WorldWideScience

Sample records for galaxies assembly cooling

  1. The Cool ISM in Galaxies

    van der Hulst, J. M.; Blok, W. J. G. de; Oswalt, Terry D.; Keel, William C.

    2013-01-01

    This chapter describes the different constituents of the observable interstellar medium (ISM) in galaxies and reviews the relationships between the ISM and the star formation in galaxies. The emphasis is on the component which is most widespread and most easily observable, the neutral atomic

  2. Power semiconductor device adaptive cooling assembly

    2011-01-01

    The invention relates to a power semiconductor device (100) cooling assembly for cooling a power semiconductor device (100), wherein the assembly comprises an actively cooled heat sink (102) and a controller (208; 300), wherein the controller (208; 300) is adapted for adjusting the cooling

  3. A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster

    McDonald, M.; Bayliss, M.; Benson, B. A.; Foley, R. J.; Ruel, J.; Sullivan, P.; Veilleux, S.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.; hide

    2012-01-01

    In the cores of some galaxy clusters the hot intracluster plasma is dense enough that it should cool radiatively in the cluster s lifetime, leading to continuous "cooling flows" of gas sinking towards the cluster center, yet no such cooling flow has been observed. The low observed star formation rates and cool gas masses for these "cool core" clusters suggest that much of the cooling must be offset by astrophysical feedback to prevent the formation of a runaway cooling flow. Here we report X-ray, optical, and infrared observations of the galaxy cluster SPT-CLJ2344-4243 at z = 0.596. These observations reveal an exceptionally luminous (L(sub 2-10 keV) = 8.2 10(exp 45) erg/s) galaxy cluster which hosts an extremely strong cooling flow (M(sub cool) = 3820 +/- 530 Stellar Mass/yr). Further, the central galaxy in this cluster appears to be experiencing a massive starburst (740 +/- 160 Stellar Mass/ yr), which suggests that the feedback source responsible for preventing runaway cooling in nearby cool core clusters may not yet be fully established in SPT-CLJ2344-4243. This large star formation rate implies that a significant fraction of the stars in the central galaxy of this cluster may form via accretion of the intracluster medium, rather than the current picture of central galaxies assembling entirely via mergers.

  4. THE ASSEMBLY OF GALAXY CLUSTERS

    Berrier, Joel C.; Stewart, Kyle R.; Bullock, James S.; Purcell, Chris W.; Barton, Elizabeth J.; Wechsler, Risa H.

    2009-01-01

    We study the formation of 53 galaxy cluster-size dark matter halos (M = 10 14.0-14.76 M sun ) formed within a pair of cosmological Λ cold dark matter N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host ∼0.3 L * galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'preprocessing' in the group environment prior to their accretion into the cluster. On average, 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; less than 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (∼<6 Gyr) than a field halo of the same mass. These results suggest that local cluster processes such as ram pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass, and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with ∼20% incorporated into the cluster halo more than 7 Gyr ago and ∼20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate timescale for late-type to early-type transformation within the cluster environment to be ∼6 Gyr.

  5. Galaxy Formation by Cosmic Strings and Cooling of Baryonic Matter

    Mizuo, IZAWA; Humitaka, SATO; Department of Physics, University of Tokyo; Department of Physics, Kyoto University

    1987-01-01

    Cooling and contraction of baryonic matter are investigated ina galaxy formation scenario by string loops. It is found that ~3% of virialized baryonic matter has cooled down and contracted. This virialized object may have a disk-halo structure and be considered a galaxy.

  6. Condition of the existence of cooling flow in galaxies

    Volkov, E.V.

    1986-01-01

    A criterion for the existence of subsonic spherical symmetrical flow of cooling gas in galaxies has been found. Some equations are given describing the behaviour of gas in the gravitational field of a galaxy in the framework of a stationary accretion model. The results of numerical calculations of a nonstationary accretion of gas on a cD galaxy are presented. The gas is initially in a hydrostatic equilibrium

  7. ISM stripping from cluster galaxies and inhomogeneities in cooling flows

    Soker, Noam; Bregman, Joel N.; Sarazin, Craig L.

    1990-01-01

    Analyses of the x ray surface brightness profiles of cluster cooling flows suggest that the mass flow rate decreases towards the center of the cluster. It is often suggested that this decrease results from thermal instabilities, in which denser blobs of gas cool rapidly and drop below x ray emitting temperatures. If the seeds for the thermal instabilities are entropy perturbations, these perturbations must enter the flow already in the nonlinear regime. Otherwise, the blobs would take too long to cool. Here, researchers suggest that such nonlinear perturbations might start as blobs of interstellar gas which are stripped out of cluster galaxies. Assuming that most of the gas produced by stellar mass loss in cluster galaxies is stripped from the galaxies, the total rate of such stripping is roughly M sub Interstellar Matter (ISM) approx. 100 solar mass yr(-1). It is interesting that the typical rates of cooling in cluster cooling flows are M sub cool approx. 100 solar mass yr(-1). Thus, it is possible that a substantial portion of the cooling gas originates as blobs of interstellar gas stripped from galaxies. The magnetic fields within and outside of the low entropy perturbations can help to maintain their identities, both by suppressing thermal conduction and through the dynamical effects of magnetic tension. One significant question concerning this scenario is: Why are cooling flows seen only in a fraction of clusters, although one would expect gas stripping to be very common. It may be that the density perturbations only survive and cool efficiently in clusters with a very high intracluster gas density and with the focusing effect of a central dominant galaxy. Inhomogeneities in the intracluster medium caused by the stripping of interstellar gas from galaxies can have a number of other effects on clusters. For example, these density fluctuations may disrupt the propagation of radio jets through the intracluster gas, and this may be one mechanism for producing Wide

  8. STAR FORMATION EFFICIENCY IN THE COOL CORES OF GALAXY CLUSTERS

    McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher; Rupke, David S. N.

    2011-01-01

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and Hα (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to Hα luminosity, the UV spectral energy distribution, and the far-UV and Hα morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given Hα luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/Hα ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) ∼ 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from ∼0.05 M sun yr -1 in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to ∼5 M sun yr -1 in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, Hα, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14 +18 -8 %. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

  9. THE FIRST GALAXIES: ASSEMBLY UNDER RADIATIVE FEEDBACK FROM THE FIRST STARS

    Pawlik, Andreas H.; Milosavljević, Miloš; Bromm, Volker

    2013-01-01

    We investigate how radiative feedback from the first stars affects the assembly of the first dwarf galaxies. To this end, we perform cosmological zoomed smoothed particle hydrodynamics simulations of a dwarf galaxy assembling inside a halo reaching a virial mass ∼10 9 M ☉ at z = 10. The simulations follow the non-equilibrium chemistry and cooling of primordial gas and the subsequent conversion of the cool dense gas into massive metal-free stars. To quantify the radiative feedback, we compare a simulation in which stars emit both molecular hydrogen dissociating and hydrogen/helium ionizing radiation with a simulation in which stars emit only molecular hydrogen dissociating radiation, and further with a simulation in which stars remain dark. Photodissociation and photoionization exert a strong negative feedback on the assembly of the galaxy inside the main minihalo progenitor. Gas condensation is strongly impeded, and star formation is strongly suppressed in comparison with the simulation in which stars remain dark. The feedback on the gas from either dissociating or ionizing radiation implies a suppression of the central dark matter densities in the minihalo progenitor by factors of up to a few, which is a significant deviation from the singular isothermal density profile characterizing the dark matter distribution inside the virial radius in the absence of radiative feedback. The evolution of gas densities, star formation rates, and the distribution of dark matter becomes insensitive to the inclusion of dissociating radiation in the late stages of the minihalo assembly, and it becomes insensitive to the inclusion of ionizing radiation once the minihalo turns into an atomically cooling galaxy. The formation of a rotationally supported extended disk inside the dwarf galaxy is a robust outcome of our simulations not affected by the inclusion of radiation. Low-mass galaxies in the neighborhood of the dwarf galaxy show a large scatter in the baryon fraction which is

  10. THE FIRST GALAXIES: ASSEMBLY WITH BLACK HOLE FEEDBACK

    Jeon, Myoungwon; Pawlik, Andreas H.; Bromm, Volker; Milosavljević, Miloš; Greif, Thomas H.; Glover, Simon C. O.; Klessen, Ralf S.

    2012-01-01

    We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the BH accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the BH as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from an HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.

  11. The First Galaxies: Assembly with Black Hole Feedback

    Jeon, Myoungwon; Pawlik, Andreas H.; Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Milosavljević, Miloš; Klessen, Ralf S.

    2012-07-01

    We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the BH accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the BH as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from an HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.

  12. Models of steady state cooling flows in elliptical galaxies

    Vedder, P.W.; Trester, J.J.; Canizares, C.R.

    1988-01-01

    A comprehensive set of steady state models for spherically symmetric cooling flows in early-type galaxies is presented. It is found that a reduction of the supernova (SN) rate in ellipticals produces a decrease in the X-ray luminosity of galactic cooling flows and a steepening of the surface brightness profile. The mean X-ray temperature of the cooling flow is not affected noticeably by a change in the SN rate. The external pressure around a galaxy does not markedly change the luminosity of the gas within the galaxy but does change the mean temperature of the gas. The presence of a dark matter halo in a galaxy only changes the mean X-ray temperature slightly. The addition of a distribution of mass sinks which remove material from the general accretion flow reduces L(X) very slightly, flattens the surface brightness profile, and reduces the central surface brightness level to values close to those actually observed. A reduction in the stellar mass-loss rate only slightly reduces the X-ray luminosity of the cooling flow and flattens the surface brightness by a small amount. 37 references

  13. Radio properties of central dominant galaxies in cluster cooling flows

    O'dea, C.P.; Baum, S.A.

    1986-01-01

    New VLA observations of central dominant (cd) galaxies currently thought to be in cluster cooling flows are combined with observations from the literature to examine the global properties of a heterogeneous sample of 31 cd galaxies. The radio sources tend to be of low or intermediate radio power and have small sizes (median extent about 25 kpc). The resolved sources tend to have distorted morphologies (e.g., wide-angle tails and S shapes). It is not yet clear whether the radio emission from these cd galaxies is significantly different from those not thought to be in cluster cooling flows. The result of Jones and Forman (1984), that there is a possible correlation between radio power and excess X-ray luminosity in the cluster center (above a King model fit to the X-ray surface brightness), is confirmed. 43 references

  14. The effects of assembly bias on the inference of matter clustering from galaxy-galaxy lensing and galaxy clustering

    McEwen, Joseph E.; Weinberg, David H.

    2018-04-01

    The combination of galaxy-galaxy lensing (GGL) and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. Halo occupation distribution (HOD) modeling can extend the approach down to nonlinear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with large scale environment at fixed halo mass. We investigate this problem using the mock galaxy catalogs created by Hearin & Watson (2013, HW13), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy colour is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older halos affects the cutoff of the mean occupation function for central galaxies, with halos in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. We introduce an extended, environment dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements. Crucially, we find that the galaxy-matter cross-correlation coefficient, rgm(r) ≡ ξgm(r) . [ξmm(r)ξgg(r)]-1/2, is insensitive to assembly bias on scales r ≳ 1 h^{-1} Mpc, even though ξgm(r) and ξgg(r) are both affected individually. We can therefore recover the correct ξmm(r) from the HW13 galaxy-galaxy and galaxy-matter correlations using either a standard HOD or EDHOD fitting method. For Mr ≤ -19 or Mr ≤ -20 samples the recovery of ξmm(r) is accurate to 2% or better. For a sample of red Mr ≤ -20 galaxies we achieve 2% recovery at r ≳ 2 h^{-1} Mpc with EDHOD modeling but lower accuracy at smaller scales or with a standard HOD fit. Most of our mock galaxy samples are consistent with rgm = 1 down to r = 1h-1Mpc, to within the uncertainties set by our finite simulation volume.

  15. The effects of assembly bias on the inference of matter clustering from galaxy-galaxy lensing and galaxy clustering

    McEwen, Joseph E.; Weinberg, David H.

    2018-07-01

    The combination of galaxy-galaxy lensing and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. Halo occupation distribution (HOD) modelling can extend the approach down to non-linear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with the large-scale environment at fixed halo mass. We investigate this problem using the mock galaxy catalogs created by Hearin & Watson (2013, HW13), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy colour is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older haloes affects the cutoff of the mean occupation function ⟨Ncen(Mmin)⟩ for central galaxies, with haloes in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. We introduce an extended, environment-dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements. Crucially, we find that the galaxy-matter cross-correlation coefficient, rgm(r) ≡ ξgm(r) . [ξmm(r)ξgg(r)]-1/2, is insensitive to assembly bias on scales r ≳ 1 h-1 Mpc, even though ξgm(r) and ξgg(r) are both affected individually. We can therefore recover the correct ξmm(r) from the HW13 galaxy-galaxy and galaxy-matter correlations using either a standard HOD or EDHOD fitting method. For Mr ≤ -19 or Mr ≤ -20 samples the recovery of ξmm(r) is accurate to 2 per cent or better. For a sample of red Mr ≤ -20 galaxies, we achieve 2 per cent recovery at r ≳ 2 h-1 Mpc with EDHOD modelling but lower accuracy at smaller scales or with a standard HOD fit. Most of our mock galaxy samples are consistent with rgm = 1 down to r = 1 h-1 Mpc, to within the uncertainties set by our finite simulation volume.

  16. Galaxy and Mass Assembly (GAMA): small-scale anisotropic galaxy clustering and the pairwise velocity dispersion of galaxies

    Loveday, J.; Christodoulou, L.; Norberg, P.; Peacock, J. A.; Baldry, I. K.; Bland-Hawthorn, J.; Brown, M. J. I.; Colless, M.; Driver, S. P.; Holwerda, B. W.; Hopkins, A. M.; Kafle, P. R.; Liske, J.; Lopez-Sanchez, A. R.; Taylor, E. N.

    2018-03-01

    The galaxy pairwise velocity dispersion (PVD) can provide important tests of non-standard gravity and galaxy formation models. We describe measurements of the PVD of galaxies in the Galaxy and Mass Assembly (GAMA) survey as a function of projected separation and galaxy luminosity. Due to the faint magnitude limit (r PVD to smaller scales (r⊥ = 0.01 h - 1 Mpc) than previous work. The measured PVD at projected separations r⊥ ≲ 1 h - 1 Mpc increases near monotonically with increasing luminosity from σ12 ≈ 200 km s - 1 at Mr = -17 mag to σ12 ≈ 600 km s - 1 at Mr ≈ -22 mag. Analysis of the Gonzalez-Perez et al. (2014) GALFORM semi-analytic model yields no such trend of PVD with luminosity: the model overpredicts the PVD for faint galaxies. This is most likely a result of the model placing too many low-luminosity galaxies in massive haloes.

  17. Fuel assembly cooling experience at the FFTF/IEM cell

    McGuinness, P.W.

    1985-01-01

    In the Fast Flux Test Facility (FFTF), sodium wetted irradiated fuel assemblies are discharged to the Interim Examination and Maintenance (IEM) Cell for disassembly and post-irradiation examination in an inert argon atmosphere. While in the IEM Cell, fuel assemblies are cooled by the IEM Cell Subassembly Cooling System. This paper describes the cooling system design, performance, and lessons learned, including a discussion of two overtemperature incidents. 2 refs., 6 figs

  18. Revisiting the Cooling Flow Problem in Galaxies, Groups, and Clusters of Galaxies

    McDonald, M.; Gaspari, M.; McNamara, B. R.; Tremblay, G. R.

    2018-05-01

    We present a study of 107 galaxies, groups, and clusters spanning ∼3 orders of magnitude in mass, ∼5 orders of magnitude in central galaxy star formation rate (SFR), ∼4 orders of magnitude in the classical cooling rate ({\\dot{M}}cool}\\equiv {M}gas}(rsample, we measure the ICM cooling rate, {\\dot{M}}cool}, using archival Chandra X-ray data and acquire the SFR and systematic uncertainty in the SFR by combining over 330 estimates from dozens of literature sources. With these data, we estimate the efficiency with which the ICM cools and forms stars, finding {ε }cool}\\equiv {SFR}/{\\dot{M}}cool}=1.4 % +/- 0.4% for systems with {\\dot{M}}cool}> 30 M ⊙ yr‑1. For these systems, we measure a slope in the SFR–{\\dot{M}}cool} relation greater than unity, suggesting that the systems with the strongest cool cores are also cooling more efficiently. We propose that this may be related to, on average, higher black hole accretion rates in the strongest cool cores, which could influence the total amount (saturating near the Eddington rate) and dominant mode (mechanical versus radiative) of feedback. For systems with {\\dot{M}}cool}< 30 M ⊙ yr‑1, we find that the SFR and {\\dot{M}}cool} are uncorrelated and show that this is consistent with star formation being fueled at a low (but dominant) level by recycled ISM gas in these systems. We find an intrinsic log-normal scatter in SFR at a fixed {\\dot{M}}cool} of 0.52 ± 0.06 dex (1σ rms), suggesting that cooling is tightly self-regulated over very long timescales but can vary dramatically on short timescales. There is weak evidence that this scatter may be related to the feedback mechanism, with the scatter being minimized (∼0.4 dex) for systems for which the mechanical feedback power is within a factor of two of the cooling luminosity.

  19. Galaxy and Mass Assembly (GAMA): Morphological transformation of galaxies across the green valley

    Bremer, M. N.; Phillipps, S.; Kelvin, L. S.; De Propris, R.; Kennedy, Rebecca; Moffett, Amanda J.; Bamford, S.; Davies, L. J. M.; Driver, S. P.; Häußler, B.; Holwerda, B.; Hopkins, A.; James, P. A.; Liske, J.; Percival, S.; Taylor, E. N.

    2018-05-01

    We explore constraints on the joint photometric and morphological evolution of typical low redshift galaxies as they move from the blue cloud through the green valley and on to the red sequence. We select Galaxy And Mass Assembly (GAMA) survey galaxies with 10.25 sensitive K-band profiles of red and green galaxy populations are very similar while g-band profiles indicate more disc-like morphologies for the green galaxies: apparent (optical) morphological differences arise primarily from radial mass-to-light ratio variations. Two-component fits show that most green galaxies have significant bulge and disc components and that the blue to red evolution is driven by colour change in the disc. Together, these strongly suggest that galaxies evolve from blue to red through secular disc fading and that a strong bulge is present prior to any decline in star formation. The relative abundance of the green population implies a typical time-scale for traversing the green valley ˜1-2 Gyr and is independent of environment, unlike that of the red and blue populations. While environment likely plays a rôle in triggering the passage across the green valley, it appears to have little effect on time taken. These results are consistent with a green valley population dominated by (early type) disc galaxies that are insufficiently supplied with gas to maintain previous levels of disc star formation, eventually attaining passive colours. No single event is needed to quench their star formation.

  20. Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

    Khosroshahi, Habib G.; Raouf, Mojtaba; Miraghaei, Halime; Brough, Sarah; Croton, Darren J.; Graham, Alister; Driver, Simon; Baldry, Ivan; Brown, Michael; Prescott, Matt; Wang, Lingyu

    2017-01-01

    We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and unrelaxed galaxy groups from the Galaxy and Mass Assembly survey. The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy (BGG), e.g., the luminosity gap between the two most luminous members, and the offset between the position of the BGG and the luminosity centroid of the group. We find that the radio luminosity of the largest galaxy in the group strongly depends on its environment, such that the BGGs in dynamically young (evolving) groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old (relaxed) groups. This observation has been successfully reproduced by a newly developed semi-analytic model that allows us to explore the various causes of these findings. We find that the fraction of radio-loud BGGs in the observed dynamically young groups is ∼2 times that of the dynamically old groups. We discuss the implications of this observational constraint on the central galaxy properties in the context of galaxy mergers and the super massive black hole accretion rate.

  1. Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

    Khosroshahi, Habib G.; Raouf, Mojtaba; Miraghaei, Halime [School of Astronomy, Institute for Research in Fundamental Sciences (IPM), Tehran, 19395-5746 (Iran, Islamic Republic of); Brough, Sarah [Australian Astronomical Observatory, P.O. Box 915, North Ryde, NSW 1670 (Australia); Croton, Darren J.; Graham, Alister [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia); Driver, Simon [International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Baldry, Ivan [Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Brown, Michael [School of Physics, Monash University, Clayton, VIC 3800 (Australia); Prescott, Matt [Astrophysics Group, The University of Western Cape, Robert Sobukwe Road, Bellville 7530 (South Africa); Wang, Lingyu, E-mail: habib@ipm.ir [SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD, Groningen (Netherlands)

    2017-06-20

    We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and unrelaxed galaxy groups from the Galaxy and Mass Assembly survey. The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy (BGG), e.g., the luminosity gap between the two most luminous members, and the offset between the position of the BGG and the luminosity centroid of the group. We find that the radio luminosity of the largest galaxy in the group strongly depends on its environment, such that the BGGs in dynamically young (evolving) groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old (relaxed) groups. This observation has been successfully reproduced by a newly developed semi-analytic model that allows us to explore the various causes of these findings. We find that the fraction of radio-loud BGGs in the observed dynamically young groups is ∼2 times that of the dynamically old groups. We discuss the implications of this observational constraint on the central galaxy properties in the context of galaxy mergers and the super massive black hole accretion rate.

  2. Galaxy And Mass Assembly (GAMA): The mechanisms for quiescent galaxy formation at z < 1

    Rowlands, K.; Wild, V.; Bourne, N.; Bremer, M.; Brough, S.; Driver, S. P.; Hopkins, A. M.; Owers, M. S.; Phillipps, S.; Pimbblet, K.; Sansom, A. E.; Wang, L.; Alpaslan, M.; Bland-Hawthorn, J.; Colless, M.; Holwerda, B. W.; Taylor, E. N.

    2018-01-01

    One key problem in astrophysics is understanding how and why galaxies switch off their star formation, building the quiescent population that we observe in the local Universe. From the Galaxy And Mass Assembly and VIsible MultiObject Spectrograph Public Extragalactic Redshift surveys, we use spectroscopic indices to select quiescent and candidate transition galaxies. We identify potentially rapidly transitioning post-starburst (PSB) galaxies and slower transitioning green-valley galaxies. Over the last 8 Gyr, the quiescent population has grown more slowly in number density at high masses ({M}_\\ast >10^{11}{M_{⊙}) than at intermediate masses ({M}_\\ast >10^{10.6}{M_{⊙}). There is evolution in both the PSB and green-valley stellar mass functions, consistent with higher mass galaxies quenching at earlier cosmic times. At intermediate masses ({M}_\\ast >10^{10.6}{M_{⊙}), we find a green-valley transition time-scale of 2.6 Gyr. Alternatively, at z ∼ 0.7, the entire growth rate could be explained by fast-quenching PSB galaxies, with a visibility time-scale of 0.5 Gyr. At lower redshift, the number density of PSBs is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth. The importance of the fast-quenching route may rapidly diminish at z 10^{11}{M_{⊙}), there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population. This could be resolved if not all high-mass PSB and green-valley galaxies are transitioning from star forming to quiescent, for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation, or if they fail to completely quench their star formation.

  3. Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

    Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

    2017-09-01

    We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

  4. Star formation and mass assembly in high redshift galaxies

    Santini, P.; Fontana, A.; Grazian, A.; Salimbeni, S.; Fiore, F.; Fontanot, F.; Boutsia, K.; Castellano, M.; Cristiani, S.; de Santis, C.; Gallozzi, S.; Giallongo, E.; Menci, N.; Nonino, M.; Paris, D.; Pentericci, L.; Vanzella, E.

    2009-09-01

    Aims: The goal of this work is to infer the star formation properties and the mass assembly process of high redshift (0.3 ≤ z MUSIC catalog, which has multiwavelength coverage from 0.3 to 24 μm and either spectroscopic or accurate photometric redshifts. We describe how the catalog has been extended by the addition of mid-IR fluxes derived from the MIPS 24 μm image. We compared two different estimators of the star formation rate (SFR hereafter). One is the total infrared emission derived from 24 μm, estimated using both synthetic and empirical IR templates. The other one is a multiwavelength fit to the full galaxy SED, which automatically accounts for dust reddening and age-star formation activity degeneracies. For both estimates, we computed the SFR density and the specific SFR. Results: We show that the two SFR indicators are roughly consistent, once the uncertainties involved are taken into account. However, they show a systematic trend, IR-based estimates exceeding the fit-based ones as the star formation rate increases. With this new catalog, we show that: a) at z>0.3, the star formation rate is correlated well with stellar mass, and this relationship seems to steepen with redshift if one relies on IR-based estimates of the SFR; b) the contribution to the global SFRD by massive galaxies increases with redshift up to ≃ 2.5, more rapidly than for galaxies of lower mass, but appears to flatten at higher z; c) despite this increase, the most important contributors to the SFRD at any z are galaxies of about, or immediately lower than, the characteristic stellar mass; d) at z≃ 2, massive galaxies are actively star-forming, with a median {SFR} ≃ 300 M_⊙ yr-1. During this epoch, our targeted galaxies assemble a substantial part of their final stellar mass; e) the specific SFR (SSFR) shows a clear bimodal distribution. Conclusions: The analysis of the SFR density and the SSFR seems to support the downsizing scenario, according to which high mass galaxies

  5. Rhapsody-G simulations I: the cool cores, hot gas and stellar content of massive galaxy clusters

    Hahn, Oliver; Martizzi, Davide; Wu, Hao-Yi

    2017-01-01

    We present the rhapsody-g suite of cosmological hydrodynamic zoom simulations of 10 massive galaxy clusters at the M vir ~10 15 M ⊙ scale. These simulations include cooling and subresolution models for star formation and stellar and supermassive black hole feedback. The sample is selected to capture the whole gamut of assembly histories that produce clusters of similar final mass. We present an overview of the successes and shortcomings of such simulations in reproducing both the stellar properties of galaxies as well as properties of the hot plasma in clusters. In our simulations, a long-lived cool-core/non-cool-core dichotomy arises naturally, and the emergence of non-cool cores is related to low angular momentum major mergers. Nevertheless, the cool-core clusters exhibit a low central entropy compared to observations, which cannot be alleviated by thermal active galactic nuclei feedback. For cluster scaling relations, we find that the simulations match well the M 500 –Y 500 scaling of Planck Sunyaev–Zeldovich clusters but deviate somewhat from the observed X-ray luminosity and temperature scaling relations in the sense of being slightly too bright and too cool at fixed mass, respectively. Stars are produced at an efficiency consistent with abundance-matching constraints and central galaxies have star formation rates consistent with recent observations. In conclusion, while our simulations thus match various key properties remarkably well, we conclude that the shortcomings strongly suggest an important role for non-thermal processes (through feedback or otherwise) or thermal conduction in shaping the intracluster medium.

  6. Spitzer mid-infrared spectra of cool-core galaxy clusters

    de Messières, G.E.; O'Connell, R.W.; McNamara, B.R.; Donahue, M.; Nulsen, P.E.J.; Voit, G.M.; Wise, M.W.; Smith, B.; Higdon, J.; Higdon, S.; Bastian, N.

    2010-01-01

    We have obtained mid-infrared spectra of nine cool-core galaxy clusters with the Infrared Spectrograph aboard the Spitzer Space Telescope. X-ray, ultraviolet and optical observations have demonstrated that each of these clusters hosts a cooling flow which seems to be fueling vigorous star formation

  7. A KiDS weak lensing analysis of assembly bias in GAMA galaxy groups

    Dvornik, Andrej; Cacciato, Marcello; Kuijken, Konrad; Viola, Massimo; Hoekstra, Henk; Nakajima, Reiko; van Uitert, Edo; Brouwer, Margot; Choi, Ami; Erben, Thomas; Fenech Conti, Ian; Farrow, Daniel J.; Herbonnet, Ricardo; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M.; McFarland, John; Norberg, Peder; Schneider, Peter; Sifón, Cristóbal; Valentijn, Edwin; Wang, Lingyu

    2017-07-01

    We investigate possible signatures of halo assembly bias for spectroscopically selected galaxy groups from the Galaxy And Mass Assembly (GAMA) survey using weak lensing measurements from the spatially overlapping regions of the deeper, high-imaging-quality photometric Kilo-Degree Survey. We use GAMA groups with an apparent richness larger than 4 to identify samples with comparable mean host halo masses but with a different radial distribution of satellite galaxies, which is a proxy for the formation time of the haloes. We measure the weak lensing signal for groups with a steeper than average and with a shallower than average satellite distribution and find no sign of halo assembly bias, with the bias ratio of 0.85^{+0.37}_{-0.25}, which is consistent with the Λ cold dark matter prediction. Our galaxy groups have typical masses of 1013 M⊙ h-1, naturally complementing previous studies of halo assembly bias on galaxy cluster scales.

  8. EVOLUTION OF THE GALAXY-DARK MATTER CONNECTION AND THE ASSEMBLY OF GALAXIES IN DARK MATTER HALOS

    Yang Xiaohu; Zhang Youcai; Han Jiaxin [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Nandan Road 80, Shanghai 200030 (China); Mo, H. J. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305 (United States); Van den Bosch, Frank C., E-mail: xhyang@shao.ac.cn [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06520-8101 (United States)

    2012-06-10

    We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z {approx} 4, the conditional SMF at z {approx} 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z {approx} 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z {approx} 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the {Lambda}CDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M{sup 0.3} and M{sup {approx}>4.0} at the massive and low-mass ends, respectively. The ratio M{sub *,c}/M reveals a maximum of {approx}0.03 at a halo mass M {approx} 10{sup 11.8} h{sup -1} M{sub Sun }, much lower than the universal baryon fraction ({approx}0.17). At higher redshifts the maximum in M{sub *,c}/M remains close to {approx}0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host

  9. The Properties of the Massive Star-forming Galaxies with an Outside-in Assembly Mode

    Wang, Enci; Kong, Xu; Wang, Huiyuan; Wang, Lixin; Lin, Lin; Gao, Yulong; Liu, Qing

    2017-08-01

    Previous findings show that massive ({M}* > {10}10 {M}⊙ ) star-forming (SF) galaxies usually have an “inside-out” stellar mass assembly mode. In this paper, we have for the first time selected a sample of 77 massive SF galaxies with an “outside-in” assembly mode (called the “targeted sample”) from the Mapping Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. For comparison, two control samples are constructed from the MaNGA sample matched in stellar mass: a sample of 154 normal SF galaxies and a sample of 62 quiescent galaxies. In contrast to normal SF galaxies, the targeted galaxies appear to be smoother and more bulge-dominated and have a smaller size and higher concentration, star formation rate, and gas-phase metallicity as a whole. However, they have a larger size and lower concentration than quiescent galaxies. Unlike the normal SF sample, the targeted sample exhibits a slightly positive gradient of the 4000 Å break and a pronounced negative gradient of Hα equivalent width. Furthermore, the median surface mass density profile is between those of the normal SF and quiescent samples, indicating that the gas accretion of quiescent galaxies is not likely to be the main approach for the outside-in assembly mode. Our results suggest that the targeted galaxies are likely in the transitional phase from normal SF galaxies to quiescent galaxies, with rapid ongoing central stellar mass assembly (or bulge growth). We discuss several possible formation mechanisms for the outside-in mass assembly mode.

  10. Elevation or Suppression? The Resolved Star Formation Main Sequence of Galaxies with Two Different Assembly Modes

    Liu, Qing; Wang, Enci; Lin, Zesen; Gao, Yulong; Liu, Haiyang; Berhane Teklu, Berzaf; Kong, Xu

    2018-04-01

    We investigate the spatially resolved star formation main sequence in star-forming galaxies using Integral Field Spectroscopic observations from the Mapping Nearby Galaxies at the Apache Point Observatory survey. We demonstrate that the correlation between the stellar mass surface density (Σ*) and star formation rate surface density (ΣSFR) holds down to the sub-galactic scale, leading to the sub-galactic main sequence (SGMS). By dividing galaxies into two populations based on their recent mass assembly modes, we find the resolved main sequence in galaxies with the “outside-in” mode is steeper than that in galaxies with the “inside-out” mode. This is also confirmed on a galaxy-by-galaxy level, where we find the distributions of SGMS slopes for individual galaxies are clearly separated for the two populations. When normalizing and stacking the SGMS of individual galaxies on one panel for the two populations, we find that the inner regions of galaxies with the “inside-out” mode statistically exhibit a suppression in star formation, with a less significant trend in the outer regions of galaxies with the “outside-in” mode. In contrast, the inner regions of galaxies with “outside-in” mode and the outer regions of galaxies with “inside-out” mode follow a slightly sublinear scaling relation with a slope ∼0.9, which is in good agreement with previous findings, suggesting that they are experiencing a universal regulation without influences of additional physical processes.

  11. Fuel assembly for gas-cooled nuclear reactors

    Yellowlees, J.M.

    1976-01-01

    A fuel assembly is described for gas-cooled nuclear reactor which consists of a wrapper tube within which are positioned a number of spaced apart beds in a stack, with each bed containing spherical coated particles of fuel; each of the beds has a perforated top and bottom plate; gaseous coolant passes successively through each of the beds; through each of the beds also passes a bypass tube; part of the gas travels through the bed and part passes through the bypass tube; the gas coolant which passes through both the bed and the bypass tube mixes in the space on the outlet side of the bed before entering the next bed

  12. ANISOTROPIC THERMAL CONDUCTION AND THE COOLING FLOW PROBLEM IN GALAXY CLUSTERS

    Parrish, Ian J.; Sharma, Prateek; Quataert, Eliot

    2009-01-01

    We examine the long-standing cooling flow problem in galaxy clusters with three-dimensional magnetohydrodynamics simulations of isolated clusters including radiative cooling and anisotropic thermal conduction along magnetic field lines. The central regions of the intracluster medium (ICM) can have cooling timescales of ∼200 Myr or shorter-in order to prevent a cooling catastrophe the ICM must be heated by some mechanism such as active galactic nucleus feedback or thermal conduction from the thermal reservoir at large radii. The cores of galaxy clusters are linearly unstable to the heat-flux-driven buoyancy instability (HBI), which significantly changes the thermodynamics of the cluster core. The HBI is a convective, buoyancy-driven instability that rearranges the magnetic field to be preferentially perpendicular to the temperature gradient. For a wide range of parameters, our simulations demonstrate that in the presence of the HBI, the effective radial thermal conductivity is reduced to ∼<10% of the full Spitzer conductivity. With this suppression of conductive heating, the cooling catastrophe occurs on a timescale comparable to the central cooling time of the cluster. Thermal conduction alone is thus unlikely to stabilize clusters with low central entropies and short central cooling timescales. High central entropy clusters have sufficiently long cooling times that conduction can help stave off the cooling catastrophe for cosmologically interesting timescales.

  13. Cool infalling gas and its interaction with the hot ISM of elliptical galaxies

    Sparks, W. B.; Macchetto, F. D.

    1990-01-01

    The authors describe work leading to the suggestion that interaction between infalling cool gas and ambient hot, coronal plasma in elliptical galaxies is responsible for emission filaments, and might remove the need for large mass depositions in cooling flows. A test of the hypothesis is undertaken - the run of surface brightness with radius for the emission lines - and the prediction agrees well with the data.

  14. Testing Numerical Models of Cool Core Galaxy Cluster Formation with X-Ray Observations

    Henning, Jason W.; Gantner, Brennan; Burns, Jack O.; Hallman, Eric J.

    2009-12-01

    Using archival Chandra and ROSAT data along with numerical simulations, we compare the properties of cool core and non-cool core galaxy clusters, paying particular attention to the region beyond the cluster cores. With the use of single and double β-models, we demonstrate a statistically significant difference in the slopes of observed cluster surface brightness profiles while the cluster cores remain indistinguishable between the two cluster types. Additionally, through the use of hardness ratio profiles, we find evidence suggesting cool core clusters are cooler beyond their cores than non-cool core clusters of comparable mass and temperature, both in observed and simulated clusters. The similarities between real and simulated clusters supports a model presented in earlier work by the authors describing differing merger histories between cool core and non-cool core clusters. Discrepancies between real and simulated clusters will inform upcoming numerical models and simulations as to new ways to incorporate feedback in these systems.

  15. The connection between galaxy formation and the assembly of stellar halos in the Local Group

    Helmi, Amina

    I will review our current understanding of the assembly of stellar halos from a theoretical perspective. I will place particular emphasis on how observations of Local Group galaxies can be used to constrain the assembly history of both their stellar and dark matter halos. Finally I will focus on

  16. THE GROWTH OF COOL CORES AND EVOLUTION OF COOLING PROPERTIES IN A SAMPLE OF 83 GALAXY CLUSTERS AT 0.3 < z < 1.2 SELECTED FROM THE SPT-SZ SURVEY

    McDonald, M.; Bautz, M. W. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T. [Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Vikhlinin, A.; Stalder, B.; Ashby, M. L. N.; Bayliss, M. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); De Haan, T. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Lin, H. W. [Caddo Parish Magnet High School, Shrevport, LA 71101 (United States); Aird, K. A. [University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Bocquet, S.; Desai, S. [Department of Physics, Ludwig-Maximilians-Universitaet, Scheinerstr. 1, D-81679 Muenchen (Germany); Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Cho, H. M. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305 (United States); Clocchiatti, A., E-mail: mcdonald@space.mit.edu [Departamento de Astronomia y Astrosifica, Pontificia Universidad Catolica (Chile); and others

    2013-09-01

    We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3 < z < 1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples. We find no significant evolution from z {approx} 0 to z {approx} 1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner {approx}100 kpc has not changed dramatically since z {approx} 1, implying that feedback must be providing nearly constant energy injection to maintain the observed ''entropy floor'' at {approx}10 keV cm{sup 2}. While the cooling properties appear roughly constant over long periods of time, we observe strong evolution in the gas density profile, with the normalized central density ({rho}{sub g,0}/{rho}{sub crit}) increasing by an order of magnitude from z {approx} 1 to z {approx} 0. When using metrics defined by the inner surface brightness profile of clusters, we find an apparent lack of classical, cuspy, cool-core clusters at z > 0.75, consistent with earlier reports for clusters at z > 0.5 using similar definitions. Our measurements indicate that cool cores have been steadily growing over the 8 Gyr spanned by our sample, consistent with a constant, {approx}150 M{sub Sun} yr{sup -1} cooling flow that is unable to cool below entropies of 10 keV cm{sup 2} and, instead, accumulates in the cluster center. We estimate that cool cores began to assemble in these massive systems at z{sub cool}=1.0{sup +1.0}{sub -0.2}, which represents the first constraints on the onset of cooling in galaxy cluster cores. At high redshift (z {approx}> 0.75), galaxy clusters may be classified as ''cooling flows

  17. The Impact of Assembly Bias on the Galaxy Content of Dark Matter Halos

    Zehavi, Idit; Contreras, Sergio; Padilla, Nelson; Smith, Nicholas J.; Baugh, Carlton M.; Norberg, Peder

    2018-01-01

    We study the dependence of the galaxy content of dark matter halos on large-scale environment and halo formation time using semi-analytic galaxy models applied to the Millennium simulation. We analyze subsamples of halos at the extremes of these distributions and measure the occupation functions for the galaxies they host. We find distinct differences among these occupation functions. The main effect with environment is that central galaxies (and in one model, also the satellites) in denser regions start populating lower-mass halos. A similar, but significantly stronger, trend exists with halo age, where early-forming halos are more likely to host central galaxies at lower halo mass. We discuss the origin of these trends and the connection to the stellar mass–halo mass relation. We find that, at fixed halo mass, older halos and to some extent also halos in dense environments tend to host more massive galaxies. Additionally, we see a reverse trend for the occupation of satellite galaxies where early-forming halos have fewer satellites, likely due to having more time for them to merge with the central galaxy. We describe these occupancy variations in terms of the changes in the occupation function parameters, which can aid in constructing realistic mock galaxy samples. Finally, we study the corresponding galaxy auto- and cross-correlation functions of the different samples and elucidate the impact of assembly bias on galaxy clustering. Our results can inform theoretical modeling of galaxy assembly bias and attempts to detect it in the real universe.

  18. THE XMM CLUSTER SURVEY: THE STELLAR MASS ASSEMBLY OF FOSSIL GALAXIES

    Harrison, Craig D.; Miller, Christopher J. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States); Richards, Joseph W.; Deadman, Paul-James [Center for Time Domain Informatics, University of California, Berkeley, CA 94720 (United States); Lloyd-Davies, E. J.; Kathy Romer, A.; Mehrtens, Nicola; Liddle, Andrew R. [Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom); Hoyle, Ben [Institute of Sciences of the Cosmos (ICCUB) and IEEC, Physics Department, University of Barcelona, Barcelona 08024 (Spain); Hilton, Matt [Astrophysics and Cosmology Research Unit, School of Mathematical Sciences, University of KwaZulu-Natal, Private Bag X54001, Durban 4000 (South Africa); Stott, John P.; Capozzi, Diego; Collins, Chris A. [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD (United Kingdom); Sahlen, Martin [Oskar Klein Centre for Cosmoparticle Physics, Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm (Sweden); Stanford, S. Adam [Physics Department, University of California, Davis, CA 95616 (United States); Viana, Pedro T. P., E-mail: craigha@umich.edu [Centro de Astrofisica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2012-06-10

    This paper presents both the result of a search for fossil systems (FSs) within the XMM Cluster Survey and the Sloan Digital Sky Survey and the results of a study of the stellar mass assembly and stellar populations of their fossil galaxies. In total, 17 groups and clusters are identified at z < 0.25 with large magnitude gaps between the first and fourth brightest galaxies. All the information necessary to classify these systems as fossils is provided. For both groups and clusters, the total and fractional luminosity of the brightest galaxy is positively correlated with the magnitude gap. The brightest galaxies in FSs (called fossil galaxies) have stellar populations and star formation histories which are similar to normal brightest cluster galaxies (BCGs). However, at fixed group/cluster mass, the stellar masses of the fossil galaxies are larger compared to normal BCGs, a fact that holds true over a wide range of group/cluster masses. Moreover, the fossil galaxies are found to contain a significant fraction of the total optical luminosity of the group/cluster within 0.5 R{sub 200}, as much as 85%, compared to the non-fossils, which can have as little as 10%. Our results suggest that FSs formed early and in the highest density regions of the universe and that fossil galaxies represent the end products of galaxy mergers in groups and clusters.

  19. The cosmic baryon cycle and galaxy mass assembly in the FIRE simulations

    Anglés-Alcázar, Daniel; Faucher-Giguère, Claude-André; Kereš, Dušan; Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

    2017-10-01

    We use cosmological simulations from the FIRE (Feedback In Realistic Environments) project to study the baryon cycle and galaxy mass assembly for central galaxies in the halo mass range Mhalo ˜ 1010-1013 M⊙. By tracing cosmic inflows, galactic outflows, gas recycling and merger histories, we quantify the contribution of physically distinct sources of material to galaxy growth. We show that in situ star formation fuelled by fresh accretion dominates the early growth of galaxies of all masses, while the re-accretion of gas previously ejected in galactic winds often dominates the gas supply for a large portion of every galaxy's evolution. Externally processed material contributes increasingly to the growth of central galaxies at lower redshifts. This includes stars formed ex situ and gas delivered by mergers, as well as smooth intergalactic transfer of gas from other galaxies, an important but previously underappreciated growth mode. By z = 0, wind transfer, I.e. the exchange of gas between galaxies via winds, can dominate gas accretion on to ˜L* galaxies over fresh accretion and standard wind recycling. Galaxies of all masses re-accrete ≳50 per cent of the gas ejected in winds and recurrent recycling is common. The total mass deposited in the intergalactic medium per unit stellar mass formed increases in lower mass galaxies. Re-accretion of wind ejecta occurs over a broad range of time-scales, with median recycling times (˜100-350 Myr) shorter than previously found. Wind recycling typically occurs at the scale radius of the halo, independent of halo mass and redshift, suggesting a characteristic recycling zone around galaxies that scales with the size of the inner halo and the galaxy's stellar component.

  20. CHANDRA OBSERVATION OF ABELL 1142: A COOL-CORE CLUSTER LACKING A CENTRAL BRIGHTEST CLUSTER GALAXY?

    Su, Yuanyuan; Weeren, Reinout van [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Buote, David A. [Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); Gastaldello, Fabio, E-mail: yuanyuan.su@cfa.harvard.edu [INAF-IASF-Milano, Via E. Bassini 15, I-20133 Milano (Italy)

    2016-04-10

    Abell 1142 is a low-mass galaxy cluster at low redshift containing two comparable brightest cluster galaxies (BCGs) resembling a scaled-down version of the Coma Cluster. Our Chandra analysis reveals an X-ray emission peak, roughly 100 kpc away from either BCG, which we identify as the cluster center. The emission center manifests itself as a second beta-model surface brightness component distinct from that of the cluster on larger scales. The center is also substantially cooler and more metal-rich than the surrounding intracluster medium (ICM), which makes Abell 1142 appear to be a cool-core cluster. The redshift distribution of its member galaxies indicates that Abell 1142 may contain two subclusters, each of which contain one BCG. The BCGs are merging at a relative velocity of ≈1200 km s{sup −1}. This ongoing merger may have shock-heated the ICM from ≈2 keV to above 3 keV, which would explain the anomalous L{sub X}–T{sub X} scaling relation for this system. This merger may have displaced the metal-enriched “cool core” of either of the subclusters from the BCG. The southern BCG consists of three individual galaxies residing within a radius of 5 kpc in projection. These galaxies should rapidly sink into the subcluster center due to the dynamical friction of a cuspy cold dark matter halo.

  1. The Eating Habits of Giants and Dwarfs: Chemo-dynamics of Halo Assembly in Nearby Galaxies

    Romanowsky, Aaron J.; SAGES Team

    2012-01-01

    I will present novel results on the halo assembly of nearby galaxies, from dwarfs to the most massive ellipticals, using Subaru imaging and Keck spectroscopy. Field stars, globular clusters, and planetary nebulae are used as wide-field chemo-dynamical tracers, mapping out halo substructures that were previously known and unknown. Comparisons are made with simulations of galaxy formation. Supported by the National Science Foundation Grants AST-0808099, AST-0909237, and AST-1109878.

  2. THE METALLICITY BIMODALITY OF GLOBULAR CLUSTER SYSTEMS: A TEST OF GALAXY ASSEMBLY AND OF THE EVOLUTION OF THE GALAXY MASS-METALLICITY RELATION

    Tonini, Chiara

    2013-01-01

    We build a theoretical model to study the origin of the globular cluster metallicity bimodality in the hierarchical galaxy assembly scenario. The model is based on empirical relations such as the galaxy mass-metallicity relation [O/H]-M star as a function of redshift, and on the observed galaxy stellar mass function up to redshift z ∼ 4. We make use of the theoretical merger rates as a function of mass and redshift from the Millennium simulation to build galaxy merger trees. We derive a new galaxy [Fe/H]-M star relation as a function of redshift, and by assuming that globular clusters share the metallicity of their original parent galaxy at the time of their formation, we populate the merger tree with globular clusters. We perform a series of Monte Carlo simulations of the galaxy hierarchical assembly, and study the properties of the final globular cluster population as a function of galaxy mass, assembly and star formation history, and under different assumptions for the evolution of the galaxy mass-metallicity relation. The main results and predictions of the model are the following. (1) The hierarchical clustering scenario naturally predicts a metallicity bimodality in the galaxy globular cluster population, where the metal-rich subpopulation is composed of globular clusters formed in the galaxy main progenitor around redshift z ∼ 2, and the metal-poor subpopulation is composed of clusters accreted from satellites, and formed at redshifts z ∼ 3-4. (2) The model reproduces the observed relations by Peng et al. for the metallicities of the metal-rich and metal-poor globular cluster subpopulations as a function of galaxy mass; the positions of the metal-poor and metal-rich peaks depend exclusively on the evolution of the galaxy mass-metallicity relation and the [O/Fe], both of which can be constrained by this method. In particular, we find that the galaxy [O/Fe] evolves linearly with redshift from a value of ∼0.5 at redshift z ∼ 4 to a value of ∼0.1 at

  3. Comparison of fuel assemblies in lead cooled fast reactors

    Perez, A.; Sanchez, H.; Aguilar, L.; Espinosa P, G., E-mail: alejandria.peval@gmail.com [Universidad Autonoma Metropolitana, Unidad Iztapalapa, San Rafael Atlixco No. 186, Col. Vicentina, 09340 Ciudad de Mexico (Mexico)

    2016-09-15

    This paper presents a comparison of the thermal-fluid processes in the core, fuel heat transfer, and thermal power between two fuel assemblies: square and hexagonal, in a lead-cooled fast reactor (Lfr). A multi-physics reduced order model for the analysis of Lfr single channel is developed in this work. The work focused on a coupling between process of neutron kinetic, fuel heat transfer process and thermal-fluid, in a single channel. The thermal power is obtained from neutron point kinetics model, considering a non-uniform power distribution. The analysis of the processes of thermal-fluid considers thermal expansion effects. The transient heat transfer in fuel is carried out in an annular geometry, and one-dimensional in radial direction for each axial node. The results presented in comparing these assemblies consider the temperature field in the fuel, in the thermal fluid and under steady state, and transient conditions. Transients consider flow of coolant and inlet temperature of coolant. The mathematical model of Lfr considers three main modules: the heat transfer in the annular fuel, the power generation with feedback effects on neutronic, and the thermal-fluid in the single channel. The modeling of nuclear reactors in general, the coupling is crucial by the feedback between the neutron processes with fuel heat transfer, and thermo-fluid, where is very common the numerical instabilities, after all it has to refine the model to achieve the design data. In this work is considered as a reference the ELSY reactor for the heat transfer analysis in the fuel and pure lead properties for analyzing the thermal-fluid. The results found shows that the hexagonal array has highest temperature in the fuel, respect to square array. (Author)

  4. Comparison of fuel assemblies in lead cooled fast reactors

    Perez, A.; Sanchez, H.; Aguilar, L.; Espinosa P, G.

    2016-09-01

    This paper presents a comparison of the thermal-fluid processes in the core, fuel heat transfer, and thermal power between two fuel assemblies: square and hexagonal, in a lead-cooled fast reactor (Lfr). A multi-physics reduced order model for the analysis of Lfr single channel is developed in this work. The work focused on a coupling between process of neutron kinetic, fuel heat transfer process and thermal-fluid, in a single channel. The thermal power is obtained from neutron point kinetics model, considering a non-uniform power distribution. The analysis of the processes of thermal-fluid considers thermal expansion effects. The transient heat transfer in fuel is carried out in an annular geometry, and one-dimensional in radial direction for each axial node. The results presented in comparing these assemblies consider the temperature field in the fuel, in the thermal fluid and under steady state, and transient conditions. Transients consider flow of coolant and inlet temperature of coolant. The mathematical model of Lfr considers three main modules: the heat transfer in the annular fuel, the power generation with feedback effects on neutronic, and the thermal-fluid in the single channel. The modeling of nuclear reactors in general, the coupling is crucial by the feedback between the neutron processes with fuel heat transfer, and thermo-fluid, where is very common the numerical instabilities, after all it has to refine the model to achieve the design data. In this work is considered as a reference the ELSY reactor for the heat transfer analysis in the fuel and pure lead properties for analyzing the thermal-fluid. The results found shows that the hexagonal array has highest temperature in the fuel, respect to square array. (Author)

  5. Limits on turbulent propagation of energy in cool-core clusters of galaxies

    Bambic, C. J.; Pinto, C.; Fabian, A. C.; Sanders, J.; Reynolds, C. S.

    2018-07-01

    We place constraints on the propagation velocity of bulk turbulence within the intracluster medium of three clusters and an elliptical galaxy. Using Reflection Grating Spectrometer measurements of turbulent line broadening, we show that for these clusters, the 90 per cent upper limit on turbulent velocities when accounting for instrumental broadening is too low to propagate energy radially to the cooling radius of the clusters within the required cooling time. In this way, we extend previous Hitomi-based analysis on the Perseus cluster to more clusters, with the intention of applying these results to a future, more extensive catalogue. These results constrain models of turbulent heating in active galactic nucleus feedback by requiring a mechanism which can not only provide sufficient energy to offset radiative cooling but also resupply that energy rapidly enough to balance cooling at each cluster radius.

  6. Cool carbon stars in the halo and in dwarf galaxies: Hα, colours, and variability

    Mauron, N.; Gigoyan, K. S.; Berlioz-Arthaud, P.; Klotz, A.

    2014-02-01

    The population of cool carbon (C) stars located far from the galactic plane is probably made of debris of small galaxies such as the Sagittarius dwarf spheroidal galaxy (Sgr), which are disrupted by the gravitational field of the Galaxy. We aim to know this population better through spectroscopy, 2MASS photometric colours, and variability data. When possible, we compared the halo results to C star populations in the Fornax dwarf spheroidal galaxy, Sgr, and the solar neighbourhood. We first present a few new discoveries of C stars in the halo and in Fornax. The number of spectra of halo C stars is now 125. Forty percent show Hα in emission. The narrow location in the JHK diagram of the halo C stars is found to differ from that of similar C stars in the above galaxies. The light curves of the Catalina and LINEAR variability databases were exploited to derive the pulsation periods of 66 halo C stars. A few supplementary periods were obtained with the TAROT telescopes. We confirm that the period distribution of the halo strongly resembles that of Fornax, and we found that it is very different from the C stars in the solar neighbourhood. There is a larger proportion of short-period Mira/SRa variables in the halo than in Sgr, but the survey for C stars in this dwarf galaxy is not complete, and the study of their variability needs to be continued to investigate the link between Sgr and the cool halo C stars. Based on observations made with the NTT and 3.6 m telescope at the European Southern Observatory (La Silla, Chile; programs 084.D-0302 and 070.D-0203), with the TAROT telescopes at La Silla and at Observatoire de la Côte d'Azur (France), and on the exploitation of the Catalina Sky Survey and the LINEAR variability databases.Appendix A is available in electronic form at http://www.aanda.org

  7. Understanding the unique assembly history of central group galaxies

    Vulcani, Benedetta; Bundy, Kevin; Lackner, Claire; Leauthaud, Alexie; Treu, Tommaso; Mei, Simona; Coccato, Lodovico; Kneib, Jean Paul; Auger, Matthew; Nipoti, Carlo

    2014-01-01

    Central galaxies (CGs) in massive halos live in unique environments with formation histories closely linked to that of the host halo. In local clusters, they have larger sizes (R e ) and lower velocity dispersions (σ) at fixed stellar mass M * , and much larger R e at a fixed σ than field and satellite galaxies (non-CGs). Using spectroscopic observations of group galaxies selected from the COSMOS survey, we compare the dynamical scaling relations of early-type CGs and non-CGs at z ∼ 0.6 to distinguish possible mechanisms that produce the required evolution. CGs are systematically offset toward larger R e at fixed σ compared to non-CGs with similar M * . The CG R e -M * relation also shows differences, primarily driven by a subpopulation (∼15%) of galaxies with large R e , while the M * -σ relations are indistinguishable. These results are accentuated when double Sérsic profiles, which better fit light in the outer regions of galaxies, are adopted. They suggest that even group-scale CGs can develop extended components by these redshifts that can increase total R e and M * estimates by factors of ∼2. To probe the evolutionary link between our sample and cluster CGs, we also analyze two cluster samples at z ∼ 0.6 and z ∼ 0. We find similar results for the more massive halos at comparable z, but much more distinct CG scaling relations at low-z. Thus, the rapid, late-time accretion of outer components, perhaps via the stripping and accretion of satellites, would appear to be a key feature that distinguishes the evolutionary history of CGs.

  8. Galaxy And Mass Assembly (GAMA): deconstructing bimodality - I. Red ones and blue ones

    Taylor, Edward N.; Hopkins, Andrew M.; Baldry, Ivan K.; Bland-Hawthorn, Joss; Brown, Michael J. I.; Colless, Matthew; Driver, Simon; Norberg, Peder; Robotham, Aaron S. G.; Alpaslan, Mehmet; Brough, Sarah; Cluver, Michelle E.; Gunawardhana, Madusha; Kelvin, Lee S.; Liske, Jochen; Conselice, Christopher J.; Croom, Scott; Foster, Caroline; Jarrett, Thomas H.; Lara-Lopez, Maritza; Loveday, Jon

    2015-01-01

    We measure the mass functions for generically red and blue galaxies, using a z 8.7 field galaxies from the Galaxy And Mass Assembly (GAMA) survey. Our motivation is that, as we show, the dominant uncertainty in existing measurements stems from how `red' and `blue' galaxies have been selected/defined. Accordingly, we model our data as two naturally overlapping populations, each with their own mass function and colour-mass relation, which enables us characterize the two populations without having to specify a priori which galaxies are `red' and `blue'. Our results then provide the means to derive objective operational definitions for the terms `red' and `blue', which are based on the phenomenology of the colour-mass diagrams. Informed by this descriptive modelling, we show that (1) after accounting for dust, the stellar colours of `blue' galaxies do not depend strongly on mass; (2) the tight, flat `dead sequence' does not extend much below log M* ˜ 10.5; instead, (3) the stellar colours of `red' galaxies vary rather strongly with mass, such that lower mass `red' galaxies have bluer stellar populations; (4) below log M* ˜ 9.3, the `red' population dissolves into obscurity, and it becomes problematic to talk about two distinct populations; as a consequence, (5) it is hard to meaningfully constrain the shape, including the existence of an upturn, of the `red' galaxy mass function below log M* ˜ 9.3. Points 1-4 provide meaningful targets for models of galaxy formation and evolution to aim for.

  9. Improvements in or relating to cooling systems for nuclear fuel assemblies

    Ljubivy, A.G.; Batjukov, V.I.; Shkhian, T.G.; Fadeev, A.I.

    1980-01-01

    A cooling system is proposed which can be used to cool a set of nuclear fuel assemblies arranged in a reactor core or placed in a container for spent fuel assemblies. The object of the invention is to provide a system which would prevent leakage of coolant from the vessel in the event of a rupture of the coolant supply pipeline externally of the vessel. In the case of the reactor cooling system the level of the coolant is stopped from dropping below the level of the active portion of the fuel assemblies and thus prevents a breakdown of the reactor. (UK)

  10. CAUGHT IN THE ACT: THE ASSEMBLY OF MASSIVE CLUSTER GALAXIES AT z = 1.62

    Lotz, Jennifer M.; Ferguson, Henry C.; Grogin, Norman; Koekemoer, Anton M.; Papovich, Casey; Tran, Kim-Vy; Faber, S. M.; Guo Yicheng; Kocevski, Dale; Lee, Kyoung-Soo; McIntosh, Daniel; Momcheva, Ivelina; Rudnick, Gregory; Saintonge, Amelie; Van der Wel, Arjen; Willmer, Christopher

    2013-01-01

    We present the recent merger history of massive galaxies in a spectroscopically confirmed proto-cluster at z = 1.62. Using Hubble Space Telescope WFC3 near-infrared imaging from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we select cluster and z ∼ 1.6 field galaxies with M star ≥ 3 × 10 10 M ☉ , to determine the frequency of double nuclei or close companions within projected separations less than 20 kpc co-moving. We find that four out of five spectroscopically confirmed massive proto-cluster galaxies have double nuclei, and 57 +13 -14 % of all M star ≥ 3 × 10 10 M ☉ cluster candidates are observed in either close pair systems or have double nuclei. In contrast, only 11% ± 3% of the field galaxies are observed in close pair/double nuclei systems. After correcting for the contribution from random projections, the implied merger rate per massive galaxy in the proto-cluster is ∼3-10 times higher than the merger rate of massive field galaxies at z ∼ 1.6. Close pairs in the cluster have minor merger stellar mass ratios (M primary : M satellite ≥ 4), while the field pairs consist of both major and minor mergers. At least half of the cluster mergers are gas-poor, as indicated by their red colors and low 24 μm fluxes. Two of the double-nucleated cluster members have X-ray detected active galactic nuclei with L x > 10 43 erg s –1 , and are strong candidates for dual or offset super-massive black holes. We conclude that the massive z = 1.62 proto-cluster galaxies are undergoing accelerated assembly via minor mergers, and discuss the implications for galaxy evolution in proto-cluster environments

  11. Galaxy And Mass Assembly: automatic morphological classification of galaxies using statistical learning

    Sreejith, Sreevarsha; Pereverzyev, Sergiy, Jr.; Kelvin, Lee S.; Marleau, Francine R.; Haltmeier, Markus; Ebner, Judith; Bland-Hawthorn, Joss; Driver, Simon P.; Graham, Alister W.; Holwerda, Benne W.; Hopkins, Andrew M.; Liske, Jochen; Loveday, Jon; Moffett, Amanda J.; Pimbblet, Kevin A.; Taylor, Edward N.; Wang, Lingyu; Wright, Angus H.

    2018-03-01

    We apply four statistical learning methods to a sample of 7941 galaxies (z test the feasibility of using automated algorithms to classify galaxies. Using 10 features measured for each galaxy (sizes, colours, shape parameters, and stellar mass), we apply the techniques of Support Vector Machines, Classification Trees, Classification Trees with Random Forest (CTRF) and Neural Networks, and returning True Prediction Ratios (TPRs) of 75.8 per cent, 69.0 per cent, 76.2 per cent, and 76.0 per cent, respectively. Those occasions whereby all four algorithms agree with each other yet disagree with the visual classification (`unanimous disagreement') serves as a potential indicator of human error in classification, occurring in ˜ 9 per cent of ellipticals, ˜ 9 per cent of little blue spheroids, ˜ 14 per cent of early-type spirals, ˜ 21 per cent of intermediate-type spirals, and ˜ 4 per cent of late-type spirals and irregulars. We observe that the choice of parameters rather than that of algorithms is more crucial in determining classification accuracy. Due to its simplicity in formulation and implementation, we recommend the CTRF algorithm for classifying future galaxy data sets. Adopting the CTRF algorithm, the TPRs of the five galaxy types are : E, 70.1 per cent; LBS, 75.6 per cent; S0-Sa, 63.6 per cent; Sab-Scd, 56.4 per cent, and Sd-Irr, 88.9 per cent. Further, we train a binary classifier using this CTRF algorithm that divides galaxies into spheroid-dominated (E, LBS, and S0-Sa) and disc-dominated (Sab-Scd and Sd-Irr), achieving an overall accuracy of 89.8 per cent. This translates into an accuracy of 84.9 per cent for spheroid-dominated systems and 92.5 per cent for disc-dominated systems.

  12. Galaxy and Mass Assembly (GAMA): Variation in Galaxy Structure Across the Green Valley

    Kelvin, Lee S.; Bremer, Malcolm N.; Phillipps, Steven; James, Philip A.; Davies, Luke J. M.; De Propris, Roberto; Moffett, Amanda J.; Percival, Susan M.; Baldry, Ivan K.; Collins, Chris A.; Alpaslan, Mehmet; Bland-Hawthorn, Joss; Brough, Sarah; Cluver, Michelle; Driver, Simon P.; Hashemizadeh, Abdolhosein; Holwerda, Benne W.; Laine, Jarkko; Lara-Lopez, Maritza A.; Liske, Jochen; Maciejewski, Witold; Napolitano, Nicola R.; Penny, Samantha J.; Popescu, Cristina C.; Sansom, Anne E.; Sutherland, Will; Taylor, Edward N.; van Kampen, Eelco; Wang, Lingyu

    2018-04-01

    Using a sample of 472 local Universe (z rules out violent transformative events as the primary end-of-life evolutionary mechanism, with a more passive scenario the favoured candidate for the majority of galaxies rapidly transitioning across the green valley.

  13. Galaxy And Mass Assembly (GAMA): the effect of galaxy group environment on active galactic nuclei

    Gordon, Yjan A.; Pimbblet, Kevin A.; Owers, Matt S.; Bland-Hawthorn, Joss; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Croom, Scott M.; Holwerda, Benne W.; Loveday, Jonathan; Mahajan, Smriti; Wang, Lingyu

    2018-04-01

    In galaxy clusters, efficiently accreting active galactic nuclei (AGNs) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialized, cluster core. Exploiting the depth and completeness (98 per cent at r 9.9 in 695 groups with 11.53 ≤ log10(M200/M⊙) ≤ 14.56 at z 13.5, AGNs are preferentially found in the infalling galaxy population with 3.6σ confidence. At lower halo masses, we observe no difference in AGN fraction between core and infalling galaxies. These observations support a model where a reduced number of low-speed interactions, ram pressure stripping and intra-group/cluster medium temperature, the dominance of which increase with halo mass, work to inhibit AGN in the cores of groups and clusters with log10(M200/M⊙) > 13.5, but do not significantly affect nuclear activity in cores of less massive structures.

  14. Galaxy And Mass Assembly (GAMA): Gas Fueling of Spiral Galaxies in the Local Universe. I. The Effect of the Group Environment on Star Formation in Spiral Galaxies

    Grootes, M. W.; Tuffs, R. J.; Popescu, C. C.; Norberg, P.; Robotham, A. S. G.; Liske, J.; Andrae, E.; Baldry, I. K.; Gunawardhana, M.; Kelvin, L. S.; Madore, B. F.; Seibert, M.; Taylor, E. N.; Alpaslan, M.; Brown, M. J. I.; Cluver, M. E.; Driver, S. P.; Bland-Hawthorn, J.; Holwerda, B. W.; Hopkins, A. M.; Lopez-Sanchez, A. R.; Loveday, J.; Rushton, M.

    2017-03-01

    -density relation of the galaxy population as a whole would appear to be primarily due to a change in the mix of disk- and spheroid-dominated morphologies in the denser group environment compared to the field, rather than to a reduced propensity of the IHM in higher-mass structures to cool and accrete onto galaxies. We also suggest that the required substantial accretion of IHM gas by satellite disk-dominated galaxies will lead to a progressive reduction in the specific angular momentum of these systems, thereby representing an efficient secular mechanism to transform morphology from star-forming disk-dominated types to more passive spheroid-dominated types.

  15. Galaxies

    1981-01-01

    Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented

  16. NOT DEAD YET: COOL CIRCUMGALACTIC GAS IN THE HALOS OF EARLY-TYPE GALAXIES

    Thom, Christopher; Tumlinson, Jason; Sembach, Kenneth R.; Werk, Jessica K.; Xavier Prochaska, J.; Oppenheimer, Benjamin D.; Peeples, Molly S.; Tripp, Todd M.; Katz, Neal S.; O'Meara, John M.; Ford, Amanda Brady; Davé, Romeel; Weinberg, David H.

    2012-01-01

    We report new observations of circumgalactic gas in the halos of early-type galaxies (ETGs) obtained by the COS-Halos Survey with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We find that detections of H I surrounding ETGs are typically as common and strong as around star-forming galaxies, implying that the total mass of circumgalactic material is comparable in the two populations. For ETGs, the covering fraction for H I absorption above 10 16 cm –2 is ∼40%-50% within ∼150 kpc. Line widths and kinematics of the detected material show it to be cold (T ∼ 5 K) in comparison to the virial temperature of the host halos. The implied masses of cool, photoionized circumgalactic medium baryons may be up to 10 9 -10 11 M ☉ . Contrary to some theoretical expectations, strong halo H I absorbers do not disappear as part of the quenching of star formation. Even passive galaxies retain significant reservoirs of halo baryons that could replenish the interstellar gas reservoir and eventually form stars. This halo gas may feed the diffuse and molecular gas that is frequently observed inside ETGs.

  17. Timing the formation and assembly of early-type galaxies via spatially resolved stellar populations analysis

    Martín-Navarro, Ignacio; Vazdekis, Alexandre; Falcón-Barroso, Jesús; La Barbera, Francesco; Yıldırım, Akın; van de Ven, Glenn

    2018-04-01

    To investigate star formation and assembly processes of massive galaxies, we present here a spatially resolved stellar population analysis of a sample of 45 elliptical galaxies (Es) selected from the Calar Alto Legacy Integral Field Area survey. We find rather flat age and [Mg/Fe] radial gradients, weakly dependent on the effective velocity dispersion of the galaxy within half-light radius. However, our analysis shows that metallicity gradients become steeper with increasing galaxy velocity dispersion. In addition, we have homogeneously compared the stellar population gradients of our sample of Es to a sample of nearby relic galaxies, i.e. local remnants of the high-z population of red nuggets. This comparison indicates that, first, the cores of present-day massive galaxies were likely formed in gas-rich, rapid star formation events at high redshift (z ≳ 2). This led to radial metallicity variations steeper than observed in the local Universe, and positive [Mg/Fe] gradients. Secondly, our analysis also suggests that a later sequence of minor dry mergers, populating the outskirts of early-type galaxies (ETGs), flattened the pristine [Mg/Fe] and metallicity gradients. Finally, we find a tight age-[Mg/Fe] relation, supporting that the duration of the star formation is the main driver of the [Mg/Fe] enhancement in massive ETGs. However, the star formation time-scale alone is not able to fully explain our [Mg/Fe] measurements. Interestingly, our results match the expected effect that a variable stellar initial mass function would have on the [Mg/Fe] ratio.

  18. Gas-Rich Mergers in LCDM: Disk Survivability and the Baryonic Assembly of Galaxies

    Stewart, K.

    2009-01-01

    We use N-body simulations and observationally-normalized relations between dark matter halo mass, stellar mass, and cold gas mass to derive robust expectations about the baryonic content of major mergers out to redshift z ∼ 2. First, we find that the majority of major mergers (m/M > 0.3) experienced by Milky Way size dark matter halos should have been gas-rich, and that gas-rich mergers are increasingly common at high redshift. Though the frequency of major mergers into galaxy halos in our simulations greatly exceeds the observed late-type galaxy fraction, the frequency of gas-poor major mergers is consistent with the observed fraction of bulge-dominated galaxies across the halo mass range M DM ∼ 10 11 - 10 13 M · . These results lend support to the conjecture that mergers with high baryonic gas fractions play an important role in building and/or preserving disk galaxies in the universe. Secondly, we find that there is a transition mass below which a galaxy's past major mergers were primarily gas-rich and above which they were gas poor. The associated stellar mass scale corresponds closely to that marking the observed bimodal division between blue, star-forming, disk-dominated systems and red, bulge-dominated systems with old populations. Finally, we find that the overall fraction of a galaxy's cold baryons deposited directly via major mergers is substantial. Approximately 30% of the cold baryonic material in M star ∼ 10 10 M · (M DM ∼ 10 11.5 M · ) galaxies is accreted as cold gas in major mergers. For more massive galaxies with M star ∼ 10 11 M · (M DM ∼ 10 13 M · the fraction of baryons amassed in mergers is even higher, ∼ 50%, but most of these accreted baryons are delivered directly in the form of stars. This baryonic mass deposition is almost unavoidable, and provides a limit on the fraction of a galaxy's cold baryons that can originate in cold flows or from hot halo cooling

  19. Gas-Rich Mergers in LCDM: Disk Survivability and the Baryonic Assembly of Galaxies

    Stewart, Kyle R.; Bullock, James S.; /UC, Irvine; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC; Maller, Ariyeh H.; /New York City Coll. Tech.

    2009-08-03

    limit on the fraction of a galaxy's cold baryons that can originate in cold flows or from hot halo cooling.

  20. Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling, and star formation in dwarf galaxies at high redshift

    Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2018-06-01

    We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling, and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose three modifications to SAMs that will provide more accurate high-redshift simulations. These include (1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; (2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and (3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

  1. Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshift

    Qin, Yuxiang; Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2018-03-01

    We study dwarf galaxy formation at high redshift (z ≥ 5) using a suite of high-resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose 3 modifications to SAMs that will provide more accurate high-redshift simulations. These include 1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; 2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and 3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.

  2. THE RELATION BETWEEN COOL CLUSTER CORES AND HERSCHEL-DETECTED STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES

    Rawle, T. D.; Egami, E.; Rex, M.; Fiedler, A.; Haines, C. P.; Pereira, M. J.; Portouw, J.; Walth, G. [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Edge, A. C. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Smith, G. P. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Altieri, B.; Valtchanov, I. [Herschel Science Centre, ESAC, ESA, P.O. Box 78, Villanueva de la Canada, 28691 Madrid (Spain); Perez-Gonzalez, P. G. [Departamento de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Van der Werf, P. P. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA, Leiden (Netherlands); Zemcov, M., E-mail: trawle@as.arizona.edu [Department of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2012-03-01

    We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500 {mu}m), we calculate the obscured star formation rate (SFR). 22{sup +6.2}{sub -5.3}% of the BCGs are detected in the far-infrared, with SFR = 1-150 M{sub Sun} yr{sup -1}. The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing H{alpha} emission is also correlated with obscured star formation. For all but the most luminous BCGs (L{sub TIR} > 2 Multiplication-Sign 10{sup 11} L{sub Sun }), only a small ({approx}<0.4 mag) reddening correction is required for SFR(H{alpha}) to agree with SFR{sub FIR}. The relatively low H{alpha} extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.

  3. The Role of Cerenkov Radiation in the Pressure Balance of Cool Core Clusters of Galaxies

    Lieu, Richard [Department of Physics, University of Alabama, Huntsville, AL 35899 (United States)

    2017-03-20

    Despite the substantial progress made recently in understanding the role of AGN feedback and associated non-thermal effects, the precise mechanism that prevents the core of some clusters of galaxies from collapsing catastrophically by radiative cooling remains unidentified. In this Letter, we demonstrate that the evolution of a cluster's cooling core, in terms of its density, temperature, and magnetic field strength, inevitably enables the plasma electrons there to quickly become Cerenkov loss dominated, with emission at the radio frequency of ≲350 Hz, and with a rate considerably exceeding free–free continuum and line emission. However, the same does not apply to the plasmas at the cluster's outskirts, which lacks such radiation. Owing to its low frequency, the radiation cannot escape, but because over the relevant scale size of a Cerenkov wavelength the energy of an electron in the gas cannot follow the Boltzmann distribution to the requisite precision to ensure reabsorption always occurs faster than stimulated emission, the emitting gas cools before it reheats. This leaves behind the radiation itself, trapped by the overlying reflective plasma, yet providing enough pressure to maintain quasi-hydrostatic equilibrium. The mass condensation then happens by Rayleigh–Taylor instability, at a rate determined by the outermost radius where Cerenkov radiation can occur. In this way, it is possible to estimate the rate at ≈2 M {sub ⊙} year{sup −1}, consistent with observational inference. Thus, the process appears to provide a natural solution to the longstanding problem of “cooling flow” in clusters; at least it offers another line of defense against cooling and collapse should gas heating by AGN feedback be inadequate in some clusters.

  4. An improved water cooled nuclear reactor and pressuriser assembly

    Gardner, F.J.; Strong, R.

    1991-01-01

    A water cooled nuclear reactor is described which comprises a reactor core, a primary water coolant circuit and a pressuriser arranged as an integral unit in a pressure vessel. The pressure vessel is divided into an upper and a lower chamber by a casing. The reactor core and primary water coolant circuit are arranged in the lower chamber and the pressuriser is arranged in the upper chamber. A plurality of spray pipes interconnect a steam space of the pressuriser with the downcomer of the primary water coolant circuit below a heat exchanger. A plurality of surge ports interconnect a water space of the pressuriser with the primary water coolant circuit. The surge ports have hydraulic diodes so that there is a low flow resistance for water from the water space of the pressuriser to the primary water coolant circuit and high flow resistance in the opposite direction. The spray pipes provide a desuperheating spray of cooled water into the pressuriser during positive volume surges of the primary water coolant. The pressuriser arrangement may also be applied to integral water cooled reactors with separate pressurisers and to dispersed pressurised water reactors. The surge ports also allow water to flow by gravity to the core in an emergency. (author)

  5. Fuel assembly for light-water cooled nuclear reactors

    Leroux, J.C.; Burfin, P.

    1995-01-01

    In order to make easier the replacement of damaged fuel rods, a fuel assembly has been designed with a cluster of parallel fuel rods maintained in guide tubes with braces and sockets fixed on each tube ends; at least one of the fixing sockets of each tube is dismountable as well as an adapter plate on the socket, in order to lock or un-lock the guide tubes from the sockets. 11 fig

  6. Globular cluster formation and evolution in the context of cosmological galaxy assembly: open questions

    Forbes, Duncan A.; Bastian, Nate; Gieles, Mark; Crain, Robert A.; Kruijssen, J. M. Diederik; Larsen, Søren S.; Ploeckinger, Sylvia; Agertz, Oscar; Trenti, Michele; Ferguson, Annette M. N.; Pfeffer, Joel; Gnedin, Oleg Y.

    2018-02-01

    We discuss some of the key open questions regarding the formation and evolution of globular clusters (GCs) during galaxy formation and assembly within a cosmological framework. The current state of the art for both observations and simulations is described, and we briefly mention directions for future research. The oldest GCs have ages greater than or equal to 12.5 Gyr and formed around the time of reionization. Resolved colour-magnitude diagrams of Milky Way GCs and direct imaging of lensed proto-GCs at z˜6 with the James Webb Space Telescope (JWST) promise further insight. GCs are known to host multiple populations of stars with variations in their chemical abundances. Recently, such multiple populations have been detected in ˜2 Gyr old compact, massive star clusters. This suggests a common, single pathway for the formation of GCs at high and low redshift. The shape of the initial mass function for GCs remains unknown; however, for massive galaxies a power-law mass function is favoured. Significant progress has been made recently modelling GC formation in the context of galaxy formation, with success in reproducing many of the observed GC-galaxy scaling relations.

  7. Thermal hydraulic analysis of Pb-Bi cooled HYPER fuel assemblies using SLTHEN code

    Tak, Nam Il; Song, Tae Y.; Park, Won S.; Kim, Chang Hyun

    2002-12-01

    In the present work, the existing SLTHEN code, which had been originally developed for subchannel analysis of sodium cooled fast reactors, was modified and applied to the Pb-Bi cooled HYPER core which consists of 237 fuel assemblies (TRU assemblies). In the analysis of single fuel assembly having chopped cosine power profile, the validation and the assessment of usefulness of the modified SLTHEN were focused. In the quantitative comparison, the results of the modified SLTHEN agreed well with those of analytical calculations and of MATRA. For the qualitative approaches, the sensitivity calculations for intra-assembly gap flow and turbulent mixing parameter were used. The sensitivity analysis results showed that the modified SLTHEN can provide reasonable simulations of subchannel thermal hydraulics. In particular, turbulent mixing parameter which is known as the most uncertain parameter in subchannel analyses did not affect largely the maximum cladding temperature. Therefore, it can be said that the results of single assembly show the usefulness of the modified SLTHEN code for thermal hydraulic analysis and design of HYPER under the conceptual design stage. In order to assess intra-assembly heat transfer, subchannel analyses were implemented for two types of 7 assemblies; 1) artificial 7 fuel assemblies to maximize intra-assembly heat transfer, 2) central 7 fuel assemblies in the HYPER reference core. The results showed that the modified SLTHEN can reasonably simulate intra-heat transfer and the amount of intra-assembly heat transfer is not so large in HYPER conditions. Particularly, intra-heat transfer did not affect the maximum coolant and the maximum cladding temperatures which are major parameters in conceptual core designs. The capability of full core thermal hydraulic analysis was confirmed by the analysis of 45 fuel assemblies in 1/6 HYPER core at the first cycle. The SLTHEN predicted that the reference design parameters are acceptable in terms of thermal

  8. THE FOSSIL RECORD OF TWO-PHASE GALAXY ASSEMBLY: KINEMATICS AND METALLICITIES IN THE NEAREST S0 GALAXY

    Arnold, Jacob A.; Romanowsky, Aaron J.; Brodie, Jean P.; Chomiuk, Laura; Strader, Jay; Spitler, Lee R.; Forbes, Duncan A.; Benson, Andrew J.

    2011-01-01

    We present a global analysis of kinematics and metallicity in the nearest S0 galaxy, NGC 3115, along with implications for its assembly history. The data include high-quality wide-field imaging from Suprime-Cam on the Subaru telescope, and multi-slit spectra of the field stars and globular clusters (GCs) obtained using Keck-DEIMOS/LRIS and Magellan-IMACS. Within two effective radii, the bulge (as traced by the stars and metal-rich GCs) is flattened and rotates rapidly (v/σ ∼> 1.5). At larger radii, the rotation declines dramatically to v/σ ∼ 0.7, but remains well aligned with the inner regions. The radial decrease in characteristic metallicity of both the metal-rich and metal-poor GC subpopulations produces strong gradients with power-law slopes of -0.17 ± 0.04 and -0.38 ± 0.06 dex dex -1 , respectively. We argue that this pattern is not naturally explained by a binary major merger, but instead by a two-phase assembly process where the inner regions have formed in an early violent, dissipative phase, followed by the protracted growth of the outer parts via minor mergers with typical mass ratios of ∼15-20:1.

  9. The Role of the Most Luminous Obscured AGNs in Galaxy Assembly at z ∼ 2

    Farrah, Duncan [Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States); Petty, Sara [Green Science Policy Institute, Berkeley, CA 94709 (United States); Connolly, Brian [Cincinnati Children’s Hospital Medical Center, 3333 Burnet Avenue, Cincinnati, OH 45229 (United States); Blain, Andrew [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Efstathiou, Andreas [School of Sciences, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia (Cyprus); Lacy, Mark [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States); Stern, Daniel; Bridge, Carrie; Eisenhardt, Peter; Moustakas, Leonidas [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Lake, Sean; Tsai, Chao-Wei [Physics and Astronomy Department, University of California, Los Angeles, CA 90095 (United States); Jarrett, Tom [Department of Astronomy, University of Cape Town, 7700 Rondebosch, Capetown 7700 (South Africa); Benford, Dominic [Observational Cosmology Lab., Code 665, NASA at Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Jones, Suzy [Department of Space, Earth, and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala (Sweden); Assef, Roberto [Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago (Chile); Wu, Jingwen [National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing, 100012 (China)

    2017-08-01

    We present Hubble Space Telescope WFC3 F160W imaging and infrared spectral energy distributions for 12 extremely luminous, obscured active galactic nuclei (AGNs) at 1.8 < z < 2.7 selected via “hot, dust-obscured” mid-infrared colors. Their infrared luminosities span (2–15) × 10{sup 13} L {sub ⊙}, making them among the most luminous objects in the universe at z ∼ 2. In all cases, the infrared emission is consistent with arising at least for the most part from AGN activity. The AGN fractional luminosities are higher than those in either submillimeter galaxies or AGNs selected via other mid-infrared criteria. Adopting the G , M {sub 20}, and A morphological parameters, together with traditional classification boundaries, infers that three-quarters of the sample are mergers. Our sample does not, however, show any correlation between the considered morphological parameters and either infrared luminosity or AGN fractional luminosity. Moreover, the asymmetries and effective radii of our sample are distributed identically to those of massive galaxies at z ∼ 2. We conclude that our sample is not preferentially associated with mergers, though a significant merger fraction is still plausible. Instead, we propose that our sample includes examples of the massive galaxy population at z ∼ 2 that harbor a briefly luminous, “flickering” AGN and in which the G and M {sub 20} values have been perturbed due to either the AGN and/or the earliest formation stages of a bulge in an inside-out manner. Furthermore, we find that the mass assembly of the central black holes in our sample leads the mass assembly of any bulge component. Finally, we speculate that our sample represents a small fraction of the immediate antecedents of compact star-forming galaxies at z ∼ 2.

  10. COMPLEX GAS KINEMATICS IN COMPACT, RAPIDLY ASSEMBLING STAR-FORMING GALAXIES

    Amorin, R.; Vilchez, J. M.; Perez-Montero, E. [Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia S/N, E-18008 Granada (Spain); Haegele, G. F.; Firpo, V. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad de la Plata, Paseo del Bosque S/N, 1900 La Plata (Argentina); Papaderos, P., E-mail: amorin@iaa.es [Centro de Astrofisica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal)

    2012-08-01

    Deep, high-resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z {approx} 0.1-0.3, most of them also known as green peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including H{alpha}, [N II] {lambda}{lambda}6548, 6584, and [S II] {lambda}{lambda}6717, 6731, consisting of the superposition of different kinematical components on a spatial extent of few kiloparsecs: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their two-dimensional spectra, whereas for another one a faint detached H{alpha} blob lacking stellar continuum is detected at the same recessional velocity {approx}7 kpc away from the galaxy. The individual narrower H{alpha} components show high intrinsic velocity dispersion ({sigma} {approx} 30-80 km s{sup -1}), suggesting together with unsharped masking Hubble Space Telescope images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to {approx}500 km s{sup -1}. The broad underlying H{alpha} components indicate in all cases large expansion velocities (full width zero intensity {>=}1000 km s{sup -1}) and very high luminosities (up to {approx}10{sup 42} erg s{sup -1}), probably showing the imprint of energetic outflows from supernovae. These intriguing results underline the importance of green peas for studying the assembly of low-mass galaxies near and far.

  11. Galaxies

    1989-01-01

    In studies of the large scale structure of the universe there is a continuing need for extensive galaxy redshift determinations. Optically selected redshift surveys are of particular importance, since flux-limited samples record much higher space densities of galaxies than samples of similar size selected in other wavebands. A considerable amount of the South African Astronomical Observatory (SAAO) observing time is currently being devoted to carrying out a large southern galaxy redshift survey. A recently completed study, the Durham-SAAO redshift survey suggests that the mean density of matter is well below the critical limit for a closed universe and also that the universe may be homogenous at very large scales. Other research conducted by the SAAO include studies on: the distribution of galaxies; Seyfert galaxies; starburst and IRAS galaxies; interacting and compact galaxies; a re-evaluation of the Cepheid distance to NGC 300, and a search for quasars behind galaxies. 1 fig

  12. Galaxies

    1987-01-01

    The size and nature of any large-scale anisotropy in the three-dimensional distribution of galaxies is still little understood. Recent studies have indicated that large fluctuations in the matter distribution on a scale from tens up to several hundreds of megaparsecs may exist. Work at the South African Astronomical Observatory (SAAO) in recent years has made major contributions to studies of the large scale distribution of galaxies, as well as to solving the problems of the galactic and extragalactic distance scale. Other studies of galaxies undertaken at SAAO include: quasars in the fields of nearby galaxies; dwarf irregular galaxies; IRAS galaxies; Seyfert galaxies; 'hot spot' galaxies; supernovae in NGC 5128 and NGC 1559 and superclusters. 4 figs

  13. Regulation of the X-ray luminosity of clusters of galaxies by cooling and supernova feedback.

    Voit, G M; Bryan, G L

    2001-11-22

    Clusters of galaxies are thought to contain about ten times as much dark matter as baryonic matter. The dark component therefore dominates the gravitational potential of a cluster, and the baryons confined by this potential radiate X-rays with a luminosity that depends mainly on the gas density in the cluster's core. Predictions of the X-rays' properties based on models of cluster formation do not, however, agree with the observations. If the models ignore the condensation of cooling gas into stars and feedback from the associated supernovae, they overestimate the X-ray luminosity because the density of the core gas is too high. An early episode of uniformly distributed supernova feedback could rectify this by heating the uncondensed gas and therefore making it harder to compress into the core, but such a process seems to require an implausibly large number of supernovae. Here we show how radiative cooling of intergalactic gas and subsequent supernova heating conspire to eliminate highly compressible low-entropy gas from the intracluster medium. This brings the core entropy and X-ray luminosities of clusters into agreement with the observations, in a way that depends little on the efficiency of supernova heating in the early Universe.

  14. Mechanical Design Concept of Fuel Assembly for Prototype GEN-IV Sodium-cooled Fast Reactor

    Yoon, K. H.; Lee, C. B.

    2014-01-01

    The prototype GEN-IV sodium-cooled fast reactor (PGSFR) is an advanced fast reactor plant design that utilizes compact modular pool-type reactors sized to enable factory fabrication and an affordable prototype test for design certification at minimum cost and risk. The design concepts of the fuel assembly (FA) were introduced for a PGSFR. Unlike that for the pressurized water reactor, there is a neutron shielding concept in the FA and recycling metal fuel. The PGSFR core is a heterogeneous, uranium-10% zirconium (U-10Zr) metal alloy fuel design with 112 assemblies: 52 inner core fuel assemblies, 60 outer core fuel assemblies, 6 primary control assemblies, 3 secondary control assemblies, 90 reflector assemblies and 102 B4C shield assemblies. This configuration is shown in Fig. 1. The core is designed to produce 150 MWe with an average temperature rise of 155 .deg. C. The inlet temperature is 390 .deg. C and the bulk outlet temperature is 545 .deg. C. The core height is 900 mm and the gas plenum length is 1,250 mm. A mechanical design of a fuel assembly for a PGSFR was established. The mechanical design concepts are well realized in the design. In addition to this, the analytical and experimental works will be carries out for verifying the design soundness

  15. Mechanical Design Concept of Fuel Assembly for Prototype GEN-IV Sodium-cooled Fast Reactor

    Yoon, K. H.; Lee, C. B. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2014-10-15

    The prototype GEN-IV sodium-cooled fast reactor (PGSFR) is an advanced fast reactor plant design that utilizes compact modular pool-type reactors sized to enable factory fabrication and an affordable prototype test for design certification at minimum cost and risk. The design concepts of the fuel assembly (FA) were introduced for a PGSFR. Unlike that for the pressurized water reactor, there is a neutron shielding concept in the FA and recycling metal fuel. The PGSFR core is a heterogeneous, uranium-10% zirconium (U-10Zr) metal alloy fuel design with 112 assemblies: 52 inner core fuel assemblies, 60 outer core fuel assemblies, 6 primary control assemblies, 3 secondary control assemblies, 90 reflector assemblies and 102 B4C shield assemblies. This configuration is shown in Fig. 1. The core is designed to produce 150 MWe with an average temperature rise of 155 .deg. C. The inlet temperature is 390 .deg. C and the bulk outlet temperature is 545 .deg. C. The core height is 900 mm and the gas plenum length is 1,250 mm. A mechanical design of a fuel assembly for a PGSFR was established. The mechanical design concepts are well realized in the design. In addition to this, the analytical and experimental works will be carries out for verifying the design soundness.

  16. The HST/ACS Coma Cluster Survey - VII. Structure and assembly of massive galaxies in the centre of the Coma cluster

    Weinzirl, Tim; Jogee, Shardha; Neistein, Eyal; Khochfar, Sadegh; Kormendy, John; Marinova, Irina; Hoyos, Carlos; Balcells, Marc; den Brok, Mark; Hammer, Derek; Peletier, Reynier F.; Kleijn, Gijs Verdoes; Carter, David; Goudfrooij, Paul; Lucey, John R.; Mobasher, Bahram; Trentham, Neil; Erwin, Peter; Puzia, Thomas

    2014-01-01

    We constrain the assembly history of galaxies in the projected central 0.5 Mpc of the Coma cluster by performing structural decomposition on 69 massive (M⋆ ≥ 109 M⊙) galaxies using high-resolution F814W images from the Hubble Space Telescope (HST) Treasury Survey of Coma. Each galaxy is modelled

  17. An alternative solution for heavy liquid metal cooled reactors fuel assemblies

    Vitale Di Maio, Damiano, E-mail: damiano.vitaledimaio@uniroma1.it [“SAPIENZA” University of Rome – DIAEE, Corso Vittorio Emanuele II, 244, 00186 Rome (Italy); Cretara, Luca; Giannetti, Fabio [“SAPIENZA” University of Rome – DIAEE, Corso Vittorio Emanuele II, 244, 00186 Rome (Italy); Peluso, Vincenzo [“ENEA”, Via Martiri di Monte Sole 4, 40129 Bologna (Italy); Gandini, Augusto [“SAPIENZA” University of Rome – DIAEE, Corso Vittorio Emanuele II, 244, 00186 Rome (Italy); Manni, Fabio [“SRS Engineering Design S.r.l.”, Vicolo delle Palle 25-25/b, 00186 Rome (Italy); Caruso, Gianfranco [“SAPIENZA” University of Rome – DIAEE, Corso Vittorio Emanuele II, 244, 00186 Rome (Italy)

    2014-10-15

    Highlights: • A new fuel assembly locking system for heavy metal cooled reactor is proposed. • Neutronic, mechanical and thermal-hydraulic evaluations of the system behavior have been performed. • A comparison with other solutions has been presented. - Abstract: In the coming future, the electric energy production from nuclear power plants will be provided by both thermal reactors and fast reactors. In order to have a sustainable energy production through fission reactors, fast reactors should provide an increasing contribution to the total electricity production from nuclear power plants. Fast reactors have to achieve economic and technical targets of Generation IV. Among these reactors, Sodium cooled Fast Reactors (SFRs) and Lead cooled Fast Reactors (LFRs) have the greatest possibility to be developed as industrial power plants within few decades. Both SFRs and LFRs require a great R and D effort to overcome some open issues which affect the present designs (e.g. sodium-water reaction for the SFRs, erosion/corrosion for LFRs, etc.). The present paper is mainly focused on LFR fuel assembly (FA) design: issues linked with the high coolant density of lead or lead–bismuth eutectic cooled reactors have been investigated and an innovative solution for the core mechanical design is here proposed and analyzed. The solution, which foresees cylindrical fuel assemblies and exploits the buoyancy force due to the lead high density, allows to simplify the FAs locking system, to reduce their length and could lead to a more uniform neutron flux distribution.

  18. Simulations of isolated dwarf galaxies formed in dark matter halos with different mass assembly histories

    González-Samaniego, A.; Avila-Reese, V.; Rodríguez-Puebla, A.; Valenzuela, O.; Colín, P.

    2014-01-01

    We present zoom-in N-body/hydrodynamics resimulations of dwarf galaxies formed in isolated cold dark matter (CDM) halos with the same virial mass (M v ≈ 2.5 × 10 10 M ☉ ) at redshift z = 0. Our goals are to (1) study the mass assembly histories (MAHs) of the halo, stellar, and gaseous components; and (2) explore the effects of the halo MAHs on the stellar/baryonic assembly of simulated dwarfs. Overall, the dwarfs are roughly consistent with observations. More specific results include: (1) the stellar-to-halo mass ratio remains roughly constant since z ∼ 1, i.e., the stellar MAHs closely follow halo MAHs. (2) The evolution of the galaxy gas fractions, f g , are episodic, showing that the supernova-driven outflows play an important role in regulating f g —and hence, the star formation rate (SFR)—however, in most cases, a large fraction of the gas is ejected from the halo. (3) The star formation histories are episodic with changes in the SFRs, measured every 100 Myr, of factors of 2-10 on average. (4) Although the dwarfs formed in late assembled halos show more extended SF histories, their z = 0 specific SFRs are still below observations. (5) The inclusion of baryons most of the time reduces the virial mass by 10%-20% with respect to pure N-body simulations. Our results suggest that rather than increasing the strength of the supernova-driven outflows, processes that reduce the star formation efficiency could help to solve the potential issues faced by CDM-based simulations of dwarfs, such as low values of the specific SFR and high stellar masses.

  19. Simulations of isolated dwarf galaxies formed in dark matter halos with different mass assembly histories

    González-Samaniego, A.; Avila-Reese, V.; Rodríguez-Puebla, A.; Valenzuela, O. [Instituto de Astronomía, Universidad Nacional Autónoma de México, A.P. 70-264, 04510 México D. F. (Mexico); Colín, P. [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, A.P. 72-3 (Xangari), Morelia, Michoacán 58089 (Mexico)

    2014-04-10

    We present zoom-in N-body/hydrodynamics resimulations of dwarf galaxies formed in isolated cold dark matter (CDM) halos with the same virial mass (M{sub v} ≈ 2.5 × 10{sup 10} M {sub ☉}) at redshift z = 0. Our goals are to (1) study the mass assembly histories (MAHs) of the halo, stellar, and gaseous components; and (2) explore the effects of the halo MAHs on the stellar/baryonic assembly of simulated dwarfs. Overall, the dwarfs are roughly consistent with observations. More specific results include: (1) the stellar-to-halo mass ratio remains roughly constant since z ∼ 1, i.e., the stellar MAHs closely follow halo MAHs. (2) The evolution of the galaxy gas fractions, f{sub g} , are episodic, showing that the supernova-driven outflows play an important role in regulating f{sub g} —and hence, the star formation rate (SFR)—however, in most cases, a large fraction of the gas is ejected from the halo. (3) The star formation histories are episodic with changes in the SFRs, measured every 100 Myr, of factors of 2-10 on average. (4) Although the dwarfs formed in late assembled halos show more extended SF histories, their z = 0 specific SFRs are still below observations. (5) The inclusion of baryons most of the time reduces the virial mass by 10%-20% with respect to pure N-body simulations. Our results suggest that rather than increasing the strength of the supernova-driven outflows, processes that reduce the star formation efficiency could help to solve the potential issues faced by CDM-based simulations of dwarfs, such as low values of the specific SFR and high stellar masses.

  20. Stress Linearization and Strength Evaluation of the BEP's Flow Plates for a Dual Cooled Fuel Assembly

    Kim, Jae Yong; Yoon, Kyung Ho; Kang, Heung Seok; Lee, Young Ho; Lee, Kang Hee; Kim, Hyung Kyu

    2009-01-01

    A fuel assembly is composed of 5 major components, such as a top end piece (TEP), a bottom end piece (BEP), spacer grids (SGs), guide tubes (GTs) and an instrumentation tube (IT) and fuel rods (FRs). There are no ASME criteria about all components except for a TEP/BEP. The TEP/BEP should satisfy stress intensity limits in case of condition A and B of ASME, Section III, Division 1 . Subsection NB. In a dual cooled fuel assembly, the array and position of fuels are changed from those of a conventional PWR fuel assembly to achieve a power uprating. The flow plates of top/bottom end pieces (TEP/BEP) have to be modified into proper shape to provide flow holes to direct the heated coolant into/out of the fuel assembly but structural intensity of these plates within a 22.241 kN axial loading should satisfy Tresca stress limits in ASME code. In this paper, stress linearization procedure and strength evaluation of a newly designed BEP for the dual cooled fuel assembly are described

  1. Transient Analysis of a Gas-cooled Fast Reactor for Single Control Assembly Withdrawal

    Choi, Hangbok

    2014-01-01

    The Energy Multiplier Module (EMZ) system response has been evaluated for control assembly withdrawal transients. Currently the EM2 core is equipped with six cylindrical drum-type control assemblies in the reflector zone for excess reactivity control and power maneuvering during the operating core life. This study investigates the system response to the control assembly withdrawal accident with various rotational speeds and reactivity worth to determine feasible control assembly design requirements from the physics viewpoint. The simulations have been conducted for single control assembly withdrawal transients without scram by a gas-cooled reactor plant simulator, which is based on a simplified plant nodal model, including the point reactor kinetics, single channel core thermal-fluid model, and a turbo-machinery performance model. Simulations were conducted for the middle-of- cycle core, when the excess reactivity of the core is the highest. Control assembly withdrawal times were varied from 1 (runaway) to 180 sec and reactivity worth was varied from 100 to 400 pcm. For a single control assembly withdrawal, the simulation has shown that the peak fuel temperature is expected to be ~1820°C when the assembly worth is 200 pcm and the runaway time is 1 sec per 180 degree rotation. The peak temperature could be reduced to ~1780°C if the assembly is rotated out in a moderate speed such as 1 degree/sec. These peak temperatures give a thermal margin of 22 to 24% to the melting point of uranium carbide fuel. The results also indicate that the current design with a single control assembly worth of 314 pcm may need adjustments in the future design. (author)

  2. Investigations on the thermal-hydraulics of a natural circulation cooled BWR fuel assembly

    Kok, H.V.; Hagen, T.H.J.J. van der; Mudde, R.F. [Delft Univ. of Technology (Netherlands)

    1995-09-01

    A scaled natural circulation loop facility has been built after the Dodewaard Boiling Water Reactor, which is the only operating natural circulation cooled BWR in the world. The loop comprises one fuel assembly, a riser with a downcomer and a condenser with a cooling system. Freon-12 is used as a scaling liquid. This paper reports on the first measurements done with this facility. Quantities like the circulation flow, carry-under and the void-fraction have been measured as a function of power, pressure, liquid level, riser length, condensate temperature and friction factors. The behavior of the circulation flow can be understood by considering the driving force. Special attention has been paid to the carry-under, which has been shown to have a very important impact on the dynamics of a natural circulation cooled BWR.

  3. K-infinite trends with burnup, enrichment, and cooling time for BWR fuel assemblies

    Broadhead, B.L.

    1998-08-01

    This report documents the work performed by ORNL for the Yucca Mountain project (YMP) M and O contractor, Framatome Cogema Fuels. The goal of this work was to obtain k inf values for infinite arrays of flooded boiling-water-reactor (BWR) fuel assemblies as a function of various burnup/enrichment and cooling-time combinations. These scenarios simulate expected limiting criticality loading conditions (for a given assembly type) for drift emplacements in a repository. Upon consultation with the YMP staff, a Quad Cities BWR fuel assembly was selected as a baseline assembly. This design consists of seven axial enrichment zones, three of which contain natural uranium oxide. No attempt was made to find a bounding or even typical assembly design due to the wide variety in fuel assembly designs necessary for consideration. The current work concentrates on establishing a baseline analysis, along with a small number of sensitivity studies which can be expected later if desired. As a result of similar studies of this nature, several effects are known to be important in the determination of the final k inf for spent fuel in a cask-like geometry. For a given enrichment there is an optimal burnup: for lower burnups, excess energy (and corresponding excess reactivity) is present in the fuel assembly; for larger burnups, the assembly is overburned and essentially driven by neighboring fuel assemblies. The majority of the burnup/enrichment scenarios included in this study were for some near-optimum burnup/enrichment combinations as determined from Energy Information Administration (EIA) data. Several calculations were performed for under- and over-burned fuel to show these effects

  4. Design of the Flow Plates for a Dual Cooled Fuel Assembly

    Kim, Jae Yong; Yoon, Kyung Ho; Lee, Young Ho; Lee, Kang Hee; Kim, Hyung Kyu

    2009-01-01

    In a dual cooled fuel assembly, the array and position of fuels are changed from those of a conventional PWR fuel assembly to achieve a power uprating. The flow plate provides flow holes to direct the heated coolant into/out of the fuel assembly and structural intensity to insure that the fuel rod is axially restrained within the spacer grids. So, flow plates of top/bottom end pieces (TEP/BEP) have to be modified into proper shape. Because the flow holes' area of a flow plate affects pressure drop, the flow holes' area must be larger than/equal to that of conventional flow plates. And design criterion of the TEP/BEP says that the flow plate should withstand a 22.241 kN axial load during handling lest a calculated stress intensity should exceed the Condition I allowable stress. In this paper, newly designed flow plates of a TEP/BEP are suggested and stress analysis is conducted to evaluate strength robustness of the flow plates for the dual cooled fuel assembly

  5. Vibration Monitoring Using Fiber Optic Sensors in a Lead-Bismuth Eutectic Cooled Nuclear Fuel Assembly

    Ben De Pauw

    2016-04-01

    Full Text Available Excessive fuel assembly vibrations in nuclear reactor cores should be avoided in order not to compromise the lifetime of the assembly and in order to prevent the occurrence of safety hazards. This issue is particularly relevant to new reactor designs that use liquid metal coolants, such as, for example, a molten lead-bismuth eutectic. The flow of molten heavy metal around and through the fuel assembly may cause the latter to vibrate and hence suffer degradation as a result of, for example, fretting wear or mechanical fatigue. In this paper, we demonstrate the use of optical fiber sensors to measure the fuel assembly vibration in a lead-bismuth eutectic cooled installation which can be used as input to assess vibration-related safety hazards. We show that the vibration characteristics of the fuel pins in the fuel assembly can be experimentally determined with minimal intrusiveness and with high precision owing to the small dimensions and properties of the sensors. In particular, we were able to record local strain level differences of about 0.2 μϵ allowing us to reliably estimate the vibration amplitudes and modal parameters of the fuel assembly based on optical fiber sensor readings during different stages of the operation of the facility, including the onset of the coolant circulation and steady-state operation.

  6. Modular jet impingement assemblies with passive and active flow control for electronics cooling

    Zhou, Feng; Dede, Ercan Mehmet; Joshi, Shailesh

    2016-09-13

    Power electronics modules having modular jet impingement assembly utilized to cool heat generating devices are disclosed. The modular jet impingement assemblies include a modular manifold having a distribution recess, one or more angled inlet connection tubes positioned at an inlet end of the modular manifold that fluidly couple the inlet tube to the distribution recess and one or more outlet connection tubes positioned at an outlet end of the modular manifold that fluidly coupling the outlet tube to the distribution recess. The modular jet impingement assemblies include a manifold insert removably positioned within the distribution recess and include one or more inlet branch channels each including an impinging slot and one or more outlet branch channels each including a collecting slot. Further a heat transfer plate coupled to the modular manifold, the heat transfer plate comprising an impingement surface including an array of fins that extend toward the manifold insert.

  7. ngVLA Key Science Goal 3: Charting the Assembly, Structure, and Evolution of Galaxies Over Cosmic Time

    Riechers, Dominik A.; Bolatto, Alberto D.; Carilli, Chris; Casey, Caitlin M.; Decarli, Roberto; Murphy, Eric Joseph; Narayanan, Desika; Walter, Fabian; ngVLA Galaxy Assembly through Cosmic Time Science Working Group, ngVLA Galaxy Ecosystems Science Working Group

    2018-01-01

    The Next Generation Very Large Array (ngVLA) will fundamentally advance our understanding of the formation processes that lead to the assembly of galaxies throughout cosmic history. The combination of large bandwidth with unprecedented sensitivity to the critical low-level CO lines over virtually the entire redshift range will open up the opportunity to conduct large-scale, deep cold molecular gas surveys, mapping the fuel for star formation in galaxies over substantial cosmic volumes. Imaging of the sub-kiloparsec scale distribution and kinematic structure of molecular gas in both normal main-sequence galaxies and large starbursts back to early cosmic epochs will reveal the physical processes responsible for star formation and black hole growth in galaxies over a broad range in redshifts. In the nearby universe, the ngVLA has the capability to survey the structure of the cold, star-forming interstellar medium at parsec-resolution out to the Virgo cluster. A range of molecular tracers will be accessible to map the motion, distribution, and physical and chemical state of the gas as it flows in from the outer disk, assembles into clouds, and experiences feedback due to star formation or accretion into central super-massive black holes. These investigations will crucially complement studies of the star formation and stellar mass histories with the Large UV/Optical/Infrared Surveyor and the Origins Space Telescope, providing the means to obtain a comprehensive picture of galaxy evolution through cosmic times.

  8. The Effects of Halo Assembly Bias on Self-Calibration in Galaxy Cluster Surveys

    Wu, Hao-Yi; Rozo, Eduardo; Wechsler, Risa H.

    2008-08-07

    Self-calibration techniques for analyzing galaxy cluster counts utilize the abundance and the clustering amplitude of dark matter halos. These properties simultaneously constrain cosmological parameters and the cluster observable-mass relation. It was recently discovered that the clustering amplitude of halos depends not only on the halo mass, but also on various secondary variables, such as the halo formation time and the concentration; these dependences are collectively termed 'assembly bias'. Applying modified Fisher matrix formalism, we explore whether these secondary variables have a significant impact on the study of dark energy properties using the self-calibration technique in current (SDSS) and the near future (DES, SPT, and LSST) cluster surveys. The impact of the secondary dependence is determined by (1) the scatter in the observable-mass relation and (2) the correlation between observable and secondary variables. We find that for optical surveys, the secondary dependence does not significantly influence an SDSS-like survey; however, it may affect a DES-like survey (given the high scatter currently expected from optical clusters) and an LSST-like survey (even for low scatter values and low correlations). For an SZ survey such as SPT, the impact of secondary dependence is insignificant if the scatter is 20% or lower but can be enhanced by the potential high scatter values introduced by a highly-correlated background. Accurate modeling of the assembly bias is necessary for cluster self-calibration in the era of precision cosmology.

  9. THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

    Gallart, Carme; Monelli, Matteo; Aparicio, Antonio; Battaglia, Giuseppina; Drozdovsky, Igor; Hidalgo, Sebastian L.; Mayer, Lucio; Bernard, Edouard J.; Cassisi, Santi; Cole, Andrew A.; Dolphin, Andrew E.; Navarro, Julio F.; Salvadori, Stefania; Skillman, Evan D.; Stetson, Peter B.; Weisz, Daniel R.

    2015-01-01

    We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation

  10. THE ACS LCID PROJECT: ON THE ORIGIN OF DWARF GALAXY TYPES—A MANIFESTATION OF THE HALO ASSEMBLY BIAS?

    Gallart, Carme; Monelli, Matteo; Aparicio, Antonio; Battaglia, Giuseppina; Drozdovsky, Igor; Hidalgo, Sebastian L. [Instituto de Astrofísica de Canarias, La Laguna, Tenerife (Spain); Mayer, Lucio [Institut für Theoretische Physik, University of Zurich, Zürich (Switzerland); Bernard, Edouard J. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Cassisi, Santi [INAF-Osservatorio Astronomico di Collurania, Teramo (Italy); Cole, Andrew A. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, TAS 7005 (Australia); Dolphin, Andrew E. [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85706 (United States); Navarro, Julio F. [Department of Physics and Astronomy, University of Victoria, PO Box 1700, STN CSC, Victoria, BC V8W 3P6 (Canada); Salvadori, Stefania [Kapteyn Astronomical Institute, Landleven 12, NL-9747 AD Groningen (Netherlands); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN (United States); Stetson, Peter B. [Herzberg Astronomy and Astrophysics, National Research Council Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Weisz, Daniel R., E-mail: monelli@iac.es [Astronomy Department, University of Washington, Box 351580, Seattle, WA (United States)

    2015-10-01

    We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than only being the result of a recent morphological transformation driven by environmental effects. We present precise star formation histories of a sample of Local Group dwarf galaxies, derived from color–magnitude diagrams reaching the oldest main-sequence turnoffs. We argue that these galaxies can be assigned to two basic types: fast dwarfs that started their evolution with a dominant and short star formation event and slow dwarfs that formed a small fraction of their stars early and have continued forming stars until the present time (or almost). These two different evolutionary paths do not map directly onto the present-day morphology (dwarf spheroidal versus dwarf irregular). Slow and fast dwarfs also differ in their inferred past location relative to the Milky Way and/or M31, which hints that slow dwarfs were generally assembled in lower-density environments than fast dwarfs. We propose that the distinction between a fast and slow dwarf galaxy primarily reflects the characteristic density of the environment where they form. At a later stage, interaction with a large host galaxy may play a role in the final gas removal and ultimate termination of star formation.

  11. Non-equilibrium chemistry and cooling in simulations of galaxy formation

    Richings, Alexander James

    2015-01-01

    In this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions between ions and molecules have reached a steady state. However, this assumption may not be valid if the

  12. Static stress analysis of coupling superconducting solenoid coil assembly for muon ionization cooling experiment

    Pan Heng; Wang Li; Wu Hong; Guo Xinglong; Xu Fengyu

    2010-01-01

    The stresses in the coupling superconducting solenoid coil assembly, which is applied in the Muon Ionization Cooling Experiment (MICE), are critical for the structure design and mechanical stability because of a large diameter and relative high magnetic field. This paper presents an analytical stress solution for the MICE coupling coil assembly. The stress due to winding tension is calculated by assuming the coil package as a set of combined cylinders. The thermal and electromechanical stresses are obtained by solving the partial differential equations of displacement based on the power series expansion method. The analytical stress solution is proved to be feasible by calculating stresses in a tested superconducting solenoid with 2.58 m bore at room temperature. The analytical result of the MICE coupling coil is in good agreement with that of the finite element which shows that the transverse shear stress induced by Lorentz force is principally dominant to magnet instability. (authors)

  13. Experimental investigation of a two-phase closed thermosyphon assembly for passive containment cooling system

    Nam, Kyung Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of); Kim, Sang Nyung [Kyunghee Univ., Gyeonggi-do (Korea, Republic of)

    2017-06-15

    After the Fukushima accident, increasing interest has been raised in passive safety systems that maintain the integrity of the containment building. To improve the reliability and safety of nuclear power plants, long-term passive cooling concepts have been developed for advanced reactors. In a previous study, the proposed design was based on an ordinary cylindrical Two-Phase Closed Thermosyphon (TPCT). The exact assembly size and number of TPCTs should be elaborated upon through accurate calculations based on experiments. While the ultimate goal is to propose an effective MPHP design for the PCCS and experimentally verify its performance, a TPCT assembly that was manufactured based on the conceptual design in this paper was tested.

  14. Subchannel analysis of sodium-cooled reactor fuel assemblies with annular fuel pins

    Memmott, Matthew; Buongiorno, Jacopo; Hejzlar, Pavel

    2009-01-01

    Using a RELAP5-3D subchannel analysis model, the thermal-hydraulic behavior of sodium-cooled fuel assemblies with internally and externally cooled annular fuel rods was investigated, in an effort to enhance the economic performance of sodium-fast reactors by increasing the core power density, decreasing the core pressure drop, and extending the fuel discharge burnup. Both metal and oxide fuels at high and low conversion ratios (CR=0.25 and CR=1.00) were investigated. The externally and internally cooled annular fuel design is most beneficial when applied to the low CR core, as clad temperatures are reduced by up to 62.3degC for the oxide fuel, and up to 18.5degC for the metal fuel. This could result in a power uprates of up to ∼44% for the oxide fuel, and up to ∼43% for the metal fuel. The use of duct ribs was explored to flatten the temperature distribution at the core outlet. Subchannel analyses revealed that no fuel melting would occur in the case of complete blockage of the hot interior-annular channel for both metal and oxide fuels. Also, clad damage would not occur for the metal fuel if the power uprate is 38% or less, but would indeed occur for the oxide fuel. (author)

  15. OPTICAL LINE EMISSION IN BRIGHTEST CLUSTER GALAXIES AT 0 < z < 0.6: EVIDENCE FOR A LACK OF STRONG COOL CORES 3.5 Gyr AGO?

    McDonald, Michael

    2011-01-01

    In recent years the number of known galaxy clusters beyond z ∼> 0.2 has increased drastically with the release of multiple catalogs containing >30,000 optically detected galaxy clusters over the range 0 0.3, hinting at an earlier epoch of strong cooling. We compare the evolution of emission-line nebulae to the X-ray-derived cool core (CC) fraction from the literature over the same redshift range and find overall agreement, with the exception that an upturn in the strong CC fraction is not observed at z > 0.3. The overall agreement between the evolution of CCs and optical line emission at low redshift suggests that emission-line surveys of galaxy clusters may provide an efficient method of indirectly probing the evolution of CCs and thus provide insights into the balance of heating and cooling processes at early cosmic times.

  16. Multiple lead seal assembly for a liquid-metal-cooled fast-breeder nuclear reactor

    Hutter, E.; Pardini, J.A.

    1977-01-01

    A reusable multiple lead seal assembly provides leak-free passage of stainless-steel-clad instrument leads through the cover on the primary tank of a liquid-metal-cooled fast-breeder nuclear reactor. The seal isolates radioactive argon cover gas and sodium vapor within the primary tank from the exterior atmosphere and permits reuse of the assembly and the stainless-steel-clad instrument leads. Leads are placed in flutes in a seal body, and a seal shell is then placed around the seal body. Circumferential channels in the body and inner surface of the shell are contiguous and together form a conduit which intersects each of the flutes, placing them in communication with a port through the wall of the seal shell. Liquid silicone rubber sealant is injected into the flutes through the port and conduit; the sealant fills the space in the flutes not occupied by the leads themselves and dries to a rubbery hardness. A nut, threaded onto a portion of the seal body not covered by the seal shell, jacks the body out of the shell and shears the sealant without damage to the body, shell, or leads. The leads may then be removed from the body. The sheared sealant is cleaned from the body, leads, and shell and the assembly may then be reused with the same or different leads. 3 claims, 6 figures

  17. EVIDENCE FOR WIDESPREAD COOLING IN AN ACTIVE REGION OBSERVED WITH THE SDO ATMOSPHERIC IMAGING ASSEMBLY

    Viall, Nicholeen M.; Klimchuk, James A.

    2012-01-01

    A well-known behavior of EUV light curves of discrete coronal loops is that the peak intensities of cooler channels or spectral lines are reached at progressively later times than hotter channels. This time lag is understood to be the result of hot coronal loop plasma cooling through these lower respective temperatures. However, loops typically comprise only a minority of the total emission in active regions (ARs). Is this cooling pattern a common property of AR coronal plasma, or does it only occur in unique circumstances, locations, and times? The new Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) data provide a wonderful opportunity to answer this question systematically for an entire AR. We measure the time lag between pairs of SDO/AIA EUV channels using 24 hr of images of AR 11082 observed on 2010 June 19. We find that there is a time-lag signal consistent with cooling plasma, just as is usually found for loops, throughout the AR including the diffuse emission between loops for the entire 24 hr duration. The pattern persists consistently for all channel pairs and choice of window length within the 24 hr time period, giving us confidence that the plasma is cooling from temperatures of greater than 3 MK, and sometimes exceeding 7 MK, down to temperatures lower than ∼0.8 MK. This suggests that the bulk of the emitting coronal plasma in this AR is not steady; rather, it is dynamic and constantly evolving. These measurements provide crucial constraints on any model which seeks to describe coronal heating.

  18. Application of assembly module to high-temperature gas-cooled reactor full-scope simulation system

    Li Sifeng; Li Fu; Ma Yuanle; Shi Lei

    2007-01-01

    According to the circumstances that exist in the reactor full-scope simulators development as long development cycle, very difficult upgrade and narrow range of applicability, a kind of new model was developed based on assembly module which root in Linux kernel and successfully applied to the design of high-temperature gas-cooled reactor full-scope simulator system. The simulation results are coincident with the experimental ones, and it indicates that the new model based on assembly module is feasible to design of high-temperature gas cooled reactor simulation system. (authors)

  19. Data Mining Techniques to Estimate Plutonium, Initial Enrichment, Burnup, and Cooling Time in Spent Fuel Assemblies

    Trellue, Holly Renee [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Fugate, Michael Lynn [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Tobin, Stephen Joesph [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2015-03-19

    The Next Generation Safeguards Initiative (NGSI), Office of Nonproliferation and Arms Control (NPAC), National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE) has sponsored a multi-laboratory, university, international partner collaboration to (1) detect replaced or missing pins from spent fuel assemblies (SFA) to confirm item integrity and deter diversion, (2) determine plutonium mass and related plutonium and uranium fissile mass parameters in SFAs, and (3) verify initial enrichment (IE), burnup (BU), and cooling time (CT) of facility declaration for SFAs. A wide variety of nondestructive assay (NDA) techniques were researched to achieve these goals [Veal, 2010 and Humphrey, 2012]. In addition, the project includes two related activities with facility-specific benefits: (1) determination of heat content and (2) determination of reactivity (multiplication). In this research, a subset of 11 integrated NDA techniques was researched using data mining solutions at Los Alamos National Laboratory (LANL) for their ability to achieve the above goals.

  20. Optimization of the fuel assembly for the Canadian SuperCritical Water-cooled Reactor (SCWR)

    French, C., E-mail: Corey.French@cnsc-ccsn.gc.ca [Canadian Nuclear Safety Commission, Ottawa, Ontario (Canada); Bonin, H.; Chan, P.K. [Royal Military College of Ontario, Kingston, Ontario (Canada)

    2013-07-01

    An approach to develop a parametric optimization tool to support the Canadian Supercritical Water-cooled Reactor (SCWR) fuel design is presented in this work. The 2D benchmark lattices for 78-pin and 64-pin fuel assemblies are used as the initial models from which fuel performance and subsequent optimization stem from. A tandem optimization procedure is integrated which employs the steepest descent method. The physics codes WIMS-AECL, MCNP6 and SERPENT are used to calculate and verify select performance factors. The results are used as inputs to an optimization algorithm that yield optimal fresh fuel isotopic composition and lattice geometry. Preliminary results on verifications of infinite lattice reactivity are demonstrated in this paper. (author)

  1. The Recent and Continuing Assembly of Field Elliptical Galaxies by Red Mergers

    van Dokkum, Pieter G.

    2005-12-01

    We present a study of tidal debris associated with 126 nearby red galaxies, selected from the 1.2 deg2 Multiwavelength Survey by Yale-Chile and the 9.3 deg2 NOAO Deep Wide-Field Survey. In the full sample, 67 galaxies (53%) show morphological signatures of tidal interactions consisting of broad fans of stars, tails, and other asymmetries at very faint surface brightness levels. When restricting the sample to the 86 bulge-dominated early-type galaxies, the fraction of tidally disturbed galaxies rises to 71%, which implies that for every ``normal'' undisturbed elliptical there are two that show clear signs of interactions. The tidal features are red and smooth and often extend over >50 kpc. Of the tidally distorted galaxies, about two-thirds are remnants, and one-third are interacting with a companion galaxy. The companions are usually bright red galaxies as well; the median R-band luminosity ratio of the tidal pairs is 0.31, and the median color difference after correcting for the slope of the color-magnitude relation is -0.02 in B-R. If the ongoing mergers are representative for the progenitors of the remnants, ~35% of bulge-dominated galaxies experienced a merger with mass ratio >1:4 in the recent past. With further assumptions it is estimated that the present-day mass accretion rate of galaxies on the red sequence ΔM/M=0.09+/-0.04 Gyr-1. For a constant or increasing mass accretion rate with redshift, we find that red mergers may lead to an evolution of a factor of >~2 in the stellar mass density in luminous red galaxies over the redshift range 0interesting to determine whether this mode of merging only plays an important role at low redshift or is relevant for galaxies at any redshift if they exceed a critical mass scale.

  2. Development of numerical simulation system for thermal-hydraulic analysis in fuel assembly of sodium-cooled fast reactor

    Ohshima, Hiroyuki; Uwaba, Tomoyuki [Japan Atomic Energy Agency (4002 Narita, O-arai, Ibaraki 311-1393, Japan) (Japan); Hashimoto, Akihiko; Imai, Yasutomo [NDD Corporation (1-1-6 Jounan, Mito, Ibaraki 310-0803, Japan) (Japan); Ito, Masahiro [NESI Inc. (4002 Narita, O-arai, Ibaraki 311-1393, Japan) (Japan)

    2015-12-31

    A numerical simulation system, which consists of a deformation analysis program and three kinds of thermal-hydraulics analysis programs, is being developed in Japan Atomic Energy Agency in order to offer methodologies to clarify thermal-hydraulic phenomena in fuel assemblies of sodium-cooled fast reactors under various operating conditions. This paper gives the outline of the system and its applications to fuel assembly analyses as a validation study.

  3. Testing the hierarchical assembly of massive galaxies using accurate merger rates out to z ˜ 1.5

    Rodrigues, Myriam; Puech, M.; Flores, H.; Hammer, F.; Pirzkal, N.

    2018-04-01

    We established an accurate comparison between observationally and theoretically estimated major merger rates over a large range of mass (log Mbar/M⊙ =9.9-11.4) and redshift (z = 0.7-1.6). For this, we combined a new estimate of the merger rate from an exhaustive count of pairs within the virial radius of massive galaxies at z ˜ 1.265 and cross-validated with their morphology, with estimates from the morpho-kinematic analysis of two other samples. Theoretical predictions were estimated using semi-empirical models with inputs matching the properties of the observed samples, while specific visibility time-scales scaled to the observed samples were used. Both theory and observations are found to agree within 30 per cent of the observed value, which provides strong support to the hierarchical assembly of galaxies over the probed ranges of mass and redshift. Here, we find that ˜60 per cent of population of local massive (Mstellar =1010.3-11.6 M⊙) galaxies would have undergone a wet major merger since z = 1.5, consistently with previous studies. Such recent mergers are expected to result in the (re-)formation of a significant fraction of local disc galaxies.

  4. Mapping the particle acceleration in the cool core of the galaxy cluster RX J1720.1+2638

    Giacintucci, S.; Markevitch, M.; Brunetti, G.; Venturi, T.; ZuHone, J. A.; Mazzotta, P.; Bourdin, H.

    2014-01-01

    We present new deep, high-resolution radio images of the diffuse minihalo in the cool core of the galaxy cluster RX J1720.1+2638. The images have been obtained with the Giant Metrewave Radio Telescope at 317, 617, and 1280 MHz and with the Very Large Array at 1.5, 4.9, and 8.4 GHz, with angular resolutions ranging from 1'' to 10''. This represents the best radio spectral and imaging data set for any minihalo. Most of the radio flux of the minihalo arises from a bright central component with a maximum radius of ∼80 kpc. A fainter tail of emission extends out from the central component to form a spiral-shaped structure with a length of ∼230 kpc, seen at frequencies 1.5 GHz and below. We find indication of a possible steepening of the total radio spectrum of the minihalo at high frequencies. Furthermore, a spectral index image shows that the spectrum of the diffuse emission steepens with increasing distance along the tail. A striking spatial correlation is observed between the minihalo emission and two cold fronts visible in the Chandra X-ray image of this cool core. These cold fronts confine the minihalo, as also seen in numerical simulations of minihalo formation by sloshing-induced turbulence. All these observations favor the hypothesis that the radio-emitting electrons in cluster cool cores are produced by turbulent re-acceleration.

  5. Sub-channel analysis of LBE-cooled fuel assemblies of accelerator driven systems

    Cheng, X.; Hwang, D.H.

    2005-01-01

    In the frame of the European PDS-XADS project, two concepts of the sub-critical reactor core cooled by liquid lead-bismuth eutectic (LBE) were proposed. In this paper, the local thermal-hydraulic behavior of both LBE-cooled fuel assemblies was analyzed. For this purpose, the sub-channel analysis code MATRA was selected, and modification was made for its applications to XADS conditions. Compared to the small core concept, the large core concept has a much lower temperatures of coolant, cladding and fuel pins. This enables a short-term realization of the core design using available technologies. The high power density of the small core results in high local temperatures of coolant, cladding and fuel. Both coolant velocity and cladding temperature are such that special attention has to be paid to avoid corrosion and erosion damage of cladding materials. A parametric study shows that under the parameters considered, mixing coefficient has the biggest effect on the coolant temperature distribution, whereas the cladding temperature is strongly affected by the selection of heat transfer correlations. (author)

  6. COUPLED SIMULATION OF GAS COOLED FAST REACTOR FUEL ASSEMBLY WITH NESTLE CODE SYSTEM

    Filip Osusky

    2018-05-01

    Full Text Available The paper is focused on coupled calculation of the Gas Cooled Fast Reactor. The proper modelling of coupled neutronics and thermal-hydraulics is the corner stone for future safety assessment of the control and emergency systems. Nowadays, the system and channel thermal-hydraulic codes are accepted by the national regulatory authorities in European Union for license purposes, therefore the code NESTLE was used for the simulation. The NESTLE code is a coupled multigroup neutron diffusion code with thermal-hydraulic sub-channel code. In the paper, the validation of NESTLE code 5.2.1 installation is presented. The processing of fuel assembly homogeneous parametric cross-section library for NESTLE code simulation is made by the sequence TRITON of SCALE code package system. The simulated case in the NESTLE code is one fuel assembly of GFR2400 concept with reflective boundary condition in radial direction and zero flux boundary condition in axial direction. The results of coupled calculation are presented and are consistent with the GFR2400 study of the GoFastR project.

  7. The assembly histories of quiescent galaxies since z = 0.7 from absorption line spectroscopy

    Choi, Jieun; Conroy, Charlie [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Moustakas, John [Department of Physics and Astronomy, Siena College, Loudonville, NY 12110 (United States); Graves, Genevieve J. [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Holden, Bradford P. [UCO/Lick Observatories, University of California, Santa Cruz, CA 95064 (United States); Brodwin, Mark [Department of Physics and Astronomy, University of Missouri, Kansas City, MO 64110 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton, Vic 3800 (Australia); Van Dokkum, Pieter G. [Department of Astrophysical Sciences, Yale University, New Haven, CT 06520 (United States)

    2014-09-10

    We present results from modeling the optical spectra of a large sample of quiescent galaxies between 0.1 < z < 0.7 from the Sloan Digital Sky Survey (SDSS) and the AGN and Galaxy Evolution Survey (AGES). We examine how the stellar ages and abundance patterns of galaxies evolve over time as a function of stellar mass from 10{sup 9.6}-10{sup 11.8} M {sub ☉}. Galaxy spectra are stacked in bins of mass and redshift and modeled over a wavelength range from 4000 Å to 5500 Å. Full spectrum stellar population synthesis modeling provides estimates of the age and the abundances of the elements Fe, Mg, C, N, and Ca. We find negligible evolution in elemental abundances at fixed stellar mass over roughly 7 Gyr of cosmic time. In addition, the increase in stellar ages with time for massive galaxies is consistent with passive evolution since z = 0.7. Taken together, these results favor a scenario in which the inner ∼0.3-3 R {sub e} of massive quiescent galaxies have been passively evolving over the last half of cosmic time. Interestingly, the derived stellar ages are considerably younger than the age of the universe at all epochs, consistent with an equivalent single-burst star formation epoch of z ≲ 1.5. These young stellar population ages coupled with the existence of massive quiescent galaxies at z > 1 indicate the inhomogeneous nature of the z ≲ 0.7 quiescent population. The data also permit the addition of newly quenched galaxies at masses below ∼10{sup 10.5} M {sub ☉} at z < 0.7. Additionally, we analyze very deep Keck DEIMOS spectra of the two brightest quiescent galaxies in a cluster at z = 0.83. There is tentative evidence that these galaxies are older than their counterparts in low-density environments. In the Appendix, we demonstrate that our full spectrum modeling technique allows for accurate and reliable modeling of galaxy spectra to low S/N (∼20 Å{sup –1}) and/or low spectral resolution (R ∼ 500).

  8. THE STRUCTURE OF THE CIRCUMGALACTIC MEDIUM OF GALAXIES: COOL ACCRETION INFLOW AROUND NGC 1097

    Bowen, David V.; Jenkins, Edward B. [Princeton University Observatory, Ivy Lane, Princeton, NJ 08544 (United States); Chelouche, Doron [Department of Physics, University of Haifa, Mount Carmel, Haifa 31905 (Israel); Tripp, Todd M. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Pettini, Max [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0EZ (United Kingdom); York, Donald G. [Department of Astronomy and Astrophysics, University of Chicago, Enrico Fermi Institute, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Frye, Brenda L. [Department of Astronomy/Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States)

    2016-07-20

    We present Hubble Space Telescope far-UV spectra of four QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of ρ = 48–165 kpc. NGC 1097 is a nearby spiral galaxy that has undergone at least two minor merger events, but no apparent major mergers, and is relatively isolated with respect to other nearby bright galaxies. This makes NGC 1097 a good case study for exploring baryons in a paradigmatic bright-galaxy halo. Ly α absorption is detected along all sightlines and Si iii λ 1206 is found along the three sightlines with the smallest ρ ; metal lines of C ii, Si ii, and Si iv are only found with certainty toward the innermost sightline. The kinematics of the absorption lines are best replicated by a model with a disk-like distribution of gas approximately planar to the observed 21 cm H i disk, which is rotating more slowly than the inner disk, and into which gas is infalling from the intergalactic medium. Some part of the absorption toward the innermost sightline may arise either from a small-scale outflow or from tidal debris associated with the minor merger that gives rise to the well known “dog-leg” stellar stream that projects from NGC 1097. When compared to other studies, NGC 1097 appears to be a “typical” absorber, although the large dispersion in absorption line column density and equivalent width in a single halo goes perhaps some way toward explaining the wide range of these values seen in higher- z studies.

  9. Galaxy And Mass Assembly (GAMA): the galaxy stellar mass function to z = 0.1 from the r-band selected equatorial regions

    Wright, A. H.; Robotham, A. S. G.; Driver, S. P.; Alpaslan, M.; Andrews, S. K.; Baldry, I. K.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; da Cunha, E.; Davies, L. J. M.; Graham, Alister W.; Holwerda, B. W.; Hopkins, A. M.; Kafle, P. R.; Kelvin, L. S.; Loveday, J.; Maddox, S. J.; Meyer, M. J.; Moffett, A. J.; Norberg, P.; Phillipps, S.; Rowlands, K.; Taylor, E. N.; Wang, L.; Wilkins, S. M.

    2017-09-01

    We derive the low-redshift galaxy stellar mass function (GSMF), inclusive of dust corrections, for the equatorial Galaxy And Mass Assembly (GAMA) data set covering 180 deg2. We construct the mass function using a density-corrected maximum volume method, using masses corrected for the impact of optically thick and thin dust. We explore the galactic bivariate brightness plane (M⋆-μ), demonstrating that surface brightness effects do not systematically bias our mass function measurement above 107.5 M⊙. The galaxy distribution in the M-μ plane appears well bounded, indicating that no substantial population of massive but diffuse or highly compact galaxies are systematically missed due to the GAMA selection criteria. The GSMF is fitted with a double Schechter function, with M^\\star =10^{10.78± 0.01± 0.20} M_{⊙}, φ ^\\star _1=(2.93± 0.40)× 10^{-3} h_{70}^3 Mpc-3, α1 = -0.62 ± 0.03 ± 0.15, φ ^\\star _2=(0.63± 0.10)× 10^{-3} h_{70}^3 Mpc-3 and α2 = -1.50 ± 0.01 ± 0.15. We find the equivalent faint end slope as previously estimated using the GAMA-I sample, although we find a higher value of M^\\star. Using the full GAMA-II sample, we are able to fit the mass function to masses as low as 107.5 M⊙, and assess limits to 106.5 M⊙. Combining GAMA-II with data from G10-COSMOS, we are able to comment qualitatively on the shape of the GSMF down to masses as low as 106 M⊙. Beyond the well-known upturn seen in the GSMF at 109.5, the distribution appears to maintain a single power-law slope from 109 to 106.5. We calculate the stellar mass density parameter given our best-estimate GSMF, finding Ω _\\star = 1.66^{+0.24}_{-0.23}± 0.97 h^{-1}_{70} × 10^{-3}, inclusive of random and systematic uncertainties.

  10. Thermal-hydraulic numerical simulation of fuel sub-assembly for Sodium-cooled Fast Reactor

    Saxena, Aakanksha

    2014-01-01

    The thesis focuses on the numerical simulation of sodium flow in wire wrapped sub-assembly of Sodium-cooled Fast Reactor (SFR). First calculations were carried out by a time averaging approach called RANS (Reynolds- Averaged Navier-Stokes equations) using industrial code STAR-CCM+. This study gives a clear understanding of heat transfer between the fuel pin and sodium. The main variables of the macroscopic flow are in agreement with correlations used hitherto. However, to obtain a detailed description of temperature fluctuations around the spacer wire, more accurate approaches like LES (Large Eddy Simulation) and DNS (Direct Numerical Simulation) are clearly needed. For LES approach, the code TRIO U was used and for the DNS approach, a research code was used. These approaches require a considerable long calculation time which leads to the need of representative but simplified geometry. The DNS approach enables us to study the thermal hydraulics of sodium that has very low Prandtl number inducing a very different behavior of thermal field in comparison to the hydraulic field. The LES approach is used to study the local region of sub-assembly. This study shows that spacer wire generates the local hot spots (∼20 C) on the wake side of spacer wire with respect to the sodium flow at the region of contact with the fuel pin. Temperature fluctuations around the spacer wire are low (∼1 C-2 C). Under nominal operation, the spectral analysis shows the absence of any dominant peak for temperature oscillations at low frequency (2-10 Hz). The obtained spectra of temperature oscillations can be used as an input for further mechanical studies to determine its impact on the solid structures. (author) [fr

  11. No Assembly Required: Mergers are Mostly Irrelevant for the Growth of Low-mass Dwarf Galaxies

    Fitts, Alex; Boylan-Kolchin, Michael; Bullock, James S.; Weisz, Daniel R.; El-Badry, Kareem; Wheeler, Coral; Faucher-Giguère, Claude-André; Quataert, Eliot; Hopkins, Philip F.; Kereš, Dušan; Wetzel, Andrew; Hayward, Christopher C.

    2018-06-01

    We investigate the merger histories of isolated dwarf galaxies based on a suite of 15 high-resolution cosmological zoom-in simulations, all with masses of Mhalo ≈ 1010 M⊙ (and M⋆ ˜ 105 - 107 M⊙) at z = 0, from the Feedback in Realistic Environments (FIRE) project. The stellar populations of these dwarf galaxies at z = 0 are formed essentially entirely "in situ": over 90% of the stellar mass is formed in the main progenitor in all but two cases, and all 15 of the galaxies have >70% of their stellar mass formed in situ. Virtually all galaxy mergers occur prior to z ˜ 3, meaning that accreted stellar populations are ancient. On average, our simulated dwarfs undergo 5 galaxy mergers in their lifetimes, with typical pre-merger galaxy mass ratios that are less than 1:10. This merger frequency is generally comparable to what has been found in dissipationless simulations when coupled with abundance matching. Two of the simulated dwarfs have a luminous satellite companion at z = 0. These ultra-faint dwarfs lie at or below current detectability thresholds but are intriguing targets for next-generation facilities. The small contribution of accreted stars make it extremely difficult to discern the effects of mergers in the vast majority of dwarfs either photometrically or using resolved-star color-magnitude diagrams (CMDs). The important implication for near-field cosmology is that star formation histories of comparably massive galaxies derived from resolved CMDs should trace the build-up of stellar mass in one main system across cosmic time as opposed to reflecting the contributions of many individual star formation histories of merged dwarfs.

  12. Numerical Analysis on the Free Fall Motion of the Control Rod Assembly for the Sodium Cooled Fast Reactor

    Oh, Se-Hong; Choi, Choengryul; Son, Sung-Man [ELSOLTEC, Yongin (Korea, Republic of); Kim, Jae-Yong; Yoon, Kyung-Ho [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    On receiving the scram signal, the control rod assemblies are released to fall into the reactor core by its weight. Thus drop time and falling velocity of the control rod assembly must be estimated for the safety evaluation. However, because of its complex shape, it is difficult to estimate the drop time by theoretical method. In this study, numerical analysis has been carried out in order to estimate drop time and falling velocity of the control rod assembly to provide the underlying data for the design optimization. Numerical analysis has been carried out to estimate the drop time and falling velocity of the control rod assembly for sodium-cooled fast reactor. Before performing the numerical analysis for the control rod assembly, sphere dropping experiment has been carried out for verification of the CFD methodology. The result of the numerical analysis for the method verification is almost same as the result of the experiment. Falling velocity and drag force increase rapidly in the beginning. And then it goes to the stable state. When the piston head of the control rod assembly is inserted into the damper, the drag force increases instantaneously and the falling velocity decreases quickly. The falling velocity is reduced about 14 % by damper. The total drop time of the control rod assembly is about 1.47s. In the next study, the experiment for the control rod assembly will be carried out, and its result is going to be compared with the CFD analysis result.

  13. Effect of supporting structure stiffness on the drive train assembly of an induced draft cooling tower under seismic effects

    Raghavan, N.; Ramasubramanian, S.; Khan, K.

    2005-01-01

    In a nuclear power project an induced draft cooling tower, as a safety-related structure and part of the main cooling system, has to perform satisfactorily under designated seismic effects. While the structural elements can be designed by conventional methods to ensure adequate safety, the seismic qualification of the mechanical components poses a challenge. The paper describes a methodology adopted for the seismic qualification of a typical Drive Train Assembly for the axial flow fan of an induced draft cooling tower, to ensure the structural integrity and functional operability of the assembly during Operating Base Earthquake and Safe Shutdown Earthquake conditions. This is achieved by performing a detailed finite element analysis of the rotating equipment assembly consisting of the electric motor, gear box and fan along with the drive shaft between the motor and the gear box. The various components are modeled using beam elements, plate elements and spring elements to idealize the flexible connections and supports. The floor response spectra derived from a dynamic analysis of the overall structure under stipulated seismic acceleration spectra are the main excitation inputs into the system. The results validate the adequacy of gaps for movement and the strengths of the couplings and bolts to withstand the applied loads. The assumed modeling and analysis methodology are seen to be acceptable procedures for seismic qualification of important components of the cooling tower. (authors)

  14. Study of a fuel assembly for the nuclear reactor of IV generation cooled with supercritical water

    Barragan M, A.; Martin del Campo M, C.; Francois L, J. L.; Espinosa P, G.

    2011-11-01

    In this work a neutron study is presented about a square assembly design of double line of fuel rods, with moderator box to the center of the arrangement, for a nuclear reactor cooled with supercritical water (SCWR). The SCWR reactor was chosen by the characteristics of its design, mainly because is based in light water reactors (PWR and BWR), and the operational experience that has of them allow to use models and similar programs to simulate the fuel and the nucleus of this type of reactors. To develop the necessary models and to carry out the design and analysis of the SCWR reactor, the neutron codes MCNPX and Helios were used. The reason of using both codes, is because the code MCNPX used thoroughly in the neutron simulation of these reactors, it has been our reference code to analyze the results obtained with the Helios code which results are more efficient because its calculation times are minors. In the nucleus design the same parameters for both codes were considered. The results show that the design with Helios is a viable option to simulate these reactors since their values of the neutrons multiplication factor are very similar to those obtained with MCNPX. On the other hand, it could be corroborated that the CASMO-4 code is inadequate to simulate the fuel to the temperature conditions and water pressure in the SCWR. (Author)

  15. Fertile assembly for a fast neutron nuclear reactor cooled by liquid sodium, with regulation of the cooling rate

    Pradal, L.; Berte, M.; Chiarelli, C.

    1985-01-01

    The assembly has a casing in which are arranged the fertile elements, the liquid sodium flowing through the casing along these elements. It includes several apertured diaphragms transverse to the rods to regulate the liquid sodium flow rate. At least one diaphragm, in its central part around its aperture, of a material soluble in liquid sodium, such as copper. The invention applies, more particularly, to fast neutron nuclear reactor having a heterogeneous core. The coolant flow can increase with time to match the increased power generated by the fertile assembly along its life [fr

  16. Galaxy Mass Assembly with VLT & HST and lessons for E-ELT/MOSAIC

    Hammer, François; Flores, Hector; Puech, Mathieu

    2015-02-01

    The fraction of distant disks and mergers is still debated, while 3D-spectroscopy is revolutionizing the field. However its limited spatial resolution imposes a complimentary HST imagery and a robust analysis procedure. When applied to observations of IMAGES galaxies at z = 0.4-0.8, it reveals that half of the spiral progenitors were in a merger phase, 6 billion year ago. The excellent correspondence between methodologically-based classifications of morphologies and kinematics definitively probes a violent origin of disk galaxies as proposed by Hammer et al. (2005). Examination of nearby galaxy outskirts reveals fossil imprints of such ancient merger events, under the form of well organized stellar streams. Perhaps our neighbor, M31, is the best illustration of an ancient merger, which modeling in 2010 leads to predict the gigantic plane of satellites discovered by Ibata et al. (2013). There are still a lot of discoveries to be done until the ELT era, which will open an avenue for detailed and accurate 3D-spectroscopy of galaxies from the earliest epochs to the present.

  17. Experience from the transportation of irradiated WWER-440 fuel assemblies at the Kozloduy NPP site after a short cooling time

    Stoyanova, I.; Kamenov, A.; Byrzev, L.; Christoskov, I.

    2003-01-01

    Results from the analysis and experimental verification of the radiation and shielding characteristics of non-standard loading patterns of the VSPOT transport cask used for transportation of irradiated fuel assemblies after a short cooling time (120 180 days) on the site of the Kozloduy NPP are presented. An additional safety criterion related to the introduced modifications to the standard procedure of using the transport cask is formulated and discussed (Authors)

  18. Detection of [O III] at z ∼ 3: A Galaxy Above the Main Sequence, Rapidly Assembling Its Stellar Mass

    Vishwas, Amit; Ferkinhoff, Carl; Nikola, Thomas; Parshley, Stephen C.; Schoenwald, Justin P.; Stacey, Gordon J.; Higdon, Sarah J. U.; Higdon, James L.; Weiss, Axel; Güsten, Rolf; Menten, Karl M.

    2018-04-01

    We detect bright emission in the far-infrared (far-IR) fine structure [O III] 88 μm line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z = 3.127, using the second-generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a submillimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of 7.1 × 109 ≤ft(\\tfrac{10}{μ }\\right) L ⊙ likely arises from H II regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of (1.2–5.2) × 106 ≤ft(\\tfrac{10}{μ }\\right) equivalent O5.5 or higher stars, where μ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of ∼2 × 108 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ in ionized gas, that is 0.33% of the estimated total molecular gas mass of 6 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We compile multi-band photometry tracing rest-frame ultraviolet to millimeter continuum emission to further constrain the properties of this dusty high-redshift, star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 ≤ft(\\tfrac{10}{μ }\\right) M ⊙ yr‑1 and already has a stellar mass of 8 × 1010 ≤ft(\\tfrac{10}{μ }\\right) M ⊙. We also constrain the age of the current starburst to be ≤slant 5 Myr, making G12v2.43 a gas-rich galaxy lying above the star-forming main sequence at z ∼ 3, undergoing a growth spurt, and it could be on the main sequence within the derived gas depletion timescale of ∼66 Myr.

  19. The Galaxy Evolution Probe

    Glenn, Jason; Galaxy Evolution Probe Team

    2018-01-01

    The Galaxy Evolution Probe (GEP) is a concept for a far-infrared observatory to survey large regions of sky for star-forming galaxies from z = 0 to beyond z = 3. Our knowledge of galaxy formation is incomplete and requires uniform surveys over a large range of redshifts and environments to accurately describe mass assembly, star formation, supermassive black hole growth, interactions between these processes, and what led to their decline from z ~ 2 to the present day. Infrared observations are sensitive to dusty, star-forming galaxies, which have bright polycyclic aromatic hydrocarbon (PAH) emission features and warm dust continuum in the rest-frame mid infrared and cooler thermal dust emission in the far infrared. Unlike previous far-infrared continuum surveys, the GEP will measure photometric redshifts commensurate with galaxy detections from PAH emission and Si absorption features, without the need for obtaining spectroscopic redshifts of faint counterparts at other wavelengths.The GEP design includes a 2 m diameter telescope actively cooled to 4 K and two instruments: (1) An imager covering 10 to 300 um with 25 spectral resolution R ~ 8 bands (with lower R at the longest wavelengths) to detect star-forming galaxies and measure their redshifts photometrically. (2) A 23 – 190 um, R ~ 250 dispersive spectrometer for redshift confirmation and identification of obscured AGN using atomic fine-structure lines. Lines including [Ne V], [O IV], [O III], [O I], and [C II] will probe gas physical conditions, radiation field hardness, and metallicity. Notionally, the GEP will have a two-year mission: galaxy surveys with photometric redshifts in the first year and a second year devoted to follow-up spectroscopy. A comprehensive picture of star formation in galaxies over the last 10 billion years will be assembled from cosmologically relevant volumes, spanning environments from field galaxies and groups, to protoclusters, to dense galaxy clusters.Commissioned by NASA, the

  20. Drop performance test of conceptually designed control rod assembly for prototype generation IV sodium-cooled fast reactor

    Lee, Young Kyu; Lee, Jae Han; Kim, Hoe Woong; KIm, Sung Kyun; Kim, Jong Bum [Sodium-cooled Fast Reactor NSSS Design Division, Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-06-15

    The control rod assembly controls reactor power by adjusting its position during normal operation and shuts down chain reactions by its free drop under scram conditions. Therefore, the drop performance of the control rod assembly is important for the safety of a nuclear reactor. In this study, the drop performance of the conceptually designed control rod assembly for the prototype generation IV sodium-cooled fast reactor that is being developed at the Korea Atomic Energy Research Institute as a next-generation nuclear reactor was experimentally investigated. For the performance test, the test facility and test procedure were established first, and several free drop performance tests of the control rod assembly under different flow rate conditions were then carried out. Moreover, performance tests under several types and magnitudes of seismic loading conditions were also conducted to investigate the effects of seismic loading on the drop performance of the control rod assembly. The drop time of the conceptually designed control rod assembly for 0% of the tentatively designed flow rate was measured to be 1.527 seconds, and this agrees well with the analytically calculated drop time. It was also observed that the effect of seismic loading on the drop time was not significant.

  1. Experience from transportation of irradiated WWER-440 fuel assemblies at Kozloduy NPP site after a short cooling time

    Stoyanova, I.; Kamenov, A.; Byrzev, L.; Christoskov, I.

    2003-01-01

    The presented results from the computation and analysis of the radiation characteristics of the irradiated fuel assemblies by the date of their transportation according to the selected loading patterns of the VSPOT cask and following the modified technology of transportation, i.e. without replacement of the pool solution by pure condensate, as well as the corresponding experimental results, confirm the applicability of the newly introduced safety criterion for the selection of a loading pattern of the cask with irradiated fuel assemblies after a short cooling time. The comparison between measured and computed surface dose rates shows that during the procedure of transfer of irradiated fuel assemblies from the pools of Units 1 and 2 to the pools of Kozloduy NPP Units 3 and 4 all safety limits, incl. the radiation protection requirements, were met

  2. About calculation results of heat transfer in the fuel assembly clusters cooled by water with supercritical parameters

    Grabezhnaya, V.A.

    2008-01-01

    Paper reviews the numerical investigation into the heat transfer in the supercritical water cooled fuel assemblies on the basis of the various commercial codes. The turbulence available models specified in the codes describe adequately the experimental data in tubes within the range of flow temperatures away from the pseudocritical point, as well as under high mass velocities. There are k-ε type turbulence models that show qualitatively the local acceleration (slowdown) of the heat transfer in tubes, but they fail to describe the mentioned phenomena quantitatively. To determine the effect of grid spacers on the suppression of the heat transfer local slowdown and on the heat transfer acceleration in fuel assemblies and to ensure more accurate calculation of the fuel element cladding maximum temperature one should perform a number of the experiments making use of the fuel assembly models [ru

  3. Development and characterization of the control assembly system for the large 2400 MWth Generation IV gas-cooled fast reactor

    Girardin, G.; Rimpault, G.; Morin, F.; Bosq, J.C.; Coddington, P.; Mikityuk, K.; Chawla, R.

    2008-01-01

    The present paper is related to the design and neutronic characterization of the principal control assembly system for the reference large (2400 MWth) Generation IV gas-cooled fast reactor (GFR), which makes use of ceramic-ceramic (CERCER) plate-type fuel-elements with (U-Pu) carbide fuel contained within a SiC inert matrix. For the neutronic calculations, the deterministic code system ERANOS-2.0 has been used, in association with a full core model including a European fast reactor (EFR)-type pattern for the control assemblies as a starting point. More specifically, the core contains a total of 33 control (control system device: CSD) and safety (diverse safety device: DSD) assemblies implemented in three banks. In the design of the new control assembly system, particular attention was given to the heat generation within the assemblies, so that both neutronic and thermal-hydraulic constraints could be appropriately accounted for. The thermal-hydraulic calculations have been performed with the code COPERNIC, significant coolant mass flow rates being found necessary to maintain acceptable cladding temperatures of the absorber pins. Complementary to the design study, neutronic investigations have been performed to assess the impact of the control assemblies in the GFR core in greater detail (rod interactions, shift of the flux, peaking factors, etc.). Thus, considerable shadowing effects have been observed between the first bank and the safety bank, as also between individual assemblies within the first bank. Large anti-shadowing effects also occur, the most prominent being that between the two CSD banks, where the total assembly worth is almost doubled in comparison to the sum of the individual values. Additional investigations have been performed and, in this context, it has been found that computation of the first-order eigenvalue and the eigenvalue separation is a robust tool to anticipate control assembly interactions in a large fast-spectrum core. One interesting

  4. ZOMG - II. Does the halo assembly history influence central galaxies and gas accretion?

    Romano-Díaz, Emilio; Garaldi, Enrico; Borzyszkowski, Mikolaj; Porciani, Cristiano

    2017-08-01

    The growth rate and the internal dynamics of galaxy-sized dark-matter haloes depend on their location within the cosmic web. Haloes that sit at the nodes grow in mass till the present time and are dominated by radial orbits. Conversely, haloes embedded in prominent filaments do not change much in size and are dominated by tangential orbits. Using zoom hydrodynamical simulations including star formation and feedback, we study how gas accretes on to these different classes of objects, which, for simplicity, we dub 'accreting' and 'stalled' haloes. We find that all haloes get a fresh supply of newly accreted gas in their inner regions, although this slowly decreases with time, in particular for the stalled haloes. The inflow of new gas is always higher than (but comparable with) that of recycled material. Overall, the cold-gas fraction increases (decreases) with time for the accreting (stalled) haloes. In all cases, a stellar disc and a bulge form at the centre of the simulated haloes. The total stellar mass is in excellent agreement with expectations based on the abundance-matching technique. Many properties of the central galaxies do not seem to correlate with the large-scale environment in which the haloes reside. However, there are two notable exceptions that characterize stalled haloes with respect to their accreting counterparts: (I) The galaxy disc contains much older stellar populations. (II) Its vertical scaleheight is larger by a factor of 2 or more. This thickening is likely due to the heating of the long-lived discs by mergers and close flybys.

  5. Critical Current and Stability of MgB$_2$ Twisted-Pair DC Cable Assembly Cooled by Helium Gas

    AUTHOR|(CDS)2069632; Ballarino, Amalia; Yang, Yifeng; Young, Edward Andrew; Bailey, Wendell; Beduz, Carlo

    2013-01-01

    Long length superconducting cables/bus-bars cooled by cryogenic gases such as helium operating over a wider temperature range are a challenging but exciting technical development prospects, with applications ranging from super-grid transmission to future accelerator systems. With limited existing knowledge and previous experiences, the cryogenic stability and quench protection of such cables are crucial research areas because the heat transfer is reduced and temperature gradient increased compared to liquid cryogen cooled cables. V-I measurements on gas-cooled cables over a significant length are an essential step towards a fully cryogenic stabilized cable with adequate quench protection. Prototype twisted-pair cables using high-temperature superconductor and MgB2 tapes have been under development at CERN within the FP7 EuCARD project. Experimental studies have been carried out on a 5-m-long multiple MgB$_2$ cable assembly at different temperatures between 20 and 30 K. The subcables of the assembly showed sim...

  6. A VLT Large Programme to Study Galaxies at z ~ 2: GMASS — the Galaxy Mass Assembly Ultra-deep Spectroscopic Survey

    Kurk, Jaron; Cimatti, Andrea; Daddi, Emanuele; Mignoli, Marco; Bolzonella, Micol; Pozzetti, Lucia; Cassata, Paolo; Halliday, Claire; Zamorani, Gianni; Berta, Stefano; Brusa, Marcella; Dickinson, Mark; Franceschini, Alberto; Rodighiero, Guilia; Rosati, Piero; Renzini, Alvio

    2009-03-01

    We report on the motivation, sample selection and first results of our VLT FORS2 Large Programme (173.A-0687), which has obtained the longest targeted spectra of distant galaxies obtained so far with the VLT. These long exposures, up to 77 hours for objects included in three masks, were required to detect spectral features of extremely faint galaxies, such as absorption lines of passive galaxies at z > 1.4, a population that had previously escaped attention due to its faintness in the optical wavelength regime, but which represents a critical phase in the evolution of massive galaxies. The ultra-deep spectroscopy allowed us to estimate the stellar metallicity of star-forming galaxies at z ~ 2, to trace colour bimodality up to z = 2 and to characterise a galaxy cluster progenitor at z = 1.6. The approximately 200 spectra produced by GMASS constitute a lasting legacy, populating the “redshift desert” in GOODS-S.

  7. Nondestructive determination of burnup and fissile isotope balance in spent fuel assemblies of water cooled reactors

    Pinel, J.

    1983-03-01

    Two non-destructive methods for measuring fuel assemblies in storage pools have been developed: a gamma fuel scanning method, using the 134 Cs - 137 Cs and 144 Ce gamma rays, and the measurement of the neutron flux emitted by the fuel assembly. For interpreting the measurement, we have used calculated correlations to establish a connection between the measured phenomena and the parameters to be determined. A measurement campaign involving 58 assemblies from the C.N.A. reactor was conducted in the reprocessing plant of LA HAGUE. The results obtained show that the objectives can be achevied within an industrial environment [fr

  8. The COSMOS2015 galaxy stellar mass function . Thirteen billion years of stellar mass assembly in ten snapshots

    Davidzon, I.; Ilbert, O.; Laigle, C.; Coupon, J.; McCracken, H. J.; Delvecchio, I.; Masters, D.; Capak, P.; Hsieh, B. C.; Le Fèvre, O.; Tresse, L.; Bethermin, M.; Chang, Y.-Y.; Faisst, A. L.; Le Floc'h, E.; Steinhardt, C.; Toft, S.; Aussel, H.; Dubois, C.; Hasinger, G.; Salvato, M.; Sanders, D. B.; Scoville, N.; Silverman, J. D.

    2017-09-01

    We measure the stellar mass function (SMF) and stellar mass density of galaxies in the COSMOS field up to z 6. We select them in the near-IR bands of the COSMOS2015 catalogue, which includes ultra-deep photometry from UltraVISTA-DR2, SPLASH, and Subaru/Hyper Suprime-Cam. At z> 2.5 we use new precise photometric redshifts with error σz = 0.03(1 + z) and an outlier fraction of 12%, estimated by means of the unique spectroscopic sample of COSMOS ( 100 000 spectroscopic measurements in total, more than one thousand having robust zspec> 2.5). The increased exposure time in the DR2, along with our panchromatic detection strategy, allow us to improve the completeness at high z with respect to previous UltraVISTA catalogues (e.g. our sample is >75% complete at 1010 ℳ⊙ and z = 5). We also identify passive galaxies through a robust colour-colour selection, extending their SMF estimate up to z = 4. Our work provides a comprehensive view of galaxy-stellar-mass assembly between z = 0.1 and 6, for the first time using consistent estimates across the entire redshift range. We fit these measurements with a Schechter function, correcting for Eddington bias. We compare the SMF fit with the halo mass function predicted from ΛCDM simulations, finding that at z> 3 both functions decline with a similar slope in thehigh-mass end. This feature could be explained assuming that mechanisms quenching star formation in massive haloes become less effective at high redshifts; however further work needs to be done to confirm this scenario. Concerning the SMF low-mass end, it shows a progressive steepening as it moves towards higher redshifts, with α decreasing from -1.47+0.02-0.02 at z ≃ 0.1 to -2.11+0.30-0.13 at z ≃ 5. This slope depends on the characterisation of the observational uncertainties, which is crucial to properly remove the Eddington bias. We show that there is currently no consensus on the method to quantify such errors: different error models result in different best

  9. Thermal-hydraulic study of the LBE-cooled fuel assembly in the MYRRHA reactor: Experiments and simulations

    Pacio, J., E-mail: Julio.pacio@kit.edu [Karlsruhe Institute of Technology (KIT), Institute for Nuclear and Energy Technologies (IKET), Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Wetzel, T. [Karlsruhe Institute of Technology (KIT), Institute for Nuclear and Energy Technologies (IKET), Hermann-von-Helmholtz Platz 1, 76344 Eggenstein-Leopoldshafen (Germany); Doolaard, H.; Roelofs, F. [Nuclear Research and Consultancy Group (NRG), Westerduinweg 3, 1755 ZG Petten (Netherlands); Van Tichelen, K. [Belgian Nuclear Reseach Center (SCK-CEN), Boeretang 200, Mol (Belgium)

    2017-02-15

    Heavy liquid metals (HLMs), such as lead-bismuth eutectic (LBE) and pure lead are prominent candidate coolants for many advanced systems based on fast neutrons. In particular, LBE is used in the first-of-its-kind MYRRHA fast reactor, to be built in Mol (Belgium), which can be operated either in critical mode or as a sub-critical accelerator-driven system. With a strong focus on safety, key thermal-hydraulic aspects of these systems, such as the proper cooling of fuel assemblies, must be assessed. Considering the complex geometry and low Prandtl number of LBE (Pr ∼ 0.025), this flow scenario is challenging for the models used in Computational Fluid Dynamics (CFD), e.g. for relating the turbulent transport of momentum and heat. Thus, reliable experimental data for the relevant scenario are needed for validation. In this general context, this topic is studied both experimentally and numerically in the framework of the European FP7 project SEARCH (2011–2015). An experimental campaign, including a 19-rod bundle with wire spacers, cooled by LBE is undertaken at KIT. With prototypical geometry and operating conditions, it is intended to evaluate the validity of current empirical correlations for the MYRRHA conditions and, at the same time, to provide validation data for the CFD simulations performed at NRG. The results of one benchmarking case are presented in this work. Moreover, this validated approach is then used for simulating a complete MYRRHA fuel assembly (127 rods).

  10. Investigation of cooling methods and thickness considerations in the filter/window assembly for synchrotron radiation beamlines

    Wang, Z.; Kuzay, T.M.; Hahn, U.

    1993-01-01

    Synchrotron x-ray windows are vacuum separators and are usually made of thin beryllium metal. Filters are provided upstream to absorb the soft x-rays so that the window can be protected from overheating, which could result in failure. The filters are made of thin carbon products or sometimes beryllium, the same material as the window. When the synchrotron x-rays pass through a filter or window, part of the photons will be absorbed by the filter or window. The absorbed photons cause heat to build up within the filter or window. Successful filter and window designs should effectively dissipate the heat generated by the absorbed photons and guarantee the safety of the filter and window. The cooling methods typically used in a filter or window design are conduction and radiation cooling or a combination of the two. The different cooling methods were first examined with regard to efficiency and effectiveness in different temperature ranges. Analysis results are presented for temperature distribution and corresponding thermal stresses in the filter and window. Another important issue to be resolved in designing a filter/window assembly is how to select the thickness of the filters and windows. This paper focuses on the criteria for choosing the thickness of a filter: whether it is better to use a few thick filters or a series of thin ones; how to determine the minimum/maximum thickness; and the difference in thickness considerations for the window versus the filter. Numerical investigations are presented

  11. The Greater Impact of Mergers on the Growth of Massive Galaxies: Implications for Mass Assembly and Evolution since z sime 1

    Bundy, Kevin; Fukugita, Masataka; Ellis, Richard S.; Targett, Thomas A.; Belli, Sirio; Kodama, Tadayuki

    2009-06-01

    Using deep infrared observations conducted with the MOIRCS imager on the Subaru Telescope in the northern GOODS field combined with public surveys in GOODS-S, we investigate the dependence on stellar mass, M *, and galaxy type of the close pair fraction (5 h -1 kpc implied merger rate. In terms of combined depth and survey area, our publicly available mass-limited sample represents a significant improvement over earlier infrared surveys used for this purpose. In common with some recent studies, we find that the fraction of paired systems that could result in major mergers is low (~4%) and does not increase significantly with redshift to z ≈ 1.2, with vprop(1 + z)1.6±1.6. Our key finding is that massive galaxies with M *>1011 M sun are more likely to host merging companions than less massive systems (M * ~ 1010 M sun). We find evidence for a higher pair fraction for red, spheroidal hosts compared to blue, late-type systems, in line with expectations based on clustering at small scales. The so-called "dry" mergers between early-type galaxies devoid of star formation (SF) represent nearly 50% of close pairs with M *>3 × 1010 M sun at z ~ 0.5, but less than 30% at z ~ 1. This result can be explained by the increasing abundance of red, early-type galaxies at these masses. We compare the volumetric merger rate of galaxies with different masses to mass-dependent trends in galaxy evolution. Our results reaffirm the conclusion of Bundy et al. that major mergers do not fully account for the formation of spheroidal galaxies since z ~ 1. In terms of mass assembly, major mergers contribute little to galaxy growth below M * ~ 3 × 1010 M sun but play a more significant role among galaxies with M * gsim 1011 M sun ~ 30% of which have undergone mostly dry mergers over the observed redshift range. Overall, the relatively rapid and recent coalescence of high-mass galaxies mirrors the expected hierarchical growth of halos and is consistent with recent model predictions, even if

  12. Optimization of the fuel assembly for the Canadian Supercritical Water-cooled Reactor (SCWR)

    French, C.; Bonin, H.; Chan, P., E-mail: Corey.French@rmc.ca [Royal Military College of Canada, Dept. of Chemistry and Chemical Engineering, Kingston, Ontario (Canada)

    2013-07-01

    A parametric optimization of the Canadian Supercritical Water-cooled Reactor (SCWR) lattice geometry and fresh fuel content is performed in this work. With the potential to improve core physics and performance, significant gains to operating and safety margins could be achieved through slight progressions. The fuel performance codes WIMS-AECL and SERPENT are used to calculate performance factors, and use them as inputs to an optimization algorithm. (author)

  13. Change On The S-Z Effect Induced By The Cooling Flow CF On The Hot Electronic Gas At The Center OF The Clusters Of Galaxies

    Enkelejd Caca

    2015-06-01

    Full Text Available ABSTRACT Building more accurate profiles for temperature and density of hot electronic gas concentrated in the center of clusters of galaxies is a constant problem in survey of Sunyeav Zeldovich effect SZ. An effect that consists in the inverse Compton effect of the hot electronic gas interacting with Cosmic Microwave Back- ground CMB photons passing through Intra Cluster Medium ICM. So far the Isothermal model is used for temperature profiling in the calculation of the inverse Compton effect but based on the recent improved observations from satellites which showed that the hot electronic gas presents a feature called Cooling Flow CF. Temperatures in this model differs towards the edges of the Clusters of Galaxies leading to a change on the Compton parameter in comparison with Isothermal model. In this paper are processed data provided by X-ray satellite Chandra. The X-ray analysis is based on two models for the electron density and temperature profile. A sample of 12 clusters of galaxies are analyzed and by building the temperature profiles using CF model the differences on the Compton parameter are 10-100 in comparison with Isothermal model. Therefore to increase the accuracy of evaluation of the Compton parameter we should take into account the change of the electronic gas tempera- ture change that affect changes in both CMB spectrum and temperature from SZ effect.

  14. Exploring the luminosity evolution and stellar mass assembly of 2SLAQ luminous red galaxies between redshifts 0.4 and 0.8

    Banerji, Manda; Ferreras, Ignacio; Abdalla, Filipe B.; Hewett, Paul; Lahav, Ofer

    2010-03-01

    We present an analysis of the evolution of 8625 luminous red galaxies (LRGs) between z = 0.4 and 0.8 in the 2dF and Sloan Digital Sky Survey LRG and QSO (2SLAQ) survey. The LRGs are split into redshift bins and the evolution of both the luminosity and stellar mass function with redshift is considered and compared to the assumptions of a passive evolution scenario. We draw attention to several sources of systematic error that could bias the evolutionary predictions made in this paper. While the inferred evolution is found to be relatively unaffected by the exact choice of spectral evolution model used to compute K + e corrections, we conclude that photometric errors could be a source of significant bias in colour-selected samples such as this, in particular when using parametric maximum likelihood based estimators. We find that the evolution of the most massive LRGs is consistent with the assumptions of passive evolution and that the stellar mass assembly of the LRGs is largely complete by z ~ 0.8. Our findings suggest that massive galaxies with stellar masses above 1011Msolar must have undergone merging and star formation processes at a very early stage (z >~ 1). This supports the emerging picture of downsizing in both the star formation as well as the mass assembly of early-type galaxies. Given that our spectroscopic sample covers an unprecedentedly large volume and probes the most massive end of the galaxy mass function, we find that these observational results present a significant challenge for many current models of galaxy formation.

  15. QUASARS PROBING QUASARS. VIII. THE PHYSICAL PROPERTIES OF THE COOL CIRCUMGALACTIC MEDIUM SURROUNDING z ∼ 2–3 MASSIVE GALAXIES HOSTING QUASARS

    Lau, Marie Wingyee; Prochaska, J. Xavier [Department of Astronomy and Astrophysics, UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States); Hennawi, Joseph F., E-mail: lwymarie@ucolick.org [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69115 Heidelberg (Germany)

    2016-10-01

    We characterize the physical properties of the cool T  ∼ 10{sup 4} K circumgalactic medium (CGM) surrounding z  ∼ 2–3 quasar host galaxies, which are predicted to evolve into present-day massive ellipticals. Using a statistical sample of 14 quasar pairs with projected separation <300 kpc and spectra of high dispersion and high signal-to-noise ratio, we find extreme kinematics with low metal ion lines typically spanning ≈500 km s{sup −1}, exceeding any previously studied galactic population. The CGM is significantly enriched, even beyond the virial radius, with a median metallicity [M/H] ≈ −0.6. The α /Fe abundance ratio is enhanced, suggesting that halo gas is primarily enriched by core-collapse supernovae. The projected cool gas mass within the virial radius is estimated to be 1.9 × 10{sup 11} M {sub ⊙} ( R {sub ⊥}/160 kpc){sup 2}, accounting for ≈1/3 of the baryonic budget of the galaxy halo. The ionization state of CGM gas increases with projected distance from the foreground quasars, contrary to expectation if the quasar dominates the ionizing radiation flux. However, we also found peculiarities not exhibited in the CGM of other galaxy populations. In one absorption system, we may be detecting unresolved fluorescent Ly α emission, and another system shows strong N v lines. Taken together, these anomalies suggest that transverse sightlines are—at least in some cases—possibly illuminated. We also discovered a peculiar case where detection of the C ii fine-structure line implies an electron density >100 cm{sup −3} and sub-parsec-scale gas clumps.

  16. Integrity Evaluation of Control Rod Assembly for Sodium-Cooled Fast Reactor due to Drop Impact

    Lee, Hyun Seung; Yoon, Kyung Ho; Kim, Hyung Kyu; Cheon, Jin Sik; Lee, Chan Bock [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2017-03-15

    The CA (Control Assembly) of an SFR has a CRA(Control Rod Assembly) with an inner duct and control rod. During an emergency situation, the CRA falls into the duct of the CA for a rapid shut-down. The drop time and impact velocity of the CRA are important parameters with respect to the reactivity insertion time and the structural integrity of the CRA. The objective of this study was to investigate the dynamic behavior and integrity of the CRA owing to a drop impact. The impact analysis of the CRA under normal/abnormal drop conditions was carried out using the commercial FEM code LS-DYNA. Results of the drop impact analysis demonstrated that the CRA maintained structural integrity, and could be safely inserted into the flow hole of the damper under abnormal conditions.

  17. Integrity Evaluation of Control Rod Assembly for Sodium-Cooled Fast Reactor due to Drop Impact

    Lee, Hyun Seung; Yoon, Kyung Ho; Kim, Hyung Kyu; Cheon, Jin Sik; Lee, Chan Bock

    2017-01-01

    The CA (Control Assembly) of an SFR has a CRA(Control Rod Assembly) with an inner duct and control rod. During an emergency situation, the CRA falls into the duct of the CA for a rapid shut-down. The drop time and impact velocity of the CRA are important parameters with respect to the reactivity insertion time and the structural integrity of the CRA. The objective of this study was to investigate the dynamic behavior and integrity of the CRA owing to a drop impact. The impact analysis of the CRA under normal/abnormal drop conditions was carried out using the commercial FEM code LS-DYNA. Results of the drop impact analysis demonstrated that the CRA maintained structural integrity, and could be safely inserted into the flow hole of the damper under abnormal conditions.

  18. SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). II. COOL EVOLVED STARS

    Boyer, Martha L.; Meixner, Margaret; Gordon, Karl D.; Shiao, Bernie; Srinivasan, Sundar; Van Loon, Jacco Th.; McDonald, Iain; Kemper, F.; Zaritsky, Dennis; Block, Miwa; Engelbracht, Charles W.; Misselt, Karl; Babler, Brian; Bracker, Steve; Meade, Marilyn; Whitney, Barbara; Hora, Joe; Robitaille, Thomas; Indebetouw, Remy; Sewilo, Marta

    2011-01-01

    We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled 'Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC', or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 μm). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ∼20% of the global SMC flux (extended + point-source) at 3.6 μm, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] - [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC.

  19. CONSTRAINTS ON THE ASSEMBLY AND DYNAMICS OF GALAXIES. I. DETAILED REST-FRAME OPTICAL MORPHOLOGIES ON KILOPARSEC SCALE OF z ∼ 2 STAR-FORMING GALAXIES

    Foerster Schreiber, N. M.; Genzel, R.; Davies, R.; Shapley, A. E.; Erb, D. K.; Bouche, N.; Steidel, C. C.; Cresci, G.

    2011-01-01

    We present deep and high-resolution Hubble Space Telescope NIC2 F160W imaging at 1.6 μm of six z ∼ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n e ∼ 5 kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), multiplicity (Ψ), and M 20 coefficients. The estimated strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Hα emission reveal no significant differences, suggesting similar global distributions of the ongoing star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z ∼ 2 galaxy types (K-selected quiescent, active galactic nucleus, and star forming; 24 μm selected dusty, infrared-luminous) indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z ∼ 2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Ψ and M 20 . The combined NIC2 and SINFONI data set yields insights of unprecedented detail into the nature of mass accretion at high redshift.

  20. Enormous Disc of Cool Gas Surrounding the Nearby Powerful Radio Galaxy NGC 612 (PKS 0131-36)

    2008-05-22

    galaxies in clus- ters appear to be much more devoid of H I gas, as sug- gested by a recent H I survey of the VIRGO cluster by di Serego Alighieri et...120th Street, New York, N.Y. 10027, USA 2Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, the Netherlands 3Kapteyn...NGC 612. This paper is part of an ongoing study to map the large-scale neutral hydrogen properties of nearby radio galaxies and it presents the first

  1. INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS

    Bird, Jonathan C.; Kazantzidis, Stelios; Weinberg, David H. [Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States); Guedes, Javiera [Institute for Astronomy, ETH Zuerich, Wolgang-Pauli-Strasse 27, CH-8093 Zuerich (Switzerland); Callegari, Simone [Anthropology Institute and Museum, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Mayer, Lucio [Institute for Theoretical Physics, University of Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland); Madau, Piero [Department of Astronomy and Astrophysics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2013-08-10

    We analyze the present day structure and assembly history of a high-resolution hydrodynamic simulation of the formation of a Milky-Way-(MW)-like disk galaxy, from the ''Eris'' simulation suite, dissecting it into cohorts of stars formed at different epochs of cosmic history. At z = 0, stars with t{sub form} < 2 Gyr mainly occupy the stellar spheroid, with the oldest (earliest forming) stars having more centrally concentrated profiles. The younger age cohorts populate disks of progressively longer radial scale lengths and shorter vertical scale heights. At a given radius, the vertical density profiles and velocity dispersions of stars vary smoothly as a function of age, and the superposition of old, vertically extended and young, vertically compact cohorts gives rise to a double-exponential profile like that observed in the MW. Turning to formation history, we find that the trends of spatial structure and kinematics with stellar age are largely imprinted at birth, or immediately thereafter. Stars that form during the active merger phase at z > 3 are quickly scattered into rounded, kinematically hot configurations. The oldest disk cohorts form in structures that are radially compact and relatively thick, while subsequent cohorts form in progressively larger, thinner, colder configurations from gas with increasing levels of rotational support. The disk thus forms ''inside out'' in a radial sense and ''upside down'' in a vertical sense. Secular heating and radial migration influence the final state of each age cohort, but the changes they produce are small compared to the trends established at formation. The predicted correlations of stellar age with spatial and kinematic structure are in good qualitative agreement with the correlations observed for mono-abundance stellar populations in the MW.

  2. Structural behaviour of fuel assemblies for water cooled reactors. Proceedings of a technical meeting

    2005-07-01

    At the invitation of the Government of France and in response to a proposal of the IAEA Technical Working Group on Water Reactor Fuel Performance and Technology (TWGFPT), the IAEA convened a Technical Meeting on Fuel Assembly Structural Behaviour in Cadarache, France, from 22 to 26 November 2004. The meeting was hosted by the CEA Cadarache Centre, AREVA Framatome-ANP and Electricite de France. The meeting aimed to provide in depth technical exchanges on PWR and WWER operational experience in the field of fuel assembly mechanical behaviour and the potential impact of future high burnup fuel management on fuel reliability. It addressed in-service experience and remedial solutions, loop testing experience, qualification and damage assessment methods (analytic or experimental ones), mechanical behaviour of the fuel assembly including dynamic and fluid structure interaction aspects, modelling and numerical analysis methods, and impact of the in-service evolution of the structural materials. Sixty-seven participants from 17 countries presented 30 papers in the course of four sessions. The topics covered included the impact of hydraulic loadings on fuel assembly (FA)performance, FA bow and control rod (CR) drop kinetics, vibrations and rod-to-grid wear and fretting, and, finally, evaluation and modelling of accident conditions, mainly from seismic causes. FA bow, CR drop kinetics and hydraulics are of great importance under conditions of higher fuel duties including burnup increase, thermal uprates and longer fuel cycles. Vibrations and rod-to-grid wear and fretting have been identified as a key cause of fuel failure at PWRs during the past several years. The meeting demonstrated that full-scale hydraulic tests and modelling provide sufficient information to develop remedies to increase FA skeleton resistance to hydraulic loads, including seismic ones, vibrations and wear. These proceedings are presented as a book with an attached CD-ROM. The first part of the CD

  3. The ACS LCID Project: On the Origin of Dwarf Galaxy Types—A Manifestation of the Halo Assembly Bias?

    Gallart, Carme; Monelli, Matteo; Mayer, Lucio; Aparicio, Antonio; Battaglia, Giuseppina; Bernard, Edouard J.; Cassisi, Santi; Cole, Andrew A.; Dolphin, Andrew E.; Drozdovsky, Igor; Hidalgo, Sebastian L.; Navarro, Julio F.; Salvadori, Stefania; Skillman, Evan D.; Stetson, Peter B.; Weisz, Daniel R.

    2015-01-01

    We discuss how knowledge of the whole evolutionary history of dwarf galaxies, including details on the early star formation events, can provide insight on the origin of the different dwarf galaxy types. We suggest that these types may be imprinted by the early conditions of formation rather than

  4. Engine piston assembly and forged piston member therefor having a cooling recess

    Cooper, B.C.; Erickson, K.L.; Green, J.A.; Nyez, D.S.

    1989-09-19

    This patent describes a forged steel piston member for reciprocating movement in an engine. It comprises: an upper portion of substantially cylindrical shape and having a central axis, a top surface, a tubular wall depending from the top surface and having a peripheral groove adapted to receive a sealing ring, a lower end surface, and an inwardly facing wall surface extending upwardly from the lower end surface. The upper portion further includes an outwardly facing wall surface spaced radially inwardly from the inwardly facing wall surface and a downwardly facing transition portion blendingly associated with the inwardly and outwardly facing wall surfaces to collectively define an annular cooling recess, the transition portion being elevational spaced a relatively short distance from the top surface; and the inwardly facing wall surface being a machined surface of revolution about the central axis integral or one-piece forging.

  5. MELCOR Modeling of Air-Cooled PWR Spent Fuel Assemblies in Water empty Fuel Pools

    Herranz, L. E.; Lopez, C.

    2013-07-01

    The OECD Spent Fuel Project (SFP) investigated fuel degradation in case of a complete Loss-Of- Coolant-Accident in a PWR spent fuel pool. Analyses of the SFP PWR ignition tests have been conducted with the 1.86.YT.3084.SFP MELCOR version developed by SNL. The main emphasis has been placed on assessing the MELCOR predictive capability to get reasonable estimates of time-to-ignition and fire front propagation under two configurations: hot neighbor (i.e., adiabatic scenario) and cold neighbor (i.e., heat transfer to adjacent fuel assemblies). A detailed description of hypotheses and approximations adopted in the MELCOR model are provided in the paper. MELCOR results accuracy was notably different between both scenarios. The reasons are highlighted in the paper and based on the results understanding a set of remarks concerning scenarios modeling is given.

  6. Configurable double-sided modular jet impingement assemblies for electronics cooling

    Zhou, Feng; Dede, Ercan Mehmet

    2018-05-22

    A modular jet impingement assembly includes an inlet tube fluidly coupled to a fluid inlet, an outlet tube fluidly coupled to a fluid outlet, and a modular manifold having a first distribution recess extending into a first side of the modular manifold, a second distribution recess extending into a second side of the modular manifold, a plurality of inlet connection tubes positioned at an inlet end of the modular manifold, and a plurality of outlet connection tubes positioned at an outlet end of the modular manifold. A first manifold insert is removably positioned within the first distribution recess, a second manifold insert is removably positioned within the second distribution recess, and a first and second heat transfer plate each removably coupled to the modular manifold. The first and second heat transfer plates each comprise an impingement surface.

  7. LUMINOUS AND HIGH STELLAR MASS CANDIDATE GALAXIES AT z ≈ 8 DISCOVERED IN THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY

    Yan Haojing; Finkelstein, Steven L.; Huang, Kuang-Han; Ryan, Russell E.; Ferguson, Henry C.; Koekemoer, Anton M.; Grogin, Norman A.; Dickinson, Mark; Newman, Jeffrey A.; Somerville, Rachel S.; Davé, Romeel; Faber, S. M.; Papovich, Casey; Guo Yicheng; Giavalisco, Mauro; Lee, Kyoung-soo; Reddy, Naveen; Siana, Brian D.; Cooray, Asantha R.; Hathi, Nimish P.

    2012-01-01

    One key goal of the Hubble Space Telescope Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey is to track galaxy evolution back to z ≈ 8. Its two-tiered ''wide and deep'' strategy bridges significant gaps in existing near-infrared surveys. Here we report on z ≈ 8 galaxy candidates selected as F105W-band dropouts in one of its deep fields, which covers 50.1 arcmin 2 to 4 ks depth in each of three near-infrared bands in the Great Observatories Origins Deep Survey southern field. Two of our candidates have J 1 mag brighter than any previously known F105W-dropouts. We derive constraints on the bright end of the rest-frame ultraviolet luminosity function of galaxies at z ≈ 8, and show that the number density of such very bright objects is higher than expected from the previous Schechter luminosity function estimates at this redshift. Another two candidates are securely detected in Spitzer Infrared Array Camera images, which are the first such individual detections at z ≈ 8. Their derived stellar masses are on the order of a few × 10 9 M ☉ , from which we obtain the first measurement of the high-mass end of the galaxy stellar mass function at z ≈ 8. The high number density of very luminous and very massive galaxies at z ≈ 8, if real, could imply a large stellar-to-halo mass ratio and an efficient conversion of baryons to stars at such an early time.

  8. DETECTION OF OUTFLOWING AND EXTRAPLANAR GAS IN DISKS IN AN ASSEMBLING GALAXY CLUSTER AT z = 0.37

    Freeland, Emily; Tran, Kim-Vy H.; Irwin, Trevor; Giordano, Lea; Saintonge, Amélie; Gonzalez, Anthony H.; Zaritsky, Dennis; Just, Dennis

    2011-01-01

    We detect ionized gas characteristics indicative of winds in three disk-dominated galaxies that are members of a super-group at z = 0.37 that will merge to form a Coma-mass cluster. All three galaxies are IR luminous (L IR > 4 × 10 10 L ☉ , SFR > 8 M ☉ yr –1 ) and lie outside the X-ray cores of the galaxy groups. We find that the most IR-luminous galaxy has strong blueshifted and redshifted emission lines with velocities of ∼ ± 200 km s –1 and a third, blueshifted (∼900 km s –1 ) component. This galaxy's line widths (Hβ, [O III]λ5007, [N II], Hα) correspond to velocities of 100-1000 km s –1 . We detect extraplanar gas in two of the three galaxies with SFR >8 M ☉ yr –1 whose orientations are approximately edge-on and which have integral field unit (IFU) spaxels off the stellar disk. IFU maps reveal that the extraplanar gas extends to r h ∼ 10 kpc; [N II] and Hα line widths correspond to velocities of ∼200-400 km s –1 in the disk and decrease to ∼50-150 km s –1 above the disk. Multi-wavelength observations indicate that the emission is dominated by star formation. Including the most IR-luminous galaxy we find that 18% of supergroup members with SFR >8 M ☉ yr –1 show ionized gas characteristics indicative of outflows. This is a lower limit as showing that gas is outflowing in the remaining, moderately inclined, galaxies requires a non-trivial decoupling of contributions to the emission lines from rotational and turbulent motion. Ionized gas mass loss in these winds is ∼0.1 M ☉ yr –1 for each galaxy, although the winds are likely to entrain significantly larger amounts of mass in neutral and molecular gases.

  9. SUB-KILOPARSEC IMAGING OF COOL MOLECULAR GAS IN TWO STRONGLY LENSED DUSTY, STAR-FORMING GALAXIES

    Spilker, J. S.; Marrone, D. P. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Aravena, M. [Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile); Béthermin, M.; Breuck, C. de [European Southern Observatory, Karl Schwarzschild Straße 2, D-85748 Garching (Germany); Bothwell, M. S. [Cavendish Laboratory, University of Cambridge, JJ Thompson Ave, Cambridge CB3 0HA (United Kingdom); Carlstrom, J. E. [Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Chapman, S. C.; Rotermund, K. M. [Dalhousie University, Halifax, Nova Scotia (Canada); Collier, J. D.; Galvin, T.; Grieve, K.; O’Brien, A. [University of Western Sydney, Locked Bag 1797, Penrith, NSW 2751 (Australia); Fassnacht, C. D. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Gonzalez, A. H.; Ma, J. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); González-López, J. [Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago (Chile); Hezaveh, Y. [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305 (United States); Malkan, M., E-mail: jspilker@as.arizona.edu [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States); and others

    2015-10-01

    We present spatially resolved imaging obtained with the Australia Telescope Compact Array (ATCA) of three CO lines in two high-redshift gravitationally lensed dusty star-forming galaxies, discovered by the South Pole Telescope. Strong lensing allows us to probe the structure and dynamics of the molecular gas in these two objects, at z = 2.78 and z = 5.66, with effective source-plane resolution of less than 1 kpc. We model the lensed emission from multiple CO transitions and the dust continuum in a consistent manner, finding that the cold molecular gas as traced by low-J CO always has a larger half-light radius than the 870 μm dust continuum emission. This size difference leads to up to 50% differences in the magnification factor for the cold gas compared to dust. In the z = 2.78 galaxy, these CO observations confirm that the background source is undergoing a major merger, while the velocity field of the other source is more complex. We use the ATCA CO observations and comparable resolution Atacama Large Millimeter/submillimeter Array dust continuum imaging of the same objects to constrain the CO–H{sub 2} conversion factor with three different procedures, finding good agreement between the methods and values consistent with those found for rapidly star-forming systems. We discuss these galaxies in the context of the star formation—gas mass surface density relation, noting that the change in emitting area with observed CO transition must be accounted for when comparing high-redshift galaxies to their lower redshift counterparts.

  10. EVOLUTION IN THE H I GAS CONTENT OF GALAXY GROUPS: PRE-PROCESSING AND MASS ASSEMBLY IN THE CURRENT EPOCH

    Hess, Kelley M. [Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Rondebosch 7701 (South Africa); Wilcots, Eric M., E-mail: hess@ast.uct.ac.za, E-mail: ewilcots@astro.wisc.edu [Department of Astronomy, University of Wisconsin-Madison, Madison, WI 53706 (United States)

    2013-11-01

    We present an analysis of the neutral hydrogen (H I) content and distribution of galaxies in groups as a function of their parent dark matter halo mass. The Arecibo Legacy Fast ALFA survey α.40 data release allows us, for the first time, to study the H I properties of over 740 galaxy groups in the volume of sky common to the Sloan Digital Sky Survey (SDSS) and ALFALFA surveys. We assigned ALFALFA H I detections a group membership based on an existing magnitude/volume-limited SDSS Data Release 7 group/cluster catalog. Additionally, we assigned group ''proximity' membership to H I detected objects whose optical counterpart falls below the limiting optical magnitude—thereby not contributing substantially to the estimate of the group stellar mass, but significantly to the total group H I mass. We find that only 25% of the H I detected galaxies reside in groups or clusters, in contrast to approximately half of all optically detected galaxies. Further, we plot the relative positions of optical and H I detections in groups as a function of parent dark matter halo mass to reveal strong evidence that H I is being processed in galaxies as a result of the group environment: as optical membership increases, groups become increasingly deficient of H I rich galaxies at their center and the H I distribution of galaxies in the most massive groups starts to resemble the distribution observed in comparatively more extreme cluster environments. We find that the lowest H I mass objects lose their gas first as they are processed in the group environment, and it is evident that the infall of gas rich objects is important to the continuing growth of large scale structure at the present epoch, replenishing the neutral gas supply of groups. Finally, we compare our results to those of cosmological simulations and find that current models cannot simultaneously predict the H I selected halo occupation distribution for both low and high mass halos.

  11. Fine 3D neutronic characterization of a gas-cooled fast reactor based on plate-type sub-assemblies

    Bosq, J. C.; Peneliau, Y.; Rimpault, G.; Vanier, M.

    2006-01-01

    CEA neutronic studies have allowed the definition of a first 2400 MWth reference gas-cooled fast reactor core using plate-type sub-assemblies, for which the main neutronic characteristics were calculated by the so-called ERANOS 'design calculation scheme' relying on several method approximations. The last stage has consisted in a new refine characterization, using the reference calculation scheme, in order to confirm the impact of the approximations of the design route. A first core lay-out taking into account control rods was proposed and the reactivity penalty due to the control rod introduction in this hexagonal core lay-out was quantified. A new adjusted core was defined with an increase of the plutonium content. This leads to a significant decrease of the breeding gain which needs to be recovered in future design evolutions in order to achieve the self breeding goal. Finally, the safety criteria associated to the control rods were calculated with a first estimation of the uncertainties. All these criteria are respected, even if the safety analysis of GFR concepts and the determination of these uncertainties should be further studied and improved. (authors)

  12. Thermal-hydraulic calculation and analysis on helium cooled ceramic breeder pebble bed assembly for in-pile irradiation and in-situ tritium extraction

    Guo Chunqiu; Xie Jiachun; Liu Xingmin

    2013-01-01

    In-pile irradiation and in-situ tritium extraction experiment is one of associated domestic research projects in ITER special program. According to the technical requirements of in-pile irradiation experiment of helium cooled ceramic breeder (ceramic) pebble bed assembly in a research reactor, the feasibility of the design for the in-pile irradiation and in-situ tritium extraction experiment of ceramic pebble bed assembly was evaluated. By conducting thermal-hydraulic design calculation with different in-pile irradiation channels, locations and structure parameters for ceramic pebble bed assembly, a reasonable design scheme of ceramic pebble bed assembly satisfying the design requirements for in-pile irradiation was obtained. (authors)

  13. The Merging Galaxy Cluster A520 - A Broken-Up Cool Core, A Dark Subcluster, and an X-Ray Channel

    Wang, Qian H.S.; Markevitch, Maxim; Giacintucci, Simona

    2016-01-01

    We present results from a deep Chandra X-ray observation of a merging galaxy cluster A520. A high-resolution gas temperature map reveals a long trail of dense, cool clumpsapparently the fragments of a cool core that has been stripped from the infalling subcluster by ram pressure. The clumps should still be connected by the stretched magnetic field lines. The observed temperature variations imply that thermal conductivity is suppressed by a factor greater than 100 across the presumed direction of the magnetic field (as found in other clusters), and is also suppressed along the field lines by a factor of several. Two massive clumps in the periphery of A520, visible in the weak-lensing mass map and the X-ray image, have apparently been completely stripped of gas during the merger, but then re-accreted the surrounding high-entropy gas upon exit from the cluster. The mass clump that hosted the stripped cool core is also re-accreting hotter gas. An X-ray hydrostatic mass estimate for the clump that has the simplest geometry agrees with the lensing mass. Its current gas mass to total mass ratio is very low, 1.5 percent to 3 percent, which makes it a "dark subcluster." We also found a curious low X-ray brightness channel (likely a low-density sheet in projection) going across the cluster along the direction of an apparent secondary merger. The channel may be caused by plasma depletion in a region of an amplified magnetic field (with plasma Beta approximately equal to 10-20). The shock in A520 will be studied in a separate paper.

  14. Galaxy And Mass Assembly (GAMA): gas fuelling of spiral galaxies in the local Universe II. - direct measurement of the dependencies on redshift and host halo mass of stellar mass growth in central disc galaxies

    Grootes, M. W.; Dvornik, A.; Laureijs, R. J.; Tuffs, R. J.; Popescu, C. C.; Robotham, A. S. G.; Liske, J.; Brown, M. J. I.; Holwerda, B. W.; Wang, L.

    2018-06-01

    We present a detailed analysis of the specific star formation rate-stellar mass (sSFR-M*) of z ≤ 0.13 disc central galaxies using a morphologically selected mass-complete sample (M* ≥ 109.5 M⊙). Considering samples of grouped and ungrouped galaxies, we find the sSFR-M* relations of disc-dominated central galaxies to have no detectable dependence on host dark-matter halo (DMH) mass, even where weak-lensing measurements indicate a difference in halo mass of a factor ≳ 5. We further detect a gradual evolution of the sSFR-M* relation of non-grouped (field) central disc galaxies with redshift, even over a Δz ≈ 0.04 (≈5 × 108 yr) interval, while the scatter remains constant. This evolution is consistent with extrapolation of the `main sequence of star-forming-galaxies' from previous literature that uses larger redshift baselines and coarser sampling. Taken together, our results present new constraints on the paradigm under which the SFR of galaxies is determined by a self-regulated balance between gas inflows and outflows, and consumption of gas by star formation in discs, with the inflow being determined by the product of the cosmological accretion rate and a fuelling efficiency - \\dot{M}_{b,halo}ζ. In particular, maintaining the paradigm requires \\dot{M}_{b,halo}ζ to be independent of the mass Mhalo of the host DMH. Furthermore, it requires the fuelling efficiency ζ to have a strong redshift dependence (∝(1 + z)2.7 for M* = 1010.3 M⊙ over z = 0-0.13), even though no morphological transformation to spheroids can be invoked to explain this in our disc-dominated sample. The physical mechanisms capable of giving rise to such dependencies of ζ on Mhalo and z for discs are unclear.

  15. Galaxy and mass assembly (GAMA): the consistency of GAMA and WISE derived mass-to-light ratios

    Kettlety, T.; Hesling, J.; Phillipps, S.; Bremer, M. N.; Cluver, M. E.; Taylor, E. N.; Bland-Hawthorn, J.; Brough, S.; De Propris, R.; Driver, S. P.; Holwerda, B. W.; Kelvin, L. S.; Sutherland, W.; Wright, A. H.

    2018-01-01

    Recent work has suggested that mid-IR wavelengths are optimal for estimating the mass-to-light ratios of stellar populations and hence the stellar masses of galaxies. We compare stellar masses deduced from spectral energy distribution (SED) models, fitted to multiwavelength optical-NIR photometry, to luminosities derived from WISE photometry in the W1 and W2 bands at 3.6 and 4.5 μm for non-star forming galaxies. The SED-derived masses for a carefully selected sample of low-redshift (z ≤ 0.15) passive galaxies agree with the prediction from stellar population synthesis models such that M*/LW1 ≃ 0.6 for all such galaxies, independent of other stellar population parameters. The small scatter between masses predicted from the optical SED and from the WISE measurements implies that random errors (as opposed to systematic ones such as the use of different initial mass functions) are smaller than previous, deliberately conservative, estimates for the SED fits. This test is subtly different from simultaneously fitting at a wide range of optical and mid-IR wavelengths, which may just generate a compromised fit: we are directly checking that the best-fitting model to the optical data generates an SED whose M*/LW1 is also consistent with separate mid-IR data. We confirm that for passive low-redshift galaxies a fixed M*/LW1 = 0.65 can generate masses at least as accurate as those obtained from more complex methods. Going beyond the mean value, in agreement with expectations from the models, we see a modest change in M*/LW1 with SED fitted stellar population age but an insignificant one with metallicity.

  16. CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY

    Swift, Jonathan J.; Johnson, John Asher; Morton, Timothy D.; Montet, Benjamin T.; Muirhead, Philip S.; Crepp, Justin R.; Fabrycky, Daniel C.

    2013-01-01

    The Kepler space telescope has opened new vistas in exoplanet discovery space by revealing populations of Earth-sized planets that provide a new context for understanding planet formation. Approximately 70% of all stars in the Galaxy belong to the diminutive M dwarf class, several thousand of which lie within Kepler's field of view, and a large number of these targets show planet transit signals. The Kepler M dwarf sample has a characteristic mass of 0.5 M ☉ representing a stellar population twice as common as Sun-like stars. Kepler-32 is a typical star in this sample that presents us with a rare opportunity: five planets transit this star, giving us an expansive view of its architecture. All five planets of this compact system orbit their host star within a distance one-third the size of Mercury's orbit, with the innermost planet positioned a mere 4.3 stellar radii from the stellar photosphere. New observations limit possible false positive scenarios, allowing us to validate the entire Kepler-32 system making it the richest known system of transiting planets around an M dwarf. Based on considerations of the stellar dust sublimation radius, a minimum mass protoplanetary nebula, and the near period commensurability of three adjacent planets, we propose that the Kepler-32 planets formed at larger orbital radii and migrated inward to their present locations. The volatile content inferred for the Kepler-32 planets and order of magnitude estimates for the disk migration rates suggest that these planets may have formed beyond the snow line and migrated in the presence of a gaseous disk. If true, then this would place an upper limit on their formation time of ∼10 Myr. The Kepler-32 planets are representative of the full ensemble of planet candidates orbiting the Kepler M dwarfs for which we calculate an occurrence rate of 1.0 ± 0.1 planet per star. The formation of the Kepler-32 planets therefore offers a plausible blueprint for the formation of one of the largest

  17. Galaxy And Mass Assembly (GAMA): the G02 field, Herschel-ATLAS target selection and Data Release 3 arXiv

    Baldry, I.K.; Brown, M.J.I.; Robotham, A.S.G.; Driver, S.P.; Dunne, L.; Alpaslan, M.; Brough, S.; Cluver, M.E.; Eardley, E.; Farrow, D.J.; Heymans, C.; Hildebrandt, H.; Hopkins, A.M.; Kelvin, L.S.; Loveday, J.; Moffett, A.J.; Norberg, P.; Owers, M.S.; Taylor, E.N.; Wright, A.H.; Bamford, S.P.; Bland-Hawthorn, J.; Bourne, N.; Bremer, M.N.; Colless, M.; Conselice, C.J.; Croom, S.M.; Davies, L.J.M.; Foster, C.; Grootes, M.W.; Holwerda, B.W.; Jones, D.H.; Kafle, P.R.; Kuijken, K.; Lara-Lopez, M.A.; Lopez-Sanchez, A.R.; Meyer, M.J.; Phillipps, S.; Sutherland, W.J.; van Kampen, E.; Wilkins, S.M.

    We describe data release 3 (DR3) of the Galaxy And Mass Assembly (GAMA) survey. The GAMA survey is a spectroscopic redshift and multi-wavelength photometric survey in three equatorial regions each of 60.0 deg^2 (G09, G12, G15), and two southern regions of 55.7 deg^2 (G02) and 50.6 deg^2 (G23). DR3 consists of: the first release of data covering the G02 region and of data on H-ATLAS sources in the equatorial regions; and updates to data on sources released in DR2. DR3 includes 154809 sources with secure redshifts across four regions. A subset of the G02 region is 95.5% redshift complete to r<19.8 over an area of 19.5 deg^2, with 20086 galaxy redshifts, that overlaps substantially with the XXL survey (X-ray) and VIPERS (redshift survey). In the equatorial regions, the main survey has even higher completeness (98.5%), and spectra for about 75% of H-ATLAS filler targets were also obtained. This filler sample extends spectroscopic redshifts, for probable optical counterparts to H-ATLAS sub-mm sources, to 0.8 ma...

  18. Development of the control assembly pattern and dynamic analysis of the Generation IV large gas-cooled fast reactor (GFR)

    Girardin, G.

    2009-07-15

    During the past ten years, different independent factors, such as the rapidly increasing worldwide demand in energy, societal concerns about greenhouse gas emissions, and the high and volatile prices for fossil fuels, have contributed to the renewed interest in nuclear technology. In this context, the Generation IV International Forum (GIF) launched the initiative to collaborate on the research and development efforts needed for the next generation of nuclear reactors. A particular goal set for Generation IV systems is closure of the nuclear fuel cycle; they are expected to offer a better utilization of natural resources, as also a minimization of long-lived radioactive wastes. Among the systems selected by the GIF, the Gas-cooled Fast Reactor (GFR) is a highly innovative system with advanced fuel geometry and materials. The principal aim of the present research is to develop and qualify the control assembly (CA) pattern and corresponding CA implementation scheme for the 2400 MWth reference GFR design. The work has been carried out in three successive phases: (1) validation of the neutronics tools, (2) the CA pattern development and related static analysis, and (3) dynamic core behaviour studies for hypothetical CA driven transients. The deterministic code system ERANOS and its associated nuclear data libraries for fast reactors were developed and validated for sodium-cooled reactors. In order to validate ERANOS for GFR applications, a systematic reanalysis of the GFR-relevant integral data generated at PSI during the GCFR-PROTEUS experimental program of the 1970’s was undertaken. The reference PROTEUS test lattice has been analyzed with ERANOS-2.0 and its associated, adjusted nuclear data library ERALIB1. Benchmark calculations were performed with the Monte Carlo code MCNPX, allowing one to both check the deterministic results and to analyze the sensitivity to different modern data libraries. For the main reaction rate ratios, the new analysis of the GCFR

  19. Development of the control assembly pattern and dynamic analysis of the Generation IV large gas-cooled fast reactor (GFR)

    Girardin, G.

    2009-07-01

    During the past ten years, different independent factors, such as the rapidly increasing worldwide demand in energy, societal concerns about greenhouse gas emissions, and the high and volatile prices for fossil fuels, have contributed to the renewed interest in nuclear technology. In this context, the Generation IV International Forum (GIF) launched the initiative to collaborate on the research and development efforts needed for the next generation of nuclear reactors. A particular goal set for Generation IV systems is closure of the nuclear fuel cycle; they are expected to offer a better utilization of natural resources, as also a minimization of long-lived radioactive wastes. Among the systems selected by the GIF, the Gas-cooled Fast Reactor (GFR) is a highly innovative system with advanced fuel geometry and materials. The principal aim of the present research is to develop and qualify the control assembly (CA) pattern and corresponding CA implementation scheme for the 2400 MWth reference GFR design. The work has been carried out in three successive phases: (1) validation of the neutronics tools, (2) the CA pattern development and related static analysis, and (3) dynamic core behaviour studies for hypothetical CA driven transients. The deterministic code system ERANOS and its associated nuclear data libraries for fast reactors were developed and validated for sodium-cooled reactors. In order to validate ERANOS for GFR applications, a systematic reanalysis of the GFR-relevant integral data generated at PSI during the GCFR-PROTEUS experimental program of the 1970’s was undertaken. The reference PROTEUS test lattice has been analyzed with ERANOS-2.0 and its associated, adjusted nuclear data library ERALIB1. Benchmark calculations were performed with the Monte Carlo code MCNPX, allowing one to both check the deterministic results and to analyze the sensitivity to different modern data libraries. For the main reaction rate ratios, the new analysis of the GCFR

  20. THE UV–OPTICAL COLOR GRADIENTS IN STAR-FORMING GALAXIES AT 0.5 < z < 1.5: ORIGINS AND LINK TO GALAXY ASSEMBLY

    Liu, F. S.; Jiang, Dongfei; Li, Yao; Li, Dingpeng; Guo, Yicheng; Koo, David C.; Faber, S. M.; Yesuf, Hassen M.; Barro, Guillermo; Fang, Jerome J.; Zheng, Xianzhong; Wang, Weichen; Mao, Shude

    2016-01-01

    The rest-frame UV–optical (i.e., NUV − B ) color index is sensitive to the low-level recent star formation and dust extinction, but it is insensitive to the metallicity. In this Letter, we have measured the rest-frame NUV − B color gradients in ∼1400 large ( r _e > 0.″18), nearly face-on ( b / a > 0.5) main sequence star-forming galaxies (SFGs) between redshift 0.5 and 1.5 in the CANDELS/GOODS-S and UDS fields. With this sample, we study the origin of UV–optical color gradients in the SFGs at z ∼ 1 and discuss their link with the buildup of stellar mass. We find that the more massive, centrally compact, and more dust extinguished SFGs tend to have statistically more negative raw color gradients (redder centers) than the less massive, centrally diffuse, and less dusty SFGs. After correcting for dust reddening based on optical-spectral energy distribution fitting, the color gradients in the low-mass ( M _* 10"1"0"."5 M _⊙) SFGs still retain shallow negative color gradients. These findings imply that dust reddening is likely the principal cause of negative color gradients in the low-mass SFGs, while both increased central dust reddening and buildup of compact old bulges are likely the origins of negative color gradients in the high-mass SFGs. These findings also imply that at these redshifts the low-mass SFGs buildup their stellar masses in a self-similar way, while the high-mass SFGs grow inside out.

  1. The rapid formation of a large rotating disk galaxy three billion years after the Big Bang.

    Genzel, R; Tacconi, L J; Eisenhauer, F; Schreiber, N M Förster; Cimatti, A; Daddi, E; Bouché, N; Davies, R; Lehnert, M D; Lutz, D; Nesvadba, N; Verma, A; Abuter, R; Shapiro, K; Sternberg, A; Renzini, A; Kong, X; Arimoto, N; Mignoli, M

    2006-08-17

    Observations and theoretical simulations have established a framework for galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark-matter haloes; mergers of haloes and galaxies then led to the hierarchical build-up of galaxy mass. It remains unclear, however, over what timescales galaxies were assembled and when and how bulges and disks--the primary components of present-day galaxies--were formed. It is also puzzling that the most massive galaxies were more abundant and were forming stars more rapidly at early epochs than expected from models. Here we report high-angular-resolution observations of a representative luminous star-forming galaxy when the Universe was only 20% of its current age. A large and massive rotating protodisk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole. The high surface densities of gas, the high rate of star formation and the moderately young stellar ages suggest rapid assembly, fragmentation and conversion to stars of an initially very gas-rich protodisk, with no obvious evidence for a major merger.

  2. The CGM of Massive Galaxies: Where Cold Gas Goes to Die?

    Howk, Jay

    2017-08-01

    We propose to survey the cold HI content and metallicity of the circumgalactic medium (CGM) around 50 (45 new, 5 archival) z 0.5 Luminous Red Galaxies (LRGs) to directly test a fundamental prediction of galaxy assembly models: that cold, metal-poor accretion does not survive to the inner halos of very massive galaxies. Accretion and feedback through the CGM play key roles in our models of the star formation dichotomy in galaxies. Low mass galaxies are thought to accrete gas in cold streams, while high mass galaxies host hot, dense halos that heat incoming gas and prevent its cooling, thereby quenching star formation. HST/COS has provided evidence for cold, metal-poor streams in the halos of star-forming galaxies (consistent with cold accretion). Observations have also demonstrated the presence of cool gas in the halos of passive galaxies, a potential challenge to the cold/hot accretion model. Our proposed observations will target the most massive galaxies and address the origin of the cool CGM gas by measuring the metallicity. This experiment is enabled by our novel approach to deriving metallicities, allowing the use of much fainter QSOs. It cannot be done with archival data, as these rare systems are not often probed along random sight lines. The H I column density (and metallicity) measurements require access to the UV. The large size of our survey is crucial to robustly assess whether the CGM in these galaxies is unique from that of star-forming systems, a comparison that provides the most stringent test of cold-mode accretion/quenching models to date. Conversely, widespread detections of metal-poor gas in these halos will seriously challenge the prevailing theory.

  3. Sodium-cooled fast reactor (SFR) fuel assembly design with graphite-moderating rods to reduce the sodium void reactivity coefficient

    Won, Jong Hyuck; Cho, Nam Zin, E-mail: nzcho@kaist.ac.kr; Park, Hae Min; Jeong, Yong Hoon, E-mail: jeongyh@kaist.ac.kr

    2014-12-15

    Highlights: • The graphite rod-inserted SFR fuel assembly is proposed to achieve low sodium void reactivity. • The neutronics/thermal-hydraulics analyses are performed for the proposed SFR cores. • The sodium void reactivity is improved about 960–1030 pcm compared to reference design. - Abstract: The concept of a graphite-moderating rod-inserted sodium-cooled fast reactor (SFR) fuel assembly is proposed in this study to achieve a low sodium void reactivity coefficient. Using this concept, two types of SFR cores are analyzed; the proposed SFR type 1 core has new SFR fuel assemblies at the inner/mid core regions while the proposed SFR type 2 core has a B{sub 4}C absorber sandwich in the middle of the active core region as well as new SFR fuel assemblies at the inner/mid core regions. For the proposed SFR core designs, neutronics and thermal-hydraulic analyses are performed using the DIF3D, REBUS3, and the MATRA-LMR codes. In the neutronics analysis, the sodium void reactivity coefficient is obtained in various void situations. The two types of proposed core designs reduce the sodium void reactivity coefficient by about 960–1030 pcm compared to the reference design. However, the TRU enrichment for the proposed SFR core designs is increased. In the thermal hydraulic analysis, the temperature distributions are calculated for the two types of proposed core designs and the mass flow rate is optimized to satisfy the design constraints for the highest power generating assembly. The results of this study indicate that the proposed SFR assembly design concept, which adopts graphite-moderating rods which are inserted into the fuel assembly, can feasibly minimize the sodium void reactivity coefficient. Single TRU enrichment and an identical fuel slug diameter throughout the SFR core are also achieved because the radial power peak can be flattened by varying the number of moderating rods in each core region.

  4. Development of the control assembly pattern and dynamic analysis of the generation IV large gas-cooled fast reactor (GFR)

    Girardin, G.

    2009-01-01

    Among the systems selected by the GIF, the Gas-cooled Fast Reactor (GFR) is a highly innovative system with advanced fuel geometry and materials. It is in the context of the large, 2400 MWth reference GFR design that the present doctoral research has been conducted, the principal aim having been to develop and qualify the control assembly (CA) pattern and corresponding CA implementation scheme for this system. The work has been carried out in three successive and complementary phases: (1) validation of the neutronics tools, (2) the CA pattern development and related static analysis, and (3) dynamic core behavior studies for hypothetical CA driven transients. During the first phase of the thesis, the reference PROTEUS test lattice from these experiments has been analyzed with ERANOS-2.0 and its associated, adjusted nuclear data library ERALIB1. Additionally, benchmark calculations were performed with the Monte Carlo code MCNPX, allowing one to both check the deterministic results and to analyze the sensitivity to different modern data libraries. It has been found that, for the main reaction rate ratios, the new analysis of the GCFR-PROTEUS reference lattice generally yields good agreement - within 1σ measurement uncertainty - with experimental values and with the Monte Carlo simulations. As shown by the analysis, the predictions were in somewhat better agreement in the case of the adjusted ERALIB1 library. The applicability of ERANOS-2.0/ERALIB1 as the reference neutronics tool for the GFR analysis could thus be demonstrated. Furthermore, neutronics aspects related to the novel features of the GFR, for which new experimental investigations are needed, were highlighted. In the second phase of the research, the CA pattern was developed for the GFR, based on iterative neutronics and thermal-hydraulics calculations, 2D and 3D neutronics models for the reactor core having first been set up using the reference ERANOS-2.0/ERALIB1 computational scheme. For the thermal

  5. Witnessing the assembly of galaxies in an extended gas-rich structure at z 3.25

    Mackenzie, Ruari

    2017-08-01

    The direct study of star formation in Damped Lyman Alpha systems (DLAs), the reservoirs of the majority of neutral gas at high redshift, has previously been hampered by the lack of deep integral field spectroscopy for sensitive searches of faint host galaxies. Building on our successful HST shot-in-the-dark survey that has probed the in-situ star formation rate of z 2-3 DLAs, we have initiated a MUSE follow-up of 6 DLA signlines to overcome this bottleneck. In the first sightline we have studied, we have uncovered a 40 kpc Lyman alpha emitting nebula, composed of two clumps within 50 kpc of the DLA, suggestive of a merger or an extended protodisk. Within this structure, which is the largest nebula known to be associated with a z 3 DLA, we also found a compact continuum source with spectrophotometry consistent with a Lyman Break Galaxy at the same redshift. Aside from the LBG, the rest of the Lyman alpha structure has no continuum counterpart in deep UV and visible imaging. The LBG alone seems unable to power the Lyman alpha nebula and the morphology supports our conclusion that, most likely, this structure is powered by in-situ star formation below detection limit. However, from the Lyman alpha alone the origin of this incredible structure remains ambiguous. With this proposal, we aim to acquire high resolution, deep infrared imaging with HST to probe the rest-frame optical emission to search for the underlying stellar emission of this object and to infer the stellar mass of the LBG. With the powerful combination of HST and MUSE data, we will unravel the nature of this unique system.

  6. Distant Galaxy Clusters Hosting Extreme Central Galaxies

    McDonald, Michael

    2014-09-01

    The recently-discovered Phoenix cluster harbors the most star-forming central cluster galaxy of any cluster in the known Universe, by nearly a factor of 10. This extreme system appears to be fulfilling early cooling flow predictions, although the lack of similar systems makes any interpretation difficult. In an attempt to find other "Phoenix-like" clusters, we have cross-correlated archival all-sky surveys (in which Phoenix was detected) and isolated 4 similarly-extreme systems which are also coincident in position and redshift with an overdensity of red galaxies. We propose here to obtain Chandra observations of these extreme, Phoenix-like systems, in order to confirm them as relaxed, rapidly-cooling galaxy clusters.

  7. Determination of mixture coefficients in tests simulating channels of a fuel assembly in a water cooled reactor

    Ferreira, W.R.

    1983-09-01

    Here, the mixture coefficients are determined in tests which simulate two symmetric and two assymetric coolant channels of a water cooled reactor. It was studies the effects of coolant flow and of the distance among the coolant channels on these coefficients. The technique used to determine the mixture coefficients was to introduce a tracer (methylene blue) into the flow. The determination of the tracer concentration at the end of the channels was made by means of spectrophotometric analysis. (author)

  8. Black hole feedback on the first galaxies

    Jeon, Myoungwon; Pawlik, Andreas H.; Greif, Thomas H.; Glover, Simon C. O.; Bromm, Volker; Milosavljević, Miloš; Klessen, Ralf S.

    2012-09-01

    We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through selfconsistent, cosmological simulations. X-ray radiation fromthe accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback startingwith the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.

  9. Superclusters and galaxy formation

    Einasto, J; Joeveer, M; Saar, E [Tartu Astrophysical Observatory, Toravere, Estonia (USSR)

    1980-01-03

    A study of the structure of superclusters in the Southern galactic hemisphere using Zwicky clusters as principal tracers of the large-scale structure of the Universe is reported. The data presented suggest that the formation of galaxies was a two stage process involving larger spatial dimensions than earlier workers have postulated. In the first stage proto-superclusters and big holes had to form from the non-dissipative dark matter while in the second hot gas, by cooling and settling down into the potential wells caused by dark matter, will form galaxies and clusters of galaxies.

  10. DISCOVERY OF 'WARM DUST' GALAXIES IN CLUSTERS AT z {approx} 0.3: EVIDENCE FOR STRIPPING OF COOL DUST IN THE DENSE ENVIRONMENT?

    Rawle, T. D.; Rex, M.; Egami, E.; Walth, G.; Pereira, M. J. [Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States); Chung, S. M.; Gonzalez, A. H. [Department of Astronomy, University of Florida, Gainesville, FL 32611-2055 (United States); Perez-Gonzalez, P. G. [Departamento de Astrofisica, Facultad de CC. Fisicas,Universidad Complutense de Madrid, E-28040 Madrid (Spain); Smail, I. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Altieri, B.; Valtchanov, I. [Herschel Science Centre, ESAC, ESA, P.O. Box 78, Villanueva de la Canada, E-28691 Madrid (Spain); Appleton, P.; Fadda, D. [IPAC, California Institute of Technology, Pasadena, CA 91125 (United States); Alba, A. Berciano [ASTRON, Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo (Netherlands); Blain, A. W. [Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom); Dessauges-Zavadsky, M. [Observatoire de Geneve, Universite de Geneve, 51 Ch. des Maillettes, CH-1290 Sauverny (Switzerland); Van der Werf, P. P. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, NL-2300 RA Leiden (Netherlands); Zemcov, M., E-mail: trawle@as.arizona.edu [Department of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2012-09-10

    Using far-infrared imaging from the 'Herschel Lensing Survey', we derive dust properties of spectroscopically confirmed cluster member galaxies within two massive systems at z {approx} 0.3: the merging Bullet Cluster and the more relaxed MS2137.3-2353. Most star-forming cluster sources ({approx}90%) have characteristic dust temperatures similar to local field galaxies of comparable infrared (IR) luminosity (T{sub dust} {approx} 30 K). Several sub-luminous infrared galaxy (LIRG; L{sub IR} < 10{sup 11} L{sub Sun }) Bullet Cluster members are much warmer (T{sub dust} > 37 K) with far-infrared spectral energy distribution (SED) shapes resembling LIRG-type local templates. X-ray and mid-infrared data suggest that obscured active galactic nuclei do not contribute significantly to the infrared flux of these 'warm dust' galaxies. Sources of comparable IR luminosity and dust temperature are not observed in the relaxed cluster MS2137, although the significance is too low to speculate on an origin involving recent cluster merging. 'Warm dust' galaxies are, however, statistically rarer in field samples (>3{sigma}), indicating that the responsible mechanism may relate to the dense environment. The spatial distribution of these sources is similar to the whole far-infrared bright population, i.e., preferentially located in the cluster periphery, although the galaxy hosts tend toward lower stellar masses (M{sub *} < 10{sup 10} M{sub Sun }). We propose dust stripping and heating processes which could be responsible for the unusually warm characteristic dust temperatures. A normal star-forming galaxy would need 30%-50% of its dust removed (preferentially stripped from the outer reaches, where dust is typically cooler) to recover an SED similar to a 'warm dust' galaxy. These progenitors would not require a higher IR luminosity or dust mass than the currently observed normal star-forming population.

  11. DARK MATTER CORES IN THE FORNAX AND SCULPTOR DWARF GALAXIES: JOINING HALO ASSEMBLY AND DETAILED STAR FORMATION HISTORIES

    Amorisco, N. C.; Zavala, J.; De Boer, T. J. L.

    2014-01-01

    We combine the detailed star formation histories of the Fornax and Sculptor dwarf spheroidals with the mass assembly history of their dark matter (DM) halo progenitors to estimate if the energy deposited by Type II supernovae (SNe II) is sufficient to create a substantial DM core. Assuming the efficiency of energy injection of the SNe II into DM particles is ε gc = 0.05, we find that a single early episode, z ≳ z infall , that combines the energy of all SNe II due to explode over 0.5 Gyr is sufficient to create a core of several hundred parsecs in both Sculptor and Fornax. Therefore, our results suggest that it is energetically plausible to form cores in cold dark matter (CDM) halos via early episodic gas outflows triggered by SNe II. Furthermore, based on CDM merger rates and phase-space density considerations, we argue that the probability of a subsequent complete regeneration of the cusp is small for a substantial fraction of dwarf-size halos

  12. First Cool-down and Test at 4.5 K of the ATLAS Superconducting Barrel Toroid Assembled in the LHC Experimental Cavern

    Barth, K; Dudarev, A; Passardi, Giorgio; Pengo, R; Pezzetti, M; Pirrote, O; Ten Kate, H; Baynham, E; Mayri, C

    2008-01-01

    The large ATLAS superconducting magnets system consists of the Barrel, two End-Caps Toroids and the Central Solenoid. The eight separate coils making the Barrel Toroid (BT) have been individually tested with success in a dedicated surface test facility in 2004 and 2005 and afterwards assembled in the underground cavern of the ATLAS experiment. In order to fulfil all the cryogenic scenarios foreseen for these magnets with a cold mass of 370 tons, two separate helium refrigerators and a complex helium distribution system have been used. This paper describes the results of the first cool-down, steady-state operation at 4.5 K and quench recovery of the BT in its final configuration.

  13. Cooling pancakes

    Bond, J.R.; Wilson, J.R.

    1984-01-01

    In theories of galaxy formation with a damping cut-off in the density fluctuation spectrum, the first non-linear structures to form are Zeldovich pancakes in which dissipation separates gas from any collisionless dark matter then present. One-dimensional numerical simulations of the collapse, shock heating, and subsequent thermal evolution of pancakes are described. Neutrinos (or any other cool collisionless particles) are followed by direct N-body methods and the gas by Eulerian hydrodynamics with conduction as well as cooling included. It is found that the pressure is relatively uniform within the shocked region and approximately equals the instantaneous ram pressure acting at the shock front. An analytic theory based upon this result accurately describes the numerical calculations. (author)

  14. Spatially Resolved Hα Maps and Sizes of 57 Strongly Star-forming Galaxies at z ~ 1 from 3D-HST: Evidence for Rapid Inside-out Assembly of Disk Galaxies

    Nelson, Erica June; van Dokkum, Pieter G.; Brammer, Gabriel; Förster Schreiber, Natascha; Franx, Marijn; Fumagalli, Mattia; Patel, Shannon; Rix, Hans-Walter; Skelton, Rosalind E.; Bezanson, Rachel; Da Cunha, Elisabete; Kriek, Mariska; Labbe, Ivo; Lundgren, Britt; Quadri, Ryan; Schmidt, Kasper B.

    2012-03-01

    We investigate the buildup of galaxies at z ~ 1 using maps of Hα and stellar continuum emission for a sample of 57 galaxies with rest-frame Hα equivalent widths >100 Å in the 3D-HST grism survey. We find that the Hα emission broadly follows the rest-frame R-band light but that it is typically somewhat more extended and clumpy. We quantify the spatial distribution with the half-light radius. The median Hα effective radius re (Hα) is 4.2 ± 0.1 kpc but the sizes span a large range, from compact objects with re (Hα) ~ 1.0 kpc to extended disks with re (Hα) ~ 15 kpc. Comparing Hα sizes to continuum sizes, we find =1.3 ± 0.1 for the full sample. That is, star formation, as traced by Hα, typically occurs out to larger radii than the rest-frame R-band stellar continuum; galaxies are growing their radii and building up from the inside out. This effect appears to be somewhat more pronounced for the largest galaxies. Using the measured Hα sizes, we derive star formation rate surface densities, ΣSFR. We find that ΣSFR ranges from ~0.05 M ⊙ yr-1 kpc-2 for the largest galaxies to ~5 M ⊙ yr-1 kpc-2 for the smallest galaxies, implying a large range in physical conditions in rapidly star-forming z ~ 1 galaxies. Finally, we infer that all galaxies in the sample have very high gas mass fractions and stellar mass doubling times <500 Myr. Although other explanations are also possible, a straightforward interpretation is that we are simultaneously witnessing the rapid formation of compact bulges and large disks at z ~ 1.

  15. SPATIALLY RESOLVED Hα MAPS AND SIZES OF 57 STRONGLY STAR-FORMING GALAXIES AT z ∼ 1 FROM 3D-HST: EVIDENCE FOR RAPID INSIDE-OUT ASSEMBLY OF DISK GALAXIES

    Nelson, Erica June; Van Dokkum, Pieter G.; Skelton, Rosalind E.; Bezanson, Rachel; Lundgren, Britt; Brammer, Gabriel; Förster Schreiber, Natascha; Franx, Marijn; Fumagalli, Mattia; Patel, Shannon; Labbe, Ivo; Rix, Hans-Walter; Da Cunha, Elisabete; Schmidt, Kasper B.; Kriek, Mariska; Quadri, Ryan

    2012-01-01

    We investigate the buildup of galaxies at z ∼ 1 using maps of Hα and stellar continuum emission for a sample of 57 galaxies with rest-frame Hα equivalent widths >100 Å in the 3D-HST grism survey. We find that the Hα emission broadly follows the rest-frame R-band light but that it is typically somewhat more extended and clumpy. We quantify the spatial distribution with the half-light radius. The median Hα effective radius r e (Hα) is 4.2 ± 0.1 kpc but the sizes span a large range, from compact objects with r e (Hα) ∼ 1.0 kpc to extended disks with r e (Hα) ∼ 15 kpc. Comparing Hα sizes to continuum sizes, we find e (Hα)/r e (R) > =1.3 ± 0.1 for the full sample. That is, star formation, as traced by Hα, typically occurs out to larger radii than the rest-frame R-band stellar continuum; galaxies are growing their radii and building up from the inside out. This effect appears to be somewhat more pronounced for the largest galaxies. Using the measured Hα sizes, we derive star formation rate surface densities, Σ SFR . We find that Σ SFR ranges from ∼0.05 M ☉ yr –1 kpc –2 for the largest galaxies to ∼5 M ☉ yr –1 kpc –2 for the smallest galaxies, implying a large range in physical conditions in rapidly star-forming z ∼ 1 galaxies. Finally, we infer that all galaxies in the sample have very high gas mass fractions and stellar mass doubling times <500 Myr. Although other explanations are also possible, a straightforward interpretation is that we are simultaneously witnessing the rapid formation of compact bulges and large disks at z ∼ 1.

  16. Massive stars in galaxies

    Humphreys, R.M.

    1987-01-01

    The relationship between the morphologic type of a galaxy and the evolution of its massive stars is explored, reviewing observational results for nearby galaxies. The data are presented in diagrams, and it is found that the massive-star populations of most Sc spiral galaxies and irregular galaxies are similar, while those of Sb spirals such as M 31 and M 81 may be affected by morphology (via differences in the initial mass function or star-formation rate). Consideration is also given to the stability-related upper luminosity limit in the H-R diagram of hypergiant stars (attributed to radiation pressure in hot stars and turbulence in cool stars) and the goals of future observation campaigns. 88 references

  17. Projection Of The Stellar To Halo Mass Relation Into The Scaling Relations Of A Disc Galaxy Population

    Mancillas, Brisa; Ávila-Reese, Vladimir; Rodríguez-Puebla, Aldo; Valls-Gabaud, David

    2017-06-01

    Several pieces of evidence suggest that disk formation is the generic process of assembly of galaxies, while the spheroidal component arises from the merging/interactions of disks as well as from their secular evolution. To understand galaxy formation and evolution, a cosmological framework is required. The current cosmological paradigm is summarized in the so-called Λ-cold dark matter model (ΛCDM). The statistical connection between the masses of the observed galaxies and those of the simulated CDM halos in large volumes leads us to the galaxy-halo mass relation, which summarizes the main astrophysical processes of galaxy formation and evolution (gas heating and cooling, SF, SN- and AGN-driven feedback, etc.). An important question is how this relation constrained by semi-empirical methods (e.g., Rodriguez-Puebla et al. 2014) is "projected" into the disk galaxy scaling relations and other galaxy correlations. To explore this question, we generate a synthetic catalog of thousands of disk/halo systems by means of an extended Mo, Mao & White (1998) model, and by using as input the baryonic-to-halo mass relation, fbar(Mh), of local disk galaxy as recently constrained by Calette et al. (2015).

  18. The EAGLE simulations: atomic hydrogen associated with galaxies

    Crain, Robert A.; Bahé, Yannick M.; Lagos, Claudia del P.; Rahmati, Alireza; Schaye, Joop; McCarthy, Ian G.; Marasco, Antonino; Bower, Richard G.; Schaller, Matthieu; Theuns, Tom; van der Hulst, Thijs

    2017-01-01

    We examine the properties of atomic hydrogen (H I) associated with galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations of galaxy formation. EAGLE's feedback parameters were calibrated to reproduce the stellar mass function and galaxy sizes at z = 0.1, and we

  19. Galaxy collisions

    Combes, F.

    1987-01-01

    Galaxies are not isolated systems of stars and gas, ''independent universes'' as believed by astronomers about ten years ago, but galaxies are formed and evolve by interaction with their environment, and in particular with their nearest neighbors. Gravitational interactions produce enormous tides in the disk of spiral galaxies, generate spiral arms and trigger bursts of star formation. Around elliptical galaxies, the collision with a small companion produces a series of waves, or shells. A galaxy interaction leads, in most cases, to the coalescence of the two coliders; therefore all galaxies are not formed just after the Big-Bang, when matter recombines: second generation galaxies are still forming now by galaxy mergers, essentially elliptical galaxies, but also compact dwarfs. Collisions between galaxies could also trigger activity in nuclei for radiogalaxies and quasars [fr

  20. Isolated galaxies

    Einasto, Maret

    1990-01-01

    To test for the possible presence of really isolated galaxies, which form a randomly distributed population in voids, we compare the distribution of most isolated galaxies in an observed sample with distributions of the same number of random points using the nearest neighbour test. The results show that the random population of really isolated galaxies does not exist - even the most isolated galaxies are connected with systems of galaxies, forming their outlying parts. (author)

  1. MASSIV: Mass Assembly Survey with SINFONI in VVDS. III. Evidence for positive metallicity gradients in z ~ 1.2 star-forming galaxies

    Queyrel, J.; Contini, T.; Kissler-Patig, M.; Epinat, B.; Amram, P.; Garilli, B.; Le Fèvre, O.; Moultaka, J.; Paioro, L.; Tasca, L.; Tresse, L.; Vergani, D.; López-Sanjuan, C.; Perez-Montero, E.

    2012-03-01

    Aims: The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. Methods: We present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z ~ 1.2 in the MASSIV survey. Using the N2 ratio between the [N ii]6584 and Hα rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, we measured the metallicity of the sample galaxies. We developed a tool to extract spectra in annular regions, leading to a spatially resolved estimate of the oxygen abundance in each galaxy. We were able to derive a metallicity gradient for 26 galaxies in our sample and discovered a significant fraction of galaxies with a "positive" gradient. Using a simple chemical evolution model, we derived infall rates of pristine gas onto the disks. Results: Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. We suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. We also identify two interesting correlations in our sample: a) galaxies with higher gas velocity dispersion have shallower/positive gradients; and b) metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one. This last observation can be explained by the infall of metal-poor gas into the center of the disks. We address the question of the origin of this infall under the influence of gas flows triggered by interactions and/or cold gas accretion. All the data published in this paper are publicly available at the time of publication following this link: http://cosmosdb.lambrate.inaf.it/VVDS-SINFONI. This work is based on observations collected at the European Southern Observatory (ESO) Very Large Telescope, Paranal, Chile, as part of the Programs 179.A-0823, 78.A-0177, and 75.A-0318. This

  2. Testing the Large-scale Environments of Cool-core and Non-cool-core Clusters with Clustering Bias

    Medezinski, Elinor; Battaglia, Nicholas; Cen, Renyue; Gaspari, Massimo; Strauss, Michael A.; Spergel, David N. [Department of Astrophysical Sciences, 4 Ivy Lane, Princeton, NJ 08544 (United States); Coupon, Jean, E-mail: elinorm@astro.princeton.edu [Department of Astronomy, University of Geneva, ch. dEcogia 16, CH-1290 Versoix (Switzerland)

    2017-02-10

    There are well-observed differences between cool-core (CC) and non-cool-core (NCC) clusters, but the origin of this distinction is still largely unknown. Competing theories can be divided into internal (inside-out), in which internal physical processes transform or maintain the NCC phase, and external (outside-in), in which the cluster type is determined by its initial conditions, which in turn leads to different formation histories (i.e., assembly bias). We propose a new method that uses the relative assembly bias of CC to NCC clusters, as determined via the two-point cluster-galaxy cross-correlation function (CCF), to test whether formation history plays a role in determining their nature. We apply our method to 48 ACCEPT clusters, which have well resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ galaxy catalog. We find that the relative bias of NCC over CC clusters is b = 1.42 ± 0.35 (1.6 σ different from unity). Our measurement is limited by the small number of clusters with core entropy information within the BOSS footprint, 14 CC and 34 NCC clusters. Future compilations of X-ray cluster samples, combined with deep all-sky redshift surveys, will be able to better constrain the relative assembly bias of CC and NCC clusters and determine the origin of the bimodality.

  3. Testing the Large-scale Environments of Cool-core and Non-cool-core Clusters with Clustering Bias

    Medezinski, Elinor; Battaglia, Nicholas; Cen, Renyue; Gaspari, Massimo; Strauss, Michael A.; Spergel, David N.; Coupon, Jean

    2017-01-01

    There are well-observed differences between cool-core (CC) and non-cool-core (NCC) clusters, but the origin of this distinction is still largely unknown. Competing theories can be divided into internal (inside-out), in which internal physical processes transform or maintain the NCC phase, and external (outside-in), in which the cluster type is determined by its initial conditions, which in turn leads to different formation histories (i.e., assembly bias). We propose a new method that uses the relative assembly bias of CC to NCC clusters, as determined via the two-point cluster-galaxy cross-correlation function (CCF), to test whether formation history plays a role in determining their nature. We apply our method to 48 ACCEPT clusters, which have well resolved central entropies, and cross-correlate with the SDSS-III/BOSS LOWZ galaxy catalog. We find that the relative bias of NCC over CC clusters is b = 1.42 ± 0.35 (1.6 σ different from unity). Our measurement is limited by the small number of clusters with core entropy information within the BOSS footprint, 14 CC and 34 NCC clusters. Future compilations of X-ray cluster samples, combined with deep all-sky redshift surveys, will be able to better constrain the relative assembly bias of CC and NCC clusters and determine the origin of the bimodality.

  4. Galaxy mergers

    Roos, N.

    1981-01-01

    This thesis contains a series of four papers dealing with the effects of interactions among galaxies during the epoch of cluster formation. Galaxy interactions are investigated and the results incorporated in numerical simulations of the formation of groups and clusters of galaxies. The role of galaxy interactions is analysed in the more general context of simulations of an expanding universe. The evolution of galaxies in rich clusters is discussed. The results of the investigations are presented and their relation to other work done in the field are briefly reviewed and an attempt is made to link galaxy mergers to the occurrence of activity in galactic nuclei. (Auth.)

  5. THE REST-FRAME OPTICAL LUMINOSITY FUNCTION OF CLUSTER GALAXIES AT z < 0.8 AND THE ASSEMBLY OF THE CLUSTER RED SEQUENCE

    Rudnick, Gregory; Von der Linden, Anja; De Lucia, Gabriella; White, Simon; Pello, Roser; Aragon-Salamanca, Alfonso; Marchesini, Danilo; Clowe, Douglas; Halliday, Claire; Jablonka, Pascale; Milvang-Jensen, Bo; Poggianti, Bianca; Saglia, Roberto; Simard, Luc; Zaritsky, Dennis

    2009-01-01

    We present the rest-frame optical luminosity function (LF) of red-sequence galaxies in 16 clusters at 0.4 < z < 0.8 drawn from the ESO Distant Cluster Survey (EDisCS). We compare our clusters to an analogous sample from the Sloan Digital Sky Survey (SDSS) and match the EDisCS clusters to their most likely descendants. We measure all LFs down to M ∼ M * + (2.5-3.5). At z < 0.8, the bright end of the LF is consistent with passive evolution but there is a significant buildup of the faint end of the red sequence toward lower redshift. There is a weak dependence of the LF on cluster velocity dispersion for EDisCS but no such dependence for the SDSS clusters. We find tentative evidence that red-sequence galaxies brighter than a threshold magnitude are already in place, and that this threshold evolves to fainter magnitudes toward lower redshifts. We compare the EDisCS LFs with the LF of coeval red-sequence galaxies in the field and find that the bright end of the LFs agree. However, relative to the number of bright red galaxies, the field has more faint red galaxies than clusters at 0.6 < z < 0.8 but fewer at 0.4 < z < 0.6, implying differential evolution. We compare the total light in the EDisCS cluster red sequences to the total red-sequence light in our SDSS cluster sample. Clusters at 0.4 < z < 0.8 must increase their luminosity on the red sequence (and therefore stellar mass in red galaxies) by a factor of 1-3 by z = 0. The necessary processes that add mass to the red sequence in clusters predict local clusters that are overluminous as compared to those observed in the SDSS. The predicted cluster luminosities can be reconciled with observed local cluster luminosities by combining multiple previously known effects.

  6. Galaxy Formation

    Sparre, Martin

    Galaxy formation is an enormously complex discipline due to the many physical processes that play a role in shaping galaxies. The objective of this thesis is to study galaxy formation with two different approaches: First, numerical simulations are used to study the structure of dark matter and how...... galaxies form stars throughout the history of the Universe, and secondly it is shown that observations of gamma-ray bursts (GRBs) can be used to probe galaxies with active star formation in the early Universe. A conclusion from the hydrodynamical simulations is that the galaxies from the stateof...... is important, since it helps constraining chemical evolution models at high redshift. A new project studying how the population of galaxies hosting GRBs relate to other galaxy population is outlined in the conclusion of this thesis. The core of this project will be to quantify how the stellar mass function...

  7. Growing Galaxies Gently

    2010-10-01

    New observations from ESO's Very Large Telescope have, for the first time, provided direct evidence that young galaxies can grow by sucking in the cool gas around them and using it as fuel for the formation of many new stars. In the first few billion years after the Big Bang the mass of a typical galaxy increased dramatically and understanding why this happened is one of the hottest problems in modern astrophysics. The results appear in the 14 October issue of the journal Nature. The first galaxies formed well before the Universe was one billion years old and were much smaller than the giant systems - including the Milky Way - that we see today. So somehow the average galaxy size has increased as the Universe has evolved. Galaxies often collide and then merge to form larger systems and this process is certainly an important growth mechanism. However, an additional, gentler way has been proposed. A European team of astronomers has used ESO's Very Large Telescope to test this very different idea - that young galaxies can also grow by sucking in cool streams of the hydrogen and helium gas that filled the early Universe and forming new stars from this primitive material. Just as a commercial company can expand either by merging with other companies, or by hiring more staff, young galaxies could perhaps also grow in two different ways - by merging with other galaxies or by accreting material. The team leader, Giovanni Cresci (Osservatorio Astrofisico di Arcetri) says: "The new results from the VLT are the first direct evidence that the accretion of pristine gas really happened and was enough to fuel vigorous star formation and the growth of massive galaxies in the young Universe." The discovery will have a major impact on our understanding of the evolution of the Universe from the Big Bang to the present day. Theories of galaxy formation and evolution may have to be re-written. The group began by selecting three very distant galaxies to see if they could find evidence

  8. CONSTRAINTS ON THE ASSEMBLY AND DYNAMICS OF GALAXIES. II. PROPERTIES OF KILOPARSEC-SCALE CLUMPS IN REST-FRAME OPTICAL EMISSION OF z ∼ 2 STAR-FORMING GALAXIES

    Foerster Schreiber, N. M.; Genzel, R.; Davies, R.; Genel, S.; Lutz, D.; Tacconi, L. J.; Shapley, A. E.; Bouche, N.; Cresci, G.; Erb, D. K.; Newman, S.; Shapiro, K. L.; Steidel, C. C.; Sternberg, A.

    2011-01-01

    We study the properties of luminous stellar 'clumps' identified in deep, high-resolution Hubble Space Telescope NIC2/F160W imaging at 1.6 μm of six z ∼ 2 star-forming galaxies with existing near-infrared integral field spectroscopy from SINFONI at the Very Large Telescope. Individual clumps contribute ∼0.5%-15% of the galaxy-integrated rest-frame ∼5000 A emission, with median of ∼2%; the total contribution of clump light ranges from 10% to 25%. The median intrinsic clump size and stellar mass are ∼1 kpc and ∼10 9 M sun , in the ranges for clumps identified in rest-UV or line emission in other studies. The clump sizes and masses in the subset of disks are broadly consistent with expectations for clump formation through gravitational instabilities in gas-rich, turbulent disks given the host galaxies' global properties. By combining the NIC2 data with Advanced Camera for Surveys (ACS)/F814W imaging available for one source, and adaptive-optics-assisted SINFONI Hα data for another, we infer modest color, M/L, and stellar age variations within each galaxy. In these two objects, sets of clumps identified at different wavelengths do not fully overlap; NIC2-identified clumps tend to be redder/older than ACS- or Hα-identified clumps without rest-frame optical counterparts. There is evidence for a systematic trend of older ages at smaller galactocentric radii among the clumps, consistent with scenarios where inward migration of clumps transports material toward the central regions. From constraints on a bulge-like component at radii ∼< 1-3 kpc, none of the five disks in our sample appears to contain a compact massive stellar core, and we do not discern a trend of bulge stellar mass fraction with stellar age of the galaxy. Further observations are necessary to probe the buildup of stellar bulges and the role of clumps in this process.

  9. Interstellar matter within elliptical galaxies

    Jura, Michael

    1988-01-01

    Multiwavelength observations of elliptical galaxies are reviewed, with an emphasis on their implications for theoretical models proposed to explain the origin and evolution of the interstellar matter. Particular attention is given to interstellar matter at T less than 100 K (atomic and molecular gas and dust), gas at T = about 10,000 K, and gas at T = 10 to the 6th K or greater. The data are shown to confirm the occurrence of mass loss from evolved stars, significant accretion from companion galaxies, and cooling inflows; no evidence is found for large mass outflow from elliptical galaxies.

  10. DESI focal plate mechanical integration and cooling

    Lambert, A. R.; Besuner, R. W.; Claybaugh, T. M.; Silber, J. H.

    2016-08-01

    The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique[1]. The spectra of 40 million galaxies over 14000 sq. deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad-band spectrographs. This paper describes the mechanical integration of the DESI focal plate and the thermal system design. The DESI focal plate is comprised of ten identical petal assemblies. Each petal contains 500 robotic fiber positioners. Each petal is a complete, self-contained unit, independent from the others, with integrated power supply, controllers, fiber routing, and cooling services. The major advantages of this scheme are: (1) supports installation and removal of complete petal assemblies in-situ, without disturbing the others, (2) component production, assembly stations, and test procedures are repeated and parallelizable, (3) a complete, full-scale prototype can be built and tested at an early date, (4) each production petal can be surveyed and tested as a complete unit, prior to integration, from the fiber tip at the focal surface to the fiber slit at the spectrograph. The ten petal assemblies will be installed in a single integration ring, which is mounted to the DESI corrector. The aluminum integration ring attaches to the steel corrector barrel via a flexured steel adapter, isolating the focal plate from differential thermal expansions. The plate scale will be kept stable by conductive cooling of the petal assembly. The guider and wavefront sensors (one per petal) will be convectively cooled by forced flow of air. Heat will be removed from the system at ten liquid-cooled cold plates, one per petal, operating at ambient temperature. The entire focal plate structure is enclosed in an insulating shroud, which serves as a thermal barrier

  11. Power electronics cooling apparatus

    Sanger, Philip Albert; Lindberg, Frank A.; Garcen, Walter

    2000-01-01

    A semiconductor cooling arrangement wherein a semiconductor is affixed to a thermally and electrically conducting carrier such as by brazing. The coefficient of thermal expansion of the semiconductor and carrier are closely matched to one another so that during operation they will not be overstressed mechanically due to thermal cycling. Electrical connection is made to the semiconductor and carrier, and a porous metal heat exchanger is thermally connected to the carrier. The heat exchanger is positioned within an electrically insulating cooling assembly having cooling oil flowing therethrough. The arrangement is particularly well adapted for the cooling of high power switching elements in a power bridge.

  12. THE AGORA HIGH-RESOLUTION GALAXY SIMULATIONS COMPARISON PROJECT

    Kim, Ji-hoon; Conroy, Charlie; Goldbaum, Nathan J.; Krumholz, Mark R.; Abel, Tom; Agertz, Oscar; Gnedin, Nickolay Y.; Kravtsov, Andrey V.; Bryan, Greg L.; Ceverino, Daniel; Christensen, Charlotte; Hummels, Cameron B.; Dekel, Avishai; Guedes, Javiera; Hahn, Oliver; Hobbs, Alexander; Hopkins, Philip F.; Iannuzzi, Francesca; Keres, Dusan; Klypin, Anatoly

    2014-01-01

    We introduce the Assembling Galaxies Of Resolved Anatomy (AGORA) project, a comprehensive numerical study of well-resolved galaxies within the ΛCDM cosmology. Cosmological hydrodynamic simulations with force resolutions of ∼100 proper pc or better will be run with a variety of code platforms to follow the hierarchical growth, star formation history, morphological transformation, and the cycle of baryons in and out of eight galaxies with halo masses M vir ≅ 10 10 , 10 11 , 10 12 , and 10 13 M ☉ at z = 0 and two different ('violent' and 'quiescent') assembly histories. The numerical techniques and implementations used in this project include the smoothed particle hydrodynamics codes GADGET and GASOLINE, and the adaptive mesh refinement codes ART, ENZO, and RAMSES. The codes share common initial conditions and common astrophysics packages including UV background, metal-dependent radiative cooling, metal and energy yields of supernovae, and stellar initial mass function. These are described in detail in the present paper. Subgrid star formation and feedback prescriptions will be tuned to provide a realistic interstellar and circumgalactic medium using a non-cosmological disk galaxy simulation. Cosmological runs will be systematically compared with each other using a common analysis toolkit and validated against observations to verify that the solutions are robust—i.e., that the astrophysical assumptions are responsible for any success, rather than artifacts of particular implementations. The goals of the AGORA project are, broadly speaking, to raise the realism and predictive power of galaxy simulations and the understanding of the feedback processes that regulate galaxy 'metabolism'. The initial conditions for the AGORA galaxies as well as simulation outputs at various epochs will be made publicly available to the community. The proof-of-concept dark-matter-only test of the formation of a galactic halo with a z = 0 mass of M

  13. Liquid metal cooled nuclear reactor

    Leigh, K.M.

    1980-01-01

    A liquid metal cooled nuclear reactor is described, wherein coolant is arranged to be flowed upwardly through a fuel assembly and having one or more baffles located above the coolant exit of the fuel assembly, the baffles being arranged so as to convert the upwardly directed motion of liquid metal coolant leaving the fuel assembly into a substantially horizontal motion. (author)

  14. Galaxy formation

    Gribbin, J.

    1979-01-01

    The current debate on the origin and evolution of galaxies is reviewed and evidence to support the so-called 'isothermal' and 'adiabatic' fluctuation models considered. It is shown that new theories have to explain the formation of both spiral and elliptical galaxies and the reason for their differences. It is stated that of the most recent models the best indicates that rotating spiral galaxies are formed naturally when gas concentrates in the centre of a great halo and forms stars while ellipticals are explained by later interactions between spiral galaxies and merging, which can cancel out the rotation while producing an elliptical galaxy in which the stars, coming from two original galaxies, follow very elliptical, anisotropic orbits. (UK)

  15. PAIRING OF SUPERMASSIVE BLACK HOLES IN UNEQUAL-MASS GALAXY MERGERS

    Callegari, Simone; Mayer, Lucio; Kazantzidis, Stelios; Colpi, Monica; Governato, Fabio; Quinn, Thomas; Wadsley, James

    2009-01-01

    We examine the pairing process of supermassive black holes (SMBHs) down to scales of 20-100 pc using a set of N-body/SPH simulations of binary mergers of disk galaxies with mass ratios of 1:4 and 1:10. Our numerical experiments are designed to represent merger events occurring at various cosmic epochs. The initial conditions of the encounters are consistent with the ΛCDM paradigm of structure formation, and the simulations include the effects of radiative cooling, star formation (SF), and supernovae feedback. We find that the pairing of SMBHs depends sensitively on the amount of baryonic mass preserved in the center of the companion galaxies during the last phases of the merger. In particular, due to the combination of gasdynamics and SF, we find that a pair of SMBHs can form efficiently in 1:10 minor mergers, provided that galaxies are relatively gas-rich (gas fractions of 30% of the disk mass) and that the mergers occur at relatively high redshift (z ∼ 3), when dynamical friction timescales are shorter. Since 1:10 mergers are most common events during the assembly of galaxies, and mergers are more frequent at high redshift when galaxies are also more gas-rich, our results have positive implications for future gravitational wave experiments such as the Laser Interferometer Space Antenna.

  16. The dark side of galaxy colour

    Hearin, Andrew P.; Watson, Douglas F.

    2013-10-01

    We present age distribution matching, a theoretical formalism for predicting how galaxies of luminosity L and colour C occupy dark matter haloes. Our model supposes that there are just two fundamental properties of a halo that determine the colour and brightness of the galaxy it hosts: the maximum circular velocity Vmax and the redshift zstarve that correlates with the epoch at which the star formation in the galaxy ceases. The halo property zstarve is intended to encompass physical characteristics of halo mass assembly that may deprive the galaxy of its cold gas supply and, ultimately, quench its star formation. The new, defining feature of the model is that, at fixed luminosity, galaxy colour is in monotonic correspondence with zstarve, with the larger values of zstarve being assigned redder colours. We populate an N-body simulation with a mock galaxy catalogue based on age distribution matching and show that the resulting mock galaxy distribution accurately describes a variety of galaxy statistics. Our model suggests that halo and galaxy assembly are indeed correlated. We make publicly available our low-redshift, Sloan Digital Sky Survey Mr < -19 mock galaxy catalogue, and main progenitor histories of all z = 0 haloes, at http://logrus.uchicago.edu/~aphearin

  17. PRECIPITATION-REGULATED STAR FORMATION IN GALAXIES

    Voit, G. Mark; O’Shea, Brian W.; Donahue, Megan; Bryan, Greg L.

    2015-01-01

    Galaxy growth depends critically on the interplay between radiative cooling of cosmic gas and the resulting energetic feedback that cooling triggers. This interplay has proven exceedingly difficult to model, even with large supercomputer simulations, because of its complexity. Nevertheless, real galaxies are observed to obey simple scaling relations among their primary observable characteristics. Here we show that a generic emergent property of the interplay between cooling and feedback can explain the observed scaling relationships between a galaxy's stellar mass, its total mass, and its chemical enrichment level, as well as the relationship between the average orbital velocity of its stars and the mass of its central black hole. These relationships naturally result from any feedback mechanism that strongly heats a galaxy's circumgalactic gas in response to precipitation of colder clouds out of that gas, because feedback then suspends the gas in a marginally precipitating state

  18. A search for megamaser galaxies

    Norris, R.P.; Gardner, F.F.; Whiteoak, J.B.

    1989-01-01

    The results are reported of a search for OH megamaser emission from a sample of 32 galaxies selected from the IRAS Point Source Catalog on the basis of their infrared properties. For each galaxy (other than those few already observed elsewhere) we have obtained an optical redshift and have searched for both OH and H I emission. The search yielded one new OH megamaser galaxy and H I was detected towards nine objects. We conclude that there are unlikely to be any OH megamasers in the Southern Hemisphere with flux densities comparable to that of Arp 220 (280 mJy), although there may be a population of weaker megamasers. From the statistics of our search we conclude that no special conditions are required to explain the known OH megamasers other than those expected in a cool, dusty, active galaxy. (author)

  19. Development of Mathematical Model and Analysis Code for Estimating Drop Behavior of the Control Rod Assembly in the Sodium Cooled Fast Reactor

    Oh, Se-Hong; Kang, SeungHoon; Choi, Choengryul; Yoon, Kyung Ho; Cheon, Jin Sik

    2016-01-01

    On receiving the scram signal, the control rod assemblies are released to fall into the reactor core by its weight. Thus drop time and falling velocity of the control rod assembly must be estimated for the safety evaluation. There are three typical ways to estimate the drop behavior of the control rod assembly in scram action: Experimental, numerical and theoretical methods. But experimental and numerical(CFD) method require a lot of cost and time. Thus, these methods are difficult to apply to the initial design process. In this study, mathematical model and theoretical analysis code have been developed in order to estimate drop behavior of the control rod assembly to provide the underlying data for the design optimization. Mathematical model and theoretical analysis code have been developed in order to estimate drop behavior of the control rod assembly to provide the underlying data for the design optimization. A simplified control rod assembly model is considered to minimize the uncertainty in the development process. And the hydraulic circuit analysis technique is adopted to evaluate the internal/external flow distribution of the control rod assembly. Finally, the theoretical analysis code(named as HEXCON) has been developed based on the mathematical model. To verify the reliability of the developed code, CFD analysis has been conducted. And a calculation using the developed analysis code was carried out under the same condition, and both results were compared

  20. Cooling techniques

    Moeller, S.P.

    1994-01-01

    After an introduction to the general concepts of cooling of charged particle beams, some specific cooling methods are discussed, namely stochastic, electron and laser cooling. The treatment concentrates on the physical ideas of the cooling methods and only very crude derivations of cooling times are given. At the end three other proposed cooling schemes are briefly discussed. (orig.)

  1. Determining initial enrichment, burnup, and cooling time of pressurized-water-reactor spent fuel assemblies by analyzing passive gamma spectra measured at the Clab interim-fuel storage facility in Sweden

    Favalli, A., E-mail: afavalli@lanl.gov [Los Alamos National Laboratory, Los Alamos, NM (United States); Vo, D. [Los Alamos National Laboratory, Los Alamos, NM (United States); Grogan, B. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Jansson, P. [Uppsala University, Uppsala (Sweden); Liljenfeldt, H. [Oak Ridge National Laboratory, Oak Ridge, TN (United States); Mozin, V. [Lawrence Livermore National Laboratory, Livermore, CA (United States); Schwalbach, P. [European Commission, DG Energy, Euratom Safeguards Luxemburg, Luxemburg (Luxembourg); Sjöland, A. [Swedish Nuclear Fuel and Waste Management Company, Stockholm (Sweden); Tobin, S.J.; Trellue, H. [Los Alamos National Laboratory, Los Alamos, NM (United States); Vaccaro, S. [European Commission, DG Energy, Euratom Safeguards Luxemburg, Luxemburg (Luxembourg)

    2016-06-01

    The purpose of the Next Generation Safeguards Initiative (NGSI)–Spent Fuel (SF) project is to strengthen the technical toolkit of safeguards inspectors and/or other interested parties. The NGSI–SF team is working to achieve the following technical goals more easily and efficiently than in the past using nondestructive assay measurements of spent fuel assemblies: (1) verify the initial enrichment, burnup, and cooling time of facility declaration; (2) detect the diversion or replacement of pins; (3) estimate the plutonium mass [which is also a function of the variables in (1)]; (4) estimate the decay heat; and (5) determine the reactivity of spent fuel assemblies. Since August 2013, a set of measurement campaigns has been conducted at the Central Interim Storage Facility for Spent Nuclear Fuel (Clab), in collaboration with Swedish Nuclear Fuel and Waste Management Company (SKB). One purpose of the measurement campaigns was to acquire passive gamma spectra with high-purity germanium and lanthanum bromide scintillation detectors from Pressurized Water Reactor and Boiling Water Reactor spent fuel assemblies. The absolute {sup 137}Cs count rate and the {sup 154}Eu/{sup 137}Cs, {sup 134}Cs/{sup 137}Cs, {sup 106}Ru/{sup 137}Cs, and {sup 144}Ce/{sup 137}Cs isotopic ratios were extracted; these values were used to construct corresponding model functions (which describe each measured quantity’s behavior over various combinations of burnup, cooling time, and initial enrichment) and then were used to determine those same quantities in each measured spent fuel assembly. The results obtained in comparison with the operator declared values, as well as the methodology developed, are discussed in detail in the paper.

  2. Determining initial enrichment, burnup, and cooling time of pressurized-water-reactor spent fuel assemblies by analyzing passive gamma spectra measured at the Clab interim-fuel storage facility in Sweden

    Favalli, A.; Vo, D.; Grogan, B.; Jansson, P.; Liljenfeldt, H.; Mozin, V.; Schwalbach, P.; Sjöland, A.; Tobin, S. J.; Trellue, H.; Vaccaro, S.

    2016-06-01

    The purpose of the Next Generation Safeguards Initiative (NGSI)-Spent Fuel (SF) project is to strengthen the technical toolkit of safeguards inspectors and/or other interested parties. The NGSI-SF team is working to achieve the following technical goals more easily and efficiently than in the past using nondestructive assay measurements of spent fuel assemblies: (1) verify the initial enrichment, burnup, and cooling time of facility declaration; (2) detect the diversion or replacement of pins; (3) estimate the plutonium mass [which is also a function of the variables in (1)]; (4) estimate the decay heat; and (5) determine the reactivity of spent fuel assemblies. Since August 2013, a set of measurement campaigns has been conducted at the Central Interim Storage Facility for Spent Nuclear Fuel (Clab), in collaboration with Swedish Nuclear Fuel and Waste Management Company (SKB). One purpose of the measurement campaigns was to acquire passive gamma spectra with high-purity germanium and lanthanum bromide scintillation detectors from Pressurized Water Reactor and Boiling Water Reactor spent fuel assemblies. The absolute 137Cs count rate and the 154Eu/137Cs, 134Cs/137Cs, 106Ru/137Cs, and 144Ce/137Cs isotopic ratios were extracted; these values were used to construct corresponding model functions (which describe each measured quantity's behavior over various combinations of burnup, cooling time, and initial enrichment) and then were used to determine those same quantities in each measured spent fuel assembly. The results obtained in comparison with the operator declared values, as well as the methodology developed, are discussed in detail in the paper.

  3. A study of the friction and wear processes of the structural components of fuel assemblies for water-cooled and water moderated power reactors

    Makarov, V.; Afanasiev, A.; Matvienko, I.; Drozdov, Y.; Puchkov, V.

    2011-01-01

    The friction forces affect the fuel assembly (FA) strength at all the stages of its lifecycle. The paper covers the methods and the results of the pre-irradiation experimental studies of the static and dynamic processes the friction forces are involved in. These comprise the FA assembling at the manufacturer, fuel rod flow-induced vibration and fretting-wear in the fuel rod-to-cell friction pairs, rod cluster control assembly (RCCA) movement in the FA guide tubes, FA bowing, FA loading-unloading into the core, irradiation-induced growth and thermal-mechanical fuel rod-to-spacer grid interaction. (authors)

  4. Galaxy formation

    Silk, J.; Di Cintio, A.; Dvorkin, I.

    2014-01-01

    Galaxy formation is at the forefront of observation and theory in cosmology. An improved understanding is essential for improving our knowledge both of the cosmological parameters, of the contents of the universe, and of our origins. In these lectures intended for graduate students, galaxy formation theory is reviewed and confronted with recent observational issues. In lecture 1, the following topics are presented: star formation considerations, including IMF, star formation efficiency and star formation rate, the origin of the galaxy luminosity function, and feedback in dwarf galaxies. In lecture 2, we describe formation of disks and massive spheroids, including the growth of supermassive black holes, negative feedback in spheroids, the AGN-star formation connection, star formation rates at high redshift and the baryon fraction in galaxies.

  5. Dry cooling towers - the Schmehausen example

    Weber, P.

    1977-01-01

    In a prototype, there are often problems which require special static, constructive, and assembling measures for their solution. In the case of the Schmehausen dry cooling tower, the demands on the assembling technology are particularly high. (orig.) [de

  6. Fuel assembly

    Kurihara, Kunitoshi; Azekura, Kazuo.

    1992-01-01

    In a reactor core of a heavy water moderated light water cooled pressure tube type reactor, no sufficient effects have been obtained for the transfer width to a negative side of void reactivity change in a region of a great void coefficient. Then, a moderation region divided into upper and lower two regions is disposed at the central portion of a fuel assembly. Coolants flown into the lower region can be discharged to the cooling region from an opening disposed at the upper end portion of the lower region. Light water flows from the lower region of the moderator region to the cooling region of the reactor core upper portion, to lower the void coefficient. As a result, the reactivity performance at low void coefficient, i.e., a void reaction rate is transferred to the negative side. Thus, this flattens the power distribution in the fuel assembly, increases the thermal margin and enables rapid operaiton and control of the reactor core, as well as contributes to the increase of fuel burnup ratio and reduction of the fuel cycle cost. (N.H.)

  7. Nuclear reactor fuel assembly

    Marmonier, Pierre; Mesnage, Bernard; Nervi, J.C.

    1975-01-01

    This invention refers to fuel assemblies for a liquid metal cooled fast neutron reactor. Each assembly is composed of a hollow vertical casing, of regular polygonal section, containing a bundle of clad pins filled with a fissile or fertile substance. The casing is open at its upper end and has a cylindrical foot at its lower end for positioning the assembly in a housing provided in the horizontal diagrid, on which the core assembly rests. A set of flat bars located on the external surface of the casing enables it to be correctly orientated in its housing among the other core assemblies [fr

  8. Fuel assembly

    Ueda, Sei; Ando, Ryohei; Mitsutake, Toru.

    1995-01-01

    The present invention concerns a fuel assembly suitable to a BWR-type reactor and improved especially with the nuclear characteristic, heat performance, hydraulic performance, dismantling or assembling performance and economical property. A part of poison rods are formed as a large-diameter/multi-region poison rods having a larger diameter than a fuel rod. A large number of fuel rods are disposed surrounding a large diameter water rod and a group of the large-diameter/multi-region poison rods in adjacent with the water rod. The large-diameter water rod has a burnable poison at the tube wall portion. At least a portion of the large-diameter poison rods has a coolant circulation portion allowing coolants to circulate therethrough. Since the large-diameter poison rods are disposed at a position of high neutron fluxes, a large neutron multiplication factor suppression effect can be provided, thereby enabling to reduce the number of burnable poison rods relative to fuels. As a result, power peaking in the fuel assembly is moderated and a greater amount of plutonium can be loaded. In addition the flow of cooling water which tends to gather around the large diameter water rod can be controlled to improve cooling performance of fuels. (N.H.)

  9. Deficiency of normal galaxies among Markaryan galaxies

    Iyeveer, M.M.

    1986-01-01

    Comparison of the morphological types of Markaryan galaxies and other galaxies in the Uppsala catalog indicates a strong deficiency of normal ellipticals among the Markaryan galaxies, for which the fraction of type E galaxies is ≤ 1% against 10% among the remaining galaxies. Among the Markaryan galaxies, an excess of barred galaxies is observed - among the Markaryan galaxies with types Sa-Scd, approximately half or more have bars, whereas among the remaining galaxies of the same types bars are found in about 1/3

  10. The formation and evolution of galaxies in an expanding universe

    Ceverino-Rodriguez, Daniel

    This PhD thesis is part of an ongoing effort in improving the theory of galaxy formation in a LCDM Universe. We include more realistic models of radiative cooling, star formation, and stellar feedback. A special attention has been given to the role of supernova explosions and stellar winds in the galaxy assembly. These processes happen at very small scales (parsecs), but they affect the inter-stellar medium (ISM) at Kpc-scales and regulate the formation of a whole galaxy. Previous attempts of mimicking these effects in simulations of galaxy formation use very simplified assumptions. We develop a much more realistic prescription for modeling the feedback, which minimizes any ad hoc sub-grid physics. We start with developing high resolution models of the ISM and formulate the conditions required for its realistic functionality: formation of a multi-phase medium with hot chimneys, super-bubbles, cold molecular phase, and very slow consumption of gas. We find that this can be achieved only by doing what the real Universe does: formation of dense (> 10 H atoms cm -3 ), cold ( T [approximate] 100 K) molecular phase, where star formation happens, and which young stars disrupt. Another important ingredient is the effect of runaway stars: massive binary stars ejected from molecular clouds when one of the companions becomes a supernova. These stars can move to 10-100 parsecs away from molecular clouds before exploding themselves as supernovae. This greatly facilitates the feedback. Once those effects are implemented into cosmological simulations, galaxy formation proceeds more realistically. For example, we do not have the overcooling problem. The angular momentum problem (resulting in a too massive bulge) is also reduced substantially: the rotation curves are nearly flat. The galaxy formation also becomes more violent. Just as often observed in absorption lines studies, there are substantial outflows from forming and active galaxies. At high redshifts we routinely find gas

  11. Galaxy Formation

    Longair, Malcolm S

    2008-01-01

    This second edition of Galaxy Formation is an up-to-date text on astrophysical cosmology, expounding the structure of the classical cosmological models from a contemporary viewpoint. This forms the background to a detailed study of the origin of structure and galaxies in the Universe. The derivations of many of the most important results are derived by simple physical arguments which illuminate the results of more advanced treatments. A very wide range of observational data is brought to bear upon these problems, including the most recent results from WMAP, the Hubble Space Telescope, galaxy surveys like the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey, studies of Type 1a supernovae, and many other observations.

  12. Powerful warm infrared sources in early-type galaxies

    Dressel, L.L.

    1988-01-01

    IRAS far-infrared sources have been identified with 129 S0, Sa, Sb, and Sc galaxies in a statistically complete sample of 738 galaxies brighter than 14.5 mag and smaller than 4.0 arcmin. In most cases, the far-IR colors and the ratios of far-IR flux to radio flux density are those of normal galactic disks and/or starbursts. The most powerful far-IR sources in S0 and Sa galaxies are just as powerful as the strongest far-IR sources in Sb and Sc galaxies. Bright-IR sources in S0 and Sa galaxies are warm; those in Sc galaxies are cool. Sb galaxies have both warm and cool IR sources. Bright warm IR sources occur much more frequently in barred galaxies than in galaxies without bars for types S0, Sa, and Sb. Bright, cool IR sources are found with increasing frequency along the Hubble sequence, regardless of the presence or absence of a bar. At least some S0 galaxies with warm, bright IR sources have peculiar morphologies and ambiguous classifications. 22 references

  13. Predicting galaxy star formation rates via the co-evolution of galaxies and haloes

    Watson, Douglas F.; Hearin, Andrew P.; Berlind, Andreas A.; Becker, Matthew R.; Behroozi, Peter S.; Skibba, Ramin A.; Reyes, Reinabelle; Zentner, Andrew R.; van den Bosch, Frank C.

    2015-01-01

    In this paper, we test the age matching hypothesis that the star formation rate (SFR) of a galaxy of fixed stellar mass is determined by its dark matter halo formation history, e.g. more quiescent galaxies reside in older haloes. We present new Sloan Digital Sky Survey measurements of the galaxy two-point correlation function and galaxy-galaxy lensing as a function of stellar mass and SFR, separated into quenched and star-forming galaxy samples to test this simple model. We find that our age matching model is in excellent agreement with these new measurements. We also find that our model is able to predict: (1) the relative SFRs of central and satellite galaxies, (2) the SFR dependence of the radial distribution of satellite galaxy populations within galaxy groups, rich groups, and clusters and their surrounding larger scale environments, and (3) the interesting feature that the satellite quenched fraction as a function of projected radial distance from the central galaxy exhibits an ˜r-.15 slope, independent of environment. These accurate predictions are intriguing given that we do not explicitly model satellite-specific processes after infall, and that in our model the virial radius does not mark a special transition region in the evolution of a satellite. The success of the model suggests that present-day galaxy SFR is strongly correlated with halo mass assembly history.

  14. And the Title for Densest Galaxy Goes To…

    Kohler, Susanna

    2015-07-01

    than even that! It's such an unusual stellar system that it defies classification in the usual categories, which is why Sandoval and collaborators created a new name for this type of object: hypercompact cluster. In spite of the differences between these two stellar systems, the team argues that there is evidence that they were formed the same way. They believe that both objects are galactic centers that have been tidally stripped of all of the outlying stars and gas, leaving only the dense cores behind. They argue that this could be caused by mergers of M59 and M85 with intermediate mass galaxies. If true, searching for more of these unique objects could provide us with clues to how galaxies were assembled. Citation: Michael Sandoval et al. 2015 ApJ 808 L32 doi:10.1088/2041-8205/808/1/L32 Bonus: Check out this cool visualization from the authors of how tidal stripping of a small galaxy might happen. This is one theory of how UCDs are formed. Click here to view the video on YouTube.

  15. ARCHANGEL: Galaxy Photometry System

    Schombert, James

    2011-07-01

    ARCHANGEL is a Unix-based package for the surface photometry of galaxies. While oriented for large angular size systems (i.e. many pixels), its tools can be applied to any imaging data of any size. The package core contains routines to perform the following critical galaxy photometry functions: sky determination; frame cleaning; ellipse fitting; profile fitting; and total and isophotal magnitudes. The goal of the package is to provide an automated, assembly-line type of reduction system for galaxy photometry of space-based or ground-based imaging data. The procedures outlined in the documentation are flux independent, thus, these routines can be used for non-optical data as well as typical imaging datasets. ARCHANGEL has been tested on several current OS's (RedHat Linux, Ubuntu Linux, Solaris, Mac OS X). A tarball for installation is available at the download page. The main routines are Python and FORTRAN based, therefore, a current installation of Python and a FORTRAN compiler are required. The ARCHANGEL package also contains Python hooks to the PGPLOT package, an XML processor and network tools which automatically link to data archives (i.e. NED, HST, 2MASS, etc) to download images in a non-interactive manner.

  16. Galaxy Tagging: photometric redshift refinement and group richness enhancement

    Kafle, P. R.; Robotham, A. S. G.; Driver, S. P.; Deeley, S.; Norberg, P.; Drinkwater, M. J.; Davies, L. J.

    2018-06-01

    We present a new scheme, galtag, for refining the photometric redshift measurements of faint galaxies by probabilistically tagging them to observed galaxy groups constructed from a brighter, magnitude-limited spectroscopy survey. First, this method is tested on the DESI light-cone data constructed on the GALFORM galaxy formation model to tests its validity. We then apply it to the photometric observations of galaxies in the Kilo-Degree Imaging Survey (KiDS) over a 1 deg2 region centred at 15h. This region contains Galaxy and Mass Assembly (GAMA) deep spectroscopic observations (i-bandhttps://github.com/pkaf/galtag.git.

  17. Where do galaxies end?

    Shull, J. Michael, E-mail: michael.shull@colorado.edu [CASA, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USAAND (United States); Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA (United Kingdom)

    2014-04-01

    Our current view of galaxies considers them as systems of stars and gas embedded in extended halos of dark matter, much of it formed by the infall of smaller systems at earlier times. The true extent of a galaxy remains poorly determined, with the 'virial radius' (R {sub vir}) providing a characteristic separation between collapsed structures in dynamical equilibrium and external infalling matter. Other physical estimates of the extent of gravitational influence include the gravitational radius, gas accretion radius, and 'galactopause' arising from outflows that stall at 100-200 kpc over a range of outflow parameters and confining gas pressures. Physical criteria are proposed to define bound structures, including a more realistic definition of R {sub vir}(M {sub *}, M{sub h} , z{sub a} ) for stellar mass M {sub *} and halo mass M{sub h} , half of which formed at 'assembly redshifts' ranging from z{sub a} ≈ 0.7-1.3. We estimate the extent of bound gas and dark matter around L* galaxies to be ∼200 kpc. The new virial radii, with mean (R {sub vir}) ≈ 200 kpc, are 40%-50% smaller than values estimated in recent Hubble Space Telescope/Cosmic Origins Spectrograph detections of H I and O VI absorbers around galaxies. In the new formalism, the Milky Way stellar mass, log M {sub *} = 10.7 ± 0.1, would correspond to R{sub vir}=153{sub −16}{sup +25} kpc for half-mass halo assembly at z{sub a} = 1.06 ± 0.03. The frequency per unit redshift of low-redshift O VI absorption lines in QSO spectra suggests absorber sizes ∼150 kpc when related to intervening 0.1L* galaxies. This formalism is intended to clarify semantic differences arising from observations of extended gas in galactic halos, circumgalactic medium (CGM), and filaments of the intergalactic medium (IGM). Astronomers should refer to bound gas in the galactic halo or CGM, and unbound gas at the CGM-IGM interface, on its way into the IGM.

  18. Superclusters and galaxy formation

    Einasto, J.; Joeveer, M.; Saar, E.

    1979-01-01

    The spatial distribution of Galaxies and Galaxy congestions in the southern galactic hemisphere is studied. The rich galaxy congestions, containing many elliptic Galaxies and radiogalaxies, are linked with each other by chains of scanty congestions with moderate content of elliptic Galaxies and radiogalaxies. The flat formation, linking the density pikes and the intermediate chains, can reasonably be called supercongestion. In the central region of supercongestions there is a thin layer of Galaxies consisting of only spiral Galaxies. The neighbouring supercongestions touch each other, while the intersupercongestion space contains no Galaxy congestions and almost no Galaxies. It is shown that such a structure was, apparently, formed before the formation of Galaxies

  19. Fuel assembly

    Nomata, Terumitsu.

    1993-01-01

    Among fuel pellets to be loaded to fuel cans of a fuel assembly, fuel pellets having a small thermal power are charged in a region from the end of each of spacers up to about 50mm on the upstream of coolants that flow vertically at the periphery of fuel rods. Coolants at the periphery of fuel rods are heated by the heat generation, to result in voids. However, since cooling effect on the upstream of the spacers is low due to influences of the spacers. Further, since the fuel pellets disposed in the upstream region have small thermal power, a void coefficient is not increased. Even if a thermal power exceeding cooling performance should be generated, there is no worry of causing burnout in the upstream region. Even if burnout should be caused, safety margin and reliability relative to burnout are improved, to increase an allowable thermal power, thereby enabling to improve integrity and reliability of fuel rods and fuel assemblies. (N.H.)

  20. Cooling Grapple System for FMEF hot cell

    Semmens, L.S.; Frandsen, G.B.; Tome, R.

    1983-01-01

    A Cooling Grapple System was designed and built to handle fuel assemblies within the FMEF hot cell. The variety of functions for which it is designed makes it unique from grapples presently in use. The Cooling Grapple can positively grip and transport assemblies vertically, retrieve assemblies from molten sodium where six inches of grapple tip is submerged, cool 7 kw assemblies in argon, and service an in-cell area of 372 m 2 (4000 ft 2 ). Novel and improved operating and maintenance features were incorporated in the design including a shear pin and mechanical catcher system to prevent overloading the grapple while allowing additional reaction time for crane shutdown

  1. S0 galaxies in Formax

    Bedregal...[], A. G.; Aragón-Salamanca, A.; Merrifield, M. R.

    2006-01-01

    Galaxies: elliptical and lenticular, cD: galaxies: kinematics and dynamics Udgivelsesdato: Oct.1......Galaxies: elliptical and lenticular, cD: galaxies: kinematics and dynamics Udgivelsesdato: Oct.1...

  2. Liquid metal cooled fast breeder nuclear reactors

    Thatcher, G.; Mitchell, A.J.

    1981-01-01

    Fuel sub-assemblies for liquid metal-cooled fast breeder reactors are described which each incorporate a fluid flow control valve for regulating the rate of flow through the sub-assembly. These small electro-magnetic valves seek to maintain the outlet coolant temperature of at least some of the breeder sub-assemblies substantially constant throughout the life of the fuel assembly without severely pressurising the sub-assembly. (U.K.)

  3. Galaxy formation and physical bias

    Cen, Renyue; Ostriker, Jeremiah P.

    1992-01-01

    We have supplemented our code, which computes the evolution of the physical state of a representative piece of the universe to include, not only the dynamics of dark matter (with a standard PM code), and the hydrodynamics of the gaseous component (including detailed collisional and radiative processes), but also galaxy formation on a heuristic but plausible basis. If, within a cell the gas is Jeans' unstable, collapsing, and cooling rapidly, it is transformed to galaxy subunits, which are then followed with a collisionless code. After grouping them into galaxies, we estimate the relative distributions of galaxies and dark matter and the relative velocities of galaxies and dark matter. In a large scale CDM run of 80/h Mpc size with 8 x 10 exp 6 cells and dark matter particles, we find that physical bias b is on the 8/h Mpc scale is about 1.6 and increases towards smaller scales, and that velocity bias is about 0.8 on the same scale. The comparable HDM simulation is highly biased with b = 2.7 on the 8/h Mpc scale. Implications of these results are discussed in the light of the COBE observations which provide an accurate normalization for the initial power spectrum. CDM can be ruled out on the basis of too large a predicted small scale velocity dispersion at greater than 95 percent confidence level.

  4. Fred Hoyle: Contributions to the Theory of Galaxy Formation

    Efstathiou, G.

    2003-01-01

    I review two fundamental contributions that Fred Hoyle made to the theory of galaxy formation. Hoyle was the first to propose that protogalaxies acquired their angular momentum via tidal torques from neighbouring perturbations during a period of gravitational instability. To my knowledge, he was also the first to suggest that the masses of galaxies could be explained by the requirement that primordial gas clouds cool radiatively on a suitable timescale. Tidal torques and cooling arguments pla...

  5. Cooling device for reactor container

    Arai, Kenji.

    1996-01-01

    Upon assembling a static container cooling system to an emergency reactor core cooling system using dynamic pumps in a power plant, the present invention provides a cooling device of lowered center of gravity and having a good cooling effect by lowering the position of a cooling water pool of the static container cooling system. Namely, the emergency reactor core cooling system injects water to the inside of a pressure vessel using emergency cooling water stored in a suppression pool as at least one water source upon loss of reactor coolant accident. In addition, a cooling water pool incorporating a heat exchanger is disposed at the circumference of the suppression pool at the outside of the container. A dry well and the heat exchanger are connected by way of steam supply pipes, and the heat exchanger is connected with the suppression pool by way of a gas exhaustion pipe and a condensate returning pipeline. With such a constitution, the position of the heat exchanger is made higher than an ordinary water level of the suppression pool. As a result, the emergency cooling water of the suppression pool water is injected to the pressure vessel by the operation of the reactor cooling pumps upon loss of coolant accident to cool the reactor core. (I.S.)

  6. Direct cooled power electronics substrate

    Wiles, Randy H [Powell, TN; Wereszczak, Andrew A [Oak Ridge, TN; Ayers, Curtis W [Kingston, TN; Lowe, Kirk T [Knoxville, TN

    2010-09-14

    The disclosure describes directly cooling a three-dimensional, direct metallization (DM) layer in a power electronics device. To enable sufficient cooling, coolant flow channels are formed within the ceramic substrate. The direct metallization layer (typically copper) may be bonded to the ceramic substrate, and semiconductor chips (such as IGBT and diodes) may be soldered or sintered onto the direct metallization layer to form a power electronics module. Multiple modules may be attached to cooling headers that provide in-flow and out-flow of coolant through the channels in the ceramic substrate. The modules and cooling header assembly are preferably sized to fit inside the core of a toroidal shaped capacitor.

  7. Sodium cooled fast reactor

    Hokkyo, N; Inoue, K; Maeda, H

    1968-11-21

    In a sodium cooled fast neutron reactor, an ultrasonic generator is installed at a fuel assembly hold-down mechanism positioned above a blanket or fission gas reservoir located above the core. During operation of the reactor an ultrsonic wave of frequency 10/sup 3/ - 10/sup 4/ Hz is constantly transmitted to the core to resonantly inject the primary bubble with ultrasonic energy to thereby facilitate its growth. Hence, small bubbles grow gradually to prevent the sudden boiling of sodium if an accident occurs in the cooling system during operation of the reactor.

  8. Nuclear reactor fuel assembly

    1975-01-01

    A description is given of a nuclear reactor fuel assembly comprising a cluster of fuel elements supported by transversal grids so that their axes are parallel to and at a distance from each other, in order to establish interstices for the axial flow of a coolant. At least one of the interstices is occupied by an axial duct reserved for an auxiliary cooling fluid and is fitted with side holes through which the auxiliary cooling fluid is sprayed into the cluster. Deflectors extend as from a transversal grid in a position opposite the holes to deflect the cooling fluid jet towards those parts of the fuel elements that are not accessible to the auxiliary coolant. This assembly is intended for reactors cooled by light or heavy water [fr

  9. Crashing galaxies, cosmic fireworks

    Keel, W.C.

    1989-01-01

    The study of binary systems is reviewed. The history of the study of interacting galaxies, the behavior of gas in binary systems, studies to identify the processes that occur when galaxies interact, and the relationship of Seyfert galaxies and quasars to binary systems are discussed. The development of an atlas of peculiar galaxies (Arp, 1966) and methods for modeling galaxy interactions are examined

  10. Cooling towers

    Boernke, F.

    1975-01-01

    The need for the use of cooling systems in power plant engineering is dealt with from the point of view of a non-polluting form of energy production. The various cooling system concepts up to the modern natural-draught cooling towers are illustrated by examples. (TK/AK) [de

  11. Nuclear fuel assembly

    1975-01-01

    The nuclear fuel assembly described includes a cluster of fuel elements supported at a distance from each other so that their axes are parallel in order to establish secondary channels between them reserved for the coolant. Several ducts for an auxiliary cooling fluid are arranged in the cluster. The wall of each duct is pierced with coolant ejection holes which are placed circumferentially to a pre-determined pattern established according to the position of the duct in the cluster and by the axial distance of the ejection hole along the duct. This assembly is intended for reactors cooled by light or heavy water [fr

  12. Spherical galaxies.

    Telles, J. E.; de Souza, R. E.; Penereiro, J. C.

    1990-11-01

    RESUMEN. Presentamos fotometria fotografica de 8 objetos y espectrosco- pla para 3 galaxias, las cuales son buenos candidatos para galaxias esfericas. Los resultados fotometricos se presentan en la forma de iso- fotas y de perfiles radiales promedlo, de los cuales se derivan para- metros estructurales. Estas observaciones combinadas con parametros di- namicos obtenidos de observaciones espectrosc6picas, son consistentes con el plano fundamental derivado por Djorgovski y Davis (1987). ABSTRACT. We present photographic surface photometry for 8 objects and spectroscopy for 3 galaxies which are good candidates for spherical galaxies. Photometric results are presented in the form of isophotes and mean radial profiles from which we derived structural parameters. These observations combined with dynamical parameters obtained from spectroscopic observations are consistent with the fundamental plane derived by Djorgovski and Davis (1987). Keq wo : CALAXIES-ELLIPTICAL

  13. Prototype-based analysis of GAMA galaxy catalogue data

    Nolte, A.; Wang, L.; Biehl, M; Verleysen, Michel

    2018-01-01

    We present a prototype-based machine learning analysis of labeled galaxy catalogue data containing parameters from the Galaxy and Mass Assembly (GAMA) survey. Using both an unsupervised and supervised method, the Self-Organizing Map and Generalized Relevance Matrix Learning Vec- tor Quantization, we

  14. The many phases of massive galaxies : a near-infrared spectroscopic study of galaxies in the early universe

    Kriek, Mariska Therese

    2007-01-01

    A key issue in astronomy today is understanding the star-formation and assembly history of massive galaxies. Stellar population studies show that the bulk of the stars in low-redshift massive galaxies is formed at z~2 or even higher. Furthermore, there are strong indications that about 50% of the

  15. Low pressure cooling seal system for a gas turbine engine

    Marra, John J

    2014-04-01

    A low pressure cooling system for a turbine engine for directing cooling fluids at low pressure, such as at ambient pressure, through at least one cooling fluid supply channel and into a cooling fluid mixing chamber positioned immediately downstream from a row of turbine blades extending radially outward from a rotor assembly to prevent ingestion of hot gases into internal aspects of the rotor assembly. The low pressure cooling system may also include at least one bleed channel that may extend through the rotor assembly and exhaust cooling fluids into the cooling fluid mixing chamber to seal a gap between rotational turbine blades and a downstream, stationary turbine component. Use of ambient pressure cooling fluids by the low pressure cooling system results in tremendous efficiencies by eliminating the need for pressurized cooling fluids for sealing this gap.

  16. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    Gallagher, John S., III; Wyse, Rosemary F. G.

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  17. Mapping stellar content to dark matter haloes - III. Environmental dependence and conformity of galaxy colours

    Zu, Ying; Mandelbaum, Rachel

    2018-05-01

    Recent studies suggest that the quenching properties of galaxies are correlated over several megaparsecs. The large-scale `galactic conformity' phenomenon around central galaxies has been regarded as a potential signature of `galaxy assembly bias' or `pre-heating', both of which interpret conformity as a result of direct environmental effects acting on galaxy formation. Building on the iHOD halo quenching framework developed in Zu and Mandelbaum, we discover that our fiducial halo mass quenching model, without any galaxy assembly bias, can successfully explain the overall environmental dependence and the conformity of galaxy colours in Sloan Digital Sky Survey, as measured by the mark correlation functions of galaxy colours and the red galaxy fractions around isolated primaries, respectively. Our fiducial iHOD halo quenching mock also correctly predicts the differences in the spatial clustering and galaxy-galaxy lensing signals between the more versus less red galaxy subsamples, split by the red-sequence ridge line at fixed stellar mass. Meanwhile, models that tie galaxy colours fully or partially to halo assembly bias have difficulties in matching all these observables simultaneously. Therefore, we demonstrate that the observed environmental dependence of galaxy colours can be naturally explained by the combination of (1) halo quenching and (2) the variation of halo mass function with environment - an indirect environmental effect mediated by two separate physical processes.

  18. Chemical evolution of galaxies

    Vigroux, Laurent

    1979-01-01

    This research thesis addresses theories on the chemical evolution of galaxies which aim at explaining abundances of different elements in galaxies, and more particularly aims at improving the model by modifying hypotheses. After a description of the simple model and of its uncertainties, the author shows how it is possible to understand the evolution of the main elements. Predictions obtained with this model are then compared with the present knowledge on galaxies by considering them according to an increasing complexity: Sun's neighbourhood, our galaxy, other spiral galaxies, elliptical galaxies, and finally galaxy clusters. A specific attention is given to irregular galaxies which are the simplest systems [fr

  19. Muon ionization cooling experiment

    CERN. Geneva

    2003-01-01

    A neutrino factory based on a muon storage ring is the ultimate tool for studies of neutrino oscillations, including possibly leptonic CP violation. It is also the first step towards muon colliders. The performance of this new and promising line of accelerators relies heavily on the concept of ionisation cooling of minimum ionising muons, for which much R&D is required. The concept of a muon ionisation cooling experiment has been extensively studied and first steps are now being taken towards its realisation by a joint international team of accelerator and particle physicists. The aim of the workshop is to to explore at least two versions of an experiment based on existing cooling channel designs. If such an experiment is feasible, one shall then select, on the basis of effectiveness, simplicity, availability of components and overall cost, a design for the proposed experiment, and assemble the elements necessary to the presentation of a proposal. Please see workshop website.

  20. Modeling for Stellar Feedback in Galaxy Formation Simulations

    Núñez, Alejandro; Ostriker, Jeremiah P.; Naab, Thorsten; Oser, Ludwig; Hu, Chia-Yu; Choi, Ena

    2017-02-01

    Various heuristic approaches to model unresolved supernova (SN) feedback in galaxy formation simulations exist to reproduce the formation of spiral galaxies and the overall inefficient conversion of gas into stars. Some models, however, require resolution-dependent scalings. We present a subresolution model representing the three major phases of supernova blast wave evolution—free expansion, energy-conserving Sedov-Taylor, and momentum-conserving snowplow—with energy scalings adopted from high-resolution interstellar-medium simulations in both uniform and multiphase media. We allow for the effects of significantly enhanced SN remnant propagation in a multiphase medium with the cooling radius scaling with the hot volume fraction, {f}{hot}, as {(1-{f}{hot})}-4/5. We also include winds from young massive stars and AGB stars, Strömgren sphere gas heating by massive stars, and a mechanism that limits gas cooling that is driven by radiative recombination of dense H II regions. We present initial tests for isolated Milky Way-like systems simulated with the Gadget-based code SPHgal with improved SPH prescription. Compared to pure thermal SN input, the model significantly suppresses star formation at early epochs, with star formation extended both in time and space in better accord with observations. Compared to models with pure thermal SN feedback, the age at which half the stellar mass is assembled increases by a factor of 2.4, and the mass-loading parameter and gas outflow rate from the galactic disk increase by a factor of 2. Simulation results are converged for a variation of two orders of magnitude in particle mass in the range (1.3-130) × 104 solar masses.

  1. Monolithic View of Galaxy Formation and Evolution

    Cesare Chiosi

    2014-07-01

    Full Text Available We review and critically discuss the current understanding of galaxy formation and evolution limited to Early Type Galaxies (ETGs as inferred from the observational data and briefly contrast the hierarchical and quasi-monolithic paradigms of formation and evolution. Since in Cold Dark Matter (CDM cosmogony small scale structures typically collapse early and form low-mass haloes that subsequently can merge to assembly larger haloes, galaxies formed in the gravitational potential well of a halo are also expected to merge thus assembling their mass hierarchically. Mergers should occur all over the Hubble time and large mass galaxies should be in place only recently. However, recent observations of high redshift galaxies tell a different story: massive ETGs are already in place at high redshift. To this aim, we propose here a revision of the quasi-monolithic scenario as an alternative to the hierarchical one, in which mass assembling should occur in early stages of a galaxy lifetime and present recent models of ETGs made of Dark and Baryonic Matter in a Λ-CDM Universe that obey the latter scheme. The galaxies are followed from the detachment from the linear regime and Hubble flow at z ≥ 20 down to the stage of nearly complete assembly of the stellar content (z ∼ 2 − 1 and beyond.  It is found that the total mass (Mh = MDM + MBM and/or initial over-density of the proto-galaxy drive the subsequent star formation histories (SFH. Massive galaxies (Mh ~ _1012M⊙ experience a single, intense burst of star formation (with rates ≥ 103M⊙/yr at early epochs, consistently with observations, with a weak dependence on the initial over-density; intermediate mass haloes (Mh~_ 1010 − 1011M⊙ have star formation histories that strongly depend on their initial over-density; finally, low mass haloes (Mh ~_ 109M⊙ always have erratic, burst-like star forming histories. The present-day properties (morphology, structure, chemistry and photometry of the

  2. Fuel arrangement for high temperature gas cooled reactor

    Tobin, J.M.

    1978-01-01

    Disclosed is a fuel arrangement for a high temperature gas cooled reactor including fuel assemblies with separate directly cooled fissile and fertile fuel elements removably inserted in an elongated moderator block also having a passageway for control elements

  3. Cooled spool piston compressor

    Morris, Brian G. (Inventor)

    1993-01-01

    A hydraulically powered gas compressor receives low pressure gas and outputs a high pressure gas. The housing of the compressor defines a cylinder with a center chamber having a cross-sectional area less than the cross-sectional area of a left end chamber and a right end chamber, and a spool-type piston assembly is movable within the cylinder and includes a left end closure, a right end closure, and a center body that are in sealing engagement with the respective cylinder walls as the piston reciprocates. First and second annual compression chambers are provided between the piston enclosures and center housing portion of the compressor, thereby minimizing the spacing between the core gas and a cooled surface of the compressor. Restricted flow passageways are provided in the piston closure members and a path is provided in the central body of the piston assembly, such that hydraulic fluid flows through the piston assembly to cool the piston assembly during its operation. The compressor of the present invention may be easily adapted for a particular application, and is capable of generating high gas pressures while maintaining both the compressed gas and the compressor components within acceptable temperature limits.

  4. Study of a fuel assembly for the nuclear reactor of IV generation cooled with supercritical water; Estudio de un ensamble de combustible para el reactor nuclear de generacion IV enfriado con agua supercritica

    Barragan M, A.; Martin del Campo M, C.; Francois L, J. L. [UNAM, Facultad de Ingenieria, Departamento de Sistemas Energeticos, Ciudad Universitaria, 04510 Mexico D. F. (Mexico); Espinosa P, G., E-mail: albrm29@yahoo.com [Universidad Autonoma Metropolitana, Unidad Iztapalapa, Area de Ingenieria en Recursos Energeticos, Av. San Rafael Atlixco 186, Col. Vicentina, 09340 Mexico D. F. (MX)

    2011-11-15

    In this work a neutron study is presented about a square assembly design of double line of fuel rods, with moderator box to the center of the arrangement, for a nuclear reactor cooled with supercritical water (SCWR). The SCWR reactor was chosen by the characteristics of its design, mainly because is based in light water reactors (PWR and BWR), and the operational experience that has of them allow to use models and similar programs to simulate the fuel and the nucleus of this type of reactors. To develop the necessary models and to carry out the design and analysis of the SCWR reactor, the neutron codes MCNPX and Helios were used. The reason of using both codes, is because the code MCNPX used thoroughly in the neutron simulation of these reactors, it has been our reference code to analyze the results obtained with the Helios code which results are more efficient because its calculation times are minors. In the nucleus design the same parameters for both codes were considered. The results show that the design with Helios is a viable option to simulate these reactors since their values of the neutrons multiplication factor are very similar to those obtained with MCNPX. On the other hand, it could be corroborated that the CASMO-4 code is inadequate to simulate the fuel to the temperature conditions and water pressure in the SCWR. (Author)

  5. Liquid metal cooled fast breeder nuclear reactors

    Gatley, J.A.

    1979-01-01

    Breeder fuel sub-assemblies with electromagnetic brakes and fluidic valves for liquid metal cooled fast breeder reactors are described. The electromagnetic brakes are of relatively small proportions and the valves are of the controlled vortex type. The outlet coolant temperature of at least some of the breeder sub-assemblies are maintained by these means substantially constant throughout the life of the fuel assembly without severely pressurising the sub-assembly. (UK)

  6. Spray cooling

    Rollin, Philippe.

    1975-01-01

    Spray cooling - using water spraying in air - is surveyed as a possible system for make-up (peak clipping in open circuit) or major cooling (in closed circuit) of the cooling water of the condensers in thermal power plants. Indications are given on the experiments made in France and the systems recently developed in USA, questions relating to performance, cost and environmental effects of spray devices are then dealt with [fr

  7. Recent star formation in interacting galaxies

    Joseph, R.D.; Wright, G.S.

    1985-01-01

    The subset of galaxy-galaxy interactions which have resulted in a merger are, as a class, ultraluminous IR galaxies. Their IR luminosities span a narrow range which overlaps with the most luminous Seyfert galaxies. However, in contrast with Seyfert galaxies, the available optical, IR, and radio properties of mergers show no evidence for a compact non-thermal central source, and are easily understood in terms of a burst of star formation of extraordinary intensity and spatial extent; they are 'super starbursts'. We argue that super starbursts occur in the evolution of most mergers, and discuss the implications of super starbursts for the suggestion that mergers evolve into elliptical galaxies. Finally, we note that merger-induced shocks are likely to leave the gas from both galaxies in dense molecular form which will rapidly cool, collapse, and fragment. Thus a merger might in fact be expected to result in a burst of star formation of exceptional intensity and spatial extent, i.e. a super starburst. (author)

  8. REVERSAL OF FORTUNE: INCREASED STAR FORMATION EFFICIENCIES IN THE EARLY HISTORIES OF DWARF GALAXIES?

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-01-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe

  9. Reversal of Fortune: Increased Star Formation Efficiencies in the Early Histories of Dwarf Galaxies?

    Madau, Piero; Weisz, Daniel R.; Conroy, Charlie

    2014-08-01

    On dwarf galaxy scales, the different shapes of the galaxy stellar mass function and the dark halo mass function require a star-formation efficiency (SFE) in these systems that is currently more than 1 dex lower than that of Milky Way-size halos. Here, we argue that this trend may actually be reversed at high redshift. Specifically, by combining the resolved star-formation histories of nearby isolated dwarfs with the simulated mass-growth rates of dark matter halos, we show that the assembly of these systems occurs in two phases: (1) an early, fast halo accretion phase with a rapidly deepening potential well, characterized by a high SFE; and (2) a late, slow halo accretion phase where, perhaps as a consequence of reionization, the SFE is low. Nearby dwarfs have more old stars than predicted by assuming a constant or decreasing SFE with redshift, a behavior that appears to deviate qualitatively from the trends seen among more massive systems. Taken at face value, the data suggest that at sufficiently early epochs, dwarf galaxy halos above the atomic cooling mass limit can be among the most efficient sites of star formation in the universe.

  10. Fuel sub-assembly

    Jolly, R.

    1982-01-01

    A fuel sub-assembly for a liquid metal cooled nuclear reactor is described in which the bundle of fuel pins are braced apart by a series of spaced grids. The grids at the lower end are capable of yielding, thus allowing pins swollen by irradiation to be withdrawn with a reduced risk of damage. (U.K.)

  11. Mass Distribution in Galaxy Cluster Cores

    Hogan, M. T.; McNamara, B. R.; Pulido, F.; Vantyghem, A. N. [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON, N2L 3G1 (Canada); Nulsen, P. E. J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Russell, H. R. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Edge, A. C. [Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham DH1 3LE (United Kingdom); Main, R. A., E-mail: m4hogan@uwaterloo.ca [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 3H8 (Canada)

    2017-03-01

    Many processes within galaxy clusters, such as those believed to govern the onset of thermally unstable cooling and active galactic nucleus feedback, are dependent upon local dynamical timescales. However, accurate mapping of the mass distribution within individual clusters is challenging, particularly toward cluster centers where the total mass budget has substantial radially dependent contributions from the stellar ( M {sub *}), gas ( M {sub gas}), and dark matter ( M {sub DM}) components. In this paper we use a small sample of galaxy clusters with deep Chandra observations and good ancillary tracers of their gravitating mass at both large and small radii to develop a method for determining mass profiles that span a wide radial range and extend down into the central galaxy. We also consider potential observational pitfalls in understanding cooling in hot cluster atmospheres, and find tentative evidence for a relationship between the radial extent of cooling X-ray gas and nebular H α emission in cool-core clusters. At large radii the entropy profiles of our clusters agree with the baseline power law of K ∝ r {sup 1.1} expected from gravity alone. At smaller radii our entropy profiles become shallower but continue with a power law of the form K ∝ r {sup 0.67} down to our resolution limit. Among this small sample of cool-core clusters we therefore find no support for the existence of a central flat “entropy floor.”.

  12. Fuel cell sub-assembly

    Chi, Chang V.

    1983-01-01

    A fuel cell sub-assembly comprising a plurality of fuel cells, a first section of a cooling means disposed at an end of the assembly and means for connecting the fuel cells and first section together to form a unitary structure.

  13. Brightest Cluster Galaxies in REXCESS Clusters

    Haarsma, Deborah B.; Leisman, L.; Bruch, S.; Donahue, M.

    2009-01-01

    Most galaxy clusters contain a Brightest Cluster Galaxy (BCG) which is larger than the other cluster ellipticals and has a more extended profile. In the hierarchical model, the BCG forms through many galaxy mergers in the crowded center of the cluster, and thus its properties give insight into the assembly of the cluster as a whole. In this project, we are working with the Representative XMM-Newton Cluster Structure Survey (REXCESS) team (Boehringer et al 2007) to study BCGs in 33 X-ray luminous galaxy clusters, 0.055 < z < 0.183. We are imaging the BCGs in R band at the Southern Observatory for Astrophysical Research (SOAR) in Chile. In this poster, we discuss our methods and give preliminary measurements of the BCG magnitudes, morphology, and stellar mass. We compare these BCG properties with the properties of their host clusters, particularly of the X-ray emitting gas.

  14. An automatic taxonomy of galaxy morphology using unsupervised machine learning

    Hocking, Alex; Geach, James E.; Sun, Yi; Davey, Neil

    2018-01-01

    We present an unsupervised machine learning technique that automatically segments and labels galaxies in astronomical imaging surveys using only pixel data. Distinct from previous unsupervised machine learning approaches used in astronomy we use no pre-selection or pre-filtering of target galaxy type to identify galaxies that are similar. We demonstrate the technique on the Hubble Space Telescope (HST) Frontier Fields. By training the algorithm using galaxies from one field (Abell 2744) and applying the result to another (MACS 0416.1-2403), we show how the algorithm can cleanly separate early and late type galaxies without any form of pre-directed training for what an 'early' or 'late' type galaxy is. We then apply the technique to the HST Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) fields, creating a catalogue of approximately 60 000 classifications. We show how the automatic classification groups galaxies of similar morphological (and photometric) type and make the classifications public via a catalogue, a visual catalogue and galaxy similarity search. We compare the CANDELS machine-based classifications to human-classifications from the Galaxy Zoo: CANDELS project. Although there is not a direct mapping between Galaxy Zoo and our hierarchical labelling, we demonstrate a good level of concordance between human and machine classifications. Finally, we show how the technique can be used to identify rarer objects and present lensed galaxy candidates from the CANDELS imaging.

  15. Nuclear fuel assemblies

    Butterfield, R.S.; Garner, D.L.M.

    1977-01-01

    Reference is made to nuclear fuel assemblies designed for cooling on the 'tube-in-shell' principle in which the fuel is contained by a shell and is cooled by coolant passed through tubes extending through the shell. It has been proposed to employ coated particle fuel as a porous bed on the tube side and the bleed coolant from the tubes into direct contact with the fuel particles. In this way heat is extracted both by direct contact with the fuel and by heat transfer through the coolant tube walls. The system described aims to provide an improved structure of tube and shell for a fuel assembly of this kind and is particularly suitable for use in a gas cooled fast reactor, being able to withstand the neutron flux and high temperature conditions in these reactors. Constructional details are given. (U.K.)

  16. Fuel injection assembly for use in turbine engines and method of assembling same

    Berry, Jonathan Dwight; Johnson, Thomas Edward; York, William David; Uhm, Jong Ho

    2015-12-15

    A fuel injection assembly for use in a turbine engine is provided. The fuel injection assembly includes an end cover, an endcap assembly, a fluid supply chamber, and a plurality of tube assemblies positioned at the endcap assembly. Each of the tube assemblies includes housing having a fuel plenum and a cooling fluid plenum. The cooling fluid plenum is positioned downstream from the fuel plenum and separated from the fuel plenum by an intermediate wall. The plurality of tube assemblies also include a plurality of tubes that extends through the housing. Each of the plurality of tubes is coupled in flow communication with the fluid supply chamber and a combustion chamber positioned downstream from the tube assembly. The plurality of tube assemblies further includes an aft plate at a downstream end of the cooling fluid plenum. The plate includes at least one aperture.

  17. Do satellite galaxies trace matter in galaxy clusters?

    Wang, Chunxiang; Li, Ran; Gao, Liang; Shan, Huanyuan; Kneib, Jean-Paul; Wang, Wenting; Chen, Gang; Makler, Martin; Pereira, Maria E. S.; Wang, Lin; Maia, Marcio A. G.; Erben, Thomas

    2018-04-01

    The spatial distribution of satellite galaxies encodes rich information of the structure and assembly history of galaxy clusters. In this paper, we select a red-sequence Matched-filter Probabilistic Percolation cluster sample in SDSS Stripe 82 region with 0.1 ≤ z ≤ 0.33, 20 0.7. Using the high-quality weak lensing data from CS82 Survey, we constrain the mass profile of this sample. Then we compare directly the mass density profile with the satellite number density profile. We find that the total mass and number density profiles have the same shape, both well fitted by an NFW profile. The scale radii agree with each other within a 1σ error (r_s,gal=0.34_{-0.03}^{+0.04} Mpc versus r_s=0.37_{-0.10}^{+0.15} Mpc).

  18. THE ORIGIN OF NEUTRAL HYDROGEN CLOUDS IN NEARBY GALAXY GROUPS: EXPLORING THE RANGE OF GALAXY INTERACTIONS

    Chynoweth, Katie M.; Polisensky, Emil; Holley-Bockelmann, Kelly; Langston, Glen I.

    2011-01-01

    We combine high-resolution N-body simulations with deep observations of neutral hydrogen (H I) in nearby galaxy groups in order to explore two well-known theories of H I cloud formation: H I stripping by galaxy interactions and dark-matter minihalos with embedded H I gas. This paper presents new data from three galaxy groups-Canes Venatici I, NGC 672, and NGC 45-and assembles data from our previous galaxy group campaign to generate a rich H I cloud archive to compare to our simulated data. We find no H I clouds in the Canes Venatici I, NGC 672, or NGC 45 galaxy groups. We conclude that H I clouds in our detection space are most likely to be generated through recent, strong galaxy interactions. We find no evidence of H I clouds associated with dark-matter halos above M HI ∼ 10 6 M sun , within ±700 km s -1 of galaxies, and within 50 kpc projected distance of galaxies.

  19. Cosmic Collisions The Hubble Atlas of Merging Galaxies

    Christensen, Lars Lindberg; Martin, Davide

    2009-01-01

    Lars Lindberg Christensen, Raquel Yumi Shida & Davide De Martin Cosmic Collisions: The Hubble Atlas of Merging Galaxies Like majestic ships in the grandest night, galaxies can slip ever closer until their mutual gravitational interaction begins to mold them into intricate figures that are finally, and irreversibly, woven together. It is an immense cosmic dance, choreographed by gravity. Cosmic Collisions contains a hundred new, many thus far unpublished, images of colliding galaxies from the NASA/ESA Hubble Space Telescope. It is believed that many present-day galaxies, including the Milky Way, were assembled from such a coalescence of smaller galaxies, occurring over billions of years. Triggered by the colossal and violent interaction between the galaxies, stars form from large clouds of gas in firework bursts, creating brilliant blue star clusters. The importance of these cosmic encounters reaches far beyond the stunning Hubble images. They may, in fact, be among the most important processes that shape ...

  20. Ventilative Cooling

    Heiselberg, Per Kvols; Kolokotroni, Maria

    This report, by venticool, summarises the outcome of the work of the initial working phase of IEA ECB Annex 62 Ventilative Cooling and is based on the findings in the participating countries. It presents a summary of the first official Annex 62 report that describes the state-of-the-art of ventil......This report, by venticool, summarises the outcome of the work of the initial working phase of IEA ECB Annex 62 Ventilative Cooling and is based on the findings in the participating countries. It presents a summary of the first official Annex 62 report that describes the state......-of-the-art of ventilative cooling potentials and limitations, its consideration in current energy performance regulations, available building components and control strategies and analysis methods and tools. In addition, the report provides twenty six examples of operational buildings using ventilative cooling ranging from...

  1. z~2: An Epoch of Disk Assembly

    Simons, Raymond C.; Kassin, Susan A.; Weiner, Benjamin; Heckman, Timothy M.; Trump, Jonathan; SIGMA, DEEP2

    2018-01-01

    At z = 0, the majority of massive star-forming galaxies contain thin, rotationally supported gas disks. It was once accepted that galaxies form thin disks early: collisional gas with high velocity dispersion should dissipate energy, conserve angular momentum, and develop strong rotational support in only a few galaxy crossing times (~few hundred Myr). However, this picture is complicated at high redshift, where the processes governing galaxy assembly tend to be violent and inhospitable to disk formation. We present results from our SIGMA survey of star-forming galaxy kinematics at z = 2. These results challenge the simple picture described above: galaxies at z = 2 are unlike local well-ordered disks. Their kinematics tend to be much more disordered, as quantified by their low ratios of rotational velocity to gas velocity dispersion (Vrot/σg): less than 35% of galaxies have Vrot/σg > 3. For comparison, nearly 100% of local star-forming galaxies meet this same threshold. We combine our high redshift sample with a similar low redshift sample from the DEEP2 survey. This combined sample covers a continuous redshift baseline over 0.1 < z < 2.5, spanning 10 Gyrs of cosmic time. Over this period, galaxies exhibit remarkably smooth kinematic evolution on average. All galaxies tend towards rotational support with time, and it is reached earlier in higher mass systems. This is due to both a significant decline in gas velocity dispersion and a mild rise in ordered rotational motions. These results indicate that z = 2 is a period of disk assembly, during which the strong rotational support present in today’s massive disk galaxies is only just beginning to emerge.

  2. Galaxy angular momentum

    Thompson, L.A.

    1974-01-01

    In order to test the theories which purport to explain the origin of galaxy angular momentum, this study presents new data for about 1000 individual galaxies in eight rich clusters. The clusters which are studied include Virgo, A 119, A 400, A 1656 (Coma), A 2147, A 2151 (Hercules), A 2197, and A 2199. Selected samples of these data are used to investigate systematic alignment effects in clusters of galaxies and to investigate the intrinsic ellipticities of E, SO, and spiral galaxies. The following new results are reported: Galaxies in the cluster A 2197 show a significant alignment effect (chi 2 probability less than 0.0002), and the preferential direction of alignment corresponds approximately to the major axis of the overall cluster elongation. None of the other seven clusters show any significant alignment trends. The spiral galaxy samples in four clusters (Virgo, A 1656, A 2151, and A 2197) were large enough to analyze the number distributions of forward and reverse winding spirals. Large and small spiral galaxies have identical ellipticity distributions. Large E and SO galaxies tend to be more spherical, and small E and SO galaxies more flattened. The intrinsic ellipticities of E, SO, and spiral galaxies are the same for galaxies in the ''field'' and for galaxies in rich clusters. Six models of galaxy formation are reviewed, and the major []mphasis is placed on how each model explains the origin of galaxy angular momentum. (Diss. Abstr. Int., B)

  3. Dynamics of Cosmic Neutrinos in Galaxies

    Sapar A.

    2014-06-01

    Full Text Available The cosmic background of massive (about 1 eV rest-energy neutrinos can be cooled to extremely low temperatures, reaching almost completely degenerated state. The Fermi velocity of the neutrinos becomes less than 100 km/s. The equations of dynamics for the cosmic background neutrinos are derived for the spherical and axisymmetrical thin circular disk galaxies. The equations comprise the gravitational potential and gravity of the uniform baryonic disk galaxies. Then the equations are integrated analytically over the disk radius. The constant radial neutrino flux in spherical galaxies favors formation of the wide unipotential wells in them. The neutrino flux in the axisymmetrical galaxies suggests to favor the evolution in the direction of a spherically symmetrical potential. The generated unipotential wells are observed as plateaux in the velocity curves of circular stellar orbits. The constant neutrino density at galactic centers gives the linear part of the curves. The derived system of quasilinear differential equations for neutrinos in the axisymmetrical galaxies have been reduced to the system of the Lagrange-Charpit equations: the coupled differential equations, specifying the local neutrino velocities and dynamics of motion along trajectories, and an additional interconnected equation of the neutrino mass conservation, which can be applied for the determination of density of the neutrino component in galaxies.

  4. Polar ring galaxies in the Galaxy Zoo

    Finkelman, Ido; Funes, José G.; Brosch, Noah

    2012-05-01

    We report observations of 16 candidate polar-ring galaxies (PRGs) identified by the Galaxy Zoo project in the Sloan Digital Sky Survey (SDSS) data base. Deep images of five galaxies are available in the SDSS Stripe82 data base, while to reach similar depth we observed the remaining galaxies with the 1.8-m Vatican Advanced Technology Telescope. We derive integrated magnitudes and u-r colours for the host and ring components and show continuum-subtracted Hα+[N II] images for seven objects. We present a basic morphological and environmental analysis of the galaxies and discuss their properties in comparison with other types of early-type galaxies. Follow-up photometric and spectroscopic observations will allow a kinematic confirmation of the nature of these systems and a more detailed analysis of their stellar populations.

  5. Star Formation in Irregular Galaxies.

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  6. Combining Galaxy-Galaxy Lensing and Galaxy Clustering

    Park, Youngsoo [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Krause, Elisabeth [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Dodelson, Scott [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Jain, Bhuvnesh [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Amara, Adam [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Becker, Matt [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Bridle, Sarah [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Clampitt, Joseph [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Crocce, Martin [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Honscheid, Klaus [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Gaztanaga, Enrique [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Sanchez, Carles [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Wechsler, Risa [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2015-01-01

    Combining galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth rate of large scale structure, a quantity that will shed light on the mechanism driving the acceleration of the Universe. The Dark Energy Survey (DES) is a prime candidate for such an analysis, with its measurements of both the distribution of galaxies on the sky and the tangential shears of background galaxies induced by these foreground lenses. By constructing an end-to-end analysis that combines large-scale galaxy clustering and small-scale galaxy-galaxy lensing, we also forecast the potential of a combined probes analysis on DES datasets. In particular, we develop a practical approach to a DES combined probes analysis by jointly modeling the assumptions and systematics affecting the different components of the data vector, employing a shared halo model, HOD parametrization, photometric redshift errors, and shear measurement errors. Furthermore, we study the effect of external priors on different subsets of these parameters. We conclude that DES data will provide powerful constraints on the evolution of structure growth in the universe, conservatively/ optimistically constraining the growth function to 8%/4.9% with its first-year data covering 1000 square degrees, and to 4%/2.3% with its full five-year data covering 5000 square degrees.

  7. Formation of galaxies

    Szalay, A.S.

    1984-12-01

    The present theories of galaxy formation are reviewed. The relation between peculiar velocities and the correlation function of galaxies points to the possibility that galaxies do not form uniformly everywhere. Scale invariant properties of the cluster-cluster correlations are discussed. Comparing the correlation functions in a dimensionless way, galaxies appear to be stronger clustered, in contrast with the comparison of the dimensional amplitudes of the correlation functions. Theoretical implications of several observations as Lyman-α clouds, correlations of faint galaxies are discussed. None of the present theories of galaxy formation can account for all facts in a natural way. 29 references

  8. Nuclear fuel assembly

    Betten, P.R.

    1976-01-01

    Under the invention the fuel assembly is particularly suitable for liquid metal cooled fast neutron breeder reactors. Hence, according to the invention a fuel assembly cladding includes inward corrugations with respect to the remainder of the cladding according to a recurring pattern determined by the pitch of the metal wire helically wound round the fuel rods of the assembly. The parts of the cladding pressed inwards correspond to the areas in which the wire encircling the peripheral fuel rods is generally located apart from the cladding, thereby reducing the play between the cladding and the peripheral fuel rods situated in these areas. The reduction in the play in turn improves the coolant flow in the internal secondary channels of the fuel assembly to the detriment of the flow in the peripheral secondary channels and thereby establishes a better coolant fluid temperature profile [fr

  9. The galaxy clustering crisis in abundance matching

    Campbell, Duncan; van den Bosch, Frank C.; Padmanabhan, Nikhil; Mao, Yao-Yuan; Zentner, Andrew R.; Lange, Johannes U.; Jiang, Fangzhou; Villarreal, Antonio

    2018-06-01

    Galaxy clustering on small scales is significantly underpredicted by sub-halo abundance matching (SHAM) models that populate (sub-)haloes with galaxies based on peak halo mass, Mpeak. SHAM models based on the peak maximum circular velocity, Vpeak, have had much better success. The primary reason for Mpeak-based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on Vpeak. Despite success in predicting clustering, a simple Vpeak-based SHAM model results in predictions for galaxy growth that are at odds with observations. We evaluate three possible remedies that could `save' mass-based SHAM: (1) SHAM models require a significant population of `orphan' galaxies as a result of artificial disruption/merging of sub-haloes in modern high-resolution dark matter simulations; (2) satellites must grow significantly after their accretion; and (3) stellar mass is significantly affected by halo assembly history. No solution is entirely satisfactory. However, regardless of the particulars, we show that popular SHAM models based on Mpeak cannot be complete physical models as presented. Either Vpeak truly is a better predictor of stellar mass at z ˜ 0 and it remains to be seen how the correlation between stellar mass and Vpeak comes about, or SHAM models are missing vital component(s) that significantly affect galaxy clustering.

  10. Hunting for Dark Matter in Spheroidal Galaxies

    Steele, Rebecca; Holwerda, Benne; Kielkopf, John F.

    2018-06-01

    Searches for blended spectra have been highly successful in identifying strongly lensing galaxies: these spectra show a low-redshift passive galaxy with much stronger emission lines from the source being lensed. We have recently identified 112 strong lensing candidates in the Galaxy and Mass Assembly Survey (GAMA). The improved sensitivity and redshift determination makes this a very clean sample of two-galaxy spectra, spanning both lower-mass galaxy strong lenses as well as a higher redshiftregime (z > 0.4). As a first step of a PhD project, we will vet the 112 candidate strong gravitational lenses using the new Kilo Degree Survey (KiDS), which is both deeper and sharper than existing Sloan images. Once confirmed, these lower mass gravitational lenses can be targeted with the soon-to-launch James Webb Space Telescope or the Hubble Space Telescope for follow-up observations. Models of the gravitational lenses give us direct measures of the dark matter content of these low-mass galaxies, thought to be dominated by dark matter.

  11. Fuel assembly

    Hiraiwa, Koji; Ueda, Makoto

    1989-01-01

    In a fuel assembly used for a light water cooled reactor such as a BWR type reactor, a water rod is divided axially into an upper outer tube and a lower outer tube by means of a plug disposed from the lower end of a water rod to a position 1/4 - 1/2 of the entire length for the water rod. Inlet apertures and exit apertures for moderators are respectively perforated for the divided outer tube and upper and lower portions. Further, an upper inner tube with less neutron irradiation growing amount than the outer tube is perforated on the plug in the outer tube, while a lower inner tube with greater neutron irradiation growing amount than the outer tube is suspended from the lower surface of the plug in the outer tube. Then, the opening area for the exit apertures disposed to the upper outer tube and the lower outer tube is controlled depending on the difference of the neutron irradiation growing amount between the upper inner tube and the upper outer tube, and the difference of the neutron irradiation growing amount between the lower inner tube and the lower outer tube. This enables effective spectral shift operation and improve the fuel economy. (T.M.)

  12. Photometric redshift requirements for lens galaxies in galaxy-galaxy lensing analyses

    Nakajima, R.; Mandelbaum, R.; Seljak, U.; Cohn, J. D.; Reyes, R.; Cool, R.

    2012-03-01

    Weak gravitational lensing is a valuable probe of galaxy formation and cosmology. Here we quantify the effects of using photometric redshifts (photo-z) in galaxy-galaxy lensing, for both sources and lenses, both for the immediate goal of using galaxies with photo-z as lenses in the Sloan Digital Sky Survey (SDSS) and as a demonstration of methodology for large, upcoming weak lensing surveys that will by necessity be dominated by lens samples with photo-z. We calculate the bias in the lensing mass calibration as well as consequences for absolute magnitude (i.e. k-corrections) and stellar mass estimates for a large sample of SDSS Data Release 8 (DR8) galaxies. The redshifts are obtained with the template-based photo-z code ZEBRA on the SDSS DR8 ugriz photometry. We assemble and characterize the calibration samples (˜9000 spectroscopic redshifts from four surveys) to obtain photometric redshift errors and lensing biases corresponding to our full SDSS DR8 lens and source catalogues. Our tests of the calibration sample also highlight the impact of observing conditions in the imaging survey when the spectroscopic calibration covers a small fraction of its footprint; atypical imaging conditions in calibration fields can lead to incorrect conclusions regarding the photo-z of the full survey. For the SDSS DR8 catalogue, we find σΔz/(1+z)= 0.096 and 0.113 for the lens and source catalogues, with flux limits of r= 21 and 21.8, respectively. The photo-z bias and scatter is a function of photo-z and template types, which we exploit to apply photo-z quality cuts. By using photo-z rather than spectroscopy for lenses, dim blue galaxies and L* galaxies up to z˜ 0.4 can be used as lenses, thus expanding into unexplored areas of parameter space. We also explore the systematic uncertainty in the lensing signal calibration when using source photo-z, and both lens and source photo-z; given the size of existing training samples, we can constrain the lensing signal calibration (and

  13. Cooling towers

    Korik, L.; Burger, R.

    1992-01-01

    What is the effect of 0.6C (1F) temperature rise across turbines, compressors, or evaporators? Enthalpy charts indicate for every 0.6C (1F) hotter water off the cooling tower will require an additional 2 1/2% more energy cost. Therefore, running 2.2C (4F) warmer due to substandard cooling towers could result in a 10% penalty for overcoming high heads and temperatures. If it costs $1,250,000.00 a year to operate the system, $125,000.00 is the energy penalty for hotter water. This paper investigates extra fuel costs involved in maintaining design electric production with cooling water 0.6C (1F) to 3C (5.5F) hotter than design. If design KWH cannot be maintained, paper will calculate dollar loss of saleable electricity. The presentation will conclude with examining the main causes of deficient cold water production. State-of-the-art upgrading and methodology available to retrofit existing cooling towers to optimize lower cooling water temperatures will be discussed

  14. Clusters of Galaxies

    Huchtmeier, W. K.; Richter, O. G.; Materne, J.

    1981-09-01

    The large-scale structure of the universe is dominated by clustering. Most galaxies seem to be members of pairs, groups, clusters, and superclusters. To that degree we are able to recognize a hierarchical structure of the universe. Our local group of galaxies (LG) is centred on two large spiral galaxies: the Andromeda nebula and our own galaxy. Three sr:naller galaxies - like M 33 - and at least 23 dwarf galaxies (KraanKorteweg and Tammann, 1979, Astronomische Nachrichten, 300, 181) can be found in the evironment of these two large galaxies. Neighbouring groups have comparable sizes (about 1 Mpc in extent) and comparable numbers of bright members. Small dwarf galaxies cannot at present be observed at great distances.

  15. Cosmology and galaxy formation

    Rees, M.J.

    1977-01-01

    Implications of the massive halos and ''missing mass'' for galaxy formation are addressed; it is suggested that this mass consists of ''Population III'' stars that formed before the galaxies did. 19 references

  16. Diffuse interstellar gas in disk galaxies

    Vladilo, G.

    1989-01-01

    The physical properties of the diffuse gas in our Galaxy are reviewed and considered as a starting point for interstellar (IS) studies of disk galaxies. Attention is focussed on the atomic and ionic component, detected through radio, optical, ultraviolet (UV) and X-ray observations. The cooling and heating processes in the IS gas are briefly recalled in order to introduce current models of disk and halo gas. Observations of nearby galaxies critical to test IS models are considered, including 21-cm surveys, optical and UV absorptions of bright, extragalactic sources, and X-ray emission from hot halos. Finally, further steps necessary to develop a global model for the structure and evolution of the interstellar medium are indicated. (author)

  17. The luminosities of cool supergiants in the Magellanic Clouds, and the Humphreys-Davidson limit revisited

    Davies, Ben; Crowther, Paul A.; Beasor, Emma R.

    2018-05-01

    The empirical upper luminosity boundary Lmax of cool supergiants, often referred to as the Humphreys-Davidson limit, is thought to encode information on the general mass-loss behaviour of massive stars. Further, it delineates the boundary at which single stars will end their lives stripped of their hydrogen-rich envelope, which in turn is a key factor in the relative rates of Type-II to Type-Ibc supernovae from single star channels. In this paper we have revisited the issue of Lmax by studying the luminosity distributions of cool supergiants (SGs) in the Large and Small Magellanic Clouds (LMC/SMC). We assemble samples of cool SGs in each galaxy which are highly-complete above log L/L⊙=5.0, and determine their spectral energy distributions from the optical to the mid-infrared using modern multi-wavelength survey data. We show that in both cases Lmax appears to be lower than previously quoted, and is in the region of log L/L⊙=5.5. There is no evidence for Lmax being higher in the SMC than in the LMC, as would be expected if metallicity-dependent winds were the dominant factor in the stripping of stellar envelopes. We also show that Lmax aligns with the lowest luminosity of single nitrogen-rich Wolf-Rayet stars, indicating of a change in evolutionary sequence for stars above a critical mass. From population synthesis analysis we show that the Geneva evolutionary models greatly over-predict the numbers of cool SGs in the SMC. We also argue that the trend of earlier average spectral types of cool SGs in lower metallicity environments represents a genuine shift to hotter temperatures. Finally, we use our new bolometric luminosity measurements to provide updated bolometric corrections for cool supergiants.

  18. Star clusters in evolving galaxies

    Renaud, Florent

    2018-04-01

    Their ubiquity and extreme densities make star clusters probes of prime importance of galaxy evolution. Old globular clusters keep imprints of the physical conditions of their assembly in the early Universe, and younger stellar objects, observationally resolved, tell us about the mechanisms at stake in their formation. Yet, we still do not understand the diversity involved: why is star cluster formation limited to 105M⊙ objects in the Milky Way, while some dwarf galaxies like NGC 1705 are able to produce clusters 10 times more massive? Why do dwarfs generally host a higher specific frequency of clusters than larger galaxies? How to connect the present-day, often resolved, stellar systems to the formation of globular clusters at high redshift? And how do these links depend on the galactic and cosmological environments of these clusters? In this review, I present recent advances on star cluster formation and evolution, in galactic and cosmological context. The emphasis is put on the theory, formation scenarios and the effects of the environment on the evolution of the global properties of clusters. A few open questions are identified.

  19. Cooling tower

    Norbaeck, P; Heneby, H

    1976-01-22

    Cooling towers to be transported on road vehicles as a unit are not allowed to exceed certain dimensions. In order to improve the efficiency of such a cooling tower (of cross-flow design and box-type body) with given dimensions, it is proposed to arrange at least one of the scrubbing bodies displaceable within a module or box. Then it can be moved out of the casing into working position, thereby increasing the front surface available for the inlet of air (and with it the efficiency) by nearly a factor of two.

  20. Sagittarius Dwarf Galaxy

    Ibata, R.; Murdin, P.

    2000-11-01

    The Sagittarius DWARF GALAXY is the closest member of the Milky Way's entourage of satellite galaxies. Discovered by chance in 1994, its presence had previously been overlooked because it is largely hidden by the most crowded regions of our own Galaxy with which it is merging....

  1. Tidal interaction of galaxies

    Kozlov, N.N.; Syunyaev, R.A.; Ehneev, T.M.

    1974-01-01

    One of the hypotheses explaining the occurrence of anomalous details in interacting galaxies has been investigated. Pairs of galaxies with 'tails' oppositely directed or neighbouring galaxies with cofferdams 'bridges', as if connecting the galaxies, are called interacting galaxies. The hypothesis connects the origin of cofferdams and 'tails' of interacting galaxies with tidal effects ; the action of power gravitational forces in the intergalactic space. A source of such forces may be neighbouring stellar systems or invisible bodies, for instance, 'dead' quasars after a gravitational collapse. The effect of large masses of matter on the galaxy evolution has been investigated in the Institute of Applied Mathematics of the Academy of Sciences of the USSSR in 1971-1972 by numerical simulation of the process on a digital computer with the subsequent data transmission on a display. Different versions of a massive body flight relative to a galaxy disk are considered. Photographs of a display screen at different moments of time are presented. As a result of mathematical simulation of galaxies gravitational interactions effects are discovered which resemble real structures in photographs of galaxies. It seems to be premature to state that namely these mechanisms cause the formation of 'tails' and cofferdams between galaxies. However, even now it is clear that the gravitational interaction strongly affects the dynamics of the stellar system evolution. Further studies should ascertain a true scale of this effect and its genuine role in galaxy evolution

  2. Fabrication process of expanded cooling jackets

    Weber, C.M.

    1980-01-01

    The present invention concerns the fabrication process of heat exchangers and in particular, the fabrication and assembly process of cooling jackets of the system driving the control rods used in nuclear reactors. The cooling jackets are assembled for cooling the stator of a tubular motor displacing the control rods. The fabrication and assembling of the cooling jacket is made up by the following operations: - a sleeve has an inner fluid inlet and outlet ways, - an external socket is fitted to the sleeve, - on the external socket a continuous welding is realized, which join the socket to the sleeve, and define a serie of parallel welded turns, - a pressure is established between the sleeve and the socket by a fluid through the outlet or inlet ways of the sleeve. When the other way is sealed up, the socket expands between the welded turns, and the fluid can pass through the jacket [fr

  3. Influence of baryonic physics in simulations of spiral galaxies

    Halle, A.

    2013-01-01

    The modelling of baryonic physics in numerical simulations of disc galaxies allows us to study the evolution of the different components, the physical state of the gas and the star formation. The present work aims at investigating in particular the role of the cold and dense molecular phase, which could play a role of gas reservoir in the outer galaxy discs, with low star formation efficiency. After a presentation of galaxies with a focus on spiral galaxies, their interstellar medium and dynamical evolution, we review the current state of hydrodynamical numerical simulations and the implementation of baryonic physics. We then present the simulations we performed. These include the cooling to low temperatures, and a molecular hydrogen component. The cooling functions we use include cooling by metals, for temperatures as low as 100 K, and cooling by H 2 due to collisions with H, He and other H 2 molecules. We use a TreeSPH type code that considers the stellar and gaseous components and black matter as particles. We especially test the impact of the presence of molecular hydrogen in simulations with several feedback efficiencies, and find that the molecular hydrogen allows in all cases some slow stellar formation to occur in the outer disc, with an effect on the vertical structure of the disc that is sensitive to the feedback efficiency. Molecular hydrogen is therefore able to play the role of gas reservoir in external parts of spiral galaxies, which accrete gas from cosmic filaments all along their lives

  4. Black-hole-regulated star formation in massive galaxies.

    Martín-Navarro, Ignacio; Brodie, Jean P; Romanowsky, Aaron J; Ruiz-Lara, Tomás; van de Ven, Glenn

    2018-01-18

    Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

  5. Black-hole-regulated star formation in massive galaxies

    Martín-Navarro, Ignacio; Brodie, Jean P.; Romanowsky, Aaron J.; Ruiz-Lara, Tomás; van de Ven, Glenn

    2018-01-01

    Supermassive black holes, with masses more than a million times that of the Sun, seem to inhabit the centres of all massive galaxies. Cosmologically motivated theories of galaxy formation require feedback from these supermassive black holes to regulate star formation. In the absence of such feedback, state-of-the-art numerical simulations fail to reproduce the number density and properties of massive galaxies in the local Universe. There is, however, no observational evidence of this strongly coupled coevolution between supermassive black holes and star formation, impeding our understanding of baryonic processes within galaxies. Here we report that the star formation histories of nearby massive galaxies, as measured from their integrated optical spectra, depend on the mass of the central supermassive black hole. Our results indicate that the black-hole mass scales with the gas cooling rate in the early Universe. The subsequent quenching of star formation takes place earlier and more efficiently in galaxies that host higher-mass central black holes. The observed relation between black-hole mass and star formation efficiency applies to all generations of stars formed throughout the life of a galaxy, revealing a continuous interplay between black-hole activity and baryon cooling.

  6. Air-cooled, hydrogen-air fuel cell

    Shelekhin, Alexander B. (Inventor); Bushnell, Calvin L. (Inventor); Pien, Michael S. (Inventor)

    1999-01-01

    An air-cooled, hydrogen-air solid polymer electrolyte (SPE) fuel cell with a membrane electrode assembly operatively associated with a fluid flow plate having at least one plate cooling channel extending through the plate and at least one air distribution hole extending from a surface of the cathode flow field into the plate cooling channel.

  7. Stochastic cooling

    Bisognano, J.; Leemann, C.

    1982-03-01

    Stochastic cooling is the damping of betatron oscillations and momentum spread of a particle beam by a feedback system. In its simplest form, a pickup electrode detects the transverse positions or momenta of particles in a storage ring, and the signal produced is amplified and applied downstream to a kicker. The time delay of the cable and electronics is designed to match the transit time of particles along the arc of the storage ring between the pickup and kicker so that an individual particle receives the amplified version of the signal it produced at the pick-up. If there were only a single particle in the ring, it is obvious that betatron oscillations and momentum offset could be damped. However, in addition to its own signal, a particle receives signals from other beam particles. In the limit of an infinite number of particles, no damping could be achieved; we have Liouville's theorem with constant density of the phase space fluid. For a finite, albeit large number of particles, there remains a residue of the single particle damping which is of practical use in accumulating low phase space density beams of particles such as antiprotons. It was the realization of this fact that led to the invention of stochastic cooling by S. van der Meer in 1968. Since its conception, stochastic cooling has been the subject of much theoretical and experimental work. The earliest experiments were performed at the ISR in 1974, with the subsequent ICE studies firmly establishing the stochastic cooling technique. This work directly led to the design and construction of the Antiproton Accumulator at CERN and the beginnings of p anti p colliding beam physics at the SPS. Experiments in stochastic cooling have been performed at Fermilab in collaboration with LBL, and a design is currently under development for a anti p accumulator for the Tevatron

  8. The AGORA High-resolution Galaxy Simulations Comparison Project

    Kim Ji-hoon; Abel Tom; Agertz Oscar; Bryan Greg L.; Ceverino Daniel; Christensen Charlotte; Conroy Charlie; Dekel Avishai; Gnedin Nickolay Y.; Goldbaum Nathan J.; Guedes Javiera; Hahn Oliver; Hobbs Alexander; Hopkins Philip F.; Hummels Cameron B.

    2014-01-01

    The Astrophysical Journal Supplement Series 210.1 (2014): 14 reproduced by permission of the AAS We introduce the Assembling Galaxies Of Resolved Anatomy (AGORA) project, a comprehensive numerical study of well-resolved galaxies within the ΛCDM cosmology. Cosmological hydrodynamic simulations with force resolutions of ∼100 proper pc or better will be run with a variety of code platforms to follow the hierarchical growth, star formation history, morphological transformation, and the cycle o...

  9. Apparatus for lifting spent fuel assembly

    Hirasawa, Yoshinari; Sato, Isao; Yoneda, Yoshiyuki.

    1976-01-01

    Object: To increase the efficiency of cooling of a used fuel assembly being moved within a guide tube in the axial direction thereof by directly cooling the assembly with cooling gas fed into the guide tube, thus facilitating the handling of the spent fuel assembly. Structure: An end of a lock portion is inserted into the top portion of a spent fuel assembly, the assembly being hooked on the lock portion. The lock portion is provided on its outer periphery with a seal member and a centering member and at its tip with a pawl capable of being projected and retracted in the radial direction. Thus, when the lock portion is moved along the guide tube, the used fuel assembly can be moved along the guide tube by maintaining the concentric relation thereto. Meanwhile, when cooling gas is fed into the guide tube, it is blown into the used fuel assembly to directly cool the same. Thus, the cooling efficiency can be increased. (Moriyama, M.)

  10. The First Galaxies Theoretical Predictions and Observational Clues

    Mobasher, Bahram; Bromm, Volker

    2013-01-01

    New observations of the period between the cosmic recombination and the end of reionization are posing intriguing questions about where the first generations of stars were formed, how the first galaxies were assembled, whether these galaxies have low redshift counterparts, and what role the early galaxies played in the reionization process. Combining the new observational data with theoretical models can shed new light on open issues regarding the star formation process, its role in the reionization of the Universe, and the metal enrichment in galaxies at those early epochs. This volume brings together leading experts in the field to discuss our current level of understanding and what may come in the near future as our observational as well as theoretical tools improve. The book confronts the theory of how the first stars, black holes, and galaxies formed with current and planned observations. This synthesis is very timely, just ahead of the establishment of major new facilities, such as the James Webb Space ...

  11. Chemical evolution of galaxies

    Matteucci, Francesca

    2012-01-01

    The term “chemical evolution of galaxies” refers to the evolution of abundances of chemical species in galaxies, which is due to nuclear processes occurring in stars and to gas flows into and out of galaxies. This book deals with the chemical evolution of galaxies of all morphological types (ellipticals, spirals and irregulars) and stresses the importance of the star formation histories in determining the properties of stellar populations in different galaxies. The topic is approached in a didactical and logical manner via galaxy evolution models which are compared with observational results obtained in the last two decades: The reader is given an introduction to the concept of chemical abundances and learns about the main stellar populations in our Galaxy as well as about the classification of galaxy types and their main observables. In the core of the book, the construction and solution of chemical evolution models are discussed in detail, followed by descriptions and interpretations of observations of ...

  12. WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

    Lin, Lihwai; Cooper, Michael C.; Willmer, Christopher N. A.; Jian, Hung-Yu; Chiueh, Tzihong; Koo, David C.; Guhathakurta, Puragra; Patton, David R.; Yan, Renbin; Coil, Alison L.; Croton, Darren J.; Gerke, Brian F.; Lotz, Jennifer; Newman, Jeffrey A.

    2010-01-01

    We study the environments of wet, dry, and mixed galaxy mergers at 0.75 c ) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability of pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z ∼ 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 ± 0.3 dry mergers since this time, accounting for (38 ± 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our findings suggest that dry mergers are crucial in the mass assembly of massive red galaxies in dense environments, such as brightest cluster galaxies in galaxy groups and clusters.

  13. A very cool cooling system

    Antonella Del Rosso

    2015-01-01

    The NA62 Gigatracker is a jewel of technology: its sensor, which delivers the time of the crossing particles with a precision of less than 200 picoseconds (better than similar LHC detectors), has a cooling system that might become the precursor to a completely new detector technique.   The 115 metre long vacuum tank of the NA62 experiment. The NA62 Gigatracker (GTK) is composed of a set of three innovative silicon pixel detectors, whose job is to measure the arrival time and the position of the incoming beam particles. Installed in the heart of the NA62 detector, the silicon sensors are cooled down (to about -20 degrees Celsius) by a microfluidic silicon device. “The cooling system is needed to remove the heat produced by the readout chips the silicon sensor is bonded to,” explains Alessandro Mapelli, microsystems engineer working in the Physics department. “For the NA62 Gigatracker we have designed a cooling plate on top of which both the silicon sensor and the...

  14. Chemical Evolution and the Formation of Dwarf Galaxies in the Early Universe

    Cote, Benoit; JINA-CEE, NuGrid, ChETEC

    2018-06-01

    Stellar abundances in local dwarf galaxies offer a unique window into the nature and nucleosynthesis of the first stars. They also contain clues regarding how galaxies formed and assembled in the early stages of the universe. In this talk, I will present our effort to connect nuclear astrophysics with the field of galaxy formation in order to define what can be learned about galaxy evolution using stellar abundances. In particular, I will describe the current state of our numerical chemical evolution pipeline which accounts for the mass assembly history of galaxies, present how we use high-redshift cosmological hydrodynamic simulations to calibrate our models and to learn about the formation of dwarf galaxies, and address the challenge of identifying the dominant r-process site(s) using stellar abundances.

  15. Galaxy Zoo: dust in spiral galaxies star

    Masters, Karen L.; Nichol, Robert; Bamford, Steven; Mosleh, Moein; Lintott, Chris J.; Andreescu, Dan; Edmondson, Edward M.; Keel, William C.; Murray, Phil; Raddick, M. Jordan; Schawinski, Kevin; Slosar, Anze; Szalay, Alexander S.; Thomas, Daniel; Vandenberg, Jan

    2010-01-01

    We investigate the effect of dust on spiral galaxies by measuring the inclination dependence of optical colours for 24 276 well-resolved Sloan Digital Sky Survey (SDSS) galaxies visually classified via the Galaxy Zoo project. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4 mag for the ugri passbands (estimating 0.3 mag of extinction in z band). We split the sample into ‘bulgy’ (early-type) and ‘discy’ (late-typ...

  16. Cool Sportswear

    1982-01-01

    New athletic wear design based on the circulating liquid cooling system used in the astronaut's space suits, allows athletes to perform more strenuous activity without becoming overheated. Techni-Clothes gear incorporates packets containing a heat-absorbing gel that slips into an insulated pocket of the athletic garment and is positioned near parts of the body where heat transfer is most efficient. A gel packet is good for about one hour. Easily replaced from a supply of spares in an insulated container worn on the belt. The products, targeted primarily for runners and joggers and any other athlete whose performance may be affected by hot weather, include cooling headbands, wrist bands and running shorts with gel-pack pockets.

  17. Nuclear reactor fuel sub-assemblies

    Ford, J.; Bishop, J.F.W.

    1981-01-01

    An improved fuel sub-assembly for liquid metal cooled fast breeder nuclear reactors is described which facilitates dismantling operations for reprocessing purposes. The method of dismantling is described. (U.K.)

  18. Cooling systems

    Coutant, C.C.

    1978-01-01

    Progress on the thermal effects project is reported with regard to physiology and distribution of Corbicula; power plant effects studies on burrowing mayfly populations; comparative thermal responses of largemouth bass from northern and southern populations; temperature selection by striped bass in Cherokee Reservoir; fish population studies; and predictive thermoregulation by fishes. Progress is also reported on the following; cause and ecological ramifications of threadfin shad impingement; entrainment project; aquaculture project; pathogenic amoeba project; and cooling tower drift project

  19. Circumgalactic Matter Matters in Galaxy Evolution

    Werk, Jessica

    2018-01-01

    The circumgalactic medium (CGM; non-ISM gas within a galaxy virial radius) regulates the gas flows that shape the assembly and evolution of galaxies. Owing to the vastly improved capabilities in space-based UV spectroscopy with the installation of HST/COS, observations and simulations of the CGM have emerged as the new frontier of galaxy evolution studies. In the last decade, we have learned that the CGM of Milky Way mass galaxies likely contains enough material to harbor most of the metals lost in galaxy winds and to sustain star-formation for billions of years. Remarkably, this implies that most of the heavy elements on earth cycled back and forth multiple times through the Milky Way’s own CGM before the formation of the solar system. In this talk, I will describe constraints we have placed on the origin and fate of this material by studying the gas kinematics, metallicity and ionization state. I will conclude by posing several unanswered questions about the CGM that will be addressed with future survey data and hydrodynamic simulations in a cosmological context.

  20. Isolated galaxies, pairs, and groups of galaxies

    Kuneva, I.; Kalinkov, M.

    1990-01-01

    The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G 1 be any galaxy and G 2 be its nearest neighbor at a distance R 2 . If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G 1 is an isolated galaxy. Let the midpoint of G 1 and G 2 be O 2 and r 2 =R 2 2. For the volume V 2 , defined with the radius r 2 , the density D 2 less than k mu, the galaxy G 2 is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3)), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten

  1. Halo Histories vs. Galaxy Properties at z=0, III: The Properties of Star-Forming Galaxies

    Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.

    2018-05-01

    We measure how the properties of star-forming central galaxies correlate with large-scale environment, δ, measured on 10 h-1Mpc scales. We use galaxy group catalogs to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disk scale length Rexp, and Sersic index of the galaxy light profile, nS. We find that, at all stellar masses, there is an inverse correlation between SFR and δ, meaning that above-average star forming centrals live in underdense regions. For nS and Rexp, there is no correlation with δ at M_\\ast ≲ 10^{10.5} M⊙, but at higher masses there are positive correlations; a weak correlation with Rexp and a strong correlation with nS. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, \\dot{M}_h. In this model, galaxies are assigned to halos using the abundance matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but \\dot{M}_h is used to map onto SFR. The best-fit model requires some scatter in the \\dot{M}_h-SFR relation. The Rexp and nS measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, λ. Halo spin does not correlate with δ at low halo masses, but for higher mass halos, high-spin halos live in higher density environments at fixed Mh. Put together with the earlier installments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

  2. Diversity among galaxy clusters

    Struble, M.F.; Rood, H.J.

    1988-01-01

    The classification of galaxy clusters is discussed. Consideration is given to the classification scheme of Abell (1950's), Zwicky (1950's), Morgan, Matthews, and Schmidt (1964), and Morgan-Bautz (1970). Galaxies can be classified based on morphology, chemical composition, spatial distribution, and motion. The correlation between a galaxy's environment and morphology is examined. The classification scheme of Rood-Sastry (1971), which is based on clusters's morphology and galaxy population, is described. The six types of clusters they define include: (1) a cD-cluster dominated by a single large galaxy, (2) a cluster dominated by a binary, (3) a core-halo cluster, (4) a cluster dominated by several bright galaxies, (5) a cluster appearing flattened, and (6) an irregularly shaped cluster. Attention is also given to the evolution of cluster structures, which is related to initial density and cluster motion

  3. Galaxy formation and evolution

    Mo, Houjun; White, Simon

    2010-01-01

    The rapidly expanding field of galaxy formation lies at the interface between astronomy, particle physics, and cosmology. Covering diverse topics from these disciplines, all of which are needed to understand how galaxies form and evolve, this book is ideal for researchers entering the field. Individual chapters explore the evolution of the Universe as a whole and its particle and radiation content; linear and nonlinear growth of cosmic structure; processes affecting the gaseous and dark matter components of galaxies and their stellar populations; the formation of spiral and elliptical galaxies; central supermassive black holes and the activity associated with them; galaxy interactions; and the intergalactic medium. Emphasizing both observational and theoretical aspects, this book provides a coherent introduction for astronomers, cosmologists, and astroparticle physicists to the broad range of science underlying the formation and evolution of galaxies.

  4. The origin of galaxies

    Carr, B.J.

    1982-01-01

    The existence of galaxies implies that the early Universe must have contained initial density fluctuations. Overdense regions would then expand more slowly than the background and eventually - providing the fluctuations were not damped out first - they would stop expanding altogether and collapse to form bound objects. To understand how galaxies form we therefore need to know: how the initial density fluctuations arise, under what circumstances they evolve into bound objects, and how the bound objects develop the observed characteristics of galaxies. (author)

  5. Galaxy correlations and cosmology

    Fall, S.M.

    1979-01-01

    Correlations in the distribution of galaxies provide some important clues about the structure and evolution of the Universe on scales larger than individual galaxies. In recent years much effort has been devoted to estimating and interpreting galaxy correlations. This is a review of these efforts. It is meant to provide both an introductory overview of the subject and a critical assessment of some recent developments

  6. Neighbours of our galaxy

    Wielebinski, R.

    1982-01-01

    Large telescope and radio-astronomy bring remote regions of the universe into view. Radio waves are emitted by all celestial objects. Precise examination of our own galaxy, the Milky Way, is useful for investigating more remote objects. Some of the remote galaxies are noteworthy, because they emit up to 1,000 times more radio waves than their neighbours. Centaurus A is an example of such an active galaxy. (orig.)

  7. Bacteriophage Assembly

    Anastasia A. Aksyuk

    2011-02-01

    Full Text Available Bacteriophages have been a model system to study assembly processes for over half a century. Formation of infectious phage particles involves specific protein-protein and protein-nucleic acid interactions, as well as large conformational changes of assembly precursors. The sequence and molecular mechanisms of phage assembly have been elucidated by a variety of methods. Differences and similarities of assembly processes in several different groups of bacteriophages are discussed in this review. The general principles of phage assembly are applicable to many macromolecular complexes.

  8. Fuel assemblies

    Nakatsuka, Masafumi.

    1979-01-01

    Purpose: To prevent scattering of gaseous fission products released from fuel assemblies stored in an fbr type reactor. Constitution; A cap provided with means capable of storing gas is adapted to amount to the assembly handling head, for example, by way of threading in a storage rack of spent fuel assemblies consisting of a bottom plate, a top plate and an assembly support mechanism. By previously eliminating the gas inside of the assembly and the cap in the storage rack, gaseous fission products upon loading, if released from fuel rods during storage, are stored in the cap and do not scatter in the storage rack. (Horiuchi, T.)

  9. Sequence assembly

    Scheibye-Alsing, Karsten; Hoffmann, S.; Frankel, Annett Maria

    2009-01-01

    Despite the rapidly increasing number of sequenced and re-sequenced genomes, many issues regarding the computational assembly of large-scale sequencing data have remain unresolved. Computational assembly is crucial in large genome projects as well for the evolving high-throughput technologies and...... in genomic DNA, highly expressed genes and alternative transcripts in EST sequences. We summarize existing comparisons of different assemblers and provide a detailed descriptions and directions for download of assembly programs at: http://genome.ku.dk/resources/assembly/methods.html....

  10. GALAXY OUTFLOWS WITHOUT SUPERNOVAE

    Sur, Sharanya [Indian Institute of Astrophysics, 2nd Block, Koramangala, Bangalore 560034 (India); Scannapieco, Evan [School of Earth and Space Exploration, Arizona State University, P.O. Box 876004, Tempe-85287 (United States); Ostriker, Eve C., E-mail: sharanya.sur@iiap.res.in, E-mail: sharanya.sur@asu.edu [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

    2016-02-10

    High surface density, rapidly star-forming galaxies are observed to have ≈50–100 km s{sup −1} line of sight velocity dispersions, which are much higher than expected from supernova driving alone, but may arise from large-scale gravitational instabilities. Using three-dimensional simulations of local regions of the interstellar medium, we explore the impact of high velocity dispersions that arise from these disk instabilities. Parametrizing disks by their surface densities and epicyclic frequencies, we conduct a series of simulations that probe a broad range of conditions. Turbulence is driven purely horizontally and on large scales, neglecting any energy input from supernovae. We find that such motions lead to strong global outflows in the highly compact disks that were common at high redshifts, but weak or negligible mass loss in the more diffuse disks that are prevalent today. Substantial outflows are generated if the one-dimensional horizontal velocity dispersion exceeds ≈35 km s{sup −1}, as occurs in the dense disks that have star-formation rate (SFR) densities above ≈0.1 M{sub ⊙} yr{sup −1} kpc{sup −2}. These outflows are triggered by a thermal runaway, arising from the inefficient cooling of hot material coupled with successive heating from turbulent driving. Thus, even in the absence of stellar feedback, a critical value of the SFR density for outflow generation can arise due to a turbulent heating instability. This suggests that in strongly self-gravitating disks, outflows may be enhanced by, but need not caused by, energy input from supernovae.

  11. Galaxy Zoo: dust in spiral galaxies

    Masters, Karen L.; Nichol, Robert; Bamford, Steven; Mosleh, Moein; Lintott, Chris J.; Andreescu, Dan; Edmondson, Edward M.; Keel, William C.; Murray, Phil; Raddick, M. Jordan; Schawinski, Kevin; Slosar, Anže; Szalay, Alexander S.; Thomas, Daniel; Vandenberg, Jan

    2010-05-01

    We investigate the effect of dust on spiral galaxies by measuring the inclination dependence of optical colours for 24276 well-resolved Sloan Digital Sky Survey (SDSS) galaxies visually classified via the Galaxy Zoo project. We find clear trends of reddening with inclination which imply a total extinction from face-on to edge-on of 0.7, 0.6, 0.5 and 0.4mag for the ugri passbands (estimating 0.3mag of extinction in z band). We split the sample into `bulgy' (early-type) and `discy' (late-type) spirals using the SDSS fracdeV (or fDeV) parameter and show that the average face-on colour of `bulgy' spirals is redder than the average edge-on colour of `discy' spirals. This shows that the observed optical colour of a spiral galaxy is determined almost equally by the spiral type (via the bulge-disc ratio and stellar populations), and reddening due to dust. We find that both luminosity and spiral type affect the total amount of extinction, with discy spirals at Mr ~ -21.5mag having the most reddening - more than twice as much as both the lowest luminosity and most massive, bulge-dominated spirals. An increase in dust content is well known for more luminous galaxies, but the decrease of the trend for the most luminous has not been observed before and may be related to their lower levels of recent star formation. We compare our results with the latest dust attenuation models of Tuffs et al. We find that the model reproduces the observed trends reasonably well but overpredicts the amount of u-band attenuation in edge-on galaxies. This could be an inadequacy in the Milky Way extinction law (when applied to external galaxies), but more likely indicates the need for a wider range of dust-star geometries. We end by discussing the effects of dust on large galaxy surveys and emphasize that these effects will become important as we push to higher precision measurements of galaxy properties and their clustering. This publication has been made possible by the participation of more than

  12. SDSS-IV MaNGA: Stellar angular momentum of about 2300 galaxies: unveiling the bimodality of massive galaxy properties

    Graham, Mark T.; Cappellari, Michele; Li, Hongyu; Mao, Shude; Bershady, Matthew; Bizyaev, Dmitry; Brinkmann, Jonathan; Brownstein, Joel R.; Bundy, Kevin; Drory, Niv; Law, David R.; Pan, Kaike; Thomas, Daniel; Wake, David A.; Weijmans, Anne-Marie; Westfall, Kyle B.; Yan, Renbin

    2018-03-01

    We measure λ _{R_e}, a proxy for galaxy specific stellar angular momentum within one effective radius, and the ellipticity, ɛ, for about 2300 galaxies of all morphological types observed with integral field spectroscopy as part of the MaNGA survey, the largest such sample to date. We use the (λ _{R_e}, ɛ ) diagram to separate early-type galaxies into fast and slow rotators. We also visually classify each galaxy according to its optical morphology and two-dimensional stellar velocity field. Comparing these classifications to quantitative λ _{R_e} measurements reveals tight relationships between angular momentum and galaxy structure. In order to account for atmospheric seeing, we use realistic models of galaxy kinematics to derive a general approximate analytic correction for λ _{R_e}. Thanks to the size of the sample and the large number of massive galaxies, we unambiguously detect a clear bimodality in the (λ _{R_e}, ɛ ) diagram which may result from fundamental differences in galaxy assembly history. There is a sharp secondary density peak inside the region of the diagram with low λ _{R_e} and ɛ their distribution of the misalignments between the photometric and kinematic position angles. We confirm that genuine slow rotators start appearing above M ≥ 2 × 1011M⊙ where a significant number of high-mass fast rotators also exist.

  13. Turbulent heating in galaxy clusters brightest in X-rays

    Zhuravleva, I.; Churazov, E.; Schekochihin, A. A.; Allen, S. W.; Arévalo, P.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2014-11-01

    The hot (107 to 108 kelvin), X-ray-emitting intracluster medium (ICM) is the dominant baryonic constituent of clusters of galaxies. In the cores of many clusters, radiative energy losses from the ICM occur on timescales much shorter than the age of the system. Unchecked, this cooling would lead to massive accumulations of cold gas and vigorous star formation, in contradiction to observations. Various sources of energy capable of compensating for these cooling losses have been proposed, the most promising being heating by the supermassive black holes in the central galaxies, through inflation of bubbles of relativistic plasma. Regardless of the original source of energy, the question of how this energy is transferred to the ICM remains open. Here we present a plausible solution to this question based on deep X-ray data and a new data analysis method that enable us to evaluate directly the ICM heating rate from the dissipation of turbulence. We find that turbulent heating is sufficient to offset radiative cooling and indeed appears to balance it locally at each radius--it may therefore be the key element in resolving the gas cooling problem in cluster cores and, more universally, in the atmospheres of X-ray-emitting, gas-rich systems on scales from galaxy clusters to groups and elliptical galaxies.

  14. Fred Hoyle: contributions to the theory of galaxy formation

    Efstathiou, George

    I review two fundamental contributions that Fred Hoyle made to the theory of galaxy formation. Hoyle was the first to propose that protogalaxies acquired their angular momentum via tidal torques from neighbouring perturbations during a period of gravitational instability. To my knowldege, he was also the first to suggest that the masses of galaxies could be explained by the requirement that primordial gas clouds cool radiatively on a suitable timescale. Tidal torques and cooling arguments play a central role in the modern theory of galaxy formation. It is a measure of Hoyle's breadth and inventiveness that he recognized the importance of these processes at such an early stage in the history of the subject.

  15. The Interstellar Medium in External Galaxies: Summaries of contributed papers

    Hollenbach, David J. (Editor); Thronson, Harley A., Jr. (Editor)

    1990-01-01

    The Second Wyoming Conference entitled, The Interstellar Medium in External Galaxies, was held on July 3 to 7, 1989, to discuss the current understanding of the interstellar medium in external galaxies and to analyze the basic physical processes underlying interstellar phenomena. The papers covered a broad range of research on the gas and dust in external galaxies and focused on such topics as the distribution and morphology of the atomic, molecular, and dust components; the dynamics of the gas and the role of the magnetic field in the dynamics; elemental abundances and gas depletions in the atomic and ionized components; cooling flows; star formation; the correlation of the nonthermal radio continuum with the cool component of the interstellar medium; the origin and effect of hot galactic halos; the absorption line systems seen in distant quasars; and the effect of galactic collisions.

  16. FMIT Test assemblies. Progress report

    Nygren, R.E.; Opperman, E.K.

    1978-08-01

    This progress report is a reference document for a number of inter-related tasks supporting the Fusion Materials Irradiation Test (FMIT) Facility being developed by the Hanford Engineering Development Laboratory. The report describes the basic configuration of test assemblies and supporting rationale based on the neutron flux distribution. Perturbed and unperturbed flux profiles are discussed as well as heating rates and cooling requirements

  17. Nuclear reactor fuel sub-assemblies

    Dodd, J.A.

    1981-01-01

    An improved fuel sub-assembly for a liquid metal cooled fast breeder reactor, is described, in which fatigue damage due to buffeting by cross-current flows is reduced and protection is provided against damage by contact with other reactor structures during loading and unloading of the sub-assembly. (U.K.)

  18. GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

    Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano

    2012-01-01

    Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 μm) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

  19. Dry cooling systems with plastic surfaces

    Roma, Carlo; Leonelli, Vincenzo

    1975-01-01

    Research and experiments made on dry cooling systems with plastic surfaces are described. The demonstration program planned in Italy for a 100Gcal/h dry cooling system is exposed, and an installation intended for a large 1300Mwe nuclear power station is described with reference to the assembly (exploitation and maintenance included). The performance and economic data relating to this installation are also exposed [fr

  20. Cool snacks

    Grunert, Klaus G; Brock, Steen; Brunsø, Karen

    2016-01-01

    Young people snack and their snacking habits are not always healthy. We address the questions whether it is possible to develop a new snack product that adolescents will find attractive, even though it is based on ingredients as healthy as fruits and vegetables, and we argue that developing...... such a product requires an interdisciplinary effort where researchers with backgrounds in psychology, anthropology, media science, philosophy, sensory science and food science join forces. We present the COOL SNACKS project, where such a blend of competences was used first to obtain thorough insight into young...... people's snacking behaviour and then to develop and test new, healthier snacking solutions. These new snacking solutions were tested and found to be favourably accepted by young people. The paper therefore provides a proof of principle that the development of snacks that are both healthy and attractive...

  1. Cool visitors

    2006-01-01

    Pictured, from left to right: Tim Izo (saxophone, flute, guitar), Bobby Grant (tour manager), George Pajon (guitar). What do the LHC and a world-famous hip-hop group have in common? They are cool! On Saturday, 1st July, before their appearance at the Montreux Jazz Festival, three members of the 'Black Eyed Peas' came on a surprise visit to CERN, inspired by Dan Brown's Angels and Demons. At short notice, Connie Potter (Head of the ATLAS secretariat) organized a guided tour of ATLAS and the AD 'antimatter factory'. Still curious, lead vocalist Will.I.Am met CERN physicist Rolf Landua after the concert to ask many more questions on particles, CERN, and the origin of the Universe.

  2. The Role Of Mergers In Galaxy Formation And Transformations

    Conselice, Christopher J.; Mundy, Carl; Duncan, Kenneth

    2017-06-01

    Baryonic assembly of galaxies is one of the largest questions in extragalactic studies, which relates to many other issues, including environment, feedback, star formation, gas accretion and merging. In fact, all of these processes are related and must be accounted for and understood to paint a full picture of galaxy assembly. Perhaps the most straightforward of these processes to measure are the merging and star formation histories. I will present results of combining in a new reanalysis of the three deepest and large NIR surveys take to date: UDS, Ultra-VISTA and VIDEO as part of the REFINE project. Using consistently measured stellar masses and photometric redshifts for galaxies in these fields up to z =3, I will show how the major and minor merger rate can consistently be measured across these fields. Our new method involves a full use of the PDF for photo-zs and stellar masses. We show how the merger fraction and rate are lower than previous results and the implications for this for other methods of galaxy assembly and feedback mechanisms. Invited Talk presented at the conference Galaxy Evolution Across Time, 12-16 June, Paris, France

  3. THE SLOAN GREAT WALL. MORPHOLOGY AND GALAXY CONTENT

    Einasto, M.; Liivamaegi, L. J.; Tempel, E.; Saar, E.; Tago, E.; Einasto, P.; Enkvist, I.; Einasto, J.; MartInez, V. J.; Heinaemaeki, P.; Nurmi, P.

    2011-01-01

    We present the results of a study of the morphology and galaxy content of the Sloan Great Wall (SGW), the richest galaxy system in the nearby universe. We use the luminosity density field to determine superclusters in the SGW, and the fourth Minkowski functional V 3 and the morphological signature (the K 1 -K 2 shapefinder curve) to show the different morphologies of the SGW, from a single filament to a multibranching, clumpy planar system. We show that the richest supercluster in the SGW, SCl 126, and especially its core, resembles a very rich filament, while another rich supercluster in the SGW, SCl 111, resembles a 'multispider'-an assembly of high-density regions connected by chains of galaxies. We study the substructure of individual galaxy populations determined by their color in these superclusters using Minkowski functionals and find that in the high-density core of the SGW the clumpiness of red and blue galaxies is similar, but in the outskirts of superclusters the distribution of red galaxies is clumpier than that of blue galaxies. At intermediate densities, the systems of blue galaxies have tunnels through them. We assess the statistical significance of our results using the halo model and smoothed bootstrap. We study the galaxy content and the properties of groups of galaxies in the two richest superclusters of the SGW, paying special attention to bright red galaxies (BRGs) and the first ranked (the most luminous) galaxies in SGW groups. The BRGs are the nearby luminous red galaxies; they are mostly bright and red and typically reside in groups (several groups host five or more BRGs). About one-third of the BRGs are spirals. The scatter of colors of elliptical BRGs is smaller than that of spiral BRGs. About half of the BRGs and of first ranked galaxies in groups have large peculiar velocities. Groups with elliptical BRGs as their first ranked galaxies populate superclusters more uniformly than the groups that have a spiral BRG as their first ranked

  4. The formation of galaxies

    Gunn, J.E.

    1983-01-01

    The presently fashionable ideas for galaxy formation are reviewed briefly, and it is concluded that the standard isothermal heirarchy fits the available data best. A simple infall picture is presented which explains many of the observed properties of disk galaxies. (orig.)

  5. The galaxy builders

    Cho, Adrian

    2018-06-01

    Philip Hopkins, a theoretical astrophysicist at the California Institute of Technology in Pasadena, likes to prank his colleagues. An expert in simulating the formation of galaxies, Hopkins sometimes begins his talks by projecting images of his creations next to photos of real galaxies and defying his audience to tell them apart. "We can even trick astronomers," Hopkins says. For decades, scientists have tried to simulate how the trillions of galaxies in the observable universe arose from clouds of gas after the big bang. But only in the past few years have the simulations begun to reproduce both the details of individual galaxies and their distribution of masses and shapes. As the fake universes improve, their role is also changing. Previously, information flowed one way: from the astronomers studying real galaxies to the modelers trying to simulate them. Now, insight is flowing the other way, too, with the models helping guide astronomers and astrophysicists. The models suggest that the earliest galaxies were oddly pickle-shaped, that wafer-thin spiral galaxies are surprisingly rugged in the face of collisions, and, perhaps most important, that galaxies must form stars far more slowly than astrophysicists expected. Progress is coming so fast, says Tiziana Di Matteo, a numerical cosmologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, that "the whole thing has reached this little golden age."

  6. The Evolution of Galaxies

    Palouš, Jan

    2007-01-01

    Roč. 17, - (2007), s. 34-40 ISSN 1220-5168. [Heliospere and galaxy. Sinaia, 03.05.2007-05.05.2007] R&D Projects: GA MŠk(CZ) LC06014 Institutional research plan: CEZ:AV0Z10030501 Keywords : ISM structure * stars formation * evolution of galaxies Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics

  7. Dwarf Elliptical Galaxies

    Caldwell, N.; Murdin, P.

    2000-11-01

    DWARF SPHEROIDAL GALAXIES were first identified by Shapley, who had noticed two very diffuse collections of stars on Harvard patrol plates. Although these systems had about as many stars as a GLOBULAR CLUSTER, they were of much lower density, and hence much larger radius, and thus were considered distinct galaxies. These two, named Fornax and Sculptor after the constellations in which they ap...

  8. Hubble's Menagerie of Galaxies

    Srimath

    astronom ers have even w ondered ifH ubble's galaxy typ es form an evolutionary sequence: does one type of galaxy evolve into another? 1. T he D iscovery of G alaxies. A stronom ers began to ponder these issues only after they discovered w hat ...

  9. Our galaxy is exploding

    Closets, Francois de.

    1977-01-01

    Improvements made in radioastronomy, and infrared, X and γ emission studies of the Galaxy have allowed to study the galactic nucleus, which is characterized by an intense activity. The most recent hypotheses made to explain this activity and replace it in the general context of the evolution of the galaxies are presented [fr

  10. Our aging galaxy

    Lyngaa, G.

    1980-01-01

    The origin and evolution of the galaxies is described, according to the presently prevailing theories. The various types of galaxy and their structures are described, and also the formation of stars from the gas clouds. The spiral structure and the evolution of the disc are discussed. Finally the future development on the time scale of thousands of millions of years is briefly discussed. (JIW)

  11. The Seyfert galaxy population

    Meurs, E.

    1982-01-01

    A large sample of Seyfert galaxies, many of which are Markarian galaxies, has been observed with the WSRT in lambda 21 cm continuum radiation. The results are presented, and the number of radio detected Seyferts has now increased considerably. A number of accurate optical positions are given that were needed to identify radio sources with the Seyfert galaxies observed. Optical and radio luminosity functions of Seyfert galaxies are derived. The results are compared with such functions for other categories of objects that may be related to these galaxies. The discussions focus on the possible connections between normal galaxies, Seyferts, and optically selected quasars. Three investigations are reported on individual objects that are related to Seyfert galaxies. WSRT observations of four bright, optically selected quasars are presented. The identification of an X-ray discovered BL Lacertae object is discussed. Its radio emission is on a much lower level than for other BL Lacs. Perhaps it is a radio-quiet object in this class, suggesting a comparable difference in radio emission for BL Lacs as is known for quasars. Photo-electric photometry for the Seyfert galaxy NGC 1566 is reported. Besides a monitoring programme, multi-aperture photometry is described. (Auth.)

  12. Visibility of galaxies

    Disney, M.J.

    1976-01-01

    It is stated that counts of galaxies could be seriously biased by selection effects, largely influenced by the brightness of the night sky. To illustrate this suppose the Earth were situated near the center of a giant elliptical galaxy. The mean surface brightness of the sky would then appear some 8 to 9 mag. brighter than is observed from our position in the Galaxy. Extragalactic space would then appear to be empty void; spiral and irregular galaxies would be invisible, and all that could be easily detected would be the core regions of galaxy ellipticals very similar to our own. Much of the Universe would be blinded by the surface brightness of the parent galaxy. This blinding, however, is a relative matter and the question arises as to what extent we are blinded by the spiral galaxy in which we exist. Strong indirect evidence exists that our knowledge of galaxies is heavily biased by the sky background, and the true population of extragalactic space may be very different from that seen. Other relevant work is also discussed, and further investigational work is indicated. (U.K.)

  13. Starbursts and IRAS galaxies

    Belfort, P.

    1987-01-01

    Several observational hints suggest that most of the IRAS galaxies are undergoing bursts of star formation. A simple photometric model of starburst galaxy was developed in order to check whether starburst events are really able to account for the far-infrared and optical properties of all the IRAS galaxies with HII region-like spectra. FIR activities up to a few hundred are actually easily reached with rather small bursts in red host-galaxies, and L IR /L B , EW(Hα) and U-B) versus (B-V) diagrams can be used to estimate burst strength and extinction. But more observations are required to conclude about the most extreme cases. Four typical infrared-selected IRAS galaxies are presented and their burst strength and extinction estimated

  14. MULTIPLE GALAXY COLLISIONS

    2002-01-01

    Here is a sampling of 15 ultraluminous infrared galaxies viewed by NASA's Hubble Space Telescope. Hubble's sharp vision reveals more complexity within these galaxies, which astronomers are interpreting as evidence of a multiple-galaxy pileup. These images, taken by the Wide Field and Planetary Camera 2, are part of a three-year study of 123 galaxies within 3 billion light-years of Earth. The study was conducted in 1996, 1997, and 1999. False colors were assigned to these photos to enhance fine details within these coalescing galaxies. Credits: NASA, Kirk Borne (Raytheon and NASA Goddard Space Flight Center, Greenbelt, Md.), Luis Colina (Instituto de Fisica de Cantabria, Spain), and Howard Bushouse and Ray Lucas (Space Telescope Science Institute, Baltimore, Md.)

  15. Gas accretion onto galaxies

    Davé, Romeel

    2017-01-01

    This edited volume presents the current state of gas accretion studies from both observational and theoretical perspectives, and charts our progress towards answering the fundamental yet elusive question of how galaxies get their gas. Understanding how galaxies form and evolve has been a central focus in astronomy for over a century. These studies have accelerated in the new millennium, driven by two key advances: the establishment of a firm concordance cosmological model that provides the backbone on which galaxies form and grow, and the recognition that galaxies grow not in isolation but within a “cosmic ecosystem” that includes the vast reservoir of gas filling intergalactic space. This latter aspect in which galaxies continually exchange matter with the intergalactic medium via inflows and outflows has been dubbed the “baryon cycle”. The topic of this book is directly related to the baryon cycle, in particular its least well constrained aspect, namely gas accretion. Accretion is a rare area of ast...

  16. Spectral evolution of galaxies

    Rocca-Volmerange, B.

    1989-01-01

    A recent striking event in Observational Cosmology is the discovery of a large population of galaxies at extreme cosmological distances (extended from spectral redshifts ≅ 1 to ≥ 3) corresponding to a lookback time of 80% of the Universe's age. However when galaxies are observed at such remote epochs, their appearances are affected by at least two simultaneous effects which are respectively a cosmological effect and the intrinsic evolution of their stellar populations which appear younger than in our nearby galaxies. The fundamental problem is first to disentangle the respective contributions of these two effects to apparent magnitudes and colors of distant galaxies. Other effects which are likely to modify the appearance of galaxies are amplification by gravitational lensing and interaction with environment will also be considered. (author)

  17. The Physical Origin of Galaxy Morphologies and Scaling Laws

    Steinmetz, Matthias; Navarro, Julio F.

    2002-01-01

    We propose a numerical study designed to interpret the origin and evolution of galaxy properties revealed by space- and ground-based imaging and spectroscopical surveys. Our aim is to unravel the physical processes responsible for the development of different galaxy morphologies and for the establishment of scaling laws such as the Tully-Fisher relation for spirals and the Fundamental Plane of ellipticals. In particular, we plan to address the following major topics: (1) The morphology and observability of protogalaxies, and in particular the relationship between primordial galaxies and the z approximately 3 'Ly-break' systems identified in the Hubble Deep Field and in ground-based searches; (2) The origin of the disk and spheroidal components in galaxies, the timing and mode of their assembly, the corresponding evolution in galaxy morphologies and its sensitivity to cosmological parameters; (3) The origin and redshift evolution of the scaling laws that link the mass, luminosity size, stellar content, and metal abundances of galaxies of different morphological types. This investigation will use state-of-the-art N-body/gasdynamical codes to provide a spatially resolved description of the galaxy formation process in hierarchically clustering universes. Coupled with population synthesis techniques. our models can be used to provide synthetic 'observations' that can be compared directly with observations of galaxies both nearby and at cosmologically significant distances. This study will thus provide insight into the nature of protogalaxies and into the formation process of galaxies like our own Milky Way. It will also help us to assess the cosmological significance of these observations within the context of hierarchical theories of galaxy formation and will supply a theoretical context within which current and future observations can be interpreted.

  18. The galaxy ancestor problem

    Disney, M. J.; Lang, R. H.

    2012-11-01

    The Hubble Space Telescope (HST) findsgalaxies whose Tolman dimming exceeds 10 mag. Could evolution alone explain these as our ancestor galaxies or could they be representatives of quite a different dynasty whose descendants are no longer prominent today? We explore the latter hypothesis and argue that surface brightness selection effects naturally bring into focus quite different dynasties from different redshifts. Thus, the HST z = 7 galaxies could be examples of galaxies whose descendants are both too small and too choked with dust to be recognizable in our neighbourhood easily today. Conversely, the ancestors of the Milky Way and its obvious neighbours would have completely sunk below the sky at z > 1.2, unless they were more luminous in the past, although their diffused light could account for the missing re-ionization flux. This Succeeding Prominent Dynasties Hypothesis (SPDH) fits the existing observations both naturally and well even without evolution, including the bizarre distributions of galaxy surface brightness found in deep fields, the angular size ˜(1 + z)-1 law, 'downsizing' which turns out to be an 'illusion' in the sense that it does not imply evolution, 'infant mortality', that is, the discrepancy between stars born and stars seen, the existence of 'red nuggets', and finally the recently discovered and unexpected excess of quasar absorption line damped Lyα systems at high redshift. If galaxies were not significantly brighter in the past and the SPDH were true, then a large proportion of galaxies could remain sunk from sight, possibly at all redshifts, and these sunken galaxies could supply the missing re-ionization flux. We show that fishing these sunken galaxies out of the sky by their optical emissions alone is practically impossible, even when they are nearby. More ingenious methods are needed to detect them. It follows that disentangling galaxy evolution through studying ever higher redshift galaxies may be a forlorn hope because one could

  19. Galaxies Coming of Age in Cosmic Blobs

    2009-06-01

    The "coming of age" of galaxies and black holes has been pinpointed, thanks to new data from NASA's Chandra X-ray Observatory and other telescopes. This discovery helps resolve the true nature of gigantic blobs of gas observed around very young galaxies. About a decade ago, astronomers discovered immense reservoirs of hydrogen gas -- which they named "blobs" - while conducting surveys of young distant galaxies. The blobs are glowing brightly in optical light, but the source of immense energy required to power this glow and the nature of these objects were unclear. A long observation from Chandra has identified the source of this energy for the first time. The X-ray data show that a significant source of power within these colossal structures is from growing supermassive black holes partially obscured by dense layers of dust and gas. The fireworks of star formation in galaxies are also seen to play an important role, thanks to Spitzer Space Telescope and ground-based observations. "For ten years the secrets of the blobs had been buried from view, but now we've uncovered their power source," said James Geach of Durham University in the United Kingdom, who led the study. "Now we can settle some important arguments about what role they played in the original construction of galaxies and black holes." Galaxies are believed to form when gas flows inwards under the pull of gravity and cools by emitting radiation. This process should stop when the gas is heated by radiation and outflows from galaxies and their black holes. Blobs could be a sign of this first stage, or of the second. Based on the new data and theoretical arguments, Geach and his colleagues show that heating of gas by growing supermassive black holes and bursts of star formation, rather than cooling of gas, most likely powers the blobs. The implication is that blobs represent a stage when the galaxies and black holes are just starting to switch off their rapid growth because of these heating processes. This

  20. Divertor cooling device

    Nakayama, Tadakazu; Hayashi, Katsumi; Handa, Hiroyuki

    1993-01-01

    Cooling water for a divertor cooling system cools the divertor, thereafter, passes through pipelines connecting the exit pipelines of the divertor cooling system and the inlet pipelines of a blanket cooling system and is introduced to the blanket cooling system in a vacuum vessel. It undergoes emission of neutrons, and cooling water in the divertor cooling system containing a great amount of N-16 which is generated by radioactivation of O-16 is introduced to the blanket cooling system in the vacuum vessel by way of pipelines, and after cooling, passes through exit pipelines of the blanket cooling system and is introduced to the outside of the vacuum vessel. Radiation of N-16 in the cooling water is decayed sufficiently with passage of time during cooling of the blanket, thereby enabling to decrease the amount of shielding materials such as facilities and pipelines, and ensure spaces. (N.H.)

  1. The evolution of the intergalactic medium and the origin of the galaxy luminosity function

    Valls-Gabaud, David; Blanchard, Alain; Mamon, Gary

    1993-01-01

    The coupling of the Press and Schechter prescription with the CDM scenario and the Hoyle-Rees-Ostriker cooling criterion leads to a galaxy formation scenario in which galaxies are overproduced by a large factor. Although star formation might be suppressed in the smaller halos, a large amount of energy per galactic mass is needed to account for the present number density of galaxies. The evolution of the intergalactic medium (IGM) provides a simple criterion to prevent galaxy formation without requiring feedback, since halos with small virial temperatures are not able to retain the infalling hot gas of the IGM. If the ionizing background has decreased since z is approximately 1 - 2, then this criterion explains the slope of the luminosity function at the faint end. In addition, this scenario predicts two populations of dwarf galaxies, well differentiated in age, gas content, stellar populations, and clustering properties, which can be identified with dE and dIm galaxies.

  2. Are spiral galaxies heavy smokers?

    Davies, J.; Disney, M.; Phillipps, S

    1990-01-01

    The dustiness of spiral galaxies is discussed. Starburst galaxies and the shortage of truly bright spiral galaxies is cited as evidence that spiral galaxies are far dustier than has been thought. The possibility is considered that the dust may be hiding missing mass

  3. WORKSHOP: Beam cooling

    Anon.

    1994-01-01

    Cooling - the control of unruly particles to provide well-behaved beams - has become a major new tool in accelerator physics. The main approaches of electron cooling pioneered by Gersh Budker at Novosibirsk and stochastic cooling by Simon van der Meer at CERN, are now complemented by additional ideas, such as laser cooling of ions and ionization cooling of muons

  4. Rebuilding Spiral Galaxies

    2005-01-01

    Major Observing Programme Leads to New Theory of Galaxy Formation Summary Most present-day large galaxies are spirals, presenting a disc surrounding a central bulge. Famous examples are our own Milky Way or the Andromeda Galaxy. When and how did these spiral galaxies form? Why do a great majority of them present a massive central bulge? An international team of astronomers [1] presents new convincing answers to these fundamental questions. For this, they rely on an extensive dataset of observations of galaxies taken with several space- and ground-based telescopes. In particular, they used over a two-year period, several instruments on ESO's Very Large Telescope. Among others, their observations reveal that roughly half of the present-day stars were formed in the period between 8,000 million and 4,000 million years ago, mostly in episodic burst of intense star formation occurring in Luminous Infrared Galaxies. From this and other evidence, the astronomers devised an innovative scenario, dubbed the "spiral rebuilding". They claim that most present-day spiral galaxies are the results of one or several merger events. If confirmed, this new scenario could revolutionise the way astronomers think galaxies formed. PR Photo 02a/05: Luminosity - Oxygen Abundance Relation for Galaxies (VLT) PR Photo 02b/05: The Spiral Rebuilding Scenario A fleet of instruments How and when did galaxies form? How and when did stars form in these island universes? These questions are still posing a considerable challenge to present-day astronomers. Front-line observational results obtained with a fleet of ground- and space-based telescopes by an international team of astronomers [1] provide new insights into these fundamental issues. For this, they embarked on an ambitious long-term study at various wavelengths of 195 galaxies with a redshift [2] greater than 0.4, i.e. located more than 4000 million light-years away. These galaxies were studied using ESO's Very Large Telescope, as well as the

  5. The nature of assembly bias - III. Observational properties

    Lacerna, Ivan; Padilla, Nelson; Stasyszyn, Federico

    2014-10-01

    We analyse galaxies in groups in the Sloan Digital Sky Survey (SDSS) and find a weak but significant assembly-type bias, where old central galaxies have a higher clustering amplitude (61 ± 9 per cent) at scales >1 h-1 Mpc than young central galaxies of equal host halo mass (Mh ˜ 1011.8 h- 1 M⊙). The observational sample is volume limited out to z = 0.1 with Mr - 5 log (h) ≤ -19.6. We construct a mock catalogue of galaxies that shows a similar signal of assembly bias (46 ± 9 per cent) at the same halo mass. We then adapt the model presented by Lacerna & Padilla (Paper I) to redefine the overdensity peak height, which traces the assembly bias such that galaxies in equal density peaks show the same clustering regardless of their stellar age, but this time using observational features such as a flux limit. The proxy for peak height, which is proposed as a better alternative than the virial mass, consists in the total mass given by the mass of neighbour host haloes in cylinders centred at each central galaxy. The radius of the cylinder is parameterized as a function of stellar age and virial mass. The best-fitting sets of parameters that make the assembly bias signal lower than 5-15 per cent for both SDSS and mock central galaxies are similar. The idea behind the parameterization is not to minimize the bias, but it is to use this method to understand the physical features that produce the assembly bias effect. Even though the tracers of the density field used here differ significantly from those used in Paper I, our analysis of the simulated catalogue indicates that the different tracers produce correlated proxies, and therefore the reason behind assembly bias is the crowding of peaks in both simulations and the SDSS.

  6. Dwarf galaxies : Important clues to galaxy formation

    Tolstoy, E

    2003-01-01

    The smallest dwarf galaxies are the most straight forward objects in which to study star formation processes on a galactic scale. They are typically single cell star forming entities, and as small potentials in orbit around a much larger one they are unlikely to accrete much (if any) extraneous

  7. The population of early-type galaxies: how it evolves with time and how it differs from passive and late-type galaxies

    Tamburri, S.; Saracco, P.; Longhetti, M.; Gargiulo, A.; Lonoce, I.; Ciocca, F.

    2014-10-01

    -mass galaxies both ETGs and LTGs (M∗> 3-4 × 1011 M⊙) does not increase from z ~ 2.5, contrary to the lower mass galaxies. This suggests that the most massive galaxies formed at z> 2.5-3 and that the assembly of such high-mass galaxies is not effective at lower redshift.

  8. ASSEMBLY TRANSFER SYSTEM DESCRIPTION DOCUMENT

    Gorpani, B.

    2000-01-01

    The Assembly Transfer System (ATS) receives, cools, and opens rail and truck transportation casks from the Carrier/Cask Handling System (CCHS). The system unloads transportation casks consisting of bare Spent Nuclear Fuel (SNF) assemblies, single element canisters, and Dual Purpose Canisters (DPCs). For casks containing DPCs, the system opens the DPCs and unloads the SNF. The system stages the assemblies, transfer assemblies to and from fuel-blending inventory pools, loads them into Disposal Containers (DCs), temporarily seals and inerts the DC, decontaminates the DC and transfers it to the Disposal Container Handling System. The system also prepares empty casks and DPCs for off-site shipment. Two identical Assembly Transfer System lines are provided in the Waste Handling Building (WHB). Each line operates independently to handle the waste transfer throughput and to support maintenance operations. Each system line primarily consists of wet and dry handling areas. The wet handling area includes a cask transport system, cask and DPC preparation system, and a wet assembly handling system. The basket transport system forms the transition between the wet and dry handling areas. The dry handling area includes the dry assembly handling system, assembly drying system, DC preparation system, and DC transport system. Both the wet and dry handling areas are controlled by the control and tracking system. The system operating sequence begins with moving transportation casks to the cask preparation area. The cask preparation operations consist of cask cavity gas sampling, cask venting, cask cool-down, outer lid removal, and inner shield plug lifting fixture attachment. Casks containing bare SNF (no DPC) are filled with water and placed in the cask unloading pool. The inner shield plugs are removed underwater. For casks containing a DPC, the cask lid(s) is removed, and the DPC is penetrated, sampled, vented, and cooled. A DPC lifting fixture is attached and the cask is placed

  9. Renewable Heating And Cooling

    Renewable heating and cooling is a set of alternative resources and technologies that can be used in place of conventional heating and cooling technologies for common applications such as water heating, space heating, space cooling and process heat.

  10. Liquid metal cooled fast breeder nuclear reactor

    Scott, D.

    1979-01-01

    A liquid metal cooled fast breeder nuclear reactor has a core comprising a plurality of fuel assemblies supported on a diagrid and submerged in a pool of liquid metal coolant within a containment vessel, the diagrid being of triple component construction and formed of a short cylindrical plenum mounted on a conical undershell and loosely embraced by a fuel store carrier. The plenum merely distributes coolant through the fuel assemblies, the load of the assemblies being carried by the undershell by means of struts which penetrate the plenum. The reactor core, fuel store carrier and undershell provide secondary containment for the plenum. (UK)

  11. Galaxy-galaxy lensing in EAGLE: comparison with data from 180 deg2 of the KiDS and GAMA surveys

    Velliscig, Marco; Cacciato, Marcello; Hoekstra, Henk; Schaye, Joop; Heymans, Catherine; Hildebrandt, Hendrik; Loveday, Jon; Norberg, Peder; Sifón, Cristóbal; Schneider, Peter; van Uitert, Edo; Viola, Massimo; Brough, Sarah; Erben, Thomas; Holwerda, Benne W.; Hopkins, Andrew M.; Kuijken, Konrad

    2017-11-01

    We present predictions for the galaxy-galaxy lensing (GGL) profile from the EAGLE hydrodynamical cosmological simulation at redshift z = 0.18, in the spatial range 0.02 < R/(h- 1 Mpc) < 2, and for five logarithmically equispaced stellar mass bins in the range 10.3 < log10(Mstar/ M⊙) < 11.8. We compare these excess surface density profiles to the observed signal from background galaxies imaged by the Kilo Degree Survey around spectroscopically confirmed foreground galaxies from the Galaxy And Mass Assembly (GAMA) survey. Exploiting the GAMA galaxy group catalogue, the profiles of central and satellite galaxies are computed separately for groups with at least five members to minimize contamination. EAGLE predictions are in broad agreement with the observed profiles for both central and satellite galaxies, although the signal is underestimated at R ≈ 0.5-2 h- 1 Mpc for the highest stellar mass bins. When central and satellite galaxies are considered simultaneously, agreement is found only when the selection function of lens galaxies is taken into account in detail. Specifically, in the case of GAMA galaxies, it is crucial to account for the variation of the fraction of satellite galaxies in bins of stellar mass induced by the flux-limited nature of the survey. We report the inferred stellar-to-halo mass relation and we find good agreement with recent published results. We note how the precision of the GGL profiles in the simulation holds the potential to constrain fine-grained aspects of the galaxy-dark matter connection.

  12. A GMBCG galaxy cluster catalog of 55,880 rich clusters from SDSS DR7

    Hao, Jiangang; McKay, Timothy A.; Koester, Benjamin P.; Rykoff, Eli S.; Rozo, Eduardo; Annis, James; Wechsler, Risa H.; Evrard, August; Siegel, Seth R.; Becker, Matthew; Busha, Michael; /Fermilab /Michigan U. /Chicago U., Astron. Astrophys. Ctr. /UC, Santa Barbara /KICP, Chicago /KIPAC, Menlo Park /SLAC /Caltech /Brookhaven

    2010-08-01

    We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.

  13. Restaurant food cooling practices.

    Brown, Laura Green; Ripley, Danny; Blade, Henry; Reimann, Dave; Everstine, Karen; Nicholas, Dave; Egan, Jessica; Koktavy, Nicole; Quilliam, Daniela N

    2012-12-01

    Improper food cooling practices are a significant cause of foodborne illness, yet little is known about restaurant food cooling practices. This study was conducted to examine food cooling practices in restaurants. Specifically, the study assesses the frequency with which restaurants meet U.S. Food and Drug Administration (FDA) recommendations aimed at reducing pathogen proliferation during food cooling. Members of the Centers for Disease Control and Prevention's Environmental Health Specialists Network collected data on food cooling practices in 420 restaurants. The data collected indicate that many restaurants are not meeting FDA recommendations concerning cooling. Although most restaurant kitchen managers report that they have formal cooling processes (86%) and provide training to food workers on proper cooling (91%), many managers said that they do not have tested and verified cooling processes (39%), do not monitor time or temperature during cooling processes (41%), or do not calibrate thermometers used for monitoring temperatures (15%). Indeed, 86% of managers reported cooling processes that did not incorporate all FDA-recommended components. Additionally, restaurants do not always follow recommendations concerning specific cooling methods, such as refrigerating cooling food at shallow depths, ventilating cooling food, providing open-air space around the tops and sides of cooling food containers, and refraining from stacking cooling food containers on top of each other. Data from this study could be used by food safety programs and the restaurant industry to target training and intervention efforts concerning cooling practices. These efforts should focus on the most frequent poor cooling practices, as identified by this study.

  14. Core/coil assembly for use in superconducting magnets and method for assembling the same

    Kassner, David A.

    1979-01-01

    A core/coil assembly for use in a superconducting magnet of the focusing or bending type used in syncronous particle accelerators comprising a coil assembly contained within an axial bore of the stacked, washer type, carbon steel laminations which comprise the magnet core assembly, and forming an interference fit with said laminations at the operating temperature of said magnet. Also a method for making such core/coil assemblies comprising the steps of cooling the coil assembly to cryogenic temperatures and drawing it rapidly upwards into the bore of said stacked laminations.

  15. Investigating the Merger Origin of Early-type Galaxies using Ultra-deep Optical Images

    Duc, P.-A.; Cuillandre, J.-C.; Alatalo, K.; Blitz, L.; Bois, M.; Bournaud, F.; Bureau, M.; Cappellari, M.; Côté, P.; Davies, R. L.; Davis, T. A.; de Zeeuw, P. T.; Emsellem, E.; Ferrarese, L.; Ferriere, E.; Gwyn, S.; Khochfar, S.; Krajnovic, D.; Kuntschner, H.; Lablanche, P.-Y.; MacArthur, L.; McDermid, R. M.; Michel-Dansac, L.; Morganti, R.; Naab, T.; Oosterloo, T.; Sarzi, M.; Scott, N.; Serra, P.; Weijmans, A.; Young, L. M.

    2011-01-01

    The mass assembly of galaxies leaves various imprints on their surroundings, such as shells, streams and tidal tails. The frequency and properties of these fine structures depend on the mechanism driving the mass assembly: e.g. a monolithic collapse, rapid cold-gas accretion followed by violent disk

  16. SHOCKED POSTSTARBUST GALAXY SURVEY. I. CANDIDATE POST-STARBUST GALAXIES WITH EMISSION LINE RATIOS CONSISTENT WITH SHOCKS

    Alatalo, Katherine; Rich, Jeffrey A. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Cales, Sabrina L. [Yale Center for Astronomy and Astrophysics, Physics Department, Yale University, New Haven, CT 06511 (United States); Appleton, Philip N.; Lanz, Lauranne [Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States); Kewley, Lisa J.; Medling, Anne M. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston ACT 2611 (Australia); Lacy, Mark; Nyland, Kristina, E-mail: kalatalo@carnegiescience.edu [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)

    2016-06-01

    There are many mechanisms by which galaxies can transform from blue, star-forming spirals, to red, quiescent early-type galaxies, but our current census of them does not form a complete picture. Recent observations of nearby case studies have identified a population of galaxies that quench “quietly.” Traditional poststarburst searches seem to catch galaxies only after they have quenched and transformed, and thus miss any objects with additional ionization mechanisms exciting the remaining gas. The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify transforming galaxies, in which the nebular lines are excited via shocks instead of through star formation processes. Utilizing the Oh-Sarzi-Schawinski-Yi (OSSY) measurements on the Sloan Digital Sky Survey Data Release 7 catalog, we applied Balmer absorption and shock boundary criteria to identify 1067 SPOG candidates (SPOGs*) within z = 0.2. SPOGs* represent 0.2% of the OSSY sample galaxies that exceed the continuum signal-to-noise cut (and 0.7% of the emission line galaxy sample). SPOGs* colors suggest that they are in an earlier phase of transition than OSSY galaxies that meet an “E+A” selection. SPOGs* have a 13% 1.4 GHz detection rate from the Faint Images of the Radio Sky at Twenty Centimeters Survey, higher than most other subsamples, and comparable only to low-ionization nuclear emission line region hosts, suggestive of the presence of active galactic nuclei (AGNs). SPOGs* also have stronger Na i D absorption than predicted from the stellar population, suggestive of cool gas being driven out in galactic winds. It appears that SPOGs* represent an earlier phase in galaxy transformation than traditionally selected poststarburst galaxies, and that a large proportion of SPOGs* also have properties consistent with disruption of their interstellar media, a key component to galaxy transformation. It is likely that many of the known pathways to transformation undergo a SPOG phase. Studying this sample of

  17. Cosmology and galaxy formation

    Jones, B.J.T.; Gonzalez, E.M.

    1985-05-01

    The aim of the present series of lectures is to be unashamedly pedagogical and present, in simple terms, an overview of our current thinking about our universe and the way in which we believe galaxies have formed. (orig./WL)

  18. Interpretation of galaxy counts

    Tinsely, B.M.

    1980-01-01

    New models are presented for the interpretation of recent counts of galaxies to 24th magnitude, and predictions are shown to 28th magnitude for future comparison with data from the Space Telescope. The results supersede earlier, more schematic models by the author. Tyson and Jarvis found in their counts a ''local'' density enhancement at 17th magnitude, on comparison with the earlier models; the excess is no longer significant when a more realistic mixture of galaxy colors is used. Bruzual and Kron's conclusion that Kron's counts show evidence for evolution at faint magnitudes is confirmed, and it is predicted that some 23d magnitude galaxies have redshifts greater than unity. These may include spheroidal systems, elliptical galaxies, and the bulges of early-type spirals and S0's, seen during their primeval rapid star formation

  19. Current star formation in S0 galaxies: NGC 4710

    Wrobel, J.M.

    1990-01-01

    Elliptical (E) and lenticular (S0) galaxies lack the substantial interstellar medium (ISM) found in the star-forming spiral galaxies. However, significant numbers of E and S0 galaxies are known to contain detectable amounts of interstellar matter (e.g., Jura 1988). Thus, it is worth investigating whether these galaxies are currently able to form stars from their ISM, or whether they should be consigned to the dustbin of inert objects (Thronson and Bally 1987). The results strongly imply that current star formation is responsible for NGC 4710's far infrared and radio continuum properties. If this is indeed the case, then one expects this star formation to be fueled by molecular gas, which is presumably dominated by H2 and can be traced by the CO-12 J=1 to 0 line. Both Kenney and Young (1988) and Sage and Wrobel (1989) have detected such an emission line from NGC 4710, and infer the presence of more than 10(exp 8) solar mass of H2. The origin of the molecular gas in NGC 4710 remains a mystery. The galaxy is very deficient in HI (Kenney and Young, in preparation), suggesting that it originally was a spiral galaxy from which the outer, mainly atomic, gas was stripped by the ram pressure of the Virgo Cluster's intracluster medium, leaving only a central interstellar medium (ISM) rich in molecular gas. Alternatively, the CO may have originated via stellar mass loss with subsequent cooling, cooling flows, or capture from a gas-rich companion. Information on the morphology and kinematics of the CO can be compared with that of the galaxy's other gases and stars to distinguish among these various possible origins for the molecular gas. Major axis CO mapping with single dishes indicate an unresolved source. Thus, a millimeter array is currently being used to image NGC 4710 in CO to provide the needed morphological and kinematical data

  20. Multi-wavelength study of young and massive galaxy clusters

    Lemonon, Ludovic

    1999-01-01

    Clusters of galaxies are the most massive objects gravitationally bound observed. They are the consequence of the evolution of most important perturbations in the cosmological microwave background. Their formation depends strongly of the cosmology, so they represent key objects to understand the Universe. The aim of this thesis is to study the processes of formation in clusters of galaxies well far away than previous studies clone, by high-resolution observations obtained by using most powerful telescope in each studied wavelength: X-ray, visible, infrared and radio. After data reductions of 12 clusters located at 0.1; z; 0.3, I was able to classified them in three categories: dynamically perturbed clusters, with substructures in their X-ray/optical image or velocity distribution of galaxies; cooling flows clusters, more relaxed than previous, with huge amount of gas cooling in their center; AGN contaminated, where the central dominant galaxy is an AGN which contaminate considerably the X-ray emission. I have obtained a measurement of the baryonic fraction of the Universe mass, and an estimation of the Universe matter density parameter at the mega-parsec scale, claiming for a low density universe. The ISOCAM data showed the effect of the ICM interactions on the star formation in cluster galaxies, and demonstrated that optical and mid-IR deduced star-formation are not basically compatible. They also showed how IR-emitting galaxies distribute in clusters, most noticeably how 15 um galaxies are located preferably on the edge of clusters. X-ray and radio data showed that clusters at z 0.25 could be find in several dynamical state, similarly with nearby ones, from relaxed to severely perturbed. All clusters present signs of past or present merging, in agreement with hierarchical structure formation scenario. This clusters database is an excellent starting point to study process of merging in clusters since they showed different aspect of this evolution. (author) [fr

  1. Implications of Galaxy Buildup for Putative IMF Variations in Massive Galaxies

    Blancato, Kirsten; Genel, Shy; Bryan, Greg

    2017-08-01

    Recent observational evidence for initial mass function (IMF) variations in massive quiescent galaxies at z = 0 challenges the long-established paradigm of a universal IMF. While a few theoretical models relate the IMF to birth cloud conditions, the physical driver underlying these putative IMF variations is still largely unclear. Here we use post-processing analysis of the Illustris cosmological hydrodynamical simulation to investigate possible physical origins of IMF variability with galactic properties. We do so by tagging stellar particles in the simulation (each representing a stellar population of ≈ {10}6 {M}⊙ ) with individual IMFs that depend on various physical conditions, such as velocity dispersion, metallicity, or star formation rate, at the time and place in which the stars are formed. We then follow the assembly of these populations throughout cosmic time and reconstruct the overall IMF of each z = 0 galaxy from the many distinct IMFs it is composed of. Our main result is that applying the observed relations between IMF and galactic properties to the conditions at the star formation sites does not result in strong enough IMF variations between z = 0 galaxies. Steeper physical IMF relations are required for reproducing the observed IMF trends, and some stellar populations must form with more extreme IMFs than those observed. The origin of this result is the hierarchical nature of massive galaxy assembly, and it has implications for the reliability of the strong observed trends, for the ability of cosmological simulations to capture certain physical conditions in galaxies, and for theories of star formation aiming to explain the physical origin of a variable IMF.

  2. The EAGLE simulations: atomic hydrogen associated with galaxies

    Crain, Robert A.; Bahé, Yannick M.; Lagos, Claudia del P.; Rahmati, Alireza; Schaye, Joop; McCarthy, Ian G.; Marasco, Antonino; Bower, Richard G.; Schaller, Matthieu; Theuns, Tom; van der Hulst, Thijs

    2017-02-01

    We examine the properties of atomic hydrogen (H I) associated with galaxies in the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations of galaxy formation. EAGLE's feedback parameters were calibrated to reproduce the stellar mass function and galaxy sizes at z = 0.1, and we assess whether this calibration also yields realistic H I properties. We estimate the self-shielding density with a fitting function calibrated using radiation transport simulations, and correct for molecular hydrogen with empirical or theoretical relations. The `standard-resolution' simulations systematically underestimate H I column densities, leading to an H I deficiency in low-mass (M⋆ < 1010 M⊙) galaxies and poor reproduction of the observed H I mass function. These shortcomings are largely absent from EAGLE simulations featuring a factor of 8 (2) better mass (spatial) resolution, within which the H I mass of galaxies evolves more mildly from z = 1 to 0 than in the standard-resolution simulations. The largest volume simulation reproduces the observed clustering of H I systems, and its dependence on H I richness. At fixed M⋆, galaxies acquire more H I in simulations with stronger feedback, as they become associated with more massive haloes and higher infall rates. They acquire less H I in simulations with a greater star formation efficiency, since the star formation and feedback necessary to balance the infall rate is produced by smaller gas reservoirs. The simulations indicate that the H I of present-day galaxies was acquired primarily by the smooth accretion of ionized, intergalactic gas at z ≃ 1, which later self-shields, and that only a small fraction is contributed by the reincorporation of gas previously heated strongly by feedback. H I reservoirs are highly dynamic: over 40 per cent of H I associated with z = 0.1 galaxies is converted to stars or ejected by z = 0.

  3. Liquid metal cooled fast breeder nuclear reactors

    Duncombe, E.; Thatcher, G.

    1979-01-01

    The invention described relates to a liquid metal cooled fast breeder nuclear reactor in which the fuel assembly has an inner zone comprised mainly of fissile material and a surrounding outer zone comprised mainly of breeder material. According to the invention the sub-assemblies in the outer zone include electro-magnetic braking devices (magnets, pole pieces and armature) for regulating the flow of coolant through the sub-assemblies. The magnetic fields of the electro-magnetic breaking devices are temperature sensitive so that as the power output of the breeder sub-assemblies increases the electro-magnetic resistance to coolant flow is reduced thereby maintaining the temperature of the coolant outlets from the sub-assemblies substantially constant. (UK)

  4. Automated galaxy surface photometry

    Cawson, M.G.M.; Kibblewhite, E.J.; Disney, M.J.; Phillipps, S.

    1987-01-01

    Two-dimensional surface photometry of a very large number of galaxies on a deep Schmidt plate has been obtained using the Automatic Plate Measuring System (APM). A method of photometric calibration, suitable for APM measurements, via pixel-by-pixel comparison with CCD frames of a number of the brighter galaxies is described and its advantages are discussed. The same method is used to demonstrate the consistency of measurement of the APM machine when used for surface photometry. (author)

  5. The dependence of galactic outflows on the properties and orientation of zCOSMOS galaxies at z ∼ 1

    Bordoloi, R.; Lilly, S. J.; Hardmeier, E.; Carollo, C. M.; Contini, T.; Kneib, J.-P.; Fevre, O. Le; Garilli, B.; Mainieri, V.; Renzini, A.; Scodeggio, M.; Zamorani, G.; Bardelli, S.; Bolzonella, M.; Bongiorno, A.; Caputi, K.; Cucciati, O.; De la Torre, S.; De Ravel, L.; Iovino, A.

    2014-01-01

    We present an analysis of cool outflowing gas around galaxies, traced by Mg II absorption lines in the coadded spectra of a sample of 486 zCOSMOS galaxies at 1 ≤ z ≤ 1.5. These galaxies span a range of stellar masses (9.45 ≤ log 10 [M * /M ☉ ] ≤ 10.7) and star formation rates (0.14 ≤ log 10 [SFR/M ☉ yr –1 ] ≤ 2.35). We identify the cool outflowing component in the Mg II absorption and find that the equivalent width of the outflowing component increases with stellar mass. The outflow equivalent width also increases steadily with the increasing star formation rate of the galaxies. At similar stellar masses, the blue galaxies exhibit a significantly higher outflow equivalent width as compared to red galaxies. The outflow equivalent width shows strong correlation with the star formation surface density (Σ SFR ) of the sample. For the disk galaxies, the outflow equivalent width is higher for the face-on systems as compared to the edge-on ones, indicating that for the disk galaxies, the outflowing gas is primarily bipolar in geometry. Galaxies typically exhibit outflow velocities ranging from –150 km s –1 ∼–200 km s –1 and, on average, the face-on galaxies exhibit higher outflow velocity as compared to the edge-on ones. Galaxies with irregular morphologies exhibit outflow equivalent width as well as outflow velocities comparable to face on disk galaxies. These galaxies exhibit mass outflow rates >5-7 M ☉ yr –1 and a mass loading factor (η = M-dot out /SFR) comparable to the star formation rates of the galaxies.

  6. Evolution of galaxies

    Palous, J.

    1987-01-01

    The proceedings contain 87 papers divided into 8 chapters. The chapter Bipolar outflows and star formations contains papers on optical and infrared observations of young bipolar outflow objects and the theory thereof, and on observations of cometary nebulae. The chapter Masers and early stellar evolution discusses molecular masers and star forming regions. The following chapter contains papers on initial mass function and star formation rates in galaxies. The chapter Clusters and star formation contains data on OB associations and open star clusters, their development and observations, CO and H 2 in our galaxy, the four vector model of radio emission and an atlas of the wavelength dependence of ultraviolet extinction in the Galaxy. The most voluminous is the chapter Evolution of galaxies. It contains papers on the theories of the physical and chemodynamic development of galaxies of different types, rotation research and rotation velocities of galaxies and their arms, and on mathematical and laboratory models of morphological development. Chapter seven contains papers dealing with active extragalactic objects, quasars and active galactic nuclei. The last chapter discusses cosmological models, the theory of the inflationary universe, and presents an interpretation of the central void and X-ray background. (M.D.). 299 figs., 48 tabs., 1651 refs

  7. Coma cluster of galaxies

    1999-01-01

    Atlas Image mosaic, covering 34' x 34' on the sky, of the Coma cluster, aka Abell 1656. This is a particularly rich cluster of individual galaxies (over 1000 members), most prominently the two giant ellipticals, NGC 4874 (right) and NGC 4889 (left). The remaining members are mostly smaller ellipticals, but spiral galaxies are also evident in the 2MASS image. The cluster is seen toward the constellation Coma Berenices, but is actually at a distance of about 100 Mpc (330 million light years, or a redshift of 0.023) from us. At this distance, the cluster is in what is known as the 'Hubble flow,' or the overall expansion of the Universe. As such, astronomers can measure the Hubble Constant, or the universal expansion rate, based on the distance to this cluster. Large, rich clusters, such as Coma, allow astronomers to measure the 'missing mass,' i.e., the matter in the cluster that we cannot see, since it gravitationally influences the motions of the member galaxies within the cluster. The near-infrared maps the overall luminous mass content of the member galaxies, since the light at these wavelengths is dominated by the more numerous older stellar populations. Galaxies, as seen by 2MASS, look fairly smooth and homogeneous, as can be seen from the Hubble 'tuning fork' diagram of near-infrared galaxy morphology. Image mosaic by S. Van Dyk (IPAC).

  8. PEARS Emission Line Galaxies

    Pirzkal, Nor; Rothberg, Barry; Ly, Chun; Rhoads, James E.; Malhotra, Sangeeta; Grogin, Norman A.; Dahlen, Tomas; Meurer, Gerhardt R.; Walsh, Jeremy; Hathi, Nimish P.; hide

    2012-01-01

    We present a full analysis of the Probing Evolution And Reionization Spectroscopically (PEARS) slitless grism spectroscopic data obtained vl'ith the Advanced Camera for Surveys on HST. PEARS covers fields within both the Great Observatories Origins Deep Survey (GOODS) North and South fields, making it ideal as a random surveY of galaxies, as well as the availability of a wide variety of ancillary observations to support the spectroscopic results. Using the PEARS data we are able to identify star forming galaxies within the redshift volume 0 galaxies down to a limiting flux of approx 10 - 18 erg/s/sq cm . The ELRs have also been compared to the properties of the host galaxy, including morphology, luminosity, and mass. From this analysis we find three key results: 1) The computed line luminosities show evidence of a flattening in the luminosity function with increasing redshift; 2) The star forming systems show evidence of disturbed morphologies, with star formation occurring predominantly within one effective (half-light) radius. However, the morphologies show no correlation with host stellar mass; and 3) The number density of star forming galaxies with M(*) >= 10(exp 9) Solar M decreases by an order of magnitude at z<=0.5 relative to the number at 0.5 < z < 0.9 in support of the argument for galaxy downsizing.

  9. The Milky Way galaxy

    Woerden, H. van; Allen, R.J.; Burton, W.B.

    1985-01-01

    IAU Symposium 106, held at the Kapteyn Institute in Groningen, presents an overview of all major aspects of galactic astronomy. The vast subject is covered in 20 authoritative review papers and 22 invited papers, each with discussion, plus 81 shorter contributions. The book opens with 4 reviews by historians of science, outlining the history of galactic research. Part 2 deals with (i) galactic rotation, (ii) the large-scale distributions of matter, of both old and young stellar populations, and of the atomic, molecular and high-energy components of the interstellar medium, (iii) small-scale structure in the gas, (iv) the galactic nucleus, (v) the high-velocity clouds. Part 3 discusses the dynamics of the local group of Galaxies and of the Milky Way-Magellanic clouds system, the dynamical and chemical evolution of the Galaxy and of its disk and halo components and the formation of the Galaxy. The controversial subject of spiral structure and star formation is analyzed in several extensive reviews and lively discussions, featuring both observational and theoretical developments. Results of extragalactic research are blended with studies of our Galaxy throughout the book, and there is a separate comparison between Andromeda and Milky Way Galaxies. The Symposium featured the first maps produced by IRAS, and results from most major telescopes in a variety of wavebands. Many review papers present material not published elsewhere. The book closes with a lecture on life in the Galaxy and with an imaginative symposium summary. (orig.)

  10. Galaxy Clusters as Tele-ALP-scopes

    CERN. Geneva

    2015-01-01

    Axion-like particles have good theoretical motivation and are characterized by conversion to photons in astrophysical magnetic fields. Galaxy clusters are the most efficient convertors of axion-like particles to photons in the universe. I discuss the physics and phenomenology of ALPs, and describe their astrophysical implications, with particular reference to the recently observed 3.5 keV X-ray line that is a candidate for a dark matter decay line. I discuss interpretations of this line in terms of dark matter decaying to an axion-like particle, that then converts to a photon in cluster magnetic fields, and describe the compatibility of this scenario with data and the different phenomenology for cool-core and non-cool-core clusters.

  11. Design configuration of GCFR core assemblies

    LaBar, M.P.; Lee, G.E.; Meyer, R.J.

    1980-05-01

    The current design configurations of the core assemblies for the gas-cooled fast reactor (GCFR) demonstration plant reactor core conceptual design are described. Primary emphasis is placed upon the design innovations that have been incorporated in the design of the core assemblies since the establishment of the initial design of an upflow GCFR core. A major feature of the design configurations is that they are prototypical of core assemblies for use in commercial plants; a larger number of the same assemblies would be used in a commercial plant

  12. Mapping Nearby Galaxies at APO: The MaNGA IFU Galaxy Survey

    Law, David R.; MaNGA Team

    2014-01-01

    MaNGA is a new survey that will begin in August 2014 as part of SDSS-IV with the aim of obtaining integral-field spectroscopy for an unprecedented sample of 10,000 nearby galaxies. MaNGA's key goals are to understand the "life cycle" of present day galaxies from imprinted clues of their birth and assembly, through their ongoing growth via star formation and merging, to their death from quenching at late times. To achieve these goals, MaNGA will channel the impressive capabilities of the SDSS-III BOSS spectrographs in a fundamentally new direction by marshaling the unique power of 2D spectroscopy. MaNGA will deploy 17 pluggable Integral Field Units (IFUs) made by grouping fibers into hexagonal bundles ranging from 19 to 127 fibers each. The spectra obtained by MaNGA will cover the wavelength range 3600-10,000 Angstroms (with a velocity resolution of ~ 60 km/s) and will characterize the internal composition and the dynamical state of a sample of 10,000 galaxies with stellar masses greater than 10^9 Msun and an average redshift of z ~ 0.03. Such IFU observations enable a leap forward because they provide an added dimension to the information available for each galaxy. MaNGA will provide two-dimensional maps of stellar velocity and velocity dispersion, mean stellar age and star formation history, stellar metallicity, element abundance ratio, stellar mass surface density, ionized gas velocity, ionized gas metallicity, star formation rate, and dust extinction for a statistically powerful sample. This legacy dataset will address urgent questions in our understanding of galaxy formation, including 1) The formation history of galaxy subcomponents, including the disk, bulge, and dark matter halo, 2) The nature of present-day galaxy growth via merging and gas accretion, and 3) The processes responsible for terminating star formation in galaxies. Finally, MaNGA will also play a vital role in the coming era of advanced IFU instrumentation, serving as the low-z anchor for

  13. Peculiar early-type galaxies with central star formation

    Ge Chong; Gu Qiusheng

    2012-01-01

    Early-type galaxies (ETGs) are very important for understanding the formation and evolution of galaxies. Recent observations suggest that ETGs are not simply old stellar spheroids as we previously thought. Widespread recent star formation, cool gas and dust have been detected in a substantial fraction of ETGs. We make use of the radial profiles of g — r color and the concentration index from the Sloan Digital Sky Survey database to pick out 31 peculiar ETGs with central blue cores. By analyzing the photometric and spectroscopic data, we suggest that the blue cores are caused by star formation activities rather than the central weak active galactic nucleus. From the results of stellar population synthesis, we find that the stellar population of the blue cores is relatively young, spreading from several Myr to less than one Gyr. In 14 galaxies with H I observations, we find that the average gas fraction of these galaxies is about 0.55. The bluer galaxies show a higher gas fraction, and the total star formation rate (SFR) correlates very well with the H I gas mass. The star formation history of these ETGs is affected by the environment, e.g. in the denser environment the H I gas is less and the total SFR is lower. We also discuss the origin of the central star formation of these early-type galaxies.

  14. Galaxies and gas in a cold dark matter universe

    Katz, Neal; Hernquist, Lars; Weinberg, David H.

    1992-01-01

    We use a combined gravity/hydrodynamics code to simulate the formation of structure in a random 22 Mpc cube of a cold dark matter universe. Adiabatic compression and shocks heat much of the gas to temperatures of 10 exp 6 - 10 exp 7 K, but a fraction of the gas cools radiatively to about 10 exp 4 K and condenses into discrete, highly overdense lumps. We identify these lumps with galaxies. The high-mass end of their baryonic mass function fits the form of the observed galaxy luminosity function. They retain independent identities after their dark halos merge, so gravitational clustering produces groups of galaxies embedded in relatively smooth envelopes of hot gas and dark matter. The galaxy correlation function is approximately an r exp -2.1 power law from separations of 35 kpc to 7 Mpc. Galaxy fluctuations are biased relative to dark matter fluctuations by a factor b about 1.5. We find no significant 'velocity bias' between galaxies and dark matter particles. However, virial analysis of the simulation's richest group leads to an estimated Omega of about 0.3, even though the simulation adopts Omega = 1.

  15. A dusty, normal galaxy in the epoch of reionization

    Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg

    2015-01-01

    Candidates for the modest galaxies that formed most of the stars in the early universe, at redshifts $z > 7$, have been found in large numbers with extremely deep restframe-UV imaging. But it has proved difficult for existing spectrographs to characterise them in the UV. The detailed properties...... of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant UV-selected galaxy detected in dust emission is only at $z = 3.25$, and recent results have cast doubt on whether...... dust and molecules can be found in typical galaxies at this early epoch. Here we report thermal dust emission from an archetypal early universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be $z = 7.5\\pm0.2$ from a spectroscopic detection...

  16. Matching Supernovae to Galaxies

    Kohler, Susanna

    2016-12-01

    One of the major challenges for modern supernova surveys is identifying the galaxy that hosted each explosion. Is there an accurate and efficient way to do this that avoids investing significant human resources?Why Identify Hosts?One problem in host galaxy identification. Here, the supernova lies between two galaxies but though the centroid of the galaxy on the right is closer in angular separation, this may be a distant background galaxy that is not actually near the supernova. [Gupta et al. 2016]Supernovae are a critical tool for making cosmological predictions that help us to understand our universe. But supernova cosmology relies on accurately identifying the properties of the supernovae including their redshifts. Since spectroscopic followup of supernova detections often isnt possible, we rely on observations of the supernova host galaxies to obtain redshifts.But how do we identify which galaxy hosted a supernova? This seems like a simple problem, but there are many complicating factors a seemingly nearby galaxy could be a distant background galaxy, for instance, or a supernovas host could be too faint to spot.The authors algorithm takes into account confusion, a measure of how likely the supernova is to be mismatched. In these illustrations of low (left) and high (right) confusion, the supernova is represented by a blue star, and the green circles represent possible host galaxies. [Gupta et al. 2016]Turning to AutomationBefore the era of large supernovae surveys, searching for host galaxies was done primarily by visual inspection. But current projects like the Dark Energy Surveys Supernova Program is finding supernovae by the thousands, and the upcoming Large Synoptic Survey Telescope will likely discover hundreds of thousands. Visual inspection will not be possible in the face of this volume of data so an accurate and efficient automated method is clearly needed!To this end, a team of scientists led by Ravi Gupta (Argonne National Laboratory) has recently

  17. INTERACTIONS OF GALAXIES IN THE GALAXY CLUSTER ENVIRONMENT

    Park, Changbom; Hwang, Ho Seong

    2009-01-01

    We study the dependence of galaxy properties on the clustercentric radius and the environment attributed to the nearest neighbor galaxy using the Sloan Digital Sky Survey galaxies associated with the Abell galaxy clusters. We find that there exists a characteristic scale where the properties of galaxies suddenly start to depend on the clustercentric radius at fixed neighbor environment. The characteristic scale is 1-3 times the cluster virial radius depending on galaxy luminosity. Existence of the characteristic scale means that the local galaxy number density is not directly responsible for the morphology-density relation in clusters because the local density varies smoothly with the clustercentric radius and has no discontinuity in general. What is really working in clusters is the morphology-clustercentric radius-neighbor environment relation, where the neighbor environment means both neighbor morphology and the local mass density attributed to the neighbor. The morphology-density relation appears working only because of the statistical correlation between the nearest neighbor distance and the local galaxy number density. We find strong evidence that the hydrodynamic interactions with nearby early-type galaxies is the main drive to quenching star formation activity of late-type galaxies in clusters. The hot cluster gas seems to play at most a minor role down to one tenth of the cluster virial radius. We also find that the viable mechanisms which can account for the clustercentric radius dependence of the structural and internal kinematics parameters are harassment and interaction of galaxies with the cluster potential. The morphology transformation of the late-type galaxies in clusters seems to have taken place through both galaxy-galaxy hydrodynamic interactions and galaxy-cluster/galaxy-galaxy gravitational interactions.

  18. INTERACTIONS OF GALAXIES IN THE GALAXY CLUSTER ENVIRONMENT

    Park, Changbom; Hwang, Ho Seong [School of Physics, Korea Institute for Advanced Study, Seoul 130-722 (Korea, Republic of)], E-mail: cbp@kias.re.kr, E-mail: hshwang@kias.re.kr

    2009-07-10

    We study the dependence of galaxy properties on the clustercentric radius and the environment attributed to the nearest neighbor galaxy using the Sloan Digital Sky Survey galaxies associated with the Abell galaxy clusters. We find that there exists a characteristic scale where the properties of galaxies suddenly start to depend on the clustercentric radius at fixed neighbor environment. The characteristic scale is 1-3 times the cluster virial radius depending on galaxy luminosity. Existence of the characteristic scale means that the local galaxy number density is not directly responsible for the morphology-density relation in clusters because the local density varies smoothly with the clustercentric radius and has no discontinuity in general. What is really working in clusters is the morphology-clustercentric radius-neighbor environment relation, where the neighbor environment means both neighbor morphology and the local mass density attributed to the neighbor. The morphology-density relation appears working only because of the statistical correlation between the nearest neighbor distance and the local galaxy number density. We find strong evidence that the hydrodynamic interactions with nearby early-type galaxies is the main drive to quenching star formation activity of late-type galaxies in clusters. The hot cluster gas seems to play at most a minor role down to one tenth of the cluster virial radius. We also find that the viable mechanisms which can account for the clustercentric radius dependence of the structural and internal kinematics parameters are harassment and interaction of galaxies with the cluster potential. The morphology transformation of the late-type galaxies in clusters seems to have taken place through both galaxy-galaxy hydrodynamic interactions and galaxy-cluster/galaxy-galaxy gravitational interactions.

  19. H1 in RSA galaxies

    Richter, OTTO-G.

    1993-01-01

    The original Revised Shapley-Ames (RSA) galaxy sample of almost 1300 galaxies has been augmented with further bright galaxies from the RSA appendix as well as newer galaxy catalogs. A complete and homogeneous, strictly magnitude-limited all-sky sample of 2345 galaxies brighter than 13.4 in apparent blue magnitude was formed. New 21 cm H1 line observations for more than 600 RSA galaxies have been combined with all previously available H1 data from the literature. This new extentise data act allows detailed tests of widely accepted 'standard' reduction and analysis techniques.

  20. Statistical measures of galaxy clustering

    Porter, D.H.

    1988-01-01

    Consideration is given to the large-scale distribution of galaxies and ways in which this distribution may be statistically measured. Galaxy clustering is hierarchical in nature, so that the positions of clusters of galaxies are themselves spatially clustered. A simple identification of groups of galaxies would be an inadequate description of the true richness of galaxy clustering. Current observations of the large-scale structure of the universe and modern theories of cosmology may be studied with a statistical description of the spatial and velocity distributions of galaxies. 8 refs

  1. Cooled Water Production System,

    The invention refers to the field of air conditioning and regards an apparatus for obtaining cooled water . The purpose of the invention is to develop...such a system for obtaining cooled water which would permit the maximum use of the cooling effect of the water -cooling tower.

  2. Process fluid cooling system

    Farquhar, N.G.; Schwab, J.A.

    1977-01-01

    A system of heat exchangers is disclosed for cooling process fluids. The system is particularly applicable to cooling steam generator blowdown fluid in a nuclear plant prior to chemical purification of the fluid in which it minimizes the potential of boiling of the plant cooling water which cools the blowdown fluid

  3. Too Fast, Too Furious: A Galaxy's Fatal Plunge

    2004-01-01

    Trailing 200,000-light-year-long streamers of seething gas, a galaxy that was once like our Milky Way is being shredded as it plunges at 4.5 million miles per hour through the heart of a distant cluster of galaxies. In this unusually violent collision with ambient cluster gas, the galaxy is stripped down to its skeletal spiral arms as it is eviscerated of fresh hydrogen for making new stars. The galaxy's untimely demise is offering new clues to solving the mystery of what happens to spiral galaxies in a violent universe. Views of the early universe show that spiral galaxies were once much more abundant in rich clusters of galaxies. But they seem to have been vanishing over cosmic time. Where have these "missing bodies" gone? Astronomers are using a wide range of telescopes and analysis techniques to conduct a "CSI" or Crime Scene Investigator-style look at what is happening to this galaxy inside its cluster's rough neighborhood. "It's a clear case of galaxy assault and battery," says William Keel of the University of Alabama. "This is the first time we have a full suite of results from such disparate techniques showing the crime being committed, and the modus operandi." Keel and colleagues are laying out the "forensic evidence" of the galaxy's late life, in a series of presentations today in Atlanta, Ga., at the 203rd meeting of the American Astronomical Society. Astronomers have assembled the evidence by combining a variety of diagnostic observations from telescopes analyzing the galaxy's appearance in X-ray, optical, and radio light. Parallel observations at different wavelengths trace how stars, gas, and dust are being tossed around and torn from the fragile galaxy, called C153. Though such "distressed" galaxies have been seen before, this one's demise is unusually swift and violent. The galaxy belongs to a cluster of galaxies that slammed into another cluster about 100 million years ago. This galaxy took the brunt of the beating as it fell along a trajectory

  4. Regenerator cross arm seal assembly

    Jackman, Anthony V.

    1988-01-01

    A seal assembly for disposition between a cross arm on a gas turbine engine block and a regenerator disc, the seal assembly including a platform coextensive with the cross arm, a seal and wear layer sealingly and slidingly engaging the regenerator disc, a porous and compliant support layer between the platform and the seal and wear layer porous enough to permit flow of cooling air therethrough and compliant to accommodate relative thermal growth and distortion, a dike between the seal and wear layer and the platform for preventing cross flow through the support layer between engine exhaust and pressurized air passages, and air diversion passages for directing unregenerated pressurized air through the support layer to cool the seal and wear layer and then back into the flow of regenerated pressurized air.

  5. Formation of galaxies from massive neutrinos

    Davis, M.; Lecar, M.; Pryor, C.; Witten, E.

    1981-01-01

    Neutrinos with nonzero rest mass strongly influence galaxy formation in the early universe. If stable neutrinos have rest masses on the order of 100 eV, they close the universe, but they erase initial perturbations on mass scales less than 4 x 10 15 M/sub sun/. However, if in addition there exist unstable neutrinos with rest masses on the order of 100 keV, they preserve and amplify initial perturbations on galactic mass scales (10 12 M/sub sun/). These perturbations are picked up and further amplified by the lighter, stable neutrinos, as long as the heavy neutrinos decay somewhat after the lighter neutrinos go nonrelativistic. If the heavy neutrinos decay into light neutrinos, the decay products contribute about one-half of the present mass density in a hot unclustered background. The only alternative method of retaining initial perturbations until the light neutrinos become nonrelativistic is to introduce large amplitude initial fluctuations such as primordial black holes. If the light neutrinos close the universe, black hole seeds of size 10 9 M/sub sun/ would be required for galaxies of 10 12 M/sub sun/ to form. We point out that the neutrino damping mass is a steep function of the present neutrino temperature and that galaxy sized fluctuations would be preserved if T/sub ν/ <1.0 K. However, the only model we can devise to effect this cooling is shown to be in serious violation of astrophysical constraints

  6. SCT Barrel Assembly Complete

    L. Batchelor

    As reported in the April 2005 issue of the ATLAS eNews, the first of the four Semiconductor Tracker (SCT) barrels, complete with modules and services, arrived safely at CERN in January of 2005. In the months since January, the other three completed barrels arrived as well, and integration of the four barrels into the entire barrel assembly commenced at CERN, in the SR1 building on the ATLAS experimental site, in July. Assembly was completed on schedule in September, with the addition of the innermost layer to the 4-barrel assembly. Work is now underway to seal the barrel thermal enclosure. This is necessary in order to enclose the silicon tracker in a nitrogen atmosphere and provide it with faraday-cage protection, and is a delicate and complicated task: 352 silicon module powertapes, 352 readout-fibre bundles, and over 400 Detector Control System sensors must be carefully sealed into the thermal enclosure bulkhead. The team is currently verifying the integrity of the low mass cooling system, which must be d...

  7. Fuel assembly

    Abe, Hideaki; Sakai, Takao; Ishida, Tomio; Yokota, Norikatsu.

    1992-01-01

    The lower ends of a plurality of plate-like shape memory alloys are secured at the periphery of the upper inside of the handling head of a fuel assembly. As the shape memory alloy, a Cu-Zn alloy, a Ti-Pd alloy or a Fe-Ni alloy is used. When high temperature coolants flow out to the handling head, the shape memory alloy deforms by warping to the outer side more greatly toward the upper portion thereof with the temperature increase of the coolants. As the result, the shape of the flow channel of the coolants is changed so as to enlarge at the exit of the upper end of the fuel assembly. Then, the pressure loss of the coolants in the fuel assembly is decreased by the enlargement. Accordingly, the flow rate of the coolants in the fuel assembly is increased to lower the temperature of the coolants. Further, high temperature coolants and low temperature coolants are mixed sufficiently just above the fuel assembly. This can suppress the temperature fluctuation of the mixed coolants in the upper portion of the reactor core, thereby enabling to decrease a fatigue and failures of the structural components in the upper portion of the reactor core. (I.N.)

  8. Hybrid radiator cooling system

    France, David M.; Smith, David S.; Yu, Wenhua; Routbort, Jules L.

    2016-03-15

    A method and hybrid radiator-cooling apparatus for implementing enhanced radiator-cooling are provided. The hybrid radiator-cooling apparatus includes an air-side finned surface for air cooling; an elongated vertically extending surface extending outwardly from the air-side finned surface on a downstream air-side of the hybrid radiator; and a water supply for selectively providing evaporative cooling with water flow by gravity on the elongated vertically extending surface.

  9. THE EVOLUTIONARY HISTORY OF LYMAN BREAK GALAXIES BETWEEN REDSHIFT 4 AND 6: OBSERVING SUCCESSIVE GENERATIONS OF MASSIVE GALAXIES IN FORMATION

    Stark, Daniel P.; Ellis, Richard S.; Targett, Tom; Benson, Andrew; Bunker, Andrew; Bundy, Kevin; Lacy, Mark

    2009-01-01

    We present new measurements of the evolution in the Lyman break galaxy (LBG) population between z ≅ 4 and z ≅ 6. By utilizing the extensive multiwavelength data sets available in the GOODS fields, we identify 2443 B, 506 V, and 137 i'-band dropout galaxies likely to be at z ∼ 4, 5, and 6. For the subset of dropouts for which reliable Spitzer IRAC photometry is feasible (roughly 35% of the sample), we estimate luminosity-weighted ages and stellar masses. With the goal of understanding the duration of typical star formation episodes in galaxies at z ∼> 4, we examine the distribution of stellar masses and ages as a function of cosmic time. We find that at a fixed rest-UV luminosity, the average stellar masses and ages of galaxies do not increase significantly between z ≅ 6 and 4. In order to maintain this near equilibrium in the average properties of high-redshift LBGs, we argue that there must be a steady flux of young, newly luminous objects at each successive redshift. When considered along with the short duty cycles inferred from clustering measurements, these results may suggest that galaxies are undergoing star formation episodes lasting only several hundred million years. In contrast to the unchanging relationship between the average stellar mass and rest-UV luminosity, we find that the number density of massive galaxies increases considerably with time over 4 ∼ 11 M sun ) z ≅ 2-3 distant red galaxies (DRGs) were in part assembled in an LBG phase at earlier times. Integrating the growth in the stellar mass function of actively forming LBGs over 4 ∼ 3 LBGs could have contributed significantly to the quiescent DRG population, indicating that the intense star-forming systems probed by submillimeter observations are not the only route toward the assembly of DRGs at z ≅ 2.

  10. The ACS LCID project. X. the star formation history of IC 1613: Revisiting the over-cooling problem

    Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455 (United States); Hidalgo, Sebastian L.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio, E-mail: skillman@astro.umn.edu, E-mail: shidalgo@iac.es, E-mail: monelli@iac.es, E-mail: carme@iac.es, E-mail: aparicio@iac.es [Instituto de Astrofísica de Canarias, Vía Láctea s/n, E-38200 La Laguna, Tenerife, Canary Islands (Spain); and others

    2014-05-01

    We present an analysis of the star formation history (SFH) of a field near the half-light radius in the Local Group dwarf irregular galaxy IC 1613 based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. Our observations reach the oldest main sequence turn-off, allowing a time resolution at the oldest ages of ∼1 Gyr. Our analysis shows that the SFH of the observed field in IC 1613 is consistent with being constant over the entire lifetime of the galaxy. These observations rule out an early dominant episode of star formation in IC 1613. We compare the SFH of IC 1613 with expectations from cosmological models. Since most of the mass is in place at early times for low-mass halos, a naive expectation is that most of the star formation should have taken place at early times. Models in which star formation follows mass accretion result in too many stars formed early and gas mass fractions that are too low today (the 'over-cooling problem'). The depth of the present photometry of IC 1613 shows that, at a resolution of ∼1 Gyr, the star formation rate is consistent with being constant, at even the earliest times, which is difficult to achieve in models where star formation follows mass assembly.

  11. Spatially-resolved star formation histories of CALIFA galaxies. Implications for galaxy formation

    González Delgado, R. M.; Pérez, E.; Cid Fernandes, R.; García-Benito, R.; López Fernández, R.; Vale Asari, N.; Cortijo-Ferrero, C.; de Amorim, A. L.; Lacerda, E. A. D.; Sánchez, S. F.; Lehnert, M. D.; Walcher, C. J.

    2017-11-01

    This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from M⋆ 109 to 7 × 1011 M⊙. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (ΣSFR), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z > 2). Subsequent star formation is driven by M⋆ and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional to M⋆, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the ΣSFR is similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the ΣSFR scales well with morphology. The central regions of today's ETGs are where the ΣSFR reached the highest values (> 103 M⊙ Gyr-1 pc-2), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of ΣSFR in Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and ΣSFR in outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass between z = 2 and 0.4. The mass assembled in this phase is in agreement with

  12. Chemical Soups Around Cool Stars

    2009-01-01

    This artist's conception shows a young, hypothetical planet around a cool star. A soupy mix of potentially life-forming chemicals can be seen pooling around the base of the jagged rocks. Observations from NASA's Spitzer Space Telescope hint that planets around cool stars the so-called M-dwarfs and brown dwarfs that are widespread throughout our galaxy might possess a different mix of life-forming, or prebiotic, chemicals than our young Earth. Life on our planet is thought to have arisen out of a pond-scum-like mix of chemicals. Some of these chemicals are thought to have come from a planet-forming disk of gas and dust that swirled around our young sun. Meteorites carrying the chemicals might have crash-landed on Earth. Astronomers don't know if these same life-generating processes are taking place around stars that are cooler than our sun, but the Spitzer observations show their disk chemistry is different. Spitzer detected a prebiotic molecule, called hydrogen cyanide, in the disks around yellow stars like our sun, but found none around cooler, less massive, reddish stars. Hydrogen cyanide is a carbon-containing, or organic compound. Five hydrogen cyanide molecules can join up to make adenine a chemical element of the DNA molecule found in all living organisms on Earth.

  13. Heat evaluation examination of fuel assembly

    Suto, Shinya; Nakabayashi, Hiroki; Yao, Kaoru

    2007-03-01

    The cooling examination was executed by using the simulated fuel assembly to obtain the basic data of the most effective cooling system in the lazer disassembling process of the spent fuel assembly of prototype fast breeder reactor 'Monju'. As a result, the following have been understood. (1) Before the laser disassembling (there is not any duct tube cutting), it is possible to cool enough by the amount of the wind of 20m 3 /h or more flowing from the handling head side. (2) After the laser disassembling begins (duct tube is cut), 1kW or more of the heat generation cannot be cooled by ventilation from the handling head side. (3) Cooling by the flow across fuel pin is required during lazer disassembling. The basic data of the cooling system was obtained from these examination results. However, for cooling across fuel pin during the laser disassembling, it is necessary to examine shape of the side cooling nozzle, spraying angle, and flow velocity at the nozzle exit, etc. enough. (author)

  14. Optical emission line spectra of Seyfert galaxies and radio galaxies

    Osterbrock, D.E.

    1978-01-01

    Many radio galaxies have strong emission lines in their optical spectra, similar to the emission lines in the spectra of Seyfert galaxies. The range of ionization extends from [O I] and [N I] through [Ne V] and [Fe VII] to [Fe X]. The emission-line spectra of radio galaxies divide into two types, narrow-line radio galaxies whose spectra are indistinguishable from Seyfert 2 galaxies, and broad-line radio galaxies whose spectra are similar to Seyfert 1 galaxies. However on the average the broad-line radio galaxies have steeper Balmer decrements, stronger [O III] and weaker Fe II emission than the Seyfert 1 galaxies, though at least one Seyfert 1 galaxy not known to be a radio source has a spectrum very similar to typical broad-line radio galaxies. Intermediate-type Seyfert galaxies exist that show various mixtures of the Seyfert 1 and Seyfert 2 properties, and the narrow-line or Seyfert 2 property seems to be strongly correlated with radio emission. (Auth.)

  15. Seeing Baby Dwarf Galaxies

    2009-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Visible/DSS Click on image for larger version Ultraviolet/GALEX Click on image for larger version Poster Version Click on image for larger version The unique ultraviolet vision of NASA's Galaxy Evolution Explorer reveals, for the first time, dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way. The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light. The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light. Only a portion of the Leo Ring has been imaged in the ultraviolet, but this section contains the telltale ultraviolet signature of recent massive star formation within this ring of pristine gas. Astronomers have previously only seen dwarf galaxies form out of gas that has already been cycled through a galaxy and enriched with metals elements heavier than helium produced as stars evolve. The visible data come from the Digitized Sky Survey of the Space Telescope Science Institute in Baltimore, Md. The Leo Ring visible image (left

  16. A MINUET OF GALAXIES

    2002-01-01

    This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years. The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object. The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies. HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes

  17. The SAMI Galaxy Survey: gas content and interaction as the drivers of kinematic asymmetry

    Bloom, J. V.; Croom, S. M.; Bryant, J. J.; Schaefer, A. L.; Bland-Hawthorn, J.; Brough, S.; Callingham, J.; Cortese, L.; Federrath, C.; Scott, N.; van de Sande, J.; D'Eugenio, F.; Sweet, S.; Tonini, C.; Allen, J. T.; Goodwin, M.; Green, A. W.; Konstantopoulos, I. S.; Lawrence, J.; Lorente, N.; Medling, A. M.; Owers, M. S.; Richards, S. N.; Sharp, R.

    2018-05-01

    In order to determine the causes of kinematic asymmetry in the Hα gas in the SAMI (Sydney-AAO Multi-object IFS) Galaxy Survey sample, we investigate the comparative influences of environment and intrinsic properties of galaxies on perturbation. We use spatially resolved Hα velocity fields from the SAMI Galaxy Survey to quantify kinematic asymmetry (\\overline{v_asym}) in nearby galaxies and environmental and stellar mass data from the Galaxy And Mass Assembly survey. We find that local environment, measured as distance to nearest neighbour, is inversely correlated with kinematic asymmetry for galaxies with log (M*/M⊙) > 10.0, but there is no significant correlation for galaxies with log (M*/M⊙) < 10.0. Moreover, low-mass galaxies [log (M*/M⊙) < 9.0] have greater kinematic asymmetry at all separations, suggesting a different physical source of asymmetry is important in low-mass galaxies. We propose that secular effects derived from gas fraction and gas mass may be the primary causes of asymmetry in low-mass galaxies. High gas fraction is linked to high σ _m/V (where σm is Hα velocity dispersion and V the rotation velocity), which is strongly correlated with \\overline{v_asym}, and galaxies with log (M*/M⊙) < 9.0 have offset \\overline{σ _m/V} from the rest of the sample. Further, asymmetry as a fraction of dispersion decreases for galaxies with log (M*/M⊙) < 9.0. Gas mass and asymmetry are also inversely correlated in our sample. We propose that low gas masses in dwarf galaxies may lead to asymmetric distribution of gas clouds, leading to increased relative turbulence.

  18. Fuel assembly

    Nakatsuka, Masafumi; Matsuzuka, Ryuji.

    1976-01-01

    Object: To provide a fuel assembly which can decrease pressure loss of coolant to uniform temperature. Structure: A sectional area of a flow passage in the vicinity of an inner peripheral surface of a wrapper tube is limited over the entire length to prevent the temperature of a fuel element in the outermost peripheral portion from being excessively decreased to thereby flatten temperature distribution. To this end, a plurality of pincture-frame-like sheet metals constituting a spacer for supporting a fuel assembly, which has a plurality of fuel elements planted lengthwise and in given spaced relation within the wrapper tube, is disposed in longitudinal grooves and in stacked fashion to form a substantially honeycomb-like space in cross section. The fuel elements are inserted and supported in the space to form a fuel assembly. (Kamimura, M.)

  19. Fuel assemblies

    Nagano, Mamoru; Yoshioka, Ritsuo

    1983-01-01

    Purpose: To effectively utilize nuclear fuels by increasing the reactivity of a fuel assembly and reduce the concentration at the central region thereof upon completion of the burning. Constitution: A fuel assembly is bisected into a central region and a peripheral region by disposing an inner channel box within a channel box. The flow rate of coolants passing through the central region is made greater than that in the peripheral region. The concentration of uranium 235 of the fuel rods in the central region is made higher. In such a structure, since the moderating effect in the central region is improved, the reactivity of the fuel assembly is increased and the uranium concentration in the central region upon completion of the burning can be reduced, fuel economy and effective utilization of uranium can be attained. (Kamimura, M.)

  20. Tidal alignment of galaxies

    Blazek, Jonathan; Vlah, Zvonimir; Seljak, Uroš

    2015-08-01

    We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

  1. Irregular Dwarf Galaxy IC 1613

    2005-01-01

    Ultraviolet image (left) and visual image (right) of the irregular dwarf galaxy IC 1613. Low surface brightness galaxies, such as IC 1613, are more easily detected in the ultraviolet because of the low background levels compared to visual wavelengths.

  2. Cosmic rings from colliding galaxies

    Mitton, S

    1976-11-18

    Research on two ring galaxies has led to the proposal of an interaction model to account for the rings. It is envisaged that this class of galaxy is created when a compact galaxy crashes through the disc of a spiral galaxy. The results of a spectroscopic investigation of the galaxy known as the Cartwheel and of another ring galaxy 11 NZ 4 are discussed. The general picture of ring galaxies which emerges from these studies of a massive starry nucleus with a necklace of emitting gas and some spokes and along the spin axis of the wheel a small companion galaxy that is devoid of interstellar gas. An explanation of these properties is considered.

  3. Core condensation in heavy halos: a two-stage theory for galaxy formation and clustering

    White, S D.M.; Rees, M J [Cambridge Univ. Inst. of Astronomy (UK)

    1978-05-01

    It is suggested that most of the material in the Universe condensed at an early epoch into small 'dark' objects. Irrespective of their nature, these objects must subsequently have undergone hierarchical clustering, whose present scale is inferred from the large-scale distribution of galaxies. As each stage of the hierarchy forms and collapses, relaxation effects wipe out its substructure, and to a self-similar distribution of bound masses. The entire luminous content of galaxies, however, results from the cooling and fragmentation of residual gas within the transient potential wells provided by the dark matter. Every galaxy thus forms as a concentrated luminous core embedded in an extensive dark halo. The observed sizes of galaxies and their survival through later stages of the hierarchy seem inexplicable without invoking substantial dissipation; this dissipation allows the galaxies to become sufficiently concentrated to survive the disruption of their halos in groups and clusters of galaxies. A specific model is proposed in which ..cap omega.. approximately equals 0.2, the dark matter makes up 80 per cent of the total mass, and half the residual gas has been converted into luminous galaxies by the present time. This model is consistent with the inferred proportions of dark matter and gas in rich clusters, with the observed luminosity density of the Universe and with the observed radii of galaxies; further, it predicts the characteristic luminosities of bright galaxies can give a luminosity function of the observed shape.

  4. Velocity-metallicity correlation for high-z DLA galaxies

    Ledoux, C.; Petitjean, P.; Fynbo, J.P.U.

    2006-01-01

    Galaxies: halos, galaxies: high-redshift, galaxies: ISM, quasars: absorption lines, cosmology: observations Udgivelsesdato: Oct.......Galaxies: halos, galaxies: high-redshift, galaxies: ISM, quasars: absorption lines, cosmology: observations Udgivelsesdato: Oct....

  5. Detection of Lyman/alpha emission from a DLA galaxy

    Moller, P.; Fynbo, Johan Peter Uldall; Fall, S.M

    2004-01-01

    HIGH-REDSHIFT; BREAK GALAXIES; STARFORMATION; DISK GALAXIES; METAL ENRICHMENT; HOST GALAXY; ABSORPTION; ABSORBER; SYSTEMS; SPECTROSCOPY......HIGH-REDSHIFT; BREAK GALAXIES; STARFORMATION; DISK GALAXIES; METAL ENRICHMENT; HOST GALAXY; ABSORPTION; ABSORBER; SYSTEMS; SPECTROSCOPY...

  6. Warming rays in cluster cool cores

    Colafrancesco, S.; Marchegiani, P.

    2008-06-01

    Context: Cosmic rays are confined in the atmospheres of galaxy clusters and, therefore, they can play a crucial role in the heating of their cool cores. Aims: We discuss here the thermal and non-thermal features of a model of cosmic ray heating of cluster cores that can provide a solution to the cooling-flow problems. To this aim, we generalize a model originally proposed by Colafrancesco, Dar & DeRujula (2004) and we show that our model predicts specific correlations between the thermal and non-thermal properties of galaxy clusters and enables various observational tests. Methods: The model reproduces the observed temperature distribution in clusters by using an energy balance condition in which the X-ray energy emitted by clusters is supplied, in a quasi-steady state, by the hadronic cosmic rays, which act as “warming rays” (WRs). The temperature profile of the intracluster (IC) gas is strictly correlated with the pressure distribution of the WRs and, consequently, with the non-thermal emission (radio, hard X-ray and gamma-ray) induced by the interaction of the WRs with the IC gas and the IC magnetic field. Results: The temperature distribution of the IC gas in both cool-core and non cool-core clusters is successfully predicted from the measured IC plasma density distribution. Under this contraint, the WR model is also able to reproduce the thermal and non-thermal pressure distribution in clusters, as well as their radial entropy distribution, as shown by the analysis of three clusters studied in detail: Perseus, A2199 and Hydra. The WR model provides other observable features of galaxy clusters: a correlation of the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature (P_WR/P_th) ˜ (kT_inner)-2/3, a correlation of the gamma-ray luminosity with the inner cluster temperature Lγ ˜ (kT_inner)4/3, a substantial number of cool-core clusters observable with the GLAST-LAT experiment, a surface brightness of radio halos in cool-core clusters

  7. The Stormy Life of Galaxy Clusters

    Rudnick, Lawrence

    2018-01-01

    Galaxy clusters, the largest gravitationally bound structures, hold the full history of their baryonic evolution, serve as important cosmological tools and allow us to probe unique physical regimes in their diffuse plasmas. With characteristic dynamical timescales of 107-109 years, these diffuse thermal and relativistic media continue to evolve, as dark matter drives major mergers and more gentle continuing accretion. The history of this assembly is encoded in the plasmas, and a wide range of observational and theoretical investigations are aimed at decoding their signatures. X-ray temperature and density variations, low Mach number shocks, and "cold front" discontinuities all illuminate clusters' continued evolution. Radio structures and spectra are passive indicators of merger shocks, while radio galaxy distortions reveal the complex motions in the intracluster medium. Deep in cluster cores, AGNs associated with brightest cluster galaxies provide ongoing energy, and perhaps even stabilize the intracluster medium. In this talk, we will recount this evolving picture of the stormy ICM, and suggest areas of likely advance in the coming years.

  8. Optical photometry of galaxies

    Comte, G.

    1981-01-01

    The present status of the optical and near-infrared photometry of galaxies is reviewed. Part I introduces to the goals and general methods of both photographic surface photometry and integrated multicolor aperture photoelectric photometry for extended stellar systems, with a summary of the necessary corrections to the observed magnitudes and colors. Part II (surface photometry) summarizes recent results on the empirical luminosity laws for spheroidal systems and the separation of components in disk-plus-bulge systems. Part III (color problems) discusses integrated color effects (color and gas content, color-absolute magnitude relation for early-type systems, colors of interacting galaxies) and color gradient across spheroidal and disk galaxies. In part IV are summarized some constraints on the luminosity function of the stellar population in spheroidal systems given by narrow-band photometry [fr

  9. Creating lenticular galaxies with mergers

    Querejeta, Miguel; Eliche-Moral, M. Carmen; Tapia, Trinidad; Borlaff, Alejandro; van de Ven, Glenn; Lyubenova, Mariya; Martig, Marie; Falcón-Barroso, Jesús; Méndez-Abreu, Jairo; Zamorano, Jaime; Gallego, Jesús

    Lenticular galaxies (S0s) represent the majority of early-type galaxies in the local Universe, but their formation channels are still poorly understood. While galaxy mergers are obvious pathways to suppress star formation and increase bulge sizes, the marked parallelism between spiral and lenticular

  10. Cold gas accretion in galaxies

    Sancisi, Renzo; Fraternali, Filippo; Oosterloo, Tom; van der Hulst, Thijs

    Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing or recent accretion: (1) A large number of galaxies are accompanied by

  11. A Unified Scaling Law in Spiral Galaxies.

    Koda; Sofue; Wada

    2000-03-01

    We investigate the origin of a unified scaling relation in spiral galaxies. Observed spiral galaxies are spread on a plane in the three-dimensional logarithmic space of luminosity L, radius R, and rotation velocity V. The plane is expressed as L~&parl0;VR&parr0;alpha in the I passband, where alpha is a constant. On the plane, observed galaxies are distributed in an elongated region which looks like the shape of a surfboard. The well-known scaling relations L-V (Tully-Fisher [TF] relation), V-R (also the TF relation), and R-L (Freeman's law) can be understood as oblique projections of the surfboard-like plane into two-dimensional spaces. This unified interpretation of the known scaling relations should be a clue to understand the physical origin of all the relations consistently. Furthermore, this interpretation can also explain why previous studies could not find any correlation between TF residuals and radius. In order to clarify the origin of this plane, we simulate formation and evolution of spiral galaxies with the N-body/smoothed particle hydrodynamics method, including cooling, star formation, and stellar feedback. Initial conditions are set to 14 isolated spheres with two free parameters, such as mass and angular momentum. The cold dark matter (h=0.5, Omega0=1) cosmology is considered as a test case. The simulations provide the following two conclusions: (1) The slope of the plane is well reproduced but the zero point is not. This zero-point discrepancy could be solved in a low-density (Omega00.5) cosmology. (2) The surfboard-shaped plane can be explained by the control of galactic mass and angular momentum.

  12. Lopsided spiral galaxies

    Jog, Chanda J.; Combes, Francoise

    2009-01-01

    The light distribution in the disks of many galaxies is 'lopsided' with a spatial extent much larger along one half of a galaxy than the other, as seen in M101. Recent observations show that the stellar disk in a typical spiral galaxy is significantly lopsided, indicating asymmetry in the disk mass distribution. The mean amplitude of lopsidedness is 0.1, measured as the Fourier amplitude of the m=1 component normalized to the average value. Thus, lopsidedness is common, and hence it is important to understand its origin and dynamics. This is a new and exciting area in galactic structure and dynamics, in contrast to the topic of bars and two-armed spirals (m=2) which has been extensively studied in the literature. Lopsidedness is ubiquitous and occurs in a variety of settings and tracers. It is seen in both stars and gas, in the outer disk and the central region, in the field and the group galaxies. The lopsided amplitude is higher by a factor of two for galaxies in a group. The lopsidedness has a strong impact on the dynamics of the galaxy, its evolution, the star formation in it, and on the growth of the central black hole and on the nuclear fuelling. We present here an overview of the observations that measure the lopsided distribution, as well as the theoretical progress made so far to understand its origin and properties. The physical mechanisms studied for its origin include tidal encounters, gas accretion and a global gravitational instability. The related open, challenging problems in this emerging area are discussed

  13. Spectroscopy of the galaxy components of N and Seyfert galaxies

    Boroson, T.A.; Oke, J.B.; Palomar Observatory, Pasadena, CA)

    1987-01-01

    Nuclear and off-nuclear spectra of nine active galaxies are presented. The sample consists of four Seyfert galaxies, two N galaxies, one Seyfert radio galaxy, and one liner/Seyfert 2 galaxy. All of the objects show continuum emission off the nucleus. Four clearly show absorption features from a stellar population. Velocities have been measured for the off-nuclear emission and absorption lines. In the case of I Zw 1, the absorption-line velocities are inconsistent with 21-cm H I measurements of this object. 26 references

  14. Restaurant Food Cooling Practices†

    BROWN, LAURA GREEN; RIPLEY, DANNY; BLADE, HENRY; REIMANN, DAVE; EVERSTINE, KAREN; NICHOLAS, DAVE; EGAN, JESSICA; KOKTAVY, NICOLE; QUILLIAM, DANIELA N.

    2017-01-01

    Improper food cooling practices are a significant cause of foodborne illness, yet little is known about restaurant food cooling practices. This study was conducted to examine food cooling practices in restaurants. Specifically, the study assesses the frequency with which restaurants meet U.S. Food and Drug Administration (FDA) recommendations aimed at reducing pathogen proliferation during food cooling. Members of the Centers for Disease Control and Prevention’s Environmental Health Specialists Network collected data on food cooling practices in 420 restaurants. The data collected indicate that many restaurants are not meeting FDA recommendations concerning cooling. Although most restaurant kitchen managers report that they have formal cooling processes (86%) and provide training to food workers on proper cooling (91%), many managers said that they do not have tested and verified cooling processes (39%), do not monitor time or temperature during cooling processes (41%), or do not calibrate thermometers used for monitoring temperatures (15%). Indeed, 86% of managers reported cooling processes that did not incorporate all FDA-recommended components. Additionally, restaurants do not always follow recommendations concerning specific cooling methods, such as refrigerating cooling food at shallow depths, ventilating cooling food, providing open-air space around the tops and sides of cooling food containers, and refraining from stacking cooling food containers on top of each other. Data from this study could be used by food safety programs and the restaurant industry to target training and intervention efforts concerning cooling practices. These efforts should focus on the most frequent poor cooling practices, as identified by this study. PMID:23212014

  15. Valve assembly

    Sandling, M.

    1981-01-01

    An improved valve assembly, used for controlling the flow of radioactive slurry, is described. Radioactive contamination of the air during removal or replacement of the valve is prevented by sucking air from the atmosphere through a portion of the structure above the valve housing. (U.K.)

  16. Fuel assembly

    Gjertsen, R.K.; Bassler, E.A.; Huckestein, E.A.; Salton, R.B.; Tower, S.N.

    1988-01-01

    A fuel assembly adapted for use with a pressurized water nuclear reactor having capabilities for fluid moderator spectral shift control is described comprising: parallel arranged elongated nuclear fuel elements; means for providing for axial support of the fuel elements and for arranging the fuel elements in a spaced array; thimbles interspersed among the fuel elements adapted for insertion of a rod control cluster therewithin; means for structurally joining the fuel elements and the guide thimbles; fluid moderator control means for providing a volume of low neutron absorbing fluid within the fuel assembly and for removing a substantially equivalent volume of reactor coolant water therefrom, a first flow manifold at one end of the fuel assembly sealingly connected to a first end of the moderator control tubes whereby the first ends are commonly flow connected; and a second flow manifold, having an inlet passage and an outlet passage therein, sealingly connected to a second end of the moderator control tubes at a second end of the fuel assembly

  17. Galaxy S II

    Gralla, Preston

    2011-01-01

    Unlock the potential of Samsung's outstanding smartphone with this jargon-free guide from technology guru Preston Gralla. You'll quickly learn how to shoot high-res photos and HD video, keep your schedule, stay in touch, and enjoy your favorite media. Every page is packed with illustrations and valuable advice to help you get the most from the smartest phone in town. The important stuff you need to know: Get dialed in. Learn your way around the Galaxy S II's calling and texting features.Go online. Browse the Web, manage email, and download apps with Galaxy S II's 3G/4G network (or create you

  18. A chemical model for the interstellar medium in galaxies

    Bovino, S.; Grassi, Tommaso; Capelo, P. R.; Schleicher, D. R. G.; Banerjee, R.

    2016-01-01

    Aims: We present and test chemical models for three-dimensional hydrodynamical simulations of galaxies. We explore the effect of changing key parameters such as metallicity, radiation, and non-equilibrium versus equilibrium metal cooling approximations on the transition between the gas phases in the interstellar medium. Methods: The microphysics was modelled by employing the public chemistry package KROME, and the chemical networks were tested to work in a wide range of densities and temp...

  19. A machine learning approach to galaxy-LSS classification - I. Imprints on halo merger trees

    Hui, Jianan; Aragon, Miguel; Cui, Xinping; Flegal, James M.

    2018-04-01

    The cosmic web plays a major role in the formation and evolution of galaxies and defines, to a large extent, their properties. However, the relation between galaxies and environment is still not well understood. Here, we present a machine learning approach to study imprints of environmental effects on the mass assembly of haloes. We present a galaxy-LSS machine learning classifier based on galaxy properties sensitive to the environment. We then use the classifier to assess the relevance of each property. Correlations between galaxy properties and their cosmic environment can be used to predict galaxy membership to void/wall or filament/cluster with an accuracy of 93 per cent. Our study unveils environmental information encoded in properties of haloes not normally considered directly dependent on the cosmic environment such as merger history and complexity. Understanding the physical mechanism by which the cosmic web is imprinted in a halo can lead to significant improvements in galaxy formation models. This is accomplished by extracting features from galaxy properties and merger trees, computing feature scores for each feature and then applying support vector machine (SVM) to different feature sets. To this end, we have discovered that the shape and depth of the merger tree, formation time, and density of the galaxy are strongly associated with the cosmic environment. We describe a significant improvement in the original classification algorithm by performing LU decomposition of the distance matrix computed by the feature vectors and then using the output of the decomposition as input vectors for SVM.

  20. A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

    van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

    2018-04-01

    Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

  1. A relation between the characteristic stellar ages of galaxies and their intrinsic shapes

    van de Sande, Jesse; Scott, Nicholas; Bland-Hawthorn, Joss; Brough, Sarah; Bryant, Julia J.; Colless, Matthew; Cortese, Luca; Croom, Scott M.; d'Eugenio, Francesco; Foster, Caroline; Goodwin, Michael; Konstantopoulos, Iraklis S.; Lawrence, Jon S.; McDermid, Richard M.; Medling, Anne M.; Owers, Matt S.; Richards, Samuel N.; Sharp, Rob

    2018-06-01

    Stellar population and stellar kinematic studies provide unique but complementary insights into how galaxies build-up their stellar mass and angular momentum1-3. A galaxy's mean stellar age reveals when stars were formed, but provides little constraint on how the galaxy's mass was assembled. Resolved stellar dynamics4 trace the change in angular momentum due to mergers, but major mergers tend to obscure the effect of earlier interactions5. With the rise of large multi-object integral field spectroscopic surveys, such as SAMI6 and MaNGA7, and single-object integral field spectroscopic surveys (for example, ATLAS3D (ref. 8), CALIFA9, MASSIVE10), it is now feasible to connect a galaxy's star formation and merger history on the same resolved physical scales, over a large range in galaxy mass, morphology and environment4,11,12. Using the SAMI Galaxy Survey, here we present a combined study of spatially resolved stellar kinematics and global stellar populations. We find a strong correlation of stellar population age with location in the (V/σ, ɛe) diagram that links the ratio of ordered rotation to random motions in a galaxy to its observed ellipticity. For the large majority of galaxies that are oblate rotating spheroids, we find that characteristic stellar age follows the intrinsic ellipticity of galaxies remarkably well.

  2. Hot Gas Halos in Galaxies

    Mulchaey, John

    Most galaxy formation models predict that massive low-redshift disk galaxies are embedded in extended hot halos of externally accreted gas. Such gas appears necessary to maintain ongoing star formation in isolated spirals like the Milky Way. To explain the large population of red galaxies in rich groups and clusters, most galaxy evolution models assume that these hot gas halos are stripped completely when a galaxy enters a denser environment. This simple model has been remarkably successful at reproducing many observed properties of galaxies. Although theoretical arguments suggest hot gas halos are an important component in galaxies, we know very little about this gas from an observational standpoint. In fact, previous observations have failed to detect soft X-ray emission from such halos in disk galaxies. Furthermore, the assumption that hot gas halos are stripped completely when a galaxy enters a group or cluster has not been verified. We propose to combine proprietary and archival XMM-Newton observations of galaxies in the field, groups and clusters to study how hot gas halos are impacted by environment. Our proposed program has three components: 1) The deepest search to date for a hot gas halo in a quiescent spiral galaxy. A detection will confirm a basic tenet of disk galaxy formation models, whereas a non-detection will seriously challenge these models and impose new constraints on the growth mode and feedback history of disk galaxies. 2) A detailed study of the hot gas halos properties of field early-type galaxies. As environmental processes such as stripping are not expected to be important in the field, a study of hot gas halos in this environment will allow us to better understand how feedback and other internal processes impact hot gas halos. 3) A study of hot gas halos in the outskirts of groups and clusters. By comparing observations with our suite of simulations we can begin to understand what role the stripping of hot gas halos plays in galaxy

  3. Low-Surface-Brightness Galaxies: Hidden Galaxies Revealed

    Bothun, G.; Impey, C.; McGaugh, S.

    1997-07-01

    In twenty years, low surface brightness (LSB) galaxies have evolved from being an idiosyncratic notion to being one of the major baryonic repositories in the Universe. The story of their discovery and the characterization of their properties is told here. Their recovery from the noise of the night sky background is a strong testament to the severity of surface brightness selection effects. LSB galaxies have a number of remarkable properties which distinguish them from the more familiar Hubble Sequence of spirals. The two most important are 1) they evolve at a significantly slower rate and may well experience star formation outside of the molecular cloud environment, 2) they are embedded in dark matter halos which are of lower density and more extended than the halos around high surface brightness (HSB) disk galaxies. Compared to HSB disks, LSB disks are strongly dark matter dominated at all radii and show a systematic increase in $M/L$ with decreasing central surface brightness. In addition, the recognition that large numbers of LSB galaxies actually exist has changed the form of the galaxy luminosity function and has clearly increased the space density of galaxies at z =0. Recent CCD surveys have uncovered a population of red LSB disks that may be related to the excess of faint blue galaxies detected at moderate redshifts. LSB galaxies offer us a new window into galaxy evolution and formation which is every bit as important as those processes which have produced easy to detect galaxies. Indeed, the apparent youth of some LSB galaxies suggest that galaxy formation is a greatly extended process. While the discovery of LSB galaxies have lead to new insights, it remains unwise to presume that we now have a representative sample which encompasses all galaxy types and forms. (SECTION: Invited Review Paper)

  4. EVOLUTION OF GALAXY LUMINOSITY FUNCTION USING PHOTOMETRIC REDSHIFTS

    Ramos, B. H. F.; Pellegrini, P. S.; Da Costa, L. N.; Maia, M. A. G.; Ogando, R. L. C.; De Simoni, F.; Benoist, C.; Makler, M.; Mesquita, A. A.

    2011-01-01

    We examine the impact of using photometric redshifts for studying the evolution of both the global galaxy luminosity function (LF) and that for different galaxy types. To this end, we compare the LFs obtained using photometric redshifts from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) D1 field with those from the spectroscopic survey VIMOS VLT Deep Survey (VVDS) comprising ∼4800 galaxies. We find that for z ≤ 2.0, in the interval of magnitudes considered by this survey, the LFs obtained using photometric and spectroscopic redshifts show a remarkable agreement. This good agreement led us to use all four Deep fields of the CFHTLS comprising ∼386,000 galaxies to compute the LF of the combined fields and directly estimate the error in the parameters based on the field-to-field variation. We find that the characteristic absolute magnitude M* of Schechter fits fades by ∼0.7 mag from z ∼ 1.8 to z ∼ 0.3, while the characteristic density φ* increases by a factor of ∼4 in the same redshift interval. We use the galaxy classification provided by the template fitting program used to compute photometric redshifts and split the sample into galaxy types. We find that these Schechter parameters evolve differently for each galaxy type, an indication that their evolution is a combination of several effects: galaxy merging, star formation quenching, and mass assembly. All these results are compatible with those obtained by different spectroscopic surveys such as VVDS, DEEP2, and zCosmos, which reinforces the fact that photometric redshifts can be used to study galaxy evolution, at least for the redshift bins adopted so far. This is of great interest since future very large imaging surveys containing hundreds of millions of galaxies will allow us to obtain important precise measurements to constrain the evolution of the LF and to explore the dependence of this evolution on morphology and/or color helping constrain the mechanisms of galaxy evolution.

  5. Chandra Survey of Nearby Galaxies: The Catalog

    She, Rui; Feng, Hua [Department of Engineering Physics and Center for Astrophysics, Tsinghua University, Beijing 100084 (China); Ho, Luis C. [Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100087 (China)

    2017-02-01

    We searched the public archive of the Chandra X-ray Observatory as of 2016 March and assembled a sample of 719 galaxies within 50 Mpc with available Advanced CCD Imaging Spectrometer observations. By cross-correlation with the optical or near-infrared nuclei of these galaxies, 314 of them are identified to have an X-ray active galactic nucleus (AGN). The majority of them are low-luminosity AGNs and are unlikely X-ray binaries based upon their spatial distribution and luminosity functions. The AGN fraction is around 60% for elliptical galaxies and early-type spirals, but drops to roughly 20% for Sc and later types, consistent with previous findings in the optical. However, the X-ray survey is more powerful in finding weak AGNs, especially from regions with active star formation that may mask the optical AGN signature. For example, 31% of the H ii nuclei are found to harbor an X-ray AGN. For most objects, a single power-law model subject to interstellar absorption is adequate to fit the spectrum, and the typical photon index is found to be around 1.8. For galaxies with a non-detection, their stacked Chandra image shows an X-ray excess with a luminosity of a few times 10{sup 37} erg s{sup −1} on average around the nuclear region, possibly composed of faint X-ray binaries. This paper reports on the technique and results of the survey; in-depth analysis and discussion of the results will be reported in forthcoming papers.

  6. System for Cooling of Electronic Components

    Vasil'ev, L. L.; Grakovich, L. P.; Dragun, L. A.; Zhuravlev, A. S.; Olekhnovich, V. A.; Rabetskii, M. I.

    2017-01-01

    Results of computational and experimental investigations of heat pipes having a predetermined thermal resistance and a system based on these pipes for air cooling of electronic components and diode assemblies of lasers are presented. An efficient compact cooling system comprising heat pipes with an evaporator having a capillary coating of a caked copper powder and a condenser having a developed outer finning, has been deviced. This system makes it possible to remove, to the ambient air, a heat flow of power more than 300 W at a temperature of 40-50°C.

  7. Galaxy number counts: Pt. 2

    Metcalfe, N.; Shanks, T.; Fong, R.; Jones, L.R.

    1991-01-01

    Using the Prime Focus CCD Camera at the Isaac Newton Telescope we have determined the form of the B and R galaxy number-magnitude count relations in 12 independent fields for 21 m ccd m and 19 m ccd m 5. The average galaxy count relations lie in the middle of the wide range previously encompassed by photographic data. The field-to-field variation of the counts is small enough to define the faint (B m 5) galaxy count to ±10 per cent and this variation is consistent with that expected from galaxy clustering considerations. Our new data confirm that the B, and also the R, galaxy counts show evidence for strong galaxy luminosity evolution, and that the majority of the evolving galaxies are of moderately blue colour. (author)

  8. Giant Low Surface Brightness Galaxies

    Mishra, Alka; Kantharia, Nimisha G.; Das, Mousumi

    2018-04-01

    In this paper, we present radio observations of the giant low surface brightness (LSB) galaxies made using the Giant Metrewave Radio Telescope (GMRT). LSB galaxies are generally large, dark matter dominated spirals that have low star formation efficiencies and large HI gas disks. Their properties suggest that they are less evolved compared to high surface brightness galaxies. We present GMRT emission maps of LSB galaxies with an optically-identified active nucleus. Using our radio data and archival near-infrared (2MASS) and near-ultraviolet (GALEX) data, we studied morphology and star formation efficiencies in these galaxies. All the galaxies show radio continuum emission mostly associated with the centre of the galaxy.

  9. From gas to galaxies

    van der Hulst, J.M.; Sadler, E.M.; Jackson, C.A.; Hunt, L.K.; Verheijen, M.; van Gorkom, J.H.

    2004-01-01

    The unsurpassed sensitivity and resolution of the Square Kilometer Array (SKA) will make it possible for the first time to probe the continuum emission of normal star forming galaxies out to the edges of the universe. This opens the possibility for routinely using the radio continuum emission from

  10. Simulations of galaxy mergers

    Villumsen, J.V.; Yale Univ., New Haven, CT

    1982-01-01

    A number of N-body simulations of mergers of equal and unequal galaxies are presented. A new code is presented which determines the potential from a mass distribution by a fourth-order expansion in Tesseral harmonics in three dimensions as an approximation to a collisionless system. The total number of particles in the system is 1200. Two galaxies, each a spherical non-rotating system with isothermal or Hubble density profile, are put in orbit around each other where tidal effects and dynamical friction lead to merging. The final system has a Hubble profile, and in some mergers an 'isothermal' halo forms as found in cD galaxies. Equal mass mergers are more flattened than unequal mass mergers. The central surface brightness decreases except in a merger of isothermal galaxies which shows a major redistribution of energy towards a Hubble profile. Mixing is severe in equal mass mergers, where radial gradients are weakened, while in unequal mass encounters gradients can build up due to less mixing and the formation of a halo. Oblate systems with strong rotation form in high angular momentum encounters while prolate systems with little rotation are formed in near head-on collisions. (author)

  11. Formation of Triaxial Galaxy

    Jang-Hyeon Park

    1987-06-01

    Full Text Available Results of N-body simulation of dissipationless cold collapse of spherical gravitating system are presented. We compared the results with properties of elliptical galaxies. The system gradually evolved to triaxial system. The projected density profile is in good agreement with observations. In addition to triaxial instability, it seems that there is another instability.

  12. Jets in Active Galaxies

    which are rapidly rotating neutron stars emitting narrow beams of radiation. Images of ... rized into starburst galaxies and AGN powered by SMBHs. The ..... swer lies in the relativistic motion of the jets which boosts the flux density of .... radio cores, detection of ... to as synchrotron self-Compton or SSC, or those of the cosmic.

  13. The high energy galaxy

    Cesarsky, C.J.

    1986-08-01

    The galaxy is host to a wide variety of high energy events. I review here recent results on large scale galactic phenomena: cosmic-ray origin and confinement, the connexion to ultra high energy gamma-ray emission from X-ray binaries, gamma ray and synchrotron emission in interstellar space, galactic soft and hard X-ray emission

  14. Outskirts of galaxies

    Lee, Janice; Paz, Armando

    2017-01-01

    This book consists of invited reviews written by world-renowned experts on the subject of the outskirts of galaxies, an upcoming field which has been understudied so far. These regions are faint and hard to observe, yet hide a tremendous amount of information on the origin and early evolution of galaxies. They thus allow astronomers to address some of the most topical problems, such as gaseous and satellite accretion, radial migration, and merging. The book is published in conjunction with the celebration of the end of the four-year DAGAL project, an EU-funded initial training network, and with a major international conference on the topic held in March 2016 in Toledo. It thus reflects not only the views of the experts, but also the scientific discussions and progress achieved during the project and the meeting. The reviews in the book describe the most modern observations of the outer regions of our own Galaxy, and of galaxies in the local and high-redshift Universe. They tackle disks, haloes, streams, and a...

  15. Galaxy Masses : A Review

    Courteau, Stephane; Cappellari, Michele; Jong, Roelof S. de; Dutton, Aaron A.; Koopmans, L.V.E.

    2013-01-01

    Galaxy masses play a fundamental role in our understanding of structure formation models. This review addresses the variety and reliability of mass estimators that pertain to stars, gas, and dark matter. The dierent sections on masses from stellar populations, dynamical masses of gas-rich and

  16. Water cooling coil

    Suzuki, S; Ito, Y; Kazawa, Y

    1975-02-05

    Object: To provide a water cooling coil in a toroidal nuclear fusion device, in which coil is formed into a small-size in section so as not to increase dimensions, weight or the like of machineries including the coil. Structure: A conductor arranged as an outermost layer of a multiple-wind water cooling coil comprises a hollow conductor, which is directly cooled by fluid, and as a consequence, a solid conductor disposed interiorly thereof is cooled indirectly.

  17. Fuel assembly

    Yokota, Tokunobu.

    1990-01-01

    A fuel assembly used in a FBR type nuclear reactor comprises a plurality of fuel rods and a moderator guide member (water rod). A moderator exit opening/closing mechanism is formed at the upper portion of the moderator guide member for opening and closing a moderator exit. In the initial fuel charging operation cycle to the reactor, the moderator exit is closed by the moderator exit opening/closing mechanism. Then, voids are accumulated at the inner upper portion of the moderator guide member to harden spectrum and a great amount of plutonium is generated and accumulated in the fuel assembly. Further, in the fuel re-charging operation cycle, the moderator guide member is used having the moderator exit opened. In this case, voids are discharged from the moderator guide member to decrease the ratio, and the plutonium accumulated in the initial charging operation cycle is burnt. In this way, the fuel economy can be improved. (I.N.)

  18. Fuel assemblies

    Echigoya, Hironori; Nomata, Terumitsu.

    1983-01-01

    Purpose: To render the axial distribution relatively flat. Constitution: First nuclear element comprises a fuel can made of zircalloy i.e., the metal with less neutron absorption, which is filled with a plurality of UO 2 pellets and sealed by using a lower end plug, a plenum spring and an upper end plug by means of welding. Second fuel element is formed by substituting a part of the UO 2 pellets with a water tube which is sealed with water and has a space for allowing the heat expansion. The nuclear fuel assembly is constituted by using the first and second fuel elements together. In such a structure, since water reflects neutrons and decrease their leakage to increase the temperature, reactivity is added at the upper portion of the fuel assembly to thereby flatten the axial power distribution. Accordingly, stable operation is possible only by means of deep control rods while requiring no shallow control rods. (Sekiya, K.)

  19. Fuel assembly

    Kawai, Mitsuo.

    1988-01-01

    Purpose: To reduce the corrosion rate and suppress the increase of radioactive corrosion products in reactor water of nuclear fuel assemblies for use in BWR type reactors having spacer springs made of nickel based deposition reinforced type alloys. Constitution: Spacer rings made of nickel based deposition reinforced type alloy are incorporated and used as fuel assemblies after applying treatment of dipping and maintaining at high temperature water followed by heating in steams. Since this can remove the nickel leaching into reactor water at the initial stage, Co-58 as the radioactive corrosion products in the reactor water can be reduced, and the operation at in-service inspection or repairement can be facilitated to improve the working efficiency of the nuclear power plant. The dipping time is desirably more than 10 hours and more desirably more than 30 hours. (Horiuchi, T. )

  20. Fuel assembly

    Watanabe, Shoichi; Hirano, Yasushi.

    1998-01-01

    A one-half or more of entire fuel rods in a fuel assembly comprises MOX fuel rods containing less than 1wt% of burnable poisons, and at least a portion of the burnable poisons comprises gadolinium. Then, surplus reactivity at an initial stage of operation cycle is controlled to eliminate burnable poisons remained unburnt at a final stage, as well as increase thermal reactivity. In addition, the content of fission plutonium is determined to greater than the content of uranium 235, and fuel rods at corner portions are made not to incorporate burnable poisons. Fuel rods not containing burnable poisons are disposed at positions in adjacent with fuel rods facing to a water rod at one or two directions. Local power at radial center of the fuel assembly is increased to flatten the distortion of radial power distribution. (N.H.)

  1. Dusty Dwarfs Galaxies Occulting A Bright Background Spiral

    Holwerda, Benne

    2017-08-01

    The role of dust in shaping the spectral energy distributions of low mass disk galaxies remains poorly understood. Recent results from the Herschel Space Observatory imply that dwarf galaxies contain large amounts of cool (T 20K) dust, coupled with very modest optical extinctions. These seemingly contradictory conclusions may be resolved if dwarfs harbor a variety of dust geometries, e.g., dust at larger galactocentric radii or in quiescent dark clumps. We propose HST observations of six truly occulting dwarf galaxies drawn from the Galaxy Zoo catalog of silhouetted galaxy pairs. Confirmed, true occulting dwarfs are rare as most low-mass disks in overlap are either close satellites or do not have a confirmed redshift. Dwarf occulters are the key to determining the spatial extent of dust, the small scale structure introduced by turbulence, and the prevailing dust attenuation law. The recent spectroscopic confirmation of bona-fide low mass occulting dwarfs offers an opportunity to map dust in these with HST. What is the role of dust in the SED of these dwarf disk galaxies? With shorter feedback scales, how does star-formation affect their morphology and dust composition, as revealed from their attenuation curve? The resolution of HST allows us to map the dust disks down to the fine scale structure of molecular clouds and multi-wavelength imaging maps the attenuation curve and hence dust composition in these disks. We therefore ask for 2 orbits on each of 6 dwarf galaxies in F275W, F475W, F606W, F814W and F125W to map dust from UV to NIR to constrain the attenuation curve.

  2. The Cool Colors Project

    Gov. Arnold Schwarzenegger, second from left, a sample from the Cool Colors Project, a roof product ) (Jeff Chiu - AP) more Cool Colors make the front page of The Sacramento Bee (3rd highest circulation newspaper in California) on 14 August 2006! Read the article online or as a PDF. The Cool Colors Project

  3. SEEDisCs: How Clusters Form and Galaxies Transform in the Cosmic Web

    Jablonka, P.

    2017-08-01

    This presentation introduces a new survey, the Spatial Extended EDisCS Survey (SEEDisCS), which aims at understanding how clusters assemble and the level at which galaxies are preprocessed before falling on the cluster cores. I focus on the changes in galaxy properties in the cluster large scale environments, and how we can get constraints on the timescale of star formation quenching. I also discuss new ALMA CO observations, which trace the fate of the galaxy cold gas content along the infalling paths towards the cluster cores.

  4. General Assembly

    Staff Association

    2016-01-01

    5th April, 2016 – Ordinary General Assembly of the Staff Association! In the first semester of each year, the Staff Association (SA) invites its members to attend and participate in the Ordinary General Assembly (OGA). This year the OGA will be held on Tuesday, April 5th 2016 from 11:00 to 12:00 in BE Auditorium, Meyrin (6-2-024). During the Ordinary General Assembly, the activity and financial reports of the SA are presented and submitted for approval to the members. This is the occasion to get a global view on the activities of the SA, its financial management, and an opportunity to express one’s opinion, including taking part in the votes. Other points are listed on the agenda, as proposed by the Staff Council. Who can vote? Only “ordinary” members (MPE) of the SA can vote. Associated members (MPA) of the SA and/or affiliated pensioners have a right to vote on those topics that are of direct interest to them. Who can give his/her opinion? The Ordinary General Asse...

  5. Galaxies clustering around QSOs with z = 0.9-1.5 and the origin of blue field galaxies

    Hintzen, Paul; Romanishin, W.; Valdes, Francisco

    1991-01-01

    Deep CCD images were obtained in Mould-Cousins R and I passbands of 16 radio quasars with z values between 0.9 and 1.5 and absolute values of b above 35 deg, chosen from the Veron-Cetty and Veron (1984) catalog. Results indicate that, in this population of radio quasars, there is a statistically significant excess of galaxies within 15 arcsec of the quasars and brighter than R = 23 and I = 22. However, contrary to the report of Tyson (1986), no excess was found of galaxies with R less than 21 lying within 30 arcsec of quasars in this redshift range. Data were also obtained for very blue galaxies seen among objects in the general field, all of which are bluer in R-I than Magellanic irregulars at any redshift less than 3. It is suggested that this population might be comprised of low-redshift low-luminosity (H II region) galaxies of the type studied by French (1980) and/or higher redshift galaxies with strong cooling flows and forbidden O II lines.

  6. The impact of feedback and the hot halo on the rates of gas accretion onto galaxies

    Correa, Camila A.; Schaye, Joop; van de Voort, Freeke; Duffy, Alan R.; Wyithe, J. Stuart B.

    2018-04-01

    We investigate the physics that drives the gas accretion rates onto galaxies at the centers of dark matter haloes using the EAGLE suite of hydrodynamical cosmological simulations. We find that at redshifts z ≤ 2 the accretion rate onto the galaxy increases with halo mass in the halo mass range 1010 - 1011.7 M⊙, flattens between the halo masses 1011.7 - 1012.7 M⊙, and increases again for higher-mass haloes. However, the galaxy gas accretion does not flatten at intermediate halo masses when AGN feedback is switched off. To better understand these trends, we develop a physically motivated semi-analytic model of galaxy gas accretion. We show that the flattening is produced by the rate of gas cooling from the hot halo. The ratio of the cooling radius and the virial radius does not decrease continuously with increasing halo mass as generally thought. While it decreases up to ˜1013 M⊙ haloes, it increases for higher halo masses, causing an upturn in the galaxy gas accretion rate. This may indicate that in high-mass haloes AGN feedback is not sufficiently efficient. When there is no AGN feedback, the density of the hot halo is higher, the ratio of the cooling and virial radii does not decrease as much and the cooling rate is higher. Changes in the efficiency of stellar feedback can also increase or decrease the accretion rates onto galaxies. The trends can plausibly be explained by the re-accretion of gas ejected by progenitor galaxies and by the suppression of black hole growth, and hence AGN feedback, by stellar feedback.

  7. Dark matter halo properties from galaxy-galaxy lensing

    Brimioulle, Fabrice

    2013-01-01

    The scientific results over the past years have shown that the Universe is by far not only composed of baryonic matter. In fact the major energy content of 72% of the Universe appears to be represented by so-called dark energy, while even from the remaining components only about one fifth is of baryonic origin, whereas 80% have to be attributed to dark matter. Originally appearing in observations of spiral galaxy rotation curves, the need for dark matter has also been verified investigating elliptical galaxies and galaxy clusters. In fact, it appears that dark matter played a major role during structure formation in the early Universe. Shortly after the Big Bang, when the matter distribution was almost homogeneous, initially very small inhomogeneities in the matter distribution formed the seeds for the gravitational collapse of the matter structures. Numerical n-body simulations, for instance, clearly indicate that the presently observable evolutionary state and complexity of the matter structure in the Universe would not have been possible without dark matter, which significantly accelerated the structure collapse due to its gravitational interaction. As dark matter does not interact electromagnetically and therefore is non-luminous but only interacts gravitationally, the gravitational lens effect provides an excellent opportunity for its detection and estimation of its amount. Weak gravitational lensing is a technique that makes use of the random orientation of the intrinsic galaxy ellipticities and thus their uniform distribution. Gravitational tidal forces introduce a coherent distortion of the background object shapes, leading to a deviation from the uniform distribution which depends on the lens galaxy properties and therefore can be used to study them. This thesis describes the galaxy-galaxy lensing analysis of 89deg 2 of optical data, observed within the CFHTLS-WIDE survey. In the framework of this thesis the data were used in order to create photometric

  8. Cooling water distribution system

    Orr, Richard

    1994-01-01

    A passive containment cooling system for a nuclear reactor containment vessel. Disclosed is a cooling water distribution system for introducing cooling water by gravity uniformly over the outer surface of a steel containment vessel using an interconnected series of radial guide elements, a plurality of circumferential collector elements and collector boxes to collect and feed the cooling water into distribution channels extending along the curved surface of the steel containment vessel. The cooling water is uniformly distributed over the curved surface by a plurality of weirs in the distribution channels.

  9. COOL DUST IN THE OUTER RING OF NGC 1291

    Hinz, J. L.; Engelbracht, C. W.; Skibba, R.; Montiel, E.; Crocker, A.; Calzetti, D.; Donovan Meyer, J.; Sandstrom, K.; Walter, F.; Groves, B.; Meidt, S. E.; Johnson, B. D.; Hunt, L.; Aniano, G.; Draine, B.; Murphy, E. J.; Armus, L.; Dale, D. A.; Galametz, M.; Kennicutt, R. C.

    2012-01-01

    We examine Herschel Space Observatory images of one nearby prototypical outer ring galaxy, NGC 1291, and show that the ring becomes more prominent at wavelengths longer than 160 μm. The mass of cool dust in the ring dominates the total dust mass of the galaxy, accounting for at least 70% of it. The temperature of the emitting dust in the ring (T = 19.5 ± 0.3 K) is cooler than that of the inner galaxy (T = 25.7 ± 0.7 K). We discuss several explanations for the difference in dust temperature, including age and density differences in the stellar populations of the ring versus the bulge.

  10. THE CARNEGIE-IRVINE GALAXY SURVEY. II. ISOPHOTAL ANALYSIS

    Li Zhaoyu; Ho, Luis C.; Barth, Aaron J.; Peng, Chien Y.

    2011-01-01

    The Carnegie-Irvine Galaxy Survey (CGS) is a comprehensive investigation of the physical properties of a complete, representative sample of 605 bright (B T ≤ 12.9 mag) galaxies in the southern hemisphere. This contribution describes the isophotal analysis of the broadband (BVRI) optical imaging component of the project. We pay close attention to sky subtraction, which is particularly challenging for some of the large galaxies in our sample. Extensive crosschecks with internal and external data confirm that our calibration and sky subtraction techniques are robust with respect to the quoted measurement uncertainties. We present a uniform catalog of one-dimensional radial profiles of surface brightness and geometric parameters, as well as integrated colors and color gradients. Composite profiles highlight the tremendous diversity of brightness distributions found in disk galaxies and their dependence on Hubble type. A significant fraction of S0 and spiral galaxies exhibit non-exponential profiles in their outer regions. We perform Fourier decomposition of the isophotes to quantify non-axisymmetric deviations in the light distribution. We use the geometric parameters, in conjunction with the amplitude and phase of the m = 2 Fourier mode, to identify bars and quantify their size and strength. Spiral arm strengths are characterized using the m = 2 Fourier profiles and structure maps. Finally, we utilize the information encoded in the m = 1 Fourier profiles to measure disk lopsidedness. The databases assembled here and in Paper I lay the foundation for forthcoming scientific applications of CGS.

  11. THE SPITZER HIGH-REDSHIFT RADIO GALAXY SURVEY

    De Breuck, Carlos; Galametz, Audrey; Vernet, Joel; Seymour, Nick; Stern, Daniel; Eisenhardt, P. R. M.; Willner, S. P.; Fazio, G. G.; Lacy, Mark; Rettura, Alessandro; Rocca-Volmerange, Brigitte

    2010-01-01

    We present results from a comprehensive imaging survey of 70 radio galaxies at redshifts 1 3 μ m /S 1.6 μ m versus S 5 μ m /S 3 μ m criterion, we identify 42 sources where the rest-frame 1.6 μm emission from the stellar population can be measured. For these radio galaxies, the median stellar mass is high, 2 x 10 11 M sun , and remarkably constant within the range 1 3, there is tentative evidence for a factor of two decrease in stellar mass. This suggests that radio galaxies have assembled the bulk of their stellar mass by z ∼ 3, but confirmation by more detailed decomposition of stellar and active galactic nucleus (AGN) emission is needed. The rest-frame 500 MHz radio luminosities are only marginally correlated with stellar mass but are strongly correlated with the rest-frame 5 μm hot dust luminosity. This suggests that the radio galaxies have a large range of Eddington ratios. We also present new Very Large Array 4.86 and 8.46 GHz imaging of 14 radio galaxies and find that radio core dominance-an indicator of jet orientation-is strongly correlated with hot dust luminosity. While all of our targets were selected as narrow-lined, type 2 AGNs, this result can be understood in the context of orientation-dependent models if there is a continuous distribution of orientations from obscured type 2 to unobscured type 1 AGNs rather than a clear dichotomy. Finally, four radio galaxies have nearby (<6'') companions whose mid-IR colors are suggestive of their being AGNs. This may indicate an association between radio galaxy activity and major mergers.

  12. Combustor assembly for use in a turbine engine and methods of assembling same

    Uhm, Jong Ho; Johnson, Thomas Edward

    2013-05-14

    A fuel nozzle assembly for use with a turbine engine is described herein. The fuel nozzle assembly includes a plurality of fuel nozzles positioned within an air plenum defined by a casing. Each of the plurality of fuel nozzles is coupled to a combustion liner defining a combustion chamber. Each of the plurality of fuel nozzles includes a housing that includes an inner surface that defines a cooling fluid plenum and a fuel plenum therein, and a plurality of mixing tubes extending through the housing. Each of the mixing tubes includes an inner surface defining a flow channel extending between the air plenum and the combustion chamber. At least one mixing tube of the plurality of mixing tubes including at least one cooling fluid aperture for channeling a flow of cooling fluid from the cooling fluid plenum to the flow channel.

  13. The Supermassive Black Hole—Galaxy Connection

    King, Andrew

    2014-09-01

    The observed scaling relations imply that supermassive black holes (SMBH) and their host galaxies evolve together. Near-Eddington winds from the SMBH accretion discs explain many aspects of this connection. The wind Eddington factor should be in the range ˜1-30. A factor give black hole winds with velocities v˜0.1 c, observable in X-rays, just as seen in the most extreme ultrafast outflows (UFOs). Higher Eddington factors predict slower and less ionized winds, observable in the UV, as in BAL QSOs. In all cases the wind must shock against the host interstellar gas and it is plausible that these shocks should cool efficiently. There is detailed observational evidence for this in some UFOs. The wind sweeps up the interstellar gas into a thin shell and propels it outwards. For SMBH masses below a certain critical ( M- σ) value, all these outflows eventually stall and fall back, as the Eddington thrust of the wind is too weak to drive the gas to large radii. But once the SMBH mass reaches the critical M- σ value the global character of the outflow changes completely. The wind shock is no longer efficiently cooled, and the resulting thermal expansion drives the interstellar gas far from the black hole, which is unlikely to grow significantly further. Simple estimates of the maximum stellar bulge mass M b allowed by self-limited star formation show that the SMBH mass is typically about 10-3 M b at this point, in line with observation. The expansion-driven outflow reaches speeds v out≃1200 km s-1 and drives rates in cool (molecular) gas, giving a typical outflow mechanical energy L mech≃0.05 L Edd, where L Edd is the Eddington luminosity of the central SMBH. This is again in line with observation. These massive outflows may be what makes galaxies become red and dead, and can have several other potentially observable effects. In particular they have the right properties to enrich the intergalactic gas with metals. Our current picture of SMBH-galaxy coevolution is

  14. Origin, structure and evolution of galaxies

    Zhi, F.L.

    1988-01-01

    Recent developments of the origin, structure and evolution of galaxies have been reviewed. The contents of this book are: Inflationary Universe; Cosmic String; Active Galaxies; Intergalactic Medium; Waves in Disk Galaxies; Dark Matter; Gas Dynamics in Disk Galaxies; Equilibrium and Stability of Spiral Galaxies

  15. Cooling tower calculations

    Simonkova, J.

    1988-01-01

    The problems are summed up of the dynamic calculation of cooling towers with forced and natural air draft. The quantities and relations are given characterizing the simultaneous exchange of momentum, heat and mass in evaporative water cooling by atmospheric air in the packings of cooling towers. The method of solution is clarified in the calculation of evaporation criteria and thermal characteristics of countercurrent and cross current cooling systems. The procedure is demonstrated of the calculation of cooling towers, and correction curves and the effect assessed of the operating mode at constant air number or constant outlet air volume flow on their course in ventilator cooling towers. In cooling towers with the natural air draft the flow unevenness is assessed of water and air relative to its effect on the resulting cooling efficiency of the towers. The calculation is demonstrated of thermal and resistance response curves and cooling curves of hydraulically unevenly loaded towers owing to the water flow rate parameter graded radially by 20% along the cross-section of the packing. Flow rate unevenness of air due to wind impact on the outlet air flow from the tower significantly affects the temperatures of cooled water in natural air draft cooling towers of a design with lower demands on aerodynamics, as early as at wind velocity of 2 m.s -1 as was demonstrated on a concrete example. (author). 11 figs., 10 refs

  16. Possible Imprints of Cold-mode Accretion on the Present-day Properties of Disk Galaxies

    Noguchi, Masafumi

    2018-01-01

    Recent theoretical studies suggest that a significant part of the primordial gas accretes onto forming galaxies as narrow filaments of cold gas without building a shock and experiencing heating. Using a simple model of disk galaxy evolution that combines the growth of dark matter halos predicted by cosmological simulations with a hypothetical form of cold-mode accretion, we investigate how this cold-accretion mode affects the formation process of disk galaxies. It is found that the shock-heating and cold-accretion models produce compatible results for low-mass galaxies owing to the short cooling timescale in such galaxies. However, cold accretion significantly alters the evolution of disk galaxies more massive than the Milky Way and puts observable fingerprints on their present properties. For a galaxy with a virial mass {M}{vir}=2.5× {10}12 {M}ȯ , the scale length of the stellar disk is larger by 41% in the cold-accretion model than in the shock-heating model, with the former model reproducing the steep rise in the size–mass relation observed at the high-mass end. Furthermore, the stellar component of massive galaxies becomes significantly redder (0.66 in u ‑ r at {M}{vir}=2.5× {10}12 {M}ȯ ), and the observed color–mass relation in nearby galaxies is qualitatively reproduced. These results suggest that large disk galaxies with red optical colors may be the product of cold-mode accretion. The essential role of cold accretion is to promote disk formation in the intermediate-evolution phase (0.5< z< 1.5) by providing the primordial gas having large angular momentum and to terminate late-epoch accretion, quenching star formation and making massive galaxies red.

  17. Lateral restraint assembly in a nuclear reactor

    Brown, S.J.; Gorholt, W.

    1977-01-01

    A lateral restraint assembly is described for a reactor of, for example, the high temperature gas-cooled type which commonly includes a reactor core of relatively complex construction supported within a shell or vessel providing a shielded cavity for containing the reactor core. (U.K.)

  18. Fuel assemblies for use in nuclear reactors

    Schluderberg, D.C.

    1981-01-01

    A fuel assembly for use in pressurized water cooled nuclear fast breeder reactors is described in which moderator to fuel ratios, conducive to a high Pu-U-D 2 O reactor breeding ratio, are obtained whilst at the same time ensuring accurate spacing of fuel pins without the parasitic losses associated with the use of spacer grids. (U.K.)

  19. Assembling the LHC short straight sections

    Maximilien Brice

    2005-01-01

    The building where the short straight sections are being assembled, was often called ‘Lego Land’ by the workers because of the wide variety of sets of magnets and cryostats. Short straight sections contain magnets for manipulating the beam inside cryostats with liquid helium to keep the magnets at a cool 1.9 K (-271.3°C).

  20. Container for spent fuel assembly

    Sawai, Takeshi.

    1996-01-01

    The container of the present invention comprises a container main body having a body portion which can contain spent fuel assemblies and a lid, and heat pipes having an evaporation portion disposed along the outer surface of the spent fuel assemblies to be contained and a condensation portion exposed to the outside of the container main body. Further, the heat pipe is formed spirally at the evaporation portions so as to surround the outer circumference of the spent fuel assemblies, branched into a plurality of portions at the condensation portion, each of the branched portion of the condensation portion being exposed to the outside of the container main body, and is tightly in contact with the periphery of the slit portions disposed to the container main body. Then, since released after heat is transferred to the outside of the container main body from the evaporation portion of the heat pipe along the outer surface of the spent fuel assemblies by way of the condensation portion of the heat pipes exposed to the outside of the container main body, the efficiency of the heat transfer is extremely improved to enhance the effect of removing heat of spent fuel assemblies. Further, cooling effect is enhanced by the spiral form of the evaporation portion and the branched condensation portion. (N.H.)

  1. The Arecibo Galaxy Environment Survey IX: the isolated galaxy sample

    Minchin, R.F.; Auld, R.; Davies, J.I.; Karachentsev, I.D.; Keenan, O.; Momjian, E.; Rodriguez, R.; Taber, T.; Taylor, Rhys

    2016-01-01

    Roč. 455, č. 4 (2016), s. 3430-3435 ISSN 0035-8711 R&D Projects: GA MŠk LG14013; GA ČR GAP209/12/1795 Institutional support: RVO:67985815 Keywords : individual galaxies NGC 1156 * individual galaxies NGC 5523 * individual galaxies UGC 2082 Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.961, year: 2016

  2. Nearby Galaxies: Templates for Galaxies Across Cosmic Time

    Lockman, F. J.; Ott, J.

    2009-01-01

    Studies of nearby galaxies including the Milky Way have provided fundamental information on the evolution of structure in the Universe, the existence and nature of dark matter, the origin and evolution of galaxies, and the global features of star formation. Yet despite decades of work, many of the most basic aspects of galaxies and their environments remain a mystery. In this paper we describe some outstanding problems in this area and the ways in which large radio facilities will contribute ...

  3. Extreme Emission Line Galaxies in CANDELS: Broad-Band Selected, Star-Bursting Dwarf Galaxies at Z greater than 1

    vanderWel, A.; Straughn, A. N.; Rix, H.-W.; Finkelstein, S. L.; Koekemoer, A. M.; Weiner, B. J.; Wuyts, S.; Bell, E. F.; Faber, S. M.; Trump, J. R.; hide

    2012-01-01

    We identify an abundant population of extreme emission line galaxies (EELGs) at redshift z approx. 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). 69 EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broad-band magnitudes. Supported by spectroscopic confirmation of strong [OIII] emission lines . with rest-frame equivalent widths approx. 1000A in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with approx.10(exp 8) Solar Mass in stellar mass, undergoing an enormous starburst phase with M*/M* of only approx. 15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the co-moving number density (3.7x10(exp -4) Mpc(sup -3) can produce in approx.4 Gyr much of the stellar mass density that is presently contained in 10(exp 8) - 10(exp 9) Solar Mass dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z > 1.

  4. Fuel assembly

    Fujibayashi, Toru.

    1970-01-01

    Herein disclosed is a fuel assembly in which a fuel rod bundle is easily detachable by rotating a fuel rod fastener rotatably mounted to the upper surface of an upper tie-plate supporting a fuel bundle therebelow. A locking portion at the leading end of each fuel rod protrudes through the upper tie-plate and is engaged with or separated from the tie-plate by the rotation of the fastener. The removal of a desired fuel rod can therefore be remotely accomplished without the necessity of handling pawls, locking washers and nuts. (Owens, K.J.)

  5. Assembling consumption

    Assembling Consumption marks a definitive step in the institutionalisation of qualitative business research. By gathering leading scholars and educators who study markets, marketing and consumption through the lenses of philosophy, sociology and anthropology, this book clarifies and applies...... the investigative tools offered by assemblage theory, actor-network theory and non-representational theory. Clear theoretical explanation and methodological innovation, alongside empirical applications of these emerging frameworks will offer readers new and refreshing perspectives on consumer culture and market...... societies. This is an essential reading for both seasoned scholars and advanced students of markets, economies and social forms of consumption....

  6. The Formation and Physical Origin of Highly Ionized Cooling Gas

    Bordoloi, Rongmon [MIT-Kavli Center for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA, 02139 (United States); Wagner, Alexander Y. [University of Tsukuba, Center for Computational Sciences, Tennodai 1-1-1, Tsukuba, Ibaraki (Japan); Heckman, Timothy M.; Norman, Colin A., E-mail: bordoloi@mit.edu, E-mail: bordoloi@mit.edu [Department of Physics and Astronomy, John Hopkins University, 21218, Baltimore, MD (United States)

    2017-10-20

    We present a simple model that explains the origin of warm, diffuse gas seen primarily as highly ionized absorption-line systems in the spectra of background sources. We predict the observed column densities of several highly ionized transitions such as O vi, O vii, Ne viii, N v, and Mg x, and we present a unified comparison of the model predictions with absorption lines seen in the Milky Way disk, Milky Way halo, starburst galaxies, the circumgalactic medium, and the intergalactic medium at low and high redshifts. We show that diffuse gas seen in such diverse environments can be simultaneously explained by a simple model of radiatively cooling gas. We show that most such absorption-line systems are consistent with being collisionally ionized, and we estimate the maximum-likelihood temperature of the gas in each observation. This model satisfactorily explains why O vi is regularly observed around star-forming low- z L* galaxies, and why N v is rarely seen around the same galaxies. We further present some consequences of this model in quantifying the dynamics of the cooling gas around galaxies and predict the shock velocities associated with such flows. A unique strength of this model is that while it has only one free (but physically well-constrained) parameter, it nevertheless successfully reproduces the available data on O vi absorbers in the interstellar, circumgalactic, intragroup, and intergalactic media, as well as the available data on other absorption lines from highly ionized species.

  7. The Galaxy mass function up to z =4 in the GOODS-MUSIC sample: into the epoch of formation of massive galaxies

    Fontana, A.; Salimbeni, S.; Grazian, A.; Giallongo, E.; Pentericci, L.; Nonino, M.; Fontanot, F.; Menci, N.; Monaco, P.; Cristiani, S.; Vanzella, E.; de Santis, C.; Gallozzi, S.

    2006-12-01

    Aims.The goal of this work is to measure the evolution of the Galaxy Stellar Mass Function and of the resulting Stellar Mass Density up to redshift ≃4, in order to study the assembly of massive galaxies in the high redshift Universe. Methods: .We have used the GOODS-MUSIC catalog, containing 3000 Ks-selected galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8 μm band, of which 27% have spectroscopic redshifts and the remaining fraction have accurate photometric redshifts. On this sample we have applied a standard fitting procedure to measure stellar masses. We compute the Galaxy Stellar Mass Function and the resulting Stellar Mass Density up to redshift ≃4, taking into proper account the biases and incompleteness effects. Results: .Within the well known trend of global decline of the Stellar Mass Density with redshift, we show that the decline of the more massive galaxies may be described by an exponential timescale of ≃6 Gyr up to z≃ 1.5, and proceeds much faster thereafter, with an exponential timescale of ≃0.6 Gyr. We also show that there is some evidence for a differential evolution of the Galaxy Stellar Mass Function, with low mass galaxies evolving faster than more massive ones up to z≃ 1{-}1.5 and that the Galaxy Stellar Mass Function remains remarkably flat (i.e. with a slope close to the local one) up to z≃ 1{-}1.3. Conclusions: .The observed behaviour of the Galaxy Stellar Mass Function is consistent with a scenario where about 50% of present-day massive galaxies formed at a vigorous rate in the epoch between redshift 4 and 1.5, followed by a milder evolution until the present-day epoch.

  8. Dissipative dark matter and the rotation curves of dwarf galaxies

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

    2016-07-01

    There is ample evidence from rotation curves that dark matter halos around disk galaxies have nontrivial dynamics. Of particular significance are: a) the cored dark matter profile of disk galaxies, b) correlations of the shape of rotation curves with baryonic properties, and c) Tully-Fisher relations. Dark matter halos around disk galaxies may have nontrivial dynamics if dark matter is strongly self interacting and dissipative. Multicomponent hidden sector dark matter featuring a massless 'dark photon' (from an unbroken dark U(1) gauge interaction) which kinetically mixes with the ordinary photon provides a concrete example of such dark matter. The kinetic mixing interaction facilitates halo heating by enabling ordinary supernovae to be a source of these 'dark photons'. Dark matter halos can expand and contract in response to the heating and cooling processes, but for a sufficiently isolated halo could have evolved to a steady state or 'equilibrium' configuration where heating and cooling rates locally balance. This dynamics allows the dark matter density profile to be related to the distribution of ordinary supernovae in the disk of a given galaxy. In a previous paper a simple and predictive formula was derived encoding this relation. Here we improve on previous work by modelling the supernovae distribution via the measured UV and H α fluxes, and compare the resulting dark matter halo profiles with the rotation curve data for each dwarf galaxy in the LITTLE THINGS sample. The dissipative dark matter concept is further developed and some conclusions drawn.

  9. Dissipative dark matter and the rotation curves of dwarf galaxies

    Foot, R.

    2016-01-01

    There is ample evidence from rotation curves that dark matter halos around disk galaxies have nontrivial dynamics. Of particular significance are: a) the cored dark matter profile of disk galaxies, b) correlations of the shape of rotation curves with baryonic properties, and c) Tully-Fisher relations. Dark matter halos around disk galaxies may have nontrivial dynamics if dark matter is strongly self interacting and dissipative. Multicomponent hidden sector dark matter featuring a massless 'dark photon' (from an unbroken dark U(1) gauge interaction) which kinetically mixes with the ordinary photon provides a concrete example of such dark matter. The kinetic mixing interaction facilitates halo heating by enabling ordinary supernovae to be a source of these 'dark photons'. Dark matter halos can expand and contract in response to the heating and cooling processes, but for a sufficiently isolated halo could have evolved to a steady state or 'equilibrium' configuration where heating and cooling rates locally balance. This dynamics allows the dark matter density profile to be related to the distribution of ordinary supernovae in the disk of a given galaxy. In a previous paper a simple and predictive formula was derived encoding this relation. Here we improve on previous work by modelling the supernovae distribution via the measured UV and H α fluxes, and compare the resulting dark matter halo profiles with the rotation curve data for each dwarf galaxy in the LITTLE THINGS sample. The dissipative dark matter concept is further developed and some conclusions drawn.

  10. Cosmological simulations of isotropic conduction in galaxy clusters

    Smith, Britton; O'Shea, Brian W.; Voit, G. Mark; Ventimiglia, David; Skillman, Samuel W.

    2013-01-01

    Simulations of galaxy clusters have a difficult time reproducing the radial gas-property gradients and red central galaxies observed to exist in the cores of galaxy clusters. Thermal conduction has been suggested as a mechanism that can help bring simulations of cluster cores into better alignment with observations by stabilizing the feedback processes that regulate gas cooling, but this idea has not yet been well tested with cosmological numerical simulations. Here we present cosmological simulations of 10 galaxy clusters performed with five different levels of isotropic Spitzer conduction, which alters both the cores and outskirts of clusters, though not dramatically. In the cores, conduction flattens central temperature gradients, making them nearly isothermal and slightly lowering the central density, but failing to prevent a cooling catastrophe there. Conduction has little effect on temperature gradients outside of cluster cores because outward conductive heat flow tends to inflate the outer parts of the intracluster medium (ICM), instead of raising its temperature. In general, conduction tends reduce temperature inhomogeneity in the ICM, but our simulations indicate that those homogenizing effects would be extremely difficult to observe in ∼5 keV clusters. Outside the virial radius, our conduction implementation lowers the gas densities and temperatures because it reduces the Mach numbers of accretion shocks. We conclude that, despite the numerous small ways in which conduction alters the structure of galaxy clusters, none of these effects are significant enough to make the efficiency of conduction easily measurable, unless its effects are more pronounced in clusters hotter than those we have simulated.

  11. Galaxy mapping the cosmos

    Geach, James

    2014-01-01

    Each night, we are able to gaze up at the night sky and look at the thousands of stars that stretch to the end of our individual horizons. But the stars we see are only those that make up our own Milky Way galaxy-but one of hundreds of billions in the whole of the universe, each separated  by inconceivably huge tracts of empty space. In this book, astronomer James Geach tells the rich stories of both the evolution of galaxies and our ability to observe them, offering a fascinating history of how we've come to realize humanity's tiny place in the vast universe.             Taking us on a compel

  12. The Galaxy's Eating Habits

    Putman, M. E.; Thom, C.; Gibson, B. K.; Staveley-Smith, L.

    2004-06-01

    The possibility of a gaseous halo stream which was stripped from the Sagittarius dwarf galaxy is presented. The total mass of the neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic Anti-Center is 4 - 10 × 106 M⊙ (at 36 kpc, the distance to the stellar debris in this region). Both the stellar and gaseous components have negative velocities in this part of the sky, but the gaseous component extends to higher negative velocities. We suggest this gaseous stream was stripped from the main body of the dwarf 0.2 - 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10-4 cm-3. The gas would then represent the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.

  13. EGG: Empirical Galaxy Generator

    Schreiber, C.; Elbaz, D.; Pannella, M.; Merlin, E.; Castellano, M.; Fontana, A.; Bourne, N.; Boutsia, K.; Cullen, F.; Dunlop, J.; Ferguson, H. C.; Michałowski, M. J.; Okumura, K.; Santini, P.; Shu, X. W.; Wang, T.; White, C.

    2018-04-01

    The Empirical Galaxy Generator (EGG) generates fake galaxy catalogs and images with realistic positions, morphologies and fluxes from the far-ultraviolet to the far-infrared. The catalogs are generated by egg-gencat and stored in binary FITS tables (column oriented). Another program, egg-2skymaker, is used to convert the generated catalog into ASCII tables suitable for ingestion by SkyMaker (ascl:1010.066) to produce realistic high resolution images (e.g., Hubble-like), while egg-gennoise and egg-genmap can be used to generate the low resolution images (e.g., Herschel-like). These tools can be used to test source extraction codes, or to evaluate the reliability of any map-based science (stacking, dropout identification, etc.).

  14. Entropy and galaxy clustering

    Kandrup, H.E.

    1988-01-01

    The notion of a p-particle entropy Sp introduced by Kandrup (1987) is applied here to a Newtonian cosmology modeled as an expanding system of identical point masses studying the time dependence of S1 and S2 in the framework of the linearized theory considered by Fall and Saslaw (1976). It is found that if, at some initial time t0, the galaxy-galaxy correlation function vanished, then S1(t0) = S2(t0). At least for short times t - t0 thereafter, S1 and Delta S = S1 - S2 increase on a characteristic time scale. For all times t after t0, S1(t) = S2(t) or greater. 13 references

  15. Structure in radio galaxies

    Breugel, W. van.

    1980-01-01

    It is shown that radio jets are a rather common phenomenon in radio galaxies. Jets can be disguised as trails in head-tail sources, bridges in double sources or simply remain undetected because of lack of resolution and sensitivity. It is natural to associate these jets with the channels which had previously been suggested to supply energy to the extended radio lobes. The observations of optical emission suggest that a continuous non-thermal spectrum extending from 10 9 to 10 15 Hz is a common property of jets. Because significant amounts of interstellar matter are also observed in each of the galaxies surveyed it seems that models for jets which involve an interaction with this medium may be most appropriate. New information about the overall structure of extended radio sources has been obtained from the detailed multifrequency study with the WSRT. (Auth.)

  16. Galaxy clusters and cosmology

    White, S

    1994-01-01

    Galaxy clusters are the largest coherent objects in Universe. It has been known since 1933 that their dynamical properties require either a modification of the theory of gravity, or the presence of a dominant component of unseen material of unknown nature. Clusters still provide the best laboratories for studying the amount and distribution of this dark matter relative to the material which can be observed directly -- the galaxies themselves and the hot,X-ray-emitting gas which lies between them.Imaging and spectroscopy of clusters by satellite-borne X -ray telescopes has greatly improved our knowledge of the structure and composition of this intergalactic medium. The results permit a number of new approaches to some fundamental cosmological questions,but current indications from the data are contradictory. The observed irregularity of real clusters seems to imply recent formation epochs which would require a universe with approximately the critical density. On the other hand, the large baryon fraction observ...

  17. THE CFHTLS-DEEP CATALOG OF INTERACTING GALAXIES. I. MERGER RATE EVOLUTION TO z = 1.2

    Bridge, C. R.; Carlberg, R. G.; Sullivan, M.

    2010-01-01

    We present the rest-frame optical galaxy merger fraction between 0.2 vega ≤ 22.2 (∼27,000 galaxies) over 2 square degrees, we have compiled the CFHTLS-Deep Catalog of Interacting Galaxies, with ∼ 1600 merging galaxies. We find the merger fraction to be 4.3% ± 0.3% at z ∼ 0.3 and 19.0% ± 2.5% at z ∼ 1, implying evolution of the merger fraction going as (1 + z) m , with m = 2.25 ± 0.24. This result is inconsistent with a mild or non-evolving (m 4σ level of confidence. A mild trend, where by massive galaxies with M * >10 10.7 M sun are undergoing fewer mergers than less massive systems (M * ∼ 10 10 M sun ), consistent with the expectations of galaxy assembly downsizing is observed. Our results also show that interacting galaxies have on average SFRs double that found in non-interacting field galaxies. We conclude that (1) the optical galaxy merger fraction does evolve with redshift, (2) the merger fraction depends mildly on stellar mass, with lower mass galaxies having higher merger fractions at z < 1, and (3) star formation is triggered at all phases of a merger, with larger enhancements at later stages, consistent with N-body simulations.

  18. Method of fabricating a cooled electronic system

    Chainer, Timothy J; Gaynes, Michael A; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Schultz, Mark D; Simco, Daniel P; Steinke, Mark E

    2014-02-11

    A method of fabricating a liquid-cooled electronic system is provided which includes an electronic assembly having an electronics card and a socket with a latch at one end. The latch facilitates securing of the card within the socket. The method includes providing a liquid-cooled cold rail at the one end of the socket, and a thermal spreader to couple the electronics card to the cold rail. The thermal spreader includes first and second thermal transfer plates coupled to first and second surfaces on opposite sides of the card, and thermally conductive extensions extending from end edges of the plates, which couple the respective transfer plates to the liquid-cooled cold rail. The extensions are disposed to the sides of the latch, and the card is securable within or removable from the socket using the latch without removing the cold rail or the thermal spreader.

  19. The environments of Markarian galaxies

    Mackenty, J.W.; Simpson, C.; Mclean, B.

    1990-01-01

    The extensively studied Markarian sample of 1500 ultraviolet excess galaxies contains many Seyfert, starburst, and peculiar galaxies. Using the 20 minute V plates obtained for the construction of the Hubble Space Telescope Guide Star Catalog, the authors investigated the morphologies of the Markarian galaxies and the environments in which they are located. The relationship between the types of nuclear activity and the morphologies and environments of the Markarian galaxies is discussed. The authors conclude that the type of nuclear activity present in the galaxies of the Markarian sample is not dependent on either the morphology or the local environment of the galaxy. This is not to imply that nuclear activity per se is not influenced by the environment in which the nucleus is located. Rather the type of nuclear activity (at least in the Markarian population) does not appear to be determined by the environment

  20. An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10.

    Reines, Amy E; Sivakoff, Gregory R; Johnson, Kelsey E; Brogan, Crystal L

    2011-02-03

    Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

  1. Galaxy formation hydrodynamics: From cosmic flows to star-forming clouds

    Bournaud, F.

    2011-01-01

    Major progress has been made over the last few years in understanding hydrodynamical processes on cosmological scales, in particular how galaxies get their baryons. There is increasing recognition that a large part of the baryons accrete smoothly onto galaxies, and that internal evolution processes play a major role in shaping galaxies mergers are not necessarily the dominant process. However, predictions from the various assembly mechanisms are still in large disagreement with the observed properties of galaxies in the nearby Universe. Small-scale processes have a major impact on the global evolution of galaxies over a Hubble time and the usual sub-grid models account for them in a far too uncertain way. Understanding when, where and at which rate galaxies formed their stars becomes crucial to understand the formation of galaxy populations. I discuss recent improvements and current limitations in 'resolved' modeling of star formation, aiming at explicitly capturing star-foul-ling instabilities, in cosmological and galaxy-sized simulations. Such models need to develop three-dimensional turbulence in the ISM, which requires parsec-scale resolution at redshift zero. (authors)

  2. On the Dearth of Ultra-faint Extremely Metal-poor Galaxies

    Sánchez Almeida, J.; Filho, M. E.; Vecchia, C. Dalla [Instituto Astrofísica de Canarias, E-38200 La Laguna, Tenerife (Spain); Skillman, E. D., E-mail: jos@iac.es [Minnesota Institute for Astrophysics, School of Physics and Astronomy, University of Minnesota, Minneapolis, MN (United States)

    2017-02-01

    Local extremely metal-poor galaxies (XMPs) are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity–metallicity relationship, all galaxies fainter than M{sub r} ≃ −13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not common, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function (LF). The faint end of the LF is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (∼10) is overpredicted by our calculation, unless the upturn in the faint end of the LF is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn toward low luminosity of the observed galaxy LF is due to satellite galaxies.

  3. Galaxy kinematics in the XMMU J2235-2557 cluster field at z 1.4

    Pérez-Martínez, J. M.; Ziegler, B.; Verdugo, M.; Böhm, A.; Tanaka, M.

    2017-09-01

    Aims: The relationship between baryonic and dark components in galaxies varies with the environment and cosmic time. Galaxy scaling relations describe strong trends between important physical properties. A very important quantitative tool in case of spiral galaxies is the Tully-Fisher relation (TFR), which combines the luminosity of the stellar population with the characteristic rotational velocity (Vmax) taken as proxy for the total mass. In order to constrain galaxy evolution in clusters, we need measurements of the kinematic status of cluster galaxies at the starting point of the hierarchical assembly of clusters and the epoch when cosmic star formation peaks. Methods: We took spatially resolved slit FORS2 spectra of 19 cluster galaxies at z 1.4, and 8 additional field galaxies at 1 200 km s-1). This mild evolution may be driven by younger stellar populations (SP) of distant galaxies with respect to their local counterparts, and thus, an increasing luminosity is expected toward higher redshifts. However, the low-mass subsample (Vmax medium. Based on observations with the European Southern Observatory Very Large Telescope (ESO-VLT), observing run ID 091.B-0778(B).

  4. Simulations of galaxy mergers

    Villumsen, J.V.

    1982-01-01

    This work is a theoretical investigation of the mechanisms and results of mergers of elliptical galaxies. An N-body code is developed to simulate the dynamics of centrally concentrated collisionless systems. It is used for N-body simulations of the mergers of galaxies with mass ratios of 1:1, 2:1 and 3:1 with a total of 1200 or 2400 particles. The initial galaxies are spherical and non-rotating with Hubble type profiles and isotropic velocity distributions. The remnants are flattened (up to E4) and are oblate, triaxial or prolate depending on the impact parameter. Equal mass mergers are more flattened than unequal mass mergers and have significant velocity anisotropies. The remnants have Hubble type profiles with decreased central surface brightness and increased core radii and tidal radii. In some unequal mass mergers ''isothermal'' haloes tend to form. The density profiles are inconsistent with De Vaucouleurs profiles even though the initial profiles were not. The central velocity dispersion increases in 1:1 and 2:1 mass mergers but decreases in 3:1 mass mergers. Near head-on mergers lead to prolate systems with little rotation while high angular momentum mergers lead to oblate systems with strong rotation. The rotation curves show solid body rotation out to the half mass radius followed by a slow decline. Radial mixing is strong in equal mass mergers where it will weaken radial gradients. In unequal mass mergers there is little radial mixing but matter from the smaller galaxy ends up in the outer parts of the system where it can give rise to colour gradient

  5. Galaxies with long tails

    Schweizer, F.

    1978-01-01

    Two types of galaxies with long tails are described. The first occurs in pairs, each individual one having a long tail and the second occurs on its own with two tails. NGC 7252 shows several characteristics which one would expect of a merger: a pair of tidal tails despite the splendid isolation, a single nucleus, tail motions in opposite directions relative to the nucleus, and chaotic motions of a strangely looped main body. (C.F.)

  6. Chemical evolution of galaxies

    Matteucci, F.; Consiglio Nazionale delle Ricerche, Frascati

    1989-01-01

    In principle, a good model of galactic chemical evolution should fulfil the majority of well established observational constraints. The goal of this paper is to review the observational data together with the existing chemical evolution models for the Milky Way (the disk), Blue Compact and Elliptical galaxies and to show how well the models can account for the observations. Some open problems and future prospects are also discussed. (author)

  7. Laser cooling of solids

    Petrushkin, S V

    2009-01-01

    Laser cooling is an important emerging technology in such areas as the cooling of semiconductors. The book examines and suggests solutions for a range of problems in the development of miniature solid-state laser refrigerators, self-cooling solid-state lasers and optical echo-processors. It begins by looking at the basic theory of laser cooling before considering such topics as self-cooling of active elements of solid-state lasers, laser cooling of solid-state information media of optical echo-processors, and problems of cooling solid-state quantum processors. Laser Cooling of Solids is an important contribution to the development of compact laser-powered cryogenic refrigerators, both for the academic community and those in the microelectronics and other industries. Provides a timely review of this promising field of research and discusses the fundamentals and theory of laser cooling Particular attention is given to the physics of cooling processes and the mathematical description of these processes Reviews p...

  8. Emergency reactor cooling device

    Arakawa, Ken.

    1993-01-01

    An emergency nuclear reactor cooling device comprises a water reservoir, emergency core cooling water pipelines having one end connected to a water feeding sparger, fire extinguishing facility pipelines, cooling water pressurizing pumps, a diesel driving machine for driving the pumps and a battery. In a water reservoir, cooling water is stored by an amount required for cooling the reactor upon emergency and for fire extinguishing, and fire extinguishing facility pipelines connecting the water reservoir and the fire extinguishing facility are in communication with the emergency core cooling water pipelines connected to the water feeding sparger by system connection pipelines. Pumps are operated by a diesel power generator to introduce cooling water from the reservoir to the emergency core cooling water pipelines. Then, even in a case where AC electric power source is entirely lost and the emergency core cooling system can not be used, the diesel driving machine is operated using an exclusive battery, thereby enabling to inject cooling water from the water reservoir to a reactor pressure vessel and a reactor container by the diesel drive pump. (N.H.)

  9. Fuel assembly

    Chaki, Masao; Nishida, Koji; Karasawa, Hidetoshi; Kanazawa, Toru; Orii, Akihito; Nagayoshi, Takuji; Kashiwai, Shin-ichi; Masuhara, Yasuhiro

    1998-01-01

    The present invention concerns a fuel assembly, for a BWR type nuclear reactor, comprising fuel rods in 9 x 9 matrix. The inner width of the channel box is about 132mm and the length of the fuel rods which are not short fuel rods is about 4m. Two water rods having a circular cross section are arranged on a diagonal line in a portion of 3 x 3 matrix at the center of the fuel assembly, and two fuel rods are disposed at vacant spaces, and the number of fuel rods is 74. Eight fuel rods are determined as short fuel rods among 74 fuel rods. Assuming the fuel inventory in the short fuel rod as X(kg), and the fuel inventory in the fuel rods other than the short fuel rods as Y(kg), X and Y satisfy the relation: X + Y ≥ 173m, Y ≤ - 9.7X + 292, Y ≤ - 0.3X + 203 and X > 0. Then, even when the short fuel rods are used, the fuel inventory is increased and fuel economy can be improved. (I.N.)

  10. Fuel assembly

    Fushimi, Atsushi; Shimada, Hidemitsu; Aoyama, Motoo; Nakajima, Junjiro

    1998-01-01

    In a fuel assembly for an n x n lattice-like BWR type reactor, n is determined to 9 or greater, and the enrichment degree of plutonium is determined to 4.4% by weight or less. Alternatively, n is determined to 10 or greater, and the enrichment degree of plutonium is determined to 5.2% by weight or less. An average take-out burnup degree is determined to 39GWd/t or less, and the matrix is determined to 9 x 9 or more, or the average take-out burnup degree is determined to 51GWd/t, and the matrix is determined to 10 x 10 or more and the increase of the margin of the maximum power density obtained thereby is utilized for the compensation of the increase of distortion of power distribution due to decrease of the kinds of plutonium enrichment degree, thereby enabling to reduce the kind of the enrichment degree of MOX fuel rods to one. As a result, the manufacturing step for fuel pellets can be simplified to reduce the manufacturing cost for MOX fuel assemblies. (N.H.)

  11. General Assembly

    Staff Association

    2015-01-01

    Mardi 5 mai à 11 h 00 Salle 13-2-005 Conformément aux statuts de l’Association du personnel, une Assemblée générale ordinaire est organisée une fois par année (article IV.2.1). Projet d’ordre du jour : 1- Adoption de l’ordre du jour. 2- Approbation du procès-verbal de l’Assemblée générale ordinaire du 22 mai 2014. 3- Présentation et approbation du rapport d’activités 2014. 4- Présentation et approbation du rapport financier 2014. 5- Présentation et approbation du rapport des vérificateurs aux comptes pour 2014. 6- Programme 2015. 7- Présentation et approbation du projet de budget 2015 et taux de cotisation pour 2015. 8- Pas de modifications aux Statuts de l'Association du personnel proposée. 9- Élections des membres de la Commission é...

  12. General Assembly

    Staff Association

    2017-01-01

    Conformément aux statuts de l’Association du personnel, une Assemblée générale ordinaire est organisée une fois par année (article IV.2.1). Projet d’ordre du jour : Adoption de l’ordre du jour. Approbation du procès-verbal de l’Assemblée générale ordinaire du 5 avril 2016. Présentation et approbation du rapport d’activités 2016. Présentation et approbation du rapport financier 2016. Présentation et approbation du rapport des vérificateurs aux comptes pour 2016. Programme de travail 2017. Présentation et approbation du projet de budget 2017 Approbation du taux de cotisation pour 2018. Modifications aux Statuts de l'Association du personnel proposées. Élections des membres de la Commission électorale. Élections des vérifica...

  13. General Assembly

    Staff Association

    2016-01-01

    Mardi 5 avril à 11 h 00 BE Auditorium Meyrin (6-2-024) Conformément aux statuts de l’Association du personnel, une Assemblée générale ordinaire est organisée une fois par année (article IV.2.1). Projet d’ordre du jour : Adoption de l’ordre du jour. Approbation du procès-verbal de l’Assemblée générale ordinaire du 5 mai 2015. Présentation et approbation du rapport d’activités 2015. Présentation et approbation du rapport financier 2015. Présentation et approbation du rapport des vérificateurs aux comptes pour 2015. Programme de travail 2016. Présentation et approbation du projet de budget 2016 Approbation du taux de cotisation pour 2017. Modifications aux Statuts de l'Association du personnel proposée. Élections des membres de la Commissio...

  14. General assembly

    Staff Association

    2015-01-01

    Mardi 5 mai à 11 h 00 Salle 13-2-005 Conformément aux statuts de l’Association du personnel, une Assemblée générale ordinaire est organisée une fois par année (article IV.2.1). Projet d’ordre du jour : Adoption de l’ordre du jour. Approbation du procès-verbal de l’Assemblée générale ordinaire du 22 mai 2014. Présentation et approbation du rapport d’activités 2014. Présentation et approbation du rapport financier 2014. Présentation et approbation du rapport des vérificateurs aux comptes pour 2014. Programme 2015. Présentation et approbation du projet de budget 2015 et taux de cotisation pour 2015. Pas de modifications aux Statuts de l'Association du personnel proposée. Élections des membres de la Commission électorale. &am...

  15. A MULTIWAVELENGTH STUDY OF TADPOLE GALAXIES IN THE HUBBLE ULTRA DEEP FIELD

    Straughn, Amber N.; Eufrasio, Rafael T.; Gardner, Jonathan P.; Voyer, Elysse N.; Mello, Duilia de; Soto, Emmaris; Petty, Sara; Kassin, Susan; Ravindranath, Swara

    2015-01-01

    Multiwavelength data are essential in order to provide a complete picture of galaxy evolution and to inform studies of galaxies’ morphological properties across cosmic time. Here we present the results of a multiwavelength investigation of the morphologies of “tadpole” galaxies at intermediate redshift (0.314 < z < 3.175) in the Hubble Ultra Deep Field. These galaxies were previously selected from deep Hubble Space Telescope (HST) F775W data based on their distinct asymmetric knot-plus-tail morphologies. Here we use deep Wide Field Camera 3 near-infrared imaging in addition to the HST optical data in order to study the rest-frame UV/optical morphologies of these galaxies across the redshift range 0.3 < z < 3.2. This study reveals that the majority of these galaxies do retain their general asymmetric morphology in the rest-frame optical over this redshift range, if not the distinct “tadpole” shape. The average stellar mass of tadpole galaxies is lower than that of field galaxies, with the effect being slightly greater at higher redshift within the errors. Estimated from spectral energy distribution fits, the average age of tadpole galaxies is younger than that of field galaxies in the lower-redshift bin, and the average metallicity is lower (whereas the specific star formation rate for tadpoles is roughly the same as field galaxies across the redshift range probed here). These average effects combined support the conclusion that this subset of galaxies is in an active phase of assembly, either late-stage merging or cold gas accretion causing localized clumpy star formation

  16. A MULTIWAVELENGTH STUDY OF TADPOLE GALAXIES IN THE HUBBLE ULTRA DEEP FIELD

    Straughn, Amber N.; Eufrasio, Rafael T.; Gardner, Jonathan P. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Voyer, Elysse N. [Randstad at Google, 1129 San Antonio Road, Palo Alto, CA (United States); Mello, Duilia de; Soto, Emmaris [Department of Physics, The Catholic University of America, Washington, DC 20064 (United States); Petty, Sara [Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States); Kassin, Susan; Ravindranath, Swara [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

    2015-12-01

    Multiwavelength data are essential in order to provide a complete picture of galaxy evolution and to inform studies of galaxies’ morphological properties across cosmic time. Here we present the results of a multiwavelength investigation of the morphologies of “tadpole” galaxies at intermediate redshift (0.314 < z < 3.175) in the Hubble Ultra Deep Field. These galaxies were previously selected from deep Hubble Space Telescope (HST) F775W data based on their distinct asymmetric knot-plus-tail morphologies. Here we use deep Wide Field Camera 3 near-infrared imaging in addition to the HST optical data in order to study the rest-frame UV/optical morphologies of these galaxies across the redshift range 0.3 < z < 3.2. This study reveals that the majority of these galaxies do retain their general asymmetric morphology in the rest-frame optical over this redshift range, if not the distinct “tadpole” shape. The average stellar mass of tadpole galaxies is lower than that of field galaxies, with the effect being slightly greater at higher redshift within the errors. Estimated from spectral energy distribution fits, the average age of tadpole galaxies is younger than that of field galaxies in the lower-redshift bin, and the average metallicity is lower (whereas the specific star formation rate for tadpoles is roughly the same as field galaxies across the redshift range probed here). These average effects combined support the conclusion that this subset of galaxies is in an active phase of assembly, either late-stage merging or cold gas accretion causing localized clumpy star formation.

  17. Host Galaxy Properties of the Swift BAT Ultra Hard X-Ray Selected AGN

    Koss, Michael; Mushotzky, Richard; Veilleux, Sylvain; Winter, Lisa M.; Baumgartner, Wayne; Tueller, Jack; Gehrels, Neil; Valencic, Lynne

    2011-01-01

    We have assembled the largest sample of ultra hard X-ray selected (14-195 keV) AGN with host galaxy optical data to date, with 185 nearby (zBAT) sample. The BAT AGN host galaxies have intermediate optical colors (u -- r and g -- r) that are bluer than a comparison sample of inactive galaxies and optically selected AGN from the Sloan Digital Sky Survey (SDSS) which are chosen to have the same stellar mass. Based on morphological classifications from the RC3 and the Galaxy Zoo, the bluer colors of BAT AGN are mainly due to a higher fraction of mergers and massive spirals than in the comparison samples. BAT AGN in massive galaxies (log Stellar Mass >10.5) have a 5 to 10 times higher rate of spiral morphologies than in SDSS AGN or inactive galaxies. We also see enhanced far-IR emission in BAT AGN suggestive of higher levels of star formation compared to the comparison samples. BAT AGN are preferentially found in the most massive host galaxies with high concentration indexes indicative of large bulge-to-disk ratios and large supermassive black holes. The narrow-line (NL) BAT AGN have similar intrinsic luminosities as the SDSS NL Seyferts based on measurements of [O III] Lambda 5007. There is also a correlation between the stellar mass and X-ray emission. The BAT AGN in mergers have bluer colors and greater ultra hard X-ray emission compared to the BAT sample as whole. In agreement with the Unified Model of AGN, and the relatively unbiased nature of the BAT sources, the host galaxy colors and morphologies are independent of measures of obscuration such as X-ray column density or Seyfert type. The high fraction of massive spiral galaxies and galaxy mergers in BAT AGN suggest that host galaxy morphology is related to the activation and fueling of local AGN.

  18. Size matters: abundance matching, galaxy sizes, and the Tully-Fisher relation in EAGLE

    Ferrero, Ismael; Navarro, Julio F.; Abadi, Mario G.; Sales, Laura V.; Bower, Richard G.; Crain, Robert A.; Frenk, Carlos S.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

    2017-02-01

    The Tully-Fisher relation (TFR) links the stellar mass of a disc galaxy, Mstr, to its rotation speed: it is well approximated by a power law, shows little scatter, and evolves weakly with redshift. The relation has been interpreted as reflecting the mass-velocity scaling (M ∝ V3) of dark matter haloes, but this interpretation has been called into question by abundance-matching (AM) models, which predict the galaxy-halo mass relation to deviate substantially from a single power law and to evolve rapidly with redshift. We study the TFR of luminous spirals and its relation to AM using the EAGLE set of Λ cold dark matter (ΛCDM) cosmological simulations. Matching both relations requires disc sizes to satisfy constraints given by the concentration of haloes and their response to galaxy assembly. EAGLE galaxies approximately match these constraints and show a tight mass-velocity scaling that compares favourably with the observed TFR. The TFR is degenerate to changes in galaxy formation efficiency and the mass-size relation; simulations that fail to match the galaxy stellar mass function may fit the observed TFR if galaxies follow a different mass-size relation. The small scatter in the simulated TFR results because, at fixed halo mass, galaxy mass and rotation speed correlate strongly, scattering galaxies along the main relation. EAGLE galaxies evolve with lookback time following approximately the prescriptions of AM models and the observed mass-size relation of bright spirals, leading to a weak TFR evolution consistent with observation out to z = 1. ΛCDM models that match both the abundance and size of galaxies as a function of stellar mass have no difficulty reproducing the observed TFR and its evolution.

  19. Triaxiality in elliptical galaxies

    Benacchio, L; Galletta, G [Padua Univ. (Italy). Ist. di Astronomia

    1980-12-01

    The existence of a triaxial shape for elliptical galaxies has been considered in recent years to explain the new kinematical and geometrical findings, i.e. (a) the low rotation/velocity dispersion ratio found also in some flat systems, (b) the presence of twisting in the isophotes, (c) the recently found correlation between maximum twisting and maximum flattening, (d) the presence of rotation along the minor axis. A simple geometrical model of elliptical galaxies having shells with different axial ratios c/a, b/a has been produced to interpret three fundamental key-features of elliptical galaxies: (i) the distribution of the maximum flattening observed; (ii) the percentage of ellipticals showing twisting; and (iii) the correlation between maximum twisting and maximum flattening. The model has been compared with observational data for 348 elliptical systems as given by Strom and Strom. It is found that a triaxial ellipsoid with coaxial shells having axial ratios c/a and b/a mutually dependent in a linear way can satisfy the observations.

  20. Angular momentum content of galaxies

    Shaya, E.J.; Tully, R.B.

    1984-01-01

    A schema of galaxy formation is developed in which the environmental influence of large-scale structure plays a dominant role. This schema was motivated by the observation that the fraction of E and S0 galaxies is much higher in clusters than in low-density regions and by an inference that those spirals that are found in clusters probably have fallen in relatively recently from the low-density regions. It is proposed that the tidal field of the Local Supercluster acts to determine the morphology of galaxies through two complementary mechanisms. In the first place, the supercluster can apply torques to protogalaxies. Galaxies which collapsed while expanding away from the central cluster decoupled from the external tidal field and conserved the angular momentum that they acquired before collapse. Galaxies which formed in the cluster while the cluster collapsed continued to feel the tidal field. In the latter case, the spin of outer collapsing layers can be halted and reversed, and tends to cancel the spin of inner layers. The result is a reduction of the total angular momentum content of the galaxy. In addition, the supercluster tidal field can regulate accretion of fresh material onto the galaxies since the field creates a Roche limit about galaxies and material beyond this limit is lost. Any material that has not collapsed onto a galaxy by the time the galaxy falls into a cluster will be tidally stripped. The angular momentum content of that part of the protogalactic cloud which has not yet collapsed . continues to grow linearly with time due to the continued torquing by the supercluster and neighbors. Galaxies at large distances from the cluster core can continue to accrete this high angular momentum material until the present, but galaxies that enter the cluster are cut off from replenishing material