bipolar flow from a young stellar object. 30 refs.

  7. A hierarchical method for molecular docking using cloud computing.

    Science.gov (United States)

    Kang, Ling; Guo, Quan; Wang, Xicheng

    2012-11-01

    Discovering small molecules that interact with protein targets will be a key part of future drug discovery efforts. Molecular docking of drug-like molecules is likely to be valuable in this field; however, the great number of such molecules makes the potential size of this task enormous. In this paper, a method to screen small molecular databases using cloud computing is proposed. This method is called the hierarchical method for molecular docking and can be completed in a relatively short period of time. In this method, the optimization of molecular docking is divided into two subproblems based on the different effects on the protein-ligand interaction energy. An adaptive genetic algorithm is developed to solve the optimization problem and a new docking program (FlexGAsDock) based on the hierarchical docking method has been developed. The implementation of docking on a cloud computing platform is then discussed. The docking results show that this method can be conveniently used for the efficient molecular design of drugs.

  8. The Fractal Dimension of the ρ Ophiucus Molecular Cloud Complex

    Science.gov (United States)

    Lee, Yongung; Yi, Di; Kim, Y. S.; Jung, J. H.; Kang, H. W.; Lee, C. H.; Yim, I. S.; Kim, H. G.

    2016-12-01

    We estimate the fractal dimension of the ρ Ophiuchus Molecular Cloud Complex, associated with star forming regions. We selected a cube (v, l, b) database, obtained with J=1-0 transition lines of \\coand tco at a resolution of 22'' using a multibeam receiver system on the 14-m telescope of the Five College Radio Astronomy Observatory. Using a code developed within IRAF, we identified slice-clouds with two threshold temperatures to estimate the fractal dimension. With threshold temperatures of 2.25 K (3σ) and 3.75 K (5σ), the fractal dimension of the target cloud is estimated to be D = 1.52-1.54, where P ∝ A^{D/2} , which is larger than previous results. We suggest that the sampling rate (spatial resolution) of observed data must be an important parameter when estimating the fractal dimension, and that narrower or wider dispersion around an arbitrary fit line and the intercepts at NP = 100 should be checked whether they relate to rms noise level or characteristic structure of the target cloud. This issue could be investigated by analysing several high resolution databases with different quality (low or moderate sensitivity).

  9. A Uniform Catalog of Molecular Clouds in the Milky Way

    CERN Document Server

    Rice, Thomas S; Bergin, Edwin A; Beaumont, Christopher; Dame, T M

    2016-01-01

    The all-Galaxy CO survey of Dame, Hartmann, & Thaddeus (2001) is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains $2.5 \\times 10^8$ solar masses, or $25^{+10.7}_{-5.8} \\%$ of the Milky Way's estimated H$_2$ mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions - possibly due to an observational bias - but clouds in the inner Galaxy systematically have significantly (~ 30%) higher linewidths at a given size, indicating that their linewidths are set in part by Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power-law with a power index of $\\gamma=-1.6\\pm0.1$ an...

  10. The formation of the W43 complex: constraining its atomic-to-molecular transition and searching for colliding clouds

    CERN Document Server

    Motte, F; Schneider, N; Heitsch, F; Glover, S; Carlhoff, P; Hill, T; Bontemps, S; Schilke, P; Louvet, F; Hennemann, M; Didelon, P; Beuther, H

    2014-01-01

    Numerical simulations have explored the possibility to form molecular clouds through either a quasi-static, self-gravitating mechanism or the collision of gas streams or lower-density clouds. They also quantitatively predict the distribution of matter at the transition from atomic to molecular gases. We aim to observationally test these models by studying the environment of W43, a molecular cloud complex near the tip of the Galactic long bar. Using Galaxy-wide HI and 12CO surveys we searched for gas flowing toward the W43 molecular cloud complex. We also estimated the HI and H2 mass surface densities to constrain the transition from atomic to molecular gas around and within W43. We found 3 cloud ensembles within the position-velocity diagrams of 12CO and HI gases. They are separated by 20km/s along the line of sight and extend into the 13CO velocity structure of W43. Since their velocity gradients are consistent with free-fall, they could be nearby clouds attracted by, and streaming toward, the W43 10^7Msun p...

  11. Spectral Line Survey toward Molecular Clouds in the Large Magellanic Cloud

    CERN Document Server

    Nishimura, Yuri; Watanabe, Yoshimasa; Sakai, Nami; Aikawa, Yuri; Kawamura, Akiko; Yamamoto, Satoshi

    2015-01-01

    Spectral line survey observations of 7 molecular clouds in the Large Magellanic Cloud (LMC) have been conducted in the 3 mm band with the Mopra 22 m telescope to reveal chemical compositions in low metallicity conditions. Spectral lines of fundamental species such as CS, SO, CCH, HCN, HCO+, and HNC are detected in addition to those of CO and 13CO, while CH3OH is not detected in any source and N2H+ is marginally detected in two sources. The molecular-cloud scale (10 pc scale) chemical composition is found to be similar among the 7 sources regardless of different star formation activities, and hence, it represents the chemical composition characteristic to the LMC without influences of star formation activities. In comparison with chemical compositions of Galactic sources, the characteristic features are (1) deficient N-bearing molecules, (2) abundant CCH, and (3) deficient CH3OH. The feature (1) is due to a lower elemental abundance of nitrogen in the LMC, whereas the features (2) and (3) seem to originate fro...

  12. Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

    CERN Document Server

    Tatematsu, Ken'ichi; Kandori, Ryo; Umemoto, Tomofumi

    2010-01-01

    We have observed molecular cloud cores in the Orion A giant molecular cloud (GMC) in CCS, HC3N, DNC, and HN13C to study their chemical characteristics. We have detected CCS in the Orion A GMC for the first time. CCS was detected in about a third of the observed cores. The cores detected in CCS are not localized but are widely distributed over the Orion A GMC. The CCS peak intensity of the core tends to be high in the southern region of the Orion A GMC. The HC3N peak intensity of the core also tends to be high in the southern region, while there are HC3N intense cores near Orion KL, which is not seen in CCS. The core associated with Orion KL shows broad HC3N line profile, and star formation activity near Orion KL seems to enhance the HC3N emission. The column density ratio of NH3 to CCS is lower near the middle of the filament, and is higher toward the northern and southern regions along the Orion A GMC filament. This ratio is known to trace the chemical evolution in nearby dark cloud cores, but seems to be af...

  13. A model for the internal structure of molecular cloud cores

    CERN Document Server

    McLaughlin, D E; McLaughlin, Dean E; Pudritz, Ralph E

    1996-01-01

    We generalize the classic Bonnor-Ebert stability analysis of pressure-truncated, self-gravitating gas spheres, to include clouds with arbitrary equations of state. A virial-theorem analysis is also used to incorporate mean magnetic fields into such structures. The results are applied to giant molecular clouds (GMCs), and to individual dense cores, with an eye to accounting for recent observations of the internal velocity-dispersion profiles of the cores in particular. We argue that GMCs and massive cores are at or near their critical mass, and that in such a case the size-linewidth and mass-radius relations between them are only weakly dependent on their internal structures; any gas equation of state leads to essentially the same relations. We briefly consider the possibility that molecular clouds can be described by polytropic pressure-density relations (of either positive or negative index), but show that these are inconsistent with the apparent gravitational virial equilibrium, 2U + W = 0 of GMCs and of ma...

  14. A Spitzer/IRAC Survey of the Orion Molecular Clouds

    CERN Document Server

    Megeath, S T; Hora, J; Allen, L E; Fazio, G G; Hartmann, L; Myers, P C; Muzerolle, J; Pipher, J L; Siegler, N; Stauffer, J R; Young, E

    2005-01-01

    We present initial results from a survey of the Orion A and B molecular clouds made with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope. This survey encompasses a total of 5.6 square degrees with the sensitivity to detect objects below the hydrogen burning limit at an age of 1 Myr. These observations cover a number of known star forming regions, from the massive star forming clusters in the Orion Nebula and NGC 2024, to small groups of low mass stars in the L1641. We combine the IRAC photometry with photometry from the 2MASS point source catalog and use the resulting seven band data to identify stars with infrared excesses due to dusty disks and envelopes. Using the presence of an infrared excess as an indicator of youth, we show the distribution of young stars and protostars in the two molecular clouds. We find that roughly half of the stars are found in dense clusters surrounding the two regions of recent massive star formation in the Orion clouds, NGC 2024 and the Orion Nebula.

  15. The Molecular Cloud Associated with the HII Region RCW:34

    Science.gov (United States)

    Pagani, L.; Heydari-Malayeri, M.; Castets, A.

    1993-08-01

    We present millimetric multi-line observations of the molecular cloud associated with the H II region RCW 34. We believe we are able to present a coherent description of the cloud: a molecular bar on top of the H II region is divided into three elements: a dense, heated part situated in the post-shock trail, a cold, less dense part besides, left unperturbed and a diffuse component either in front of the dense parts or possibly mixed with them if the dense parts are clumpy. This diffuse component has a density of a few hundreds per cm-3, a temperature in the range 30-60 K and its opacity in 12CO is close to or less than unity. We show that this diffuse component, the existence of which is controversial, is the best explanation to the large 12CO (J: 1 → 0)/(J: 2 → 1) ratio we have observed. A simple-minded model is presented to approach its properties. The cloud is on top and partly in front of the H II region and can explain the 4.2 mag of visual extinction measured by one of us (Heydari-Malayeri 1988). The very high velocity flow detected in Hα by Heydari-Malayeri has no counterpart in radio but could be a direct visualisation of the so-called "Champagne effect" (Tonorio-Tagle 1979).

  16. Simulating the formation of molecular clouds. II. Rapid formation from turbulent initial conditions

    CERN Document Server

    Glover, S C O

    2006-01-01

    (Abridged). In this paper, we present results from a large set of numerical simulations that demonstrate that H2 formation occurs rapidly in turbulent gas. Starting with purely atomic hydrogen, large quantities of molecular hydrogen can be produced on timescales of 1 -- 2 Myr, given turbulent velocity dispersions and magnetic field strengths consistent with observations. Moreover, as our simulations underestimate the effectiveness of H2 self-shielding and dust absorption, we can be confident that the molecular fractions that we compute are strong lower limits on the true values. The formation of large quantities of H2 on the timescale required by rapid cloud formation models therefore appears to be entirely plausible. We also investigate the density and temperature distributions of gas in our model clouds. We show that the density probability distribution function is approximately log-normal, with a dispersion that agrees well with the prediction of Padoan, Nordlund & Jones (1997). The temperature distrib...

  17. Temperatures of galactic molecular clouds showing CO self-absorption

    Science.gov (United States)

    Phillips, T. G.; Knapp, G. R.; Wannier, P. G.; Huggins, P. J.; Werner, M. W.; Neugebauer, G.; Ennis, D.

    1981-01-01

    The CO J = 2-1 line has been observed and, in most cases, mapped in 10 star-forming molecular clouds (W3, NGC 1333, NGC 2071, Mon R2, CRL 961, Rho Oph, W49N, W51A, DR 21, and Cep A). The CO J = 3-2 line has been observed in W3 and DR 21. The CO lines from all these sources are strongly self-absorbed. By comparing the present results with published CO(1-0) line profiles, it is found that large corrections to the temperatures of the cloud cores, as measured by the CO(1-0) lines, are required. The corrections for self-absorption bring the CO brightness temperatures into closer agreement with the grain temperatures inferred from far-IR photometry.

  18. Compressibility and Density Fluctuations in Molecular-Cloud Turbulence

    CERN Document Server

    Pan, Liubin; Haugbolle, Troels; Nordlund, Aake

    2015-01-01

    The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence(250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence that is only mildly compressive, with the turbulent ratio of compressive to solenoidal modes ~0.3 on average, lower than the equilibrium value of 0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor is the mean cloud expansion or contraction velocity (MCs do not co...

  19. Dust emission in the Sagittarius B2 molecular cloud core

    Science.gov (United States)

    Lis, Dariusz C.; Goldsmith, Paul F.

    1989-01-01

    A model is presented for the dust emission from the Sagittarius B2 molecular cloud core which reproduces the observed spectrum between 30 and 1300 micron, as well as the distribution of the emission at 1300 micron. The model is based on the assumption that Sgr B2(N) continuum source is located behind the dust cloud associated with Sgr B2(M) continuum source. The fact that Sgr B2(N) is stronger at 1300 micron can be attributed to a local column density maximum at the position of this source. Absence of a 53 micron emission peak at the position of Sgr B2(N) suggests that the luminosity of the north source is lower than that of the middle source.

  20. Infrared reflection nebulae in Orion Molecular Cloud 2

    Science.gov (United States)

    Pendleton, Yvonne; Werner, M. W.; Capps, R.; Lester, D.

    1986-01-01

    New observations of Orion Molecular Cloud 2 have been made from 1 to 100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry, and spectrophotometry has shown that the extended emission regions associated with two of the previously known near-infrared sources, IRS 1 and IRS 4, are infrared reflection nebulae, and that the compact sources IRS 1 and IRS 4 are the main luminosity sources in the cloud. The constraints from the far-infrared observations and an analysis of the scattered light from the IRS 1 nebula show that OMC-2/IRS 1 can be characterized by L of 500 solar luminosities or less and T of roughly 1000 K. The near-infrared albedo of the grains in the IRS 1 nebula is greater than 0.08.

  1. On the nearest molecular clouds. II - MBM 12 and 16

    Science.gov (United States)

    Hobbs, L. M.; Penprase, B. E.; Welty, D. E.; Blitz, L.; Magnani, L.

    1988-01-01

    The paper presents echelle spectra recorded at the D lines of Na I for three stars projected on the high-latitude molecular cloud MBM 16 at l = 172 deg, b = -38 deg. The A stars HD 21142 at about 95 pc and HD 21134 at about 240 pc show strong D-line absorption at the same velocities as the CO emission observed at these positions. The distance to MBM 16 therefore is in the range of 60 to 95 pc. MBM 16 is only 11 deg away from MBM 12, previously placed by the same method at distance of about 65 pc. Consideration is given to the relationship between clouds 12 and 16 and the local hot low-density interstellar gas.

  2. Nearest molecular clouds. II. MBM 12 and 16

    Energy Technology Data Exchange (ETDEWEB)

    Hobbs, L.M.; Penprase, B.E.; Welty, D.E.; Blitz, L.; Magnani, L.

    1988-04-01

    The paper presents echelle spectra recorded at the D lines of Na I for three stars projected on the high-latitude molecular cloud MBM 16 at l = 172 deg, b = -38 deg. The A stars HD 21142 at about 95 pc and HD 21134 at about 240 pc show strong D-line absorption at the same velocities as the CO emission observed at these positions. The distance to MBM 16 therefore is in the range of 60 to 95 pc. MBM 16 is only 11 deg away from MBM 12, previously placed by the same method at distance of about 65 pc. Consideration is given to the relationship between clouds 12 and 16 and the local hot low-density interstellar gas. 36 references.

  3. Chemical Variation in Molecular Cloud Cores in the Orion A Cloud

    Science.gov (United States)

    Tatematsu, Ken'ichi; Hirota, Tomoya; Kandori, Ryo; Umemoto, Tomofumi

    2010-12-01

    We have observed molecular cloud cores in the Orion A giant molecular cloud (GMC) in CCS, HC3N, DNC, and HN13C to study their chemical characteristics. We detected CCS in the Orion A GMC for the first time. CCS was detected in about a third of the observed cores. The cores detected in CCS are not localized, but widely distributed over the Orion A GMC. The CCS peak intensity of the core tends to be high in the southern region of the Orion A GMC. The HC3N peak intensity of the core also tends to be high in the southern region, while there are HC3N intense cores near Orion KL, which is not seen in CCS. The core associated with Orion KL shows a broad HC3N line profile, and the star-formation activity near to Orion KL seems to enhance the HC3N emission. The column density ratio of NH3 to CCS is lower near the middle of the filament, and higher toward the northern and southern regions along the Orion A GMC filament. This ratio is known to trace the chemical evolution in nearby dark cloud cores, but seems to be affected by the core gas temperature in the Orion A GMC: cores with low NH3 to CCS column density ratios tend to have a warmer gas temperature. The value of the column density ratio of DNC to HN13 is generally similar to that in dark cloud cores, but becomes lower around Orion KL due to a higher gas temperature.

  4. Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

    CERN Document Server

    Ackermann, M; Allafort, A; Antolini, E; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bottacini, E; Brandt, T J; Bregeon, J; Brigida, M; Bruel, P; Buehler, R; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Cecchi, C; Chekhtman, A; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Conrad, J; D'Ammando, F; de Angelis, A; de Palma, F; Dermer, C D; Silva, E do Couto e; Drell, P S; Drlica-Wagner, A; Enoto, T; Falletti, L; Favuzzi, C; Fegan, S J; Ferrara, E C; Focke, W B; Fukazawa, Y; Fukui, Y; Fusco, P; Gargano, F; Gasparrini, D; Germani, S; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Guiriec, S; Hadasch, D; Hanabata, Y; Harding, A K; Hayashida, M; Hayashi, K; Horan, D; Hou, X; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Kamae, T; Katagiri, H; Kataoka, J; Kerr, M; Knödlseder, J; Kuss, M; Lande, J; Larsson, S; Lee, S -H; Longo, F; Loparco, F; Lovellette, M N; Lubrano, P; Makishima, K; Mazziotta, M N; Mehault, J; Mitthumsiri, W; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Naumann-Godo, M; Nishino, S; Norris, J P; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Orienti, M; Orlando, E; Ormes, J F; Ozaki, M; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pesce-Rollins, M; Pierbattista, M; Piron, F; Pivato, G; Porter, T A; Rainò, S; Razzano, M; Reimer, A; Reimer, O; Roth, M; Sadrozinski, H F -W; Sgrò, C; Siskind, E J; Spandre, G; Spinelli, P; Strong, A W; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J G; Thayer, J B; Tibolla, O; Tinivella, M; Torres, D F; Tramacere, A; Troja, E; Uchiyama, Y; Usher, T L; Vandenbroucke, J; Vasileiou, V; Vianello, G; Vitale, V; Waite, A P; Wang, P; Winer, B L; Wood, K S; Yang, Z; Zimmer, S

    2012-01-01

    We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between \\sim100 MeV and \\sim100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to \\sim10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity integrated CO intensity (WCO) at a 1{\\deg} \\times1{\\deg} pixel level. The correlation is found to be linear over a WCO range of ~10 fold when divided in 3 regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The Wco-to-mass conversion factor, Xco, is found to be \\sim2.3\\times1...

  5. The ionization fraction gradient across the Horsehead edge: An archetype for molecular clouds

    CERN Document Server

    Goicoechea, J R; Gerin, M; Hily-Blant, P; Bourlot, J Le

    2009-01-01

    The ionization fraction plays a key role in the chemistry and dynamics of molecular clouds. We study the H13CO+, DCO+ and HOC+ line emission towards the Horsehead, from the shielded core to the UV irradiated cloud edge, i.e., the Photodissociation Region (PDR), as a template to investigate the ionization fraction gradient in molecular clouds. We analyze a PdBI map of the H13CO+ J=1-0 line, complemented with IRAM-30m H13CO+ and DCO+ higher-J line maps and new HOC+ and CO+ observations. We compare self-consistently the observed spatial distribution and line intensities with detailed depth-dependent predictions of a PDR model coupled with a nonlocal radiative transfer calculation. The chemical network includes deuterated species, 13C fractionation reactions and HCO+/HOC+ isomerization reactions. The role of neutral and charged PAHs in the cloud chemistry and ionization balance is investigated. The detection of HOC+ reactive ion towards the Horsehead PDR proves the high ionization fraction of the outer UV irradia...

  6. ALMA RESOLVES 30 DORADUS: SUB-PARSEC MOLECULAR CLOUD STRUCTURE NEAR THE CLOSEST SUPER STAR CLUSTER

    Energy Technology Data Exchange (ETDEWEB)

    Indebetouw, Remy; Brogan, Crystal; Leroy, Adam; Hunter, Todd; Kepley, Amanda, E-mail: rindebet@nrao.edu, E-mail: cbrogan@nrao.edu, E-mail: aleroy@nrao.edu [National Radio Astronomy Observatory, 520 Edgemont Road Charlottesville, VA 22903 (United States); and others

    2013-09-01

    We present Atacama Large (sub)Millimeter Array observations of 30 Doradus-the highest resolution view of molecular gas in an extragalactic star formation region to date ({approx}0.4 pc Multiplication-Sign 0.6 pc). The 30Dor-10 cloud north of R136 was mapped in {sup 12}CO 2-1, {sup 13}CO 2-1, C{sup 18}O 2-1, 1.3 mm continuum, the H30{alpha} recombination line, and two H{sub 2}CO 3-2 transitions. Most {sup 12}CO emission is associated with small filaments and clumps ({approx}<1 pc, {approx}10{sup 3} M{sub Sun} at the current resolution). Some clumps are associated with protostars, including ''pillars of creation'' photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to a higher surface density at a given size and linewidth compared to clouds studied at 10 pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the Large Magellanic Cloud mean, but the dust abundance may be reduced by {approx}2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend toward lower dense clump filling fraction deeper in the cloud.

  7. Ionized carbon in side-illuminated molecular clouds

    Science.gov (United States)

    Boreiko, R. T.; Betz, A. L.; Zmuidzinas, J.

    1990-01-01

    The C II fine-structure line has been observed in five sources for which the ionization front/molecular cloud interface is viewed approximately edge-on. The LSR velocity of the C II emission is generally in good agreement with that observed for molecular species such as CO. However, the observed linewidths of 3-14 km/s are typically wider than those of molecular lines and often show rapid spatial variations in the observed regions. The C II brightness temperature are typically equal to or slightly higher than the dust temperature at all locations observed. In the optically thin approximation, C II excitation temperatures are 100 K or more and column densities are 10 to the 18th/sq cm for all sources except M17, which has a more intense and complicated line profile with a larger spatial extent than any other source observed.

  8. The Galactic Center Molecular Cloud Survey. II. A Lack of Dense Gas & Cloud Evolution along Galactic Center Orbits

    CERN Document Server

    Kauffmann, Jens; Zhang, Qizhou; Menten, Karl M; Goldsmith, Paul F; Lu, Xing; Guzmán, Andrés E; Schmiedeke, Anika

    2016-01-01

    We present the first systematic study of the density structure of clouds found in a complete sample covering all major molecular clouds in the Central Molecular Zone (CMZ; inner $\\sim{}200~\\rm{}pc$) of the Milky Way. This is made possible by using data from the Galactic Center Molecular Cloud Survey (GCMS), the first study resolving all major molecular clouds in the CMZ at interferometer angular resolution. We find that many CMZ molecular clouds have unusually shallow density gradients compared to regions elsewhere in the Milky Way. This is possibly a consequence of weak gravitational binding of the clouds. The resulting relative absence of dense gas on spatial scales $\\sim{}0.1~\\rm{}pc$ is probably one of the reasons why star formation (SF) in dense gas of the CMZ is suppressed by a factor $\\sim{}10$, compared to solar neighborhood clouds. Another factor suppressing star formation are the high SF density thresholds that likely result from the observed gas kinematics. Further, it is possible but not certain t...

  9. GASEOUS CO ABUNDANCE-AN EVOLUTIONARY TRACER FOR MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Liu Tie; Wu Yuefang; Zhang Huawei, E-mail: liutiepku@gmail.com, E-mail: ywu@pku.edu.cn [Department of Astronomy, Peking University, Beijing 100871 (China)

    2013-09-20

    Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of the Planck satellite with the molecular data of {sup 12}CO/{sup 13}CO/C{sup 18}O (1-0) lines from observations with the Purple Mountain Observatory 13.7 m telescope, we investigate the CO abundance, CO depletion, and CO-to-H{sub 2} conversion factor of 674 clumps in the early cold cores sample. The median and mean values of the CO abundance are 0.89 Multiplication-Sign 10{sup -4} and 1.28 Multiplication-Sign 10{sup -4}, respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median value of X{sub CO-to-H{sub 2}} for the whole sample is 2.8 Multiplication-Sign 10{sup 20} cm{sup -2} K{sup -1} km{sup -1} s. The CO abundance, CO depletion factor, and CO-to-H{sub 2} conversion factor are strongly (anti-)correlated to other physical parameters (e.g., dust temperature, dust emissivity spectral index, column density, volume density, and luminosity-to-mass ratio). To conclude, the gaseous CO abundance can be used as an evolutionary tracer for molecular clouds.

  10. On The Gas Temperature of Molecular Cloud Cores

    CERN Document Server

    Juvela, M

    2011-01-01

    We investigate the uncertainties affecting the temperature profiles of dense cores of interstellar clouds. In regions shielded from external ultraviolet radiation, the problem is reduced to the balance between cosmic ray heating, line cooling, and the coupling between gas and dust. We show that variations in the gas phase abundances, the grain size distribution, and the velocity field can each change the predicted core temperatures by one or two degrees. We emphasize the role of non-local radiative transfer effects that often are not taken into account, for example, when modelling the core chemistry. These include the radiative coupling between regions of different temperature and the enhanced line cooling near the cloud surface. The uncertainty of the temperature profiles does not necessarily translate to a significant error in the column density derived from observations. However, depletion processes are very temperature sensitive and a two degree difference can mean that a given molecule no longer traces t...

  11. Quiescent Giant Molecular Cloud Cores in the Galactic Center

    Science.gov (United States)

    Lis, D. C.; Serabyn, E.; Zylka, R.; Li, Y.

    2000-01-01

    We have used the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO) to map the far-infrared continuum emission (45-175 micrometer) toward several massive Giant Molecular Cloud (GMC) cores located near the Galactic center. The observed far-infrared and submillimeter spectral energy distributions imply low temperatures (approx. 15 - 22 K) for the bulk of the dust in all the sources, consistent with external heating by the diffuse ISRF and suggest that these GMCs do not harbor high- mass star-formation sites, in spite of their large molecular mass. Observations of FIR atomic fine structure lines of C(sub II) and O(sub I) indicate an ISRF enhancement of approx. 10(exp 3) in the region. Through continuum radiative transfer modeling we show that this radiation field strength is in agreement with the observed FIR and submillimeter spectral energy distributions, assuming primarily external heating of the dust with only limited internal luminosity (approx. 2 x 10(exp 5) solar luminosity). Spectroscopic observations of millimeter-wave transitions of H2CO, CS, and C-34S carried out with the Caltech Submillimeter Observatory (CSO) and the Institut de Radio Astronomie Millimetrique (IRAM) 30-meter telescope indicate a gas temperature of approx. 80 K, significantly higher than the dust temperatures, and density of approx. 1 x 10(exp 5)/cc in GCM0.25 + 0.01, the brightest submillimeter source in the region. We suggest that shocks caused by cloud collisions in the turbulent interstellar medium in the Galactic center region are responsible for heating the molecular gas. This conclusion is supported by the presence of wide-spread emission from molecules such as SiO, SO, and CH3OH, which are considered good shock tracers. We also suggest that the GMCs studied here are representative of the "typical", pre-starforming cloud population in the Galactic center.

  12. Observing simulations: molecular clouds and their journey in the galaxy

    Science.gov (United States)

    Duarte-Cabral, A.; Dobbs, C. L.

    2016-05-01

    In order to have a global picture of the cycle of matter in galaxies, we need to understand the interplay of large-scale galactic phenomena with the formation of giant molecular clouds (GMCs) and, ultimately, their subsequent star formation (SF). In this work, we study the population of GMCs within a smoothed particle hydrodynamics (SPH) simulation of a spiral galaxy, and investigate the link between the GMC properties and position with respect to spiral arms, both directly from the simulation (with the 3D densities of H2 and CO) and from an observer's perspective (with CO emission in PPV space).

  13. An infrared study of Orion Molecular Cloud-2 (OMC-2)

    Science.gov (United States)

    Johnson, J. J.; Gehrz, R. D.; Jones, T. J.; Hackwell, J. A.; Grasdalen, G. L.

    1990-01-01

    This paper reports 1.2-23 micron photometry for 11 discrete sources in Orion Molecular Cloud-2 (OMC-2). These data, combined with H and K photometric and K polarimetric images, are used to model the cluster sources. Most appear to be young stars of roughly solar mass. Some have circumstellar dust reradiation or reflection nebulosity. A model based on single scattering of light from an exciting star explains some features of the IRS 1 nebula, the largest reflection nebula in OMC-2. However, the red colors and high surface brightness of the IRS 1 nebula require a cool excitation source that is more luminous than far-infrared observations would indicate.

  14. A Spitzer/IRAC Survey of the Orion Molecular Clouds

    OpenAIRE

    Megeath, S. T.; Flaherty, K M; Hora, J.; Allen, L E; Fazio, G. G.; Hartmann, L.; Myers, P. C.; J. Muzerolle; Pipher, J. L.; Siegler, N.; J. R. Stauffer; Young, E.

    2005-01-01

    We present initial results from a survey of the Orion A and B molecular clouds made with the InfraRed Array Camera (IRAC) onboard the Spitzer Space Telescope. This survey encompasses a total of 5.6 square degrees with the sensitivity to detect objects below the hydrogen burning limit at an age of 1 Myr. These observations cover a number of known star forming regions, from the massive star forming clusters in the Orion Nebula and NGC 2024, to small groups of low mass stars in the L1641. We com...

  15. An infrared study of Orion Molecular Cloud-2 (OMC-2)

    Science.gov (United States)

    Johnson, J. J.; Gehrz, R. D.; Jones, T. J.; Hackwell, J. A.; Grasdalen, G. L.

    1990-01-01

    This paper reports 1.2-23 micron photometry for 11 discrete sources in Orion Molecular Cloud-2 (OMC-2). These data, combined with H and K photometric and K polarimetric images, are used to model the cluster sources. Most appear to be young stars of roughly solar mass. Some have circumstellar dust reradiation or reflection nebulosity. A model based on single scattering of light from an exciting star explains some features of the IRS 1 nebula, the largest reflection nebula in OMC-2. However, the red colors and high surface brightness of the IRS 1 nebula require a cool excitation source that is more luminous than far-infrared observations would indicate.

  16. Gravitational instability of filamentary molecular clouds, including ambipolar diffusion

    CERN Document Server

    Hosseinirad, Mohammad; Abbassi, Shahram; Roshan, Mahmood

    2016-01-01

    The gravitational instability of a filamentary molecular cloud in non-ideal magnetohydrodynamics is investigated. The filament is assumed to be in hydrostatic equilibrium. We add the effect of ambipolar diffusion to the filament which is threaded by an initial uniform axial magnetic field along its axis. We write down the fluid equations in cylindrical coordinates and perform linear perturbation analysis. We integrate the resultant differential equations and then derive the numerical dispersion relation. We find that, a more efficient ambipolar diffusion leads to an enhancement of the growth of the most unstable mode, and to increase of the fragmentation scale of the filament.

  17. Galactic Edge Clouds I: Molecular Line Observations and Chemical Modelling of Edge Cloud 2

    CERN Document Server

    Ruffle, P M E; Roberts, H; Lubowich, D A; Henkel, C; Pasachoff, J M; Brammer, G

    2007-01-01

    Edge Cloud 2 (EC2) is a molecular cloud, about 35 pc in size, with one of the largest galactocentric distances known to exist in the Milky Way. We present observations of a peak CO emission region in the cloud and use these to determine its physical characteristics. We calculate a gas temperature of 20 K and a density of n(H2) ~ 10^4 cm^-3. Based on our CO maps, we estimate the mass of EC2 at around 10^4 M_sun and continuum observations suggest a dust-to-gas mass ratio as low as 0.001. Chemical models have been developed to reproduce the abundances in EC2 and they indicate that: heavy element abundances may be reduced by a factor of five relative to the solar neighbourhood (similar to dwarf irregular galaxies and damped Lyman alpha systems); very low extinction (Av < 4 mag) due to a very low dust-to-gas ratio; an enhanced cosmic ray ionisation rate; and a higher UV field compared to local interstellar values. The reduced abundances may be attributed to the low level of star formation in this region and are...

  18. Giant Molecular Clouds in the Local Group Galaxy M33

    CERN Document Server

    Gratier, P; Rodriguez-Fernandez, N J; Schuster, K F; Kramer, C; Corbelli, E; Combes, F; Brouillet, N; van der Werf, P P; Röllig, M

    2011-01-01

    We present an analysis of the systematic CO(2-1) survey at 12" resolution covering most of the local group spiral M 33 which, at a distance of 840 kpc, is close enough that individual giant molecular clouds (GMCs) can be identified. The goal of this work is to study the properties of the GMCs in this subsolar metallicity galaxy. The CPROPS (Cloud Properties) algorithm (Rosolowsky & Leroy 2006) was used to identify 337 GMCs in M 33, the largest sample to date in an external galaxy. The sample is used to study the GMC luminosity function, or mass spectrum under the assumption of a constant N(H2)/ICO ratio. We find that n(L)dL = K*L^(-2.0\\pm0.1) for the entire sample. However, when the sample is divided into inner and outer disk samples, the exponent changes from 1.6 \\pm 0.2 for the centre 2 kpc to 2.3 \\pm 0.2 for galactocentric distances larger than 2 kpc. Based on the emission in the FUV, Halpha, 8mu, and 24mu bands, each cloud was classified in terms of its star forming activity - no star formation, embed...

  19. Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

    Science.gov (United States)

    Cordiner, Martin; Charnley, Steven; Buckle, Jane; Wash, Catherine; Millar, Tom

    2011-01-01

    From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed.

  20. Molecular line study of evolution in protostellar cloud cores

    CERN Document Server

    Kontinen, S; Heikkilä, A; Haikala, L K

    2000-01-01

    Two dense dark cloud cores representing different stages of dynamical evolution were observed in a number of molecular spectral lines. One of the cores, Cha- MMS1 in the Chamaeleon cloud I contains a Class 0 protostar, whereas the other, CrA C in the R Coronae Australis cloud, is pre-stellar. We find that the cores have very different chemical compositions. Cha-MMS1 exhibits characteristics of so-called `early-type' chemistry with high abundan- ces of carbon-chain molecules such as HC3N, but it also has a large N2H+ abundance, which is expected only to build up at later stages. In contrast, none of the carbon-chain molecules were detected in CrA C. CrA C has a higher SO abundance than Cha-MMS1, which implies that it is chemically `older' than Cha- MMS1. The most striking difference between the two cores is seen in the HC3N/SO abundance ratio, which is at least three orders of magnitude higher in Cha-MMS than in CrA C. This result is surprising since starless cores are usually thought to be chemically younger ...

  1. The YSO Population in the Vela-D Molecular Cloud

    CERN Document Server

    Strafella, F; Giannini, T; Elia, D; Maruccia, Y; Maiolo, B; Massi, F; Olmi, L; Molinari, S; Pezzuto, S

    2014-01-01

    We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D (VMR-D), a star forming (SF) region observed by both Spitzer/NASA and Herschel/ESA space telescope. The point source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSO), also including sources detected in less than four IRAC bands. Bona fide YSO are selected by using appropriate color-color and color-magnitude criteria aimed to exclude both Galatic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other SF clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolomet...

  2. Molecular clouds associated with compact HII regionsin Galactic plane

    Institute of Scientific and Technical Information of China (English)

    孙锦; 沈家健; 孙艳春; 张燕平

    2002-01-01

    13CO (J = 1 - 0) emission of massive star forming region including 15 ultracompact and 4compact HII regions in Galactic plane was mapped with the 13.7 m millimeter wave telescope of Purple Mountain Observatory. The present observations provide the first complete structure of the clouds in 13CO with a higher spatial resolution and a wide-field coverage of 28′×45′. Combined with the images of far-infrared emission and dust color temperature obtained from ISSA, various possible dynamical connections between the compact HII regions and associated clouds were found. We presente some reasons to explain the formation of new dense cold core and molecular emission cavity in the massive star formation and early evolution. The luminosities of excitation stars for all HII regions and the main parameters of associated clouds are also derived. The results show that the newborn stars' luminosities are correlated with the 13CO column densities, masses (in 55"beam) and 13CO velocity widths obviously.``

  3. Evolving Molecular Cloud Structure and the Column Density Probability Distribution Function

    CERN Document Server

    Ward, Rachel L; Sills, Alison

    2014-01-01

    The structure of molecular clouds can be characterized with the probability distribution function (PDF) of the mass surface density. In particular, the properties of the distribution can reveal the nature of the turbulence and star formation present inside the molecular cloud. In this paper, we explore how these structural characteristics evolve with time and also how they relate to various cloud properties as measured from a sample of synthetic column density maps of molecular clouds. We find that, as a cloud evolves, the peak of its column density PDF will shift to surface densities below the observational threshold for detection, resulting in an underlying lognormal distribution which has been effectively lost at late times. Our results explain why certain observations of actively star-forming, dynamically older clouds, such as the Orion molecular cloud, do not appear to have any evidence of a lognormal distribution in their column density PDFs. We also study the evolution of the slope and deviation point ...

  4. A Uniform Catalog of Molecular Clouds in the Milky Way

    Science.gov (United States)

    Rice, Thomas S.; Goodman, Alyssa A.; Bergin, Edwin A.; Beaumont, Christopher; Dame, T. M.

    2016-05-01

    The all-Galaxy CO survey of Dame et al. is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains 2.5 × 108 solar masses, or {25}-5.8+10.7% of the Milky Way's estimated H2 mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions—possibly due to an observational bias—but clouds in the inner Galaxy systematically have significantly (˜30%) higher linewidths at a given size, indicating that their linewidths are set in part by the Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power law with a power index of γ = -1.6 ± 0.1 and an upper truncation mass of M 0 = (1.0 ± 0.2) × 107 M ⊙, while the outer Galaxy mass spectrum is better described by a non-truncating power law with γ = -2.2 ± 0.1 and an upper mass of M 0 = (1.5 ± 0.5) × 106 M ⊙, indicating that the inner Galaxy is able to form and host substantially more massive GMCs than the outer Galaxy. Additionally, we have simulated how the Milky Way would appear in CO from extragalactic perspectives, for comparison with CO maps of other galaxies.

  5. Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

    DEFF Research Database (Denmark)

    van Kooten, Elishevah M. M. E.; Wielandt, Daniel Kim Peel; Schiller, Martin

    2016-01-01

    )Mg*-depleted and (54)Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived (26)Al. The (26)Mg* and (54)Cr compositions of bulk metal-rich chondrites require significant amounts (25...... product of (26)Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling (26)Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last...

  6. The Dynamics of Dense Cores in the Perseus Molecular Cloud II: The Relationship Between Dense Cores and the Cloud

    CERN Document Server

    Kirk, Helen; Johnstone, Doug; Goodman, Alyssa

    2010-01-01

    We utilize the extensive datasets available for the Perseus molecular cloud to analyze the relationship between the kinematics of small-scale dense cores and the larger structures in which they are embedded. The kinematic measures presented here can be used in conjunction with those discussed in our previous work as strong observational constraints that numerical simulations (or analytic models) of star formation should match. We find that dense cores have small motions with respect to the 13CO gas, about one third of the 13CO velocity dispersion along the same line of sight. Within each extinction region, the core-to-core velocity dispersion is about half of the total (13CO) velocity dispersion seen in the region. Large-scale velocity gradients account for roughly half of the total velocity dispersion in each region, similar to what is predicted from large-scale turbulent modes following a power spectrum of P(k) ~ k^{-4}.

  7. QUANTIFYING OBSERVATIONAL PROJECTION EFFECTS USING MOLECULAR CLOUD SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Beaumont, Christopher N. [Institute for Astronomy, University of Hawai' i, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Offner, Stella S.R. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Shetty, Rahul; Glover, Simon C. O. [Zentrum für Astronomie der Universität Heidelberg, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany); Goodman, Alyssa A., E-mail: beaumont@ifa.hawaii.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

    2013-11-10

    The physical properties of molecular clouds are often measured using spectral-line observations, which provide the only probes of the clouds' velocity structure. It is hard, though, to assess whether and to what extent intensity features in position-position-velocity (PPV) space correspond to 'real' density structures in position-position-position (PPP) space. In this paper, we create synthetic molecular cloud spectral-line maps of simulated molecular clouds, and present a new technique for measuring the reality of individual PPV structures. Using a dendrogram algorithm, we identify hierarchical structures in both PPP and PPV space. Our procedure projects density structures identified in PPP space into corresponding intensity structures in PPV space and then measures the geometric overlap of the projected structures with structures identified from the synthetic observation. The fractional overlap between a PPP and PPV structure quantifies how well the synthetic observation recovers information about the three-dimensional structure. Applying this machinery to a set of synthetic observations of CO isotopes, we measure how well spectral-line measurements recover mass, size, velocity dispersion, and virial parameter for a simulated star-forming region. By disabling various steps of our analysis, we investigate how much opacity, chemistry, and gravity affect measurements of physical properties extracted from PPV cubes. For the simulations used here, which offer a decent, but not perfect, match to the properties of a star-forming region like Perseus, our results suggest that superposition induces a ∼40% uncertainty in masses, sizes, and velocity dispersions derived from {sup 13}CO (J = 1-0). As would be expected, superposition and confusion is worst in regions where the filling factor of emitting material is large. The virial parameter is most affected by superposition, such that estimates of the virial parameter derived from PPV and PPP information

  8. Striations in molecular clouds: Streamers or MHD waves?

    CERN Document Server

    Tritsis, A

    2016-01-01

    Dust continuum and molecular observations of the low column density parts of molecular clouds have revealed the presence of elongated structures which appear to be well aligned with the magnetic field. These so-called striations are usually assumed to be streams that flow towards or away from denser regions. We perform ideal magnetohydrodynamic (MHD) simulations adopting four models that could account for the formation of such structures. In the first two models striations are created by velocity gradients between ambient, parallel streamlines along magnetic field lines. In the third model striations are formed as a result of a Kelvin-Helmholtz instability perpendicular to field lines. Finally, in the fourth model striations are formed from the nonlinear coupling of MHD waves due to density inhomogeneities. We assess the validity of each scenario by comparing the results from our simulations with previous observational studies and results obtained from the analysis of CO (J = 1 - 0) observations from the Taur...

  9. Carbon Monoxide Depletion in Orion B Molecular Cloud Cores

    CERN Document Server

    Savva, D; Phillips, R R; Gibb, A G

    2003-01-01

    We have observed several cloud cores in the Orion B (L1630) molecular cloud in the 2-1 transitions of C18O, C17O and 13C18O. We use these data to show that a model where the cores consist of very optically thick C18O clumps cannot explain their relative intensities. There is strong evidence that the C18O is not very optically thick. The CO emission is compared to previous observations of dust continuum emission to deduce apparent molecular abundances. The abundance values depend somewhat on the temperature but relative to `normal abundance' values, the CO appears to be depleted by about a factor of 10 at the core positions. CO condensation on dust grains provides a natural explanation for the apparent depletion both through gas-phase depletion of CO, and through a possible increase in dust emissivity in the cores. The high brightness of HCO+ relative to CO is then naturally accounted for by time-dependent interstellar chemistry starting from `evolved' initial conditions. Theoretical work has shown that conden...

  10. Non-ideal MHD turbulent decay in molecular clouds

    CERN Document Server

    Downes, T P

    2009-01-01

    It is well known that non-ideal magnetohydrodynamic effects are important in the dynamics of molecular clouds: both ambipolar diffusion and possibly the Hall effect have been identified as significant. We present the results of a suite of simulations with a resolution of 512-cubed of turbulent decay in molecular clouds incorporating a simplified form of both ambipolar diffusion and the Hall effect simultaneously. The initial velocity field in the turbulence is varied from being super-Alfv\\'enic and hypersonic, through to trans-Alfv\\'enic but still supersonic. We find that ambipolar diffusion increases the rate of decay of the turbulence increasing the decay from $t^{-1.25}$ to $t^{-1.4}$. The Hall effect has virtually no impact in this regard. The power spectra of density, velocity and the magnetic field are all affected by the non-ideal terms, being steepened significantly when compared with ideal MHD turbulence with exponents. The density power spectra components change from about 1.4 to about 2.1 for the i...

  11. Cloud Prediction of Protein Structure and Function with PredictProtein for Debian

    Directory of Open Access Journals (Sweden)

    László Kaján

    2013-01-01

    Full Text Available We report the release of PredictProtein for the Debian operating system and derivatives, such as Ubuntu, Bio-Linux, and Cloud BioLinux. The PredictProtein suite is available as a standard set of open source Debian packages. The release covers the most popular prediction methods from the Rost Lab, including methods for the prediction of secondary structure and solvent accessibility (profphd, nuclear localization signals (predictnls, and intrinsically disordered regions (norsnet. We also present two case studies that successfully utilize PredictProtein packages for high performance computing in the cloud: the first analyzes protein disorder for whole organisms, and the second analyzes the effect of all possible single sequence variants in protein coding regions of the human genome.

  12. Cloud prediction of protein structure and function with PredictProtein for Debian.

    Science.gov (United States)

    Kaján, László; Yachdav, Guy; Vicedo, Esmeralda; Steinegger, Martin; Mirdita, Milot; Angermüller, Christof; Böhm, Ariane; Domke, Simon; Ertl, Julia; Mertes, Christian; Reisinger, Eva; Staniewski, Cedric; Rost, Burkhard

    2013-01-01

    We report the release of PredictProtein for the Debian operating system and derivatives, such as Ubuntu, Bio-Linux, and Cloud BioLinux. The PredictProtein suite is available as a standard set of open source Debian packages. The release covers the most popular prediction methods from the Rost Lab, including methods for the prediction of secondary structure and solvent accessibility (profphd), nuclear localization signals (predictnls), and intrinsically disordered regions (norsnet). We also present two case studies that successfully utilize PredictProtein packages for high performance computing in the cloud: the first analyzes protein disorder for whole organisms, and the second analyzes the effect of all possible single sequence variants in protein coding regions of the human genome.

  13. Molecular outflows identified in the FCRAO CO survey of the Taurus Molecular Cloud

    Science.gov (United States)

    Narayanan, Gopal; Snell, Ronald; Bemis, Ashley

    2012-10-01

    Jets and outflows are an integral part of the star formation process. While there are many detailed studies of molecular outflows towards individual star-forming sites, few studies have surveyed an entire star-forming molecular cloud for this phenomenon. The 100-deg2 Five College Radio Astronomy Observatory CO survey of the Taurus Molecular Cloud provides an excellent opportunity to undertake an unbiased survey of a large, nearby, molecular cloud complex for molecular outflow activity. Our study provides information on the extent, energetics and frequency of outflows in this region, which are then used to assess the impact of outflows on the parent molecular cloud. The search identified 20 outflows in the Taurus region, eight of which were previously unknown. Both 12CO and 13CO data cubes from the Taurus molecular map were used, and dynamical properties of the outflows are derived. Even for previously known outflows, our large-scale maps indicate that many of the outflows are much larger than previously suspected, with eight of the outflows (40 per cent) being more than a parsec long. The mass, momentum and kinetic energy from the 20 outflows are compared to the repository of turbulent energy in Taurus. Comparing the energy deposition rate from outflows to the dissipation rate of turbulence, we conclude that outflows by themselves cannot sustain the observed turbulence seen in the entire cloud. However, when the impact of outflows is studied in selected regions of Taurus, it is seen that locally outflows can provide a significant source of turbulence and feedback. The L1551 dark cloud which is just south of the main Taurus complex was not covered by this survey, but the outflows in L1551 have much higher energies compared to the outflows in the main Taurus cloud. In the L1551 cloud, outflows can not only account for the turbulent energy present, but are probably also disrupting their parent cloud. We conclude that for a molecular cloud like Taurus, an L1551-like

  14. LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Kryukova, E.; Megeath, S. T.; Allen, T. S. [Department of Physics and Astronomy, University of Toledo, Toledo, OH (United States); Gutermuth, R. A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Pipher, J. [Department of Physics and Astronomy, University of Rochester, Rochester, NY (United States); Allen, L. E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Myers, P. C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States); Muzerolle, J. [Space Telescope Science Institute, Baltimore, MD (United States)

    2012-08-15

    We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 {mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 {mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L{sub Sun} and show a tail extending toward luminosities above 100 L{sub Sun }. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L{sub Sun }. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity

  15. Molecular spectral line surveys and the organic molecules in the interstellar molecular clouds

    Science.gov (United States)

    Ohishi, Masatoshi

    2008-10-01

    It is known that more than 140 interstellar and circumstellar molecules have so far been detected, mainly by means of the radio astronomy observations. Many organic molecules are also detected, including alcohols, ketons, ethers, aldehydes, and others, that are distributed from dark clouds and hot cores in the giant molecular clouds. It is believed that most of the organic molecules in space are synthesized through the grain surface reactions, and are evaporated from the grain surface when they are heated up by the UV radiation from adjacent stars. On the other hand the recent claim on the detection of glycine have raised an important issue how difficult it is to confirm secure detection of weak spectra from less abundant organic molecules in the interstellar molecular cloud. I will review recent survey observations of organic molecules in the interstellar molecular clouds, including independent observations of glycine by the 45 m radio telescope in Japan, and will discuss the procedure to securely identify weak spectral lines from organic molecules and the importance of laboratory measurement of organic species.

  16. Some Algorithms for Weather Prediction Using Thin Clouds

    Directory of Open Access Journals (Sweden)

    Moneeshaa.J

    2013-04-01

    Full Text Available Clouds are important for climatic changes in the atmosphere. Cloud images are taken by visible and infrared satellites. Both visible and infrared satellites, the clouds that are not very white are calledThin Clouds. So, the identification of a thin cloud is hard to find out. In this paper, some algorithms for spotting thin clouds are proposed. They are HSL (Hue Saturation Light, ROI (Region of Interest, Watershed, Demirel and Color Segmentation. HSL (Hue Saturation Light is used for finding the ratio of color in the cloud image, ROI (Region of Interest is used for removing the cloud and the sky elements of the cloud image, Watershed and Demirel algorithm are used to segment the Thin Clouds. The extract values from the cloud image are measured using Gaussian Filter. The weather forecasting is carried out by comparing the images in the database after performing color segmentation by k-means clustering.

  17. Molecular Outflows Identified in the FCRAO CO Survey of the Taurus Molecular Cloud

    CERN Document Server

    Narayanan, Gopal; Bemis, Ashley

    2012-01-01

    The 100 square degree FCRAO CO survey of the Taurus molecular cloud provides an excellent opportunity to undertake an unbiased survey of a large, nearby, molecular cloud complex for molecular outflow activity. Our study provides information on the extent, energetics and frequency of outflows in this region, which are then used to assess the impact of outflows on the parent molecular cloud. The search identified 20 outflows in the Taurus region, 8 of which were previously unknown. Both $^{12}$CO and $^{13}$CO data cubes from the Taurus molecular map were used, and dynamical properties of the outflows are derived. Even for previously known outflows, our large-scale maps indicate that many of the outflows are much larger than previously suspected, with eight of the flows (40%) being more than a parsec long. The mass, momentum and kinetic energy from the 20 outflows are compared to the repository of turbulent energy in Taurus. Comparing the energy deposition rate from outflows to the dissipation rate of turbulenc...

  18. The puzzling detection of D2CO in the molecular cloud L1689N

    Science.gov (United States)

    Ceccarelli, C.; Vastel, C.; Tielens, A. G. G. M.; Castets, A.; Boogert, A. C. A.; Loinard, L.; Caux, E.

    2002-01-01

    We present new observations of the D2CO emission towards the small cloud L1689N in the rho Ophiuchus complex. We surveyed five positions, three being a cut across a shock site and two probing the quiescent gas of the molecular cloud. We detected D2CO emission in the first three positions. The measured [D2CO]/[H2CO] is about 3%, whereas it is removed from the cold storage by the shock at the interface between the outflowing and quiescent gas. We review the predictions of the published models proposed to explain the observed high deuteration of formaldehyde. They fall in two basic schemes: gas phase and grain surface chemistry. None of the reviewed models is able to account for the observed [D2CO]/[H2CO] abundance ratio. A common characteristics shared by the models is apparently that all underestimate the atomic [D]/[H] ratio in the accreting gas.

  19. Observational Evidence of Dynamic Star Formation Rate in Milky Way Giant Molecular Clouds

    CERN Document Server

    Lee, Eve J; Murray, Norman

    2016-01-01

    Star formation on galactic scales is known to be a slow process, but whether it is slow on smaller scales is uncertain. We cross-correlate 5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256 star forming complexes (SFCs) to build a sample of 191 SFC-GMC complexes---collections of multiple clouds each matched to 191 SFCs. The total mass in stars harbored by these clouds is inferred from WMAP free-free fluxes. We measure the GMC mass, the virial parameter, the star formation efficiency $\\epsilon$ and the star formation rate per free-fall time $\\epsilon_{\\rm ff}$. Both $\\epsilon$ and $\\epsilon_{\\rm ff}$ range over 3--4 orders of magnitude. We find that 68.3% of the clouds fall within $\\sigma_{\\log\\epsilon}=0.79\\pm0.22\\,{\\rm dex}$ and $\\sigma_{\\log\\epsilon_{\\rm ff}}=0.91\\pm0.22\\,{\\rm dex}$ about the median. Compared to these observed scatters, a simple model with a time independent $\\epsilon_{\\rm ff}$ that depends on the host GMC properties predicts $\\sigma_{\\log\\epsilon_{\\rm ff}}=0.24$. Allowi...

  20. OH AND CN ZEEMAN OBSERVATIONS OF MAGNETIC FIELDS IN MOLECULAR CLOUDS

    Directory of Open Access Journals (Sweden)

    R. M. Crutcher

    2009-01-01

    Full Text Available Observations of the Zeeman e ect in OH and CN provide valuable information about magnetic eld strengths and directions in molecular clouds in the density range 103 < n(cm-3 < 106 that these species sample. These data make it possible to test predictions of weak eld, turbulence driven star formation and strong eld, ambipolar di usion driven star formation. Here we discuss exactly what information Zeeman observations provide and how those data may be analyzed to yield meaningful results. The data imply that the mean mass-to-ux ratio in molecular cores is - 2 - 3 times critical, which means that magnetic elds are generally not strong enough to prevent gravitational collapse. However, this information about mean eld strengths is not de nitive in excluding one or the other of the two models of star formation. Present data do suggest that magnetic elds play a very signi cant role in the evolution of molecular clouds and in the star formation process. Finally, very preliminary results are discussed from two in-progress studies; these studies have the potential to be signi cantly more de nitive in testing the predictions of star formation theory, and perhaps in discriminating between the two theories.

  1. Formation Pumping of Molecular Hydrogen in Dark Clouds

    CERN Document Server

    Islam, Farahjabeen; Viti, Serena; Casu, Silvia

    2010-01-01

    Many theoretical and laboratory studies predict H2 to be formed in highly excited ro-vibrational states. The consequent relaxation of excited levels via a cascade of infrared transitions might be observable in emission from suitable interstellar regions. In this work, we model H2 formation pumping in standard dense clouds, taking into account the H/H2 transition zone, through an accurate description of chemistry and radiative transfer. The model includes recent laboratory data on H2 formation, as well as the effects of the interstellar UV field, predicting the populations of gas-phase H2 molecules and their IR emission spectra. Calculations suggest that some vibrationally excited states of H2 might be detectable towards lines of sight where significant destruction of H2 occurs, such as X-ray sources, and provide a possible explanation as to why observational attempts resulted in no detections reported to date.

  2. Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

    Energy Technology Data Exchange (ETDEWEB)

    Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; D' Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; do Couto e Silva, E.; Drell, P. S.; Drlica-Wagner, A.; Enoto, T.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fukazawa, Y.; Fukui, Y.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Guiriec, S.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hayashi, K.; Horan, D.; Hou, X.; Hughes, R. E.; Jackson, M. S.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kerr, M.; Knödlseder, J.; Kuss, M.; Lande, J.; Larsson, S.; Lee, S. -H.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Makishima, K.; Mazziotta, M. N.; Mehault, J.; Mitthumsiri, W.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Nishino, S.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Orienti, M.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Razzano, M.; Reimer, A.; Reimer, O.; Roth, M.; Sadrozinski, H. F. -W.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Strong, A. W.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibolla, O.; Tinivella, M.; Torres, D. F.; Tramacere, A.; Troja, E.; Uchiyama, Y.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wang, P.; Winer, B. L.; Wood, K. S.; Yang, Z.; Zimmer, S.

    2012-08-08

    We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between ~100 MeV and ~100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to ~10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W CO) at a 1° × 1° pixel level. The correlation is found to be linear over a W CO range of ~10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W CO-to-mass conversion factor, X CO, is found to be ~2.3 × 1020 cm-2(K km s–1)–1 for the high-longitude part of Orion A (l > 212°), ~1.7 times higher than ~1.3 × 1020 found for the rest of Orion A and B. We interpret the apparent high X CO in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas. W CO decreases faster than the H2 column density in the region making the gas "darker" to W CO.

  3. Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

    Science.gov (United States)

    Kobayashi, Masato I. N.; Inutsuka, Shu-ichiro; Kobayashi, Hiroshi; Hasegawa, Kenji

    2017-02-01

    Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks. High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium. In this article, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H ii regions and supernova remnants. We introduce the cloud–cloud collision (CCC) terms in the evolution equation in contrast to previous work (Inutsuka et al.). The computed time evolution suggests that the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC effect is limited only in the massive end of the mass function. In addition, we identify a gas resurrection channel that allows the gas dispersed by massive stars to regenerate GMC populations or to accrete onto pre-existing GMCs. Our results show that almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60% contributes in inter-arm regions. Our results also predict that GMC mass functions have a single power-law exponent in the mass range environments across galactic disks.

  4. Mapping the Orion Molecular Cloud Complex in Radio Frequencies

    Science.gov (United States)

    Castelaz, Michael W.; Lemly, C.

    2013-01-01

    The purpose of this research project was to create a large-scale intensity map of the Orion Molecular Cloud Complex at a radio frequency of 1420 MHz. A mapping frequency of 1420 MHz was chosen because neutral hydrogen, which is the primary component of the Orion Molecular Complex, naturally emits radio waves at this frequency. The radio spectral data for this project were gathered using a 4.6-m radio telescope whose spectrometer was tuned to 1420 MHz and whose beam width was 2.7 degrees. The map created for this project consisted of an eight-by-eight grid centered on M42 spanning 21.6 degrees per side. The grid consisted of 64 individual squares spanning 2.7 degrees per side (corresponding to the beam width of the telescope). Radio spectra were recorded for each of these individual squares at an IF gain of 18. Each spectrum consisted of intensity on an arbitrary scale from 0 to 10 plotted as a function frequencies ranging from -400 kHz to +100 kHz around the origin of 1420 MHz. The data from all 64 radio spectra were imported into Wolfram Alpha, which was used to fit Gaussian functions to the data. The peak intensity and the frequency at which this peak intensity occurs could then be extracted from the Gaussian functions. Other helpful quantities that could be calculated from the Gaussian functions include flux (integral of Gaussian function over frequency range), average value of intensity (flux integral divided by frequency range), and half maximum of intensity. Because all of the radio spectra were redshifted, the velocities of the hydrogen gas clouds of the Orion Molecular Cloud Complex could be calculated using the Doppler equation. The data extracted from the Gaussian functions were then imported into Mathcad to create 2D grayscale maps with right ascension (RA) on the x-axis, declination on the y-axis, and intensity (or flux, etc.) represented on a scale from black to white (with white representing the highest intensities). These 2D maps were then imported

  5. Dense gas in high-latitude molecular clouds

    Science.gov (United States)

    Reach, William T.; Pound, Marc W.; Wilner, David J.; Lee, Youngung

    1995-01-01

    The nearby molecular clouds MBM 7, 12, 30, 32, 40, 41, and 55 were surveyed for tracers of dense gas, including the (1-0), (2-1), and (3-2) rotational lines of CS and the (1-0) lines of HCO(+) and HCN. MBM 7 and MBM 12 contain dense cores, while the other clouds contain little or no traces of dense gas. Comparison of the emission from dense gas tracers to that of (13)CO reveals that the former are more compact in angular size as well as line width. An extensive CS(2-1) survey of part of MBM 12 reveals that the emission is characterized by clumps on approximately 3 min scales as well as extended emission. Observations of the CS(1-0) and (3-2) lines using telescopes with matched beam sizes reveal that the volume density must be at least approximately 10(exp 4.5)/cc within the (3-2) emitting regions, which are approximately 0.03 pc in radius. Electron excitation of the CS rotational levels is ruled out (in the cores) by comparing the (3-2)/(1-0) line ratios with models including H2 and electron collisions. The volume density in the cores is substantially larger than in the portions of the cloud traced by CO emission. The density increases into the cores as r(exp -2), suggesting dynamical collapse. The masses of the cores are close to the virial mass, suggesting they are dynamically bound. The cores in MBM 7 and MBM 12 are thus likely to form stars; they are the nearest sites of star formation.

  6. Star Formation in the rho Ophiuchi Molecular Cloud

    CERN Document Server

    Wilking, Bruce; Allen, Lori

    2008-01-01

    A review of star formation in the Rho Ophiuchi molecular complex is presented, with particular emphasis on studies of the main cloud, L1688, since 1991. Recent photometric and parallax measurements of stars in the Upper Scorpius subgroup of the Sco-Cen OB association suggest a distance for the cloud between 120 and 140 parsecs. Star formation is ongoing in the dense cores of L1688 with a median age for young stellar objects of 0.3 Myr. The surface population appears to have a median age of 2-5 Myr and merges with low mass stars in the Upper Scorpius subgroup. Making use of the most recent X-ray and infrared photometric surveys and spectroscopic surveys of L1688, we compile a list of over 300 association members with counterparts in the 2MASS catalog. Membership criteria, such as lithium absorption, X-ray emission, and infrared excess, cover the full range of evolutionary states for young stellar objects. Spectral energy distributions are classified for many association members using infrared photometry obtain...

  7. UV Extinction Towards a Quiescent Molecular Cloud in the SMC

    CERN Document Server

    Apellániz, J Maíz

    2012-01-01

    Context: The mean UV extinction law for the Small Magellanic Cloud (SMC) is usually taken as a template for low-metallicity galaxies. However, its current derivation is based on only five stars, thus placing doubts on its universality. An increase in the number of targets with measured extinction laws in the SMC is necessary to determine its possible dependence on parameters such as metallicity and star-forming activity. Aims: To measure the UV extinction law for several stars in the quiescent molecular cloud SMC B1-1. Methods: We obtained HST/STIS slitless UV spectroscopy of a 25"x25" field of view and we combined it with ground-based NIR and visible photometry of the stars in the field. The results were processed using the Bayesian photometric package CHORIZOS to derive the visible-NIR extinction values for each star. The unextinguished Spectral Energy Distributions (SEDs) obtained in this way were then used to derive the UV extinction law for the four most extinguished stars. We also recalculated the visib...

  8. Clumps and triggered star formation in ionised molecular clouds

    CERN Document Server

    Walch, S; Bisbas, T G; Wunsch, R; Hubber, D A

    2013-01-01

    Infrared shells and bubbles are ubiquitous in the Galaxy and can generally be associated with HII regions formed around young, massive stars. In this paper, we use high-resolution 3D SPH simulations to explore the effect of a single O7 star emitting photons at 10^49 1/s and located at the centre of a molecular cloud with mass 10^4 M_sun and radius 6.4 pc; the internal structure of the cloud is characterised by its fractal dimension, D (with 2.0 <= D <= 2.8), and the variance of its (log-normal) density distribution, sigma_0^2 (with 0.36 <= sigma_0^2 <= 1.42). Our study focuses on the morphology of the swept-up cold gas and the distribution and statistics of the resulting star formation. If the fractal dimension is low, the border of the HII region is dominated by extended shell-like structures, and these break up into a small number of massive high-density clumps which then spawn star clusters; star formation occurs relatively quickly, and delivers somewhat higher stellar masses. Conversely, if th...

  9. Comparing Simulated Emission from Molecular Clouds Using Experimental Design

    CERN Document Server

    Yeremi, Miayan; Offner, Stella; Loeppky, Jason; Rosolowsky, Erik

    2014-01-01

    We propose a new approach to comparing simulated observations that enables us to determine the significance of the underlying physical effects. We utilize the methodology of experimental design, a subfield of statistical analysis, to establish a framework for comparing simulated position-position-velocity data cubes to each other. We propose three similarity metrics based on methods described in the literature: principal component analysis, the spectral correlation function, and the Cramer multi-variate two sample similarity statistic. Using these metrics, we intercompare a suite of mock observational data of molecular clouds generated from magnetohydrodynamic simulations with varying physical conditions. Using this framework, we show that all three metrics are sensitive to changing Mach number and temperature in the simulation sets, but cannot detect changes in magnetic field strength and initial velocity spectrum. We highlight the shortcomings of one-factor-at-a-time designs commonly used in astrophysics an...

  10. Planck early results. XXV. Thermal dust in nearby molecular clouds

    DEFF Research Database (Denmark)

    Bucher, M.; Delabrouille, J.; Giraud-Héraud, Y.

    2011-01-01

    , and the dust optical depth at 250 μm τ250. The temperature map illustrates the cooling of the dust particles in thermal equilibrium with the incident radiation field, from 16 - 17 K in the diffuse regions to 13 - 14 K in the dense parts. The distribution of spectral indices is centred at 1.78, with a standard......Planck allows unbiased mapping of Galactic sub-millimetre and millimetre emission from the most diffuse regions to the densest parts of molecular clouds. We present an early analysis of the Taurus molecular complex, on line-of-sight-averaged data and without component separation. The emission...... blackbody. Significant positive residuals are also detected in the molecular regions and in the 217 GHz and 100 GHz bands, mainly caused by the contribution of the J = 2 → 1 and J = 1 → 0 12CO and 13CO emission lines. We derive maps of the dust temperature T, the dust spectral emissivity index β...

  11. Dense gas in high-latitude molecular clouds

    Energy Technology Data Exchange (ETDEWEB)

    Reach, W.R.; Pound, M.W.; Wilner, D.J. (Univ. of California, Berkeley (United States)); Lee, Y.

    1992-01-01

    The authors have surveyed high-latitude molecular clouds (MBM 12, 7, 55, 40) in spectral lines that are believed to be dense-gas' tracers due to the high H[sub 2] volume density required for collisional excitation. An extensive CS (2-1) line map of MBM 12 revealed emission that is not confined to clumps. Less than 20% of the integrated line emission from the cloud originates in clearly identified clumps with size between 0.2 pc and 0.02 pc in the integrated line map. The bulk of the emission originates from a relatively smooth horseshoe' structure about 0.1 pc wide and 1 pc long. The CS (2-1) map correlates with the published Bell Labs [sup 13] CO map, with significant [sup 13] CO emission even where the CS emission is undetectable. Within the central core, the C[sup 18]O(1-0) and CS(2-1) lines are positively correlated with significant scatter. There is some indication of higher CS/[sup 13]CO in the cores than the horseshoe'. The observed correlations suggest that both the diffuse CS and [sup 13]CO originate from either numerous, unresolved clumps, or the diffuse parts of the cloud. High-spatial-resolution observations of HCO[sup +] from MBM 12 obtained with the BIMA Hat Creek array demonstrated that the main core emission is primarily on spatial scales greater than 0.004 pc. It appears that the authors have resolved most of the spatial structure of the dense-gas' tracers and have found that the emission is primarily diffuse. To understand the excitation mechanism of the CS rotational levels, a multitransitional study of the 1-0, 2-1, and 3-2 lines is being performed. The CS excitation may be governed by electron collisions in regions with H[sub 2] column densities an order of magnitude lower than the critical density' of [approx gt] 2 [times] 10[sup 4] cm[sup -3]. If electron collisions are populating the CS levels, then the CS and [sup 13]CO lines can both be produced in the outer parts of the cloud, explaining their positive correlation

  12. Star Formation in Disk Galaxies. I. Formation and Evolution of Giant Molecular Clouds via Gravitational Instability and Cloud Collisions

    CERN Document Server

    Tasker, Elizabeth J

    2008-01-01

    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 3D adaptive mesh refinement (AMR) numerical simulations that follow both the global evolution on scales of ~20kpc and resolve down to scales ~=100cm^-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 ~140Myr a large fraction of the gas in the disk has fragmented in clouds, with typical masses ~10^6Msun, similar to 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 keeps the clouds only moderately gravitationally bound, with virial pa...

  13. A Large Catalog of Accurate Distances to Molecular Clouds from PS1 Photometry

    CERN Document Server

    Schlafly, E F; Finkbeiner, D P; Rix, H -W; Bell, E F; Burgett, W S; Chambers, K C; Draper, P W; Hodapp, K W; Kaiser, N; Magnier, E A; Martin, N F; Metcalfe, N; Price, P A; Tonry, J L

    2014-01-01

    Distance measurements to molecular clouds are important, but are often made separately for each cloud of interest, employing very different different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. (2014). We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. (1985) catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the sys...

  14. The Properties of Bound and Unbound Molecular Cloud Populations Formed in Galactic Disc Simulations

    CERN Document Server

    Ward, Rachel L; Wadsley, James; Sills, Alison; Couchman, H M P

    2015-01-01

    We explore the effect of galactic environment on properties of molecular clouds. Using clouds formed in a large-scale galactic disc simulation, we measure the observable properties from synthetic column density maps. We confirm that a significant fraction of unbound clouds forms naturally in a galactic disc environment and that a mixed population of bound and unbound clouds can match observed scaling relations and distributions for extragalactic molecular clouds. By dividing the clouds into inner and outer disc populations, we compare their distributions of properties and test whether there are statistically significant differences between them. We find that clouds in the outer disc have lower masses, sizes, and velocity dispersions as compared to those in the inner disc for reasonable choices of the inner/outer boundary. We attribute the differences to the strong impact of galactic shear on the disc stability at large galactocentric radii. In particular, our Toomre analysis of the disc shows a narrowing enve...

  15. The Molecular Clouds Fueling A 1/5 Solar Metallicity Starburst

    Science.gov (United States)

    Kepley, Amanda A.; Leroy, Adam K.; Johnson, Kelsey E.; Sandstrom, Karin; Chen, C.-H. Rosie

    2016-09-01

    Using the Atacama Large Millimeter/submillimeter Array, we have made the first high spatial and spectral resolution observations of the molecular gas and dust in the prototypical blue compact dwarf galaxy II Zw 40. The {}12{CO}(2-1) and {}12{CO}(3-2) emission is clumpy and distributed throughout the central star-forming region. Only one of eight molecular clouds has associated star formation. The continuum spectral energy distribution is dominated by free-free and synchrotron; at 870 μm, only 50% of the emission is from dust. We derive a CO-to-H2 conversion factor using several methods, including a new method that uses simple photodissocation models and resolved CO line intensity measurements to derive a relationship that uniquely predicts {α }{co} for a given metallicity. We find that the CO-to-H2 conversion factor is 4-35 times that of the Milky Way (18.1-150.5 {M}⊙ {({{K}}{km}{{{s}}}-1{{pc}}2)}-1). The star formation efficiency of the molecular gas is at least 10 times higher than that found in normal spiral galaxies, which is likely due to the burst-dominated star formation history of II Zw 40 rather than an intrinsically higher efficiency. The molecular clouds within II Zw 40 resemble those in other strongly interacting systems like the Antennae: overall they have high size-linewidth coefficients and molecular gas surface densities. These properties appear to be due to the high molecular gas surface densities produced in this merging system rather than to increased external pressure. Overall, these results paint a picture of II Zw 40 as a complex, rapidly evolving system whose molecular gas properties are dominated by the large-scale gas shocks from its ongoing merger.

  16. Quantifying and Predicting the Presence of Clouds in Exoplanet Atmospheres

    CERN Document Server

    Stevenson, Kevin B

    2016-01-01

    One of the most outstanding issues in exoplanet characterization is understanding the prevalence of obscuring clouds and hazes in their atmospheres. The ability to predict the presence of clouds/hazes a priori is an important goal when faced with limited telescope resources and advancements in atmospheric characterization that rely on the detection of spectroscopic features. As a means to identify favorable targets for future studies with HST and JWST, we use published HST/WFC3 transmission spectra to determine the strength of each planet's water feature, as defined by the H2O - J index. By expressing this parameter in units of atmospheric scale height, we provide a means to efficiently compare the size of spectral features over a physically diverse sample of exoplanets. We find the H2O - J index to be strongly correlated with planet temperature when $T_{eq} 1) and those below at least one of these thresholds are increasingly likely to have predominantly cloudy atmospheres with muted spectral features (H2O -...

  17. A submillimetre survey of the kinematics of the Perseus molecular cloud - II. Molecular outflows

    CERN Document Server

    Curtis, Emily I; Swift, Jonathan J; Williams, Jonathan P

    2010-01-01

    We present a census of molecular outflows across four active regions of star formation in the Perseus molecular cloud (NGC 1333, IC348/HH211, L1448 and L1455), totalling an area of over 1000 sq arcmin. This is one of the largest surveys of outflow evolution in a single molecular cloud published to date. We analyse large-scale, sensitive CO J=3-2 datasets from the James Clerk Maxwell Telescope, including new data towards NGC 1333. Where possible we make use of our complementary 13CO and C18O data to correct for the 12CO optical depth and measure ambient cloud properties. Of the 65 submillimetre cores in our fields, we detect outflows towards 45. We compare various parameters between the outflows from Class 0 and I protostars, including their mass, momentum, energy and momentum flux. Class 0 outflows are longer, faster, more massive and have more energy than Class I outflows. The dynamical time-scales we derive from these outflows are uncorrelated to the age of the outflow driving source, computed from the prot...

  18. Heavy rainfall prediction applying satellite-based cloud data assimilation over land

    Science.gov (United States)

    Seto, Rie; Koike, Toshio; Rasmy, Mohamed

    2016-08-01

    To optimize flood management, it is crucial to determine whether rain will fall within a river basin. This requires very fine precision in prediction of rainfall areas. Cloud data assimilation has great potential to improve the prediction of precipitation area because it can directly obtain information on locations of rain systems. Clouds can be observed globally by satellite-based microwave remote sensing. Microwave observation also includes information of latent heat and water vapor associated with cloud amount, which enables the assimilation of not only cloud itself but also the cloud-affected atmosphere. However, it is difficult to observe clouds over land using satellite microwave remote sensing, because their emissivity is much lower than that of the land surface. To overcome this challenge, we need appropriate representation of heterogeneous land emissivity. We developed a coupled atmosphere and land data assimilation system with the Weather Research and Forecasting Model (CALDAS-WRF), which can assimilate soil moisture, vertically integrated cloud water content over land, and heat and moisture within clouds simultaneously. We applied this system to heavy rain events in Japan. Results show that the system effectively assimilated cloud signals and produced very accurate cloud and precipitation distributions. The system also accurately formed a consistent atmospheric field around the cloud. Precipitation intensity was also substantially improved by appropriately representing the local atmospheric field. Furthermore, combination of the method and operationally analyzed dynamical and moisture fields improved prediction of precipitation duration. The results demonstrate the method's promise in dramatically improving predictions of heavy rain and consequent flooding.

  19. The chemistry and kinematics of two molecular clouds near Sagittarius A*

    Science.gov (United States)

    Lopez, John A. P.; Cunningham, Maria R.; Jones, Paul A.; Marshall, Jonathan P.; Bronfman, Leonardo; Lo, Nadia; Walsh, Andrew J.

    2016-12-01

    We have analysed the chemical and kinematic properties of the 20 and 50 km s-1 molecular clouds in the Central Molecular Zone of the Milky Way Galaxy, as well as those of the molecular ridge bridging these two clouds. Our work has utilized 37 molecular transitions in the 0.65, 3 and 7-mm wavebands, from the Mopra and NANTEN2 telescopes. The 0.65-mm NANTEN2 data highlights a dense condensation of emission within the western part of the 20 km s-1 cloud, visible in only four other transitions, which are 3-mm H13CN (1-0), H13CO+ (1-0), HNC (1-0) and N2H+ (1-0), suggesting that the condensation is moderately optically thick and cold. We find that while the relative chemical abundances between both clouds are alike in many transitions, suggesting little variation in the chemistry between both clouds; the 20 km s-1, cold cloud is brighter than the 50 km s-1 cloud in shock and high density tracers. The spatial distribution of enhanced emission is widespread in the 20 km s-1 cloud, as shown via line ratio maps. The position velocity diagrams across both clouds indicate that the gas is well mixed. We show that the molecular ridge is most likely part of the 20 km s-1 cloud and that both of them may possibly extend to include the 50 km s-1 cloud, as part of one larger cloud. Furthermore, we expect that the 20 km s-1 cloud is being tidally sheared as a result of the gravitational potential from Sgr A*

  20. Identification of Ambient Molecular Clouds Associated with Galactic Supernova Remnant IC443

    CERN Document Server

    Lee, Jae-Joon; Snell, Ronald L; Yun, Min S; Heyer, Mark H; Burton, Michael G

    2012-01-01

    The Galactic supernova remnant (SNR) IC443 is one of the most studied core-collapse SNRs for its interaction with molecular clouds. However, the ambient molecular clouds with which IC443 is interacting have not been thoroughly studied and remain poorly understood. Using Five College Radio Astronomy Observatory 14m telescope, we obtained fully sampled maps of ~ 1{\\deg} \\times 1{\\deg} region toward IC443 in the 12CO J=1-0 and HCO+ J=1-0 lines. In addition to the previously known molecular clouds in the velocity range v_lsr = -6 to -1 km/s (-3 km/s clouds), our observations reveal two new ambient molecular cloud components: small (~ 1') bright clouds in v_lsr = -8 to -3 km/s (SCs), and diffuse clouds in v_lsr = +3 to +10 km/s (+5 km/s clouds). Our data also reveal the detailed kinematics of the shocked molecular gas in IC443, however the focus of this paper is the physical relationship between the shocked clumps and the ambient cloud components. We find strong evidence that the SCs are associated with the shocke...

  1. Molecular cloud formation as seen in synthetic Hi and molecular gas observations

    CERN Document Server

    Heiner, Jonathan S; Ballesteros-Paredes, Javier

    2014-01-01

    We present synthetic Hi and CO observations of a simulation of decaying turbulence in the thermally bistable neutral medium. We first present the simulation, with clouds initially consisting of clustered clumps. Self-gravity causes these clump clusters to form more homogeneous dense clouds. We apply a simple radiative transfer algorithm, and defining every cell with > 1 as molecular. We then produce maps of Hi, CO-free molecular gas, and CO, and investigate the following aspects: i) The spatial distribution of the warm, cold, and molecular gas, finding the well-known layered structure, with molecular gas surrounded by cold Hi, surrounded by warm Hi. ii) The velocity of the various components, with atomic gas generally flowing towards the molecular gas, and that this motion is reflected in the frequently observed bimodal shape of the Hi profiles. This conclusion is tentative, because we do not include feedback. iii) The production of Hi self-absorption (HISA) profiles, and the correlation of HISA with molecul...

  2. Prediction Based Proactive Thermal Virtual Machine Scheduling in Green Clouds

    OpenAIRE

    Supriya Kinger; Rajesh Kumar; Anju Sharma

    2014-01-01

    Cloud computing has rapidly emerged as a widely accepted computing paradigm, but the research on Cloud computing is still at an early stage. Cloud computing provides many advanced features but it still has some shortcomings such as relatively high operating cost and environmental hazards like increasing carbon footprints. These hazards can be reduced up to some extent by efficient scheduling of Cloud resources. Working temperature on which a machine is currently running can be taken as a crit...

  3. Simulating the Formation of Molecular Clouds. II. Rapid Formation from Turbulent Initial Conditions

    Science.gov (United States)

    Glover, Simon C. O.; Mac Low, Mordecai-Mark

    2007-04-01

    In this paper we present results from a large set of numerical simulations that demonstrate that H2 formation occurs rapidly in turbulent gas. Starting with purely atomic hydrogen, large quantities of molecular hydrogen can be produced on timescales of 1-2 Myr, given turbulent velocity dispersions and magnetic field strengths consistent with observations. Moreover, as our simulations underestimate the effectiveness of H2 self-shielding and dust absorption, we can be confident that the molecular fractions that we compute are strong lower limits on the true values. The formation of large quantities of molecular gas on the timescale required by rapid cloud formation models therefore appears to be entirely plausible. We also investigate the density and temperature distributions of gas in our model clouds. We show that the density probability distribution function is approximately lognormal, with a dispersion that agrees well with the prediction of Padoan and coworkers. The temperature distribution is similar to that of a polytrope, with an effective polytropic index γeff~=0.8, although at low gas densities, the scatter of the actual gas temperature around this mean value is considerable, and the polytropic approximation does not capture the full range of behavior of the gas.

  4. Molecular Oxygen in Oort Cloud Comet 1P/Halley

    CERN Document Server

    Rubin, Martin; van Dishoeck, Ewine F; Schwehm, Gerhard

    2015-01-01

    Recently the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O2, in the coma of Jupiter family comet 67P/Churyumov-Gerasimenko of O2/H2O = 3.80+/-0.85%. It could be shown that O2 is indeed a parent species and that the derived abundances point to a primordial origin. One crucial question is whether the O2 abundance is peculiar to comet 67P/Churyumov-Gerasimenko or Jupiter family comets in general or whether also Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained by the Neutral Mass Spectrometer instrument obtained during the flyby by the European Space Agency's Giotto probe at comet 1P/Halley. Our investigation indicates that a production rate of O2 of 3.7+/-1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O2 might be a rather common and abundant parent species.

  5. MOLECULAR OXYGEN IN OORT CLOUD COMET 1P/HALLEY

    Energy Technology Data Exchange (ETDEWEB)

    Rubin, M.; Altwegg, K. [Physikalisches Institut, University of Bern, Sidlerstrasse 5, CH-3012 Bern (Switzerland); Dishoeck, E. F. van [Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands); Schwehm, G. [ESA (retired) Science Operations Department, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk (Netherlands)

    2015-12-10

    Recently, the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O{sub 2}, in the coma of Jupiter family comet 67P/Churyumov–Gerasimenko of O{sub 2}/H{sub 2}O = 3.80 ± 0.85%. It could be shown that O{sub 2} is indeed a parent species and that the derived abundances point to a primordial origin. Crucial questions are whether the O{sub 2} abundance is peculiar to comet 67P/Churyumov–Gerasimenko or Jupiter family comets in general, and also whether Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained by the Neutral Mass Spectrometer instrument during the flyby by the European Space Agency's Giotto probe of comet 1P/Halley. Our investigation indicates that a production rate of O{sub 2} of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O{sub 2} might be a rather common and abundant parent species.

  6. Contraction Signatures Toward Dense Cores in the Perseus Molecular Cloud

    CERN Document Server

    Campbell, J L; Martin, P G; Caselli, P; Kauffmann, J; Pineda, J E

    2016-01-01

    We report the results of an HCO+ (3-2) and N2D+ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO+ asymmetry using a dimensionless asymmetry parameter $\\delta_v$, and identify 20 cores with significant blue or red line asymmetries in optically-thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO+ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the $\\delta_v$ and collapse model results, we find that $\\delta_v$ is a good tracer of core contraction if the optically-thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03 km/s) to supersonic (0.4 km/s), where the supersonic contraction speeds may trace global rather than local core contraction. Most cor...

  7. CO depletion --- An evolutionary tracer for molecular clouds

    CERN Document Server

    Liu, Tie; Zhang, Huawei

    2013-01-01

    Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of Planck satellite with the molecular data of $^{12}$CO/$^{13}$CO (1-0) lines from observations with the Purple Mountain Observatory (PMO) 14 m telescope, we investigate the CO abundance, CO depletion and CO-to-H$_{2}$ conversion factor of 674 clumps in the early cold cores (ECC) sample. The median and mean values of the CO abundance are 6.2$\\times10^{-5}$ and 9.1$\\times10^{-5}$, respectively. The mean and median of CO depletion factor are 2.8 and 1.4, respectively. The median value of $X_{CO-to-H_{2}}$ for the whole sample is $3.3\\times10^{20}$ cm$^{-2}$K$^{-1}$km$^{-1}$ s. The CO abundance, CO depletion factor and CO-to-H$_{2}$ conversion factor seems to be strongly correlated to other physical parameters (e.g. dust temperature, dust emissivity spectra index and column density). CO gas severely freeze out in colde...

  8. An Unbiased Survey for Molecular Clouds in the Southern Galactic Warp

    CERN Document Server

    Nakagawa, M; Mizuno, A; Fukui, Y; Nakagawa, Masanori

    2005-01-01

    We have made an unbiased survey for molecular clouds in the Galactic Warp. This survey, covering an area of 56 square degrees at l = 252 deg to 266 deg and b = -5 deg to -1 deg, has revealed 70 molecular clouds, while only 6 clouds were previously known in the region. The number of molecular clouds is, then, an order of magnitude greater than previously known in this sector at R > 14.5 kpc. The mass of the clouds is in a range from 7.8x10(2) Mo to 8.4x10(4) Mo, significantly less than the most massive giant molecular clouds in the inner disk, ~10(6) Mo, while the cloud mass spectrum characterized by a power law is basically similar to other parts of the Galaxy. The X factor, N(H2)/Wco(12CO), derived from the molecular clouds in the Warp is estimated to be 3.5(+/-1.8) times larger than that in the inner disk. The total molecular mass in the Warp is estimated as 7.3x10(5) Mo, and total mass in the far-outer Galaxy (R > 14.5 kpc) can be estimated as 2x10(7) Mo. The spatial correlation between the CO and HI distr...

  9. Millimeter dust continuum emission revealing the true mass of giant molecular clouds in the Small Magellanic Cloud

    Science.gov (United States)

    Bot, C.; Boulanger, F.; Rubio, M.; Rantakyro, F.

    2007-08-01

    Context: CO observations have been the best way so far to trace molecular gas in external galaxies, but in low metallicity environments the gas mass deduced could be largely underestimated due to enhanced photodissociation of the CO molecule. Large envelopes of H2 could therefore be missed by CO observations. Aims: At present, the kinematic information of CO data cubes are used to estimate virial masses and trace the total mass of the molecular clouds. Millimeter dust emission can also be used as a dense gas tracer and could unveil H2 envelopes lacking CO. These different tracers must be compared in different environments. Methods: This study compares virial masses to masses deduced from millimeter emission, in two GMC samples: the local molecular clouds in our Galaxy (10^4-105 M⊙), and their equivalents in the Small Magellanic Cloud (SMC), one of the nearest low metallicity dwarf galaxies. Results: In our Galaxy, mass estimates deduced from millimeter (FIRAS) emission are consistent with masses deduced from gamma ray analysis and therefore trace the total mass of the clouds. Virial masses are systematically larger (twice on average) than mass estimates from millimeter dust emission. This difference decreases toward high masses and has been reported in previous studies. This is not the case for SMC giant molecular clouds: molecular cloud masses deduced from SIMBA millimeter observations are systematically higher (twice on average for conservative values of the dust to gas ratio and dust emissivity) than the virial masses from SEST CO observations. The observed excess cannot be accounted for by any plausible change of dust properties. Taking a general form for the virial theorem, we show that a magnetic field strength of ~15 μG in SMC clouds could provide additional support for the clouds and explain the difference observed. Conclusions: We conclude that masses of SMC molecular clouds have so far been underestimated. Magnetic pressure may contribute significantly

  10. A survey for Galactic supernova remnant/molecular cloud interactions ssing carbon monoxide

    Science.gov (United States)

    Kilpatrick, Charles; Rieke, George; Bieging, John

    2016-06-01

    Supernova remnants are one of the primary engines through which stars add energy to the interstellar medium. The efficiency of this transfer of energy is enhanced where supernova remnants encounter dense interstellar gas, such as in molecular clouds. Unique signatures have been observed toward these supernova remnant/molecular cloud interactions in the form of unusual molecular line profiles and bright non-thermal radiation. The sites of these interactions also provide some of the best examples for evidence of cosmic-ray acceleration and Galactic sources of very high-energy gamma-rays. Despite the large number of individual studies that examine supernova remnant/molecular cloud interactions, very little is known about their overall rates and characteristics. This lack of information limits the usefulness of individual supernova remnant/molecular cloud interactions to enhance our understanding of supernova feedback and cosmic-ray acceleration. I will discuss recent work studying large populations of supernova remnants in the 12CO J = 2 ‑ 1 and J = 3 ‑ 2 lines and the observational signatures associated with molecular shocks from supernova ejecta. Broadened molecular lines and molecular line ratios indicative of warm gas can be used to identify and characterize populations of supernova remnant/molecular cloud interactions. From this large sample, I will discuss new constraints on the energetic processes to which supernova remnants contribute, especially the rate of GeV and TeV gamma-ray production associated with supernova remnant/molecular cloud interfaces.

  11. STELLAR 'EGGS' EMERGE FROM MOLECULAR CLOUD (Star-Birth Clouds in M16)

    Science.gov (United States)

    2002-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation'. As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules'. The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 6,500 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo:

  12. Constructing multiscale gravitational energy spectra from molecular cloud surface density PDF - interplay between turbulence and gravity

    Science.gov (United States)

    Li, Guang-Xing; Burkert, Andreas

    2016-09-01

    Gravity is believed to be important on multiple physical scales in molecular clouds. However, quantitative constraints on gravity are still lacking. We derive an analytical formula which provides estimates on multiscale gravitational energy distribution using the observed surface density probability distribution function (PDF). Our analytical formalism also enables one to convert the observed column density PDF into an estimated volume density PDF, and to obtain average radial density profile ρ(r). For a region with N_col ˜ N^{-γ _N}, the gravitational energy spectra is E_p(k)˜ k^{-4(1 - 1/γ _N)}. We apply the formula to observations of molecular clouds, and find that a scaling index of -2 of the surface density PDF implies that ρ ˜ r-2 and Ep(k) ˜ k-2. The results are valid from the cloud scale (a few parsec) to around ˜ 0.1 pc. Because of the resemblance the scaling index of the gravitational energy spectrum and the that of the kinetic energy power spectrum of the Burgers turbulence (where E ˜ k-2), our result indicates that gravity can act effectively against turbulence over a multitude of physical scales. This is the critical scaling index which divides molecular clouds into two categories: clouds like Orion and Ophiuchus have shallower power laws, and the amount of gravitational energy is too large for turbulence to be effective inside the cloud. Because gravity dominates, we call this type of cloud g-type clouds. On the other hand, clouds like the California molecular cloud and the Pipe nebula have steeper power laws, and turbulence can overcome gravity if it can cascade effectively from the large scale. We call this type of cloud t-type clouds. The analytical formula can be used to determine if gravity is dominating cloud evolution when the column density PDF can be reliably determined.

  13. Velocity Anisotropy in Self-gravitating Molecular Clouds. I. Simulation

    Science.gov (United States)

    Otto, Frank; Ji, Weiguang; Li, Hua-bai

    2017-02-01

    The complex interplay between turbulence, magnetic fields, and self-gravity leads to the formation of molecular clouds out of the diffuse interstellar medium (ISM). One avenue of studying this interplay is by analyzing statistical features derived from observations, where the interpretation of these features is greatly facilitated by comparisons with numerical simulations. Here we focus on the statistical anisotropy present in synthetic maps of velocity centroid data, which we derive from three-dimensional magnetohydrodynamic simulations of a turbulent, magnetized, self-gravitating patch of ISM. We study how the orientation and magnitude of the velocity anisotropy correlate with the magnetic field and with the structures generated by gravitational collapse. Motivated by recent observational constraints, our simulations focus on the supersonic (sonic Mach number { M }≈ 2{--}17) but sub- to trans-alfvénic (alfvénic Mach number {{ M }}{{A}}≈ 0.2{--}1.2) turbulence regime, and we consider clouds that are barely to mildly magnetically supercritical (mass-to-flux ratio equal to once or twice the critical value). Additionally we explore the impact of the turbulence driving mechanism (solenoidal or compressive) on the velocity anisotropy. While we confirm previous findings that the velocity anisotropy generally aligns well with the plane-of-sky magnetic field, our inclusion of the effects of self-gravity reveals that in regions of higher column density, the velocity anisotropy may be destroyed or even reoriented to align with the gravitationally formed structures. We provide evidence that this effect is not necessarily due to the increase of {{ M }}{{A}} inside the high-density regions.

  14. Hierarchical star cluster assembly in globally collapsing molecular clouds

    Science.gov (United States)

    Vázquez-Semadeni, Enrique; González-Samaniego, Alejandro; Colín, Pedro

    2017-05-01

    We discuss the mechanism of cluster formation in a numerical simulation of a molecular cloud (MC) undergoing global hierarchical collapse, focusing on how the gas motions in the parent cloud control the assembly of the cluster. The global collapse implies that the star formation rate (SFR) increases over time. The collapse is hierarchical because it consists of small-scale collapses within larger scale ones. The latter culminate a few Myr later than the first small-scale ones and consist of filamentary flows that accrete on to massive central clumps. The small-scale collapses consist of clumps that are embedded in the filaments and falling on to the large-scale collapse centres. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps, so that the filaments feed both gas and stars to the massive central clump. This process leads to the presence of a few older stars in a region where new protostars are forming, and also to a self-similar structure, in which each unit is composed of smaller scale subunits that approach each other and may merge. Because the older stars formed in the filaments share the infall motion of the gas on to the central clump, they tend to have larger velocities and to be distributed over larger areas than the younger stars formed in the central clump. Finally, interpreting the initial mass function (IMF) simply as a probability distribution implies that massive stars only form once the local SFR is large enough to sample the IMF up to high masses. In combination with the increase of the SFR, this implies that massive stars tend to appear late in the evolution of the MC, and only in the central massive clumps. We discuss the correspondence of these features with observed properties of young stellar clusters, finding very good qualitative agreement.

  15. BDDCS Class Prediction for New Molecular Entities

    DEFF Research Database (Denmark)

    Broccatelli, Fabio; Cruciani, Gabriele; Benet, Leslie Z.

    2012-01-01

    with in vitro assays, could anticipate disposition and potential DDIs of new molecular entities (NMEs). Here we describe a computational procedure for predicting BDDCS class from molecular structures. The model was trained on a set of 300 oral drugs, and validated on an external set of 379 oral drugs, using 17...

  16. Dissipation of Molecular Cloud Turbulence by Magnetohydrodynamic Shockwaves

    Science.gov (United States)

    Lehmann, Andrew; Wardle, Mark

    2015-08-01

    The character of star formation is intimately related to the supersonic magnetohydrodynamic (MHD) turbulent dynamics of the giant molecular clouds in which stars form. A significant amount of the turbulent energy dissipates in low velocity shock waves. These shocks cause molecular line cooling of the compressed and heated gas, and so their radiative signatures probe the nature of the turbulence. In MHD fluids the three distinct families of shocks—fast, intermediate and slow—differ in how they compress and heat the molecular gas, and so observational differences between them may also distinguish driving modes of turbulent regions.Here we use a two-fluid model to compare the characteristics of one-dimensional fast and slow MHD shocks. Fast MHD shocks are magnetically driven, forcing ion species to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where all the fluid variables only weakly change in the shock front. In contrast, slow MHD shocks are driven by gas pressure where neutral species collide with ion species in a thin hot slab that closely resembles an ordinary gas dynamic shock.We computed observational diagnostics for fast and slow shocks at velocities vs = 2-4 km/s and preshock Hydrogen nuclei densities n(H) = 102-4 cm-3. We followed the abundances of molecules relevant for a simple oxygen chemistry and include cooling by CO, H2 and H2O. Estimates of intensities of CO rotational lines show that high-J lines, above J = 6→5, are more strongly excited in slow MHD shocks. We discuss how these shocks could help interpret recently observed anomalously strong mid- and high-J CO lines emitted by warm gas in the Milky Way and external galaxies, and implications for simulations of MHD turbulence.

  17. Applying a one-dimensional PDR model to the Taurus molecular cloud and its atomic envelope

    CERN Document Server

    Heiner, J S

    2012-01-01

    In this contribution, we test our previously published one-dimensional PDR model for deriving total hydrogen volume densities from HI column density measurements in extragalactic regions by applying it to the Taurus molecular cloud, where its predictions can be compared to available data. Also, we make the first direct detailed comparison of our model to CO(1-0) and far-infrared emission. Using an incident UV flux G0 of 4.25 ({\\chi} = 5) throughout the main body of the cloud, we derive total hydrogen volume densities of \\approx 430 cm-3, consistent with the extensive literature available on Taurus. The distribution of the volume densities shows a log-normal shape with a hint of a power-law shape on the high density end. We convert our volume densities to H2 column densities assuming a cloud depth of 5 parsec and compare these column densities to observed CO emission. We find a slope equivalent to a CO conversion factor relation that is on the low end of reported values for this factor in the literature (0.9 x...

  18. Interstellar CN and CH+ in Diffuse Molecular Clouds: 12C/13C Ratios and CN Excitation

    CERN Document Server

    Ritchey, A M; Lambert, D L

    2010-01-01

    We present very high signal-to-noise ratio absorption-line observations of CN and CH+ along 13 lines of sight through diffuse molecular clouds. The data are examined to extract precise isotopologic ratios of 12CN/13CN and 12CH+/13CH+ in order to assess predictions of diffuse cloud chemistry. Our results on 12CH+/13CH+ confirm that this ratio does not deviate from the ambient 12C/13C ratio in local interstellar clouds, as expected if the formation of CH+ involves nonthermal processes. We find that 12CN/13CN, however, can be significantly fractionated away from the ambient value. The dispersion in our sample of 12CN/13CN ratios is similar to that found in recent surveys of 12CO/13CO. For sight lines where both ratios have been determined, the 12CN/13CN ratios are generally fractionated in the opposite sense compared to 12CO/13CO. Chemical fractionation in CO results from competition between selective photodissociation and isotopic charge exchange. An inverse relationship between 12CN/13CN and 12CO/13CO follows ...

  19. Unfolding the laws of star formation: the density distribution of molecular clouds.

    Science.gov (United States)

    Kainulainen, Jouni; Federrath, Christoph; Henning, Thomas

    2014-04-11

    The formation of stars shapes the structure and evolution of entire galaxies. The rate and efficiency of this process are affected substantially by the density structure of the individual molecular clouds in which stars form. The most fundamental measure of this structure is the probability density function of volume densities (ρ-PDF), which determines the star formation rates predicted with analytical models. This function has remained unconstrained by observations. We have developed an approach to quantify ρ-PDFs and establish their relation to star formation. The ρ-PDFs instigate a density threshold of star formation and allow us to quantify the star formation efficiency above it. The ρ-PDFs provide new constraints for star formation theories and correctly predict several key properties of the star-forming interstellar medium.

  20. Cloud computing approaches for prediction of ligand binding poses and pathways.

    Science.gov (United States)

    Lawrenz, Morgan; Shukla, Diwakar; Pande, Vijay S

    2015-01-22

    We describe an innovative protocol for ab initio prediction of ligand crystallographic binding poses and highly effective analysis of large datasets generated for protein-ligand dynamics. We include a procedure for setup and performance of distributed molecular dynamics simulations on cloud computing architectures, a model for efficient analysis of simulation data, and a metric for evaluation of model convergence. We give accurate binding pose predictions for five ligands ranging in affinity from 7 nM to > 200 μM for the immunophilin protein FKBP12, for expedited results in cases where experimental structures are difficult to produce. Our approach goes beyond single, low energy ligand poses to give quantitative kinetic information that can inform protein engineering and ligand design.

  1. Molecular clouds toward the super star cluster NGC 3603; possible evidence for a cloud-cloud collision in triggering the cluster formation

    Energy Technology Data Exchange (ETDEWEB)

    Fukui, Y.; Ohama, A.; Hanaoka, N.; Furukawa, N.; Torii, K.; Hasegawa, K.; Fukuda, T.; Soga, S.; Moribe, N.; Kuroda, Y.; Hayakawa, T.; Kuwahara, T.; Yamamoto, H.; Okuda, T. [Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Dawson, J. R. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); Mizuno, N.; Kawamura, A. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Onishi, T.; Maezawa, H. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531 (Japan); Mizuno, A., E-mail: fukui@a.phys.nagoya-u.ac.jp [Solar-terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan)

    2014-01-01

    We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions {sup 12}CO(J = 2-1, J = 1-0) and {sup 13}CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s{sup –1} and 28 km s{sup –1} are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s{sup –1}. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.

  2. The HI Probability Distribution Function and the Atomic-to-Molecular Transition in Molecular Clouds

    CERN Document Server

    Imara, Nia

    2016-01-01

    We characterize the column density probability distributions functions (PDFs) of the atomic hydrogen gas, HI, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic HI Survey to derive column density maps and PDFs. We find that the peaks of the HI PDFs occur at column densities ranging from ~1-2$\\times 10^{21}$ cm$^2$ (equivalently, ~0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of $\\sigma_{HI}\\approx 10^{20}$ cm$^2$ (~0.1 mag). We also investigate the HI-to-H$_2$ transition towards the cloud complexes and estimate HI surface densities ranging from 7-16 $M_\\odot$ pc$^{-2}$ at the transition. We propose that the HI PDF is a fitting tool for identifying the HI-to-H$_2$ transition column in Galactic MCs.

  3. The H I Probability Distribution Function and the Atomic-to-molecular Transition in Molecular Clouds

    Science.gov (United States)

    Imara, Nia; Burkhart, Blakesley

    2016-10-01

    We characterize the column-density probability distribution functions (PDFs) of the atomic hydrogen gas, H i, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic H i Survey to derive column-density maps and PDFs. We find that the peaks of the H i PDFs occur at column densities in the range ˜1-2 × 1021 {{cm}}-2 (equivalently, ˜0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of {σ }{{H}{{I}}}≈ {10}20 {{cm}}-2 (˜0.1 mag). We also investigate the H i-to-H2 transition toward the cloud complexes and estimate H i surface densities ranging from 7 to 16 {M}⊙ {{pc}}-2 at the transition. We propose that the H i PDF is a fitting tool for identifying the H i-to-H2 transition column in Galactic MCs.

  4. The structure of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Gredel, Roland; van Dishoeck, Ewine F.; de Vries, Cor P.; Black, John H.

    1992-04-01

    Optical absorption line observations and millimeter emission of the high-latitude cloud toward the star HD 21021 are reported. The cloud was mapped with the ESO submillimeter telescope. Maps of (C-12)O and (C-13)O emission are presented and the line profiles and velocity structure of the cloud are discussed. The optical absorption line observations allow an independent determination of the H2 column density along the line of sight. The molecular column densities found in this cloud were consistent with those measured in diffuse and translucent clouds. Attention is given to the physical and chemical properties of the cloud with reference to chemical models. Analysis indicates that small fluctuations in H2 column density and other factors can produce large variations of CO abundance and column density in clouds where carbon is just being transformed into CO.

  5. Observations of H2O maser sources in Orion-Monoceros Molecular Clouds with VERA

    CERN Document Server

    Hirota, T

    2004-01-01

    We present results of phase-referencing VLBI observations of water maser sources in Orion-Monoceros Molecular Clouds with VERA (VLBI Exploration of Radio Astrometry), which is newly constructed Japanese VLBI network. Main topics of this poster are (1) the aim of one of the first scientific projects for VERA "3-Dimensional Structure and Kinematics of Orion-Monoceros Molecular Cloud Complex"; (2) current status (sensitivity and astrometric accuracy) of phase-referencing VLBI observations with VERA; and (3) results of VLBI observations of water sources in Orion-Monoceros Molecular Clouds with VERA.

  6. Building a Tax Predictive Model Based on the Cloud Neural Network

    Institute of Scientific and Technical Information of China (English)

    田永青; 李志; 朱仲英

    2003-01-01

    Tax is very important to the whole country, so a scientific tax predictive model is needed. This paper introduces the theory of the cloud model. On this basis, it presents a cloud neural network, and analyzes the main factors which influence the tax revenue. Then if proposes a tax predictive model based on the cloud neural network. The model combines the strongpoints of the cloud model and the neural network. The experiment and simulation results show the effectiveness of the algorithm in this paper.

  7. 74 MHz Nonthermal Emission from Molecular Clouds: Evidence for a Cosmic Ray Dominated Region at the Galactic Center

    Science.gov (United States)

    Yusef-Zadeh, F.; Wardle, M.; Lis, D.; Viti, S.; Brogan, C.; Chambers, E.; Pound, M.; Rickert, M.

    2013-10-01

    We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free-free absorption along the line of sight. We focus on one cloud, G0.13-0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (α327MHz74MHz = 1.3 ± 0.3) nonthermal emission from the Galactic center region. This cloud lies adjacent to the nonthermal radio filaments of the Arc near l - 0.2° and is a strong source of 74 MHz continuum, SiO (2-1), and Fe I Kα 6.4 keV line emission. This three-way correlation provides the most compelling evidence yet that relativistic electrons, here traced by 74 MHz emission, are physically associated with the G0.13-0.13 molecular cloud and that low-energy cosmic ray electrons are responsible for the Fe I Kα line emission. The high cosmic ray ionization rate -10-13 s-1 H-1 is responsible for heating the molecular gas to high temperatures and allows the disturbed gas to maintain a high-velocity dispersion. Large velocity gradient (LVG) modeling of multitransition SiO observations of this cloud implies H2 densities -104-5 cm-3 and high temperatures. The lower limit to the temperature of G0.13-0.13 is -100 K, whereas the upper limit is as high as 1000 K. Lastly, we used a time-dependent chemical model in which cosmic rays drive the chemistry of the gas to investigate for molecular line diagnostics of cosmic ray heating. When the cloud reaches chemical equilibrium, the abundance ratios of HCN/HNC and N2H+/HCO+ are consistent with measured values. In addition, significant abundance of SiO is predicted in the cosmic ray dominated region of the Galactic center. We discuss different possibilities to account for the origin of widespread SiO emission detected from Galactic center molecular clouds.

  8. Dynamics of molecular clouds: observations, simulations, and NIF experiments

    Science.gov (United States)

    Kane, Jave O.; Martinez, David A.; Pound, Marc W.; Heeter, Robert F.; Casner, Alexis; Mancini, Roberto C.

    2015-02-01

    For over fifteen years astronomers at the University of Maryland and theorists and experimentalists at LLNL have investigated the origin and dynamics of the famous Pillars of the Eagle Nebula, and similar parsec-scale structures at the boundaries of HII regions in molecular hydrogen clouds. Eagle Nebula was selected as one of the National Ignition Facility (NIF) Science programs, and has been awarded four NIF shots to study the cometary model of pillar formation. These experiments require a long-duration drive, 30 ns or longer, to drive deeply nonlinear ablative hydrodynamics. The NIF shots will feature a new long-duration x-ray source prototyped at the Omega EP laser, in which multiple hohlraums are driven with UV light in series for 10 ns each and reradiate the energy as an extended x-ray pulse. The new source will be used to illuminate a science package with directional radiation mimicking a cluster of stars. The scaled Omega EP shots tested whether a multi-hohlraum concept is viable — whether earlier time hohlraums would degrade later time hohlraums by preheat or by ejecting ablated plumes that would deflect the later beams. The Omega EP shots illuminated three 2.8 mm long by 1.4 mm diameter Cu hohlraums for 10 ns each with 4.3 kJ per hohlraum. At NIF each hohlraum will be 4 mm long by 3 mm in diameter and will be driven with 80 kJ per hohlraum.

  9. Dispersion of Magnetic Fields in Molecular Clouds. III

    CERN Document Server

    Houde, Martin; Vaillancourt, John E; Hildebrand, Roger H

    2011-01-01

    We apply our technique on the dispersion of magnetic fields in molecular clouds to high spatial resolution Submillimeter Array polarization data obtained for Orion KL in OMC-1, IRAS 16293, and NGC 1333 IRAS 4A. We show how one can take advantage of such high resolution data to characterize the magnetized turbulence power spectrum in the inertial and dissipation ranges. For Orion KL we determine that in the inertial range the spectrum can be approximately fitted with a power law k^-(2.9\\pm0.9) and we report a value of 9.9 mpc for {\\lambda}_AD, the high spatial frequency cutoff presumably due to turbulent ambipolar diffusion. For the same parameters we have \\sim k^-(1.4\\pm0.4) and a tentative value of {\\lambda}_AD \\simeq 2.2 mpc for NGC 1333 IRAS 4A, and \\sim k^-(1.8\\pm0.3) with an upper limit of {\\lambda}_AD < 1.8 mpc for IRAS 16293. We also discuss the application of the technique to interferometry measurements and the effects of the inherent spatial filtering process on the interpretation of the results.

  10. A young SNR illuminating nearby Molecular Clouds with cosmic rays

    CERN Document Server

    Cui, Y; Santangelo, A

    2016-01-01

    The Supernova Remnant (SNR) HESS J1731-347 displays strong non-thermal TeV gamma-ray and X-ray emission, thus the object is at present time accelerating particles to very high energies. A distinctive feature of this young SNR is the nearby (~30 pc in projection) extended source HESS J1729-345, which is currently unidentified but is in spatial projection coinciding with known molecular clouds (MC). We model the SNR evolution to explore if the TeV emission from HESS J1729-345 can be explained as emission from runaway hadronic cosmic rays (CRs) that are illuminating these MCs. The observational data of HESS J1729-345 and HESS J1731-347 can be reproduced using core-collapse SN models for HESS J1731-347. Starting with different progenitor stars and their pre-supernova environment, we model potential SNR evolution histories along with the CR acceleration in the SNR and the diffusion of the CRs. A simplified 3-dimensional structure of the MCs is introduced based on 12CO data, adopting a distance of 3.2 kpc to the so...

  11. The Virial Balance of Clumps and Cores in Molecular Clouds

    CERN Document Server

    Dib, S; Kim, J; Burkert, A; Shadmehri, M; Dib, Sami; Vazquez-Semadeni, Enrique; Kim, Jongsoo; Burkert, Andreas; Shadmehri, Mohsen

    2006-01-01

    (Abridged) We study the virial balance of clumps and cores (CCs) in a set of 3D simulations of driven, MHD, isothermal molecular clouds (MCs). The simulations represent a range of magnetic field strengths in MCs from subcritical to non-magnetic regimes. We identify CCs at different threshold levels. For each object, we calculate the terms that enter the virial theorem in its Eulerian form as well as quantities commonly used in observational and theoretical work to indicate the state of gravitational binding: the Jeans number J_c, the mass-to magnetic flux ratio mu_c, the virial parameter alpha_c. Our results suggest that a) CCs are dynamical out-of-equilibrium structures.b) The surface energy terms are of the same order than their respective volume terms c) CCs can be either in the process of being compressed by the velocity field and have tau_k>0 or dispersed tau_k0 are gravitationally bound.d) There is no 1-to-1 correspondence between the state of the gravitational binding as described by the energy balance...

  12. Embedded Star Clusters in the W51 Giant Molecular Cloud

    CERN Document Server

    Kumar, M S N; Davis, C J

    2004-01-01

    We present sub-arcsecond (0.35"-0.9"), near-infrared J,H,K band photometric observations of six fields along the W51 Giant Molecular Cloud (W51 GMC). Our observations reveal four new, embedded clusters and provide a new high-resolution (0.35") view of the W51IRS2 (G49.5-0.4) region. The cluster associated with G48.9-0.3 is found to be a double cluster enclosed in a nest of near-infrared nebulosity. We construct stellar surface density maps for four major clusters in the W51 GMC. These unveil the underlying hierarchical structure. Color-color and color-magnitude diagrams for each of these clusters show clear differences in the embedded stellar populations and indicate the relative ages of these clusters. In particular, the clusters associated with the HII regions G48.9-0.3 and G49.0-0.3 are found to have a high fraction of YSOs and are therefore considered the youngest of all the near-infrared clusters in the W51 GMC. The estimated masses of the individual clusters, when summed, yield a total stellar mass of ~...

  13. $\\rm^{13}CO$ Filaments in the Taurus Molecular Cloud

    CERN Document Server

    Panopoulou, G V; Goldsmith, P F; Heyer, M H

    2014-01-01

    We have carried out a search for filamentary structures in the Taurus molecular cloud using $\\rm^{13}CO$ line emission data from the FCRAO survey of $\\rm \\sim100 \\, deg^2$. We have used the topological analysis tool, DisPerSe, and post-processed its results to include a more strict definition of filaments that requires an aspect ratio of at least 3:1 and cross section intensity profiles peaked on the spine of the filament. In the velocity-integrated intensity map only 10 of the hundreds of filamentary structures identified by DisPerSe comply with our criteria. Unlike Herschel analyses, which find a characteristic width for filaments of $\\rm \\sim0.1 \\, pc$, we find a much broader distribution of profile widths in our structures, with a peak at 0.4 pc. Furthermore, even if the identified filaments are cylindrical objects, their complicated velocity structure and velocity dispersions imply that they are probably gravitationally unbound. Analysis of velocity channel maps reveals the existence of hundreds of `velo...

  14. Comparing simulated emission from molecular clouds using experimental design

    Energy Technology Data Exchange (ETDEWEB)

    Yeremi, Miayan; Flynn, Mallory; Loeppky, Jason; Rosolowsky, Erik [University of British Columbia, Okanagan Campus, Departments of Physics and Statistics, 3333 University Way, Kelowna BC V1V 1V7 (Canada); Offner, Stella [Yale University Astronomy Department, 260 Whitney Avenue, New Haven, CT 06511 (United States)

    2014-03-10

    We propose a new approach to comparing simulated observations that enables us to determine the significance of the underlying physical effects. We utilize the methodology of experimental design, a subfield of statistical analysis, to establish a framework for comparing simulated position-position-velocity data cubes to each other. We propose three similarity metrics based on methods described in the literature: principal component analysis, the spectral correlation function, and the Cramer multi-variate two-sample similarity statistic. Using these metrics, we intercompare a suite of mock observational data of molecular clouds generated from magnetohydrodynamic simulations with varying physical conditions. Using this framework, we show that all three metrics are sensitive to changing Mach number and temperature in the simulation sets, but cannot detect changes in magnetic field strength and initial velocity spectrum. We highlight the shortcomings of one-factor-at-a-time designs commonly used in astrophysics and propose fractional factorial designs as a means to rigorously examine the effects of changing physical properties while minimizing the investment of computational resources.

  15. Millimeter continuum observations of Galactic center giant molecular cloud cores

    Science.gov (United States)

    Lis, D. C.; Carlstrom, J. E.; Keene, Jocelyn

    1991-01-01

    Results are presented of observations of 1.3- and 0.8-mm continuum emission toward the cores of three Galactic center molecular clouds with ongoing massive star formation, Sagittarius B2, C, and D, which were made in order to study possible variations in the high-mass star formation rate per unit mass between the Galactic center and the disk. The luminosity-to-mass ratio, based on the mass estimates derived from the millimeter continuum emission, is used as a tracer of the high-mass star formation rate in GMC cores. The magnitude of errors involved in using millimeter continuum emission for determining the core mass is estimated through radiative transfer modeling. It is inferred from the present millimeter data, along with previously published far-infrared data, that the Sgr C and D cores are very similar in terms of mean dust optical depth and temperature. The luminosity-to-mass ratios derived for the Sgr C and D cores are found to be consistent with those of typical disk GMC cores with comparable far-infrared luminosities.

  16. Contraction Signatures toward Dense Cores in the Perseus Molecular Cloud

    Science.gov (United States)

    Campbell, J. L.; Friesen, R. K.; Martin, P. G.; Caselli, P.; Kauffmann, J.; Pineda, J. E.

    2016-03-01

    We report the results of an HCO+ (3-2) and N2D+ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO+ asymmetry using a dimensionless asymmetry parameter δv, and identify 20 cores with significant blue or red line asymmetries in optically thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO+ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the δv and collapse model results, we find that δv is a good tracer of core contraction if the optically thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03 km s-1) to supersonic (0.4 km s-1), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/MJ > 1) are somewhat more likely to show contraction motions. We find no trend of optically thin non-thermal line width with M/MJ, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.

  17. CONTRACTION SIGNATURES TOWARD DENSE CORES IN THE PERSEUS MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Campbell, J. L. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, Ontario, M5S 3H4 (Canada); Friesen, R. K. [Dunlap Institute for Astronomy and Astrophysics, University of Toronto, 50 St. George St., Toronto, Ontario, M5S 3H4 (Canada); Martin, P. G. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George St., Toronto, Ontario, M5S 3H8 (Canada); Caselli, P.; Pineda, J. E. [Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstrasse 1, D-85741 Garching (Germany); Kauffmann, J., E-mail: jessicalynn.campbell@mail.utoronto.ca [Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2016-03-10

    We report the results of an HCO{sup +} (3–2) and N{sub 2}D{sup +} (3–2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO{sup +} asymmetry using a dimensionless asymmetry parameter δ{sub v}, and identify 20 cores with significant blue or red line asymmetries in optically thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO{sup +} profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the δ{sub v} and collapse model results, we find that δ{sub v} is a good tracer of core contraction if the optically thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03 km s{sup −1}) to supersonic (0.4 km s{sup −1}), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/M{sub J} > 1) are somewhat more likely to show contraction motions. We find no trend of optically thin non-thermal line width with M/M{sub J}, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.

  18. A New Method for Constraining Molecular Cloud Thickness: A study of Taurus, Perseus and Ophiuchus

    CERN Document Server

    Qian, Lei; Offner, Stella; Pan, Zhichen

    2015-01-01

    The core velocity dispersion (CVD) is a potentially useful tool for studying the turbulent velocity field of molecular clouds. CVD is based on centroid velocities of dense gas clumps, thus is less prone to density fluctuation and reflects more directly the cloud velocity field. Prior work demonstrated that the Taurus molecular cloud CVD resembles the well-known Larson's linewidth-size relation of molecular clouds. In this work, we studied the dependence of the CVD on the line-of-sight thickness of molecular clouds, a quantity which cannot be measured by direct means. We produced a simple statistical model of cores within clouds and analyzed the CVD of a variety of hydrodynamical simulations. We show that the relation between the CVD and the 2D projected separation of cores ($L_{2D}$) is sensitive to the cloud thickness. When the cloud is thin, the index of CVD-$L_{2D}$ relation ($\\gamma$ in the relation CVD$\\sim L_{2D}^{\\gamma}$) reflects the underlying energy spectrum ($E(k)\\sim k^{-\\beta}$) in that $\\gamma\\...

  19. The Milky Way in Molecular Clouds A New Complete CO Survey

    CERN Document Server

    Dame, T M; Thaddeus, P; Hartmann, Dap

    2000-01-01

    New large-scale CO surveys of the first and second Galactic quadrants and the nearby molecular cloud complexes in Orion and Taurus, obtained with the CfA 1.2 m telescope, have been combined with 31 other surveys obtained over the past two decades with that instrument and a similar telescope on Cerro Tololo in Chile, to produce a new composite CO survey of the entire Milky Way. The survey consists of 488,000 spectra that Nyquist or beamwidth (1/8-deg) sample the entire Galactic plane over a strip 4-10 deg wide in latitude, and beamwidth or 1/4-deg sample nearly all large local clouds at higher latitudes. A map of molecular column density predicted from complete and unbiased far-infrared and 21 cm surveys of the Galaxy was used both to determine the completeness of the present survey and to extrapolate it to the entire sky at |b| 5 deg), X shows little systematic variation with latitude from a mean value of 1.8 +/- 0.3 x 10^20 cm-2 K-1 km-1 s. Given the large sky area and large quantity of CO data analyzed, we...

  20. Measurements of Molecular Cloud Ages using the HI/ H2 Ratio

    Science.gov (United States)

    Krco, Marko; Li, Di

    2017-01-01

    We utilize a new chemical evolution model in conjunction with the HI and H2 mass measurements of 9 nearby molecular clouds in order to place lower limits on their chemical ages (the time since the cloud first attained sufficient self-shielding for molecules to persist). HI masses are measured using HI Narrow Self-Absorption (HINSA) features with data taken with the GBT. H2 masses are estimated using 13CO emission data obtained with FCRAO.Since the clouds' geometry (and volume density) are unknown, we examine each cloud under a range of assumptions. Under conditions that favor the lowest age limits, where each cloud is assumed to resemble a sheet and has the highest reasonable volume density, we arrive at age lower limits between 0.3 and 1.5 Myrs. Assuming that the clouds have no preferential orientation yields age lower limits of 4.4 Myrs or older. HI/H2 cloud mass ratios between 0.13x10-3 and 3.8x10-3 were observed. The lack of any observed clouds with higher HI/H2 ratios leaves open the question of why the youngest clouds are not observed. Our models reveal that the clouds studied here should reach a steady-state, where the only remaining HI is due to cosmic ray dissociation, within approximately 7 to 15 Myrs.We determine the HI/H2 ratio, and age lower limit for all clumps and velocity components within each cloud. Though individual clumps within a single cloud, and even along the same line of sight may exhibit very different HI/H2 ratios, they most often exhibit similar ages. This would indicate that the mixing timescale for different clumps within cloud are generally longer than the cloud ages.Ultimately we conclude that the cloud collapse timescale is at least on the order of 10Myrs.

  1. Understanding star formation in molecular clouds I. A universal probability distribution of column densities ?

    CERN Document Server

    Schneider, N; Csengeri, T; Klessen, R; Federrath, C; Tremblin, P; Girichidis, P; Bontemps, S; Andre, Ph

    2014-01-01

    Column density maps of molecular clouds are one of the most important observables in the context of molecular cloud- and star-formation (SF) studies. With Herschel it is now possible to reveal rather precisely the column density of dust, which is the best tracer of the bulk of material in molecular clouds. However, line-of-sight (LOS) contamination from fore- or background clouds can lead to an overestimation of the dust emission of molecular clouds, in particular for distant clouds. This implies too high values for column density and mass, and a misleading interpretation of probability distribution functions (PDFs) of the column density. In this paper, we demonstrate by using observations and simulations how LOS contamination affects the PDF. We apply a first-order approximation (removing a constant level) to the molecular clouds of Auriga and Maddalena (low-mass star-forming), and Carina and NGC3603(both high-mass SF regions). In perfect agreement with the simulations, we find that the PDFs become broader, ...

  2. The Formation and Destruction of Molecular Clouds and Galactic Star Formation

    CERN Document Server

    Inutsuka, Shu-ichiro; Iwasaki, Kazunari; Hosokawa, Takashi

    2015-01-01

    We describe an overall picture of galactic-scale star formation. Recent high-resolution magneto-hydrodynamical simulations of two-fluid dynamics with cooling/heating and thermal conduction have shown that the formation of molecular clouds requires multiple episodes of supersonic compression. This finding enables us to create a scenario in which molecular clouds form in interacting shells or bubbles on a galactic scale. First we estimate the ensemble-averaged growth rate of molecular clouds over a timescale larger than a million years. Next we perform radiation hydrodynamics simulations to evaluate the destruction rate of magnetized molecular clouds by the stellar FUV radiation. We also investigate the resultant star formation efficiency within a cloud which amounts to a low value (a few percent) if we adopt the power-law exponent -2.5 for the mass distribution of stars in the cloud. We finally describe the time evolution of the mass function of molecular clouds over a long timescale (>1Myr) and discuss the st...

  3. Evidence for nucleosynthetic enrichment of the protosolar molecular cloud core by multiple supernova events

    DEFF Research Database (Denmark)

    Schiller, Martin; Paton, Chad; Bizzarro, Martin

    2015-01-01

    The presence of isotope heterogeneity of nucleosynthetic origin amongst meteorites and their components provides a record of the diverse stars that contributed matter to the protosolar molecular cloud core. Understanding how and when the solar system's nucleosynthetic heterogeneity was establishe...

  4. Millimeter dust continuum emission unveiling the true mass of giant molecular clouds in the Small Magellanic Cloud

    CERN Document Server

    Bot, C; Rubio, M; Rantakyro, F

    2007-01-01

    CO observations have been so far the best way to trace molecular gas in external galaxies, but at low metallicity the gas mass deduced could be largely underestimated. At present, the kinematic information of CO data cubes are used to estimate virial masses and trace the total mass of the molecular clouds. Millimeter dust emission can also be used as a dense gas tracer and could unveil H2 envelopes lacking CO. These different tracers must be compared in different environments. This study compares virial masses to masses deduced from millimeter emission, in two GMC samples: the local molecular clouds in our Galaxy and their equivalents in the Small Magellanic Cloud (SMC), one of the nearest low metallicity dwarf galaxy. In our Galaxy, mass estimates deduced from millimeter emission are consistent with masses deduced from gamma ray analysis and trace the total mass of the clouds. Virial masses are systematically larger (twice on average) than mass estimates from millimeter dust emission. This difference decreas...

  5. Investigating the Life Cycle of Molecular Clouds in the Andromeda Galaxy

    Science.gov (United States)

    Beerman, Lori; Dalcanton, Julianne; Schruba, Andreas; Leroy, Adam K.; Johnson, Lent C.; Weisz, Daniel R.; Fouesneau, Morgan; PHAT Collaboration

    2015-01-01

    There is currently a great divide between high resolution studies of stellar clusters and molecular clouds in the Milky Way, and those done in extragalactic systems, where individual stars and clouds cannot usually be resolved. For my thesis work, I combined several astronomical data sets to investigate the life cycle of molecular clouds in the Andromeda Galaxy. The primary data sets I used are the Panchromatic Hubble Andromeda Treasury (PHAT), which catalogued over 200 million stars, and a molecular cloud catalogue that is constructed from new high spatial/spectral resolution (20 pc, 1 km/s) CARMA observations. Several ancillary data sets, including H-alpha and Spitzer IR emission maps were also used, taking advantage of broad wavelength coverage to search for indicators of star formation with different timescales. Comparisons were also made with the PHAT cluster sample, and the youngest (star formation indicator. The ages and masses of these clusters were determined by fitting the color-magnitude diagrams (CMDs) of their resolved stars to theoretical isochrones. The distribution of the youngest clusters shows a strong correlation with the molecular cloud distribution, while no correlation is evident for clusters greater than 30 Myr. Each molecular cloud in the sample was then classified as a star-forming cloud or a non-star forming cloud, based on the presence of any one of several star formation indicators. About 60% of the clouds in the sample were found to be associated with massive star formation. Based on the comparison between these observations and the results from a Monte Carlo simulation, I will also demonstrate how we can constrain the timescales for the relative phases in a cloud's life.

  6. On the origin of the Orion and Monoceros molecular cloud complexes

    Science.gov (United States)

    Franco, J.; Tenorio-Tagle, G.; Bodenheimer, P.; Rozyczka, M.; Mirabel, I. F.

    1988-01-01

    A detailed model for the origin of the Orion and Monoceros cloud complexes is presented, showing that a single high-velocity H I cloud-galaxy collision can explain their main observed features. The collision generates massive shocked layers, and self-gravity can then provide the conditions for the transformation of these layers into molecular clouds. The clouds formed by the collision maintain the motion of their parental shocked gas and reach positions located far away from the plane. According to this model, both the Orion and Monoceros complexes were formed some 60 million yr ago, when the original shocked layer was fragmented by Galactic tidal forces.

  7. Star Formation in the Molecular Cloud Associated with the Monkey Head Nebula: Sequential or Spontaneous?

    Science.gov (United States)

    Chibueze, J. O.; Imura, K.; Omodaka, T.; Handa, T.; Nagayama, T.; Fujisawa, K.; Sunada, K.; Nakano, M.; Kamezaki, T.; Yamaguchi, Y.

    2013-03-01

    We mapped the NH3 (1,1), (2,2), and (3,3) lines of the molecular cloud associated with the Monkey Head Nebula (MHN) with 1'.6 angular resolution using Kashima 34 m telescope. Its kinetic temperature distribution was contrary to what is expected for a molecular cloud at the edge of an expanding H II region and suggested that the massive star associated with S252A compact HII region formed spontaneously rather than through a sequential process.

  8. Observing molecular hydrogen clouds and dark massive objects in galactic halos

    OpenAIRE

    F. De Paolis(University of Lecce and INFN, Lecce, Italy); Ingrosso, G.; Jetzer, Ph.; Quadir, A.; Roncadelli, M.

    1995-01-01

    Molecular hydrogen clouds can contribute substantially to the galactic halo< dark matter and may lead to the birth of massive halo objects (MHOs) observed indirectly by microlensing. We present a method to detect these molecular clouds in the halo of M31 using the Doppler shift effect. We also consider the possibility to directly observe MHOs in the halo of M31 via their infrared emission.

  9. Predicting Clinical Outcomes Using Molecular Biomarkers.

    Science.gov (United States)

    Burke, Harry B

    2016-01-01

    Over the past 20 years, there has been an exponential increase in the number of biomarkers. At the last count, there were 768,259 papers indexed in PubMed.gov directly related to biomarkers. Although many of these papers claim to report clinically useful molecular biomarkers, embarrassingly few are currently in clinical use. It is suggested that a failure to properly understand, clinically assess, and utilize molecular biomarkers has prevented their widespread adoption in treatment, in comparative benefit analyses, and their integration into individualized patient outcome predictions for clinical decision-making and therapy. A straightforward, general approach to understanding how to predict clinical outcomes using risk, diagnostic, and prognostic molecular biomarkers is presented. In the future, molecular biomarkers will drive advances in risk, diagnosis, and prognosis, they will be the targets of powerful molecular therapies, and they will individualize and optimize therapy. Furthermore, clinical predictions based on molecular biomarkers will be displayed on the clinician's screen during the physician-patient interaction, they will be an integral part of physician-patient-shared decision-making, and they will improve clinical care and patient outcomes.

  10. The properties of bound and unbound molecular cloud populations formed in galactic disc simulations

    Science.gov (United States)

    Ward, Rachel L.; Benincasa, Samantha M.; Wadsley, James; Sills, Alison; Couchman, H. M. P.

    2016-01-01

    We explore the effect of galactic environment on properties of molecular clouds. Using clouds formed in a large-scale galactic disc simulation, we measure the observable properties from synthetic column density maps. We confirm that a significant fraction of unbound clouds forms naturally in a galactic disc environment and that a mixed population of bound and unbound clouds can match observed scaling relations and distributions for extragalactic molecular clouds. By dividing the clouds into inner and outer disc populations, we compare their distributions of properties and test whether there are statistically significant differences between them. We find that clouds in the outer disc have lower masses, sizes, and velocity dispersions as compared to those in the inner disc for reasonable choices of the inner/outer boundary. We attribute the differences to the strong impact of galactic shear on the disc stability at large galactocentric radii. In particular, our Toomre analysis of the disc shows a narrowing envelope of unstable masses as a function of radius, resulting in the formation of smaller, lower mass fragments in the outer disc. We also show that the star formation rate is affected by the environment of the parent cloud, and is particularly influenced by the underlying surface density profile of the gas throughout the disc. Our work highlights the strengths of using galaxy-scale simulations to understand the formation and evolution of cloud properties - and the star formation within them - in the context of their environment.

  11. Comparing Submillimeter Polarized Emission with Near-infrared Polarization of Background Stars for the Vela C Molecular Cloud

    Science.gov (United States)

    Santos, Fabio P.; Ade, Peter A. R.; Angilè, Francesco E.; Ashton, Peter; Benton, Steven J.; Devlin, Mark J.; Dober, Bradley; Fissel, Laura M.; Fukui, Yasuo; Galitzki, Nicholas; Gandilo, Natalie N.; Klein, Jeffrey; Korotkov, Andrei L.; Li, Zhi-Yun; Martin, Peter G.; Matthews, Tristan G.; Moncelsi, Lorenzo; Nakamura, Fumitaka; Netterfield, Calvin B.; Novak, Giles; Pascale, Enzo; Poidevin, Frédérick; Savini, Giorgio; Scott, Douglas; Shariff, Jamil A.; Diego Soler, Juan; Thomas, Nicholas E.; Tucker, Carole E.; Tucker, Gregory S.; Ward-Thompson, Derek

    2017-03-01

    We present a large-scale combination of near-infrared (near-IR) interstellar polarization data from background starlight with polarized emission data at submillimeter wavelengths for the Vela C molecular cloud. The near-IR data consist of more than 6700 detections probing a range of visual extinctions between 2 and 20 {mag} in and around the cloud. The submillimeter data were collected in Antarctica by the Balloon-borne Large Aperture Submillimeter Telescope for Polarimetry. This is the first direct combination of near-IR and submillimeter polarization data for a molecular cloud aimed at measuring the “polarization efficiency ratio” ({R}{eff}), a quantity that is expected to depend only on grain-intrinsic physical properties. It is defined as {p}500/({p}I/{τ }V), where p 500 and p I are polarization fractions at 500 μ {{m}} and the I band, respectively, and {τ }V is the optical depth. To ensure that the same column density of material is producing both polarization from emission and from extinction, we conducted a careful selection of near-background stars using 2MASS, Herschel, and Planck data. This selection excludes objects contaminated by the Galactic diffuse background material as well as objects located in the foreground. Accounting for statistical and systematic uncertainties, we estimate an average {R}{eff} value of 2.4 ± 0.8, which can be used to test the predictions of dust grain models designed for molecular clouds when such predictions become available. The ratio {R}{eff} appears to be relatively flat as a function of the cloud depth for the range of visual extinctions probed.

  12. Distance to the High-Latitude Molecular Cloud MBM 37 (LDN 183)

    Science.gov (United States)

    Boyle, Richard P.; Janusz, Robert; Straizys, Vytautas; Corbally, Christopher J.; Munari, Ulisse; Andersson, B.-G.; Zdanavicius, Justas; Maskoliunas, Marius; Kazlauskas, Algirdas

    2017-01-01

    The molecular cloud MBM 37 and the corresponding dust cloud LDN 183 belong to a group of high-latitude clouds near the Serpens Caput and Libra border at b = +36 deg. We determined the distance to this cloud applying the extinction Av vs. distance diagram based on two-dimensional photometric classification of about 800 stars down to V = 15 mag and about 200 stars down to V = 19 mag observed in the Vilnius seven-color system. Additionally, for the stars brighter than V = 12 mag MK types were determined spectroscopically. Distances for part of them, located nearer than 500 pc, were calculated from the Gaia parallaxes. The distance to MBM 37 is found to be at 90 pc placing it among the dust and molecular clouds closest to the Sun.

  13. New Results on the Submillimeter Polarization Spectrum of the Orion Molecular Cloud

    CERN Document Server

    Vaillancourt, J E; Hildebrand, R H; Kirby, L; Krejny, M M; Li, H; Novak, G; Houde, M; Shinnaga, H; Attard, M

    2008-01-01

    We have used the SHARP polarimeter at the Caltech Submillimeter Observatory to map the polarization at wavelengths of 350 and 450 micron in a ~2 x 3 arcmin region of the Orion Molecular Cloud. The map covers the brightest region of the OMC-1 ridge including the Kleinmann-Low (KL) nebula and the submillimeter source Orion-south. The ratio of 450-to-350 micron polarization is ~ 1.3 +/- 0.3 in the outer parts of the cloud and drops by a factor of 2 towards KL. The outer cloud ratio is consistent with measurements in other clouds at similar wavelengths and confirms previous measurements placing the minimum of the polarization ratio in dusty molecular clouds at a wavelength ~ 350 micron.

  14. An unbiased survey for dense cores in the Lynds 1630 molecular cloud

    Science.gov (United States)

    Lada, Elizabeth A.; Bally, John; Stark, Antony A.

    1991-01-01

    An unbiased, systematic survey for dense cores within the L1630 (Orion B) molecular cloud has been completed. This survey provides the first complete census of dense (n greater tha 10,000/cu cm) cores within a molecular cloud. To identify the dense gas, 3.6 square degrees of the L1630 cloud were surveyed in the J = 2-1 transition of CS. CS emission was detected over 10 percent of the area surveyed, and this emission is not uniformly distributed throughout the cloud but is confined to 42 dense cores. The size, shape, velocity dispersion, and mass of these cores are examined. Comparison of the mass contained within dense cores with the total gas mass within the surveyed region, estimated from CO emission, reveals that the dense cores constitute only a small fraction (not greater than 19 percent) of the total cloud mass.

  15. Three-dimensional simulations of molecular cloud fragmentation regulated by magnetic fields and ambipolar diffusion

    CERN Document Server

    Kudoh, Takahiro; Ogata, Youichi; Yabe, Takashi

    2007-01-01

    We employ the first fully three-dimensional simulation to study the role of magnetic fields and ion-neutral friction in regulating gravitationally-driven fragmentation of molecular clouds. The cores in an initially subcritical cloud develop gradually over an ambipolar diffusion time while the cores in an initially supercritical cloud develop in a dynamical time. The infall speeds on to cores are subsonic in the case of an initially subcritical cloud, while an extended (\\ga 0.1 pc) region of supersonic infall exists in the case of an initially supercritical cloud. These results are consistent with previous two-dimensional simulations. We also found that a snapshot of the relation between density (rho) and the strength of the magnetic field (B) at different spatial points of the cloud coincides with the evolutionary track of an individual core. When the density becomes large, both relations tend to B \\propto \\rho^{0.5}.

  16. A Search for O_2 in CO-depleted Molecular Cloud Cores with Herschel

    CERN Document Server

    Wirström, Eva S; Cordiner, Martin A; Ceccarelli, Cecilia

    2016-01-01

    The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with SWAS, Odin and Herschel have only produced two detections; upper limits to the O_2 abundance in the remaining sources observed are about 1000 times lower than predicted by chemical models. Previous atomic oxygen observations and inferences from observations of other molecules indicated that high abundances of O atoms might be present in dense cores exhibiting large amounts of CO depletion. Theoretical arguments concerning the oxygen gas-grain interaction in cold dense cores suggested that, if O atoms could survive in the gas after most of the rest of the heavy molecular material has frozen out on to dust, then O_2 could be formed efficiently in the gas. Using Herschel HIFI we searched a small sample of four depletion cores - L1544, L694-2, L429, Oph D - for emission in the low excitation O_2 N_J=3_3-1_2 line at 487.249 GHz. Molecular oxygen was not detected and we derive upper limits t...

  17. NEWLY IDENTIFIED EXTENDED GREEN OBJECTS (EGOs) FROM THE SPITZER GLIMPSE II SURVEY. II. MOLECULAR CLOUD ENVIRONMENTS

    Energy Technology Data Exchange (ETDEWEB)

    Chen Xi; Gan Conggui; Shen Zhiqiang [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China); Ellingsen, Simon P.; Titmarsh, Anita [School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania (Australia); He Jinhua, E-mail: chenxi@shao.ac.cn [Key Laboratory for the Structure and Evolution of Celestial Objects, Yunnan Astronomical Observatory/National Astronomical Observatory, Chinese Academy of Sciences, P.O. Box 110, Kunming 650011, Yunnan Province (China)

    2013-06-01

    We have undertaken a survey of molecular lines in the 3 mm band toward 57 young stellar objects using the Australia Telescope National Facility Mopra 22 m radio telescope. The target sources were young stellar objects with active outflows (extended green objects (EGOs)) newly identified from the GLIMPSE II survey. We observe a high detection rate (50%) of broad line wing emission in the HNC and CS thermal lines, which combined with the high detection rate of class I methanol masers toward these sources (reported in Paper I) further demonstrates that the GLIMPSE II EGOs are associated with outflows. The physical and kinematic characteristics derived from the 3 mm molecular lines for these newly identified EGOs are consistent with these sources being massive young stellar objects with ongoing outflow activity and rapid accretion. These findings support our previous investigations of the mid-infrared properties of these sources and their association with other star formation tracers (e.g., infrared dark clouds, methanol masers and millimeter dust sources) presented in Paper I. The high detection rate (64%) of the hot core tracer CH{sub 3}CN reveals that the majority of these new EGOs have evolved to the hot molecular core stage. Comparison of the observed molecular column densities with predictions from hot core chemistry models reveals that the newly identified EGOs from the GLIMPSE II survey are members of the youngest hot core population, with an evolutionary time scale of the order of 10{sup 3} yr.

  18. Interstellar extinction in the MBM 12 molecular cloud area in Aries

    Science.gov (United States)

    Straizys, V.; Zdanavicius, J.; Zdanavicius, K.; Laugalys, V.; Kazlauskas, A.; Cernis, K.; Boyle, R. P.; Philip, A. G. D.

    2004-12-01

    Magnitudes and color indices of 140 stars down to V = 15 mag in the seven-color Vilnius photometric system are determined with a CCD camera in the area of the Aries molecular cloud MBM 12. Spectral types, interstellar color excesses and extinctions and distances of the stars are determined from the photometric data. We conclude that the extinction starts to rise at 140-160 pc, i. e., at the distance of the Taurus dark cloud complex. The distance of the MBM 12 molecular cloud is discussed. Some new heavily reddened stars and T Tauri stars are identified. The support by the AAS Chretien Grant of 2000 is acknowledged.

  19. Massive molecular cloud cores and activities of star formation

    Institute of Scientific and Technical Information of China (English)

    Zhou Wu-Fei; Wu Yue-Fang; Wei Yue; Ju Bing-Gang

    2005-01-01

    We have mapped 23 sources in the J=1-0 lines of 12CO, 13CO and C18O with the 13.7-m telescope at Qinghai station of Purple Mountain Observatory. The samples were chosen from the massive star formation regions whose single point lines have the broad-wing profile. The mapping shows that 12 clouds have cores and 5 outflows were identified with the 12CO J=1-0 lines. Among the 12 cores, systematic velocity shifts were found in 2 cores, and blue asymmetric double-peak profile of 12CO line was found in IRAS 19529+2704, indicating that it may be an infall candidate. Physical parameters of the cores and outflows were derived from the local thermodynamic equilibrium assumption. The masses range from ~ 9.4 × 102M⊙ to ~ 2.2 × 105M⊙. The hydrogen molecule densities range from ~ 3.4 × 102cm-3 to~ 1.2 × 104cm-3. The molecular outflows have masses larger than 3.5M⊙, and kinetic energies greater than 0.9× 1038J.The outflows have significantly greater masses and kinetic energies than those from low-mass young stellar objects(YSOs). For the cores, 2MASS data are available, dozens of 2MASS sources with different colour indices and brightness are often found around IRAS source, among which the reddest 2MASS source is always within the IRAS error ellipse thus probably corresponds to the IRAS source.

  20. Understanding star formation in molecular clouds III. Probability distribution functions of molecular lines in Cygnus X

    CERN Document Server

    Schneider, N; Motte, F; Ossenkopf, V; Klessen, R S; Simon, R; Fechtenbaum, S; Herpin, F; Tremblin, P; Csengeri, T; Myers, P C; Hill, T; Cunningham, M; Federrath, C

    2015-01-01

    Column density (N) PDFs serve as a powerful tool to characterize the physical processes that influence the structure of molecular clouds. Star-forming clouds can best be characterized by lognormal PDFs for the lower N range and a power-law tail for higher N, commonly attributed to turbulence and self-gravity and/or pressure, respectively. We report here on PDFs obtained from observations of 12CO, 13CO, C18O, CS, and N2H+ in the Cygnus X North region and compare to a PDF derived from dust observations with the Herschel satellite. The PDF of 12CO is lognormal for Av~1-30, but is cut for higher Av due to optical depth effects. The PDFs of C18O and 13CO are mostly lognormal up for Av~1-15, followed by excess up to Av~40. Above that value, all CO PDFs drop, most likely due to depletion. The high density tracers CS and N2H+ exhibit only a power law distribution between Av~15 and 400, respectively. The PDF from dust is lognormal for Av~2-15 and has a power-law tail up to Av~500. Absolute values for the molecular lin...

  1. Gravitational contraction versus Supernova driving and the origin of the velocity dispersion-size relation in molecular clouds

    CERN Document Server

    Ibáñez-Mejía, Juan C; Klessen, Ralf S; Baczynski, Christian

    2015-01-01

    Molecular cloud observations show that clouds have non-thermal velocity dispersions that scale with the cloud size as $\\sigma\\propto R^{1/2}$ at constant surface density, and for varying surface density scale with both the cloud`s size and surface density, $\\sigma^2 \\propto R \\Sigma$. The energy source driving these chaotic motions remains poorly understood. We describe the velocity dispersions observed in a cloud population formed in a kiloparsec-scale numerical simulation of a magnetized, supernova-driven, self-gravitating, interstellar medium, including diffuse heating and radiative cooling. We compare the relationships between velocity dispersion, size, and surface density measured in the simulated cloud population to those found in observations of Galactic molecular clouds. We find that external supernova explosions can not drive turbulent motions of the observed magnitudes within dense clouds. On the other hand, self-gravity also induces non-thermal motions as gravitationally bound clouds begin to colla...

  2. The Chemistry and Kinematics of Two Molecular Clouds near Sagittarius A*

    CERN Document Server

    Lopez, John A P; Jones, Paul A; Marshall, Jonathan P; Bronfman, Leonardo; Lo, Nadia; Walsh, Andrew J

    2016-01-01

    We have analysed the chemical and kinematic properties of the 20 and 50 km s$^{-1}$ molecular clouds in the Central Molecular Zone of the Milky Way Galaxy, as well as those of the molecular ridge bridging these two clouds. Our work has utilized 37 molecular transitions in the 0.65, 3 and 7-mm wavebands, from the Mopra and NANTEN2 telescopes. The 0.65-mm NANTEN2 data highlights a dense condensation of emission within the western part of the 20 km s$^{-1}$ cloud, visible in only four other transitions, which are 3-mm H$^{13}$CN (1--0), H$^{13}$CO$^{+}$ (1--0), HNC (1--0) and N$_{2}$H$^{+}$ (1--0), suggesting that the condensation is moderately optically thick and cold. We find that while the relative chemical abundances between both clouds are alike in many transitions, suggesting little variation in the chemistry between both clouds; the 20 km s$^{-1}$, cold cloud is brighter than the 50 km s$^{-1}$ cloud in shock and high density tracers. The spatial distribution of enhanced emission is widespread in the 20 k...

  3. Modelling the chemical evolution of molecular clouds as a function of metallicity

    CERN Document Server

    Penteado, Em M; Rocha-Pinto, H J

    2014-01-01

    The Galaxy is in continuous elemental evolution. Since new elements produced by dying stars are delivered to the interstellar medium, the formation of new enerations of stars and planetary systems is influenced by this metal enrichment. We aim to study the role of the metallicity on the gas phase chemistry of the interstellar medium. Using a system of coupled-ordinary differential equations to model the chemical reactions, we simulate the evolution of the abundance of molecules in the gas phase for different initial interstellar elemental compositions. These varying initial elemental compositions consider the change in the "elemental abundances" predicted by a self-consistent model of the elemental evolution of the Galaxy. As far as we are aware, this is the first attempt to combine elemental evolution of the Galaxy and chemical evolution of molecular clouds. The metallicity was found to have a strong effect on the overall gas phase composition. With decreasing metallicity, the number of long carbon chains wa...

  4. Observational Approach to Molecular Cloud Evolution with the Submillimeter CI Lines

    Science.gov (United States)

    Oka, T.; Yamamoto, S.; Mt. Fuji Submillimeter-Wave Telescope Group

    Neutral carbon atoms (CI) play important role both in chemistry and cooling processes of interstellar molecular clouds. It is thus crucial to explore its large area distribution to investigate formation processes and thermal balance of molecular clouds. We have constructed a 1.2 m submillimeter-wave telescope at the summit of Mt.Fuji. The telescope was designed for the exclusive use of surveying molecular clouds in two submillimeter CI lines, 3P1--3P0 (492 GHz) and 3P2--3P1 (809 GHz), of atomic carbon. It has been operated successfully during 4 observing seasons since July 1998 in a remote way from the Hongo campus of the University of Tokyo. We have already revealed large-scale CI 492 GHz distributions of many giant molecular clouds, including Orion MC, Taurus MC, DR15, DR21, NGC2264, M17, W3, W44, W51, Rosette MC, covering more than 40 square degrees of the sky. The distribution of CI 492 GHz emission is found to be different from those of the 13CO or C18O emission in some clouds. We found the spatial order of C+/CO/C from UV sources. This is the general property of the cloud illuminated by intense UV radiation, whereas it is apparently inconsistent with the standard photodissociation region (PDR) picture. We also found CI-rich areas (C/CO˜1) in several dark clouds without strong UV sources. These results are discussed in relation to formation processes of molecular clouds and dense cloud cores.

  5. Magnetohydrodynamic simulations of mechanical stellar feedback in a sheet-like molecular cloud

    Science.gov (United States)

    Wareing, C. J.; Pittard, J. M.; Falle, S. A. E. G.

    2017-03-01

    We have used the adaptive-mesh-refinement hydrodynamic code, MG, to perform 3D magnetohydrodynamic simulations with self-gravity of stellar feedback in a sheet-like molecular cloud formed through the action of the thermal instability. We simulate the interaction of the mechanical energy input from a 15 star and a 40 M⊙ star into a 100 pc-diameter 17 000 M⊙ cloud with a corrugated sheet morphology that in projection appears filamentary. The stellar winds are introduced using appropriate Geneva stellar evolution models. In the 15 M⊙ star case, the wind forms a narrow bipolar cavity with minimal effect on the parent cloud. In the 40 M⊙ star case, the more powerful stellar wind creates a large cylindrical cavity through the centre of the cloud. After 12.5 and 4.97 Myr, respectively, the massive stars explode as supernovae (SNe). In the 15 M⊙ star case, the SN material and energy is primarily deposited into the molecular cloud surroundings over ∼105 yr before the SN remnant escapes the cloud. In the 40 M⊙ star case, a significant fraction of the SN material and energy rapidly escapes the molecular cloud along the wind cavity in a few tens of kiloyears. Both SN events compress the molecular cloud material around them to higher densities (so may trigger further star formation), and strengthen the magnetic field, typically by factors of 2-3 but up to a factor of 10. Our simulations are relevant to observations of bubbles in flattened ring-like molecular clouds and bipolar H II regions.

  6. IDENTIFICATION OF AMBIENT MOLECULAR CLOUDS ASSOCIATED WITH GALACTIC SUPERNOVA REMNANT IC 443

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jae-Joon [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of); Koo, Bon-Chul [School of Physics and Astronomy, FPRD, Seoul National University, Seoul 151-742 (Korea, Republic of); Snell, Ronald L.; Yun, Min S.; Heyer, Mark H. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Burton, Michael G., E-mail: leejjoon@kasi.re.kr [School of Physics, University of New South Wales, Sydney, NSW 2052 (Australia)

    2012-04-10

    The Galactic supernova remnant (SNR) IC 443 is one of the most studied core-collapse SNRs for its interaction with molecular clouds. However, the ambient molecular clouds with which IC 443 is interacting have not been thoroughly studied and remain poorly understood. Using the Five College Radio Astronomy Observatory 14 m telescope, we obtained fully sampled maps of the {approx}1 Degree-Sign Multiplication-Sign 1 Degree-Sign region toward IC 443 in the {sup 12}CO J = 1-0 and HCO{sup +} J = 1-0 lines. In addition to the previously known molecular clouds in the velocity range v{sub LSR} = -6 to -1 km s{sup -1} (-3 km s{sup -1} clouds), our observations reveal two new ambient molecular cloud components: small ({approx}1') bright clouds in v{sub LSR} = -8 to -3 km s{sup -1} (SCs) and diffuse clouds in v{sub LSR} = +3 to +10 km s{sup -1} (+5 km s{sup -1} clouds). Our data also reveal the detailed kinematics of the shocked molecular gas in IC 443; however, the focus of this paper is the physical relationship between the shocked clumps and the ambient cloud components. We find strong evidence that the SCs are associated with the shocked clumps. This is supported by the positional coincidence of the SCs with shocked clumps and other tracers of shocks. Furthermore, the kinematic features of some shocked clumps suggest that these are the ablated material from the SCs upon the impact of the SNR shock. The SCs are interpreted as dense cores of parental molecular clouds that survived the destruction by the pre-supernova evolution of the progenitor star or its nearby stars. We propose that the expanding SNR shock is now impacting some of the remaining cores and the gas is being ablated and accelerated, producing the shocked molecular gas. The morphology of the +5 km s{sup -1} clouds suggests an association with IC 443. On the other hand, the -3 km s{sup -1} clouds show no evidence for interaction.

  7. Understanding star formation in molecular clouds. III. Probability distribution functions of molecular lines in Cygnus X

    Science.gov (United States)

    Schneider, N.; Bontemps, S.; Motte, F.; Ossenkopf, V.; Klessen, R. S.; Simon, R.; Fechtenbaum, S.; Herpin, F.; Tremblin, P.; Csengeri, T.; Myers, P. C.; Hill, T.; Cunningham, M.; Federrath, C.

    2016-03-01

    The probability distribution function of column density (N-PDF) serves as a powerful tool to characterise the various physical processes that influence the structure of molecular clouds. Studies that use extinction maps or H2 column-density maps (N) that are derived from dust show that star-forming clouds can best be characterised by lognormal PDFs for the lower N range and a power-law tail for higher N, which is commonly attributed to turbulence and self-gravity and/or pressure, respectively. While PDFs from dust cover a large dynamic range (typically N ~ 1020-24 cm-2 or Av~ 0.1-1000), PDFs obtained from molecular lines - converted into H2 column density - potentially trace more selectively different regimes of (column) densities and temperatures. They also enable us to distinguish different clouds along the line of sight through using the velocity information. We report here on PDFs that were obtained from observations of 12CO, 13CO, C18O, CS, and N2H+ in the Cygnus X North region, and make a comparison to a PDF that was derived from dust observations with the Herschel satellite. The PDF of 12CO is lognormal for Av ~ 1-30, but is cut for higher Av because of optical depth effects. The PDFs of C18O and 13CO are mostly lognormal up to Av ~ 1-15, followed by excess up to Av ~ 40. Above that value, all CO PDFs drop, which is most likely due to depletion. The high density tracers CS and N2H+ exhibit only a power law distribution between Av ~ 15 and 400, respectively. The PDF from dust is lognormal for Av ~ 3-15 and has a power-law tail up to Av ~ 500. Absolute values for the molecular line column densities are, however, rather uncertain because of abundance and excitation temperature variations. If we take the dust PDF at face value, we "calibrate" the molecular line PDF of CS to that of the dust and determine an abundance [CS]/[H2] of 10-9. The slopes of the power-law tails of the CS, N2H+, and dust PDFs are -1.6, -1.4, and -2.3, respectively, and are thus consistent

  8. Predicting Dyspnea Inducers by Molecular Topology

    Directory of Open Access Journals (Sweden)

    María Gálvez-Llompart

    2013-01-01

    Full Text Available QSAR based on molecular topology (MT is an excellent methodology used in predicting physicochemical and biological properties of compounds. This approach is applied here for the development of a mathematical model capable to recognize drugs showing dyspnea as a side effect. Using linear discriminant analysis, it was found a four-variable regression equations enabling a predictive rate of about 81% and 73% in the training and test sets of compounds, respectively. These results demonstrate that QSAR-MT is an efficient tool to predict the appearance of dyspnea associated with drug consumption.

  9. Cloud detection using Meteosat imagery and numerical weather prediction model data

    CERN Document Server

    Feijt, A; Van der Veen, S

    2000-01-01

    The cloud detection algorithm of the Royal Netherlands Meteorological Institute (KNMI) Meteosat Cloud Detection and Characterization KNMI (Metclock) scheme is introduced. The algorithm analyzes the Meteosat infrared and visual channel measurements over an area from about 25 degrees W to 25 degrees E and from 35 degrees to 70 degrees N, encompassing Europe and a small part of northern Africa. The scheme utilizes surface temperatures from a numerical weather prediction model. Synoptic observations are used to adjust the model surface temperatures to represent satellite brightness temperatures for cloud-free conditions. The measured reflected sunlight is analyzed using a minimum reflectivity atlas. Comparison of cloud detection results with synoptic observations of cloud cover at about 800 synoptic stations over land and 50 over sea were made on a 3-h basis for 1997. In total, two million synoptic observations were used to evaluate the detection method. Of the reported cloud cover, Metclock detected 89% during d...

  10. THE PHYSICAL CONDITIONS IN A PRE-SUPER STAR CLUSTER MOLECULAR CLOUD IN THE ANTENNAE GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, K. E.; Indebetouw, R.; Evans, A. S. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Leroy, A. K.; Brogan, C. L.; Hibbard, J.; Sheth, K. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Whitmore, B. C., E-mail: kej7a@virginia.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2015-06-10

    We present an analysis of the physical conditions in an extreme molecular cloud in the Antennae merging galaxies. This cloud has properties consistant with those required to form a globular cluster. We have obtained ALMA CO and 870 μm observations of the Antennae galaxy system with ∼0.″5 resolution. This cloud stands out in the data with a radius of ≲24 pc and mass of >5 × 10{sup 6} M{sub ⊙}. The cloud appears capable of forming a globular cluster, but the lack of associated thermal radio emission indicates that star formation has not yet altered the environment. The lack of thermal radio emission places the cloud in an early stage of evolution, which we expect to be short-lived (≲1 Myr) and thus rare. Given its mass and kinetic energy, for the cloud to be confined (as its appearance strongly suggests) it must be subject to an external pressure of P/k{sub B} ≳ 10{sup 8} K cm{sup −3}–10,000 times higher than typical interstellar pressure. This would support theories that high pressures are required to form globular clusters and may explain why extreme environments like the Antennae are preferred environments for generating such objects. Given the cloud temperature of ∼25 K, the internal pressure must be dominated by non-thermal processes, most likely turbulence. We expect the molecular cloud to collapse and begin star formation in ≲1 Myr.

  11. Conjecture on imminent earthquake prediction --- from shaving foam to cloud patterns

    CERN Document Server

    Liu, Xin

    2013-01-01

    A conjecture on imminent earthquake prediction is presented. Drastic geological deformations of crustal rock strata taking place immediately (hours/days) before an earthquake may cause fast air or gas emission/absorption vertically in between ground and sky. I conjecture, inspired by an observation of strange patterns appearing on shaving foam, that this fast movement of air fluid may produce unusual cloud patterns at interfaces between atmosphere levels. This air movement is vertical and drastic, different from the horizontal and moderate meteorological air movement, hence its caused cloud patterns are expected to be different from meteorological cloud patterns. This provides a possible origin for the so-called earthquake cloud. Recognition of different earthquake cloud patterns may provide a practical way to estimate location, magnitude and strength of geological deformations of rock strata, and hence a method with support of physics for imminent earthquake prediction. In the end of this paper an experiment...

  12. Millimeter dust emission compared with other mass estimates in N11 molecular clouds in the LMC

    CERN Document Server

    Herrera, Cinthya N; Bolatto, Alberto D; Boulanger, Francois; Israel, Frank P; Rantakyro, Fredrik T

    2013-01-01

    CO and dust emission at millimeter wavelengths are independent tracers of cold interstellar matter, which have seldom been compared on the scale of GMCs in other galaxies. In this study, and for the first time in the Large Magellanic Cloud, we compute the molecular cloud masses from the mm emission of the dust and compare them with the masses derived from their CO luminosity and virial theorem. We present CO (J=1-0,2-1) and 1.2 mm continuum observations of the N11 star forming region in the LMC obtained with the SEST telescope and the SIMBA bolometer, respectively. We use the CO data to identify individual molecular clouds and measure their physical properties. The correlations between the properties of the N11 clouds are in agreement with those found in earlier studies in the LMC that sample a larger set of clouds and a larger range of cloud masses. For the N11 molecular clouds, we compare the masses estimated from the CO luminosity (Xco\\Lco), the virial theorem (Mvir) and the millimeter dust luminosity (L_d...

  13. Convex decomposition of concave clouds for the ultra-short-term power prediction of distributed photovoltaic system

    Institute of Scientific and Technical Information of China (English)

    蔡世波

    2016-01-01

    Concave clouds will cause miscalculation by the power prediction model based on cloud features for distributed photovoltaic (PV) plant.The algorithm for decomposing concave cloud into convex images is proposed .Adopting minimum polygonal approximation ( MPP) to demonstrate the contour of concave cloud , cloud features are described and the subdivision lines of convex decomposition for the concave clouds are determined by the centroid point scattering model and centroid angle func -tion, which realizes the convex decomposition of concave cloud .The result of MATLAB simulation indicates that the proposed algorithm can accurately detect cloud contour corners and recognize the concave points .The proposed decomposition algorithm has advantages of less time complexity and decomposition part numbers compared to traditional algorithms .So the established model can make the convex decomposition of complex concave clouds completely and quickly , which is available for the existing prediction algorithm for the ultra-short-term power output of distributed PV system based on the cloud features .

  14. The Molecular Cloud S242: Physical Environment and Star-formation Activities

    Science.gov (United States)

    Dewangan, L. K.; Baug, T.; Ojha, D. K.; Janardhan, P.; Devaraj, R.; Luna, A.

    2017-08-01

    We present a multi-wavelength study to probe the star-formation (SF) processes on a larger scale (˜ 1\\buildrel{\\circ}\\over{.} 05× 0\\buildrel{\\circ}\\over{.} 56) around the S242 site. The S242 molecular cloud is depicted in a velocity range from -3.25 to 4.55 km s-1 and has a spatially elongated appearance. Based on the virial analysis, the cloud is prone to gravitational collapse. The cloud harbors an elongated filamentary structure (EFS; length ˜25 pc), which is evident in the Herschel column density map, and the EFS has an observed mass per unit length of ˜200 {M}⊙ pc-1, exceeding the critical value of ˜16 {M}⊙ pc-1 (at T = 10 K). The EFS contains a chain of Herschel clumps (M clump ˜ 150-1020 {M}⊙ ), revealing the evidence of fragmentation along its length. The most massive clumps are observed at both the EFS ends, while the S242 H ii region is located at one EFS end. Based on the radio continuum maps at 1.28 and 1.4 GHz, the S242 H ii region is ionized by a B0.5V-B0V type star and has a dynamical age of ˜0.5 Myr. The photometric 1-5 μm data analysis of point-like sources traces young stellar objects (YSOs) toward the EFS and the clusters of YSOs are exclusively found at both the EFS ends, revealing the SF activities. Considering the spatial presence of massive clumps and YSO clusters at both the EFS ends, the observed results are consistent with the prediction of an SF scenario of the end-dominated collapse driven by the higher acceleration of gas.

  15. Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

    Science.gov (United States)

    Van Kooten, Elishevah M. M. E.; Wielandt, Daniel; Schiller, Martin; Nagashima, Kazuhide; Thomen, Aurélien; Olsen, Mia B.; Nordlund, Åke; Krot, Alexander N.; Bizzarro, Martin

    2016-01-01

    The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants. PMID:26858438

  16. Sensor Data Fusion for Accurate Cloud Presence Prediction Using Dempster-Shafer Evidence Theory

    Directory of Open Access Journals (Sweden)

    Jesse S. Jin

    2010-10-01

    Full Text Available Sensor data fusion technology can be used to best extract useful information from multiple sensor observations. It has been widely applied in various applications such as target tracking, surveillance, robot navigation, signal and image processing. This paper introduces a novel data fusion approach in a multiple radiation sensor environment using Dempster-Shafer evidence theory. The methodology is used to predict cloud presence based on the inputs of radiation sensors. Different radiation data have been used for the cloud prediction. The potential application areas of the algorithm include renewable power for virtual power station where the prediction of cloud presence is the most challenging issue for its photovoltaic output. The algorithm is validated by comparing the predicted cloud presence with the corresponding sunshine occurrence data that were recorded as the benchmark. Our experiments have indicated that comparing to the approaches using individual sensors, the proposed data fusion approach can increase correct rate of cloud prediction by ten percent, and decrease unknown rate of cloud prediction by twenty three percent.

  17. Sensor data fusion for accurate cloud presence prediction using Dempster-Shafer evidence theory.

    Science.gov (United States)

    Li, Jiaming; Luo, Suhuai; Jin, Jesse S

    2010-01-01

    Sensor data fusion technology can be used to best extract useful information from multiple sensor observations. It has been widely applied in various applications such as target tracking, surveillance, robot navigation, signal and image processing. This paper introduces a novel data fusion approach in a multiple radiation sensor environment using Dempster-Shafer evidence theory. The methodology is used to predict cloud presence based on the inputs of radiation sensors. Different radiation data have been used for the cloud prediction. The potential application areas of the algorithm include renewable power for virtual power station where the prediction of cloud presence is the most challenging issue for its photovoltaic output. The algorithm is validated by comparing the predicted cloud presence with the corresponding sunshine occurrence data that were recorded as the benchmark. Our experiments have indicated that comparing to the approaches using individual sensors, the proposed data fusion approach can increase correct rate of cloud prediction by ten percent, and decrease unknown rate of cloud prediction by twenty three percent.

  18. The Molecular Clouds Fueling a 1/5 Solar Metallicity Starburst

    CERN Document Server

    Kepley, Amanda A; Johnson, Kelsey E; Sandstrom, Karin; Chen, C -H Rosie

    2016-01-01

    Using the Atacama Large Millimeter/submillimeter Array, we have made the first high spatial and spectral resolution observations of the molecular gas and dust in the prototypical blue compact dwarf galaxy II Zw 40. The CO(2-1) and CO(3-2) emission is clumpy and distributed throughout the central star-forming region. Only one of eight molecular clouds has associated star formation. The continuum spectral energy distribution is dominated by free-free and synchrotron: at 870$\\mu m$, only 50% of the emission is from dust. We derive a CO-to-H$_2$ conversion factor by several methods including a new method that uses simple photodissocation models and resolved CO line intensity measurements to derive a relationship that uniquely predicts $\\alpha_{CO}$ for a given metallicity. We find that the CO-to-H$_2$ conversion factor is 4 to 35 times that of the Milky Way (18.1 to 150.5 M$_\\odot$ / (K km/s pc$^2$)). The star formation efficiency of the molecular gas at least 10 times higher than that found in normal spiral gala...

  19. Molecular Clouds in the North American and Pelican Nebulae: Structures

    CERN Document Server

    Zhang, Shaobo; Yang, Ji

    2013-01-01

    We present observations of 4.25 square degree area toward the North American and Pelican Nebulae in the $J = 1-0$ transitions of $^{12}$CO, $^{13}$CO, and C$^{18}$O. Three molecules show different emission area with their own distinct structures. These different density tracers reveal several dense clouds with surface density over 500 $M_\\odot$ pc$^{-2}$ and a mean H$_2$ column density of 5.8, 3.4, and 11.9$\\times10^{21}$ cm$^{-2}$ for $^{12}$CO, $^{13}$CO, and C$^{18}$O, respectively. We obtain a total mass of $5.4\\times10^4 M_\\odot$ ($^{12}$CO), $2.0\\times10^4 M_\\odot$ ($^{13}$CO), and $6.1\\times10^3 M_\\odot$ (C$^{18}$O) in the complex. The distribution of excitation temperature shows two phase of gas: cold gas ($\\sim$10 K) spreads across the whole cloud; warm gas ($>$20 K) outlines the edge of cloud heated by the W80 H II region. The kinetic structure of the cloud indicates an expanding shell surrounding the ionized gas produced by the H II region. There are six discernible regions in the cloud including t...

  20. Prediction based proactive thermal virtual machine scheduling in green clouds.

    Science.gov (United States)

    Kinger, Supriya; Kumar, Rajesh; Sharma, Anju

    2014-01-01

    Cloud computing has rapidly emerged as a widely accepted computing paradigm, but the research on Cloud computing is still at an early stage. Cloud computing provides many advanced features but it still has some shortcomings such as relatively high operating cost and environmental hazards like increasing carbon footprints. These hazards can be reduced up to some extent by efficient scheduling of Cloud resources. Working temperature on which a machine is currently running can be taken as a criterion for Virtual Machine (VM) scheduling. This paper proposes a new proactive technique that considers current and maximum threshold temperature of Server Machines (SMs) before making scheduling decisions with the help of a temperature predictor, so that maximum temperature is never reached. Different workload scenarios have been taken into consideration. The results obtained show that the proposed system is better than existing systems of VM scheduling, which does not consider current temperature of nodes before making scheduling decisions. Thus, a reduction in need of cooling systems for a Cloud environment has been obtained and validated.

  1. Prediction Based Proactive Thermal Virtual Machine Scheduling in Green Clouds

    Directory of Open Access Journals (Sweden)

    Supriya Kinger

    2014-01-01

    Full Text Available Cloud computing has rapidly emerged as a widely accepted computing paradigm, but the research on Cloud computing is still at an early stage. Cloud computing provides many advanced features but it still has some shortcomings such as relatively high operating cost and environmental hazards like increasing carbon footprints. These hazards can be reduced up to some extent by efficient scheduling of Cloud resources. Working temperature on which a machine is currently running can be taken as a criterion for Virtual Machine (VM scheduling. This paper proposes a new proactive technique that considers current and maximum threshold temperature of Server Machines (SMs before making scheduling decisions with the help of a temperature predictor, so that maximum temperature is never reached. Different workload scenarios have been taken into consideration. The results obtained show that the proposed system is better than existing systems of VM scheduling, which does not consider current temperature of nodes before making scheduling decisions. Thus, a reduction in need of cooling systems for a Cloud environment has been obtained and validated.

  2. A Study of the Molecular Cloud S64 with Multiple Lines of CO Isotopes

    Institute of Scientific and Technical Information of China (English)

    Lei Zhu; Yue-Fang Wu; Yue Wei

    2006-01-01

    We report on a study of the molecular cloud S64 with observations at millimeter wavelengths of multiple molecular lines of CO isotopes. A weak outflow is found, and its physical parameters are estimated. The departure of the core of S64 from the S64 HⅡ region indicates that there are still other star formation activities in that region.

  3. An Improved Technique for Measurement of Cold HI in Molecular Cloud Cores

    CERN Document Server

    Krco, Marko; Brown, Robert L; Li, Di

    2008-01-01

    The presence of atomic gas mixed with molecular species in a "molecular" cloud may significantly affect its chemistry, the excitation of some species, and can serve as probe of the cloud's evolution. Cold neutral atomic hydrogen (HI) in molecular clouds is revealed by its self absorption of background galactic HI 21-cm emission. The properties of this gas can be investigated quantitatively through observation of HI Narrow Self-Absorption (HINSA). In this paper, we present a new technique for measuring atomic gas physical parameters from HINSA observations that utilizes molecular tracers to guide the HINSA extraction. This technique offers a significant improvement in the precision with which HI column densities can be determined over previous methods, and it opens several new avenues of study of relevance to the field of star formation.

  4. A simulation of the collapse and fragmentation of cooling molecular clouds

    Science.gov (United States)

    Monaghan, Joe J.; Lattanzio, John C.

    1991-01-01

    The application of the Smoothed Particle Hydrodynamics method to the fragmentation of rotating cloud and disk systems is described, allowing for molecular cooling due to H2 and CO. A novel approach to solving Poisson's equation for disklike structures which exploits the multigrid algorithm is also described. Numerical studies are presented which investigate the evolution of both rotating clouds and Maclaurin disks, in each case with both an isothermal equation of state and with molecular cooling. The results establish the influence of molecular cooling on the fragmentation of molecular clouds. The isothermal sequences, if they fragment at all, do so into far fewer lumps than the cooling sequences. This is not due to a cooling instability as such, but rather to the reduced thermal support. One of the sequences shows a remarkable similarity to the W49A star-forming region.

  5. The Five College Radio Astronomy Observatory CO Mapping Survey of the Taurus Molecular Cloud

    CERN Document Server

    Narayanan, Gopal; Brunt, Christopher; Goldsmith, Paul F; Snell, Ronald; Li, Di

    2008-01-01

    The FCRAO Survey of the Taurus Molecular Cloud observed the 12CO and 13CO J=1-0 emission from 98 square degrees of this important, nearby star forming region. This set of data with 45" resolution comprises the highest spatial dynamic range image of an individual molecular cloud constructed to date, and provides valuable insights to the molecular gas distribution, kinematics, and the star formation process. In this contribution, we describe the observations, calibration, data processing, and characteristics of the noise and line emission of the survey. The angular distribution of 12CO and 13CO emission over 1 km/s velocity intervals and the full velocity extent of the cloud are presented. These reveal a complex, dynamic medium of cold, molecular gas.

  6. Evolution of Prolate Molecular Clouds at HII Boundaries: I. Formation of fragment-core structures

    CERN Document Server

    Kinnear, Timothy M; White, Glenn J; Goodwin, Simon

    2014-01-01

    The evolution of a prolate cloud at an Hii boundary is investigated using Smoothed Particle Hydrodynamics (SPH). The prolate molecular clouds in our investigation are set with their semi-major axis perpendicular to the radiative direction of a plane parallel ionising Extreme Ultraviolet (EUV) flux. Simulations on three high mass prolate clouds reveal that EUV radiation can trigger distinctive high density core formation embedded in a final linear structure. This contrasts with results of the previous work in which only an isotropic Far Ultraviolet (FUV) interstellar background flux was applied. A systematic investigation on a group of prolate clouds of equal mass but different initial densities and geometric shapes finds that the distribution of the cores over the final linear structure changes with the initial conditions of the prolate cloud and the strength of the EUV radiation flux. These highly condensed cores may either scatter over the full length of the final linear structure or form two groups of high...

  7. Numerical Simulations of Turbulent Molecular Clouds Regulated by Reprocessed Radiation Feedback from Nascent Super Star Clusters

    CERN Document Server

    Skinner, M Aaron

    2015-01-01

    Radiation feedback from young star clusters embedded in giant molecular clouds (GMCs) is believed to be important to the control of star formation. For the most massive and dense clouds, including those in which super star clusters (SSCs) are born, pressure from reprocessed radiation exerted on dust grains may disperse a significant portion of the cloud mass back into the interstellar medium (ISM). Using our radiaton hydrodynamics (RHD) code, Hyperion, we conduct a series of numerical simulations to test this idea. Our models follow the evolution of self-gravitating, strongly turbulent clouds in which collapsing regions are replaced by radiating sink particles representing stellar clusters. We evaluate the dependence of the star formation efficiency (SFE) on the size and mass of the cloud and $\\kappa$, the opacity of the gas to infrared (IR) radiation. We find that the single most important parameter determining the evolutionary outcome is $\\kappa$, with $\\kappa \\gtrsim 15 \\text{ cm}^2 \\text{ g}^{-1}$ needed ...

  8. Evolution of OH and CO-dark Molecular Gas Fraction Across a Molecular Cloud Boundary In Taurus

    CERN Document Server

    Xu, Duo; Yue, Nannan; Goldsmith, Paul F

    2016-01-01

    We present observations of 12CO J=1-0, 13CO J=1-0, HI, and all four ground-state transitions of the hydroxyl (OH) radical toward a sharp boundary region of the Taurus molecular cloud. Based on a PDR model that reproduces CO and [CI] emission from the same region, we modeled the three OH transitions, 1612, 1665, 1667 MHz successfully through escape probability non-LTE radiative transfer model calculations. We could not reproduce the 1720 MHz observations, due to un-modeled pumping mechanisms, of which the most likely candidate is a C-shock. The abundance of OH and CO-dark molecular gas (DMG) are well constrained. The OH abundance [OH]/[H2] decreases from 8*10-7 to 1*10-7 as Av increases from 0.4 to 2.7 mag, following an empirical law [OH]/[H2]= 1.5 * 10^{-7} + 9.0 * 10^{-7} * exp(-Av/0.81), which is higher than PDR model predictions for low extinction regions by a factor of 80. The overabundance of OH at extinctions at or below 1 mag is likely the result of a C-shock. The dark gas fraction (DGF, defined as fra...

  9. Evaluation of cloud prediction and determination of critical relative humidity for a mesoscale numerical weather prediction model

    Energy Technology Data Exchange (ETDEWEB)

    Seaman, N.L.; Guo, Z.; Ackerman, T.P. [Pennsylvania State Univ., University Park, PA (United States)

    1996-04-01

    Predictions of cloud occurrence and vertical location from the Pennsylvannia State University/National Center for Atmospheric Research nonhydrostatic mesoscale model (MM5) were evaluated statistically using cloud observations obtained at Coffeyville, Kansas, as part of the Second International satellite Cloud Climatology Project Regional Experiment campaign. Seventeen cases were selected for simulation during a November-December 1991 field study. MM5 was used to produce two sets of 36-km simulations, one with and one without four-dimensional data assimilation (FDDA), and a set of 12-km simulations without FDDA, but nested within the 36-km FDDA runs.

  10. STAR FORMATION IN THE MOLECULAR CLOUD ASSOCIATED WITH THE MONKEY HEAD NEBULA: SEQUENTIAL OR SPONTANEOUS?

    Energy Technology Data Exchange (ETDEWEB)

    Chibueze, James O.; Imura, Kenji; Omodaka, Toshihiro; Handa, Toshihiro; Kamezaki, Tatsuya; Yamaguchi, Yoshiyuki [Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065 (Japan); Nagayama, Takumi; Sunada, Kazuyoshi [Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan); Fujisawa, Kenta [Department of Physics and Informatics, Faculty of Science, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8512 (Japan); Nakano, Makoto [Faculty of Education and Welfare Science, Oita University, Oita 870-1192 (Japan); Sekido, Mamoru, E-mail: james@milkyway.sci.kagoshima-u.ac.jp [Kashima Space Research Center, National Institute of Information and Communications Technology, 893-1 Hirai, Kashima, Ibaraki 314-8501 (Japan)

    2013-01-01

    We mapped the (1,1), (2,2), and (3,3) lines of NH{sub 3} toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1.'6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H II region S252A. The cooler gas is extended over the cloud even near the extended H II region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the H{alpha} image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low- and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.

  11. Star Formation in the Molecular Cloud Associated with the Monkey Head Nebula: Sequential or Spontaneous?

    Science.gov (United States)

    Chibueze, James O.; Imura, Kenji; Omodaka, Toshihiro; Handa, Toshihiro; Nagayama, Takumi; Fujisawa, Kenta; Sunada, Kazuyoshi; Nakano, Makoto; Kamezaki, Tatsuya; Yamaguchi, Yoshiyuki; Sekido, Mamoru

    2013-01-01

    We mapped the (1,1), (2,2), and (3,3) lines of NH3 toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1.'6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H II region S252A. The cooler gas is extended over the cloud even near the extended H II region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the Hα image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low- and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.

  12. CO J = 3 -> 2 observations of translucent and high-latitude molecular clouds

    NARCIS (Netherlands)

    Dishoeck, van E.F.; Phillips, T.G.; Black, J.H.; Gredel, R.

    1991-01-01

    Measurements were carried out on the CO J = 3-2 emission line at 345 GHz from a number of translucent and high-latitude molecular clouds, as well as on the J = 2-1 and J = 1-0 lines of both the (C-12)O and (C-13)O. It is shown that the physical conditions in the high-latitude clouds are very similar

  13. Mapping of the extinction in Giant Molecular Clouds using optical star counts

    OpenAIRE

    Cambresy, L.

    1999-01-01

    This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho-Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total...

  14. Photometric investigation of the MBM 12 molecular cloud area in Aries. I. Photoelectric photometry

    CERN Document Server

    Kazlauskas, A; Laugalys, V; Straizys, V

    2002-01-01

    The results of photoelectric photometry in the Vilnius seven-color system are given for 152 stars down to 12.2 mag in the area of the molecular cloud MBM 12 and the dust clouds L1454 and L1457 in Aries. The results of photometric classification of stars are also given. The investigation of interstellar extinction in the area is described in the next paper.

  15. An Evolutionary Model for the Star Formation Efficiency in Gravitationally Collapsing Molecular Clouds

    CERN Document Server

    Zamora-Aviles, Manuel Abelardo

    2011-01-01

    We present an idealized, semi-empirical model for the star formation efficiency (SFE) in a molecular cloud (MC) formed by the collision of warm neutral medium cylindrical streams. The cloud continuously accretes mass from the surrounding diffuse gas and begins to contract gravitationally as soon as it reaches its Jeans mass. We present two fiducial cases, one for an isolated cloud and one for a giant molecular cloud (GMC), which we compare against various observational results. The total evolutionary cycle of the model clouds lasts a few tens of Myr, depending on their mass. The low- and high-mass fiducial models achieve time-averaged SFEs of 0.5 and 3%, and terminal SFEs of 39 and 15%. The GMC model adheres very well to the evolutionary scenario recently inferred by Kawamura et al. (2009) for GMCs in the LMC. The individual cloud model's evolutionary track in the Kennicutt-Schmidt diagram passes through the locus of typical low- to intermediate-mass clouds like those studied by Evans et al. (2009) at interme...

  16. A Catalog of Distances to Molecular Clouds from Pan-STARRS1

    Science.gov (United States)

    Schlafly, Eddie; Green, G.; Finkbeiner, D. P.; Rix, H.

    2014-01-01

    We present a catalog of distances to molecular clouds, derived from PanSTARRS-1 photometry. We simultaneously infer the full probability distribution function of reddening and distance of the stars towards these clouds using the technique of Green et al. (2013) (see neighboring poster). We fit the resulting measurements using a simple dust screen model to infer the distance to each cloud. The result is a large, homogeneous catalog of distances to molecular clouds. For clouds with heliocentric distances greater than about 200 pc, typical statistical uncertainties in the distances are 5%, with systematic uncertainty stemming from the quality of our stellar models of about 10%. We have applied this analysis to many of the most well-studied clouds in the δ > -30° sky, including Orion, California, Taurus, Perseus, and Cepheus. We have also studied the entire catalog of Magnani, Blitz, and Mundy (1985; MBM), though for about half of those clouds we can provide only upper limits on the distances. We compare our distances with distances from the literature, when available, and find good agreement.

  17. A QoS-Satisfied Prediction Model for Cloud-Service Composition Based on a Hidden Markov Model

    OpenAIRE

    Qingtao Wu; Mingchuan Zhang; Ruijuan Zheng; Ying Lou; Wangyang Wei

    2013-01-01

    Various significant issues in cloud computing, such as service provision, service matching, and service assessment, have attracted researchers’ attention recently. Quality of service (QoS) plays an increasingly important role in the provision of cloud-based services, by aiming for the seamless and dynamic integration of cloud-service components. In this paper, we focus on QoS-satisfied predictions about the composition of cloud-service components and present a QoS-satisfied prediction model b...

  18. A dense molecular cloud in the OMC-1/OMC-2 region

    Science.gov (United States)

    Kutner, M. L.; Evans, N. J., II; Tucker, K. D.

    1976-01-01

    H2CO emission at 2 mm is seen over a region 30 arcmin in extent which includes OMC-1 and OMC-2. The mass of this cloud, estimated from H2CO and CO observations, is about 7000 solar masses. The velocity pattern is one of rotation, with evidence for fragmentation into two or three distinct condensations. A sharp boundary to the molecular cloud is observed at the edge of the H II region in NGC 1977. It appears likely that NGC 1977 is a condensation at the northern end of the cloud, complementary to the Orion Nebula at the southern end.

  19. A dense molecular cloud in the OMC-1/OMC-2 region

    Science.gov (United States)

    Kutner, M. L.; Evans, N. J., II; Tucker, K. D.

    1976-01-01

    H2CO emission at 2 mm is seen over a region 30 arcmin in extent which includes OMC-1 and OMC-2. The mass of this cloud, estimated from H2CO and CO observations, is about 7000 solar masses. The velocity pattern is one of rotation, with evidence for fragmentation into two or three distinct condensations. A sharp boundary to the molecular cloud is observed at the edge of the H II region in NGC 1977. It appears likely that NGC 1977 is a condensation at the northern end of the cloud, complementary to the Orion Nebula at the southern end.

  20. Models of molecular clouds and the abundances of H2CO and HCO/+/

    Science.gov (United States)

    Wootten, A.; Snell, R.; Evans, N. J., II

    1980-01-01

    Observations of HCO(+) and H2CO in a sample of 13 molecular clouds have been analyzed by construction of uniform, spherical cloud models. The total densities and the abundance of HCO(+) and H2CO relative to H2 which result from these models fall into two domains: one group of clouds has a low temperature, moderate density, and high abundances; the other group has higher temperature and density, but lower abundances. The factor distinguishing these groups may be depletion onto grains in the denser sources.

  1. On the Stability and Evolution of Isolated Molecular Clouds

    Science.gov (United States)

    Langer, W.; Nelson, R.

    1998-01-01

    We present the results of three dimensional hydrodynamic models of evolving, isolated, low mass, quiescent clouds and Bok gobules, where the interstellar radiation field plays an important role in the thermal and chemical evolution, and thermal pressure provides dominant support against gravitational collapse.

  2. Can the removal of molecular cloud envelopes by external feedback affect the efficiency of star formation?

    Science.gov (United States)

    Lucas, William E.; Bonnell, Ian A.; Forgan, Duncan H.

    2017-01-01

    We investigate how star formation efficiency can be significantly decreased by the removal of a molecular cloud's envelope by feedback from an external source. Feedback from star formation has difficulties halting the process in dense gas but can easily remove the less dense and warmer envelopes where star formation does not occur. However, the envelopes can play an important role keeping their host clouds bound by deepening the gravitational potential and providing a constraining pressure boundary. We use numerical simulations to show that removal of the cloud envelopes results in all cases in a fall in the star formation efficiency (SFE). At 1.38 free-fall times our 4 pc cloud simulation experienced a drop in the SFE from 16 to six percent, while our 5 pc cloud fell from 27 to 16 per cent. At the same time, our 3 pc cloud (the least bound) fell from an SFE of 5.67 per cent to zero when the envelope was lost. The star formation efficiency per free-fall time varied from zero to ≈0.25 according to α, defined to be the ratio of the kinetic plus thermal to gravitational energy, and irrespective of the absolute star forming mass available. Furthermore the fall in SFE associated with the loss of the envelope is found to even occur at later times. We conclude that the SFE will always fall should a star forming cloud lose its envelope due to stellar feedback, with less bound clouds suffering the greatest decrease.

  3. Molecular Prediction of Pea Footrot Disease

    Directory of Open Access Journals (Sweden)

    Ebimieowei Etebu

    2011-11-01

    Full Text Available PCR based assays were developed in this study to quantitatively predict pea footrot infections in agricultural soils prior to cultivation. Pea footrot disease due to Nectria haematococca (anamorph Fusarium solani f.sp. pisi is linked to the presence of six pea pathogenicity (PEP genes (PDA1, PEP1, PEP2, PEP3, PEP4 and PEP5. Whilst molecular assays have been used recently to selectively detect these genes in soil- DNA, quantitative molecular assay has been extended to only the PEP3 gene whose role in pea pathogenicity is yet unknown. In this research, PCR-based quantification assays were developed to quantify the two pea pathogenicity genes (PDA and PEP5 with identified roles in pea pathogenicity from soil-DNA obtained from fields with pea footrot histories. Results showed that the quantitative molecular assays developed herein were both efficient. Amplification efficiency of the Q-PCR assay for the PDA and PEP5 gene were 97 and 89%, respectively. PDA and PEP5 gene copy numbers were shown to vary significantly (p = 0.01 between fields. However, the PDA gene copy numbers were relatively higher than those of the PEP5 gene in agricultural fields. The genes, especially PEP5 gene, were comparable to and positively correlated to the number of spores of pathogenic N. haematococca, and footrot disease. The PDA gene alone in soil could not cause footrot disease in peas after 8 weeks of planting; assays directed at it alone may therefore be insufficient to predict pea footrot disease. However, the molecular assay targeting the PDA alongside the PEP5 gene offers the opportunity for quantitative prediction of pea footrot infections in agricultural soils prior to cultivation.

  4. High-Latitude Molecular Clouds in an H I Filament toward the MBM 53, 54, and 55 Complex: Existence of an H2 Cloud with Low CO Intensity

    Science.gov (United States)

    Yamamoto, H.; Onishi, T.; Mizuno, A.; Fukui, Y.

    2003-07-01

    We carried out a CO survey of high Galactic latitude molecular clouds toward an H I filament that contains a molecular cloud complex, MBM 53, 54, and 55, with the NANTEN telescope. Our observation covered the whole area of the H I filament in 12CO (J=1-0) with a 4' grid spacing. The filament is found to consist of a number of clumpy molecular clouds, and we identified 110 12CO clouds in the region, whose total mass is estimated to be ~1200 Msolar. 13CO (J=1-0) observations were carried out toward the region of high 12CO intensities in order to measure the optical depth of molecular gas. There is no detection in C18O (J=1-0) line in the observed region, indicating that there are no clouds dense enough to form stars in the near future. These observations spatially resolved the entire gas distribution of MBM 53, 54, and 55 for the first time, and we have found a massive cloud, HLCG 92-35, around (l, b)~(92°, -35°) whose mass is ~330 Msolar, corresponding to ~1/4 of the total mass. This CO cloud occupies the Galactic western half of a circular H I cloud toward (l, b)=(93.5d, -35.5d), and the H I to CO mass ratio is estimated to be the largest in the observed region. The far-infrared excess over H I emission, which is a good indicator of an existence of molecular hydrogen, toward HLCG 92-35 is the largest in the observed region. The ratio of the luminosity of the infrared excess to CO mass is also significantly larger than those of the other clouds, by a factor of ~5. These facts indicate that HLCG 92-35 is a CO-forming molecular cloud, which is younger than the MBM clouds in terms of molecular cloud formation. Some past explosive event has been suggested toward the H I filament. Toward HLCG 92-35, the molecular gas distributed along the western edge of the H I cloud, which implies that the molecular gas may be formed by a compression of expanding H I shell.

  5. Properties of Low Metallicity Molecular Clouds: A 0.3 Parsec Resolution Map of SMC B1 #1

    Science.gov (United States)

    Rodea, Uriel

    2017-01-01

    Stars form in molecular clouds, therefore understanding their structure is important in understanding this key process in galaxy evolution. Studies of clouds in the Milky Way have provided insight to their internal structures, but until recently we have not been able to study clouds in low metallicity conditions at the same resolution. We use the Atacama Large Millimeter Array to map a molecular cloud in the nearby, low metallicity galaxy the SMC at 0.3 pc spatial resolution in 12CO (2-1). We use the CPROPS algorithm (Rosolowsky & Leroy 2006) to measure structural properties of the cloud (mass, size, velocity dispersion, temperature) and compare to molecular clouds in the Milky Way observed at comparable resolution. We present the results of this comparison and discuss the CO-to-H2 conversion factor, virial parameter and mass-radius-velocity dispersion relationships (i.e. Larson's Laws) for the cloud.

  6. Dynamical evolution and molecular abundances of interstellar clouds

    Science.gov (United States)

    Prasad, Sheo S.; Heere, Karen R.; Tarafdar, Shankar P.

    1991-01-01

    Dynamical models are presented that start with interstellar gas in an initial diffuse state and consider their gravitational collapse and the formation of dense cores. Frozen-in tangled magnetic fields are included to mimic forces that might oppose gravitational contraction and whose effectiveness may increase with increasing core densities. Results suggest the possibility that dense cloud cores may be dynamically evolving ephemeral objects, such that their lifespan at a given core density decreases as that density increases.

  7. The Orion Molecular Cloud 2/3 and NGC 1977 Regions

    OpenAIRE

    Peterson, Dawn E.; Megeath, Tom

    2008-01-01

    The Orion Molecular Cloud 2/3 region (hereafter, OMC-2/3) and the reflection nebula NGC 1977 encompass a section of the Orion A molecular cloud undergoing vigorous star forming activity. One of the richest assemblages of protostars in the nearest 500 pc is seen in OMC-2/3, while NGC 1977 contains a cluster of over 100 young stars. In this review, we present a census of the protostars, pre-main sequence stars, and young brown dwarfs in these regions. These are identified through sub-millimeter...

  8. A Uniform CO Survey of the Molecular Clouds in Orion and Monoceros

    CERN Document Server

    Wilson, B A; Masheder, M R W; Thaddeus, P

    2005-01-01

    We report the results of a new large scale survey of the Orion-Monoceros complex of molecular clouds made in the J = 1->0 line of CO with the Harvard-Smithsonian 1.2m millimetre-wave telescope. The survey consists of 52,288 uniformly spaced spectra that cover an area of 432 square degrees on the sky and is the most sensitive large-scale survey of the region to date. Distances to the constituent molecular clouds of the complex, estimated from an analysis of foreground and background stars, have provided information on the three dimensional structure of the entire complex.

  9. Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

    CERN Document Server

    Klassen, Mikhail; Kirk, Helen

    2016-01-01

    We present an analysis of the relationship between the orientation of magnetic fields and filaments that form in 3D magnetohydrodynamic simulations of cluster-forming, turbulent molecular cloud clumps. We examine simulated cloud clumps with size scales of L ~ 2-4 pc and densities of n ~ 400-1000 cm^-3. Many molecular clouds have Alfven Mach numbers near unity, a regime insufficiently explored by numerical simulations. We simulated two cloud clumps of different masses, one in virial equilibrium, the other strongly gravitationally bound, but with the same initial turbulent velocity field and similar mass-to-flux ratio. We apply various techniques to analyze the filamentary and magnetic structure of the resulting cloud, including the DisPerSE filament-finding algorithm in 3D. The largest structure that forms is a 1-2 parsec-long filament, with smaller connecting sub-filaments. We find that in our trans-Alfvenic clouds, wherein magnetic forces and turbulence are comparable, coherent orientation of the magnetic fi...

  10. The roles of stellar feedback and galactic environment in star forming molecular clouds

    CERN Document Server

    Rey-Raposo, Ramon; Agertz, Oscar; Alig, Christian

    2016-01-01

    Feedback from massive stars is thought to play an important role in the evolution of molecular clouds. In this work we analyse the effects of stellar winds and supernovae (SNe) in the evolution of two massive ($\\sim 10^6\\,M_\\odot$) giant molecular clouds (GMCs): one gravitationally bound collapsing cloud and one unbound cloud undergoing disruption by galactic shear. These two clouds have been extracted from a large scale galaxy model and are re-simulated at a spatial resolution of $\\sim 0.01$ pc, including feedback from winds, SNe, and the combined effect of both. We find that stellar winds stop accretion of gas onto sink particles, and can also trigger star formation in the shells formed by the winds, although the overall effect is to reduce the global star formation rate of both clouds. Furthermore, we observe that winds tend to escape through the corridors of diffuse gas. The effect of SNe is not so prominent and the star formation rate is similar to models neglecting stellar feedback. We find that most of...

  11. Dynamical cooling of galactic discs by molecular cloud collisions - origin of giant clumps in gas-rich galaxy discs

    Science.gov (United States)

    Li, Guang-Xing

    2017-10-01

    Different from Milky Way-like galaxies, discs of gas-rich galaxies are clumpy. It is believed that the clumps form because of gravitational instability. However, a necessary condition for gravitational instability to develop is that the disc must dissipate its kinetic energy effectively, this energy dissipation (also called cooling) is not well understood. We propose that collisions (coagulation) between molecular clouds dissipate the kinetic energy of the discs, which leads to a dynamical cooling. The effectiveness of this dynamical cooling is quantified by the dissipation parameter D, which is the ratio between the free-fall time t_ff≈ 1/ √{G ρ _{disc}} and the cooling time determined by the cloud collision process tcool. This ratio is related to the ratio between the mean surface density of the disc Σdisc and the mean surface density of molecular clouds in the disc Σcloud. When D cloud), cloud collision cooling is inefficient, and fragmentation is suppressed. When D > 1/3 (which roughly corresponds to Σdisc > 1/3Σcloud), cloud-cloud collisions lead to a rapid cooling through which clumps form. On smaller scales, cloud-cloud collisions can drive molecular cloud turbulence. This dynamical cooling process can be taken into account in numerical simulations as a sub-grid model to simulate the global evolution of disc galaxies.

  12. Statistical Assessment of Shapes and Magnetic Field Orientations in Molecular Clouds through Polarization Observations

    CERN Document Server

    Tassis, K; Hildebrand, R H; Kirby, L; Vaillancourt, J E

    2009-01-01

    We present a novel statistical analysis aimed at deriving the intrinsic shapes and magnetic field orientations of molecular clouds using dust emission and polarization observations by the Hertz polarimeter. Our observables are the aspect ratio of the projected plane-of-the-sky cloud image, and the angle between the mean direction of the plane-of-the-sky component of the magnetic field and the short axis of the cloud image. To overcome projection effects due to the unknown orientation of the line-of-sight, we combine observations from 24 clouds, assuming that line-of-sight orientations are random and all are equally probable. Through a weighted least-squares analysis, we find that the best-fit intrinsic cloud shape describing our sample is an oblate disk with only small degrees of triaxiality. The best-fit intrinsic magnetic field orientation is close to the direction of the shortest cloud axis, with small (~24 deg) deviations toward the long/middle cloud axes. However, due to the small number of observed clou...

  13. ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure Near the Closest Super-Star Cluster

    CERN Document Server

    Indebetouw, Remy; Chen, C -H Rosie; Leroy, Adam; Johnson, Kelsey; Muller, Erik; Madden, Suzanne; Cormier, Diane; Galliano, Frederic; Hughes, Annie; Hunter, Todd; Kawamura, Akiko; Kepley, Amanda; Lebouteiller, Vianney; Meixner, Margaret; Oliveira, Joana M; Onishi, Toshikazu; Vasyunina, Tatiana

    2013-01-01

    We present ALMA observations of 30 Doradus -- the highest resolution view of molecular gas in an extragalactic star formation region to date (~0.4pc x 0.6pc). The 30Dor-10 cloud north of R136 was mapped in 12CO 2-1, 13CO 2-1, C18O 2-1, 1.3mm continuum, the H30alpha recombination line, and two H2CO 3-2 transitions. Most 12CO emission is associated with small filaments and clumps (<1pc, ~1000 Msun at the current resolution). Some clumps are associated with protostars, including "pillars of creation" photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to higher surface density at a given size and linewidth compared to clouds studied at 10pc res...

  14. Probing the evolution of molecular cloud structure. II. From chaos to confinement

    Science.gov (United States)

    Kainulainen, J.; Beuther, H.; Banerjee, R.; Federrath, C.; Henning, T.

    2011-06-01

    We present an analysis of the large-scale molecular cloud structure and of the stability of clumpy structures in nearby molecular clouds. In our recent work, we identified a structural transition in molecular clouds by studying the probability distributions of their gas column densities. In this paper, we further examine the nature of this transition. The transition takes place at the visual extinction of A_V^tail = 2{-4} mag, or equivalently, at Σtail ≈ 40-80 M⊙ pc-2. The clumps identified above this limit have wide ranges of masses and sizes, but a remarkably constant mean volume density of overline{n ≈ 10^3} cm-3. This is 5-10 times higher than the density of the medium surrounding the clumps. By examining the stability of the clumps, we show that they are gravitationally unbound entities, and that the external pressure from the parental molecular cloud is a significant source of confining pressure for them. Then, the structural transition at A_V^tail may be linked to a transition between this population and the surrounding medium. The star-formation rates in the clouds correlate strongly with the total mass in the clumps, i.e., with the mass above A_V^tail, and drops abruptly below that threshold. These results imply that the formation of pressure-confined clumps introduces a prerequisite for star formation. Furthermore, they give a physically motivated explanation for the recently reported relation between the star-formation rates and the amount of dense material in molecular clouds. Likewise, they give rise to a natural threshold for star formation at A_V^tail.

  15. Hydrogen in diffuse molecular clouds in the Milky Way. Atomic column densities and molecular fraction along prominent lines of sight

    Science.gov (United States)

    Winkel, B.; Wiesemeyer, H.; Menten, K. M.; Sato, M.; Brunthaler, A.; Wyrowski, F.; Neufeld, D.; Gerin, M.; Indriolo, N.

    2017-03-01

    Context. Recent submillimeter and far-infrared wavelength observations of absorption in the rotational ground-state lines of various simple molecules against distant Galactic continuum sources have opened the possibility of studying the chemistry of diffuse molecular clouds throughout the Milky Way. In order to calculate abundances, the column densities of molecular and atomic hydrogen, H i, must be known. Aims: We aim at determining the atomic hydrogen column densities for diffuse clouds located on the sight lines toward a sample of prominent high-mass star-forming regions that were intensely studied with the HIFI instrument onboard Herschel. Methods: Based on Jansky Very Large Array data, we employ the 21 cm H i absorption-line technique to construct profiles of the H i opacity versus radial velocity toward our target sources. These profiles are combined with lower resolution archival data of extended H i emission to calculate the H i column densities of the individual clouds along the sight lines. We employ Bayesian inference to estimate the uncertainties of the derived quantities. Results: Our study delivers reliable estimates of the atomic hydrogen column density for a large number of diffuse molecular clouds at various Galactocentric distances. Together with column densities of molecular hydrogen derived from its surrogates observed with HIFI, the measurements can be used to characterize the clouds and investigate the dependence of their chemistry on the molecular fraction, for example. The data sets are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/600/A2

  16. Real Time Volcanic Cloud Products and Predictions for Aviation Alerts

    Science.gov (United States)

    Krotkov, Nickolay A.; Habib, Shahid; da Silva, Arlindo; Hughes, Eric; Yang, Kai; Brentzel, Kelvin; Seftor, Colin; Li, Jason Y.; Schneider, David; Guffanti, Marianne; Hoffman, Robert L.; Myers, Tim; Tamminen, Johanna; Hassinen, Seppo

    2014-01-01

    Volcanic eruptions can inject significant amounts of sulfur dioxide (SO2) and volcanic ash into the atmosphere, posing a substantial risk to aviation safety. Ingesting near-real time and Direct Readout satellite volcanic cloud data is vital for improving reliability of volcanic ash forecasts and mitigating the effects of volcanic eruptions on aviation and the economy. NASA volcanic products from the Ozone Monitoring Insrument (OMI) aboard the Aura satellite have been incorporated into Decision Support Systems of many operational agencies. With the Aura mission approaching its 10th anniversary, there is an urgent need to replace OMI data with those from the next generation operational NASA/NOAA Suomi National Polar Partnership (SNPP) satellite. The data provided from these instruments are being incorporated into forecasting models to provide quantitative ash forecasts for air traffic management. This study demonstrates the feasibility of the volcanic near-real time and Direct Readout data products from the new Ozone Monitoring and Profiling Suite (OMPS) ultraviolet sensor onboard SNPP for monitoring and forecasting volcanic clouds. The transition of NASA data production to our operational partners is outlined. Satellite observations are used to constrain volcanic cloud simulations and improve estimates of eruption parameters, resulting in more accurate forecasts. This is demonstrated for the 2012 eruption of Copahue. Volcanic eruptions are modeled using the Goddard Earth Observing System, Version 5 (GEOS-5) and the Goddard Chemistry Aerosol and Radiation Transport (GOCART) model. A hindcast of the disruptive eruption from Iceland's Eyjafjallajokull is used to estimate aviation re-routing costs using Metron Aviation's ATM Tools.

  17. Traffic Flow Prediction Model for Large-Scale Road Network Based on Cloud Computing

    Directory of Open Access Journals (Sweden)

    Zhaosheng Yang

    2014-01-01

    Full Text Available To increase the efficiency and precision of large-scale road network traffic flow prediction, a genetic algorithm-support vector machine (GA-SVM model based on cloud computing is proposed in this paper, which is based on the analysis of the characteristics and defects of genetic algorithm and support vector machine. In cloud computing environment, firstly, SVM parameters are optimized by the parallel genetic algorithm, and then this optimized parallel SVM model is used to predict traffic flow. On the basis of the traffic flow data of Haizhu District in Guangzhou City, the proposed model was verified and compared with the serial GA-SVM model and parallel GA-SVM model based on MPI (message passing interface. The results demonstrate that the parallel GA-SVM model based on cloud computing has higher prediction accuracy, shorter running time, and higher speedup.

  18. Investigating thermal evolution of the self-gravitating one dimensional molecular cloud by smoothed particle hydrodynamics

    CERN Document Server

    Nejad-Asghar, Mohsen

    2008-01-01

    The heating of the ion-neutral (or ambipolar) diffusion may affect the thermal phases of the molecular clouds. We present an investigation on the effect of this heating mechanism in the thermal instability of the molecular clouds. A weakly ionized one dimensional slab geometry, which is allowed for self-gravity and ambipolar diffusion, is chosen to study its thermal phases. We use the thermodynamic evolution of the slab to obtain the regions where slab cloud becomes thermally unstable. We investigate this evolution using the model of ambipolar diffusion with two-fluid smoothed particle hydrodynamics, as outlined by Hosking & Whitworth. Firstly, some parts of the technique are improved to test the pioneer works on behavior of the ambipolar diffusion in an isothermal self-gravitating slab. Afterwards, the improved two-fluid technique is used for thermal evolution of the slab. The results show that the thermal instability may persist inhomogeneities with a large density contrast at the intermediate parts of ...

  19. A 3D view of the outflow in the Orion Molecular Cloud 1 (OMC-1)

    DEFF Research Database (Denmark)

    Nissen, H.D.; Cunningham, N.J.; Sherson, Maiken Gustafsson;

    2012-01-01

    The fast outflow emerging from a region associated with massive star formation in the Orion Molecular Cloud 1 (OMC-1), located behind the Orion Nebula, appears to have been set in motion by an explosive event. Here we study the structure and dynamics of outflows in OMC-1. We combine radial velocity...

  20. Tracing the magnetic field morphology of the Lupus I molecular cloud

    CERN Document Server

    Franco, G A P

    2015-01-01

    Deep R-band CCD linear polarimetry collected for fields with lines-of-sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 um dust emission map shows that the principal filament of Lupus I is constituted by three main clumps acted by magnetic fields having different large-scale structure properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and its app...

  1. Probing the evolution of molecular cloud structure II: From chaos to confinement

    CERN Document Server

    Kainulainen, J; Banerjee, R; Federrath, C; Henning, T

    2011-01-01

    We present an analysis of the large-scale molecular cloud structure and of the stability of clumpy structures in nearby molecular clouds. In our recent work, we identified a structural transition in molecular clouds by studying the probability distributions of gas column densities in them. In this paper, we further examine the nature of this transition. The transition takes place at the visual extinction of A_V^tail = 2-4 mag, or equivalently, at \\Sigma^tail = 40-80 Ms pc^{-2}. The clumps identified above this limit have wide ranges of masses and sizes, but a remarkably constant mean volume density of n = 10^3 cm^{-3}. This is 5-10 times larger than the density of the medium surrounding the clumps. By examining the stability of the clumps, we show that they are gravitationally unbound entities, and that the external pressure from the parental molecular cloud is a significant source of confining pressure for them. Then, the structural transition at A_V^tail may be linked to a transition between this population...

  2. Acceleration of cosmic rays and gamma-ray emission from supernova remnant/molecular cloud associations

    CERN Document Server

    Gabici, S; Morlino, G; Nava, L

    2015-01-01

    The gamma-ray observations of molecular clouds associated with supernova remnants are considered one of the most promising ways to search for a solution of the problem of cosmic ray origin. Here we briefly review the status of the field, with particular emphasis on the theoretical and phenomenological aspects of the problem.

  3. Acceleration of cosmic rays and gamma-ray emission from supernova remnant/molecular cloud associations

    Directory of Open Access Journals (Sweden)

    Gabici Stefano

    2015-01-01

    Full Text Available The gamma-ray observations of molecular clouds associated with supernova remnants are considered one of the most promising ways to search for a solution of the problem of cosmic ray origin. Here we briefly review the status of the field, with particular emphasis on the theoretical and phenomenological aspects of the problem.

  4. Application of optimal prediction to molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Barber, IV, John Letherman [Univ. of California, Berkeley, CA (United States)

    2004-12-01

    Optimal prediction is a general system reduction technique for large sets of differential equations. In this method, which was devised by Chorin, Hald, Kast, Kupferman, and Levy, a projection operator formalism is used to construct a smaller system of equations governing the dynamics of a subset of the original degrees of freedom. This reduced system consists of an effective Hamiltonian dynamics, augmented by an integral memory term and a random noise term. Molecular dynamics is a method for simulating large systems of interacting fluid particles. In this thesis, I construct a formalism for applying optimal prediction to molecular dynamics, producing reduced systems from which the properties of the original system can be recovered. These reduced systems require significantly less computational time than the original system. I initially consider first-order optimal prediction, in which the memory and noise terms are neglected. I construct a pair approximation to the renormalized potential, and ignore three-particle and higher interactions. This produces a reduced system that correctly reproduces static properties of the original system, such as energy and pressure, at low-to-moderate densities. However, it fails to capture dynamical quantities, such as autocorrelation functions. I next derive a short-memory approximation, in which the memory term is represented as a linear frictional force with configuration-dependent coefficients. This allows the use of a Fokker-Planck equation to show that, in this regime, the noise is δ-correlated in time. This linear friction model reproduces not only the static properties of the original system, but also the autocorrelation functions of dynamical variables.

  5. The Relationship between the Dust and Gas-Phase CO across the California Molecular Cloud

    Science.gov (United States)

    Kong, S.; Lada, C. J.; Lada, E. A.; Román-Zúñiga, C.; Bieging, J. H.; Lombardi, M.; Forbrich, J.; Alves, J. F.

    2015-05-01

    We present results of an extinction-CO line survey of the southeastern part of the California molecular cloud (CMC). Deep, wide-field, near-infrared images were used to construct a sensitive, relatively high resolution (˜0.5 arcmin) (NICEST) extinction map of the region. The same region was also surveyed in the 12CO(2-1), 13CO(2-1), and C18O(2-1) emission lines at the same angular resolution. These data were used to investigate the relation between the molecular gas, traced by CO emission lines, and the dust column density, traced by extinction, on spatial scales of 0.04 pc across the cloud. We found strong spatial variations in the abundances of 13CO and C18O that were correlated with variations in gas temperature, consistent with temperature-dependent CO depletion/desorption on dust grains. The 13CO-to-C18O abundance ratio was found to increase with decreasing extinction, suggesting selective photodissociation of C18O by the ambient UV radiation field. The effect is particularly pronounced in the vicinity of an embedded cluster where the UV radiation appears to have penetrated deeply (i.e., {{A}V} ≲ 15 mag) into the cloud. We derived the cloud-averaged X-factor to be = 2.53 × 1020 c{{m}-2}{{≤ft( K km {{s}-1} \\right)}-1}, a value somewhat higher than the Milky Way average. On sub-parsec scales we find there is no single empirical value of the 12CO X-factor that can characterize the molecular gas in cold (Tk ≲ 15 K) cloud regions, with XCO ∝ AV0.74 for {{A}V} ≳ 3 mag. However, in regions containing relatively hot (Tex ≳ 25 K) molecular gas we find a clear correlation between W(12CO) and {{A}V} over a large (3 ≲ {{A}V} ≲ 25 mag) range of extinction. This results in a constant XCO = 1.5 × 1020 c{{m}-2} {{≤ft( K km {{s}-1} \\right)}-1} for the hot gas, a lower value than either the average for the CMC or the Milky Way. Overall we find an (inverse) correlation between XCO and Tex in the cloud with XCO ∝ Tex -0.7. This correlation suggests that

  6. The gravitational wakefield of a molecular cloud in a disk galaxy

    Science.gov (United States)

    Tagger, M.; Pellat, R.; Sygnet, J. F.

    1990-01-01

    A molecular cloud (considered as a point macroparticle) represents a clump of increased mass density moving in the disk of a galaxy. Its presence generates a gravitational polarization of the disk, somewhat analogous to the polarization of a dielectric medium by a test charged particle. This means that the cloud travels along with a wakefield (a region of increased mass density) which is the collective response of the stars and gas to the perturbing mass. It can represent many times the mass of the cloud, and emits spiral density waves which propagate away. In terms of statistical mechanics, this wakefield will appear as an increased two-particle correlation function which is the equivalent of the Debye sphere in a plasma - despite the absence here of negative charges. At short distances clouds will thus interact through their own gravitational field amplified by their wakefields, which might thus strongly affect their collisionality. Researchers present a calculation of this wakefield and discuss its importance in the collisional dynamics of molecular clouds.

  7. Molecular Hydrogen in Diffuse Interstellar Clouds of Arbitrary Three-Dimensional Geometry

    CERN Document Server

    Spaans, M; Spaans, Marco; Neufeld, David A.

    1997-01-01

    We have constructed three-dimensional models for the equilibrium abundance of molecular hydrogen within diffuse interstellar clouds of arbitrary geometry that are illuminated by ultraviolet radiation. The position-dependent photo- dissociation rate of H$_2$ within such clouds was computed using a 26-ray approximation to model the attenuation of the incident ultraviolet radiation field by dust and by H$_2$ line absorption. We have applied our modeling technique to the isolated diffuse cloud G236+39, assuming that the cloud has a constant density and that the thickness of the cloud along the line of sight is at every point proportional to the 100 um continuum intensity measured by IRAS. We find that our model can successfully account for observed variations in the ratio of 100 umu continuum intensity to HI column density, with larger values of that ratio occurring along lines of sight in which the molecular hydrogen fraction is expected to be largest. Using a standard chi^2 analysis to assess the goodness of fi...

  8. The molecular cloud-H II region complexes associated with SH 90 and SH 235

    Science.gov (United States)

    Lafon, G.; Baudry, A.; de La Noe, J.; Deharveng, L.

    1983-07-01

    The Sharpless regions Sh 90 and Sh 235 are characterized on the basis of monochromatic photographs (at H-alpha, N III, and O III) and H-alpha photographic interferograms made at the Observatoire de Haute-Provence and of molecular-cloud maps (at 110.201 and 89.189 GHz) made at the Observatoire de Bordeaux. Sh 90, at a distance of 2.4 kpc, is found to have an evolved-H II-region shell structure, with ionized gas flowing both away from and toward a neutral molecular cloud with a mass of about 60,000 solar mass which lies partly in front of the H II region. Sh 235, at 1.6 kpc, has two extended 100,000-300,000-solar-mass neutral clouds which partly overlap. The northern cloud, identified at -20 km/s, is related to the optical nebula; the southern cloud (at -17 km/s) contains three compact H II regions (A, B, and C) and exhibits recent star-formation processes. The 'champagne' model of H II regions proposed by Tenorio-Tagle (1979) is considered applicable to Sh 90 and to Sh 235C.

  9. On the similarity of IR-bright and IR-dark molecular clouds

    CERN Document Server

    Schneider, N; Klessen, R S; Tremblin, P; Ossenkopf, V; Peretto, N

    2014-01-01

    Are Infrared Dark Clouds (IRDCs) special in terms of their physical properties (mass, temperature, star-formation activity) or do they behave as any other star-forming molecular cloud? In this letter, we display column density and temperature maps derived from Herschel, and ATLASGAL dust continuum observations of a sample of prominent massive IRDCs, i.e. G11.11-0.12 (the 'snake'), G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using 13CO 1-0 (BU-FCRAO GRS) and 12CO 3-2 (JCMT) data, showing that our IRDCs are embedded in massive giant molecular clouds (GMCs). The probability distribution function of column densities (PDF) for all clouds have a power-law tail for high column densities, independent of their evolutionary stage (G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, G28.53-0.25 shows no signs of star-formation), we attribute to self-gravity. This is in contrast with the purely lognormal PDFs reported using near/mid-IR extinction maps. The p...

  10. Using CO line ratios to trace the physical properties of molecular clouds

    Science.gov (United States)

    Peñaloza, Camilo H.; Clark, Paul C.; Glover, Simon C. O.; Shetty, Rahul; Klessen, Ralf S.

    2017-02-01

    The carbon monoxide (CO) rotational transition lines are the most common tracers of molecular gas within giant molecular clouds (MCs). We study the ratio (R2-1/1-0) between CO's first two emission lines and examine what information it provides about the physical properties of the cloud. To study R2-1/1-0, we perform smooth particle hydrodynamic simulations with time-dependent chemistry (using GADGET-2), along with post-process radiative transfer calculations on an adaptive grid (using RADMC-3D) to create synthetic emission maps of a MC. R2-1/1-0 has a bimodal distribution that is a consequence of the excitation properties of each line, given that J = 1 reaches local thermal equilibrium while J = 2 is still sub-thermally excited in the considered clouds. The bimodality of R2-1/1-0 serves as a tracer of the physical properties of different regions of the cloud, and it helps constrain local temperatures, densities and opacities. Additionally, this bimodal structure shows an important portion of the CO emission comes from diffuse regions of the cloud, suggesting that the commonly used conversion factor of R2-1/1-0 ∼ 0.7 between both lines may need to be studied further.

  11. Star Formation in Bright Rimmed Clouds. I. Millimeter and Submillimeter Molecular Line Surveys

    CERN Document Server

    De Vries, C H; Snell, R L; Vries, Christopher H. De; Narayanan, Gopal; Snell, Ronald L.

    2002-01-01

    We present the results of the first detailed millimeter and submillimeter molecular line survey of bright rimmed clouds, observed at FCRAO in the CO (J=1-0), C18O (J=1-0), HCO+ (J=1-0), H13CO+ (J=1-0), and N2H+ (J=1-0) transitions, and at the HHT in the CO (J=2-1), HCO+ (J=3-2), HCO+ (J=4-3), H13CO+ (J=3-2), and H13CO+ (J=4-3) molecular line transitions. The source list is composed of a selection of bright rimmed clouds from the catalog of such objects compiled by Sugitani et al. (1991). We also present observations of three Bok globules done for comparison with the bright rimmed clouds. We find that the appearance of the millimeter CO and HCO+ emission is dominated by the morphology of the shock front in the bright rimmed clouds. The HCO+ (J=1-0) emission tends to trace the swept up gas ridge and overdense regions which may be triggered to collapse as a result of sequential star formation. Five of the seven bright rimmed clouds we observe seem to have an outflow, however only one shows the spectral line blue...

  12. Physical properties of molecular clouds for the entire Milky Way disk

    CERN Document Server

    Miville-Deschênes, Marc-Antoine; Lee, Eve J

    2016-01-01

    This study presents a catalog of 8107 molecular clouds that covers the entire Galactic plane and includes 98% of the $^{12}$CO emission observed within $b\\pm5^\\circ$. The catalog was produced using a hierarchical cluster identification method applied to the result of a Gaussian decomposition of the Dame et al. data. The total H$_2$ mass in the catalog is $1.2\\times10^9$ M$_\\odot$ in agreement with previous estimates. We find that 30% of the sight lines intersect only a single cloud, with another 25% intersecting only two clouds. The most probable cloud size is $R\\sim30$ pc. We find that $M\\propto R^{2.2\\pm0.2}$, with no correlation between the cloud surface density, $\\Sigma$, and $R$. In contrast with the general idea, we find a rather large range of values of $\\Sigma$, from 2 to 300 M$_\\odot$ pc$^{-2}$, and a systematic decrease with increasing Galactic radius, $R_{\\rm gal}$. The cloud velocity dispersion as well as the normalization $\\sigma_0=\\sigma_v/R^{1/2}$ both decrease systematically with $R_{\\rm gal}$...

  13. Star formation efficiencies of molecular clouds in a galactic center environment

    CERN Document Server

    Bertram, Erik; Clark, Paul C; Klessen, Ralf S

    2015-01-01

    We use the Arepo moving mesh code to simulate the evolution of molecular clouds exposed to a harsh environment similar to that found in the galactic center (GC), in an effort to understand why the star formation efficiency (SFE) of clouds in this environment is so small. Our simulations include a simplified treatment of time-dependent chemistry and account for the highly non-isothermal nature of the gas and the dust. We model clouds with a total mass of 1.3x10^5 M_{sun} and explore the effects of varying the mean cloud density and the virial parameter, alpha = E_{kin}/|E_{pot}|. We vary the latter from alpha = 0.5 to alpha = 8.0, and so many of the clouds that we simulate are gravitationally unbound. We expose our model clouds to an interstellar radiation field (ISRF) and cosmic ray flux (CRF) that are both a factor of 1000 higher than the values found in the solar neighbourhood. As a reference, we also run simulations with local solar neighbourhood values of the ISRF and the CRF in order to better constrain ...

  14. Diversity of extrasolar planets and diversity of molecular cloud cores. I. Semimajor axes

    Energy Technology Data Exchange (ETDEWEB)

    Jin, Liping; Li, Min, E-mail: jinlp@jlu.edu.cn, E-mail: minli09@mails.jlu.edu.cn [College of Physics, Jilin University, Changchun, Jilin 130012 (China)

    2014-03-01

    We show that the diversity of extrasolar planetary systems may be related to the diversity of molecular cloud cores. In previous studies of planet formation, artificial initial conditions of protoplanetary disks or steady state disks, such as the minimum mass nebula model, have often been used so that the influence of cloud core properties on planet formation is not realized. To specifically and quantitatively demonstrate our point, we calculate the dependence of disk properties on cloud core properties and show that the boundary of the giant planet formation region in a disk is a function of cloud core properties with the conventional core accretion model of giant planet formation. The gravitational stability of a disk depends on the properties of its progenitor cloud core. We also compare our calculations with observations of extrasolar planets. From the observational data of cloud cores, our model could infer the range and most frequent values of observed semimajor axes of extrasolar planets. Our calculations suggest that planet formation at the snowline alone could not completely explain the semimajor axis distribution. If the current observations are not biased, our calculations indicate that the planet formation at the snowline is inefficient. We suggest that there will be more observed planets with semimajor axis <9 AU than >9 AU, even with a longer duration of observations, if the planet formation at the snowline is inefficient.

  15. A High Performance Cloud-Based Protein-Ligand Docking Prediction Algorithm

    Directory of Open Access Journals (Sweden)

    Jui-Le Chen

    2013-01-01

    Full Text Available The potential of predicting druggability for a particular disease by integrating biological and computer science technologies has witnessed success in recent years. Although the computer science technologies can be used to reduce the costs of the pharmaceutical research, the computation time of the structure-based protein-ligand docking prediction is still unsatisfied until now. Hence, in this paper, a novel docking prediction algorithm, named fast cloud-based protein-ligand docking prediction algorithm (FCPLDPA, is presented to accelerate the docking prediction algorithm. The proposed algorithm works by leveraging two high-performance operators: (1 the novel migration (information exchange operator is designed specially for cloud-based environments to reduce the computation time; (2 the efficient operator is aimed at filtering out the worst search directions. Our simulation results illustrate that the proposed method outperforms the other docking algorithms compared in this paper in terms of both the computation time and the quality of the end result.

  16. Remote measurement of cloud microphysics and its influence in predicting high impact weather events

    Science.gov (United States)

    Bipasha, Paul S.; Jinya, John

    2016-05-01

    Understanding the cloud microphysical processes and precise retrieval of parameters governing the same are crucial for weather and climate prediction. Advanced remote sensing sensors and techniques offer an opportunity for monitoring micro-level developments in cloud structure. . Using the observations from a visible and near-infrared lidar onboard CALIPSO satellite (part of A-train) , the spatial variation of cloud structure has been studied over the Tropical monsoon region . It is found that there is large variability in the cloud microphysical parameters manifesting in distinct precipitation regimes. In particular, the severe storms over this region are driven by processes which range from the synoptic to the microphysical scale. Using INSAT-3D data, retrieval of cloud microphysical parameters like effective radius (CER) and optical depth (COD) were carried out for tropical cyclone Phailine. It was observed that there is a general increase of CER in a top-down direction, characterizing the progressively increasing number and size of precipitation hydrometeors while approaching the cloud base. The distribution of CER relative to cloud top temperature for growing convective clouds has been investigated to reveal the evolution of the particles composing the clouds. It is seen that the relatively high concentration of large particles in the downdraft zone is closely related to the precipitation efficiency of the system. Similar study was also carried using MODIS observations for cyclones over Indian Ocean (2010-2013), in which we find that that the mean effective radius is 24 microns with standard deviation 4.56, mean optical depth is 21 with standard deviation 13.98, mean cloud fraction is 0.92 with standard deviation 0.13 and mainly ice phase is dominant. Thus the remote observations of microstructure of convective storms provide very crucial information about the maintenance and potential devastation likely to be associated with it. With the synergistic

  17. Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

    Science.gov (United States)

    Klassen, Mikhail; Pudritz, Ralph E.; Kirk, Helen

    2017-02-01

    We present an analysis of the relationship between the orientation of magnetic fields and filaments that form in 3D magnetohydrodynamic simulations of cluster-forming, turbulent molecular cloud clumps. We examine simulated cloud clumps with size scales of L ∼ 2-4 pc and densities of n ∼ 400-1000 cm-3 with Alfvén Mach numbers near unity. We simulated two cloud clumps of different masses, one in virial equilibrium, the other strongly gravitationally bound, but with the same initial turbulent velocity field and similar mass-to-flux ratio. We apply various techniques to analyse the filamentary and magnetic structure of the resulting cloud, including the DISPERSE filament-finding algorithm in 3D. The largest structure that forms is a 1-2 parsec-long filament, with smaller connecting sub-filaments. We find that our simulated clouds, wherein magnetic forces and turbulence are comparable, coherent orientation of the magnetic field depends on the virial parameter. Sub-virial clumps undergo strong gravitational collapse and magnetic field lines are dragged with the accretion flow. We see evidence of filament-aligned flow and accretion flow on to the filament in the sub-virial cloud. Magnetic fields oriented more parallel in the sub-virial cloud and more perpendicular in the denser, marginally bound cloud. Radiative feedback from a 16 M⊙ star forming in a cluster in one of our simulation's ultimately results in the destruction of the main filament, the formation of an H II region, and the sweeping up of magnetic fields within an expanding shell at the edges of the H II region.

  18. Systematic search for gamma-ray emitting molecular clouds in the vicinity of supernova remnants

    CERN Document Server

    Häffner, Stephanie; Stegmann, Christian

    2013-01-01

    Observations of very-high-energy (VHE) gamma-ray emission from supernova remnants (SNR) established them as sources of accelerated particles up to energies of 100 TeV. The dominant process - leptonic or hadronic - responsible for the VHE emission is still not proven for most of the SNRs. Molecular clouds (MCs) in the vicinity of SNRs provide increased amount of target material for accelerated particles escaping the SNRs, thus making MCs potential gamma-ray sources. The predicted gamma-ray flux for MCs offset from the SNR shock depends on the applied diffusion model for VHE particles and the SNR and MC properties, which encounter large uncertainties. While the the average galactic diffusion coefficient is estimated, the spatially resolved propagation properties of VHE cosmic rays are unknown. gamma-ray emitting MCs provide a unique possibility to derive new information on the propagation of VHE particles through the ISM and on the acceleration of hadrons at SNRs. We present in this paper a strategy and first r...

  19. Evidence for Decay of Turbulence by MHD Shocks in Molecular Clouds via CO Emission

    CERN Document Server

    Larson, Rebecca L; Green, Joel D; Yang, Yao-Lun

    2015-01-01

    We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program ("COPS", PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material not associated with any protostar. Two models fit about equally well: model 1 has a density of 10$^{3}$ cm$^{-3}$, a shock velocity of 3 km s$^{-1}$, and a magnetic field strength of 4 ${\\mu}$G; model 2 has a density of 10$^{3.5}$ cm$^{-3}$, a shock velocity of $2$ km s$^{-1}$, and a magnetic field strength of 8 $\\mu$G. Timescales for decay of turbulence in this region are comparable to crossing times. Transitions of CO up to $J$ of 8, observed close to active sites of star formation, but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult to detect at individual positions, our Herschel-SPIRE survey o...

  20. The Razor's Edge of Collapse: The Transition Point from Lognormal to Powerlaw in Molecular Cloud PDFs

    CERN Document Server

    Burkhart, Blakesley; Collins, David

    2016-01-01

    We derive an analytic expression for the transitional column density value ($s_t$) between the lognormal and power-law form of the probability distribution function (PDF) in star-forming molecular clouds. Our expression for $s_t$ depends on the mean column density, the variance of the lognormal portion of the PDF, and the slope of the power-law portion of the PDF. We show that $s_t$ can be related to physical quantities such as the sonic Mach number of the flow and the power-law index for a self-gravitating isothermal sphere. This implies that the transition point between the lognormal and power-law density/column density PDF represents the critical density where turbulent and thermal pressure balance, the so-called "post-shock density." We test our analytic prediction for the transition column density using dust PDF observations reported in the literature as well as numerical MHD simulations of self-gravitating supersonic turbulence with the Enzo code. We find excellent agreement between the analytic $s_t$ a...

  1. Molecular Cloud Structure from a CO Spectral Line: Interferometric Observations of MBM-12

    Science.gov (United States)

    Ingalls, J. G.; Reach, W. T.; Bania, T. M.; Carpenter, J. M.

    2007-07-01

    We used the OVRO millimeter interferometer to measure the CO (1-0) surface brightness fluctuations as a function of velocity towards molecular cloud MBM-12. We detect no interferometer visibility at the velocity of the single-dish line core, suggesting a unity surface filling factor of emitting gas. According to our model, the line wing emission is produced by tiny (1-5 milliparsec), dilute clumps, whereas the line core emission comes from large (0.01 pc) surface-filling clumps (the beamsize is about 0.03 pc). If the model is correct, the cloud is made up of mostly transient structures.

  2. Formation of Pillars at the Boundaries between HII Regions and Molecular Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Mizuta, A; Kane, J O; Pound, M W; Remington, B A; Ryutov, D D; Takabe, H

    2006-04-20

    We investigate numerically the hydrodynamic instability of an ionization front (IF) accelerating into a molecular cloud, with imposed initial perturbations of different amplitudes. When the initial amplitude is small, the imposed perturbation is completely stabilized and does not grow. When the initial perturbation amplitude is large enough, roughly the ratio of the initial amplitude to wavelength is greater than 0.02, portions of the IF temporarily separate from the molecular cloud surface, locally decreasing the ablation pressure. This causes the appearance of a large, warm HI region and triggers nonlinear dynamics of the IF. The local difference of the ablation pressure and acceleration enhances the appearance and growth of a multimode perturbation. The stabilization usually seen at the IF in the linear regimes does not work due to the mismatch of the modes of the perturbations at the cloud surface and in density in HII region above the cloud surface. Molecular pillars are observed in the late stages of the large amplitude perturbation case. The velocity gradient in the pillars is in reasonably good agreement with that observed in the Eagle Nebula. The initial perturbation is imposed in three different ways: in density, in incident photon number flux, and in the surface shape. All cases show both stabilization for a small initial perturbation and large growth of the second harmonic by increasing amplitude of the initial perturbation above a critical value.

  3. Fitting density models to observational data - The local Schmidt law in molecular clouds

    CERN Document Server

    Lombardi, Marco; Alves, João

    2013-01-01

    We consider the general problem of fitting a parametric density model to discrete observations, taken to follow a non-homogeneous Poisson point process. This class of models is very common, and can be used to describe many astrophysical processes, including the distribution of protostars in molecular clouds. We give the expression for the likelihood of a given spatial density distribution of protostars and apply it to infer the most probable dependence of the protostellar surface density on the gas surface density. Finally, we apply this general technique to model the distribution of protostars in the Orion molecular cloud and robustly derive the local star formation scaling (Schmidt) law for a molecular cloud. We find that in this cloud the protostellar surface density, \\Sigma_YSO, is directly proportional to the square gas column density, here expressed as infrared extinction in the K-band, A_K: more precisely, \\Sigma_YSO = (1.65 +/- 0.19) A_K^(2.03 +/- 0.15) stars pc^-2.

  4. A Study of Molecular Cloud Associated with the HII Region Sh156

    Science.gov (United States)

    Kang, Meejoo; Lee, Youngung

    2005-06-01

    We have conducted observations toward the molecular cloud associated with the HII region Sh 156 in tcocom (J=1-0), ȩocom(J=1-0), and CS(J=2-1) using the TRAO 14 m telescope. Combining with existing \\cocom(J=1-0) data of the Outer Galaxy Survey, we delineated the physical properties of the cloud. We found that there is a significant sign of interaction between the HII region and the molecular gas. We estimated the masses of the molecular cloud, using three different techniques; the most plausible mass is estimated to be 1.37 × 105 M⊙, using a conversion factor of X=1.9 × 1020 \\conf, and this is similar to virial mass estimate. This implies that the cloud is gravitationally bound and in virial equilibrium even though it is closely associated with the HII region. In addition to existing outflow, we found several MSX and IRAS point sources associated with dense core regions. Thus, more star forming activities other than the existing HII region are also going on in this region.

  5. Detection of Molecular Clouds in the Interarm of the Flocculent Galaxy NGC 5055

    CERN Document Server

    Tosaki, T; Kuno, N; Nakanishi, K; Hasegawa, T; Tosaki, Tomoka; Shioya, Yasuhiro; Kuno, Nario; Nakanishi, Kouichiro; Hasegawa, Takashi

    2003-01-01

    We present high-resolution (~ 4") 12CO (J = 1 - 0) mapping observations with high - velocity resolution (~ 2.6 km s^{-1}) toward the disk of flocculent galaxy NGC 5055, using the Nobeyama Millimeter Array in order to study the physical properties of the molecular clouds in the arm and the interarm. The obtained map shows clumpy structures. Although these are mainly distributed along a spiral arm seen in near-infrared observations, some clouds are located far from the arm, namely in the interarm. These clouds in both the arm and the interarm have a typical size and mass of a few 100 pc and a few 10^6 Mo, respectively. These correspond to the largest Giant Molecular Cloud (GMC) in our Galaxy, and are slightly smaller than Giant Molecular Associations (GMAs) in the grand design spiral M 51. Their CO flux-based masses show good agreement with their virial masses. A size - velocity dispersion relation is also plotted on an extension of the relation for the Galactic GMCs. These facts suggest that the properties of ...

  6. The road toward a full, high resolution Molecular Cloud catalog of the Galaxy

    CERN Document Server

    Colombo, Dario; Ginsburg, Adam; Duarte-Cabral, Ana; Hughes, Annie

    2015-01-01

    The statistical description of Giant Molecular Cloud (GMC) properties relies heavily on the performance of automatic identification algorithms, which are often seriously affected by the survey design. The algorithm we designed, SCIMES (Spectral Clustering for Interstellar Molecular Emission Segmentation), is able to overcome some of these limitations by considering the cloud segmentation problem in the broad framework of the graph theory. The application of the code on the CO(3-2) High Resolution Survey (COHRS) data allowed for a robust decomposition of more than 12,000 objects in the Galactic Plane. Together with the wealth of Galactic Plane surveys of the recent years, this approach will help to open the door to a future, systematic cataloging of all discrete molecular features of our own Galaxy.

  7. Observational Approach to Molecular Cloud Evolutation with the Submillimeter-Wave CI Lines

    Science.gov (United States)

    Oka, T.; Yamamoto, S.

    Neutral carbon atoms (CI) play important roles both in chemistry and cooling processes of interstellar molecular clouds. It is thus crucial to explore its large area distribution to obtain information on formation processes and thermal balance of molecular clouds. However, observations of the submillimeter-wave CI lines have been limited to small areas around some representative objects. We have constructed a 1.2 m submillimeter-wave telescope at the summit of Mt.Fuji. The telescope was designed for the exclusive use of surveying molecular clouds in two submillimeter-wave CI lines, 3 P1 -3 P0 (492GHz) and 3 P2 -3 P1 (809 GHz), of atomic carbon. A superconductor-insulator-superconductor (SIS) mixer receiver was equipped on the Nasmyth focus of the telescope. The receiver noise temperatures [Trx(DSB)] are 300 K and 1000 K for the 492 GHz and the 809 GHz mixers, respectively. The intermediate frequency is centered at 2 GHz, having a 700 MHz bandwidth. An acousto-optical spectrometer (AOS) with 1024 channel outputs is used as a receiver backend. The telescope was installed at Nishi-yasugawara (alt. 3725 m), which is 200 m north of the highest peak, Kengamine (3776 m), in July 1998. It has b en operatede successfully during 4 observing seasons in a remote way from the Hongo campus of the University of Tokyo. We have already observed more than 40 square degrees of the sky with the CI 492 GHz line. The distribution of CI emission is found to be different from those of the 13 CO or C1 8 O emission in some clouds. These differences are discussed in relation to formation processes of molecular clouds.

  8. A Multi-molecular Line Study of an Entire Giant Molecular Cloud

    Science.gov (United States)

    Lo, Nadia

    2009-05-01

    A unified theory of star formation remains one of the major unsolved issues in astrophysics. Presented here are the results of multi-molecular lines mapping of the entire giant molecular cloud G333, comprised sites of low- and high-mass star forming regions in various evolution stages of star formation. The result shows the spatial distribution of CS, HCO+, HCN and HNC are similar on large scales, while N2H+ seems to trace preferentially the very densest regions, possibly due to the chemical difference, that N2H+ is sensitive to temperature and readily destroyed by CO. Two analysis methods were used to characterise this large set of data cubes: GAUSSCLUMPS and principal component analysis (PCA). We found the clumps are heavily fragmented with a beam filling factor of 0.2. We found no correlation between clump radius and line width, contradicts to Larson's Law. Possible explanation is the clumps are fragmented and unresolved with the resolution of Mopra beam, thus the decomposed clump radius is blended and no physical properties can be interpreted. PCA of the velocity dimension found no significant differences among CS, HCO+, HNC and C2H line emissions, suggesting these four molecules are `well-mixed' on large scale, possibly by turbulence. PCA of the integrated emission maps separates molecules into low (13CO and C18O) and high (the rest) density tracers, identifies anti-correlation between HCO+ and N2H+ (due to the depletion of CO). The possibility of removing the scanning patterns of the `on-the-fly' mapping with PCA was also explored. The detection of broad thermal SiO from the massive dense cold core G333.125-0.562, along with other collected transitions, suggesting the core will host massive star formation and the SiO emission arises from shocks associated with an outflow in the cold core. Result of the modelling infall with 3D radiative transfer code using the derived physical parameters have successfully reproduce the line profiles. Recent observation of the

  9. Application of uncertainty reasoning based on cloud model in time series prediction

    Institute of Scientific and Technical Information of China (English)

    张锦春; 胡谷雨

    2003-01-01

    Time series prediction has been successfully used in several application areas, such as meteoro-logical forecasting, market prediction, network traffic forecasting, etc. , and a number of techniques have been developed for modeling and predicting time series. In the traditional exponential smoothing method, a fixed weight is assigned to data history, and the trend changes of time series are ignored. In this paper, an uncertainty reasoning method, based on cloud model, is employed in time series prediction, which uses cloud logic controller to adjust the smoothing coefficient of the simple exponential smoothing method dynamically to fit the current trend of the time series. The validity of this solution was proved by experiments on various data sets.

  10. Application of uncertainty reasoning based on cloud model in time series prediction

    Institute of Scientific and Technical Information of China (English)

    张锦春; 胡谷雨

    2003-01-01

    Time series prediction has been successfully used in several application areas, such as meteorological forecasting, market prediction, network traffic forecasting, etc., and a number of techniques have been developed for modeling and predicting time series. In the traditional exponential smoothing method, a fixed weight is assigned to data history, and the trend changes of time series are ignored. In this paper, an uncertainty reasoning method, based on cloud model, is employed in time series prediction, which uses cloud logic controller to adjust the smoothing coefficient of the simple exponential smoothing method dynamically to fit the current trend of the time series. The validity of this solution was proved by experiments on various data sets.

  11. Eventful evolution of giant molecular clouds in dynamically evolving spiral arms

    Science.gov (United States)

    Baba, Junichi; Morokuma-Matsui, Kana; Saitoh, Takayuki R.

    2017-01-01

    The formation and evolution of giant molecular clouds (GMCs) in spiral galaxies have been investigated in the traditional framework of the combined quasi-stationary density wave and galactic shock model. In this study, we investigate the structure and evolution of GMCs in a dynamically evolving spiral arm using a three-dimensional N-body/hydrodynamic simulation of a barred spiral galaxy at parsec-scale resolution. This simulation incorporated self-gravity, molecular hydrogen formation, radiative cooling, heating due to interstellar far-ultraviolet radiation, and stellar feedback by both H II regions and Type II supernovae. In contrast to a simple expectation based on the traditional spiral model, the GMCs exhibited no systematic evolutionary sequence across the spiral arm. Our simulation showed that the GMCs behaved as highly dynamic objects with eventful lives involving collisional build-up, collision-induced star formation, and destruction via stellar feedback. The GMC lifetimes were predicted to be short, only a few tens of millions years. We also found that at least at the resolutions and with the feedback models used in this study, most of the GMCs without H II regions were collapsing, but half of the GMCs with H II regions were expanding owing to the H II-region feedback from stars within them. Our results support the dynamic and feedback-regulated GMC evolution scenario. Although the simulated GMCs were converging rather than virial equilibrium, they followed the observed scaling relationship well. We also analysed the effects of galactic tides and external pressure on GMC evolution and suggested that GMCs cannot be regarded as isolated systems since their evolution in disc galaxies is complicated because of these environmental effects.

  12. Eventful Evolution of Giant Molecular Clouds in Dynamically Evolving Spiral Arms

    Science.gov (United States)

    Baba, Junichi; Morokuma-Matsui, Kana; Saitoh, Takayuki R.

    2016-09-01

    The formation and evolution of giant molecular clouds (GMCs) in spiral galaxies have been investigated in the traditional framework of the combined quasi-stationary density wave and galactic shock model. In this study, we investigate the structure and evolution of GMCs in a dynamically evolving spiral arm using a three-dimensional N-body/hydrodynamic simulation of a barred spiral galaxy at parsec-scale resolution. This simulation incorporated self-gravity, molecular hydrogen formation, radiative cooling, heating due to interstellar far-ultraviolet radiation, and stellar feedback by both HII regions and Type-II supernovae. In contrast to a simple expectation based on the traditional spiral model, the GMCs exhibited no systematic evolutionary sequence across the spiral arm. Our simulation showed that the GMCs behaved as highly dynamic objects with eventful lives involving collisional build-up, collision-induced star formation, and destruction via stellar feedback. The GMC lifetimes were predicted to be short, only a few tens of millions years. We also found that, at least at the resolutions and with the feedback models used in this study, most of the GMCs without HII regions were collapsing, but half of the GMCs with HII regions were expanding owing to the HII-region feedback from stars within them. Our results support the dynamic and feedback-regulated GMC evolution scenario. Although the simulated GMCs were converging rather than virial equilibrium, they followed the observed scaling relationship well. We also analysed the effects of galactic tides and external pressure on GMC evolution and suggested that GMCs cannot be regarded as isolated systems since their evolution in disc galaxies is complicated because of these environmental effects.

  13. A Comparative Study of Giant Molecular Clouds in M51, M33 and the Large Magellanic Cloud

    CERN Document Server

    Hughes, Annie; Colombo, Dario; Schinnerer, Eva; Pety, Jerome; Leroy, Adam K; Dobbs, Clare L; Garcia-Burillo, Santiago; Thompson, Todd A; Dumas, Gaelle; Schuster, Karl F; Kramer, Carsten

    2013-01-01

    We compare the properties of giant molecular clouds (GMCs) in M51 identified by the Plateau de Bure Interferometer Whirlpool Arcsecond Survey (PAWS) with GMCs identified in wide-field, high resolution surveys of CO emission in M33 and the Large Magellanic Cloud (LMC). We find that GMCs in M51 are larger, brighter and have higher velocity dispersions relative to their size than equivalent structures in M33 and the LMC. These differences imply that there are genuine variations in the average mass surface density of the different GMC populations. To explain this, we propose that the pressure in the interstellar medium surrounding the GMCs plays a role in regulating their density and velocity dispersion. We find no evidence for a correlation between size and linewidth in any of M51, M33 or the LMC when the CO emission is decomposed into GMCs, although moderately robust correlations are apparent when regions of contiguous CO emission (with no size limitation) are used. Our work demonstrates that observational bias...

  14. Molecular Cloud-scale Star Formation in NGC 300

    CERN Document Server

    Faesi, Christopher M; Forbrich, Jan; Menten, Karl; Bouy, Herve

    2014-01-01

    We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 HII regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J=2-1) observations with the APEX telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ~10^5 Msun to 7x10^5 Msun. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine GALEX FUV, Spitzer 24 micron, and H-alpha narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our HII region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more s...

  15. FERMI LARGE AREA TELESCOPE STUDY OF COSMIC RAYS AND THE INTERSTELLAR MEDIUM IN NEARBY MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Ackermann, M. [Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany); Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Buehler, R. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Baldini, L.; Bellazzini, R.; Bregeon, J. [Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy); Ballet, J. [Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d' Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France); Barbiellini, G. [Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy); Bastieri, D. [Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy); Bonamente, E. [Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy); Brandt, T. J. [CNRS, IRAP, F-31028 Toulouse cedex 4 (France); Brigida, M. [Dipartimento di Fisica ' M. Merlin' dell' Universita e del Politecnico di Bari, I-70126 Bari (Italy); Bruel, P., E-mail: hayashi@hep01.hepl.hiroshima-u.ac.jp, E-mail: mizuno@hep01.hepl.hiroshima-u.ac.jp [Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Palaiseau (France); and others

    2012-08-10

    We report an analysis of the interstellar {gamma}-ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within {approx}300 pc from the solar system. The {gamma}-ray emission produced by interactions of cosmic rays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained {gamma}-ray emissivities above 250 MeV are (5.9 {+-} 0.1{sub stat}{sup +0.9}{sub -1.0sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1}, (10.2 {+-} 0.4{sub stat}{sup +1.2}{sub -1.7sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1}, and (9.1 {+-} 0.3{sub stat}{sup +1.5}{sub -0.6sys}) Multiplication-Sign 10{sup -27} photons s{sup -1} sr{sup -1} H-atom{sup -1} for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by {approx}20% in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, X{sub CO} = N(H{sub 2})/W{sub CO}, is found to be (0.96 {+-} 0.06{sub stat}{sup +0.15}{sub -0.12sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1}, (0.99 {+-} 0.08{sub stat}{sup +0.18}{sub -0.10sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1}, and (0.63 {+-} 0.02{sub stat}{sup +0.09}{sub -0.07sys}) Multiplication-Sign 10{sup 20} H{sub 2}-molecule cm{sup -2} (K km s{sup -1}){sup -1} for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of X{sub CO} in the vicinity of the solar system. From the

  16. The impact of X-rays on molecular cloud fragmentation and the IMF

    CERN Document Server

    Hocuk, S

    2010-01-01

    Star formation is regulated through a variety of feedback processes. In this study, we treat feedback by X-rays and discuss its implications. Our aim is to investigate whether star formation is significantly affected when a star forming cloud resides in the vicinity of a strong X-ray source. We perform an Eulerian grid simulation with embedded Lagrangian sink particles of a collapsing molecular cloud near a massive, 10^7 M_o black hole. The chemical and thermal changes caused by radiation are incorporated into the FLASH code. When there is strong X-ray feedback the star forming cloud fragments into larger clumps whereby fewer but more massive protostellar cores are formed. Competitive accretion has a strong impact on the mass function and a near-flat, non-Salpeter IMF results.

  17. THOR - The HI, OH, Recombination Line Survey of the Milky Way - HI observations of the giant molecular cloud W43

    Science.gov (United States)

    Bihr, Simon; Beuther, Henrik; Johnston, Katharine; Henning, Thomas; Ott, Juergen; Brunthaler, Andreas; THOR Collaboration

    2015-08-01

    To study the atomic, molecular and ionised emission of Giant Molecular Clouds (GMCs) in the Milky Way, we have initiated a Large Program with the VLA: 'THOR - The HI, OH, Recombination Line survey of the Milky Way'. We map the 21cm HI line, 4 OH lines, 19 Hα recombination lines and the continuum from 1-2GHz of a significant fraction of the Milky Way (l=15-67°, |b|thin with properties such as the column density calculated under this assumption. While this approach gives reasonable results for regions of low-mass star-formation, it is not sufficient to describe the atomic gas in close proximity to GMCs. In my talk, I will present a method using strong continuum sources to measure the optical depth, and thus correct the HI 21cm emission for optical depth effects and weak diffuse continuum emission. Our analysis puts a lower limit of M~6.6x106 Msun on the HI mass associated with the W43 GMC, which is a factor of 2.4 larger than the mass obtained using the optically thin assumption. The HI column densities reach NHI~150 Msun pc-2 ~ 1.9x1022 cm-2, which is an order of magnitude higher than seen in low mass star formation regions. This result challenges theoretical models that predict a threshold for the HI column density of ~10 Msun pc-2, at which the formation of molecular hydrogen should set in. Furthermore, we assume an elliptical layered structure for W43 to estimate the particle density profile. The HI particle density shows a linear decrease toward the centre of W43 and the molecular hydrogen, traced via dust observations with Herschel, shows an exponential increase toward the centre. While at the cloud edge atomic and molecular hydrogen are well mixed, the centre of the cloud is dominated by H2. We do not identify a sharp transition between hydrogen in atomic and molecular form. Our results are an important characterization of the atomic to molecular hydrogen transition in an extreme environment that challenges current theoretical models.

  18. Multipressure Polytropes as Models for the Structure and Stability of Molecular Clouds. I. Theory

    Science.gov (United States)

    McKee, Christopher F.; Holliman, John H., II

    1999-09-01

    We present a theoretical formalism for determining the structure of molecular clouds and the precollapse conditions in star-forming regions. The model consists of a pressure-bounded, self-gravitating sphere of an ideal gas that is supported by several distinct pressures. Since each pressure component is assumed to obey a polytropic law Pi(r)~ργpi, we refer to these models as ``multipressure polytropes.'' We treat the case without rotation. The time evolution of one of these polytropes depends additionally on the adiabatic index γi of each component, which is modified to account for the effects of any thermal coupling to the environment of the cloud. We derive structure equations as well as perturbation equations for performing a linear stability analysis. Special attention is given to representing properly the significant pressure components in molecular clouds: thermal motions, static magnetic fields, and turbulence. The fundamental approximation in our treatment is that the effects of turbulent motions in supporting a cloud against gravity can be approximated by a polytropic pressure component. In particular, we approximate the turbulent motions as a superposition of Alfvén waves. We generalize the standard treatment of the stability of polytropes to allow for the flow of entropy in response to a perturbation, as expected for the entropy associated with wave pressure. In contrast to the pressure components within stars, the pressure components within interstellar clouds are ``soft,'' with polytropic indices γpiγpi. We find that the motions associated with Alfvén waves are somewhat less effective in supporting clouds than are the kinetic motions in an isothermal gas.

  19. All-sky census of Galactic high-latitude molecular intermediate-velocity clouds

    Science.gov (United States)

    Röhser, T.; Kerp, J.; Lenz, D.; Winkel, B.

    2016-12-01

    Context. The H i halo clouds of the Milky Way, and in particular the intermediate-velocity clouds (IVCs), are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Aims: Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. Methods: The H i-FIR correlation was studied across the entire northern and southern Galactic hemispheres at Galactic latitudes | b | > 20° to determine the amount and distribution of molecular gas in IVCs. We used the most recent large-scale H i and FIR data, the Effelsberg Bonn-H i Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys. Results: We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates, all previously known MIVCs are recovered except for one single source. The frequency of candidates differs significantly between the northern and southern Galactic hemispheres and between negative and positive LSR velocities as well. Conclusions: In our approach we analyse the local Galactic environment. Extrapolating our results to the entire Galaxy, the global inflow of atomic and molecular IVC gas onto the Milky Way may account for the major fraction of the gaseous mass that is required to sustain the current Galactic star formation rate.

  20. The Spitzer survey of interstellar clouds in the gould belt. VI. The Auriga-California molecular cloud observed with IRAC and MIPS

    Energy Technology Data Exchange (ETDEWEB)

    Broekhoven-Fiene, Hannah; Matthews, Brenda C. [Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6 (Canada); Harvey, Paul M. [Astronomy Department, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712-0259 (United States); Gutermuth, Robert A. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Huard, Tracy L.; Miller, Jennifer F. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Tothill, Nicholas F. H. [School of Computing, Engineering and Mathematics, University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751 (Australia); Nutter, David [School of Physics and Astronomy, Cardiff University, Queen' s Buildings, The Parade, Cardiff CF24 3AA (United Kingdom); Bourke, Tyler L. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); DiFrancesco, James [National Research Council Herzberg Astronomy and Astrophysics, Victoria, BC, V9E 2E7 (Canada); Jørgensen, Jes K. [Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, DK-DK-2100 Copenhagen Ø. (Denmark); Allen, Lori E. [National Optical Astronomy Observatories, Tucson, AZ (United States); Chapman, Nicholas L. [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States); Dunham, Michael M. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States); Merín, Bruno [Herschel Science Centre, ESAC-ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid (Spain); Terebey, Susan [Department of Physics and Astronomy PS315, 5151 State University Drive, California State University at Los Angeles, Los Angeles, CA 90032 (United States); Peterson, Dawn E. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); and others

    2014-05-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg{sup 2} with IRAC and 10.47 deg{sup 2} with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

  1. THE TWO MOLECULAR CLOUDS IN RCW 38: EVIDENCE FOR THE FORMATION OF THE YOUNGEST SUPER STAR CLUSTER IN THE MILKY WAY TRIGGERED BY CLOUD–CLOUD COLLISION

    Energy Technology Data Exchange (ETDEWEB)

    Fukui, Y.; Torii, K.; Ohama, A.; Hasegawa, K.; Hattori, Y.; Sano, H.; Yamamoto, H.; Tachihara, K. [Department of Physics, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan); Ohashi, S.; Fujii, K.; Kuwahara, S. [Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 133-0033 (Japan); Mizuno, N.; Okuda, T. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Dawson, J. R. [Department of Physics and Astronomy and MQ Research Centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW 2109 (Australia); Onishi, T. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 (Japan); Mizuno, A., E-mail: torii@a.phys.nagoya-u.ac.jp [Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan)

    2016-03-20

    We present distributions of two molecular clouds having velocities of 2 and 14 km s{sup −1} toward RCW 38, the youngest super star cluster in the Milky Way, in the {sup 12}CO J = 1–0 and 3–2 and {sup 13}CO J = 1–0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3–2 emission to the J = 1–0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s{sup −1} cloud. We suggest that the collision is currently continuing toward part of the 2 km s{sup −1} cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud–cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.

  2. C18O Observations of the Dark Molecular Cloud L134 and Gas Depletion onto Dust

    Institute of Scientific and Technical Information of China (English)

    Xin-Jie Mao; Xiao-Xia Sun

    2005-01-01

    We map the dark molecular cloud core of L134 in the C18O (J =1 -0) emission line using the PMO 13.7m telescope, and present a contour map of integrated intensity of C18O (J = 1 - 0) emission. The C18O cloud is inside the distribution of extinction AB, the visual extinction of blue light, as well as inside the 13CO cloud in the L134 region. The depletion factors in this C18O cloud are generally greater than unity, which means there is gas depletion onto dust. Since only a minimum AB = 9.7 mag is available, and our observations measure both undepleted and depleted regions along the line of sight, the depletion factors could very likely be larger in the central core than the calculated value. So we conclude that depletion does occur in the bulk of the C18O cloud through a comparison between the C18O and blue extinction maps in the L134 region. There is no direct evidence as yet for star formation in L134, and so cores on the verge of collapse will not be visible in CO and other gas molecules.

  3. The location, clustering, and propagation of massive star formation in giant molecular clouds

    CERN Document Server

    Ochsendorf, B B; Chastenet, J; Tielens, A G G M; Roman-Duval, J

    2016-01-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this work, we use data from several galaxy-wide surveys to build an unbiased dataset of ~700 massive young stellar objects (MYSOs), ~200 giant molecular clouds (GMCs), and ~100 young (<10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We employ this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. We reveal that massive stars do not typically form at the highest column densities nor centers of their parent GMCs at the ~6 pc resolution of our observations. Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. We find that massive star formation is significantly boosted in clouds near SCs. Yet, whether a cloud is associated with a SC does not depend on either the cloud's mass or global surface density. These results reveal a conne...

  4. Evolution of Prolate Molecular Clouds at Hii Boundaries: II. Formation of BRCs of asymmetrical morphology

    CERN Document Server

    Kinnear, T M; White, G J; Sugitani, K; Goodwin, S

    2015-01-01

    A systematic investigation on the evolution of a prolate cloud at an Hii boundary is conducted using Smoothed Particle Hydrodynamics (SPH) in order to understand the mechanism for a variety of irregular morphological structures found at the boundaries of various Hii regions. The prolate molecular clouds in this investigation are set with their semi-major axes at inclinations between 0 and 90 degrees to a plane parallel ionizing radiation flux. A set of 4 parameters, the number density n, the ratio of major to minor axis gamma, the inclination angle phi and the incident flux F_EUV, are used to define the initial state of the simulated clouds. The dependence of the evolution of a prolate cloud under Radiation Driven Implosion (RDI) on each of the four parameters is investigated. It is found that: i) in addition to the well studied standard type A, B or C Bright Rimmed Clouds (BRCs), many other types such as asymmetrical BRCs, filamentary structures and irregular horse-head structures could also be developed at ...

  5. Giant molecular clouds in the non-grand design spiral galaxy NGC 6946

    CERN Document Server

    Rebolledo, David; Leroy, Adam; Koda, Jin; Meyer, Jennifer Donovan

    2012-01-01

    We present high spatial resolution observations of Giant Molecular Clouds (GMCs) in the eastern part of the nearby spiral galaxy NGC 6946 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have observed 12CO(1-0), 12CO(2-1) and 13CO(1-0), achieving spatial resolutions of 5.4" x 5.0", 2.5" x 2.0" and 5.6" x 5.4" respectively over a region of 6 x 6 kpc. This region extends from 1.5 kpc to 8 kpc galactocentric radius, thus avoiding the intense star formation in the central kpc. We have recovered short-spacing u-v components by using single dish observations from the Nobeyama 45m and IRAM 30m telescopes. Using the automated CPROPS algorithm we identified 44 CO cloud complexes in the 12CO(1-0) map and 64 GMCs in the 12CO(2-1) maps. The sizes, line widths, and luminosities of the GMCs are similar to values found in other extragalactic studies. We have classified the clouds into on-arm and inter-arm clouds based on the stellar mass density traced by the 3.6 um map. On-arm clouds p...

  6. Ultraviolet, optical, and infrared observations of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Welty, Daniel E.; Fowler, James R.

    1992-01-01

    Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated interstellar cloud characterized by extreme UV extinction. The low ratios of the IRAS bands with respect to I(100 microns) suggest that the radiation field incident on the cloud is lower than the average interstellar field, with further attenuation of the field within the cloud. The apparent relative enhancement of I(12 microns) compared with models of dust emission, and the extremely steep far-UV extinction together are consistent with the presence of an enhanced population of very small grains; the normal calcium depletion suggests that there has been little wholesale grain destruction. The steep far-UV extinction may help to explain the relatively high abundances of CO and CN. The disagreement in density for this cloud inferred from C2 absorption versus that inferred from CO emission may be due in part to clumping in the gas sample by the radio beams.

  7. The abundance and excitation of the carbon chains in interstellar molecular clouds

    Science.gov (United States)

    Bujarrabal, V.; Guelin, M.; Morris, M.; Thaddeus, P.

    1981-01-01

    Emission lines from the carbon chains HC3N, HC5N, HC7N and HC9N were observed at 3 mm, 7 mm, and 1.4 cm in a number of dark clouds, Orion A and IRC(plus)10216. Non-LTE models were constructed to describe excitation and column densities. Component models for the Taurus dark cloud TMC-1 suggested that relative molecular abundances do not vary substantially along the cloud ridge, whereas the H2 density does by a factor of three. Data available for other dark clouds showed that the decrease in abundance with length from one carbon chain to the next is nearly constant, being close to 2.3. The decline in carbon chain abundance with length is steeper in Orion KL than in dark clouds by a factor of approximately four. Abundance ratios derived for the carbon star IRC(plus)10216 are uncertain, due to difficulties in modeling excitation rates in this environment.

  8. Calibrating Column Density Tracers with Gamma-Ray Observations of the ρ Ophiuchi Molecular Cloud

    Science.gov (United States)

    Abrahams, Ryan D.; Teachey, Alex; Paglione, Timothy A. D.

    2017-01-01

    Diffuse gamma-ray emission from interstellar clouds results largely from cosmic ray (CR) proton collisions with ambient gas, regardless of the gas state, temperature, or dust properties of the cloud. The interstellar medium is predominantly transparent to both CRs and gamma-rays, so GeV emission is a unique probe of the total gas column density. The gamma-ray emissivity of a cloud of known column density is then a measure of the impinging CR population and may be used to map the k-scale CR distribution in the Galaxy. To this end, we test a number of commonly used column density tracers to evaluate their effectiveness in modeling the GeV emission from the relatively quiescent, nearby ρ Ophiuchi molecular cloud. We confirm that both H i and an appropriate {{{H}}}2 tracer are required to reproduce the total gas column densities probed by diffuse gamma-ray emisison. We find that the optical depth at 353 GHz ({τ }353) from Planck best reproduces the gamma-ray data overall, based on the test statistic across the entire region of interest, but near-infrared stellar extinction also performs very well, with smaller spatial residuals in the densest parts of the cloud.

  9. Ultraviolet, optical, and infrared observations of the high-latitude molecular cloud toward HD 210121

    Science.gov (United States)

    Welty, Daniel E.; Fowler, James R.

    1992-01-01

    Low-resolution UV spectra of the B3 V star HD 210121, located behind the high-latitude molecular cloud DBB 80, yield an extinction curve exhibiting a far-UV rise that is among the steepest known. The apparently simple line of sight affords an excellent opportunity for investigating the absorption and emission characteristics of a single, isolated interstellar cloud characterized by extreme UV extinction. The low ratios of the IRAS bands with respect to I(100 microns) suggest that the radiation field incident on the cloud is lower than the average interstellar field, with further attenuation of the field within the cloud. The apparent relative enhancement of I(12 microns) compared with models of dust emission, and the extremely steep far-UV extinction together are consistent with the presence of an enhanced population of very small grains; the normal calcium depletion suggests that there has been little wholesale grain destruction. The steep far-UV extinction may help to explain the relatively high abundances of CO and CN. The disagreement in density for this cloud inferred from C2 absorption versus that inferred from CO emission may be due in part to clumping in the gas sample by the radio beams.

  10. SKA studies of in-situ synchrotron radiation from molecular clouds

    CERN Document Server

    Dickinson, Clive; Crocker, R; Crutcher, R M; Davies, R D; Ferriere, K; Fuller, G; Jaffe, T; Jones, D I; Leahy, J P; Murphy, E J; Peel, M W; Orlando, E; Porter, T; Protheroe, R J; Robishaw, T; Strong, A W; Watson, R A; Yusef-Zadeh, F

    2015-01-01

    Observations of the properties of dense molecular clouds are critical in understanding the process of star-formation. One of the most important, but least understood, is the role of the magnetic fields. We discuss the possibility of using high-resolution, high-sensitivity radio observations with the SKA to measure for the first time the in-situ synchrotron radiation from these molecular clouds. If the cosmic-ray (CR) particles penetrate clouds as expected, then we can measure the B-field strength directly using radio data. So far, this signature has never been detected from the collapsing clouds themselves and would be a unique probe of the magnetic field. Dense cores are typically ~0.05 pc in size, corresponding to ~arcsec at ~kpc distances, and flux density estimates are ~mJy at 1 GHz. The SKA should be able to readily detect directly, for the first time, along lines-of-sight that are not contaminated by thermal emission or complex foreground/background synchrotron emission. Polarised synchrotron may also b...

  11. Using CO line ratios to trace the physical properties of molecular clouds

    CERN Document Server

    Peñaloza, Camilo H; Glover, Simon C O; Shetty, Rahul; Klessen, Ralf S

    2016-01-01

    The carbon monoxide (CO) rotational transition lines are the most common tracers of molecular gas within giant molecular clouds (MCs). We study the ratio ($R_{2-1/1-0}$) between CO's first two emission lines and examine what information it provides about the physical properties of the cloud. To study $R_{2-1/1-0}$ we perform smooth particle hydrodynamic simulations with time dependent chemistry (using GADGET-2), along with post-process radiative transfer calculations on an adaptive grid (using RADMC-3D) to create synthetic emission maps of a MC. $R_{2-1/1-0}$ has a bimodal distribution that is a consequence of the excitation properties of each line, given that $J=1$ reaches local thermal equilibrium (LTE) while $J=2$ is still sub-thermally excited in the considered clouds. The bimodality of $R_{2-1/1-0}$ serves as a tracer of the physical properties of different regions of the cloud and it helps constrain local temperatures, densities and opacities. Additionally this bimodal structure shows an important porti...

  12. The CH+ Abundance in Turbulent, Diffuse Molecular Clouds

    CERN Document Server

    Myers, Andrew; Li, Pak Shing

    2015-01-01

    The intermittent dissipation of interstellar turbulence is an important energy source in the diffuse ISM. Though on average smaller than the heating rates due to cosmic rays and the photoelectric effect on dust grains, the turbulent cascade can channel large amounts of energy into a relatively small fraction of the gas that consequently undergoes significant heating and chemical enrichment. In particular, this mechanism has been proposed as a solution to the long-standing problem of the high abundance of CH+ along diffuse molecular sight lines, which steady-state, low temperature models under-produce by over an order of magnitude. While much work has been done on the structure and chemistry of these small-scale dissipation zones, comparatively little attention has been paid to relating these zones to the properties of the large-scale turbulence. In this paper, we attempt to bridge this gap by estimating the temperature and CH+ column density along diffuse molecular sight-lines by post-processing 3-dimensional...

  13. The JCMT Legacy Survey of the Gould Belt: a molecular line study of the Ophiuchus molecular cloud

    CERN Document Server

    White, Glenn J; Rosolowsky, Erik; Ward-Thompson, Derek; Davis, C J; Gregson, Jon; Hatchell, Jenny; Etxaluze, Mireya; Stickler, Sarah; Buckle, Jane; Johnstone, Doug; Friesen, Rachel; Sadavoy, Sarah; Natt, Kieran V; Currie, Malcolm; Richer, J S; Pattle, Kate; Spaans, Marco; Di Francesco, James; Hogerheijde, M R

    2014-01-01

    CO, $^{13}$CO and C$^{18}$O ${\\it J}$ = 3--2 observations are presented of the Ophiuchus molecular cloud. The $^{13}$CO and C$^{18}$O emission is dominated by the Oph A clump, and the Oph B1, B2, C, E, F and J regions. The optically thin(ner) C$^{18}$O line is used as a column density tracer, from which the gravitational binding energy is estimated to be $4.5 \\times 10^{39}$ J (2282 $M_\\odot$ km$^2$ s$^{-2}$). The turbulent kinetic energy is $6.3 \\times 10^{38}$ J (320 $M_\\odot$ km$^2$ s$^{-2}$), or 7 times less than this, and therefore the Oph cloud as a whole is gravitationally bound. Thirty protostars were searched for high velocity gas, with eight showing outflows, and twenty more having evidence of high velocity gas along their lines-of-sight. The total outflow kinetic energy is $1.3 \\times 10^{38}$ J (67 $M_\\odot$ km$^2$ s$^{-2}$), corresponding to 21$\\%$ of the cloud?s turbulent kinetic energy. Although turbulent injection by outflows is significant, but does ${\\it not}$ appear to be the dominant sourc...

  14. Gaps in globular cluster streams: giant molecular clouds can cause them too

    CERN Document Server

    Amorisco, Nicola C; Vegetti, Simona; White, Simon D M

    2016-01-01

    As a result of their internal dynamical coherence, thin stellar streams formed by disrupting globular clusters (GCs) can act as detectors of dark matter (DM) substructure in the Galactic halo. Perturbations induced by close flybys amplify into detectable density gaps, providing a probe both of the abundance and of the masses of DM subhaloes. Here, we use N-body simulations to show that the Galactic population of giant molecular clouds (GMCs) can also produce gaps (and clumps) in GC streams, and so may confuse the detection of DM subhaloes. We explore the cases of streams analogous to the observed Palomar 5 and GD1 systems, quantifying the expected incidence of structure caused by GMC perturbations. Deep observations should detect such disturbances regardless of the substructure content of the Milky Way's halo. Detailed modelling will be needed to demonstrate that any detected gaps or clumps were produced by DM subhaloes rather than by molecular clouds.

  15. Supernova Remnant Kes 17: Efficient Cosmic Ray Accelerator inside a Molecular Cloud

    CERN Document Server

    Gelfand, Joseph D; Slane, Patrick O; Temim, Tea; Hughes, John P; Rakowski, Cara

    2013-01-01

    Supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number of remnants detected across the electromagnetic spectrum. In this paper, we analyze recent radio, X-ray, and gamma-ray observations of this object, determining that efficient cosmic ray acceleration is required to explain its broadband non-thermal spectrum. These observations also suggest that Kes 17 is expanding inside a molecular cloud, though our determination of its age depends on whether thermal conduction or clump evaporation is primarily responsible for its center-filled thermal X-ray morphology. Evidence for efficient cosmic ray acceleration in Kes 17 supports recent theoretical work that the strong magnetic field, turbulence, and clumpy nature of molecular clouds enhances cosmic ray production in supernova remnants. While additional observations are needed to confirm this interpretation, further study of Kes 17 is important for understanding how cosmic rays are accelerated in supernova remnants.

  16. Warm neutral halos around molecular clouds. VI - Physical and chemical modeling

    Science.gov (United States)

    Andersson, B.-G.; Wannier, P. G.

    1993-01-01

    A combined physical and chemical modeling of the halos around molecular clouds is presented, with special emphasis on the H-to-H2 transition. On the basis of H I 21 cm observations, it is shown that the halos are extended. A physical model is employed in conjunction with a chemistry code to provide a self-consistent description of the gas. The radiative transfer code provides a check with H I, CO, and OH observations. It is concluded that the warm neutral halos are not gravitationally bound to the underlying molecular clouds and are isobaric. It is inferred from the observed extent of the H I envelopes and the large observed abundance of OH in them that the generally accepted rate for H2 information on grains is too large by a factor of two to three.

  17. SUPERNOVA REMNANT KES 17: AN EFFICIENT COSMIC RAY ACCELERATOR INSIDE A MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Gelfand, Joseph D. [NYU Abu Dhabi, P.O. Box 903, New York, NY 10276 (United States); Castro, Daniel [MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue 37-241, Cambridge, MA 02139 (United States); Slane, Patrick O. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Temim, Tea [Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Hughes, John P. [Department of Physics and Astronomy Rutgers University 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Rakowski, Cara, E-mail: jg168@cosmo.nyu.edu, E-mail: cara.rakowski@gmail.com [United States Patent and Trademark Office, 600 Dulany Street, Alexandria, VA (United States)

    2013-11-10

    The supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number of remnants detected across the electromagnetic spectrum. In this paper, we analyze recent radio, X-ray, and γ-ray observations of this object, determining that efficient cosmic ray acceleration is required to explain its broadband non-thermal spectrum. These observations also suggest that Kes 17 is expanding inside a molecular cloud, though our determination of its age depends on whether thermal conduction or clump evaporation is primarily responsible for its center-filled thermal X-ray morphology. Evidence for efficient cosmic ray acceleration in Kes 17 supports recent theoretical work concluding that the strong magnetic field, turbulence, and clumpy nature of molecular clouds enhance cosmic ray production in supernova remnants. While additional observations are needed to confirm this interpretation, further study of Kes 17 is important for understanding how cosmic rays are accelerated in supernova remnants.

  18. Star Formation in Molecular Cloud Associated with IRAS 07028-110

    Institute of Scientific and Technical Information of China (English)

    QIN Sheng-Li; WU Yue-Fang; WANG Jun-Jie; ZHAO Gang; SHI Jian-Rong; MARTIN Miller

    2004-01-01

    @@ The first mapping observations in 12CO J = 2 - 1 and 12 CO J = 1 - 0 lines were made towards molecular cloud associated with IRAS 07028-1100. The results show a mono-polar outflow (primarily blueshifted component)near IRAS 07028-1100, which suggests that star formation is occurring in this region. On the basis of the MSX(Midcourse Space Experiment) band-A image, molecular cloud core contours, NVSS data and IRAS data, we identify IRAS 07028-1100 as an embedded young intermediate-mass star. According to the 2MASS data, we suggest a sequential star formation in the infrared cluster associated with IRAS 07028-1100.

  19. Gamma-Ray Emission from Supernova Remnants and Surrounding Molecular Clouds

    CERN Document Server

    Gabici, Stefano

    2016-01-01

    Galactic cosmic rays are believed to be accelerated at supernova remnant shocks. Gamma-ray observations of both supernova remnants and associated molecular clouds have been used in several occasions to test (so far quite successfully) this popular hypothesis. Despite that, a conclusive solution to the problem of cosmic ray origin is still missing, and further observational and theoretical efforts are needed. In this paper, the current status of these investigations is briefly reviewed.

  20. TRACING THE MAGNETIC FIELD MORPHOLOGY OF THE LUPUS I MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Franco, G. A. P. [Departamento de Física—ICEx—UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte (Brazil); Alves, F. O., E-mail: franco@fisica.ufmg.br, E-mail: falves@mpe.mpg.de [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstr. 1, D-85748 Garching (Germany)

    2015-07-01

    Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales.

  1. Tracing the Magnetic Field Morphology of the Lupus I Molecular Cloud

    Science.gov (United States)

    Franco, G. A. P.; Alves, F. O.

    2015-07-01

    Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales. Based on observations collected at the Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCTI, Brazil).

  2. CH as a Molecular Gas Tracer and C-shock Tracer Across a Molecular Cloud Boundary in Taurus

    Science.gov (United States)

    Xu, Duo; Li, Di

    2016-12-01

    We present new observations of all three ground-state transitions of the methylidyne (CH) radical and all four ground-state transitions of the hydroxyl (OH) radical toward a sharp boundary region of the Taurus molecular cloud. These data were analyzed in conjunction with existing CO and dust images. The derived CH abundance is consistent with previous observations of translucent clouds (0.8 ≤ A v ≤ 2.1 mag). The X(CH)-factor is nearly a constant (1.0 ± 0.06) × 1022 cm-2 K-1 km-1 s in this extinction range, with less dispersion than that of the more widely used molecular tracers CO and OH. CH turns out be a better tracer of total column density in such an intermediate extinction range than CO or OH. Compared with previous observations, CH is overabundant below 1 mag extinction. Such an overabundance of CH is consistent with the presence of a C-shock. CH has two kinematic components, one of which shifts from 5.3 to 6 km s-1, while the other stays at 6.8 km s-1 when moving from outside toward inside of the cloud. These velocity behaviors exactly match previous OH observation. The shifting of the two kinematic components indicates colliding streams or gas flow at the boundary region, which could be the cause of the C-shock.

  3. Large-Scale CO and [C I] Emission in the ρ Ophiuchi Molecular Cloud

    Science.gov (United States)

    Kulesa, Craig A.; Hungerford, Aimee L.; Walker, Christopher K.; Zhang, Xiaolei; Lane, Adair P.

    2005-05-01

    We present a comprehensive study of the ρ Ophiuchi molecular cloud that addresses aspects of the physical structure and condition of the molecular cloud and its photodissociation region (PDR) by combining far-infrared and submillimeter-wave observations with a wide range of angular scale and resolution. We present 1600 arcmin2 maps (2.3 pc2) with 0.1 pc resolution in submillimeter CO (4-->3) and [C I] (3P1-->3P0) line emission from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) and pointed observations in the CO (7-->6) and [C I] (3P2-->3P1) lines. Within the large-scale maps, smaller spectral line maps of 3000 AU resolution over ~90 arcmin2 (0.2 pc2) of the cloud in CO, CS, HCO+, and their rare isotopomers are made at the Heinrich Hertz Telescope (HHT) in Arizona. Comparison of CO, HCO+, and [C I] maps with far-infrared observations of atomic and ionic species from the Infrared Space Observatory (ISO) far-infrared and submillimeter continuum emission and near-infrared H2 emission allows clearer determination of the physical and chemical structure of the ρ Oph PDR, since each species probes a different physical region of the cloud structure. Although a homogeneous plane-parallel PDR model can reproduce many of the observations described here, the excitation conditions needed to produce the observed HCO+ and [O I] emission imply inhomogeneous structure. Strong chemical gradients are observed in HCO+ and CS; the former is ascribed to a local enhancement in the H2 ionization rate, and the latter is principally due to shocks. Under the assumption of a simple two-component gas model for the cloud, we find that [C II] and [C I] emission predominantly arises from the lower density envelopes (103-104 cm-3) that surround denser cloud condensations, or ``clumps.'' The distribution of [C I] is very similar to that of C18O and is generally consistent with illumination from the ``far'' side of the cloud. A notable exception is found at the western edge

  4. A YOUNG GIANT MOLECULAR CLOUD FORMED AT THE INTERFACE OF TWO COLLIDING SUPERSHELLS: OBSERVATIONS MEET SIMULATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Dawson, J. R. [Department of Physics and Astronomy and MQ Research Centre in Astronomy, Astrophysics and Astrophotonics, Macquarie University, NSW 2109 (Australia); Ntormousi, E. [Service d' Astrophysique, CEA/DSM/IRFU Orme des Merisiers, Bat 709 Gif-sur-Yvette F-91191 (France); Fukui, Y.; Hayakawa, T. [Department of Physics and Astrophysics, Nagoya University, Chikusa-ku, Nagoya (Japan); Fierlinger, K., E-mail: joanne.dawson@mq.edu.au [University Observatory Munich, Scheinerstr. 1, D-81679 München (Germany)

    2015-01-20

    Dense, star-forming gas is believed to form at the stagnation points of large-scale interstellar medium flows, but observational examples of this process in action are rare. We here present a giant molecular cloud (GMC) sandwiched between two colliding Milky Way supershells, which we argue shows strong evidence of having formed from material accumulated at the collision zone. Combining {sup 12}CO, {sup 13}CO, and C{sup 18}O(J = 1-0) data with new high-resolution, three-dimensional hydrodynamical simulations of colliding supershells, we discuss the origin and nature of the GMC (G288.5+1.5), favoring a scenario in which the cloud was partially seeded by pre-existing denser material, but assembled into its current form by the action of the shells. This assembly includes the production of some new molecular gas. The GMC is well interpreted as non-self-gravitating, despite its high mass (M{sub H{sub 2}}∼1.7×10{sup 5} M{sub ⊙}), and is likely pressure confined by the colliding flows, implying that self-gravity was not a necessary ingredient for its formation. Much of the molecular gas is relatively diffuse, and the cloud as a whole shows little evidence of star formation activity, supporting a scenario in which it is young and recently formed. Drip-like formations along its lower edge may be explained by fluid dynamical instabilities in the cooled gas.

  5. An all-sky census of Galactic high-latitude molecular intermediate-velocity clouds

    CERN Document Server

    Röhser, T; Lenz, D; Winkel, B

    2016-01-01

    The HI halo clouds of the Milky Way and in particular the intermediate-velocity clouds (IVCs) are thought to be connected to Galactic fountain processes. Observations of fountain clouds are important for understanding the role of matter recycling and accretion onto the Galactic disk and subsequent star formation. Here, we quantify the amount of molecular gas in the Galactic halo. We focus on the rare class of molecular IVCs (MIVCs) and search for new objects. The HI-FIR correlation is studied across the entire northern and southern Galactic hemispheres at Galactic latitudes $|b|>20^\\circ$ in order to determine the amount and distribution of molecular gas in IVCs. We use the most recent large-scale HI and FIR data, the Effelsberg Bonn-HI Survey, the Parkes Galactic All-Sky Survey, and the Planck FIR surveys. We present a catalogue of 239 MIVC candidates on the northern and southern Galactic hemispheres. Among these candidates all previously known MIVCs are recovered except for a single one only. The frequency ...

  6. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    Science.gov (United States)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2015-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  7. Large-Scale CO Maps of the Lupus Molecular Cloud Complex

    CERN Document Server

    Tothill, N F H; Parshley, S C; Stark, A A; Lane, A P; Harnett, J I; Wright, G A; Walker, C K; Bourke, T L; Myers, P C

    2009-01-01

    Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex - Lupus I, III, and IV - trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km/s. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding HI shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and ...

  8. Observational Diagnostics for Two-Fluid Turbulence in Molecular Clouds As Suggested by Simulations

    CERN Document Server

    Meyer, Chad D; Burkhart, Blakesely; Lazarian, Alex

    2013-01-01

    We present high resolution simulations of two-fluid (ion-neutral) MHD turbulence with resolutions as large as 512^3. The simulations are supersonic and mildly sub-Alfvenic, in keeping with the conditions present in molecular clouds. Such turbulence is thought to influence star formation processes in molecular clouds because typical cores form on length scales that are comparable to the dissipation scales of this turbulence in the ions. The simulations are motivated by the fact that recent studies of isophotologue lines in molecular clouds have found significant differences in the linewidth-size relationship for neutral and ion species. The goals of this paper are to explain those observations using simulations and analytic theory, present a new set of density-based diagnostics by drawing on similar diagnostics that have been obtained by studying single-fluid turbulence, and show that our two-fluid simulations play a vital role in reconciling alternative models of star formation. The velocity-dependent diagnos...

  9. The Structure of a Low-Metallicity Giant Molecular Cloud Complex

    CERN Document Server

    Leroy, A K; Bot, C; Engelbracht, C W; Gordon, K; Israel, F P; Rubio, M; Sandstrom, K; Stanimirović, S

    2009-01-01

    To understand the impact of low metallicities on giant molecular cloud (GMC) structure, we compare far infrared dust emission, CO emission, and dynamics in the star-forming complex N83 in the Wing of the Small Magellanic Cloud. Dust emission (measured by Spitzer as part of the S3MC and SAGE-SMC surveys) probes the total gas column independent of molecular line emission and traces shielding from photodissociating radiation. We calibrate a method to estimate the dust column using only the high-resolution Spitzer data and verify that dust traces the ISM in the HI-dominated region around N83. This allows us to resolve the relative structures of H2, dust, and CO within a giant molecular cloud complex, one of the first times such a measurement has been made in a low-metallicity galaxy. Our results support the hypothesis that CO is photodissociated while H2 self-shields in the outer parts of low-metallicity GMCs, so that dust/self shielding is the primary factor determining the distribution of CO emission. Four piec...

  10. Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

    Science.gov (United States)

    Heyer, M.; Goldsmith, P. F.; Yıldız, U. A.; Snell, R. L.; Falgarone, E.; Pineda, J. L.

    2016-10-01

    The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J = 2-1 emission obtained with the 10-m Submillimeter Telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J = 2-1 to J = 1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations are generated from the modulation of velocities and beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvénic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.

  11. Herbig-Haro objects and mid-infrared outflows in the Vela C molecular cloud

    CERN Document Server

    Zhang, Miaomiao; Henning, Thomas

    2014-01-01

    We have performed a deep [SII]6717/6731 wide field Herbig-Haro (HH) object survey toward the Vela C molecular cloud with a sky coverage of about 2 deg2. In total, 18 new HH objects, HH 1090-1107, are discovered and the two previously known HH objects, HH 73-74, are also detected in our [SII] images. We also present an investigation of mid-infrared outflows in the Vela C molecular cloud using the Wide-field Infrared Survey Explorer images taken from AllWISE data release. Using the method suggested by Zhang & Wang, eleven extended green objects (EGOs) are identified to be the mid-infrared outflows, including 6 new mid-infrared outflows that have not been detected previously at other wavelengths and 5 mid-infrared counterparts of the HH objects detected in this work. Using the AllWISE Source Catalog and the source classification scheme suggested by Koenig et al., we have identified 56 young stellar object (YSO) candidates in the Vela C molecular cloud. The possible driving sources of the HH objects and EGOs ...

  12. Atomic Oxygen Abundance in Molecular Clouds: Absorption Toward Sagittarius B2

    Science.gov (United States)

    Lis, D. C.; Keene, Jocelyn; Phillips, T. G.; Schilke, P.; Werner, M. W.; Zmuidzinas, J.

    2001-01-01

    We have obtained high-resolution (approximately 35 km/s) spectra toward the molecular cloud Sgr B2 at 63 micrometers, the wavelength of the ground-state fine-structure line of atomic oxygen (O(I)), using the ISO-LWS instrument. Four separate velocity components are seen in the deconvolved spectrum, in absorption against the dust continuum emission of Sgr B2. Three of these components, corresponding to foreground clouds, are used to study the O(I) content of the cool molecular gas along the line of sight. In principle, the atomic oxygen that produces a particular velocity component could exist in any, or all, of three physically distinct regions: inside a dense molecular cloud, in the UV illuminated surface layer (PDR) of a cloud, and in an atomic (H(I)) gas halo. For each of the three foreground clouds, we estimate, and subtract from the observed O(I) column density, the oxygen content of the H(I) halo gas, by scaling from a published high-resolution 21 cm spectrum. We find that the remaining O(I) column density is correlated with the observed (13)CO column density. From the slope of this correlation, an average [O(I)]/[(13)CO] ratio of 270 +/- 120 (3-sigma) is derived, which corresponds to [O(I)]/[(13)CO] = 9 for a CO to (13)CO abundance ratio of 30. Assuming a (13)CO abundance of 1x10(exp -6) with respect to H nuclei, we derive an atomic oxygen abundance of 2.7x10(exp -4) in the dense gas phase, corresponding to a 15% oxygen depletion compared to the diffuse ISM in our Galactic neighborhood. The presence of multiple, spectrally resolved velocity components in the Sgr B2 absorption spectrum allows, for the first time, a direct determination of the PDR contribution to the O(I) column density. The PDR regions should contain O(I) but not (13)CO, and would thus be expected to produce an offset in the O(I)-(13)CO correlation. Our data do not show such an offset, suggesting that within our beam O(I) is spatially coexistent with the molecular gas, as traced by (13)CO

  13. Star Formation and Outflows in Molecular Clouds: The Role of Radiative Feedback

    Science.gov (United States)

    Raskutti, Sudhir; Ostriker, Eve C.

    2015-08-01

    Radiation feedback from massive clusters is expected to play a key role in setting the rate and efficiency of star formation on the scale of Giant Molecular Clouds (GMCs). However, due to the extreme cost of implementing full radiative transfer in 3D hydrodynamic simulations, the influence of radiation feedback on GMCs has been poorly understood. We employ the recently developed Hyperion extension of the Athena code, which solves the equations of radiation hydrodynamics (RHD) using the Reduced Speed of Light (RSL) approximation and M1 closure of the moment equations, to investigate the effects of direct, non-ionizing UV radiation on cloud dynamical evolution and star formation. Our model GMCs span a range of surface densities between 10 and 500 solar masses per square parsec, making them optically thick to UV and thin to reprocessed IR.We find that radiation feedback has little effect on the density structure in the cloud or its star formation rate, both of which are set by the interaction between turbulence and gravity. Instead, the main effect of radiation is to truncate star formation and disperse gas rapidly whena sufficiently luminous cluster has formed. We show that our numerical results can be explained by a simple paradigm of feedback-limited star formation that operates across a wide range of cloud surface densities. In this model, stars form steadily in a turbulent medium with log-normally distributed surface and volume densities, and successively larger portions of the original cloud become unbound when the forces on successively denser local patches of gas become super-Eddington. The global stellar efficiency in a GMC is therefore set not by the radiative force at the mean cloud surface density, but by the Eddington ratio in the high surface density tail of the gas distribution.

  14. NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Pascucci, I.; Simon, M. N. [Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721 (United States); Edwards, S. [Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States); Heyer, M. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Rigliaco, E. [Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich (Switzerland); Hillenbrand, L. [Department of Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Gorti, U.; Hollenbach, D., E-mail: pascucci@lpl.arizona.edu [SETI Institute, Mountain View, CA 94043 (United States)

    2015-11-20

    We present a detailed analysis of narrow Na i and K i absorption resonance lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying their origin. The Na i λ5889.95 line is detected toward all but one source, while the weaker K i λ7698.96 line is detected in about two-thirds of the sample. The similarity in their peak centroids and the significant positive correlation between their equivalent widths demonstrate that these transitions trace the same atomic gas. The absorption lines are present toward both disk and diskless young stellar objects, which excludes cold gas within the circumstellar disk as the absorbing material. A comparison of Na i and CO detections and peak centroids demonstrates that the atomic gas and molecular gas are not co-located, the atomic gas being more extended than the molecular gas. The width of the atomic lines corroborates this finding and points to atomic gas about an order of magnitude warmer than the molecular gas. The distribution of Na i radial velocities shows a clear spatial gradient along the length of the Taurus molecular cloud filaments. This suggests that absorption is associated with the Taurus molecular cloud. Assuming that the gradient is due to cloud rotation, the rotation of the atomic gas is consistent with differential galactic rotation, whereas the rotation of the molecular gas, although with the same rotation axis, is retrograde. Our analysis shows that narrow Na i and K i absorption resonance lines are useful tracers of the atomic envelope of molecular clouds. In line with recent findings from giant molecular clouds, our results demonstrate that the velocity fields of the atomic and molecular gas are misaligned. The angular momentum of a molecular cloud is not simply inherited from the rotating Galactic disk from which it formed but may be redistributed by cloud–cloud interactions.

  15. THE NATURE OF TRANSITION CIRCUMSTELLAR DISKS. II. SOUTHERN MOLECULAR CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Romero, Gisela A.; Schreiber, Matthias R.; Rebassa-Mansergas, Alberto [Departamento de Fisica y Astronomia, Universidad de Valparaiso, Valparaiso (Chile); Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Merin, Bruno [Herschel Science Centre, ESAC (ESA), P.O. Box 78, 28691 Villanueva de la Canada, Madrid (Spain); Smith Castelli, Analia V. [Consejo Nacional de Investigaciones Cientificas y Tecnicas, Rivadavia 1917, C1033AAJ Buenos Aires (Argentina); Allen, Lori E. [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065 (United States); Morrell, Nidia [Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena (Chile)

    2012-04-10

    Transition disk objects are pre-main-sequence stars with little or no near-IR excess and significant far-IR excess, implying inner opacity holes in their disks. Here we present a multifrequency study of transition disk candidates located in Lupus I, III, IV, V, VI, Corona Australis, and Scorpius. Complementing the information provided by Spitzer with adaptive optics (AO) imaging (NaCo, VLT), submillimeter photometry (APEX), and echelle spectroscopy (Magellan, Du Pont Telescopes), we estimate the multiplicity, disk mass, and accretion rate for each object in our sample in order to identify the mechanism potentially responsible for its inner hole. We find that our transition disks show a rich diversity in their spectral energy distribution morphology, have disk masses ranging from {approx}<1 to 10 M{sub JUP}, and accretion rates ranging from {approx}<10{sup -11} to 10{sup -7.7} M{sub Sun} yr{sup -1}. Of the 17 bona fide transition disks in our sample, three, nine, three, and two objects are consistent with giant planet formation, grain growth, photoevaporation, and debris disks, respectively. Two disks could be circumbinary, which offers tidal truncation as an alternative origin of the inner hole. We find the same heterogeneity of the transition disk population in Lupus III, IV, and Corona Australis as in our previous analysis of transition disks in Ophiuchus while all transition disk candidates selected in Lupus V, VI turned out to be contaminating background asymptotic giant branch stars. All transition disks classified as photoevaporating disks have small disk masses, which indicates that photoevaporation must be less efficient than predicted by most recent models. The three systems that are excellent candidates for harboring giant planets potentially represent invaluable laboratories to study planet formation with the Atacama Large Millimeter/Submillimeter Array.

  16. Cloud-Based Numerical Weather Prediction for Near Real-Time Forecasting and Disaster Response

    Science.gov (United States)

    Molthan, Andrew; Case, Jonathan; Venners, Jason; Schroeder, Richard; Checchi, Milton; Zavodsky, Bradley; Limaye, Ashutosh; O'Brien, Raymond

    2015-01-01

    The use of cloud computing resources continues to grow within the public and private sector components of the weather enterprise as users become more familiar with cloud-computing concepts, and competition among service providers continues to reduce costs and other barriers to entry. Cloud resources can also provide capabilities similar to high-performance computing environments, supporting multi-node systems required for near real-time, regional weather predictions. Referred to as "Infrastructure as a Service", or IaaS, the use of cloud-based computing hardware in an on-demand payment system allows for rapid deployment of a modeling system in environments lacking access to a large, supercomputing infrastructure. Use of IaaS capabilities to support regional weather prediction may be of particular interest to developing countries that have not yet established large supercomputing resources, but would otherwise benefit from a regional weather forecasting capability. Recently, collaborators from NASA Marshall Space Flight Center and Ames Research Center have developed a scripted, on-demand capability for launching the NOAA/NWS Science and Training Resource Center (STRC) Environmental Modeling System (EMS), which includes pre-compiled binaries of the latest version of the Weather Research and Forecasting (WRF) model. The WRF-EMS provides scripting for downloading appropriate initial and boundary conditions from global models, along with higher-resolution vegetation, land surface, and sea surface temperature data sets provided by the NASA Short-term Prediction Research and Transition (SPoRT) Center. This presentation will provide an overview of the modeling system capabilities and benchmarks performed on the Amazon Elastic Compute Cloud (EC2) environment. In addition, the presentation will discuss future opportunities to deploy the system in support of weather prediction in developing countries supported by NASA's SERVIR Project, which provides capacity building

  17. Star formation in a turbulent framework: from giant molecular clouds to protostars

    Science.gov (United States)

    Guszejnov, Dávid; Hopkins, Philip F.

    2016-06-01

    Turbulence is thought to be a primary driving force behind the early stages of star formation. In this framework large, self-gravitating, turbulent clouds fragment into smaller clouds which in turn fragment into even smaller ones. At the end of this cascade we find the clouds which collapse into protostars. Following this process is extremely challenging numerically due to the large dynamical range, so in this paper we propose a semi-analytic framework which is able to model star formation from the largest, giant molecular cloud scale, to the final protostellar size scale. Because of the simplicity of the framework it is ideal for theoretical experimentation to explore the principal processes behind different aspects of star formation, at the cost of introducing strong assumptions about the collapse process. The basic version of the model discussed in this paper only contains turbulence, gravity and crude assumptions about feedback; nevertheless it can reproduce the observed core mass function and provide the protostellar system mass function (PSMF), which shows a striking resemblance to the observed initial mass function (IMF), if a non-negligible fraction of gravitational energy goes into turbulence. Furthermore we find that to produce a universal IMF protostellar feedback must be taken into account otherwise the PSMF peak shows a strong dependence on the background temperature.

  18. Modeling the Atomic-to-Molecular Transition and Chemical Distributions of Turbulent Star-Forming Clouds

    CERN Document Server

    Offner, Stella S R; Viti, Serena; Bell, Thomas A

    2013-01-01

    We use 3D-PDR, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C+, C, H2 and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric probl...

  19. MODELING THE ATOMIC-TO-MOLECULAR TRANSITION AND CHEMICAL DISTRIBUTIONS OF TURBULENT STAR-FORMING CLOUDS

    Energy Technology Data Exchange (ETDEWEB)

    Offner, Stella S. R. [Department of Astronomy, Yale University, New Haven, CT 06511 (United States); Bisbas, Thomas G.; Viti, Serena [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6B (United Kingdom); Bell, Tom A., E-mail: stella.offner@yale.edu [Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir, km 4, E-28850 Madrid (Spain)

    2013-06-10

    We use 3D-PDR, a three-dimensional astrochemistry code for modeling photodissociation regions (PDRs), to post-process hydrodynamic simulations of turbulent, star-forming clouds. We focus on the transition from atomic to molecular gas, with specific attention to the formation and distribution of H, C{sup +}, C, H{sub 2}, and CO. First, we demonstrate that the details of the cloud chemistry and our conclusions are insensitive to the simulation spatial resolution, to the resolution at the cloud edge, and to the ray angular resolution. We then investigate the effect of geometry and simulation parameters on chemical abundances and find weak dependence on cloud morphology as dictated by gravity and turbulent Mach number. For a uniform external radiation field, we find similar distributions to those derived using a one-dimensional PDR code. However, we demonstrate that a three-dimensional treatment is necessary for a spatially varying external field, and we caution against using one-dimensional treatments for non-symmetric problems. We compare our results with the work of Glover et al., who self-consistently followed the time evolution of molecule formation in hydrodynamic simulations using a reduced chemical network. In general, we find good agreement with this in situ approach for C and CO abundances. However, the temperature and H{sub 2} abundances are discrepant in the boundary regions (A{sub v} {<=} 5), which is due to the different number of rays used by the two approaches.

  20. An origin of arc structures deeply embedded in dense molecular cloud cores

    CERN Document Server

    Matsumoto, Tomoaki; Tokuda, Kazuki; Inutsuka, Shu-ichiro

    2015-01-01

    We investigated the formation of arc-like structures in the infalling envelope around protostars, motivated by the recent ALMA observations of the high-density molecular cloud core, MC27/L1527F. We performed self-gravitational hydrodynamical numerical simulations with an adaptive mesh refinement code. A filamentary cloud with a 0.1~pc width fragments into cloud cores because of perturbations due to weak turbulence. The cloud core undergoes gravitational collapse to form multiple protostars, and gravitational torque from the orbiting protostars produces arc structures extending up to a 1000~AU scale. As well as on a spatial extent, the velocity ranges of the arc structures, $\\sim0.5\\,\\mathrm{km\\,s}^{-1}$, are in agreement with the ALMA observations. We also found that circumstellar disks are often misaligned in triple system. The misalignment is caused by the tidal interaction between the protostars when they undergo close encounters because of a highly eccentric orbit of the tight binary pair.

  1. A method to determine distances to molecular clouds using near-IR photometry

    CERN Document Server

    Maheswar, G; Bhatt, H C; Mallik, S V; Dib, Sami; 10.1051/0004-6361/200912594

    2010-01-01

    Aims: We aim to develop a method to determine distances to molecular clouds using JHK near-infrared photometry. Methods: The method is based on a technique that aids spectral classification of stars lying towards the fields containing the clouds into main sequence and giants. In this technique, the observed (J-H) and (H-K_s) colours are dereddened simultaneously using trial values of A V and a normal interstellar extinction law. The best fit of the dereddened colours to the intrinsic colours giving a minimum value of Chi^2 then yields the corresponding spectral type and A_V for the star. The main sequence stars, thus classified, are then utilized in an A V versus distance plot to bracket the cloud distances. Results: We applied the method to four clouds, L1517, Chamaeleon I, Lupus 3 and NGC 7023 and estimated their distances as 167+-30, 151+-28, 157+-29 and 408+-76 pc respectively, which are in good agreement with the previous distance estimations available in the literature

  2. Luminosity Functions of Spitzer Identified Protostars in Nine Nearby Molecular Clouds

    CERN Document Server

    Kryukova, E; Gutermuth, R A; Pipher, J; Allen, T S; Allen, L E; Myers, P C; Muzerolle, J

    2012-01-01

    We identify protostars in Spitzer surveys of nine star-forming molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine photometry from 2MASS J, H, and Ks bands and Spitzer IRAC and MIPS 24 micron bands to create 1 - 24 micron spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities (Lbol), we derive a relationship between Lbol, L_MIR (integrated from 1 - 24 microns), and SED slope. Estimations of Lbol for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high mass star forming clouds peak near 1 Lsun and show a tail extending ...

  3. Mapping of the extinction in Giant Molecular Clouds using optical star counts

    CERN Document Server

    Cambresy, L

    1999-01-01

    This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho-Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total individual masses M and their maximum of extinction. I show that the relation between the mass contained within an iso-extinction contour and the extinction is similar from cloud to cloud and allows the extrapolation of the maximum of extinction in the range 5.7 to 25.5 magnitudes. I found that about half of the mass is contained in regions where the visual extinction is smaller than 1 magnitude. The star count method used on large scale (about 250 square degrees) is a powerful and relatively straightforward method to es...

  4. Calibrating Column Density Tracers with Gamma-ray Observations of the $\\rho$ Ophiuchi Molecular Cloud

    CERN Document Server

    Abrahams, Ryan D; Paglione, Timothy A D

    2016-01-01

    Diffuse gamma-ray emission from interstellar clouds results largely from cosmic ray (CR) proton collisions with ambient gas, regardless of the gas state, temperature, or dust properties of the cloud. The interstellar medium is predominantly transparent to both CRs and gamma-rays, so GeV emission is a unique probe of the total gas column density. The gamma-ray emissivity of a cloud of known column density is then a measure of the impinging CR population and may be used to map the kpc-scale CR distribution in the Galaxy. To this end, we test a number of commonly used column density tracers to evaluate their effectiveness in modeling the GeV emission from the relatively quiescent, nearby $\\rho$ Ophiuchi molecular cloud. We confirm that both \\hi\\ and an appropriate H$_2$ tracer are required to reproduce the total gas column densities probed by diffuse gamma-ray emisison. We find that the optical depth at 353 GHz $\\tau_{353}$ from Planck reproduces the gamma-ray data best overall based on the test statistic across...

  5. CO isotope studies and mass of the Sagittarius B2 molecular cloud

    Energy Technology Data Exchange (ETDEWEB)

    Lis, D.C.; Goldsmith, P.F.

    1989-02-01

    (C-13)O and (C-18)O observations of the central region of Sagittarius B2 are presented. A (C-13)O to (C-18)O abundance ratio of 9.0 + or - 1.9, consistent with the average ratio in the disk and other Galactic center sources, is obtained. Comparison of the (C-13)O column density based on the present data with H2 column density based on 1300 micron continuum data gives an upper limit of 10 to the -6th for the (C-13)O fractional abundance, a factor of two lower than the local value. The (C-12)O/H2 abundance ratio is a factor of six lower than the local value due to the lower (C-12)O to (C-13)O ratio. It is concluded that abundances of many molecular species in addition to the CO isotopes may be lower than in local clouds. The observations suggest a two-component structure for the cloud, with a constant density component and a component with density having a power-law dependence on the distance from cloud center. Values for the outer radius, total mass, and virial mass of the cloud are derived. 25 references.

  6. Photometric Investigation of the MBM 12 Molecular Cloud Area in ARIES. III. CCD Photometry

    Science.gov (United States)

    Straižys, V.; Zdanavičius, J.; Zdanavičius, K.; Kazlauskas, A.; Černis, K.; Laugalys, V.; Boyle, R. P.; Corbally, C. J.; Philip, A. G. D.

    Magnitudes and color indices of 138 stars down to l V = 15 mag in the seven-color Vilnius photometric system are determined in the area of the Aries molecular cloud MBM 12. Spectral types, color excesses, interstellar extinctions and distances of stars are determined from the photometric data. For some stars classification is verified from spectrograms. The plot of extinction vs. distance exhibits a steep rise of the extinction up to 4 mag at 300 pc which corresponds to the distance of the dust cloud at 375 pc. However, this distance may be overestimated if the heavily reddened stars found in the present study are not inside the cloud, but behind it. Additionally, a small bump of the extinction is present at 100--140 pc which can be related to the extension of the Taurus-Auriga dark cloud complex. Four known T Tauri type stars were measured and classified, and their variability confirmed. Two new T Tauri stars are suspected. More young objects may be present among the stars with peculiar color indices. Some of them can also be unresolved binaries. Some new heavily reddened stars are identified and discussed.

  7. Toward Seamless Weather-Climate Prediction with a Global Cloud Resolving Model

    Science.gov (United States)

    2016-01-14

    distribution is unlimited. TOWARD SEAMLESS WEATHER- CLIMATE PREDICTION WITH A GLOBAL CLOUD RESOLVING MODEL PI: Tim Li IPRC/SOEST, University of Hawaii at...under global warming This study uses the MRI high-resolution Atmospheric Climate Model to determine whether environmental parameters that control...ENSO Amplitude under Global Warming in Four CMIP5 Models , J. Climate , 28 (8), 3250-3274. 6. Chung, P.-H., and T. Li, 2015: Characteristics of tropical

  8. G-virial: Gravity-based structure analysis of molecular clouds

    CERN Document Server

    Li, Guang-Xing; Menten, Karl; Megeath, Tom; Shi, Xun

    2015-01-01

    We present the G-virial method (available at http://gxli.github.io/G-virial/) which aims to quantify (1) the importance of gravity in molecular clouds in the position-position-velocity (PPV) space, and (2) properties of the gas condensations in molecular clouds. Different from previous approaches that calculate the virial parameter for different regions, our new method takes gravitational interactions between all the voxels in 3D PPV data cubes into account, and generates maps of the importance of gravity. This map can be combined with the original data cube to derive relations such as the mass-radius relation. Our method is important for several reasons. First, it offers the the ability to quantify the centrally condensed structures in the 3D PPV data cubes, and enables us to compare them in an uniform framework. Second, it allows us to understand the importance of gravity at different locations in the data cube, and provides a global picture of gravity in clouds. Third, it offers a robust approach to decomp...

  9. A Deuteration Survey of the Clump Population in the Gemini OB1 Molecular Cloud

    Science.gov (United States)

    Henrici, Andrew Scott; Shirley, Yancy L.; Svoboda, Brian E.

    2017-01-01

    Recent maps of dust continuum emission from entire molecular clouds at submillimeter wavelengths have made it possible to survey and study the chemistry of entire core and clump populations within a single cloud. One very strong chemical process in star-forming regions is the fractionation of deuterium in molecules, which results in an increase in the deuterium ratio many orders of magnitude over the ISM [D]/[H] ratio and provides a chemical probe of cold, dense regions. We present a survey of DCO+ 3-2 and N2D+ 3-2 toward the clump population in the high-mass, star-forming Gemini OB1 Molecular Cloud identified from 1.1 mm continuum imaging by the Bolocam Galactic Plane Survey. The peak 1.1 mm continuum positions of 52 clumps in the range 188°≤ l ≤194° were observed with the 10m Heinrich Hertz Submillimeter Telescope. We find that DCO+ emission is detected toward 90% of the clumps with a median deuterium ratio of 0.01 while N2D+ emission is detected toward only 25% of the clumps. The DCO+ fractionation anti-correlates with gas kinetic temperature and linewidth, a measure of the amount of turbulence within the clumps. We compare the deuteration ratios of with physical properties of the clumps and their evolutionary stage.

  10. Cold and warm atomic gas around the Perseus molecular cloud I: Basic Properties

    CERN Document Server

    Stanimirovic, Snezana; Lee, Min-Young; Heiles, Carl; Miller, Jesse

    2014-01-01

    (Abridged) Using the Arecibo Observatory we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases allowing us to estimate spin temperature (T_s) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual HI clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium, CNM and WNM) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium HI survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have on average a higher total HI column density and the CNM fraction, suggesting an enhanced amount of cold HI relative to an average interstellar field. Our estimated optical depth and spin temper...

  11. Multi-line spectral imaging of dense cores in the Lupus molecular cloud

    CERN Document Server

    Benedettini, Milena; Burton, Micheal G; Viti, Serena; Molinari, Sergio; Caselli, Paola; Testi, Leonardo

    2011-01-01

    The molecular clouds Lupus 1, 3 and 4 were mapped with the Mopra telescope at 3 and 12 mm. Emission lines from high density molecular tracers were detected, i.e. NH$_3$ (1,1), NH$_3$ (2,2), N$_2$H$^+$ (1-0), HC$_3$N (3-2), HC$_3$N (10-9), CS (2-1), CH$_3$OH (2$_0-1_0$)A$^+$ and CH$_3$OH (2$_{-1}-1_{-1}$)E. Velocity gradients of more than 1 km s$^{-1}$ are present in Lupus 1 and 3 and multiple gas components are present in these clouds along some lines of sight. Lupus 1 is the cloud richest in high density cores, 8 cores were detected in it, 5 cores were detected in Lupus 3 and only 2 in Lupus 4. The intensity of the three species HC$_3$N, NH$_3$ and N$_2$H$^+$ changes significantly in the various cores: cores that are brighter in HC$_3$N are fainter or undetected in NH$_3$ and N$_2$H$^+$ and vice versa. We found that the column density ratios HC$_3$N/N$_2$H$^+$ and HC$_3$N/NH$_3$ change by one order of magnitude between the cores, indicating that also the chemical abundance of these species is different. The ...

  12. Studying the molecular gas towards the R Coronae Australis dark cloud

    CERN Document Server

    Paron, S; Ortega, M E; Cunningham, M; Jones, P A; Rubio, M

    2016-01-01

    The R Coronae Australis dark cloud is one of the closest star-forming regions to the Sun. The cloud is known to be very active in star formation, harboring many Herbig-Haro objects (HHs) and Molecular Hydrogen emission-line Objects (MHOs). In this work we present results from molecular observations (a $5.5^{'}\\times5.5^{'}$ map of $^{12}$CO J$=3-2$ and HCO$^{+}$ J$=4-3$, and a single spectrum of N$_{2}$H$^{+}$ J$=4-3$) obtained with the Atacama Submillimeter Telescope Experiment (ASTE) towards the R CrA dark cloud with an angular and spectral resolution of 22$^{"}$ and 0.11 km s$^{-1}$, respectively. From the $^{12}$CO J$=3-2$ line we found kinematical spectral features strongly suggesting the presence of outflows towards a region populated by several HHs and MHOs. Moreover, most of these objects lie within an HCO$^{+}$ maximum, suggesting that its emission arises from an increasement of its abundance due to the chemistry triggered by the outflow activity. Additionally, we are presenting the first reported de...

  13. Radiative transfer in SPH and applications in the collapse of molecular clouds

    CERN Document Server

    Stamatellos, D; Bisbas, T; Goodwin, S

    2007-01-01

    We introduce and test a new and highly efficient method for treating the thermal and radiative effects in the energy equation in SPH simulations of star formation. The method uses the density and gravitational potential of each particle to make an estimate of the particle's optical depth, which in turn regulates the particle's heating and cooling. The effects of (i) the rotational and vibrational degrees of freedom of H2, H2 dissociation, H0 ionisation, (ii) the opacity changes due to e.g. ice mantle melting, the sublimation of dust, molecular and H- contributions, and (iii) the thermal inertia, are all captured at minimal computational cost. We apply this new method to simulate the collapse of a 1-Msun molecular cloud of initially uniform density and temperature. At first, the collapse proceeds almost isothermally, with the temperature rising as ~rho^{0.08} which is similar to the Larson (2005) relation. The cloud starts heating fast when the optical depth to the of the cloud centre reaches unity. The first ...

  14. The Lognormal Probability Distribution Function of the Perseus Molecular Cloud: A Comparison of HI and Dust

    CERN Document Server

    Burkhart, Blakesley; Murray, Claire; Stanimirovic, Snezana

    2015-01-01

    The shape of the probability distribution function (PDF) of molecular clouds is an important ingredient for modern theories of star formation and turbulence. Recently, several studies have pointed out observational difficulties with constraining the low column density (i.e. Av <1) PDF using dust tracers. In order to constrain the shape and properties of the low column density probability distribution function, we investigate the PDF of multiphase atomic gas in the Perseus molecular cloud using opacity-corrected GALFA-HI data and compare the PDF shape and properties to the total gas PDF and the N(H2) PDF. We find that the shape of the PDF in the atomic medium of Perseus is well described by a lognormal distribution, and not by a power-law or bimodal distribution. The peak of the atomic gas PDF in and around Perseus lies at the HI-H2 transition column density for this cloud, past which the N(H2) PDF takes on a powerlaw form. We find that the PDF of the atomic gas is narrow and at column densities larger than...

  15. Molecular and Atomic Gas in the Large Magellanic Cloud - I. Conditions for CO Detection

    CERN Document Server

    Wong, T; Fukui, Y; Kawamura, A; Mizuno, N; Ott, J; Müller, E; Pineda, J L; Welty, D E; Kim, S; Mizuno, Y; Murai, M; Onishi, T

    2009-01-01

    We analyze the conditions for detection of CO(1-0) emission in the Large Magellanic Cloud (LMC), using the recently completed second NANTEN CO survey. In particular, we investigate correlations between CO integrated intensity and HI integrated intensity, peak brightness temperature, and line width at a resolution of 2.6' (~40 pc). We find that significant HI column density and peak brightness temperature are necessary but not sufficient conditions for CO detection, with many regions of strong HI emission not associated with molecular clouds. The large scatter in CO intensities for a given HI intensity persists even when averaging on scales of >200 pc, indicating that the scatter is not solely due to local conversion of HI into H_2 near GMCs. We focus on two possibilities to account for this scatter: either there exist spatial variations in the I(CO) to N(H_2) conversion factor, or a significant fraction of the atomic gas is not involved in molecular cloud formation. A weak tendency for CO emission to be suppr...

  16. Deeply Embedded Protostellar Population in the 20 km s-1 Cloud of the Central Molecular Zone

    CERN Document Server

    Lu, Xing; Kauffmann, Jens; Pillai, Thushara; Longmore, Steven N; Kruijssen, J M Diederik; Battersby, Cara; Gu, Qiusheng

    2015-01-01

    We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s$^{-1}$ cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H$_2$O maser observations. The submillimeter continuum emission shows five 1-pc scale clumps, each of which further fragments into several 0.1-pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H$_2$O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5 gravitationally bound dense cores without H$_2$O maser detection. In total the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potential growing more massive stars at earlier evolutionary stage, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH$_3$OH masers, we conclude that the star formation in this cloud is ...

  17. Multiple CO Outflows in Circinus The Churning of a Molecular Cloud

    CERN Document Server

    Bally, J; Lada, C J; Billawala, Y N; Bally, John; Reipurth, Bo; Lada, Charles J.; Billawala, Youssef

    1999-01-01

    We present a millimeter wave study of a cluster of bipolar CO outflows embedded in the western end of the Circinus molecular cloud complex, G317-4, that is traced by very high optical extinction. For an assumed distance of 700 pc, the entire Circinus cloud is estimated to have a mass of about 5E4 solar masses. The opaque western portion that was mapped in this study has a mass of about 10E3 solar masses, contains a number of embedded infrared sources and various compact 1.3 mm continuum sources, and has a remarkable filamentary structure with numerous cavities which appears to be the fossil remnants of past star formation activity. The profusion of outflows in this region are disentangled and linked to driving IRAS sources. Thus, the mapped portion of Circinus contains at least 10 CO emitting molecular outflows. Assuming that star formation has continued at a steady rate for the last several hundred thousand years, the Circinus cloud is expected to have produced dozens of young stars. Their outflows have seve...

  18. On the nearest molecular clouds. III - MBM 40, 53, 54, and 55

    Science.gov (United States)

    Welty, D. E.; Hobbs, L. M.; Penprase, B. E.; Blitz, L.

    1989-01-01

    In an attempt to determine the distances to four high-latitude molecular clouds (HLCs), echelle spectra near the Na I D lines, accurate MK spectral types, and photoelectric photometry for 25 nearby stars have been obtained. Fairly firm distance limits may be placed on MBM 40 (d smaller than or equal to 140 pc) and MBM 53 (d greater than or equal to 110 pc and less than or equal to 155 pc), based on the presence or absence of strong interstellar Na I absorption towards stars projected on or near those HLCs. Weak interstellar absorption lines observed toward many of the stars located near MBM 54 and 55 make the distances to those clouds less certain (about 265 pc for both). Interstellar CH absorption at 4300 A was detected in the spectrum of HD 218662, located behind MBM 53 with a CH column density of 2.1 x 10 to the 13th per sq cm, thus implying a CH abundance comparable to that observed in other molecular clouds. Morphological and velocity agreement among CO emission, the Na I absorption, the 100 micron infrared cirrus emission, and the 21 cm H I emission near these HLCs suggest a close association of the interstellar material responsible for those phenomena.

  19. On the nearest molecular clouds. III. MBM 40, 53, 54, and 55

    Energy Technology Data Exchange (ETDEWEB)

    Welty, D.E.; Hobbs, L.M.; Penprase, B.E.; Blitz, L. (Chicago Univ., IL (USA) Maryland Univ., College Park (USA))

    1989-11-01

    In an attempt to determine the distances to four high-latitude molecular clouds (HLCs), echelle spectra near the Na I D lines, accurate MK spectral types, and photoelectric photometry for 25 nearby stars have been obtained. Fairly firm distance limits may be placed on MBM 40 (d smaller than or equal to 140 pc) and MBM 53 (d greater than or equal to 110 pc and less than or equal to 155 pc), based on the presence or absence of strong interstellar Na I absorption towards stars projected on or near those HLCs. Weak interstellar absorption lines observed toward many of the stars located near MBM 54 and 55 make the distances to those clouds less certain (about 265 pc for both). Interstellar CH absorption at 4300 A was detected in the spectrum of HD 218662, located behind MBM 53 with a CH column density of 2.1 x 10 to the 13th per sq cm, thus implying a CH abundance comparable to that observed in other molecular clouds. Morphological and velocity agreement among CO emission, the Na I absorption, the 100 micron infrared cirrus emission, and the 21 cm H I emission near these HLCs suggest a close association of the interstellar material responsible for those phenomena. 44 refs.

  20. Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula. [molecular clouds, interstellar matter, and abundance

    Science.gov (United States)

    Irvine, W. M.; Schloerb, F. P.

    1985-01-01

    Two additional hyperfine components of the interstellar radical C3H were detected. In addition, methanol was discovered in interstellar clouds. The abundance of HCCN and various chemical isomers in molecular clouds was investigated.

  1. The Orion Molecular Cloud 2/3 and NGC 1977 Regions

    CERN Document Server

    Peterson, Dawn E

    2008-01-01

    The Orion Molecular Cloud 2/3 region (hereafter, OMC-2/3) and the reflection nebula NGC 1977 encompass a section of the Orion A molecular cloud undergoing vigorous star forming activity. One of the richest assemblages of protostars in the nearest 500 pc is seen in OMC-2/3, while NGC 1977 contains a cluster of over 100 young stars. In this review, we present a census of the protostars, pre-main sequence stars, and young brown dwarfs in these regions. These are identified through sub-millimeter surveys, far-red to near-infrared imaging and spectroscopy with ground-based telescopes, mid-infrared photometry from the Spitzer Space Telescope, and X-ray observations made with the Chandra X-ray Observatory. We present an overview of the distribution of molecular gas associated with these regions and the rich complex of shock heated nebulae created by the young stars interacting with the molecular gas. Finally, we discuss the relationship of OMC-2/3 and NGC 1977 to the neighboring Orion Nebula Cluster and the Orion OB...

  2. Signatures of fast and slow magnetohydrodynamic shocks in turbulent molecular clouds

    CERN Document Server

    Lehmann, Andrew

    2015-01-01

    The character of star formation is intimately related to the supersonic magnetohydrodynamic (MHD) turbulent dynamics of the giant molecular clouds in which stars form. A significant amount of the turbulent energy dissipates in low-velocity shock waves. These shocks cause molecular line cooling of the compressed and heated gas, and so their radiative signatures probe the nature of the turbulence. In MHD fluids the three distinct families of shocks---fast, intermediate and slow---differ in how they compress and heat the molecular gas, and so observational differences between them may also distinguish driving modes of turbulent regions. Here we use a two-fluid model to compare the characteristics of one-dimensional fast and slow MHD shocks propagating at low speeds (a few km/s) in molecular clouds. Fast MHD shocks are magnetically driven, forcing ion species to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where...

  3. On the Formation of Interstellar Water Ice: Constraints from a Search for Hydrogen Peroxide Ice in Molecular Clouds

    Science.gov (United States)

    Smith, R. G.; Charnely, S. B.; Pendleton, Y. J.; Wright, C. M.; Maldoni, M. M.; Robinson, G.

    2011-01-01

    Recent surface chemistry experiments have shown that the hydrogenation of molecular oxygen on interstellar dust grains is a plausible formation mechanism, via hydrogen peroxide (H2O2), for the production of water (H2O) ice mantles in the dense interstellar medium. Theoretical chemistry models also predict the formation of a significant abundance of H2O2 ice in grain mantles by this route. At their upper limits, the predicted and experimental abundances are sufficiently high that H2O2 should be detectable in molecular cloud ice spectra. To investigate this further, laboratory spectra have been obtained for H2O2/H2O ice films between 2.5 and 200 micron, from 10 to 180 K, containing 3%, 30%, and 97% H2O2 ice. Integrated absorbances for all the absorption features in low-temperature H2O2 ice have been derived from these spectra. For identifying H2O2 ice, the key results are the presence of unique features near 3.5, 7.0, and 11.3 micron. Comparing the laboratory spectra with the spectra of a group of 24 protostars and field stars, all of which have strong H2O ice absorption bands, no absorption features are found that can definitely be identified with H2O2 ice. In the absence of definite H2O2 features, the H2O2 abundance is constrained by its possible contribution to the weak absorption feature near 3.47 micron found on the long-wavelength wing of the 3 micron H2O ice band. This gives an average upper limit for H2O2, as a percentage of H2O, of 9% +/- 4%. This is a strong constraint on parameters for surface chemistry experiments and dense cloud chemistry models.

  4. Increasing data quality by predicting cloud-movement with Allsky-Cams

    Energy Technology Data Exchange (ETDEWEB)

    Adam, Jan; Buss, Jens; Noethe, Maximilian [TU Dortmund (Germany); Collaboration: FACT-Collaboration

    2016-07-01

    Clouds and related atmospheric phenomena have a big influence on the quality of astronomical observations. Especially in case of ground-based gamma telescopes such as FACT, bad atmospheric conditions impair the reconstruction of air-shower events. The First G-APD Cherenkov Telescope aims for automatic long-term monitoring. Therefore, it benefits greatly from an advanced scheduling algorithm which takes into account the current weather conditions. While there is no way to reduce the occurrence of clouds in the direction of a desired object, it is possible to increase the duty cycle by switching to an uncovered source. Hence, a quantitative rating of the sky cloudiness is needed to differentiate between covered and uncovered areas. This talk presents a method to calculate the current sky cloudiness by searching stars in 180 allsky camera images. This method can be applied to arbitrary areas, e.g., the whole sky or a few degrees around any certain source. Results and various visualisations are presented, such as the distribution of the parameters for different weather conditions. Moreover, their developement over time is shown for multiple sources in a partly clouded night. And a first approach for predicting the cloud's movement by using subsequent images and additional data such as wind profiles is discussed.

  5. Modelling the structure of molecular clouds - I. A multiscale energy equipartition

    Science.gov (United States)

    Veltchev, Todor V.; Donkov, Sava; Klessen, Ralf S.

    2016-07-01

    We present a model for describing the general structure of molecular clouds (MCs) at early evolutionary stages in terms of their mass-size relationship. Sizes are defined through threshold levels at which equipartitions between gravitational, turbulent and thermal energy |W| ˜ f(Ekin + Eth) take place, adopting interdependent scaling relations of velocity dispersion and density and assuming a lognormal density distribution at each scale. Variations of the equipartition coefficient 1 ≤ f ≤ 4 allow for modelling of star-forming regions at scales within the size range of typical MCs (≳4 pc). Best fits are obtained for regions with low or no star formation (Pipe, Polaris) as well for such with star-forming activity but with nearly lognormal distribution of column density (Rosette). An additional numerical test of the model suggests its applicability to cloud evolutionary times prior to the formation of first stars.

  6. Modelling the structure of molecular clouds: I. A multi-scale energy equipartition

    CERN Document Server

    Veltchev, Todor V; Klessen, Ralf S

    2016-01-01

    We present a model for describing the general structure of molecular clouds (MCs) at early evolutionary stages in terms of their mass-size relationship. Sizes are defined through threshold levels at which equipartitions between gravitational, turbulent and thermal energy $|W| \\sim f(E_{\\rm kin} + E_{\\rm th})$ take place, adopting interdependent scaling relations of velocity dispersion and density and assuming a lognormal density distribution at each scale. Variations of the equipartition coefficient $1\\le f\\le 4$ allow for modelling of star-forming regions at scales within the size range of typical MCs ($\\gtrsim$4 pc). Best fits are obtained for regions with low or no star formation (Pipe, Polaris) as well for such with star-forming activity but with nearly lognormal distribution of column density (Rosette). An additional numerical test of the model suggests its applicability to cloud evolutionary times prior to the formation of first stars.

  7. Molecular Shocks and the Gamma-ray Clouds of the W28 Supernova Remnant

    CERN Document Server

    Maxted, Nigel; de Wilt, Phoebe; Burton, Michael; Braiding, Catherine; Walsh, Andrew; Fukui, Yasuo; Kawamura, Akiko

    2016-01-01

    Interstellar medium clouds in the W28 region are emitting gamma-rays and it is likely that the W28 supernova remnant is responsible, making W28 a prime candidate for the study of cosmic-ray acceleration and diffusion. Understanding the influence of both supernova remnant shocks and cosmic rays on local molecular clouds can help to identify multi-wavelength signatures of probable cosmic-ray sources. To this goal, transitions of OH, SiO, NH3, HCO+ and CS have complemented CO in allowing a characterization of the chemically rich environment surrounding W28. This remnant has been an ideal test-bed for techniques that will complement arcminute-scale studies of cosmic-ray source candidates with future GeV-PeV gamma-ray observations.

  8. The X-ray shadow of the high-latitude molecular cloud MBM 12

    Science.gov (United States)

    Snowden, S. L.; Mccammon, D.; Verter, F.

    1993-01-01

    ROSAT XRT/PSPC observations show a deep shadow cast by the high-latitude molecular cloud MBM 12 in the 3/4 keV diffuse background. Modeling of the shadow implies that less than 20 percent of the typical high-latitude 3/4 keV diffuse background intensity is emitted in front of the cloud (D = 60-70 pc). A weaker shadow consistent with the lower optical depth at higher energies was observed in the 1.5 keV band. Since little shadowing was seen in the 1/4 keV band, this observation places strong constraints on the amount of 0.5-2 keV emission that is intermixed with the source of the observed 1/4 keV flux.

  9. Aperture synthesis observations of the molecular environment of the SGR A complex. I - The M-0.13-0.08 molecular cloud

    Science.gov (United States)

    Okumura, Sachiko K.; Ishiguro, Masato; Fomalont, Edward B.; Chikada, Yoshihiro; Kasuga, Takashi; Morita, Koh-Ichiro; Kawabe, Ryohei; Kobayashi, Hideyuki; Kanzawa, Tomio; Iwashita, Hiroyuki; Hasegawa, Tetsuo

    1989-12-01

    NH3 and H2O maser observations of the 20 km/s molecular cloud M-0.13-0.08 in the Sgr A complex region are reported. NH3 (1,1) and (2,2) lines were observed simultaneously, and the molecular gas temperature and density are estimated. The NH3 emission is elongated in the smae direction of the entire M-0.13-0.08 cloud and has a large velocity gradient along its major axis. Strong NH3 emission is located in the northern part of the cloud, where a perturbed velocity field and broad line widths are observed. In addition, a new H2O maser spot was detected near one of the nonthermal continuum sources. These observational results suggest the physical association between a part of the M-0.13-0.08 molecular cloud and the nonthermal continuum sources in the Sgr A complex.

  10. THE YOUNG STELLAR OBJECT POPULATION IN THE VELA-D MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Strafella, F.; Maruccia, Y.; Maiolo, B. [Dipartimento di Matematica e Fisica, Università del Salento, I-73100 Lecce (Italy); Lorenzetti, D.; Giannini, T. [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I-00040 Monte Porzio (Italy); Elia, D.; Molinari, S.; Pezzuto, S. [INAF-IAPS, Via Fosso del Cavaliere 100, I-00133 Roma (Italy); Massi, F.; Olmi, L., E-mail: francesco.strafella@le.infn.it [INAF-Osservatorio di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy)

    2015-01-10

    We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D, a star-forming region observed by both the Spitzer/NASA and Herschel/ESA space telescopes. The point-source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSOs), also including sources detected in less than four IRAC bands. Bona fide YSOs are selected by using appropriate color-color and color-magnitude criteria aimed at excluding both Galactic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other star-forming clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far-IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources intended to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 of which are starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both the Spitzer and Herschel lists, it follows that in the investigated region we find 53 protostars and that the Spitzer-selected protostars account for approximately two-thirds of the total.

  11. A Spitzer view of the giant molecular cloud Mon OB1 East/NGC 2264

    Energy Technology Data Exchange (ETDEWEB)

    Rapson, V. A. [School of Physics and Astronomy, Rochester Institute of Technology, Rochester, NY 14623 (United States); Pipher, J. L. [Department of Physics and Astronomy, University of Rochester, Rochester, NY 14627 (United States); Gutermuth, R. A. [Five College Astronomy Department, Smith College, Northampton, MA 01063 (United States); Megeath, S. T.; Allen, T. S. [Lowell Observatory, Flagstaff, AZ 86001 (United States); Myers, P. C. [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Allen, L. E., E-mail: var5998@rit.edu [National Optical Astronomy Observatories, Tucson, AZ 85719 (United States)

    2014-10-20

    We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 μm images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and Two Micron All Sky Survey photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power-law index of ∼2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main-sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding, more distributed regions show a disk fraction of 19%. This may be explained by the presence of an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.

  12. A Herschel/HIFI Legacy Survey of HF and H2O in the Galaxy: Probing Diffuse Molecular Cloud Chemistry

    CERN Document Server

    Sonnentrucker, P; Neufeld, D A; Flagey, N; Gerin, M; Goldsmith, P; Lis, D; Monje, R

    2015-01-01

    We combine Herschel observations of a total of 12 sources to construct the most uniform survey of HF and H2O in our Galactic disk. Both molecules are detected in absorption along all sight lines. The high spectral resolution of the Heterodyne Instrument for the Far-Infrared (HIFI) allows us to compare the HF and H2O distributions in 47 diffuse cloud components sampling the disk. We find that the HF and H2O velocity distributions follow each other almost perfectly and establish that HF and H2O probe the same gas-phase volume. Our observations corroborate theoretical predictions that HF is a sensitive tracer of H2 in diffuse clouds, down to molecular fractions of only a few percent. Using HF to trace H2 in our sample, we find that the N(H2O)-to-N(HF) ratio shows a narrow distribution with a median value of 1.51. Our results further suggest that H2O might be used as a tracer of H2 -within a factor 2.5- in the diffuse interstellar medium. We show that the measured factor of ~2.5 variation around the median is dri...

  13. The Razor’s Edge of Collapse: The Transition Point from Lognormal to Power-Law Distributions in Molecular Clouds

    Science.gov (United States)

    Burkhart, Blakesley; Stalpes, Kye; Collins, David C.

    2017-01-01

    We derive an analytic expression for the transitional column density value ({η }t) between the lognormal and power-law form of the probability distribution function (PDF) in star-forming molecular clouds. Our expression for {η }t depends on the mean column density, the variance of the lognormal portion of the PDF, and the slope of the power-law portion of the PDF. We show that {η }t can be related to physical quantities such as the sonic Mach number of the flow and the power-law index for a self-gravitating isothermal sphere. This implies that the transition point between the lognormal and power-law density/column density PDF represents the critical density where turbulent and thermal pressure balance, the so-called “post-shock density.” We test our analytic prediction for the transition column density using dust PDF observations reported in the literature, as well as numerical MHD simulations of self-gravitating supersonic turbulence with the Enzo code. We find excellent agreement between the analytic {η }t and the measured values from the numerical simulations and observations (to within 1.2 AV). We discuss the utility of our expression for determining the properties of the PDF from unresolved low-density material in dust observations, for estimating the post-shock density, and for determining the H i–H2 transition in clouds.

  14. A unified model for the maximum mass scales of molecular clouds, stellar clusters and high-redshift clumps

    Science.gov (United States)

    Reina-Campos, Marta; Kruijssen, J. M. Diederik

    2017-08-01

    We present a simple, self-consistent model to predict the maximum masses of giant molecular clouds (GMCs), stellar clusters and high-redshift clumps as a function of the galactic environment. Recent works have proposed that these maximum masses are set by shearing motions and centrifugal forces, but we show that this idea is inconsistent with the low masses observed across an important range of local-Universe environments, such as low-surface density galaxies and galaxy outskirts. Instead, we propose that feedback from young stars can disrupt clouds before the global collapse of the shear-limited area is completed. We develop a shear-feedback hybrid model that depends on three observable quantities: the gas surface density, the epicylic frequency and the Toomre parameter. The model is tested in four galactic environments: the Milky Way, the Local Group galaxy M31, the spiral galaxy M83 and the high-redshift galaxy zC406690. We demonstrate that our model simultaneously reproduces the observed maximum masses of GMCs, clumps and clusters in each of these environments. We find that clouds and clusters in M31 and in the Milky Way are feedback-limited beyond radii of 8.4 and 4 kpc, respectively, whereas the masses in M83 and zC406690 are shear-limited at all radii. In zC406690, the maximum cluster masses decrease further due to their inspiral by dynamical friction. These results illustrate that the maximum masses change from being shear-limited to being feedback-limited as galaxies become less gas rich and evolve towards low shear. This explains why high-redshift clumps are more massive than GMCs in the local Universe.

  15. Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: a ubiquitous tracer of molecular gas

    CERN Document Server

    Sonnentrucker, P; Phillips, T G; Gerin, M; Lis, D C; De Luca, M; Goicoechea, J R; Black, J H; Bell, T A; Boulanger, F; Cernicharo, J; Coutens, A; Dartois, E; Kazmierczak, M; Encrenaz, P; Falgarone, E; Geballe, T R; Giesen, T; Godard, B; Goldsmith, P F; Gry, C; Gupta, H; Hennebelle, P; Herbst, E; Hily-Blant, P; Joblin, C; Kolos, R; Krelowski, J; Mart\\in-Pintado, J; Menten, K M; Monje, R; Mookerjea, B; Pearson, J; Perault, M; Persson, C M; Plume, R; Salez, M; Schlemmer, S; Schmidt, M; Stutzki, J; Teyssier, D; Vastel, C; Yu, S; Caux, E; Gusten, R; Hatch, W A; Klein, T; Mehdi, I; Morris, P; Ward, J S

    2010-01-01

    We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1 - 0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure - as opposed to obtain a lower limit on - the column density of HF for the first time. As in previous observations of HF toward the source G10.6-0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)-N(H2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF abs...

  16. Molecular line mapping of the giant molecular cloud associated with RCW 106 - IV. Ammonia towards dust emission

    CERN Document Server

    Lowe, Vicki; Urquhart, James S; Marshall, Jonathan P; Horiuchi, Shinji; Lo, Nadia; Walsh, Andrew J; Jordan, Christopher H; Jones, Paul A

    2014-01-01

    Here we report observations of the two lowest inversion transitions of ammonia with the 70-m Tidbinbilla radio telescope. They were conducted to determine the kinetic temperatures in the dense clumps of the G333 giant molecular cloud associated with RCW 106 and to examine the effect that accurate temperatures have on the calculation of derived quantities such as mass. This project is part of a larger investigation to understand the timescales and evolutionary sequence associated with high-mass star formation, particularly its earliest stages. Assuming that the initial chemical composition of a giant molecular cloud is uniform, any abundance variations within will be due to evolutionary state. We have identified 63 clumps using SIMBA 1.2-mm dust continuum maps and have calculated gas temperatures for most (78 per cent) of these dense clumps. After using Spitzer GLIMPSE 8.0 $\\mu$m emission to separate the sample into IR-bright and IR-faint clumps, we use statistical tests to examine whether our classification s...

  17. The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud observed with IRAC and MIPS

    CERN Document Server

    Broekhoven-Fiene, Hannah; Harvey, Paul M; Gutermuth, Robert A; Huard, Tracy L; Tothill, Nicholas F H; Nutter, David; Bourke, Tyler L; DiFrancesco, James; Jørgensen, Jes K; Allen, Lori E; Chapman, Nicholas L; Dunham, Michael M; Merın, Bruno; Miller, Jennifer F; Terebey, Susan; Peterson, Dawn E; Stapelfeldt, Karl R

    2014-01-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70 and 160 micron observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 sq-deg with IRAC and 10.47 sq-deg with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHalpha 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YS...

  18. The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud Observed with IRAC and MIPS

    Science.gov (United States)

    Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jorgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merin, Bruno; Miller, Jennifer F.; Terebey, Susan; Peterson, Dawn E.; Stapelfeldt, Karl R.

    2014-01-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70 and 160 micrometers observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg(exp 2) with IRAC and 10.47 deg2 with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkH(alpha) 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YSO population. Although the AMC is similar in mass, size and distance to the OMC, it is forming about 15 - 20 times fewer stars.

  19. CARMA LARGE AREA STAR FORMATION SURVEY: OBSERVATIONAL ANALYSIS OF FILAMENTS IN THE SERPENS SOUTH MOLECULAR CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Fernández-López, M.; Looney, L.; Lee, K.; Segura-Cox, D. [Department of Astronomy, University of Illinois at Urbana—Champaign, 1002 West Green Street, Urbana, IL 61801 (United States); Arce, H. G.; Plunkett, A. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States); Mundy, L. G.; Storm, S.; Teuben, P. J.; Pound, M. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Isella, A.; Kauffmann, J. [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Tobin, J. J. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Rosolowsky, E. [Departments of Physics and Statistics, University of British Columbia, Okanagan Campus, 3333 University Way, Kelowna, BC V1V 1V7 (Canada); Kwon, W. [SRON Netherlands Institute for Space Research, Landleven 12, 9747-AD Groningen (Netherlands); Ostriker, E. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Tassis, K. [Department of Physics and Institute of Theoretical and Computational Physics, University of Crete, P.O. Box 2208, GR-710 03 Heraklion, Crete (Greece); Shirley, Y. L., E-mail: manferna@gmail.com [Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

    2014-08-01

    We present the N{sub 2}H{sup +} (J = 1 → 0) map of the Serpens South molecular cloud obtained as part of the CARMA Large Area Star Formation Survey. The observations cover 250 arcmin{sup 2} and fully sample structures from 3000 AU to 3 pc with a velocity resolution of 0.16 km s{sup –1}, and they can be used to constrain the origin and evolution of molecular cloud filaments. The spatial distribution of the N{sub 2}H{sup +} emission is characterized by long filaments that resemble those observed in the dust continuum emission by Herschel. However, the gas filaments are typically narrower such that, in some cases, two or three quasi-parallel N{sub 2}H{sup +} filaments comprise a single observed dust continuum filament. The difference between the dust and gas filament widths casts doubt on Herschel ability to resolve the Serpens South filaments. Some molecular filaments show velocity gradients along their major axis, and two are characterized by a steep velocity gradient in the direction perpendicular to the filament axis. The observed velocity gradient along one of these filaments was previously postulated as evidence for mass infall toward the central cluster, but these kind of gradients can be interpreted as projection of large-scale turbulence.

  20. CARMA Large Area Star Formation Survey: Observational Analysis of Filaments in the Serpens South Molecular Cloud

    CERN Document Server

    Fernández-López, M; Looney, L; Mundy, L G; Storm, S; Teuben, P J; Lee, K; Segura-Cox, D; Isella, A; Tobin, J J; Rosolowsky, E; Plunkett, A; Kwon, W; Kauffmann, J; Ostriker, E; Tassis, K; Shirley, Y L; Pound, M

    2014-01-01

    We present the N2H+(J=1-0) map of the Serpens South molecular cloud obtained as part of the CARMA Large Area Star Formation Survey (CLASSy). The observations cover 250 square arcminutes and fully sample structures from 3000 AU to 3 pc with a velocity resolution of 0.16 km/s, and they can be used to constrain the origin and evolution of molecular cloud filaments. The spatial distribution of the N2H+ emission is characterized by long filaments that resemble those observed in the dust continuum emission by Herschel. However, the gas filaments are typically narrower such that, in some cases, two or three quasi-parallel N2H+ filaments comprise a single observed dust continuum filament. The difference between the dust and gas filament widths casts doubt on Herschel ability to resolve the Serpens South filaments. Some molecular filaments show velocity gradients along their major axis, and two are characterized by a steep velocity gradient in the direction perpendicular to the filament axis. The observed velocity gra...

  1. Evidence for nucleosynthetic enrichment of the protosolar molecular cloud core by multiple supernova events.

    Science.gov (United States)

    Schiller, Martin; Paton, Chad; Bizzarro, Martin

    2015-01-15

    The presence of isotope heterogeneity of nucleosynthetic origin amongst meteorites and their components provides a record of the diverse stars that contributed matter to the protosolar molecular cloud core. Understanding how and when the solar system's nucleosynthetic heterogeneity was established and preserved within the solar protoplanetary disk is critical for unraveling the earliest formative stages of the solar system. Here, we report calcium and magnesium isotope measurements of primitive and differentiated meteorites as well as various types of refractory inclusions, including refractory inclusions (CAIs) formed with the canonical (26)Al/(27)Al of ~5 × 10(-5) ((26)Al decays to (26)Mg with a half-life of ~0.73 Ma) and CAIs that show fractionated and unidentified nuclear effects (FUN-CAIs) to understand the origin of the solar system's nucleosynthetic heterogeneity. Bulk analyses of primitive and differentiated meteorites along with canonical and FUN-CAIs define correlated, mass-independent variations in (43)Ca, (46)Ca and (48)Ca. Moreover, sequential dissolution experiments of the Ivuna carbonaceous chondrite aimed at identifying the nature and number of presolar carriers of isotope anomalies within primitive meteorites have detected the presence of multiple carriers of the short-lived (26)Al nuclide as well as carriers of anomalous and uncorrelated (43)Ca, (46)Ca and (48)Ca compositions, which requires input from multiple and recent supernovae sources. We infer that the solar system's correlated nucleosynthetic variability reflects unmixing of old, galactically-inherited homogeneous dust from a new, supernovae-derived dust component formed shortly prior to or during the evolution of the giant molecular cloud parental to the protosolar molecular cloud core. This implies that similarly to (43)Ca, (46)Ca and (48)Ca, the short-lived (26)Al nuclide was heterogeneously distributed in the inner solar system at the time of CAI formation.

  2. Non-similar collapse of singular isothermal spherical molecular cloud cores with nonzero initial velocities

    Science.gov (United States)

    Nejad-Asghar, Mohsen

    2010-12-01

    Theoretically, stars formed from the collapse of cores in molecular clouds. Historically, the core had been assumed to be a singular isothermal sphere (SIS), and the collapse had been investigated in a self-similar manner. When the rotation and magnetic fields lead to non-symmetric collapse, a spheroidal shape may occur. Here, the result of the centrifugal force and magnetic field gradient is assumed to be in the normal direction to the rotational axis, and its components are supposed to be a fraction β of the local gravitational force. In this research, a collapsing SIS core is considered to find the importance that the parameter β plays in the oblateness of the mass shells, which are the crests of the expansion waves. We apply the Adomian decomposition method to solve the system of nonlinear partial differential equations because the collapse does not occur in a spherically symmetric and self-similar manner. In this way, we obtain a semi-analytical relation for the mass infall rate Ṁ of the shells in the envelope. Near the rotational axis, Ṁ decreases with the increase of the non-dimensional radius ξ, while a direct relation is observed between Ṁ and ξ in the equatorial regions. Also, the values of Ṁ in the polar regions are greater than their equatorial values, and this difference occurs more often at smaller values of ξ. Overall, the results show that before reaching the crest of the expansion wave, the visible shape of the molecular cloud cores can evolve into oblate spheroids. The ratio of major to minor axes of oblate cores increases when increasing the parameter β, and its value can approach the observed elongated shapes of cores in the maps of molecular clouds, such as those in Taurus and Perseus.

  3. A molecular cloud complex above the galactic plane.. I. Extended CO observations of the NGC 281 region

    Science.gov (United States)

    Lee, Youngung; Jung, Jae-Hoon

    2003-03-01

    We have mapped the entire extent of the molecular cloud complex associated with NGC 281, both in 12CO ( J=1-0) and 13CO ( J=1-0), using the Taeduk Radio Astronomy Observatory (TRAO) 14 m telescope. We also observed a few selected fields with bright 13CO emission, in CS ( J=2-1) and HCO + ( J=1-0). This region is distinguished by its vertical height of ˜320 pc above the midplane of the Perseus spiral arm, at a distance of 2.9 kpc. The molecular gas in the mapped region is found to extend far beyond the H II region NGC 281 (Sh 184). The southern boundary of the CO emission closely follows the southern boundary of the 100 μm dust emission. The molecular cloud complex consists of two main clouds bisected by the H II region, as well as several other clouds distributed over a range of 90 pc along the galactic longitude direction. Except for one cloud at VLSR=-43.9 km s -1, all these clouds occupy a small, contiguous velocity range centered at VLSR=-30 km s -1. Although these clouds are weakly connected, they clearly show distinct, knotted features along the galactic longitude direction. We assigned names to each cloud (A-H), derive their various physical parameters, and discuss their physical properties. These clouds do not show any specific, systematic behavior in their velocity field, except for a small gradient along galactic longitude (for A-E). The brightest 12CO and 13CO emissions are detected toward cloud A, which is located farthest from the two main clouds. We found star formation to be ongoing in clouds A and B, though these are not as active as D and E. The associated newborn stars have FIR properties similar to those of Herbig Ae/Be stars, and several outflows are also seen. We estimated the cloud masses in three different ways, and discuss the discrepancies between the resulting values. We estimate the total mass of the mapped region to be ˜3.7×10 4 M ⊙, using a conversion factor from CO luminosity to gas mass. About half of the clouds seem to be

  4. Molecular steps of neutral sulfuric acid and dimethylamine nucleation in CLOUD

    Science.gov (United States)

    Jokinen, Tuija; Sarnela, Nina; Sipilä, Mikko; Junninen, Heikki; Lehtipalo, Katrianne; Duplissy, Jonathan; Cloud Collaboration

    2013-05-01

    We have run a set of experiments in the CLOUD chamber at CERN, Switzerland, studying the effect of dimethylamine (DMA) on sulfuric acid (SA)-water nucleation using a nitrate based Chemical Ionization Atmospheric Pressure ionization Time-Of-Flight Mass Spectrometer (CI-APi-TOF). Experiment was designed to produce neutral high m/z SA-DMA clusters in close to atmospherically relevant conditions to be detected and characterized by the CI-APi-TOF. We aimed in filling up the gap in measurement techniques from molecular level up to climatically relevant aerosol particles and thus improve our understanding of the role of sulfuric acid and DMA in atmospheric nucleation.

  5. Supernova Remnant Kes 17: Efficient Cosmic Ray Accelerator inside a Molecular Cloud

    OpenAIRE

    Gelfand, Joseph D.; Castro, Daniel; Slane, Patrick O.; Temim, Tea; Hughes, John P.; Rakowski, Cara

    2013-01-01

    Supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number of remnants detected across the electromagnetic spectrum. In this paper, we analyze recent radio, X-ray, and gamma-ray observations of this object, determining that efficient cosmic ray acceleration is required to explain its broadband non-thermal spectrum. These observations also suggest that Kes 17 is expanding inside a molecular cloud, though our determination of its age depends on whether thermal conduction or cl...

  6. Supernova Remnant Shock - Molecular Cloud Interactions: Masers as tracers of hadronic particle acceleration

    CERN Document Server

    Frail, Dale A

    2011-01-01

    We review the class of galactic supernova remnants which show strong interactions with molecular clouds, revealed through shock-excited hydroxyl masers. These remnants are preferentially found among the known GeV and TeV detections of supernova remnants. It has been argued that the masers trace out the sites of hadronic particle acceleration. We discuss what is known about the physical conditions of these shocked regions and we introduce a potential new maser tracer for identifying the sites of cosmic ray acceleration. This review includes a reasonably complete bibliography for researchers new to the topic of shock-excited masers and supernova remnants.

  7. Detection of the J = 6 - 5 transition of carbon monoxide. [in Orion molecular cloud

    Science.gov (United States)

    Goldsmith, P. F.; Erickson, N. R.; Fetterman, H. R.; Clifton, B. J.; Peck, D. D.; Tannenwald, P. E.; Koepf, G. A.; Buhl, D.; Mcavoy, N.

    1981-01-01

    The J = 6 - 5 rotational transition of carbon monoxide has been detected in emission from the KL 'plateau source' in the Orion molecular cloud. The corrected peak antenna temperature is 100 K, and the FWHM line width is 26 km/sec. These observations were carried out using the 3 m telescope of the NASA IRTF (Infrared Telescope Facility) on Mauna Kea, Hawaii, and constitute the first astronomical data obtained at submillimeter wavelengths with a heterodyne system using a laser local oscillator. The data support the idea that the high-velocity dispersion CO in Orion is optically thin and set a lower limit to its temperature of approximately 180 K.

  8. Detection of a hot molecular core in the Large Magellanic Cloud with ALMA

    CERN Document Server

    Shimonishi, Takashi; Kawamura, Akiko; Aikawa, Yuri

    2016-01-01

    We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, C17O, HCO+, H13CO+, H2CO, NO, SiO, H2CS, 33SO, 32SO2, 34SO2, and 33SO2 are detected from a compact region (0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO2 and 34SO2 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH3OH, H2CO, and HNCO are remarkably lower compared with Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the...

  9. Feedback of the HBe star IL Cep on nearby molecular cloud and star formation

    Science.gov (United States)

    Zhang, Si-Ju; Wu, Yuefang; Li, Jin Zeng; Yuan, Jing-Hua; Liu, Hong-Li; Dong, Xiaoyi; Huang, Ya-Fang

    2016-06-01

    We present investigations of the feedback of a luminous Herbig Be star, IL Cep. We mapped the vicinity of IL Cep in the J = 1-0 transitions of 12CO, 13CO and C18O molecular lines with the Purple Mountain Observatory 13.7 m telescope. Archival data from Wide-field Infrared Survey Explorer were also employed. A parsec-scale cavity that has probably been excavated by the dominant HBe star, IL Cep, is revealed. An expanding shell-like structure featured by 12CO(J = 1-0) emission was found surrounding the cavity, which embeds several 13CO(J = 1-0) molecular clumps. The density and velocity gradients imply strong stellar winds from exciting stars, this is consistent with the morphology of molecular cloud. The 12CO(J = 1-0) spectra show broad blue wings with a width of about 3.5 km s-1. We suggest that the broad blue wings could be emission from the molecular gas shocked by stellar winds, while the main narrow component may originate from pre-shocked gas. Several bright bow-shaped rims have been detected at 12 μm, which serve as the interface of the molecular cloud facing UV dissipation from the exciting stars. The rims all have an orientation facing IL Cep, this may indicate the pre-dominant effects of IL Cep on its surroundings. A very young star candidate (about 104.8 yr) was found in the head of one bright rim, but its triggered origin is uncertain. All results achieved in this paper suggest that IL Cep has violent effects on its surroundings.

  10. Two physical regimes for the Giant HII Regions and Giant Molecular Clouds in the Antennae Galaxies

    CERN Document Server

    Zaragoza-Cardiel, Javier; Beckman, John E; García-Lorenzo, Begoña; Erroz-Ferrer, Santiago; Gutiérrez, Leonel

    2014-01-01

    We have combined observations of the Antennae galaxies from the radio interferometer ALMA (Atacama Large Millimetre/submillimetre Array) and from the optical interferometer GH$\\alpha$FaS (Galaxy Halpha Fabry-Perot System). The two sets of observations have comparable angular and spectral resolutions, enabling us to identify 142 giant molecular clouds and 303 HII regions. We have measured, and compare, their basic physical properties (radius, velocity dispersion, luminosity). For the HII regions we find two physical regimes, one for masses $>10^{5.4} \\mathrm{M_{\\odot}}$ of ionized gas, which the gas density increases with gas mass, the other for masses $<10^{5.4} \\mathrm{M_{\\odot}}$ of ionized gas where the gas density decreases with gas mass. For the GMCs we find, in contrast to previous studies in other galaxies over a generally lower mass range of clouds, that the gas density increases with the total gas mass, hinting at two regimes for these clouds if we consider both sources of data. We also find that ...

  11. Effects of magnetic fields on the cosmic-ray ionization of molecular cloud cores

    CERN Document Server

    Padovani, Marco

    2011-01-01

    Low-energy cosmic rays are the dominant source of ionization for molecular cloud cores. The ionization fraction, in turn, controls the coupling of the magnetic field to the gas and hence the dynamical evolution of the cores. The purpose of this work is to compute the attenuation of the cosmic-ray flux rate in a cloud core taking into account magnetic focusing, magnetic mirroring, and all relevant energy loss processes. We adopt a standard cloud model characterized by a mass-to-flux ratio supercritical by a factor of about 2 to describe the density and magnetic field distribution of a low-mass starless core, and we follow the propagation of cosmic rays through the core along flux tubes enclosing different amount of mass. We then extend our analysis to cores with different mass-to-flux ratios. We find that mirroring always dominates over focusing, implying a reduction of the cosmic-ray ionization rate by a factor of about 2-3 over most of a solar-mass core with respect to the value in the intercloud medium outs...

  12. Statistical link between the structure of molecular clouds and their density distribution

    CERN Document Server

    Donkov, Sava; Klessen, Ralf S

    2016-01-01

    We introduce the concept of a class of equivalence of molecular clouds represented by an abstract spherically symmetric, isotropic object. This object is described by use of abstract scales in respect to a given mass density distribution. Mass and average density are ascribed to each scale and thus are linked to the density distribution: a power-law type and an arbitrary continuous one. In the latter case, we derive a differential relationship between the mean density at a given scale and the structure parameter which defines the mass-density relationship. The two-dimensional (2D) projection of the cloud along the line of sight is also investigated. Scaling relations of mass and mean density are derived in the considered cases of power-law and arbitrary continuous distributions. We obtain relations between scaling exponents in the 2D and 3D cases. The proposed classes of equivalence are representative for the general structure of real clouds with various types of column-density distributions: power law, logno...

  13. Spiral shocks, triggering of star formation and the velocity dispersion in Giant Molecular Clouds

    CERN Document Server

    Bonnell, I A; Robitaille, T R; Pringle, J E

    2006-01-01

    We present numerical simulations of the passage of clumpy gas through a galactic spiral shock and the subsequent formation of giant molecular clouds (GMCs). The spiral shock forms dense clouds while dissipating kinetic energy, producing regions that are locally gravitationally bound and collapse to form stars. The effect of the clumpiness of gas as it passes through the shock is to generate chaotic internal motions in the gas. The kinematics of these motions are found to agree with the observed velocity-dispersion/size relation found in star-forming regions. In contrast to the standard picture where continuously driven turbulence generates the density inhomogeneities in star-forming clouds, we find here that it is the clumpiness of the interstellar gas that produces the chaotic motions as it passes through the spiral shock and initiates the star formation process. The velocity dispersion can be understood as being due to the random mass loading of clumps as they converge in the spiral shock. In this model the...

  14. Cloud droplet activation mechanisms of amino acid aerosol particles: insight from molecular dynamics simulations

    Directory of Open Access Journals (Sweden)

    Xin Li

    2013-07-01

    Full Text Available Atmospheric amino acids constitute a large fraction of water-soluble organic nitrogen compounds in aerosol particles, and have been confirmed as effective cloud condensation nuclei (CCN materials in laboratory experiments. We present a molecular dynamics (MD study of six amino acids with different structures and chemical properties that are relevant to the remote marine atmospheric aerosol–cloud system, with the aim of investigating the detailed mechanism of their induced changes in surface activity and surface tension, which are important properties for cloud drop activation. Distributions and orientations of the amino acid molecules are studied; these l-amino acids are serine (SER, glycine (GLY, alanine (ALA, valine (VAL, methionine (MET and phenylalanine (PHE and are categorised as hydrophilic and amphiphilic according to their affinities to water. The results suggest that the presence of surface-concentrated amphiphilic amino acid molecules give rise to enhanced Lennard–Jones repulsion, which in turn results in decreased surface tension of a planar interface and an increased surface tension of the spherical interface of droplets with diameters below 10 nm. The observed surface tension perturbation for the different amino acids under study not only serves as benchmark for future studies of more complex systems, but also shows that amphiphilic amino acids are surface active. The MD simulations used in this study reproduce experimental results of surface tension measurements for planar interfaces and the method is therefore applicable for spherical interfaces of nano-size for which experimental measurements are not possible to conduct.

  15. Charge of interstellar dust in dense molecular clouds: Effect of cosmic rays

    CERN Document Server

    Ivlev, Alexei; Galli, Daniele; Caselli, Paola

    2015-01-01

    The local cosmic-ray (CR) spectra are calculated for typical characteristic regions of a cold dense molecular cloud, to investigate two so far neglected mechanisms of dust charging: collection of suprathermal CR electrons and protons by grains, and photoelectric emission from grains due to the UV radiation generated by CRs. The two mechanisms add to the conventional charging by ambient plasma, produced in the cloud by CRs. We show that the CR-induced photoemission can dramatically modify the charge distribution function for submicron grains. We demonstrate the importance of the obtained results for dust coagulation: While the charging by ambient plasma alone leads to a strong Coulomb repulsion between grains and inhibits their further coagulation, the combination with the photoemission provides optimum conditions for the growth of large dust aggregates in a certain region of the cloud, corresponding to the densities $n(\\mathrm{H_2})$ between $\\sim10^4$ cm$^{-3}$ and $\\sim10^6$ cm$^{-3}$. The charging effect o...

  16. Resolving Giant Molecular Clouds in NGC 300: A First Look with the Submillimeter Array

    CERN Document Server

    Faesi, Christopher; Forbrich, Jan

    2016-01-01

    We present the first high angular resolution study of giant molecular clouds (GMCs) in the nearby spiral galaxy NGC 300, based on observations from the Submillimeter Array (SMA). We target eleven 500 pc-sized regions of active star formation within the galaxy in the CO(J=2-1) line at 40 pc spatial and 1 km/s spectral resolution and identify 45 individual GMCs. We characterize the physical properties of these GMCs, and find that they are similar to GMCs in the disks of the Milky Way and other nearby spiral galaxies. For example, the GMC mass spectrum in our sample has a slope of 1.80+/-0.07. Twelve clouds are spatially resolved by our observations, of which ten have virial mass estimates that agree to within a factor of two with mass estimates derived directly from CO integrated intensity, suggesting that the majority of these GMCs are bound. The resolved clouds show consistency with Larson's fundamental relations between size, linewidth, and mass observed in the Milky Way. We find that the linewidth scales wi...

  17. Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions

    CERN Document Server

    Glover, S C O

    2006-01-01

    We study the formation of H2 in the ISM, using a modified version of the astrophysical magnetohydrodynamical code ZEUS-MP that includes a non-equilibrium treatment of the formation and destruction of H2. We use a local approximation to compute the shielding of H2 against photodissociation, making three-dimensional high-resolution simulations of cloud formation feasible with modest computational resources. Our modification to ZEUS-MP also includes a detailed treatment of the thermal behaviour of the gas. In this paper, we focus on the problem of molecular cloud formation in gravitationally unstable, initially static gas. (In a subsequent paper, we consider turbulent flow). We show that in these conditions, H2 formation is driven by gravitational collapse, and so occurs over one or more gravitational free-fall timescales. For initial densities consistent with those observed in the cold, neutral atomic phase of the interstellar medium, this corresponds to a cloud formation timescale t > 10 Myr. We also show that...

  18. A FUSE Survey of Interstellar Molecular Hydrogen in the Small and Large Magellanic Clouds

    CERN Document Server

    Tumlinson, J; Rachford, B L; Browning, M K; Snow, T P; Fullerton, A W; Jenkins, E B; Savage, B D; Crowther, P A; Moos, H W; Sembach, K R; Sonneborn, G; York, D G; Tumlinson, Jason; Rachford, Brian L.; Browning, Matthew K.; Snow, Theodore P.; Fullerton, Alex W.; Jenkins, Edward B.; Savage, Blair D.; Crowther, Paul A.; Sembach, Kenneth R.; Sonneborn, George; York, Donald G.

    2001-01-01

    We describe a moderate-resolution FUSE survey of H2 along 70 sight lines to the Small and Large Magellanic Clouds, using hot stars as background sources. FUSE spectra of 67% of observed Magellanic Cloud sources (52% of LMC and 92% of SMC) exhibit absorption lines from the H2 Lyman and Werner bands between 912 and 1120 A. Our survey is sensitive to N(H2) >= 10^14 cm^-2; the highest column densities are log N(H2) = 19.9 in the LMC and 20.6 in the SMC. We find reduced H2 abundances in the Magellanic Clouds relative to the Milky Way, with average molecular fractions = 0.010 (+0.005, -0.002) for the SMC and = 0.012 (+0.006, -0.003) for the LMC, compared with = 0.095 for the Galactic disk over a similar range of reddening. The dominant uncertainty in this measurement results from the systematic differences between 21 cm radio emission and Lya in pencil-beam sight lines as measures of N(HI). These results imply that the diffuse H2 masses of the LMC and SMC are 8 x 10^6 Msun and 2 x 10^6 Msun, respectively, 2% and...

  19. Neural Network predictions of Diatomic and Triatomic Molecular Data

    Science.gov (United States)

    Blake Laing, W.

    1997-11-01

    The arrangement of molecules in periodic systems offers an enhanced comprehension of trends in molecular properties, a more efficient method of sorting and searching of molecular databases, and bases for the prediction of new data. Neural networks have the ability to "learn" existing data and to forecast a large amount of new data without a smoothing equation.(R. Hefferlin, B. Davis, W. B. Laing, "The Learning and Prediction of Triatomic Molecular Data with Neural Networks," International Arctic Seminar 1997, Murmansk, Russia)(J. Wohlers, W. B. Laing, R. Hefferlin, and B. Daivs, "Least-Squares and Neural-Network Forecasting from Citical Data: Diatomic Molecular Internuclear Separations and Triatomic Heats of Atomization and Ionization Potentials," Advances in Molecular Similarity: JIA book series, in press) This report will present periodic systems of molecules as well as neural network predictions for additional properties of diatomic and triatomic molecules.

  20. The Detection of a Hot Molecular Core in the Large Magellanic Cloud with ALMA

    Science.gov (United States)

    Shimonishi, Takashi; Onaka, Takashi; Kawamura, Akiko; Aikawa, Yuri

    2016-08-01

    We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, C17O, HCO+, H13CO+, H2CO, NO, SiO, H2CS, 33SO, 32SO2, 34SO2, and 33SO2 are detected from a compact region (˜0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO2 and 34SO2 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH3OH, H2CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO2 and its isotopologue line detections in ST11 imply that SO2 can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.