Science.gov

Sample records for galaxy group implication

  1. Galaxy groups

    SciTech Connect

    Brent Tully, R.

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10{sup 12}M{sub ⊙} are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of Ω{sub matter}∼0.15 in a flat topology, with a 68% probability of being less than 0.44.

  2. INTERGALACTIC GAS IN GROUPS OF GALAXIES: IMPLICATIONS FOR DWARF SPHEROIDAL FORMATION AND THE MISSING BARYONS PROBLEM

    SciTech Connect

    Freeland, E.; Wilcots, E. E-mail: ewilcots@astro.wisc.edu

    2011-09-10

    Radio galaxies with bent jets are predominantly located in groups and clusters of galaxies. We use bent-double radio sources, under the assumption that their jets are bent by ram pressure, to probe intragroup medium (IGM) gas densities in galaxy groups. This method provides a direct measurement of the intergalactic gas density and allows us to probe intergalactic gas at large radii and in systems whose IGM is too cool to be detected by the current generation of X-ray telescopes. We find gas with densities of 10{sup -3} to 10{sup -4} cm{sup -3} at group radii from 15 to 700 kpc. A rough estimate of the total baryonic mass in intergalactic gas is consistent with the missing baryons being located in the IGM of galaxy groups. The neutral gas will be easily stripped from dwarf galaxies with total masses of 10{sup 6}-10{sup 7} M{sub sun} in the groups studied here. Indications are that intragroup gas densities in less-massive systems like the Local Group should be high enough to strip gas from dwarfs like Leo T and, in combination with tides, produce dwarf spheroidals.

  3. Diffuse X-ray emission from the NGC 2300 group of galaxies - Implications for dark matter and galaxy evolution in small groups

    NASA Technical Reports Server (NTRS)

    Mulchaey, John S.; Davis, David S.; Mushotzky, Richard F.; Burstein, David

    1993-01-01

    The discovery of diffuse X-ray emission from the NGC 2300 group of galaxies using the ROSAT Position Sensitive Proportional Counter is reported. The gas distributions is roughly symmetric and extends to a radius of at least 0.2/h(50) Mpc. A Raymond-Smith hot plasma model provides an excellent fit the X-ray spectrum with a best-fit value temperature of 0.9 + -/15 or - 0.14 keV and abundance 0.06 + 0/.12 or - 0.05 solar. The assumption of gravitational confinement leads to a total mass of the group of 3.0 + 0.4 or - 0.5 x 10 exp 13 solar. Baryons can reasonably account for 4 percent of this mass, and errors could push this number not higher than 10-15 percent. This is one of the strongest pieces of evidence that dark matter dominates small groups such as this one. The intragroup medium in this system has the lowest metal abundance yet found in diffuse gas in a group or cluster.

  4. Radio properties of fossil galaxy groups

    NASA Astrophysics Data System (ADS)

    Miraghaei, H.; Khosroshahi, H. G.

    2016-09-01

    We study 1.4 GHz radio properties of a sample of fossil galaxy groups using GMRT radio observations and the FIRST survey catalog. Fossil galaxy groups, having no recent major mergers in their dominant galaxies and also group scale mergers, give us the opportunity to investigate the effect of galaxy merger on AGN activity. In this work, we compare the radio properties of a rich sample of fossil groups with a sample of normal galaxy groups and clusters and show that the brightest group galaxies in fossil groups are under luminous at 1.4 GHz, relative to the general population of the brightest group galaxies, indicating that the dynamically relaxed nature of fossil groups has influenced the AGN activity in their dominant galaxy.

  5. Galaxy Group Properties in Observations and Simulations

    NASA Astrophysics Data System (ADS)

    Nurmi, Pasi

    2016-10-01

    In this project, we compare different properties of galaxy groups in cosmological N-body simulations and SDSS galaxy group catalogs. In the first part of the project (Nurmi et al. 2013) we compared the basic properties of the groups like the luminosity functions, group richness and velocity dispersion distributions and studied how good is the agreement between the mock group catalog and the SDSS group catalog. Here we continue the earlier study and use updated galaxy group catalog (SDSS DR10) and new simulation data (Guo et al. 2013). We reanalyse earlier group properties and include new properties in the analysis like group environment, star formation rates and group masses. Our analysis show that there are clear differences between the simulated and observed properties of galaxy groups, especially for small groups with a few members. Also, the high luminosities are clearly overestimated in the simulations compared with the SDSS group data.

  6. Numerical simulation of galaxies in the M81 galaxy group.

    NASA Astrophysics Data System (ADS)

    Li, P. S.; Thronson, H. A., Jr.

    The M81 galaxy group is a typical nearby galaxy group which consists of 15 members, including M82 and NGC 3077. Recent observations of the M81 group using the VLA (Yun, Ho, Lo, 1994) show a large scale H I map of the whole system, with M81, M82 and NGC 3077 inter-connected by a large amount of H I gas. In addition, two gas concentrations are observed at the eastern side of M81. The authors simulate the system numerically to reproduce the morphology, the spatial distribution of these 3 galaxies, and the H I gas surrounding the system.

  7. Properties of satellite galaxies in nearby groups

    NASA Astrophysics Data System (ADS)

    Vennik, Jaan

    2016-10-01

    We studied the variation of stellar mass and various star-formation characteristics of satellite galaxies in a volume limited sample of nearby groups as a function of their group-centric distance and of their relative line-of-sight velocity in the group rest frame. We found clear radial dependencies, e.g. massive, red and passive satellites being distributed predominantly near the center of composite group. We also found some evidence of velocity modulation of star-forming properties of satellite galaxies near the group virial radius. We conclude that using kinematical data, it should be feasible to separate dynamical classes of bound, in-falling and 'backsplash' satellite galaxies.

  8. Local Group Galaxy Emission-line Survey

    NASA Astrophysics Data System (ADS)

    Blaha, Cindy; Baildon, Taylor; Mehta, Shail; Garcia, Edgar; Massey, Philip; Hodge, Paul W.

    2015-01-01

    We present the results of the Local Group Galaxy Emission-line Survey of Hα emission regions in M31, M33 and seven dwarf galaxies in (NGC6822, IC10, WLM, Sextans A and B, Phoenix and Pegasus). Using data from the Local Group Galaxy Survey (LGGS - see Massey et al, 2006), we used continuum-subtracted Ha emission line images to define emission regions with a faint flux limit of 10 -17 ergs-sec-1-cm-2above the background. We have obtained photometric measurements for roughly 7450 Hα emission regions in M31, M33 and five of the seven dwarf galaxies (no regions for Phoenix or Pegasus). Using these regions, with boundaries defined by Hα-emission flux limits, we also measured fluxes for the continuum-subtracted [OIII] and [SII] images and constructed a catalog of Hα fluxes, region sizes and [OIII]/ Hα and [SII]/ Hα line ratios. The HII region luminosity functions and size distributions for the spiral galaxies M31 and M33 are compared with those of the dwarf galaxies NGC 6822 and IC10. For M31 and M33, the average [SII]/ Hα and [OIII]/ Hα line ratios, plotted as a function of galactocentric radius, display a linear trend with shallow slopes consistent with other studies of metallicity gradients in these galaxies. The galaxy-wide averages of [SII]/ Hα line ratios correlate with the masses of the dwarf galaxies following the previously established dwarf galaxy mass-metallicity relationship. The slope of the luminosity functions for the dwarf galaxies varies with galaxy mass. The Carleton Catalog of this Local Group Emission-line Survey will be made available on-line.

  9. Dynamical theory of dense groups of galaxies

    NASA Technical Reports Server (NTRS)

    Mamon, Gary A.

    1990-01-01

    It is well known that galaxies associate in groups and clusters. Perhaps 40% of all galaxies are found in groups of 4 to 20 galaxies (e.g., Tully 1987). Although most groups appear to be so loose that the galaxy interactions within them ought to be insignificant, the apparently densest groups, known as compact groups appear so dense when seen in projection onto the plane of the sky that their members often overlap. These groups thus appear as dense as the cores of rich clusters. The most popular catalog of compact groups, compiled by Hickson (1982), includes isolation among its selection critera. Therefore, in comparison with the cores of rich clusters, Hickson's compact groups (HCGs) appear to be the densest isolated regions in the Universe (in galaxies per unit volume), and thus provide in principle a clean laboratory for studying the competition of very strong gravitational interactions. The $64,000 question here is then: Are compact groups really bound systems as dense as they appear? If dense groups indeed exist, then one expects that each of the dynamical processes leading to the interaction of their member galaxies should be greatly enhanced. This leads us to the questions: How stable are dense groups? How do they form? And the related question, fascinating to any theorist: What dynamical processes predominate in dense groups of galaxies? If HCGs are not bound dense systems, but instead 1D change alignments (Mamon 1986, 1987; Walke & Mamon 1989) or 3D transient cores (Rose 1979) within larger looser systems of galaxies, then the relevant question is: How frequent are chance configurations within loose groups? Here, the author answers these last four questions after comparing in some detail the methods used and the results obtained in the different studies of dense groups.

  10. Galaxies in extreme environments: Isolated galaxies versus compact groups

    NASA Astrophysics Data System (ADS)

    Durbala, Adriana

    2009-06-01

    This Dissertation comprises two distinct studies of galaxies in dramatically different environments: extreme isolation versus compact groups. We emphasize empirically how "nature" (i.e. internal, secular processes) plays the dominant role in defining the evolution of isolated galaxies and how "nurture" dictates the fate of galaxies in very crowded environments. Two chapters report on a detailed photometric study of a well-defined sample of N ~100 isolated Sb-Sc spiral galaxies. Data source is Sloan Digital Sky Survey. Using i-band images we perform three kinds of measures: (a) bulge/disk/bar decomposition, (b) CAS parametrization (Concentration, Asymmetry, Clumpiness), and (c) Fourier decomposition/analysis of spiral arms and bar properties including dynamical measures of the torque. Having quantified a large set of properties we look for: (i) the interplay between different components of the same galaxy, (ii) trends along the morphological sequence Sb-Sbc-Sc, and (iii) statistical differences between our "isolated" sample and samples of galaxies of similar morphology constructed without regard for isolation. We find that the majority of isolated late-type disk galaxies host pseudobulges rather than classical bulges. The pseudobulges probably form through internal secular processes and bars may play an important role. A clear separation is noted between Sb and Sbc/Sc in various measures, i.e. the former are redder, brighter, have larger disks and bars, more luminous bulges, are more concentrated, more symmetric and dumpier than the latter. Isolated galaxies host larger bars than galaxies in samples defined without isolation constraints. Longer bars are not necessarily stronger, but show a higher contrast in Fourier analysis. Another chapter is a multiwavelength study of Seyfert's Sextet, the highest density galaxy aggregate in the local Universe. Four of its five galaxies are interpreted as remnant bulges of accreted spirals and are now embedded in a luminous halo

  11. Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the SMAKCED project. I. Kinematically decoupled cores and implications for infallen groups in clusters

    SciTech Connect

    Toloba, E.; Guhathakurta, P.; Boissier, S.; Boselli, A.; Den Brok, M.; Falcón-Barroso, J.; Ryś, A.; Janz, J.; Lisker, T.; Laurikainen, E.; Salo, H.; Paudel, S.

    2014-03-10

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  12. Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters

    NASA Astrophysics Data System (ADS)

    Toloba, E.; Guhathakurta, P.; van de Ven, G.; Boissier, S.; Boselli, A.; den Brok, M.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Paudel, S.; Peletier, R. F.; Ryś, A.; Salo, H.

    2014-03-01

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  13. The properties of fossil groups of galaxies

    NASA Astrophysics Data System (ADS)

    Eigenthaler, P.; Zeilinger, W. W.

    2009-12-01

    Numerical simulations as well as optical and X-ray observations over the last few years have shown that poor groups of galaxies can evolve to what is called a fossil group. Dynamical friction as the driving process leads to the coalescence of individual galaxies in ordinary poor groups leaving behind nothing more than a central, massive elliptical galaxy supposed to contain the merger history of the whole group. Due to merging timescales for less-massive galaxies and gas cooling timescales of the X-ray intragroup medium exceeding a Hubble time, a surrounding faint-galaxy population having survived this galactic cannibalism as well as an extended X-ray halo similar to that found in ordinary groups, is expected. Recent studies suggest that fossil groups are very abundant and could be the progenitors of brightest cluster galaxies (BCGs) in the centers of rich galaxy clusters. However, only a few objects are known to the literature. This article aims to summarize the results of observational fossil group research over the last few years and presents ongoing work by the authors. Complementary to previous research, the SDSS and RASS surveys have been cross-correlated to identify new fossil structures yielding 34 newly detected fossil group candidates. Observations with ISIS at the 4.2 m William Herschel Telescope on La Palma have been carried out to study the stellar populations of the central ellipticals of 6 fossil groups. In addition multi-object spectroscopy with VLTs VIMOS has been performed to study the shape of the OLF of one fossil system.

  14. Multiple Core Galaxies: Implications for M31

    NASA Technical Reports Server (NTRS)

    Smith, B. F.; Miller, R. H.; Cuzzi, Jeffrey N. (Technical Monitor)

    1994-01-01

    It is generally perceived that two cores cannot survive very long within the nuclear regions of a galaxy. The recent HST discovery of a double nucleus in M31 brings this question into prominence. Physical conditions in the nuclear regions of a typical galaxy help a second core survive so it can orbit for a long time, possibly for thousands of orbits. Given the nearly uniform mass density in a core, tidal forces within a core radius are compressive in all directions and help the core survive the buffeting it takes as it orbits near the center of the galaxy. We use numerical experiments to illustrate these physical principles. Modifications to the experimental method allow the full power of the experiments to be concentrated on the nuclear regions. Spatial resolution of about 0.2 parsec comfortably resolves detail within the 1.4 parsec core radius of the second, but brighter, core (P1) in M31. The same physical principles apply in other astronomical situations, such as dumbbell galaxies, galaxies orbiting near the center of a galaxy cluster, and subclustering in galaxy clusters. The experiments also illustrate that galaxy encounters and merging are quite sensitive to external tidal forces, such as those produced by the gravitational potential in a group or cluster of galaxies.

  15. Neutral Hydrogen in Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Grcevich, Jana

    The gas content of the faintest and lowest mass dwarf galaxies provide means to study the evolution of these unique objects. The evolutionary histories of low mass dwarf galaxies are interesting in their own right, but may also provide insight into fundamental cosmological problems. These include the nature of dark matter, the disagreement between the number of observed Local Group dwarf galaxies and that predicted by lambda cold dark matter models, and the discrepancy between the observed census of baryonic matter in the Milky Way's environment and theoretical predictions. This thesis explores these questions by studying the neutral hydrogen (HI) component of dwarf galaxies. First, limits on the HI mass of the ultra-faint dwarfs are presented, and the HI content of all Local Group dwarf galaxies is examined from an environmental standpoint. We find that those Local Group dwarfs within 270 kpc of a massive host galaxy are deficient in HI as compared to those at larger galactocentric distances. Ram-pressure arguments are invoked, which suggest halo densities greater than 2-3 x 10-4 cm-3 out to distances of at least 70 kpc, values which are consistent with theoretical models and suggest the halo may harbor a large fraction of the host galaxy's baryons. We also find that accounting for the incompleteness of the dwarf galaxy count, known dwarf galaxies whose gas has been removed could have provided at most 2.1 x 108 M⊙ of HI gas to the Milky Way. Second, we examine the possibility of discovering unknown gas-rich ultra-faint galaxies in the Local Group using HI. The GALFA-HI Survey catalog is searched for compact, isolated HI clouds which are most similar to the expected HI characteristics of low mass dwarf galaxies. Fifty-one Local Group dwarf galaxy candidates are identified through column density, brightness temperature, and kinematic selection criteria, and their properties are explored. Third, we present hydrodynamic simulations of dwarf galaxies experiencing a

  16. AGN feedback in galaxy clusters and groups

    NASA Astrophysics Data System (ADS)

    Hardcastle, Martin

    2016-07-01

    Mechanical feedback via Active Galactic Nuclei (AGN) jets in the centres of galaxy groups and clusters is a crucial ingredient in current models of galaxy formation and cluster evolution. Jet feedback is believed to regulate gas cooling and thus star formation in the most massive galaxies, but a robust physical understanding of this feedback mode is currently lacking. Athena will provide (1) the first kinematic measurements on relevant spatial scales of the hot gas in galaxy, group and cluster haloes as it absorbs the impact of AGN jets, and (2) vastly improved ability to map thermodynamic conditions on scales well-matched to the jets, lobes and gas disturbances produced by them. I will present new predictions of Athena's ability to measure the energetic impact of powerful jets based on our most recent set of numerical models.

  17. HI in Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Grcevich, Jana; Putman, M. E.; Peek, J. E. G.

    2007-12-01

    The HI content of the newly discovered satellites of the Milky Way has not been previously studied. We use HIPASS (HI Parkes All Sky Survey), LAB (Leiden/Argentine/Bonn), and GALFA (Galactic Arecibo L-band Feed Array) survey data to explore HI in the environment of the newly discovered dwarf galaxies and add this information to what was previously known about HI in the dwarf spheroidal and lower mass dwarf irregular galaxies of the Local Group. All of the new satellites discovered in the Sloan Digital Sky Survey data have limits on their HI masses which range from < 13 M⊙ to 3 x 104 M⊙ except for Leo T, which has an HI mass of approximately 105 M⊙. We find that galaxies within 300 kpc of the Milky Way or Andromeda are all undetected in HI to low limits, or have ambiguous detections, while those further than 300 kpc are predominantly detected with masses > 105 M⊙. The most favored explanation for the lack of HI in dwarf galaxies at small galactocentric distances is ram pressure stripping of the gas in the dwarf galaxy by the larger galaxy's hot halo gas. The HI content will also be discussed in terms of the fuel it provides to the Milky Way and the star formation history of the dwarfs. Finally, we discuss the discovery in the GALFA data of discrete HI clouds with dynamical characteristics similar to known dwarf galaxies.

  18. HI in Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Grcevich, Jana; Putman, Mary; Peek, Joshua E. G.

    2008-08-01

    The HI content of the newly discovered satellites of the Milky Way has not been previously studied. We use HIPASS (HI Parkes All Sky Survey), LAB (Leiden/Argentine/Bonn), and GALFA (Galactic Arecibo L-band Feed Array) survey data to explore HI in the environment of the newly discovered dwarf galaxies and add this information to what was previously known about HI in the dwarf spheroidal and lower mass dwarf irregular galaxies of the Local Group. All of the new satellites discovered in the Sloan Digital Sky Survey data have limits on their HI masses which range from <13 Msolar to 3×104 Msolar except for Leo T, which has and HI mass of approximately 105 Msolar. We find that galaxies within 300 kpc of the Milky Way or Andromeda are all undetected in HI to low limits, or have ambiguous detections, while those further than 300 kpc are predominantly detected with masses >105 Msolar. The most favored explanation for the lack of HI in dwarf galaxies at small galactocentric distances is ram pressure stripping of the gas in the dwarf galaxy by the larger galaxy's hot halo gas. Finally, we discuss the discovery in the GALFA data of discrete HI clouds with characteristics similar to known dwarf galaxies.

  19. Stellar halos around Local Group galaxies

    NASA Astrophysics Data System (ADS)

    McConnachie, Alan W.

    2016-08-01

    The Local Group is now home to 102 known galaxies and candidates, with many new faint galaxies continuing to be discovered. The total stellar mass range spanned by this population covers a factor of close to a billion, from the faintest systems with stellar masses of order a few thousand to the Milky Way and Andromeda, with stellar masses of order 1011 M ⊙. Here, I discuss the evidence for stellar halos surrounding Local Group galaxies spanning from dwarf scales (with the case of the Andromeda II dwarf spheroidal), though to intermediate mass systems (M33) and finishing with M31. Evidence of extended stellar populations and merging is seen across the luminosity function, indicating that the processes that lead to halo formation are common at all mass scales.

  20. Choirs H I galaxy groups: The metallicity of dwarf galaxies

    SciTech Connect

    Sweet, Sarah M.; Drinkwater, Michael J.; Meurer, Gerhardt; Bekki, Kenji; Dopita, Michael A.; Nicholls, David C.; Kilborn, Virginia

    2014-02-10

    We present a recalibration of the luminosity-metallicity relation for gas-rich, star-forming dwarfs to magnitudes as faint as M{sub R} ∼ –13. We use the Dopita et al. metallicity calibrations to calibrate the relation for all the data in this analysis. In metallicity-luminosity space, we find two subpopulations within a sample of high-confidence Sloan Digital Sky Survey (SDSS) DR8 star-forming galaxies: 52% are metal-rich giants and 48% are metal-medium galaxies. Metal-rich dwarfs classified as tidal dwarf galaxy (TDG) candidates in the literature are typically of metallicity 12 + log(O/H) = 8.70 ± 0.05, while SDSS dwarfs fainter than M{sub R} = –16 have a mean metallicity of 12 + log(O/H) = 8.28 ± 0.10, regardless of their luminosity, indicating that there is an approximate floor to the metallicity of low-luminosity galaxies. Our hydrodynamical simulations predict that TDGs should have metallicities elevated above the normal luminosity-metallicity relation. Metallicity can therefore be a useful diagnostic for identifying TDG candidate populations in the absence of tidal tails. At magnitudes brighter than M{sub R} ∼ –16, our sample of 53 star-forming galaxies in 9 H I gas-rich groups is consistent with the normal relation defined by the SDSS sample. At fainter magnitudes, there is an increase in dispersion of the metallicity of our sample, suggestive of a wide range of H I content and environment. In our sample, we identify three (16% of dwarfs) strong TDG candidates (12 + log(O/H) > 8.6) and four (21%) very metal-poor dwarfs (12 + log(O/H) < 8.0), which are likely gas-rich dwarfs with recently ignited star formation.

  1. Segregation effects in DEEP2 galaxy groups

    NASA Astrophysics Data System (ADS)

    Nascimento, R. S.; Ribeiro, A. L. B.; Lopes, P. A. A.

    2016-09-01

    We investigate segregation phenomena in galaxy groups in the range of 0.2 < z < 1. We study a sample of groups selected from the 4th Data Release of the DEEP2 galaxy redshift survey. We used only groups with at least 8 members within a radius of 4 Mpc. Outliers were removed with the shifting gapper techinque and, then, the virial properties were estimated for each group. The sample was divided into two stacked systems: low(z ≤ 0.6) and high (z > 0.6) redshift groups. Assuming that the color index (U - B)0 can be used as a proxy for the galaxy type, we found that the fraction of blue (star-forming) objects is higher in the high-z sample, with blue objects being dominant at MB > -19.5 for both samples, and red objects being dominant at MB < -19.5 only for the low-z sample. Also, the radial variation of the red fraction indicates that there are more red objects with R < R200 in the low-z sample than in the high-z sample. Our analysis indicates statistical evidence of kinematic segregation, at the 99% c.l., for the low-z sample: redder and brighter galaxies present lower velocity dispersions than bluer and fainter ones. We also find a weaker evidence for spatial segregation between red and blue objects, at the 70% c.l. The analysis of the high-z sample reveals a different result: red and blue galaxies have velocity dispersion distributions not statistically distinct, although redder objects are more concentrated than the bluer ones at the 95% c.l. From the comparison of blue/red and bright/faint fractions, and considering the approximate lookback timescale between the two samples (˜3 Gyr), our results are consistent with a scenario where bright red galaxies had time to reach energy equipartition, while faint blue/red galaxies in the outskirts infall to the inner parts of the groups, thus reducing spatial segregation from z ˜ 0.8 to z ˜ 0.4.

  2. Intracluster Light in Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    DeMaio, Tahlia; Gonzalez, Anthony; Zabludoff, Ann I.; Zaritsky, Dennis F.

    2016-01-01

    We present recent results from our study on the origin and assembly history of the intracluster starlight (ICL) for a sample of 29 galaxy groups and clusters with 3x1013groups and clusters show clear negative color gradients. Such negative colour (and equivalently, metallicity) gradients can arise from tidal stripping of L* galaxies and/or the disruption of dwarf galaxies, but not major mergers with the brightest cluster galaxy (BCG). We also find ICL luminosities of 3-9 L* in the range 10 < r < 110 kpc for these clusters. Dwarf disruption alone cannot explain the total luminosity of the ICL and remain consistent with the observed evolution in the faint-end slope of the luminosity function. The results of our study are suggestive of a formation history in which the ICL is built-up by a combination of stripping of L* galaxies and/or dwarf disruption and disfavor significant contribution by major mergers with the BCG.This sample of groups and clusters is the largest with HST/WFC3 data for ICL analysis that spans two orders of magnitude in halo mass at redshifts >0.3. Because of this we can investigate how the ICL color profile changes as a function of cluster mass for the first time, as well as expand previous studies of the changing fraction of cluster luminosity that is contained in the BCG+ICL as a function of halo mass. We present our preliminary results and describe our next steps using this sample to investigate the intracluster light in massive halos.

  3. The circular velocity function of group galaxies

    SciTech Connect

    Abramson, Louis E.; Williams, Rik J.; Benson, Andrew J.; Kollmeier, Juna A.; Mulchaey, John S.

    2014-09-20

    A robust prediction of ΛCDM cosmology is the halo circular velocity function (CVF), a dynamical cousin of the halo mass function. The correspondence between theoretical and observed CVFs is uncertain, however: cluster galaxies are reported to exhibit a power-law CVF consistent with N-body simulations, but that of the field is distinctly Schechter-like, flattened compared to ΛCDM expectations at circular velocities v {sub c} ≲ 200 km s{sup –1}. Groups offer a powerful probe of the role environment plays in this discrepancy as they bridge the field and clusters. Here, we construct the CVF for a large, mass- and multiplicity-complete sample of group galaxies from the Sloan Digital Sky Survey. Using independent photometric v {sub c} estimators, we find no transition from field to ΛCDM-shaped CVF above v {sub c} = 50 km s{sup –1} as a function of group halo mass. All groups with 12.4 ≲ log M {sub halo}/M {sub ☉} ≲ 15.1 (Local Group analogs to rich clusters) display similar Schechter-like CVFs marginally suppressed at low v {sub c} compared to that of the field. Conversely, some agreement with N-body results emerges for samples saturated with late-type galaxies, with isolated late-types displaying a CVF similar in shape to ΛCDM predictions. We conclude that the flattening of the low-v {sub c} slope in groups is due to their depressed late-type fractions—environment affecting the CVF only to the extent that it correlates with this quantity—and that previous cluster analyses may suffer from interloper contamination. These results serve as useful benchmarks for cosmological simulations of galaxy formation.

  4. Diverse Group of Galaxy Types, NGC 3190 Field

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Ultraviolet image of a diverse group of galaxy types. NGC 3190 is a dusty edge on spiral galaxy. NGC 3187 is highly distorted. The two are separated by only 35 kilo-parsecs (about half the diameter of our own Milky Way galaxy). A ring, elliptical, and other irregular galaxies are also present.

  5. The evolution of galaxy groups and clusters

    NASA Astrophysics Data System (ADS)

    Mazzotta, Pasquale

    2016-07-01

    The Athena mission will implement the Hot and Energetic Universe science theme which poses the question of How does ordinary matter assemble into the large-scale structures we see today?. Groups and Galaxy clusters are key laboratories to understand the role of the various physical processes governing the baryonic matter from the kilo-parsec scale of super-massive black holes to the mega-parsec one of the clusters outskirts on assembling and evolving large scale structures. We will focus on the study of the galaxy groups and clusters evolution with the Athen a mission. We will review the status of current constraints in light of the newest results obtained from state of the art cosmological simulations and will discuss the perspectives out to the mission launch time in 2028.

  6. Fossil groups of galaxies: Are they groups? Are they fossils?

    NASA Astrophysics Data System (ADS)

    Dupke, Renato de Alencar; Miller, Eric; de Oliveira, Claudia Mendes; Sodre, Laerte; Rykoff, Eli; de Oliveira, Raimundo Lopes; Proctor, Rob

    2010-11-01

    Fossil groups present a puzzle to current theories of structure formation. Despite the low number of bright galaxies, their high velocity dispersions and high TX indicate cluster-like potential wells. Measured concentration parameters seem very high indicating early formation epochs in contradiction with the observed lack of large and well defined cooling cores. There are very few fossil groups with good quality X-ray data and their idiosyncrasies may enhance these apparent contradictions. The standard explanation for their formation suggests that bright galaxies within half the virial radii of these systems were wiped out by cannibalism forming the central galaxy. Since dry mergers, typically invoked to explain the formation of the central galaxies, are not expected to change the IGM energetics significantly, thus not preventing the formation of cooling cores, we investigate the scenario where recent gaseous (wet) mergers formed the central galaxy injecting energy and changing the chemistry of the IGM in fossil groups. We show a test for this scenario using fossil groups with enough X-ray flux in the Chandra X-ray Observatory archive by looking at individual metal abundance ratio distributions near the core. Secondary SN II powered winds would tend to erase the dominance of SN IA ejecta in the core of these systems and would help to erase previously existing cold cores. Strong SN II-powered galactic winds resulting from galaxy merging would be trapped by their deep potential wells reducing the central enhancement of SN Ia/SN II iron mass fraction ratio. The results indicate that there is a decrement in the ratio of SN Ia to SN II iron mass fraction in the central regions of the systems analyzed, varying from 99±1% in the outer regions to 85±2% within the cooling radius (Figure 1) and would inject enough energy into the IGM preventing central gas cooling. The results are consistent with a scenario of later formation epoch for fossil groups, as they are defined

  7. THE VELOCITY FIELD AROUND GROUPS OF GALAXIES

    SciTech Connect

    Hartwick, F. D. A.

    2011-06-15

    A statistical method is presented for determining the velocity field in the immediate vicinity of groups of galaxies using only positional and redshift information with the goal of studying the perturbation of the Hubble flow around groups more distant than the Local Group. The velocities are assumed to obey a Hubble-like expansion law, i.e., V = H{sub exp} R, where the expansion rate H{sub exp} is to be determined. The method is applied to a large, representative group catalog and evidence is found for a sub-Hubble expansion rate within two well-defined radii beyond the virial radii of the groups. This result is consistent with that of Teerikorpi et al. who found a similar expansion law around three nearby groups and extends it to a more representative volume of space.

  8. The global warming of group satellite galaxies

    NASA Astrophysics Data System (ADS)

    Yozin, C.; Bekki, K.

    2016-08-01

    Recent studies adopting λRe, a proxy for specific angular momentum, have highlighted how early-type galaxies (ETGs) are composed of two kinematical classes for which distinct formation mechanisms can be inferred. With upcoming surveys expected to obtain λRe from a broad range of environments (e.g. SAMI, MaNGA), we investigate in this numerical study how the λRe-ɛe distribution of fast-rotating dwarf satellite galaxies reflects their evolutionary state. By combining N-body/SPH simulations of progenitor disc galaxies (stellar mass ≃109 M⊙), their cosmologically-motivated sub-halo infall history and a characteristic group orbit/potential, we demonstrate the evolution of a satellite ETG population driven by tidal interactions (e.g. harassment). As a general result, these satellites remain intrinsically fast-rotating oblate stellar systems since their infall as early as z = 2; mis-identifications as slow rotators often arise due to a bar/spiral lifecycle which plays an integral role in their evolution. Despite the idealistic nature of its construction, our mock λRe-ɛe distribution at z < 0.1 reproduces its observational counterpart from the ATLAS3D/SAURON projects. We predict therefore how the observed λRe-ɛe distribution of a group evolves according to these ensemble tidal interactions.

  9. A COMPARISON OF THE CLUSTERING PROPERTIES BETWEEN GALAXIES AND GROUPS OF GALAXIES

    SciTech Connect

    Deng Xinfa

    2013-03-01

    In this study, I apply cluster analysis and perform comparative studies of clustering properties between galaxies and groups of galaxies. It is found that the number of objects N{sub max} of the richest system and the maximal length D{sub max} of the largest system for groups in all samples are apparently larger than ones for galaxies, and that galaxies preferentially form isolated, paired, and small systems, while groups preferentially form grouped and clustered systems. These results show that groups are more strongly clustered than galaxies, which is consistent with statistical results of the correlation function.

  10. Evolution of Galaxy Groups in the Illustris Simulation

    NASA Astrophysics Data System (ADS)

    Raouf, Mojtaba; Khosroshahi, Habib G.; Dariush, A.

    2016-06-01

    We present the first study of the evolution of galaxy groups in the Illustris simulation. We focus on dynamically relaxed and unrelaxed galaxy groups representing dynamically evolved and evolving galaxy systems, respectively. The evolutionary state of a group is probed from its luminosity gap and separation between the brightest group galaxy and the center of mass of the group members. We find that the Illustris simulation overproduces galaxy systems with a large luminosity gap, known as fossil systems, in comparison to observations and the probed semi-analytical predictions. However, this simulation is just as successful as the probed semi-analytic model in recovering the correlation between luminosity gap and offset of the luminosity centroid. We find evolutionary tracks based on luminosity gap that indicate that a group with a large luminosity gap is rooted in one with a small luminosity gap, regardless of the position of the brightest group galaxy within the halo. This simulation helps to explore, for the first time, the black hole mass and its accretion rate in galaxy groups. For a given stellar mass of the brightest group galaxies, the black hole mass is larger in dynamically relaxed groups with a lower rate of mass accretion. We find this to be consistent with the latest observational studies of radio activity in the brightest group galaxies in fossil groups. We also find that the intragalactic medium in dynamically evolved groups is hotter for a given halo mass than that in evolving groups, again consistent with earlier observational studies.

  11. Impact of High Velocity Interactions on Galaxy Evolution in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Machacek, Marie E.; Jones, C.; Forman, W. R.; Kraft, R. P.; Ashby, M. L.; Hardcastle, M. J.

    2007-05-01

    Galaxy interactions in cool groups dominate galaxy evolution at high redshift. Observations of galaxies interacting in nearby galaxy groups, where the same dynamical processes that transform galaxies at high redshift can be studied in detail, are critical to our understanding of galaxy and group evolution. X-ray observations of hot gas features, e.g. surface brightness edges and wakes, reveal that high velocity interactions play a significant role in the transformation of galaxies in groups, yet, because these encounters are difficult to identify in other wavebands, few have been studied. We present two case studies of high velocity galaxy-galaxy and galaxy-gas interactions in galaxy groups: NGC4782(3C278) and NGC4783 in LGG316, and NGC6872 and NGC6876 in the Pavo group. From Chandra and XMM-Newton X-ray data, we measure the hot gas temperature, density and metal abundance in the galaxies and the intragroup medium (IGM) to characterize the thermodynamic state of the group, constrain 3D motions of the galaxies through the IGM, and determine the dominant processes transferring matter and energy between the galaxy and group gas. We compare these results with VLA observations of NGC4782/3 and Spitzer IRAC observations of NGC6872 and NGC6876 to study the impact of these interactions on nuclear activity, radio jet evolution, and star formation in these galaxies, and on the heating and enrichment of the IGM. This work was supported in part by the Smithsonian Institution, the Chandra Science Center, NASA contracts AR5-6011X, GO6-7068X, NNX06AG34G, JPL1279244 and the Royal Society.

  12. Optical and X-ray Properties of Groups of Galaxies

    NASA Astrophysics Data System (ADS)

    dell'Antonio, I. P.; Geller, M. J.; Fabricant, D.

    1992-12-01

    We study the optical and x-ray properties of 30 groups of galaxies observed with EINSTEIN. We have obtained redshifts for the galaxies in the group fields down to a limiting magnitude M_B<= 15.7. Typically this corresponds to ~ 18 redshifts per group. Our sample contains 14 MKW-AWM clusters, three of which are actually superpositions of two groups. We compare the velocity dispersions and virial masses we derive from the optical data with the x-ray luminosity and structure. We find remarkable correlations between the x-ray structure and optical galaxy positions. The x-ray emission associated with the galaxies is extended even in more distant groups. This emission is probably due to hot gas in the individual galaxy potentials, which implies that the poor clusters of galaxies are dynamically young. This is consistent with results from N-body simulations of group formation.

  13. NUV signatures of environment driven galaxy quenching in SDSS groups

    NASA Astrophysics Data System (ADS)

    Crossett, Jacob P.; Pimbblet, Kevin A.; Jones, D. Heath; Brown, Michael J. I.; Stott, John P.

    2016-09-01

    We have investigated the effect of group environment on residual star formation in galaxies, using GALEX NUV galaxy photometry with the SDSS group catalogue of Yang et al. (2007). We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass matched samples of satellite (non-central), and non-grouped galaxies, we found a >4σ difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction >3σ higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of ˜2 lower for satellite galaxies between 1010.5M⊙ and 1010.7M⊙, showing that higher mass galaxies are more able to form stars when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower Sérsic indices (n < 3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot (2003) with multiple burst, or exponentially declining star formation histories to find that many of the (NUV - r) blue non-grouped galaxies can be explained by a slow (˜2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV - r) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur.

  14. THE EVOLUTION OF CENTRAL GROUP GALAXIES IN HYDRODYNAMICAL SIMULATIONS

    SciTech Connect

    Feldmann, R.; Carollo, C. M.; Mayer, L.; Lake, G.; Renzini, A.; Quinn, T.; Stinson, G. S.; Yepes, G.

    2010-01-20

    We trace the evolution of central galaxies in three approx10{sup 13} M{sub sun} galaxy groups simulated at high resolution in cosmological hydrodynamical simulations. In all three cases, the evolution in the group potential leads, at z = 0, to central galaxies that are massive, gas-poor early-type systems supported by stellar velocity dispersion and which resemble either elliptical or S0 galaxies. Their z approx 2-2.5 main progenitors are massive (M{sub *} approx (3-10) x 10{sup 10} M{sub sun}), star-forming (20-60 M{sub sun} yr{sup -1}) galaxies which host substantial reservoirs of cold gas (approx5 x 10{sup 9} M{sub sun}) in extended gas disks. Our simulations thus show that star-forming galaxies observed at z approx 2 are likely the main progenitors of central galaxies in galaxy groups at z = 0. At z approx 2 the stellar component of all galaxies is compact, with a half-mass radius <1 kpc. The central stellar density stays approximatively constant from such early epochs down to z = 0. Instead, the galaxies grow inside out, by acquiring a stellar envelope outside the innermost approx2 kpc. Consequently the density within the effective radius decreases by up to 2 orders of magnitude. Both major and minor mergers contribute to most (70{sup +20}{sub -15}%) of the mass accreted outside the effective radius and thus drive an episodical evolution of the half-mass radii, particularly below z = 1. In situ star formation and secular evolution processes contribute to 14{sup +18}{sub -9}% and 16{sup +6}{sub -11}%, respectively. Overall, the simulated galaxies grow by a factor approx4-5 in mass and size since redshift z approx 2. The short cooling time in the center of groups can foster a 'hot accretion' mode. In one of the three simulated groups this leads to a dramatic rejuvenation of the central group galaxy at z < 1, affecting its morphology, kinematics, and colors. This episode is eventually terminated by a group-group merger. Mergers also appear to be responsible for

  15. The Evolution of Central Group Galaxies in Hydrodynamical Simulations

    NASA Astrophysics Data System (ADS)

    Feldmann, R.; Carollo, C. M.; Mayer, L.; Renzini, A.; Lake, G.; Quinn, T.; Stinson, G. S.; Yepes, G.

    2010-01-01

    We trace the evolution of central galaxies in three ~1013 M sun galaxy groups simulated at high resolution in cosmological hydrodynamical simulations. In all three cases, the evolution in the group potential leads, at z = 0, to central galaxies that are massive, gas-poor early-type systems supported by stellar velocity dispersion and which resemble either elliptical or S0 galaxies. Their z ~ 2-2.5 main progenitors are massive (M * ~ (3-10) × 1010 M sun), star-forming (20-60 M sun yr-1) galaxies which host substantial reservoirs of cold gas (~5 × 109 M sun) in extended gas disks. Our simulations thus show that star-forming galaxies observed at z ~ 2 are likely the main progenitors of central galaxies in galaxy groups at z = 0. At z ~ 2 the stellar component of all galaxies is compact, with a half-mass radius <1 kpc. The central stellar density stays approximatively constant from such early epochs down to z = 0. Instead, the galaxies grow inside out, by acquiring a stellar envelope outside the innermost ~2 kpc. Consequently the density within the effective radius decreases by up to 2 orders of magnitude. Both major and minor mergers contribute to most (70+20 -15%) of the mass accreted outside the effective radius and thus drive an episodical evolution of the half-mass radii, particularly below z = 1. In situ star formation and secular evolution processes contribute to 14+18 -9% and 16+6 -11%, respectively. Overall, the simulated galaxies grow by a factor ~4-5 in mass and size since redshift z ~ 2. The short cooling time in the center of groups can foster a "hot accretion" mode. In one of the three simulated groups this leads to a dramatic rejuvenation of the central group galaxy at z < 1, affecting its morphology, kinematics, and colors. This episode is eventually terminated by a group-group merger. Mergers also appear to be responsible for the suppression of cooling flows in the other two groups. Passive stellar evolution and minor galaxy mergers gradually restore

  16. Local Group dwarf galaxies: nature and nurture

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Scannapieco, Cecilia; White, Simon

    2012-02-01

    We investigate the formation and evolution of dwarf galaxies in a high-resolution, hydrodynamical cosmological simulation of a Milky Way sized halo and its environment. Our simulation includes gas cooling, star formation, supernova feedback, metal enrichment and ultraviolet heating. In total, 90 satellites and more than 400 isolated dwarf galaxies are formed in the simulation, allowing a systematic study of the internal and environmental processes that determine their evolution. We find that 95 per cent of satellite galaxies are gas free at z= 0, and identify three mechanisms for gas loss: supernova feedback, tidal stripping and photoevaporation due to re-ionization. Gas-rich satellite galaxies are only found with total masses above ˜5 × 109 M⊙. In contrast, for isolated dwarf galaxies, a total mass of ˜109 M⊙ constitutes a sharp transition; less massive galaxies are predominantly gas free at z= 0, more massive, isolated dwarf galaxies are often able to retain their gas. In general, we find that the total mass of a dwarf galaxy is the main factor which determines its star formation, metal enrichment and its gas content, but that stripping may explain the observed difference in gas content between field dwarf galaxies and satellites with total masses close to 109 M⊙. We also find that a morphological transformation via tidal stripping of infalling, luminous dwarf galaxies whose dark matter is less concentrated than their stars cannot explain the high total mass-to-light ratios of the faint dwarf spheroidal galaxies.

  17. 3D structure of nearby groups of galaxies

    NASA Astrophysics Data System (ADS)

    Makarova, L.; Makarov, D.; Klypin, A.; Gottlöber, S.

    2016-10-01

    Using high accuracy distance estimates, we study the three-dimensional distribution of galaxies in five galaxy groups at a distance less than 5 Mpc from the Milky Way. Due to proximity of these groups our sample of galaxies is nearly complete down to extremely small dwarf galaxies with absolute magnitudes M B = -12. We find that the average number-density profile of the groups shows a steep power-law decline dn/dV ˜ R-3 at distances R=(100-500) kpc consistent with predictions of the standard cosmological model. We also find that there is no indication of a truncation or a cutoff in the density at the expected virial radius: the density profile extends at least to 1.5 Mpc. Vast majority of galaxies within 1.5 Mpc radius around group centres are gas-rich star-forming galaxies. Early-type galaxies are found only in the central ˜ 300 kpc region. Lack of dwarf spheroidal and dwarf elliptical galaxies in the field and in the outskirts of large groups is a clear indication that these galaxies experienced morphological transformation when they came close to the central region of forming galaxy group.

  18. On the formation of polar ring galaxies and tidal dwarf galaxies in gas-rich galaxy groups

    NASA Astrophysics Data System (ADS)

    Kilborn, Virginia; Sweet, Sarah; Meurer, Gerhardt; Drinkwater, Michael

    2015-08-01

    We are conducting a study of the properties of galaxies and dwarfs in 16 gas-rich galaxy groups identified in the Survey for Ionization in Neutral Gas Galaxies (SINGG; Meurer et al. 2006). We have found a young gas-rich coalescing galaxy group, J1051-17. Key features of this system are gas-rich tidal tails, studded with dwarf galaxies extending 200 kpc which merge in to a low surface brightness polar disk orbiting a very red edge-on host hosting a central AGN. Accretion from the polar disk may be feeding the AGN and powering a galactic wind. The example of this system suggests that tidal interactions with gas rich satellites may be a key process that aligns satellites in to polar planes while fuelling accretion down to the very centres of the host. We discuss the formation scenario of this polar ring galaxy, and investigate the formation of tidal dwarf galaxies in the wider group sample.

  19. Multifrequency studies of galaxies and groups. I. Environmental effect on galaxy stellar mass and morphology

    NASA Astrophysics Data System (ADS)

    Poudel, A.; Heinämäki, P.; Nurmi, P.; Teerikorpi, P.; Tempel, E.; Lietzen, H.; Einasto, M.

    2016-05-01

    Context. To understand the role of the environment in galaxy formation, evolution, and present-day properties, it is essential to study the multifrequency behavior of different galaxy populations under various environmental conditions. Aims: We study the stellar mass functions of different galaxy populations in groups as a function of their large-scale environments using multifrequency observations. Methods: We cross-matched the SDSS DR10 group catalog with GAMA Data Release 2 and Wide-field Survey Explorer (WISE) data to construct a catalog of 1651 groups and 11 436 galaxies containing photometric information in 15 different wavebands ranging from ultraviolet (0.152 μm) to mid-infrared (22 μm). We performed the spectral energy distribution (SED) fitting of galaxies using the MAGPHYS code and estimate the rest-frame luminosities and stellar masses. We used the 1 /Vmax method to estimate the galaxy stellar mass and luminosity functions, and the luminosity density field of galaxies to define the large-scale environment of galaxies. Results: The stellar mass functions of both central and satellite galaxies in groups are different in low- and high-density, large-scale environments. Satellite galaxies in high-density environments have a steeper low-mass end slope compared to low-density environments, independent of the galaxy morphology. Central galaxies in low-density environments have a steeper low-mass end slope, but the difference disappears for fixed galaxy morphology. The characteristic stellar mass of satellite galaxies is higher in high-density environments and the difference exists only for galaxies with elliptical morphologies. Conclusions: Galaxy formation in groups is more efficient in high-density, large-scale environments. Groups in high-density environments have higher abundances of satellite galaxies, irrespective of the satellite galaxy morphology. The elliptical satellite galaxies are generally more massive in high-density environments. The stellar

  20. Automatic Detection of Galaxy Groups by Probabilistic Hough Transform

    NASA Astrophysics Data System (ADS)

    Ibrahem, R. T.; Tino, P.; Pearson, R. J.; Ponman, T. J.; Babul, A.

    2015-12-01

    Galaxy groups play a significant role in explaining the evolution of the universe. Given the amounts of available survey data, automated discovery of galaxy groups is of utmost interest. We introduce a novel methodology, based on probabilistic Hough transform, for finding galaxy groups embedded in a rich background. The model takes advantage of a typical signature pattern of galaxy groups known as "fingers-of-God". It also allows us to include prior astrophysical knowledge as an inherent part of the method. The proposed method is first tested in large scale controlled experiments with 2-D patterns and then verified on 3-D realistic mock data (comparing with the well-known friends-of-friends method used in astrophysics). The experiments suggest that our methodology is a promising new candidate for galaxy group finders developed within a machine learning framework.

  1. The statistical nature of the brightest group galaxies

    SciTech Connect

    Shen, Shiyin; Yang, Xiaohu; Mo, Houjun; Van den Bosch, Frank; More, Surhud

    2014-02-10

    We examine the statistical properties of the brightest group galaxies (BGGs) by using a complete spectroscopic sample of groups/clusters of galaxies selected from the Data Release 7 of the Sloan Digital Sky Survey. We test whether BGGs and other bright members of groups are consistent with an ordered population among the total population of group galaxies. We find that the luminosity distributions of BGGs do not follow the predictions from the order statistics (OS). The average luminosities of BGGs are systematically brighter than OS predictions. On the other hand, by properly taking into account the brightening effect of the BGGs, the luminosity distributions of the second brightest galaxies are in excellent agreement with the expectations of OS. The brightening of BGGs relative to the OS expectation is consistent with a scenario that the BGGs on average have overgrown about 20% masses relative to the other member galaxies. The growth (ΔM) is not stochastic but correlated with the magnitude gap (G {sub 1,} {sub 2}) between the brightest and the second brightest galaxy. The growth (ΔM) is larger for the groups having more prominent BGGs (larger G {sub 1,} {sub 2}) and averagely contributes about 30% of the final G {sub 1,} {sub 2} of the groups of galaxies.

  2. Galaxy Groups: Proceedings from a Swinburne University Workshop

    NASA Astrophysics Data System (ADS)

    Kilborn, Virginia A.; Bekki, Kenji; Brough, Sarah; Doyle, Marianne T.; Evstigneeva, Ekaterina A.; Forbes, Duncan A.; Koribalski, Bärbel S.; Owers, Matthew S.; Power, Chris; Drinkwater, Michael J.; Rohde, David J.; Blake, Christopher A.; Couch, Warrick J.; Pracy, Michael B.; Gibson, Brad K.

    We present the proceedings from a two-day workshop held at Swinburne University on 2005 May 24-25. The workshop participants highlighted current Australian research on both theoretical and observational aspects of galaxy groups. These proceedings include short one-page summaries of a number of the talks presented at the workshop. The talks presented ranged from reconciling N-body simulations with observations, to the HI content of galaxies in groups and the existence of `dark galaxies'. The formation and existence of ultra-compact dwarfs in groups, and a new supergroup in Eridanus were also discussed.

  3. Chemical abundances of massive stars in Local Group galaxies

    NASA Astrophysics Data System (ADS)

    Venn, Kim A.; Kaufer, Andreas; Tolstoy, Eline; Kudritzki, Rolf-Peter; Przybilla, Norbert; Smartt, Stephen J.; Lennon, Daniel J.

    The relative abundances of elements in galaxies can provide valuable information on the stellar and chemical evolution of a galaxy. While nebulae can provide abundances for a variety of light elements, stars are the only way to directly determine the abundances of iron-group and s-process and r-process elements in a galaxy. The new 8m and 10m class telescopes and high-efficiency spectrographs now make high-quality spectral observations of bright supergiants possible in dwarf galaxies in the Local Group. We have been concentrating on elemental abundances in the metal-poor dwarf irregular galaxies, NGC 6822, WLM, Sextants A, and GR 8. Comparing abundance ratios to those predicted from their star formation histories, determined from color-magnitude diagrams, and comparing those ratios between these galaxies can give us new insights into the evolution of these dwarf irregular galaxies. Iron-group abundances also allow us to examine the metallicities of the stars in these galaxies directly, which affects their inferred mass loss rates and predicted stellar evolution properties.

  4. The Merger History, AGN and Dwarf Galaxies of Hickson Compact Group 59

    NASA Technical Reports Server (NTRS)

    Konstantopoulos, I. S.; Gallagher, S. C.; Fedotov, K.; Durrell, P. R.; Tzanavaris, P.; Hill, A. R.; Zabludoff, A. I.; Maier, M. L.; Elmegreen, D. M.; Charlton, J. C.; Johnson, K. E.; Brandt, W. N.; Walker, L. M.; Eracleous, M.; Maybhate, A.; Gronwall, C.; English, J.; Hornschemeier, A. E.; Mulchaey, J. S.

    2011-01-01

    Compact group galaxies often appear unaffected by their unusually dense environment. Closer examination can, however, reveal the subtle, cumulative effects of multiple galaxy interactions. Hickson Compact Group (HCG) 59 is an excellent example of this situation. We present a photometric study of this group in the optical (HST), infrared (Spitzer) and X-ray (Chandra) regimes aimed at characterizing the star formation and nuclear activity in its constituent galaxies and intra-group medium. We associate five dwarf galaxies with the group and update the velocity dispersion, leading to an increase in the dynamical mass of the group of up to a factor of 10 (to 2.8 x 10(exp 13) Stellar Mass), and a subsequent revision of its evolutionary stage. Star formation is proceeding at a level consistent with the morphological types of the four main galaxies, of which two are star-forming and the other two quiescent. Unlike in some other compact groups, star-forming complexes across HCG 59 closely follow mass-radius scaling relations typical of nearby galaxies. In contrast, the ancient globular cluster populations in galaxies HCG 59A and B show intriguing irregularities, and two extragalactic HII regions are found just west of B. We age-date a faint stellar stream in the intra-group medium at approx. 1 Gyr to examine recent interactions. We detect a likely low-luminosity AGN in HCG 59A by its approx. 10(exp 40) erg/s X-ray emission; the active nucleus rather than star formation can account for the UV+IR SED. We discuss the implications of our findings in the context of galaxy evolution in dense environments.

  5. The DEEP2 Galaxy Redshift Survey: The Voronoi-Delaunay Method Catalog of Galaxy Groups

    SciTech Connect

    Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Marinoni, Christian; Yan, Renbin; Coil, Alison L.; Conroy, Charlie; Cooper, Michael C.; Faber, S.M.; Finkbeiner, Douglas P.; Guhathakurta, Puragra; Kaiser, Nick; Koo, David C.; Phillips, Andrew C.; Weiner, Benjamin J.; /Maryland U.

    2012-02-14

    We use the first 25% of the DEEP2 Galaxy Redshift Survey spectroscopic data to identify groups and clusters of galaxies in redshift space. The data set contains 8370 galaxies with confirmed redshifts in the range 0.7 {<=} z {<=} 1.4, over one square degree on the sky. Groups are identified using an algorithm (the Voronoi-Delaunay Method) that has been shown to accurately reproduce the statistics of groups in simulated DEEP2-like samples. We optimize this algorithm for the DEEP2 survey by applying it to realistic mock galaxy catalogs and assessing the results using a stringent set of criteria for measuring group-finding success, which we develop and describe in detail here. We find in particular that the group-finder can successfully identify {approx}78% of real groups and that {approx}79% of the galaxies that are true members of groups can be identified as such. Conversely, we estimate that {approx}55% of the groups we find can be definitively identified with real groups and that {approx}46% of the galaxies we place into groups are interloper field galaxies. Most importantly, we find that it is possible to measure the distribution of groups in redshift and velocity dispersion, n({sigma}, z), to an accuracy limited by cosmic variance, for dispersions greater than 350 km s{sup -1}. We anticipate that such measurements will allow strong constraints to be placed on the equation of state of the dark energy in the future. Finally, we present the first DEEP2 group catalog, which assigns 32% of the galaxies to 899 distinct groups with two or more members, 153 of which have velocity dispersions above 350 km s{sup -1}. We provide locations, redshifts and properties for this high-dispersion subsample. This catalog represents the largest sample to date of spectroscopically detected groups at z {approx} 1.

  6. Compact configurations within small evolving groups of galaxies

    NASA Astrophysics Data System (ADS)

    Mamon, G. A.

    Small virialized groups of galaxies are evolved with a gravitational N-body code, where the galaxies and a diffuse background are treated as single particles, but with mass and luminosity profiles attached, which enbles the estimation of parameters such as internal energies, half-mass radii, and the softened potential energies of interaction. The numerical treatment includes mergers, collisional stripping, tidal limitation by the mean-field of the background (evaluated using a combination of instantaneous and impulsive formulations), galaxy heating from collisons, and background heating from dynamical friction. The groups start out either as dense as appear the groups in Hickson's (1982) catalog, or as loose as appear those in Turner and Gott's (1976a) catalog, and they are simulated many times (usually 20) with different initial positions and velocities. Dense groups of galaxies with massive dark haloes coalesce into a single galaxy and lose their compact group appearance in approximately 3 group half-mass crossing times, while dense groups of galaxies without massive haloes survive the merger instability for 15 half-mass crossing times (in a more massive background to keep the same total group mass).

  7. Galaxy and Group Baryonic Mass Functions for the RESOLVE Survey

    NASA Astrophysics Data System (ADS)

    Eckert, Kathleen D.; Kannappan, Sheila; Moffett, Amanda J.; Baker, Ashley; Stark, David; Berlind, Andreas A.; Storey-Fisher, Kate; Erickcek, Adrienne L.; Norris, Mark A.; Resolve Team

    2015-01-01

    We present a comparison of the galaxy and group baryonic mass functions for a subvolume of the RESOLVE (Resolved Spectroscopy Of a Local VolumE) survey. RESOLVE occupies A and B semester volumes totaling ~52,000 cubic Mpc, complete in baryonic mass to ~10^9.3 Msun and 10^9.0 Msun respectively, with galaxies and groups ranging in halo mass from 10^11-10^14 Msun. The A semester volume is surrounded by the larger ECO catalog, which lacks complete HI data but occupies ~561,000 cubic Mpc. We define the observed baryonic mass of a galaxy or group to be the sum of its stellar and cold atomic hydrogen components, with the latter inferred indirectly for much of ECO. For groups, we infer the total baryonic mass by summing the observed components of each constituent galaxy and add the likely hot halo gas based on prescriptions from observations and semi-analytic models. We perform subhalo/halo abundance matching between observed galaxies/groups and dark matter simulations, and we compare derived halo properties based on matching on luminosity vs. on observed baryonic mass (or on inferred total baryonic mass for groups). We also present a status update on the galaxy and group velocity functions for these surveys, which will allow for more direct comparison with dark matter simulations. This project was supported by NSF funding for the RESOLVE survey (AST-0955368).

  8. Massive stars in the galaxies of the Local Group

    NASA Astrophysics Data System (ADS)

    Massey, Philip

    2013-07-01

    The star-forming galaxies of the Local Group act as our laboratories for testing massive star evolutionary models. In this review, I briefly summarize what we believe we know about massive star evolution, and the connection between OB stars, Luminous Blue Variables, yellow supergiants, red supergiants, and Wolf-Rayet stars. The difficulties and recent successes in identifying these various types of massive stars in the neighboring galaxies of the Local Group will be discussed.

  9. Population studies in groups and clusters of galaxies. III. A catalog of galaxies in five nearby groups

    SciTech Connect

    Ferguson, H.C.; Sandage, A. Mount Wilson and Las Campanas Observatories, Pasadena, CA Space Telescope Science Institute, Baltimore, MD )

    1990-07-01

    Five nearby groups of galaxies have been surveyed using large-scale plates from the 2.5 m duPont Telescope at Las Campanas Observatory. Catalogs of galaxies brighter than B(T) = 20 are presented for the Leo, Dorado, NGC 1400, NGC 5044, and Antlia groups. A total of 1044 galaxies are included, from visual inspection of 14 plates, covering 31 deg square. Galaxies have been classified in the extended Hubble system, and group memberships have been assigned based on velocity (where available) and morphology. About half the galaxies listed are likely members of one of the nearby groups. The catalogs are complete to B(T) = 18, although the completeness limits vary slightly from group to group. Based on King model fits to the surface density profiles, the core radii of the groups range from 0.3 to 1 Mpc, and central densities range from 120 to 1900 galaxies Mpc exp-3 brighter than M(BT) = -12.5. Dynamical analysis indicates that all of the groups are likely to be gravitationally bound. 64 refs.

  10. Properties of Galaxies and Groups: Nature versus Nurture

    NASA Astrophysics Data System (ADS)

    Niemi, Sami-Matias

    2011-09-01

    Due to the inherently nonlinear nature of gravity cosmological N-body simulations have become an invaluable tool when the growth of structure is being studied and modelled closer to the present epoch. Large simulations with high dynamical range have made it possible to model the formation and growth of cosmic structure with unprecedented accuracy. Moreover, galaxies, the basic building blocks of the Universe, can also be modelled in cosmological context. However, despite all the simulations and successes in recent decades, there are still many unanswered questions in the field of galaxy formation and evolution. One of the longest standing issue being the significance of the formation place and thus initial conditions to a galaxy's evolution in respect to environment, often formulated simply as "nature versus nurture" like in human development and psychology. Unfortunately, our understanding of galaxy evolution in different environments is still limited, albeit, for example, the morphology-density relation has shown that the density of the galaxy's local environment can affect its properties. Consequently, the environment should play a role in galaxy evolution, however despite the efforts, the exact role of the galaxy's local environment to its evolution remains open. This thesis introduction discusses briefly the background cosmology, cosmological N-body simulations and semi-analytical models. The second part is reserved for groups of galaxies, whether they are gravitationally bound, and what this may imply for galaxy evolution. The third part of the thesis concentrates on describing results of a case study of isolated field elliptical galaxies. The final chapter discusses another case study of luminous infra-red galaxies.

  11. Galaxy And Mass Assembly (GAMA): galaxy radial alignments in GAMA groups

    NASA Astrophysics Data System (ADS)

    Schneider, Michael D.; Cole, Shaun; Frenk, Carlos S.; Kelvin, Lee; Mandelbaum, Rachel; Norberg, Peder; Bland-Hawthorn, Joss; Brough, Sarah; Driver, Simon; Hopkins, Andrew; Liske, Jochen; Loveday, Jon; Robotham, Aaron

    2013-08-01

    We constrain the distributions of projected radial alignment angles of satellite galaxy shapes within the Galaxy And Mass Assembly survey group catalogue. We identify the galaxy groups using spectroscopic redshifts and measure galaxy projected ellipticities from Sloan Digital Sky Survey imaging. With a sample of 3850 groups with 13 655 satellite galaxies with high quality shape measurements, we find a less than 2σ signal of radial alignments in the mean projected ellipticity components and the projected position angle when using galaxy shape estimates optimized for weak lensing measurements. Our radial alignment measurement increases to greater than 3σ significance relative to the expectation for no alignments if we use 2D Sérsic model fits to define galaxy orientations. Our weak measurement of radial alignments is in conflict with predictions from dark-matter N-body simulations, which we interpret as evidence for large misalignments of baryons and dark matter in group and cluster satellites. Within our uncertainties, that are dominated by our small sample size, we find only weak and marginally significant trends of the radial alignment angle distributions on projected distance from the group centre, host halo mass, and redshift that could be consistent with a tidal torquing mechanism for radial alignments. Using our lensing optimized shape estimators, we estimate that intrinsic alignments of galaxy group members may contribute a systematic error to the mean differential projected surface mass density of groups inferred from weak lensing observations by -1 ± 20 per cent at scales around 300 h-1 kpc from the group centre assuming a photometric redshift rms error of 10 per cent, and given our group sample with median redshift of 0.17 and median virial masses ˜1013 h-1 M⊙.

  12. Comparisons of the galaxy age, stellar velocity dispersion and K-band luminosity distributions between grouped galaxies and isolated ones

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Deng, Xin-Fa

    2016-02-01

    In two volume-limited Main galaxy samples of the Sloan Digital Sky Survey Data Release 10 (SDSS DR10), we compare the age, stellar velocity dispersion and K-band luminosity distributions of grouped galaxies with those of isolated galaxies, to explore the environmental dependence of these properties of galaxies. It is found that grouped galaxies have preferentially larger stellar velocity dispersions and are preferentially older than isolated galaxies. We also note apparent difference of K-band luminosity distribution at both extremes of density in the luminous volume-limited Main galaxy sample: grouped galaxies are preferentially more luminous than isolated galaxies, while this difference in the faint volume-limited Main galaxy sample is very small.

  13. Test of Current Ideas about Compact Groups of Galaxies

    NASA Astrophysics Data System (ADS)

    Rabaca, Carlos Roberto

    1997-12-01

    In this dissertation we test a number of current ideas about compact groups by focusing on some fundamental paradoxes that they pose about galaxy evolution. Conflicts between observations and models have led some to propose that compact groups are not real physical systems. We tested the physical reality of the groups by studying the strength of the interaction-induced enhancement in the optical and infrared luminosity functions. We also searched for optical interaction tracers in two famous groups: VV 172 and Seyfert's Sextet. The presence of a luminosity enhancement was verified, relative to a sample of isolated field galaxies, supporting the reality of, at least, some of the groups. The luminosity function enhancement was found to be smaller than the one observed in samples of paired galaxies and, especially, merger candidates. We also addressed the question of which groups were most likely physical with a statistical analysis of their environment relative to field galaxies, loose groups, and clusters of galaxies. Groups of only three accordant members were found to be more likely chance alignments and to be located closer to denser aggregates of galaxies than field galaxies. Models for compact groups predict that they are dynamically unstable to rapid coalescence. We searched for the (theoretically) expected population of merger remnants by comparing the optical luminosity function of the groups as units with that of field ellipticals. We found very few field ellipticals with luminosities as high as those expected from compact group mergers even allowing for some dimming. The detection of optical diffuse light in the potential of VV 172 is a further indication that these systems are physically dense and more dynamically evolved than predicted by the theoretical models. A detailed analysis of Seyfert's Sextet using Hubble Space Telescope images revealed that a quiescent coalescence event may be occurring among the galaxies in that compact group. Compact groups

  14. SPIDER - IX. Classifying galaxy groups according to their velocity distribution

    NASA Astrophysics Data System (ADS)

    Ribeiro, A. L. B.; de Carvalho, R. R.; Trevisan, M.; Capelato, H. V.; La Barbera, F.; Lopes, P. A. A.; Schilling, A. C.

    2013-09-01

    We introduce a new method to study the velocity distribution of galaxy systems, the Hellinger Distance (HD), designed for detecting departures from a Gaussian velocity distribution. Testing different approaches to measure normality of a distribution, we conclude that HD is the least vulnerable method to type I and II statistical errors. We define a relaxed galactic system as the one with unimodal velocity distribution and a normality deviation below a critical value (HD < 0.05). In this work, we study the Gaussian nature of the velocity distribution of the Berlind group sample, and of the FoF groups from the Millennium simulation. For the Berlind group sample (z < 0.1), 67 per cent of the systems are classified as relaxed, while for the Millennium sample we find 63 per cent (z = 0). We verify that in multi-modal groups the average mass of modes in high-multiplicity (N ≥ 20) systems are significantly larger than in low-multiplicity ones (N < 20), suggesting that groups experience a mass growth at an increasing virialization rate towards z = 0, with larger systems accreting more massive subunits. We also investigate the connection between galaxy properties ([Fe/H], Age, eClass, g - r, Rpetro and <μpetro>) and the Gaussianity of the velocity distribution of the groups. Bright galaxies (Mr ≤ -20.7) residing in the inner and outer regions of groups do not show significant differences in the listed quantities regardless if the group has a Gaussian (G) or a Non-Gaussian (NG) velocity distribution. However, the situation is significantly different when we examine the faint galaxies (-20.7 < Mr ≤ -17.9). In G groups, there is a remarkable difference between the galaxy properties of the inner and outer galaxy populations, testifying how the environment is affecting the galaxies. Instead, in NG groups there is no segregation between the properties of galaxies in the inner and outer regions, showing that the properties of these galaxies still reflect the physical

  15. THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

    SciTech Connect

    Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Coil, Alison L.; Cooper, Michael C.; Dutton, Aaron A.; Faber, S. M.; Guhathakurta, Puragra; Koo, David C.; Phillips, Andrew C.; Noeske, Kai; Rosario, David J.; Weiner, Benjamin J.; Willmer, Christopher N. A.; Yan, Renbin

    2012-05-20

    We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 < z < 1.5 and 1295 groups at z > 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above {approx}300 km s{sup -1} to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests.

  16. Multi-wavelengths studies of fossil galaxy groups

    NASA Astrophysics Data System (ADS)

    Khosroshahi, H. G.

    2016-09-01

    Fossil systems are understood to be the end product of galaxy mergers within groups and clusters. Their halo morphology points to their relaxed/virialised nature, thus allowing them to employed as observational probes for the evolution of cosmic structures, their thermodynamics and dark matter distribution. Cosmological simulations, and their underlying models, are broadly consistent with the early formation epoch for fossils. In a series of studies we have looked into the dark matter, IGM and galaxy properties, across a wide range of wavelengths, from X-ray through optical and IR to the Radio, to achieve a better understating of fossil systems, the attributed halo age, IGM heating and their AGNs and use them as laboratories to probe galaxy formation models. We combine luminosity gap with luminosity segregation to identify the most dynamically relaxed systems which allows us to reveal brand new connections between galaxies and their environments.

  17. Galaxy evolution in nearby galaxy groups - III. A GALEX view of NGC 5846, the largest group in the local universe

    NASA Astrophysics Data System (ADS)

    Marino, Antonietta; Mazzei, Paola; Rampazzo, Roberto; Bianchi, Luciana

    2016-06-01

    We explore the co-evolution of galaxies in nearby groups (Vhel ≤ 3000 km s-1) with a multiwavelength approach. We analyse GALEX far-UV (FUV) and near-UV (NUV) imaging, and Sloan Digital Sky Survey u, g, r, i, z data of groups spanning a large range of dynamical phases. We characterize the photometric properties of spectroscopically confirmed galaxy members and investigate the global properties of the groups through a dynamical analysis. Here, we focus on NGC 5846, the third most massive association of early-type galaxies (ETGs) after the Virgo and Fornax clusters. The group, composed of 90 members, is dominated by ETGs (about 80 per cent), and among ETGs about 40 per cent are dwarfs. Results are compared with those obtained for three groups in the LeoII cloud, which are radically different both in member-galaxy population and dynamical properties. The FUV-NUV cumulative colour distribution and the normalized UV luminosity function (LF) significantly differ due to the different fraction of late-type galaxy population. The UV LF of NGC 5846 resembles that of the Virgo cluster, however our analysis suggests that star formation episodes are still occurring in most of the group galaxies, including ETGs. The NUV-i colour distribution, the optical-UV colour-colour diagram, and NUV-r versus Mr colour-magnitude relation suggest that the gas contribution cannot be neglected in the evolution of ETG-type group members. Our analysis highlights that NGC 5846 is still in an active phase of its evolution, notwithstanding the dominance of dwarf and bright ETGs and its virialized configuration.

  18. Loose groups of galaxies in the Perseus-Pisces survey

    NASA Astrophysics Data System (ADS)

    Trasarti-Battistoni, R.

    1998-06-01

    We present a large catalog of loose groups of galaxies in the Southern Galactic Hemisphere, selected from the Perseus-Pisces redshift Survey (PPS). Particular care is taken in order to obtain group samples as homogeneous as possible to previously published catalogs. All our catalogs contain about 200 groups, significantly more than in most previous studies where group samples were obtained from galaxy data sets of comparable quality to (but smaller extent than) PPS. Groups are identified with the adaptive Friends-Of-Friends (FOF) algorithm of \\cite[Huchra & Geller (1982),]{HG82} with suitable normalizations D_0=0.231 \\ h(-1) Mpc and V_0=350 \\ km \\ s(-1) at cz_0=1000 \\ km \\ s(-1) . The luminosity function (LF) normalization phi_ *=0.02 \\ h(3) \\ Mpc(-3) appropriate for PPS yields a number density threshold delta n/n ~ 180 for the adopted D_0, instead of delta n/n ~ 80 used in previous studies of other samples. However, the customary choice of D_0 obtained (through the LF) from a fixed mass overdensity delta rho / rho =80, well motivated in theory, suffers from important observational uncertainties and sample-to-sample variations of the LF normalization, and from major uncertainties in the relation between galaxy density n and mass density rho . We discuss how to self-consistently match FOF parameters among different galaxy samples. We then separately vary several FOF and sample parameters, and discuss their effect on group properties. Loose groups in PPS nicely trace the large scale structure (LSS) in the parent galaxy sample. The group properties vary little with different redshift corrections, redshift cut-off, and galaxy LF, but are rather sensitive to the adopted links D_0 and V_0. More precisely, the typical group size (velocity dispersion) is linearly related to the adopted distance (velocity) link, while it is rather insensitive to the adopted velocity (distance) link. Physical properties of groups in PPS and in directly comparable samples show good

  19. Elliptical galaxies kinematics within general relativity with renormalization group effects

    SciTech Connect

    Rodrigues, Davi C.

    2012-09-01

    The renormalization group framework can be applied to Quantum Field Theory on curved space-time, but there is no proof whether the beta-function of the gravitational coupling indeed goes to zero in the far infrared or not. In a recent paper [1] we have shown that the amount of dark matter inside spiral galaxies may be negligible if a small running of the General Relativity coupling G is present (δG/G{sub 0}∼<10{sup −7} across a galaxy). Here we extend the proposed model to elliptical galaxies and present a detailed analysis on the modeling of NGC 4494 (an ordinary elliptical) and NGC 4374 (a giant elliptical). In order to compare our results to a well known alternative model to the standard dark matter picture, we also evaluate NGC 4374 with MOND. In this galaxy MOND leads to a significative discrepancy with the observed velocity dispersion curve and has a significative tendency towards tangential anisotropy. On the other hand, the approach based on the renormalization group and general relativity (RGGR) could be applied with good results to these elliptical galaxies and is compatible with lower mass-to-light ratios (of about the Kroupa IMF type)

  20. ON THE BARYON FRACTIONS IN CLUSTERS AND GROUPS OF GALAXIES

    SciTech Connect

    Dai Xinyu; Bregman, Joel N.; Kochanek, Christopher S.; Rasia, Elena

    2010-08-10

    We present the baryon fractions of 2MASS groups and clusters as a function of cluster richness using total and gas masses measured from stacked ROSAT X-ray data and stellar masses estimated from the infrared galaxy catalogs. We detect X-ray emission even in the outskirts of clusters, beyond r {sub 200} for richness classes with X-ray temperatures above 1 keV. This enables us to more accurately determine the total gas mass in these groups and clusters. We find that the optically selected groups and clusters have flatter temperature profiles and higher stellar-to-gas mass ratios than the individually studied, X-ray bright clusters. We also find that the stellar mass in poor groups with temperatures below 1 keV is comparable to the gas mass in these systems. Combining these results with individual measurements for clusters, groups, and galaxies from the literature, we find a break in the baryon fraction at {approx}1 keV. Above this temperature, the baryon fraction scales with temperature as f{sub b} {proportional_to} T {sup 0.20{+-}0.03}. We see significantly smaller baryon fractions below this temperature and the baryon fraction of poor groups joins smoothly onto that of systems with still shallower potential wells such as normal and dwarf galaxies where the baryon fraction scales with the inferred velocity dispersion as f{sub b} {proportional_to} {sigma}{sup 1.6}. The small scatter in the baryon fraction at any given potential well depth favors a universal baryon loss mechanism and a preheating model for the baryon loss. The scatter is, however, larger for less massive systems. Finally, we note that although the broken power-law relation can be inferred from data points in the literature alone, the consistency between the baryon fractions for poor groups and massive galaxies inspires us to fit the two categories of objects (galaxies and clusters) with one relation.

  1. New dwarf galaxy candidates in the Centaurus group

    NASA Astrophysics Data System (ADS)

    Müller, Oliver; Jerjen, Helmut; Binggeli, Bruno

    2015-11-01

    Context. Recent studies of the distribution and kinematics of the Milky Way and Andromeda satellite galaxy systems have confirmed the existence of coplanar, corotating structures of galaxies. In addition to the "missing satellite problem", these structures pose a major challenge to the standard ΛCDM scenario of structure formation. Aims: We complement the efforts made by the dwarf galaxy community to extend these studies to other nearby galaxy groups by systematically searching for faint unresolved dwarf members with a low surface brightness in the Southern Centaurus group of galaxies. The aim is to determine whether these coplanar, corotating structures are a universal phenomenon. Methods: We imaged an area of 60 sq. deg (0.3 Mpc2) around the M 83 subgroup with the wide-field Dark Energy Camera (DECam) at the CTIO 4 m Blanco telescope in g and r down to a limiting surface brightness of μr ≈ 30 mag arcsec-2. Various image-filtering techniques were applied to the DECam data to enhance the visibility of extremely low-surface brightness objects. Results: We report the discovery of 16 new dwarf galaxy candidates in the direction of the M 83 subgroup, roughly doubling the number of known dwarfs in that region. The photometric properties of the candidates, when compared to those of the Local Group, suggest membership in the M 83 subgroup. The faintest objects have a central star density of ≈1.3 L⊙ pc-2 and a total magnitude of g = 20.25, corresponding to Mg = -9.55 at the nominal distance of 4.9 Mpc. The sky distribution of the new objects is significantly prolonged toward Cen A, suggesting that many of them belong to the Cen A subgroup or a common halo. We also provide updated surface photometry for the brighter, known dwarf members in the surveyed area. Conclusions: Modern survey CCD cameras and sophisticated detection algorithms can be used to systematically probe the faint end of the galaxy luminosity function around the M 83 subgroup of galaxies. We aim at

  2. The radial distribution of galaxies in groups and clusters

    NASA Astrophysics Data System (ADS)

    Budzynski, J. M.; Koposov, S. E.; McCarthy, I. G.; McGee, S. L.; Belokurov, V.

    2012-06-01

    We present a new catalogue of 55 121 groups and clusters centred on luminous red galaxies from Sloan Digital Sky Survey Data Release 7 in the redshift range 0.15 ≤z≤ 0.4. We provide halo mass (M500) estimates for each of these groups derived from a calibration between the optical richness of bright galaxies (Mr≤-20.5) within 1 Mpc and X-ray-derived mass for a small subset of 129 groups and clusters with X-ray measurements. For 20 157 high-mass groups and clusters with M500 > 1013.7 M⊙, we find that the catalogue has a purity of >97 per cent and a completeness of ˜90 per cent. We derive the mean (stacked) surface number density profiles of galaxies as a function of total halo mass in different mass bins. We find that derived profiles can be well described by a projected Navarro-Frenk-White profile with a concentration parameter (≈ 2.6) that is approximately a factor of 2 lower than that of the dark matter (as predicted by N-body cosmological simulations) and nearly independent of halo mass. Interestingly, in spite of the difference in shape between the galaxy and dark matter radial distributions, both exhibit a high degree of self-similarity. We also stack the satellite profiles based on other observables, namely redshift, brightest cluster galaxy (BCG) luminosity and satellite luminosity and colour. We see no evidence for strong variation in profile shape with redshift over the range we probe or with BCG luminosity (or BCG luminosity fraction), but we do find a strong dependence on satellite luminosity and colours, in agreement with previous studies. A self-consistent comparison to several recent semi-analytic models of galaxy formation indicates that (1) beyond ≈0.3r500 current models are able to reproduce both the shape and normalization of the satellite profiles, and (2) within ≈0.3r500 the predicted profiles are sensitive to the details of the satellite-BCG merger time-scale calculation. The former is a direct result of the models

  3. The formation of Local Group planes of galaxies

    NASA Astrophysics Data System (ADS)

    Shaya, Ed J.; Tully, R. Brent

    2013-12-01

    The confinement of most satellite galaxies in the Local Group to thin planes presents a challenge to the theory of hierarchical galaxy clustering. The Pan-Andromeda Archaeological Survey (PAndAS) collaboration has identified a particularly thin configuration with kinematic coherence among companions of M31 and there have been long-standing claims that the dwarf companions to the Milky Way lie in a plane roughly orthogonal to the disc of our galaxy. This discussion investigates the possible origins of four Local Group planes: the plane similar, but not identical to that identified by the PAndAS collaboration, an adjacent slightly tilted plane and two planes in the vicinity of the Milky Way: one with very nearby galaxies and the other with more distant ones. Plausible orbits are found by using a combination of Numerical Action methods and a backward in time integration procedure. This investigation assumes that the companion galaxies formed at an early time in accordance with the standard cosmological model. For M31, M33, IC10 and Leo I, solutions are found that are consistent with measurements of their proper motions. For galaxies in planes, there must be commonalities in their proper motions, and this constraint greatly limits the number of physically plausible solutions. Key to the formation of the planar structures has been the evacuation of the Local Void and consequent build-up of the Local Sheet, a wall of this void. Most of the M31 companion galaxies were born in early-forming filamentary or sheet-like substrata that chased M31 out of the void. M31 is a moving target because of its attraction towards the Milky Way, and the result has been alignments stretched towards our galaxy. In the case of the configuration around the Milky Way, it appears that our galaxy was in a three-way competition for companions with M31 and Centaurus A. Only those within a modest band fell our way. The Milky Way's attraction towards the Virgo Cluster resulted in alignment along the

  4. Most Distant Group of Galaxies Known in the Universe

    NASA Astrophysics Data System (ADS)

    2002-04-01

    New VLT Discovery Pushes Back the Beginnings Summary Using the ESO Very Large Telescope (VLT) , a team of astronomers from The Netherlands, Germany, France and the USA [1] have discovered the most distant group of galaxies ever seen , about 13.5 billion light-years away. It has taken the light now recorded by the VLT about nine-tenths of the age of the Universe to cover the huge distance. We therefore observe those galaxies as they were at a time when the Universe was only about 10% of its present age . The astronomers conclude that this group of early galaxies will develop into a rich cluster of galaxies, such as those seen in the nearby Universe. The newly discovered structure provides the best opportunity so far for studying when and how galaxies began to form clusters after the initial Big Bang , one of the greatest puzzles in modern cosmology. PR Photo 11a/02 : Sky field with the distant cluster of galaxies. PR Photo 11b/02 : Spectra of some of the galaxies in the cluster. Radio Galaxies as cosmic signposts A most intriguing question in modern astronomy is how the first groupings or "clusters" of galaxies emerged from the gas produced in the Big Bang. Some theoretical models predict that densely populated galaxy clusters ("rich clusters" in current astronomical terminology) are built up through a step-wise process. Clumps develop in the primeval gas, and stars condense out of these clumps to form small galaxies. Then these small galaxies merge together to form larger units. The peculiar class of "radio galaxies" is particularly important for investigating such scenarios. They are called so because their radio emission - a result of violent processes believed to be related to massive black holes located at the centres of these galaxies - is stronger by 5 - 10 orders of magnitude than that of our own Milky Way galaxy. In fact, this radio emission is often so intense that the galaxies can be spotted at extremely large distances, and thus at the remote epoch when

  5. ROSAT observations of the galaxy group AWM 7.

    NASA Astrophysics Data System (ADS)

    Neumann, D. M.; Boehringer, H.

    1995-09-01

    We present results of ROSAT/PSPC and HRI observations of the AWM 7 group of galaxies, which is a poor galaxy cluster and forms part of the Perseus-Pisces filament. The X-ray emission originates from intracluster gas at temperatures of 1.7 to 4.5keV. The cluster obviously is elliptical with a position angle perpendicular to the position angle of the dominant elliptical galaxy NGC 1129, which is offset from the cluster X-ray centre by 30kpc. The analysis of the PSPC imaging and spectral data yield a gravitational mass of 2-5x10^14^Msun_within a radius of 1.2Mpc and a cooling flow with a mass deposition rate of up to 60-66Msun_/yr.

  6. Searching for merging groups of galaxies with Suzaku

    NASA Astrophysics Data System (ADS)

    Mitsuishi, Ikuyuki; Maejima, Masato; Babazaki, Yasunori; Kobayashi, Hiroaki; Matsumoto, Hironori; Tawara, Yuzuru; Yamasaki, Noriko Y.; Sasaki, Shin; Sousbie, Thierry

    2015-08-01

    Observational studies for merging group systems are important in terms of understanding dynamical evolution into cluster systems from group-scale halos in structure formation of the Universe. However, observational samples are very limited due to mainly its low surface brightness. Thus, to search for new merging group-scale halos, 11 fields were selected in total and Suzaku X-ray observatory which possesses both high sensitivity especially in the soft energy band below 1 keV and stable background was used. Seven fields are regions located around junctions of galaxy filaments where intense structure formation is expected. The other regions include an optically-identified group in the field of view where an interaction between central and satellite galaxies is observed in optical. A galaxy-galaxy merger including a central massive galaxy can be an indicator of a major merger for group systems because a single massive galaxy can be a perturber for such low mass systems. We conducted both imaging and spectral analysis for all the fields and discovered significant excess X-ray signals compared to background components from all the fields in their images and spectra. At least 5 systems show complex morphologies with multiple peaks in their intensity maps and no corresponding early-type galaxies exist for some of the peaks, which suggests that the systems are experiencing on-going mergers. Resultant temperatures, abundances, luminosities are 1-2 keV, <0.5 solar and 1042-43 erg s-1, respectively and thus the spectral analysis revealed that the excess X-ray emissions originate from group-scale halos associated with a merging event even though no significant deviation was found compared with a known Lx-kT relation (Kawahara et al. 2011, Mitsuishi et al. 2014, Mitsuishi et al. in prep.). In this conference, we will report on the details of our analysis and results using multiwavelength data such as radio, infrared, optical and X-ray to comprehend the merger phenomena and

  7. Loose Groups of Galaxies in the Las Campanas Redshift Survey

    NASA Astrophysics Data System (ADS)

    Tucker, Douglas L.; Oemler, Augustus, Jr.; Hashimoto, Yasuhiro; Shectman, Stephen A.; Kirshner, Robert P.; Lin, Huan; Landy, Stephen D.; Schechter, Paul L.; Allam, Sahar S.

    2000-10-01

    A ``friends-of-friends'' percolation algorithm has been used to extract a catalog of δn/n=80 density enhancements (groups) from the six slices of the Las Campanas Redshift Survey (LCRS). The full catalog contains 1495 groups and includes 35% of the LCRS galaxy sample. A clean sample of 394 groups has been derived by culling groups from the full sample that either are too close to a slice edge, have a crossing time greater than a Hubble time, have a corrected velocity dispersion of zero, or contain a 55" ``orphan'' (a galaxy with a mock redshift that was excluded from the original LCRS redshift catalog due to its proximity to another galaxy-i.e., within 55"). Median properties derived from the clean sample include a line-of-sight velocity dispersion σlos=164 km s-1, crossing time tcr=0.10 H-10, harmonic radius Rh=0.58 h-1 Mpc, pairwise separation Rp=0.64 h-1 Mpc, virial mass Mvir=1.90×1013 h-1 Msolar, total group R-band luminosity Ltot=1.30×1011 h-2 Lsolar, and R-band mass-to-light ratio M/L=171 h Msolar/Lsolar the median number of observed members in a group is three.

  8. THE GALAXY CONTENT OF SDSS CLUSTERS AND GROUPS

    SciTech Connect

    Hansen, Sarah M.; Wechsler, Risa H.; Koester, Benjamin P.

    2009-07-10

    Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of brightest cluster galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {<=} z {<=} 0.3. The size of the data set allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r {sub 200} of clusters with mass above 3 x 10{sup 13} h {sup -1} M {sub sun}, the luminosity function (LF) of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite LF does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25} M{sub i} - 5log{sub 10} h =-19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity, and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L {sub BCG} {approx} M {sup 0.3} {sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub logL} {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.

  9. The Galaxy Content of SDSS Clusters And Groups

    SciTech Connect

    Hansen, Sarah M.; Sheldon, Erin S.; Wechsler, Risa H.; Koester, Benjamin P.; /Chicago U., Astron. Astrophys. Ctr.

    2007-11-09

    Imaging data from the Sloan Digital Sky Survey are used to characterize the population of galaxies in groups and clusters detected with the MaxBCG algorithm. We investigate the dependence of Brightest Cluster Galaxy (BCG) luminosity, and the distributions of satellite galaxy luminosity and satellite color, on cluster properties over the redshift range 0.1 {le} z {le} 0.3. The size of the dataset allows us to make measurements in many bins of cluster richness, radius and redshift. We find that, within r200 of clusters with mass above 3x10{sup 13}h{sup -1}M{sub {circle_dot}}, the luminosity function of both red and blue satellites is only weakly dependent on richness. We further find that the shape of the satellite luminosity function does not depend on cluster-centric distance for magnitudes brighter than {sup 0.25}M{sub i} - 5log{sub 10}h = -19. However, the mix of faint red and blue galaxies changes dramatically. The satellite red fraction is dependent on cluster-centric distance, galaxy luminosity and cluster mass, and also increases by {approx}5% between redshifts 0.28 and 0.2, independent of richness. We find that BCG luminosity is tightly correlated with cluster richness, scaling as L{sub BCG} {approx} M{sup 0.3}{sub 200}, and has a Gaussian distribution at fixed richness, with {sigma}{sub log}L {approx} 0.17 for massive clusters. The ratios of BCG luminosity to total cluster luminosity and characteristic satellite luminosity scale strongly with cluster richness: in richer systems, BCGs contribute a smaller fraction of the total light, but are brighter compared to typical satellites. This study demonstrates the power of cross-correlation techniques for measuring galaxy populations in purely photometric data.

  10. CO in Hickson compact group galaxies with enhanced warm H2 emission: Evidence for galaxy evolution?

    NASA Astrophysics Data System (ADS)

    Lisenfeld, U.; Appleton, P. N.; Cluver, M. E.; Guillard, P.; Alatalo, K.; Ogle, P.

    2014-10-01

    Context. Galaxies in Hickson Compact Groups (HCGs) are believed to experience morphological transformations from blue, star-forming galaxies to red, early-type galaxies. Galaxies with a high ratio between the luminosities of the warm H2 to the 7.7 μm PAH emission (so-called Molecular Hydrogen Emission Galaxies, MOHEGs) are predominantly in an intermediate phase, the green valley. Their enhanced H2 emission suggests that the molecular gas is affected in the transition. Aims: We study the properties of the molecular gas traced by CO in galaxies in HCGs with measured warm H2 emission in order to look for evidence of the perturbations affecting the warm H2 in the kinematics, morphology and mass of the molecular gas. Methods: We observed the CO(1-0) emission of 20 galaxies in HCGs and complemented our sample with 11 CO(1-0) spectra from the literature. Most of the galaxies have measured warm H2 emission, and 14 of them are classified as MOHEGs. We mapped some of these galaxies in order to search for extra-galactic CO emission. We analyzed the molecular gas mass derived from CO(1-0), MH2, and its kinematics, and then compared it to the mass of the warm molecular gas, the stellar mass and star formation rate (SFR). Results: Our results are the following. (i) The mass ratio between the CO-derived and the warm H2 molecular gas is in the same range as found for field galaxies. (ii) Some of the galaxies, mostly MOHEGs, have very broad CO linewidths of up to 1000 km s-1 in the central pointing. The line shapes are irregular and show various components. (iii) In the mapped objects we found asymmetric distributions of the cold molecular gas. (iv) The star formation efficiency (=SFR/MH2) of galaxies in HCGs is very similar to isolated galaxies. No significant difference between MOHEGs and non-MOHEGs or between early-type and spiral galaxies has been found. In a few objects the SFE is significantly lower, indicating the presence of molecular gas that is not actively forming stars

  11. Deep Fabry-Perot Hα observations of two Sculptor group galaxies, NGC 247 and 300

    NASA Astrophysics Data System (ADS)

    Hlavacek-Larrondo, J.; Marcelin, M.; Epinat, B.; Carignan, C.; de Denus-Baillargeon, M.-M.; Daigle, O.; Hernandez, O.

    2011-09-01

    It has been suggested that diffuse ionized gas can extend all the way to the end of the H I disc, and even beyond, such as in the case of the warped galaxyNGC 253 (Bland-Hawthorn et al.). Detecting ionized gas at these radii could carry significant implications as to the distribution of dark matter in galaxies. With the aim of detecting this gas, we carried out a deep Hα kinematical analysis of two Sculptor group galaxies, NGC 247 and 300. The Fabry-Perot data were taken at the 36-cm Marseille Telescope in La Silla, Chile, offering a large field of view. With almost 20 hours of observations for each galaxy, very faint diffuse emission is detected. Typical emission measures of 0.1 cm-6 pc are reached. For NGC 247, emission extending up to a radius comparable with that of the H I disc (r˜ 13 arcmin) is found, but no emission is seen beyond the H I disc. For NGC 300, we detect ionized gas on the entirety of our field of view (rmax˜ 14 arcmin), and find that the bright H II regions are embedded in a diffuse background. Using the deep data, extended optical rotation curves are obtained, as well as mass models. These are the most extended optical rotation curves thus far for these galaxies. We find no evidence suggesting that NGC 247 has a warped disc, and to account for our non-detection of Hα emission beyond its H I disc, as opposed to the warped galaxy NGC 253, our results favour the model in which, only through a warp, ionization by hot young stars in the central region of a galaxy can let photons escape and ionize the interstellar medium in the outer parts.

  12. Understanding the unique assembly history of central group galaxies

    SciTech Connect

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

    2014-12-10

    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{sub e} ) and lower velocity dispersions (σ) at fixed stellar mass M {sub *}, and much larger R{sub 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{sub e} at fixed σ compared to non-CGs with similar M {sub *}. The CG R{sub e} -M {sub *} relation also shows differences, primarily driven by a subpopulation (∼15%) of galaxies with large R{sub e} , while the M {sub *}-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{sub e} and M {sub *} 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.

  13. Faint Dwarf Galaxies in Hickson Compact Group 90

    NASA Astrophysics Data System (ADS)

    Ordenes-Briceño, Yasna; Taylor, Matthew A.; Puzia, Thomas H.; Muñoz, Roberto P.; Eigenthaler, Paul; Georgiev, Iskren Y.; Goudfrooij, Paul; Hilker, Michael; Lançon, Ariane; Mamon, Gary; Mieske, Steffen; Miller, Bryan W.; Peng, Eric W.; Sánchez-Janssen, Rubén

    2016-08-01

    We report the discovery of a very diverse set of five low-surface brightness (LSB) dwarf galaxy candidates in Hickson Compact Group 90 (HCG 90) detected in deep U- and I-band images obtained with VLT/VIMOS. These are the first LSB dwarf galaxy candidates found in a compact group of galaxies. We measure spheroid half-light radii in the range 0.7 ≲ reff/kpc ≲ 1.5 with luminosities of -11.65 ≲ MU ≲ -9.42 and -12.79 ≲ MI ≲ -10.58 mag, corresponding to a color range of (U - I)0 ≃ 1.1 - 2.2 mag and surface brightness levels of μU ≃ 28.1 mag/arcsec2 and μI ≃ 27.4 mag/arcsec2. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z⊙ metallicities we obtain stellar masses in the range M_*|_{Z_odot } ˜eq 10^{5.7-6.3} M_{odot } and M_*|_{0.02 Z_odot } ˜eq 10^{6.3-8} M_{odot }. Three dwarfs are older than 1 Gyr, while the other two significantly bluer dwarfs are younger than ˜2 Gyr at any mass/metallicity combination. Altogether, the new LSB dwarf galaxy candidates share properties with dwarf galaxies found throughout the Local Volume and in nearby galaxy clusters such as Fornax. We find a pair of candidates with ˜2 kpc projected separation, which may represent one of the closest dwarf galaxy pairs found. We also find a nucleated dwarf candidate, with a nucleus size of reff ≃ 46 - 63 pc and magnitude MU, 0 = -7.42 mag and (U - I)0 = 1.51 mag, which is consistent with a nuclear stellar disc with a stellar mass in the range 104.9 - 6.5 M⊙.

  14. ACTIVITY IN GALACTIC NUCLEI OF COMPACT GROUP GALAXIES IN THE LOCAL UNIVERSE

    SciTech Connect

    Sohn, Jubee; Lee, Myung Gyoon; Lee, Gwang-Ho; Hwang, Ho Seong; Lee, Jong Chul E-mail: mglee@astro.snu.ac.kr E-mail: hhwang@cfa.harvard.edu

    2013-07-10

    We study the nuclear activity of galaxies in local compact groups. We use a spectroscopic sample of 238 galaxies in 58 compact groups from the Sloan Digital Sky Survey data release 7 to estimate the fraction of active galactic nucleus (AGN) host galaxies in compact groups, and to compare it with those in cluster and field regions. We use emission-line ratio diagrams to identify AGN host galaxies and find that the AGN fraction of compact group galaxies is 17%-42% depending on the AGN classification method. The AGN fraction in compact groups is not the highest among the galaxy environments. This trend remains even if we use several subsamples segregated by galaxy morphology and optical luminosity. The AGN fraction for early-type galaxies decreases with increasing galaxy number density, but the fraction for late-type galaxies changes little. We find no mid-infrared detected AGN host galaxies in our sample of compact groups using Wide-field Infrared Survey Explorer data. These results suggest that the nuclear activity of compact group galaxies (mostly early types) is not strong because of lack of gas supply even though they may experience frequent galaxy-galaxy interactions and mergers that could trigger nuclear activity.

  15. The Astrophysics of galaxy groups and clusters with Athena

    NASA Astrophysics Data System (ADS)

    Ettori, Stefano

    The complete story of how groups and clusters of galaxies grow, and how they dissipate the gravitational and non-thermal components of their energy budget over cosmic time, is still beyond our grasp. X-ray observations of the evolving cluster population provide a unique opportunity to address such fundamental open questions as: • How do hot diffuse baryons accrete and dynamically evolve in dark matter potentials? • How and when was the energy that we observe in the ICM generated and distributed? • Where and when are heavy elements produced and how are they circulated? Athena, the next-generation X-ray observatory with large collecting area and an unprecedented combination of high spectral and angular resolution, offers the only way to make major advances in answering these questions. We present the impact of Athena on the study of galaxy group and cluster astrophysics. We focus on observations of nearby (z < 0.5) systems, where Athen+ will revolutionize our understanding of the basic process of energy transfer into the ICM, transform our view of the outer regions of galaxy clusters where material continues to accrete, and allow us to track the generation and diffusion of metals in the intracluster gas.

  16. Towards a phylogenetic analysis of galaxy evolution: a case study with the dwarf galaxies of the Local Group

    NASA Astrophysics Data System (ADS)

    Fraix-Burnet, D.; Choler, P.; Douzery, E. J. P.

    2006-09-01

    Context: .The Hubble tuning-fork diagram has always been the preferred scheme for classifying galaxies. It is based only on morphology. In contrast, biologists have long taken the genealogical relatedness of living entities into account for classification purposes. Aims: .Assuming branching evolution of galaxies as a "descent with modification", we show here that the concepts and tools of phylogenetic systematics that are widely used in biology can be heuristically transposed to the case of galaxies. Methods: .This approach, which we call "astrocladistics", is applied to dwarf galaxies of the Local Group and provides the first evolutionary tree for real galaxies. Results: .The trees that we present here are solid enough to support the existence of a hierarchical organisation in the diversity of dwarf galaxies of the Local Group. They also show that these galaxies all stem from a common ancestral kind of object. We find that some kinds of dIrrs are progenitors of both dSphs and other kinds of dIrrs. We also identify three evolutionary groups, each one with its own characteristics and own evolution. Conclusions: .The present work opens a new way to analysing galaxy evolution and a path towards a new systematics of galaxies. Work on other galaxies in the Universe is in progress.

  17. THE SUPPRESSION OF STAR FORMATION AND THE EFFECT OF THE GALAXY ENVIRONMENT IN LOW-REDSHIFT GALAXY GROUPS

    SciTech Connect

    Rasmussen, Jesper; Mulchaey, John S.; Bai, Lei; Ponman, Trevor J.; Raychaudhury, Somak; Dariush, Ali

    2012-10-01

    Understanding the interaction between galaxies and their surroundings is central to building a coherent picture of galaxy evolution. Here we use Galaxy Evolution Explorer imaging of a statistically representative sample of 23 galaxy groups at z Almost-Equal-To 0.06 to explore how local and global group environments affect the UV properties and dust-corrected star formation rates (SFRs) of their member galaxies. The data provide SFRs out to beyond 2R{sub 200} in all groups, down to a completeness limit and limiting galaxy stellar mass of 0.06 M{sub Sun} yr{sup -1} and 1 Multiplication-Sign 10{sup 8} M{sub Sun }, respectively. At fixed galaxy stellar mass, we find that the fraction of star-forming group members is suppressed relative to the field out to an average radius of R Almost-Equal-To 1.5 Mpc Almost-Equal-To 2R{sub 200}, mirroring results for massive clusters. For the first time, we also report a similar suppression of the specific SFR within such galaxies, on average by 40% relative to the field, thus directly revealing the impact of the group environment in quenching star formation within infalling galaxies. At fixed galaxy density and stellar mass, this suppression is stronger in more massive groups, implying that both local and global group environments play a role in quenching. The results favor an average quenching timescale of {approx}> 2 Gyr and strongly suggest that a combination of tidal interactions and starvation is responsible. Despite their past and ongoing quenching, galaxy groups with more than four members still account for at least {approx}25% of the total UV output in the nearby universe.

  18. Fossil group origins. II. Unveiling the formation of the brightest group galaxies through their scaling relations

    NASA Astrophysics Data System (ADS)

    Méndez-Abreu, J.; Aguerri, J. A. L.; Barrena, R.; Sánchez-Janssen, R.; Boschin, W.; Castro-Rodriguez, N.; Corsini, E. M.; Del Burgo, C.; D'Onghia, E.; Girardi, M.; Iglesias-Páramo, J.; Napolitano, N.; Vilchez, J. M.; Zarattini, S.

    2012-01-01

    Context. Fossil systems are galaxy associations dominated by a relatively isolated, bright elliptical galaxy, surrounded by a group of smaller galaxies lacking L∗ objects. Because of this extreme environment, fossil groups (FGs) are ideal laboratories for studying the mass assembly of brightest group galaxies (BGGs). Aims: We analyzed the near-infrared photometric and structural properties of a sample of 20 BGGs present in FGs to better understand their formation mechanisms. They represent the largest sample studied to date. Methods.Ks-band deep images were used to study the structural properties of our sample galaxies. Their surface-brightness distribution was fitted to a Sérsic profile using the GASP2D algorithm. Then, the standard scaling relations were derived for the first time for these galaxies and compared with those of normal ellipticals and brightest cluster galaxies in non-fossil systems. Results: The BGGs presented in this study represent a subset of the most massive galaxies in the Universe. We find that their ellipticity profiles are continuously increasing with the galactocentric radius. Our fossil BCGs follow closely the fundamental plane described by normal ellipticals. However, they depart from both the log σ0 vs. log LKs and log re vs. log LKs relations described by intermediate-mass ellipticals. This occurs in the sense that our BGGs have larger effective radii and smaller velocity dispersions than those predicted by these relations. We also find that more elliptical galaxies systematically deviate from the previous relations, while rounder objects do not. No similar correlation was found with the Sérsic index. Conclusions: The derived scaling relations can be interpreted in terms of the formation scenario of the BGGs. Because our BGGs follow the fundamental plane tilt but have larger effective radii than expected for intermediate-mass ellipticals, we suggest that they only went through dissipational mergers in an early stage of their

  19. Mirror neurons: their implications for group psychotherapy.

    PubMed

    Schermer, Victor L

    2010-10-01

    Recently discovered mirror neurons in the motor cortex of the brain register the actions and intentions of both the organism and others in the environment. As such, they may play a significant role in social behavior and groups. This paper considers the potential implications of mirror neurons and related neural networks for group therapists, proposing that mirror neurons and mirror systems provide "hard-wired" support for the group therapist's belief in the centrality of relationships in the treatment process and exploring their value in accounting for group-as-a-whole phenomena. Mirror neurons further confirm the holistic, social nature of perception, action, and intention as distinct from a stimulus-response behaviorism. The implications of mirror neurons and mirroring processes for the group therapist role, interventions, and training are also discussed.

  20. THE ORIENTATIONS OF GALAXY GROUPS AND FORMATION OF THE LOCAL SUPERCLUSTER

    SciTech Connect

    Godlowski, Wlodzimierz; Flin, Piotr E-mail: sfflin@cyf-kr.edu.p

    2010-01-10

    We analyzed the orientation of galaxy groups in the Local Supercluster (LSC). It is strongly correlated with the distribution of neighboring groups in the scale up to about 20 Mpc. The group major axis is in alignment with both the line joining the two brightest galaxies and the direction toward the center of the LSC, i.e., Virgo cluster. These correlations suggest that two brightest galaxies were formed in filaments of matter directed toward the protosupercluster center. Afterward, the hierarchical clustering leads to aggregation of galaxies around these two galaxies. The groups are formed on the same or similarly oriented filaments. This picture is in agreement with the predictions of numerical simulations.

  1. Towards a realistic population of simulated galaxy groups and clusters

    NASA Astrophysics Data System (ADS)

    Le Brun, Amandine M. C.; McCarthy, Ian G.; Schaye, Joop; Ponman, Trevor J.

    2014-06-01

    We present a new suite of large-volume cosmological hydrodynamical simulations called cosmo-OWLS. They form an extension to the OverWhelmingly Large Simulations (OWLS) project, and have been designed to help improve our understanding of cluster astrophysics and non-linear structure formation, which are now the limiting systematic errors when using clusters as cosmological probes. Starting from identical initial conditions in either the Planck or WMAP7 cosmologies, we systematically vary the most important `sub-grid' physics, including feedback from supernovae and active galactic nuclei (AGN). We compare the properties of the simulated galaxy groups and clusters to a wide range of observational data, such as X-ray luminosity and temperature, gas mass fractions, entropy and density profiles, Sunyaev-Zel'dovich flux, I-band mass-to-light ratio, dominance of the brightest cluster galaxy and central massive black hole (BH) masses, by producing synthetic observations and mimicking observational analysis techniques. These comparisons demonstrate that some AGN feedback models can produce a realistic population of galaxy groups and clusters, broadly reproducing both the median trend and, for the first time, the scatter in physical properties over approximately two decades in mass (1013 M⊙ ≲ M500 ≲ 1015 M⊙) and 1.5 decades in radius (0.05 ≲ r/r500 ≲ 1.5). However, in other models, the AGN feedback is too violent (even though they reproduce the observed BH scaling relations), implying that calibration of the models is required. The production of realistic populations of simulated groups and clusters, as well as models that bracket the observations, opens the door to the creation of synthetic surveys for assisting the astrophysical and cosmological interpretation of cluster surveys, as well as quantifying the impact of selection effects.

  2. Searching for diffuse light in the M96 galaxy group

    SciTech Connect

    Watkins, Aaron E.; Mihos, J. Christopher; Harding, Paul; Feldmeier, John J.

    2014-08-10

    We present deep, wide-field imaging of the M96 galaxy group (also known as the Leo I Group). Down to surface brightness limits of μ{sub B} = 30.1 and μ{sub V} = 29.5, we find no diffuse, large-scale optical counterpart to the 'Leo Ring', an extended H I ring surrounding the central elliptical M105 (NGC 3379). However, we do find a number of extremely low surface brightness (μ{sub B} ≳ 29) small-scale streamlike features, possibly tidal in origin, two of which may be associated with the Ring. In addition, we present detailed surface photometry of each of the group's most massive members—M105, NGC 3384, M96 (NGC 3368), and M95 (NGC 3351)—out to large radius and low surface brightness, where we search for signatures of interaction and accretion events. We find that the outer isophotes of both M105 and M95 appear almost completely undisturbed, in contrast to NGC 3384 which shows a system of diffuse shells indicative of a recent minor merger. We also find photometric evidence that M96 is accreting gas from the H I ring, in agreement with H I data. In general, however, interaction signatures in the M96 Group are extremely subtle for a group environment, and provide some tension with interaction scenarios for the formation of the Leo H I Ring. The lack of a significant component of diffuse intragroup starlight in the M96 Group is consistent with its status as a loose galaxy group in which encounters are relatively mild and infrequent.

  3. KPNO 0.9m H(alpha) Imaging Survey of ``Transforming Galaxies" in Local Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Haines, Christopher; O'Sullivan, Ewan; Raychaudhury, Somak; Gargiulo, Adriana; Campusano, Luis

    2012-02-01

    We propose to use the KPNO 0.9-m telescope to obtain panoramic H(alpha) imaging of ~200 galaxies in two nearby (32, 35 Mpc) galaxy groups NGC 4261 and NGC 5353 from the CLoGS local group survey. In rich clusters ram-pressure stripping has been shown to be very effective at removing the gas contents and quenching star formation in infalling spiral galaxies. It is much less clear how galaxies are affected by the much lower ram pressures found in galaxy groups, or if other environmental processes begin to dominate. Given that >50% of galaxies in the local volume reside in groups, it is vital we gain new insights into which mechanisms drive the SFR-density relation in groups. The proposed H(alpha) imaging will allow us to resolve where star-formation is occuring in each galaxy. This can effectively discriminate between ram-pressure stripping characterized by truncated H(alpha) disks, the much gentler starvation mechanism which produces anemic spirals, and nuclear star-bursts triggered by low-velocity encounters which should be most frequent in groups.

  4. KPNO 0.9m H(alpha) Imaging Survey of ``Transforming Galaxies'' in Local Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Haines, Christopher; O'Sullivan, Ewan; Raychaudhury, Somak; Egami, Eiichi; Campusano, Luis

    2012-08-01

    We propose to use the KPNO 0.9-m telescope to obtain panoramic H(alpha) imaging of ~135 galaxies in ten nearby galaxy groups (60- 80 Mpc) from the Complete Local-Volume Groups Sample (CLoGS). In rich clusters ram-pressure stripping has been shown to be very effective at removing the gas contents and quenching star formation in infalling spiral galaxies. It is much less clear how galaxies are affected by the much lower ram pressures found in galaxy groups, or if other environmental processes begin to dominate. Given that >50% of galaxies in the local volume reside in groups, it is vital that we gain new insights into which mechanisms drive the SFR-density relation in groups. The proposed H(alpha) imaging will allow us to resolve where star-formation is occurring in each galaxy. This can effectively discriminate between ram-pressure stripping characterized by truncated H(alpha) disks, the much gentler starvation mechanism which produces anemic spirals, and nuclear starbursts triggered by low-velocity encounters and mergers which should be most frequent in groups.

  5. Star formation in globular clusters and dwarf galaxies and implications for the early evolution of galaxies

    NASA Technical Reports Server (NTRS)

    Lin, Douglas N. C.; Murray, Stephen D.

    1991-01-01

    Based upon the observed properties of globular clusters and dwarf galaxies in the Local Group, we present important theoretical constraints on star formation in these systems. These constraints indicate that protoglobular cluster clouds had long dormant periods and a brief epoch of violent star formation. Collisions between protocluster clouds triggered fragmentation into individual stars. Most protocluster clouds dispersed into the Galactic halo during the star formation epoch. In contrast, the large spread in stellar metallicity in dwarf galaxies suggests that star formation in their pregenitors was self-regulated: we propose the protocluster clouds formed from thermal instability in the protogalactic clouds and show that a population of massive stars is needed to provide sufficient UV flux to prevent the collapsing protogalactic clouds from fragmenting into individual stars. Based upon these constraints, we propose a unified scenario to describe the early epochs of star formation in the Galactic halo as well as the thick and thin components of the Galactic disk.

  6. Analysis of the structure of disk galaxies in the NGC 2300 group

    NASA Astrophysics Data System (ADS)

    Il'ina, M. A.; Sil'chenko, O. K.

    2016-10-01

    Data from the 6-m telescope of the Special Astrophysical Observatory obtained using the SCORPIO instrument in imaging mode are used to study member galaxies of the NGC 2300 group. Surface photometry has been carried out for the five largest galaxies in the group, whose isophotal parameters and the parameters of their large-scale structural components (disks and bulges) have been determined. The morphological type of the central galaxy in the group has been refined, and shown to be elliptical. Studies of structural features in non-central disk galaxies have revealed an enhanced percent of bars: bars were found in all disk galaxies of this group, with all of these being compact structures. The similarity of the structural features of the disks of the group galaxies suggests that these disksmay be being restructured in the process of the current merger of the two X-ray subgroups comprising NGC 2300: the group NGC 2300 itself and the group NGC 2276.

  7. Evolution of Group Galaxies from the First Red-Sequence Cluster Survey

    NASA Astrophysics Data System (ADS)

    Li, I. H.; Yee, H. K. C.; Hsieh, B. C.; Gladders, M.

    2012-04-01

    We study the evolution of the red-galaxy fraction (f red) in 905 galaxy groups with 0.15 <= z < 0.52. The galaxy groups are identified by the "probability friends-of-friends" algorithm from the first Red-Sequence Cluster Survey (RCS1) photometric-redshift sample. There is a high degree of uniformity in the properties of the red sequence of the group galaxies, indicating that the luminous red-sequence galaxies in the groups are already in place by z ~ 0.5 and that they have a formation epoch of z >~ 2. In general, groups at lower redshifts exhibit larger f red than those at higher redshifts, showing a group Butcher-Oemler effect. We investigate the evolution of f red by examining its dependence on four parameters, one of which can be classified as intrinsic and three of which can be classified as environmental: galaxy stellar mass (M *), total group stellar mass (M *, grp, a proxy for group halo mass), normalized group-centric radius (r grp), and local galaxy density (Σ5). We find that M * is the dominant parameter such that there is a strong correlation between f red and galaxy stellar mass. Furthermore, the dependence of f red on the environmental parameters is also a strong function of M *. Massive galaxies (M * >~ 1011 M ⊙) show little dependence of f red on r grp, M *, grp, and Σ5 over the redshift range. The dependence of f red on these parameters is primarily seen for galaxies with lower masses, especially for M * <~ 1010.6 M ⊙. We observe an apparent "group down-sizing" effect, in that galaxies in lower-mass halos, after controlling for galaxy stellar mass, have lower f red. We find a dependence of f red on both r grp and Σ5 after the other parameters are controlled. At a fixed r grp, there is a significant dependence of f red on Σ5, while r grp gradients of f red are seen for galaxies in similar Σ5 regions. This indicates that galaxy group environment has a residual effect over that of local galaxy density (or vice versa), and both parameters need

  8. Ultra hot gas in the Galaxy: possible origins and implications

    NASA Astrophysics Data System (ADS)

    Ozernoy, L.; Titarchuk, L.; Ramaty, R.

    A remarkable enhancement of the 6.7 keV line emission and associated thermal continuum emission from the Galactic ridge toward the Galactic center discovered recently by Ginga satellite opens new opportunity of exploring high-energy phenomena in the Galaxy. This emission is thought to originate in a hot optically thin gas, and the central enhancement seems to be associated with an ultra hot (T~=108 K), rarefied [n~(3-6).10-2 cm-3] interior of the 200-pc expanding molecular ring in the Galactic center. Assuming that this interior is a superbubble resulting from an adiabatic explosion, we analyze the dynamics of the explosive phenomenon. Some implications of the presence of a cold (molecular) and a warm (radio emitting) gas between us and the ultra hot superbubble, such as fluorescence of iron lines in the cold gas and scattering of iron lines in warm (hot) gas are discussed.

  9. Ultra hot gas in the Galaxy: possible origins and implications

    NASA Astrophysics Data System (ADS)

    Ozernoy, L.; Titarchuk, L.; Ramaty, R.

    1992-06-01

    A remarkable enhancement of the 6.7 keV line emission and associated thermal continuum emission from the Galactic ridge toward the Galactic center discovered recently by Ginga satellite opens new opportunity of exploring high-energy phenomena in the Galaxy. This emission is thought to originate in a hot optically thin gas, and the central enhancement seems to be associated with an ultra hot (T≊108 K), rarefied [n˜(3-6)ṡ10-2 cm-3] interior of the 200-pc expanding molecular ring in the Galactic center. Assuming that this interior is a superbubble resulting from an adiabatic explosion, we analyze the dynamics of the explosive phenomenon. Some implications of the presence of a cold (molecular) and a warm (radio emitting) gas between us and the ultra hot superbubble, such as fluorescence of iron lines in the cold gas and scattering of iron lines in warm (hot) gas are discussed.

  10. The Hubble Sequence in Groups: The Birth of the Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Feldmann, R.; Carollo, C. M.; Mayer, L.

    2011-08-01

    The physical mechanisms and timescales that determine the morphological signatures and the quenching of star formation of typical (~L*) elliptical galaxies are not well understood. To address this issue, we have simulated the formation of a group of galaxies with sufficient resolution to track the evolution of gas and stars inside about a dozen galaxy group members over cosmic history. Galaxy groups, which harbor many elliptical galaxies in the universe, are a particularly promising environment to investigate morphological transformation and star formation quenching, due to their high galaxy density, their relatively low velocity dispersion, and the presence of a hot intragroup medium. Our simulation reproduces galaxies with different Hubble morphologies and, consequently, enables us to study when and where the morphological transformation of galaxies takes place. The simulation does not include feedback from active galactic nuclei showing that it is not an essential ingredient for producing quiescent, red elliptical galaxies in galaxy groups. Ellipticals form, as suspected, through galaxy mergers. In contrast with what has often been speculated, however, these mergers occur at z > 1, before the merging progenitors enter the virial radius of the group and before the group is fully assembled. The simulation also shows that quenching of star formation in the still star-forming elliptical galaxies lags behind their morphological transformation, but, once started, takes less than a billion years to complete. As long envisaged the star formation quenching happens as the galaxies approach and enter the finally assembled group, due to quenching of gas accretion and (to a lesser degree) stripping. A similar sort is followed by unmerged, disk galaxies, which, as they join the group, are turned into the red-and-dead disks that abound in these environments.

  11. Galex Catalog And Atlas Of Our Local Group Of Galaxies

    NASA Astrophysics Data System (ADS)

    Madore, Barry

    The NASA Galaxy Evolution Explorer (GALEX) mission contains the most comprehensive collection of ultraviolet imaging of Local Group galaxies likely to exist for decades. Unfortunately, this impressive resource will be under-utilized because the standard GALEX pipeline and source catalogs are not designed to properly measure point sources in crowded fields. We propose to solve this problem and unlock this great wealth of data obtained by NASA by constructing the GALEX Catalog and Atlas of Our Local Group Galaxies which shall include 49 GALEX observed Local Group members within 1.5 Mpc including the Large and Small Magellanic Clouds in their entirety. The PSF- fitting photometry method has already been tested and increases the number of detected point sources by 300% over the standard GALEX pipeline. Our catalogs will provide approximately 5-6 million point source measurements. We have also developed a novel method for producing wide field background-balanced mosaics of GALEX data. This has already been implemented for the Magellanic Clouds and the method will be applied to the other largest Local Group Members (M31 and M33). The Atlas images we produce will combine imaging data from all GALEX surveys to achieve maximum depth. Quality assurance of the images and catalogs will be done by the proposers in the course of undertaking a number of science-driven projects that require cross-matching the ultraviolet point sources of the Magellanic Clouds to similar resolution optical (MCPS) and infrared (SAGE) source catalogs. The Catalogs and Atlas (including the Magellanic Clouds cross-matched catalogs) will be made available to the astronomical community by providing them to the Mikulski Archive for Space Telescopes (MAST, the official GALEX archive) as a High Level Science Product as well as assimilated on an object-by- object basis into the NASA/IPAC Extragalactic Database (NED) and thereby made immediately accessible in VO-compatible format. This program will enhance

  12. GALAXIES IN X-RAY GROUPS. III. SATELLITE COLOR AND MORPHOLOGY TRANSFORMATIONS

    SciTech Connect

    George, Matthew R.; Ma, Chung-Pei; Bundy, Kevin; Leauthaud, Alexie; Vulcani, Benedetta; Tinker, Jeremy; Wechsler, Risa H.; Finoguenov, Alexis

    2013-06-20

    While the star formation rates and morphologies of galaxies have long been known to correlate with their local environment, the process by which these correlations are generated is not well understood. Galaxy groups are thought to play an important role in shaping the physical properties of galaxies before entering massive clusters at low redshift, and transformations of satellite galaxies likely dominate the buildup of local environmental correlations. To illuminate the physical processes that shape galaxy evolution in dense environments, we study a sample of 116 X-ray selected galaxy groups at z = 0.2-1 with halo masses of 10{sup 13}-10{sup 14} M{sub Sun} and centroids determined with weak lensing. We analyze morphologies based on Hubble Space Telescope imaging and colors determined from 31 photometric bands for a stellar mass-limited population of 923 satellite galaxies and a comparison sample of 16,644 field galaxies. Controlling for variations in stellar mass across environments, we find significant trends in the colors and morphologies of satellite galaxies with group-centric distance and across cosmic time. Specifically at low stellar mass (log (M{sub *}/M{sub Sun }) = 9.8-10.3), the fraction of disk-dominated star-forming galaxies declines from >50% among field galaxies to <20% among satellites near the centers of groups. This decline is accompanied by a rise in quenched galaxies with intermediate bulge+disk morphologies, and only a weak increase in red bulge-dominated systems. These results show that both color and morphology are influenced by a galaxy's location within a group halo. We suggest that strangulation and disk fading alone are insufficient to explain the observed morphological dependence on environment, and that galaxy mergers or close tidal encounters must play a role in building up the population of quenched galaxies with bulges seen in dense environments at low redshift.

  13. THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. I. WHICH ENVIRONMENT AFFECTS GALAXY EVOLUTION?

    SciTech Connect

    Carollo, C. Marcella; Cibinel, Anna; Lilly, Simon J.; Miniati, Francesco; Cameron, Ewan; Peng, Yingjie; Pipino, Antonio; Rudick, Craig S.; Norberg, Peder; Silverman, John D.; Van Gorkom, Jacqueline; Finoguenov, Alexis

    2013-10-20

    The Zurich Environmental Study (ZENS) is based on a sample of ∼1500 galaxy members of 141 groups in the mass range ∼10{sup 12.5-14.5} M{sub ☉} within the narrow redshift range 0.05 < z < 0.0585. ZENS adopts novel approaches, described here, to quantify four different galactic environments, namely: (1) the mass of the host group halo; (2) the projected halo-centric distance; (3) the rank of galaxies as central or satellites within their group halos; and (4) the filamentary large-scale structure density. No self-consistent identification of a central galaxy is found in ∼40% of <10{sup 13.5} M{sub ☉} groups, from which we estimate that ∼15% of groups at these masses are dynamically unrelaxed systems. Central galaxies in relaxed and unrelaxed groups generally have similar properties, suggesting that centrals are regulated by their mass and not by their environment. Centrals in relaxed groups have, however, ∼30% larger sizes than in unrelaxed groups, possibly due to accretion of small satellites in virialized group halos. At M > 10{sup 10} M{sub ☉}, satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.

  14. New distances to galaxies in the Centaurus A group

    NASA Astrophysics Data System (ADS)

    Karachentsev, I. D.; Sharina, M. E.; Dolphin, A. E.; Grebel, E. K.; Geisler, D.; Guhathakurta, P.; Hodge, P. W.; Karachentseva, V. E.; Sarajedini, A.; Seitzer, P.

    2002-04-01

    We present Hubble Space Telescope/WFPC2 images of seventeen dwarf galaxies in the Centaurus A group. Their distances derived from the magnitudes of the tip of the red giant branch are 5.2 Mpc (KK112), 3.2 Mpc (ESO 321-014), 3.5 Mpc (KK179), 3.4 Mpc (NGC 5102), 4.6 Mpc (KK200), 3.7 Mpc (ESO 324-024), 4.7 Mpc (KK208), 4.6 Mpc (ESO 444-084), 4.4 Mpc (IC 4316), 4.5 Mpc (NGC 5264), 3.6 Mpc (KK211), 3.6 Mpc (KK213), 3.4 Mpc (ESO 325-011), 3.8 Mpc (KK217), 4.0 Mpc (KK221), 4.8 Mpc (NGC 5408), and 3.6 Mpc (PGC 51659). The galaxies are concentrated in two spatially separated groups around NGC 5128 = Cen A and NGC 5236 = M 83. The Cen A group itself has a mean distance of 3.63+/- 0.07 Mpc, a velocity dispersion of 89 km s-1, a mean projected radius of 263 kpc, an estimated orbital mass of 2.1x 1012 Msun, and an orbital mass-to-blue luminosity ratio of 64 Msun/Lsun. For the M 83 group we derived a mean distance of 4.57+/- 0.05 Mpc, a velocity dispersion of 62 km s-1, a mean projected radius of 142 kpc, an estimated orbital mass of 0.8x 1012 Msun, and Morb/LB = 37 Msun/Lsun. The M 83 group moves away from the Cen A group, which yields a radius of the zero-velocity surface of the Cen A group of R0 < 1.26 Mpc. The total mass within R0, M0 < 2.7x 1012 Msun, agrees with the orbital mass estimate. The centroids of both the groups have very small peculiar velocities, (+18+/- 24) km s-1 (Cen A) and (-17+/-27) km s-1 (M 83) with respect to the local Hubble flow with H0 = 70 km s-1 Mpc-1. Based on observations made with the NASA/ESA Hubble Space Telescope. The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Figure 3 is only available in electronic form at http://www.edpsciences.org

  15. Two-Body Escape Speeds in Merged Four-Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Valtonen, M. J.; Wiren, S.

    1994-01-01

    In the neighbourhood of the Local Group of galaxies, some high speeds of relative motion are observed. In particular, the speeds of Maffei 1 and IC 342 relative to the Andromeda galaxy are in the range 250-300 km s^-1^, which are rather high velocities for the local neighbourhood. Here we study groups of four galaxies, initially composed of two binaries, and follow their evolution through two mergers until only two galaxies remain. We find that the speed of separation of the two galaxies can reach the above-mentioned range of values if (a) the rotation curves of the galaxies rise to this same range of values, and (b) the mass of the group is not excessive. We use these conditions to estimate the mass-to- light ratio of the galaxies in the local area.

  16. BRIGHTEST SATELLITE GALAXY ALIGNMENT OF SLOAN DIGITAL SKY SURVEY GALAXY GROUPS

    SciTech Connect

    Li Zhigang; Wang Yougang; Chen Xuelei; Yang Xiaohu; Xie Lizhi; Wang Xin E-mail: wangygcluster@gmail.com E-mail: lzxie@bao.ac.cn E-mail: wangxin@pha.jhu.edu

    2013-05-01

    We study the alignment signal between the distribution of the brightest satellite galaxies (BSGs) and the major axes of their host groups using the Sloan Digital Sky Survey group catalog constructed by Yang et al. After correcting for the effect of group ellipticity, a statistically significant ({approx}5{sigma}) major-axis alignment is detected and the alignment angle is found to be 43. Degree-Sign 0 {+-} 0. Degree-Sign 4. More massive and richer groups show a stronger BSG alignment. The BSG alignment around blue brightest central galaxies (BCGs) is slightly stronger than that around red BCGs. Red BSGs have a much stronger major-axis alignment than blue BSGs. Unlike BSGs, other satellites do not show very significant alignment with their group's major axis. We further explore BSG alignment using the semi-analytic model (SAM) constructed by Guo et al. In general, we found good agreement of the model with observations: BSGs in the SAM show a strong major-axis alignment that depends on group mass and richness in the same way as in observations and none of the other satellites exhibit prominent alignment. However, a discrepancy also exists in that the SAM shows a BSG color dependence opposite of that in observations, which is most probably induced by a missing large-scale environment ingredient in the SAM. The combination of two popular scenarios can explain the BSG alignment we detected. First, satellites merged into the group along the surrounding filaments, which are strongly aligned with the major axis of the group. Second, BSGs entered their host group more recently than other satellites, so they have preserved more information about their assembling history and major-axis alignment. In the SAM, we found positive evidence for the second scenario in the fact that BSGs merged into groups statistically more recently than other satellites. We also found that most of the BSGs (80%) were BCGs before they merged into groups and earlier merging BSGs tend to be closer to

  17. Mass dependent galaxy transformation mechanisms in the complex environment of SuperGroup Abell 1882

    NASA Astrophysics Data System (ADS)

    Sengupta, Aparajita

    We present our data and results from panchromatic photometry and optical spectrometry of the nearest (extremely rich) filamentary large scale structure, SuperGroup Abell 1882. It is a precursor of a cluster and is an inevitable part of the narrative in the study of galaxy transformations. There has been strong empirical evidence over the past three decades that galaxy environment affects galaxy properties. Blue disky galaxies transform into red bulge-like galaxies as they traverse into the deeper recesses of a cluster. However, we have little insight into the story of galaxy evolution in the early stages of cluster formation. Besides, in relaxed clusters that have been studied extensively, several evolutionary mechanisms take effect on similar spatial and temporal scales, making it almost impossible to disentangle different local and global mechanisms. A SuperGroup on the other hand, has a shallower dark-matter potential. Here, the accreting galaxies are subjected to evolutionary mechanisms over larger time and spatial scales. This separates processes that are otherwise superimposed in rich cluster-filament interfaces. As has been found from cluster studies, galaxy color and morphology tie very strongly with local galaxy density even in a complex and nascent structure like Abell 1882. Our major results indicate that there is a strong dependence of galaxy transformations on the galaxy masses themselves. Mass- dependent evolutionary mechanisms affect galaxies at different spatial scales. The galaxy color also varies with radial projected distance from the assumed center of the structure for a constant local galaxy density, indicating the underlying large scale structure as a second order evolutionary driver. We have looked for clues to the types of mechanisms that might cause the transformations at various mass regimes. We have found the thoroughly quenched low mass galaxies confined to the groups, whereas there are evidences of intermediate-mass quenched galaxies

  18. Hot Gas and AGN Feedback in Galaxies and Nearby Groups

    NASA Astrophysics Data System (ADS)

    Jones, Christine; Forman, William; Bogdan, Akos; Randall, Scott; Kraft, Ralph; Churazov, Eugene

    2013-07-01

    Massive galaxies harbor a supermassive black hole at their centers. At high redshifts, these galaxies experienced a very active quasar phase, when, as their black holes grew by accretion, they produced enormous amounts of energy. At the present epoch, these black holes still undergo occasional outbursts, although the mode of their energy release is primarily mechanical rather than radiative. The energy from these outbursts can reheat the cooling gas in the galaxy cores and maintain the red and dead nature of the early-type galaxies. These outbursts also can have dramatic effects on the galaxy-scale hot coronae found in the more massive galaxies. We describe research in three areas related to the hot gas around galaxies and their supermassive black holes. First we present examples of galaxies with AGN outbursts that have been studied in detail. Second, we show that X-ray emitting low-luminosity AGN are present in 80% of the galaxies studied. Third, we discuss the first examples of extensive hot gas and dark matter halos in optically faint galaxies.

  19. On the Formation of Elliptical Galaxies via Mergers in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Taranu, Dan; Dubinski, John; Yee, Howard K. C.

    2015-08-01

    Giant elliptical galaxies have long been thought to form through gas-rich "major" mergers of two roughly equal-mass spiral galaxies. However, ellipticals are often found at the centers of groups and are likely to have undergone several significant mergers since z=2. We test the hypothesis that ellipticals form through multiple, mainly minor and dry mergers in groups, using hundreds of N-body simulations of mergers in groups of three to twenty-five spirals (Taranu et al. 2013).Realistic mock observations of the central merger remnants show that they have similar surface brightness profiles to local ellipticals. The size-luminosity and velocity dispersion-luminosity relations have modest (~0.1 dex) scatter, with similar slopes; however, most remnants are too large and have too low dispersions for their luminosities. Some remnants show substantial (v/σ > 0.1) rotational support, but most are slow rotators with v/σ << 0.5.Ellipticals also follow a tight "fundamental plane" scaling relation between size R, mean surface brightness μ and velocity dispersion σ: R ∝ σ^a μ^b. This relation has small (<0.06 dex) scatter and significantly different coefficients from the expected scaling (a "tilt"). The remnants lie on a similar fundamental plane, with even smaller scatter (0.02 dex) and a tilt in the correct sense - albeit weaker than observed. This tilt is caused by variable dark matter fractions within the effective radius, such that massive merger remnants have larger central dark matter fractions than their lower-mass counterparts (Taranu et al. 2015).These results suggest that massive ellipticals can originate from multiple, mainly minor and dry mergers of spirals at z<2, producing tight scaling relations in the process. However, significant gas dissipation and/or more compact progenitor spirals may be needed to produce lower-mass, rapidly-rotating ellipticals. I will also show preliminary results from simulations with more realistic progenitor galaxies (including

  20. Galaxy Group Stephan's Quintet Video File HubbleMinute: Battle Royale in Stephan's Quintet

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The Hubble Space Telescope's closeup view of Stephan's Quintet, a group of five galaxies, reveals a string of brighter star clusters that separate like a diamond necklace. Astronomers studying the compact galaxy group Stephan's Quintet have seen creative destruction in the many collisions taking place among its galaxies. This HubbleMinute discusses what astronomers are learning and hope to learn from exploring the quintet.

  1. Group-galaxy correlations in redshift space as a probe of the growth of structure

    NASA Astrophysics Data System (ADS)

    Mohammad, F. G.; de la Torre, S.; Bianchi, D.; Guzzo, L.; Peacock, J. A.

    2016-05-01

    We investigate the use of the cross-correlation between galaxies and galaxy groups to measure redshift-space distortions (RSD) and thus probe the growth rate of cosmological structure. This is compared to the classical approach based on using galaxy auto-correlation. We make use of realistic simulated galaxy catalogues that have been constructed by populating simulated dark matter haloes with galaxies through halo occupation prescriptions. We adapt the classical RSD dispersion model to the case of the group-galaxy cross-correlation function and estimate the RSD parameter β by fitting both the full anisotropic correlation function ξs(rp, π) and its multipole moments. In addition, we define a modified version of the latter statistics by truncating the multipole moments to exclude strongly non-linear distortions at small transverse scales. We fit these three observable quantities in our set of simulated galaxy catalogues and estimate statistical and systematic errors on β for the case of galaxy-galaxy, group-group, and group-galaxy correlation functions. When ignoring off-diagonal elements of the covariance matrix in the fitting, the truncated multipole moments of the group-galaxy cross-correlation function provide the most accurate estimate, with systematic errors below 3 per cent when fitting transverse scales larger than 10 h-1 Mpc. Including the full data covariance enlarges statistical errors but keep unchanged the level of systematic error. Although statistical errors are generally larger for groups, the use of group-galaxy cross-correlation can potentially allow the reduction of systematics while using simple linear or dispersion models.

  2. TIDAL INTERACTION AS THE ORIGIN OF EARLY-TYPE DWARF GALAXIES IN GROUP ENVIRONMENTS

    SciTech Connect

    Paudel, Sanjaya; Ree, Chang H.

    2014-11-20

    We present a sample of dwarf galaxies that suffer ongoing disruption by the tidal forces of nearby massive galaxies. By analyzing structural and stellar population properties using the archival imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS), we find that they are likely a ''smoking gun'' example of the formation through tidal stirring of early-type dwarf galaxies (dEs) in the galaxy group environment. The inner cores of these galaxies are fairly intact and the observed light profiles are well fit by the Sérsic functions while the tidally stretched stellar halos are prominent in the outer parts. They are all located within a sky-projected distance of 50 kpc from the centers of the host galaxies and no dwarf galaxies have relative line-of-sight velocities larger than 205 km s{sup –1} to their hosts. We derive the Composite Stellar Population properties of these galaxies by fitting the SDSS optical spectra to a multiple-burst composite stellar population model. We find that these galaxies accumulate a significant fraction of stellar mass within the last 1 Gyr and contain a majority stellar population with an intermediate age of 2 to 4 Gyr. Based on this evidence, we argue that tidal stirring, particularly through the galaxy-galaxy interaction, might have an important role in the formation and evolution of dEs in the group environment where the influence of other gas stripping mechanism might be limited.

  3. Evidence for Tidal Interactions and Mergers as the Origin of Galaxy Morphology Evolution in Compact Groups

    NASA Astrophysics Data System (ADS)

    Coziol, R.; Plauchu-Frayn, I.

    2007-06-01

    We present the results of a morphological study based on NIR images of 25 galaxies, with different levels of nuclear activity (star formation or AGN), in eight compact groups (CGs) of galaxies. We independently perform two different analyses: a study of the deviations of the isophotal levels from pure ellipses and a study of morphological asymmetries. The results yielded by the two analyses are highly consistent. For the first time, it is possible to show that deviations from pure ellipses are produced by inhomogeneous stellar mass distributions related to galaxy interactions and mergers. We find evidence of mass asymmetries in 74% of the galaxies in our sample. In 59% of these cases, the asymmetries come in pairs and are consistent with tidal effects produced by the proximity of companion galaxies. The symmetric galaxies are generally small in size or mass and inactive, and have an early-type morphology. They may have already lost their gas and least-attached envelope of stars to their more massive companions. In 20% of the galaxies we find evidence for cannibalism: a big galaxy swallowing a smaller companion. In 36% of the early-type galaxies the color gradient is positive (blue nucleus) or flat. Summing up these results, as much as 52% of the galaxies in our sample could show evidence of an ongoing or past merger. Our observations also suggest that galaxies in CGs merge more frequently under ``dry'' conditions (that is, once they have lost most of their gas). The high frequency of interacting and merging galaxies observed in our study is consistent with the bias of our sample toward CGs of type B, which represent the most active phase in the evolution of the groups. In these groups we also find a strong correlation between asymmetries and nuclear activity in early-type galaxies. This correlation allows us to identify tidal interactions and mergers as the cause of galaxy morphology transformation in CGs.

  4. Jets and Outflows in Radio Galaxies: Implications for AGN Feedback

    NASA Astrophysics Data System (ADS)

    Torresi, Eleonora; Grandi, Paola; Costantini, Elisa; Palumbo, Giorgio G. C.

    One of the main debated astrophysical problems is the role of the AGN feedback in galaxy formation. It is known that massive black holes have a profound effect on the formation and evolution of galaxies, but how black holes and galaxies communicate is still an unsolved problem. For Radio Galaxies, feedback studies have mainly focused on jet/cavity systems in the most massive and X-ray luminous galaxy clusters. The recent high-resolution detection of warm absorbers in some Broad Line Radio Galaxies allow us to investigate the interplay between the nuclear engine and the surrounding medium from a different perspective. We report on the detection of warm absorbers in two Broad Line Radio Galaxies, 3C 382 and 3C 390.3, and discuss the physical and energetic properties of the absorbing gas. Finally, we attempt a comparison between radio-loud and radio-quiet outflows.

  5. Photometric and Kinematical Study of Nearby Groups of Galaxies Around IC 65 and NGC 6962

    NASA Astrophysics Data System (ADS)

    Vennik, J.; Tago, E.

    The IC 65 group (z = 0.0089) of four late type galaxies - IC 65, UGC 608, UGC 622, and PGC 138291 - has been studied earlier in the 21 cm HI line by van Moorsel (1983, A&AS, 54, 1), who found disturbed HI envelopes of bright group members, and detected a new HI-rich LSB galaxy.

  6. The Effect of Halo Mass on the H I Content of Galaxies in Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Yoon, Ilsang; Rosenberg, Jessica L.

    2015-10-01

    We combine data from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA Survey (ALFALFA) to study the cold atomic gas content of galaxies in groups and clusters in the local universe. A careful cross-matching of galaxies in the SDSS, ALFALFA, and SDSS group catalogs provides a sample of group galaxies with stellar masses {10}8.4{M}ȯ ≤slant {M}*≤slant {10}10.6{M}ȯ and group halo masses {10}12.5{h}-1{M}ȯ ≤slant {M}h≤slant {10}15.0{h}-1{M}ȯ . Controlling our sample in stellar mass and redshift, we find no significant radial variation in the galaxy H i gas-to-stellar mass ratio for the halo mass range in our sample. However, the fraction of galaxies detected in ALFALFA declines steadily toward the centers of groups, with the effect being most prominent in the most massive halos. In the outskirts of massive halos a hint of a depressed detection fraction for low-mass galaxies suggests pre-processing that decreases the H i in these galaxies before they fall into massive clusters. We interpret the decline in the ALFALFA detection of galaxies in the context of a threshold halo mass for ram pressure stripping for a given galaxy stellar mass. The lack of an observable decrease in the galaxy H i gas-to-stellar mass ratio with the position of galaxies within groups and clusters highlights the difficulty of detecting the impact of environment on the galaxy H i content in a shallow H i survey.

  7. The Effect of Halo Mass on the H I Content of Galaxies in Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Yoon, Ilsang; Rosenberg, Jessica L.

    2015-10-01

    We combine data from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA Survey (ALFALFA) to study the cold atomic gas content of galaxies in groups and clusters in the local universe. A careful cross-matching of galaxies in the SDSS, ALFALFA, and SDSS group catalogs provides a sample of group galaxies with stellar masses {10}8.4{M}⊙ ≤slant {M}*≤slant {10}10.6{M}⊙ and group halo masses {10}12.5{h}-1{M}⊙ ≤slant {M}h≤slant {10}15.0{h}-1{M}⊙ . Controlling our sample in stellar mass and redshift, we find no significant radial variation in the galaxy H i gas-to-stellar mass ratio for the halo mass range in our sample. However, the fraction of galaxies detected in ALFALFA declines steadily toward the centers of groups, with the effect being most prominent in the most massive halos. In the outskirts of massive halos a hint of a depressed detection fraction for low-mass galaxies suggests pre-processing that decreases the H i in these galaxies before they fall into massive clusters. We interpret the decline in the ALFALFA detection of galaxies in the context of a threshold halo mass for ram pressure stripping for a given galaxy stellar mass. The lack of an observable decrease in the galaxy H i gas-to-stellar mass ratio with the position of galaxies within groups and clusters highlights the difficulty of detecting the impact of environment on the galaxy H i content in a shallow H i survey.

  8. Groups of Galaxies in the CDFS: Tracing the Evolution of Galaxies from z=1.6 to the Present Day

    NASA Astrophysics Data System (ADS)

    Mulchaey, John

    2012-10-01

    Although groups are the most common environment experienced by galaxies, we still know surprisingly little about the mechanisms that drive galaxy evolution in these systems. While galaxy-galaxy encounters and mergers are thought to be common in groups, recent observations and simulations suggest encounters with the hot intragroup medium may also be important. To help distinguish between these possibilities, groups with and without a hot intragroup medium must be studied over a range of redshifts. Such studies have been limited because groups tend to be very faint in X-rays and difficult to detect at even moderate redshifts. Fortunately, the recently completed 4 Msec Chandra observation of the CDFS now allows the hot intragroup gas to be detected in ordinary groups out to z=1 and beyond. Here, we propose to use archival HST images from GEMS, GOODS and CANDELS to study the galaxy populations in a unique sample of 40 X-ray groups and approximately 100 non-X-ray groups in the CDFS in the redshift range z=0.5 to z=1.6. The ACS and WFC3 images will be used to search for signs of interactions and disturbances in these galaxies which will allow a detailed analysis of the effects of interactions as a function of group mass and redshift. Since the depth of the Chandra exposure in the CDFS is unlikely to be matched for any other fields, our group sample will be the only one with sufficient X-ray data to allow such a study for the forseeable future.

  9. Kinematics of dwarf galaxies in gas-rich groups, and the survival and detectability of tidal dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Sweet, Sarah M.; Drinkwater, Michael J.; Meurer, Gerhardt; Kilborn, Virginia; Audcent-Ross, Fiona; Baumgardt, Holger; Bekki, Kenji

    2016-01-01

    We present DEIMOS multi-object spectroscopy (MOS) of 22 star-forming dwarf galaxies located in four gas-rich groups, including six newly discovered dwarfs. Two of the galaxies are strong tidal dwarf galaxy (TDG) candidates based on our luminosity-metallicity relation definition. We model the rotation curves of these galaxies. Our sample shows low mass-to-light ratios (M/L = 0.73 ± 0.39 M⊙/L⊙) as expected for young, star-forming dwarfs. One of the galaxies in our sample has an apparently strongly falling rotation curve, reaching zero rotational velocity outside the turnover radius of rturn = 1.2re. This may be (1) a polar ring galaxy, with a tilted bar within a face-on disc; (2) a kinematic warp. These scenarios are indistinguishable with our current data due to limitations of slit alignment inherent to MOS-mode observations. We consider whether TDGs can be detected based on their tidal radius, beyond which tidal stripping removes kinematic tracers such as Hα emission. When the tidal radius is less than about twice the turnover radius, the expected falling rotation curve cannot be reliably measured. This is problematic for as much as half of our sample, and indeed more generally, galaxies in groups like these. Further to this, the Hα light that remains must be sufficiently bright to be detected; this is only the case for three (14 per cent) galaxies in our sample. We conclude that the falling rotation curves expected of TDGs are intrinsically difficult to detect.

  10. Galaxies

    SciTech Connect

    Not Available

    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.

  11. Cluster of galaxies & Cosmology - X-ray analysis of fossil group RXJ1720.1+2360

    NASA Astrophysics Data System (ADS)

    Lozada, Monica

    2012-09-01

    We present the results on the X-ray analysis of fossil group of galaxies RXJ1720.1+2360. Fossil Groups are systems associated to extended emission in X-rays with one single central elliptical galaxy surrounded by very faint companions. This unusual lack of bright galaxies in the group is presumably due to galactic cannibalism. In this study we present for the first time the imaging and spectral analysis of the XMM-Newton data of RXJ1720.1+2360. This work is part of a systematic study to determine the X-ray properties of fossil groups.

  12. The environmental history of group and cluster galaxies in a Λ cold dark matter universe

    NASA Astrophysics Data System (ADS)

    De Lucia, Gabriella; Weinmann, Simone; Poggianti, Bianca M.; Aragón-Salamanca, Alfonso; Zaritsky, Dennis

    2012-06-01

    We use publicly available galaxy merger trees, obtained applying semi-analytic techniques to a large high-resolution cosmological simulation, to study the environmental history of group and cluster galaxies. Our results highlight the existence of an intrinsic history bias which makes the nature versus nurture (as well as the mass versus environment) debate inherently ill posed. In particular, we show that (i) surviving massive satellites were accreted later than their less massive counterparts, from more massive haloes and (ii) the mixing of galaxy populations is incomplete during halo assembly, which creates a correlation between the time a galaxy becomes satellite and its present distance from the parent halo centre. The weakest trends are found for the most massive satellites, as a result of efficient dynamical friction and late formation times of massive haloes. A large fraction of the most massive group/cluster members are accreted on to the main progenitor of the final halo as central galaxies, while about half of the galaxies with low and intermediate stellar masses are accreted as satellites. Large fractions of group and cluster galaxies (in particular those of low stellar mass) have therefore been ‘pre-processed’ as satellites of groups with mass ˜1013 M⊙. To quantify the relevance of hierarchical structure growth on the observed environmental trends, we have considered observational estimates of the passive galaxy fractions and their variation as a function of halo mass and clustercentric distance. Comparisons with our theoretical predictions require relatively long times (˜5-7 Gyr) for the suppression of star formation in group and cluster satellites. It is unclear how such a gentle mode of strangulation can be achieved by simply relaxing the assumption of instantaneous stripping of the hot gas reservoir associated with accreting galaxies, or if the difficulties encountered by recent galaxy formation models in reproducing the observed trends

  13. RESOLVING THE GALAXIES WITHIN A GIANT Ly{alpha} NEBULA: WITNESSING THE FORMATION OF A GALAXY GROUP?

    SciTech Connect

    Prescott, Moire K. M.; Dey, Arjun; Jannuzi, Buell T.; Brodwin, Mark; Chaffee, Frederic H.; Desai, Vandana; Soifer, B. T.; Eisenhardt, Peter; Le Floc'h, Emeric; Matsuda, Yuichi

    2012-06-20

    Detailed analysis of the substructure of Ly{alpha} nebulae can put important constraints on the physical mechanisms at work and the properties of galaxies forming within them. Using high-resolution Hubble Space Telescope (HST) imaging of a Ly{alpha} nebula at z Almost-Equal-To 2.656, we have taken a census of the compact galaxies in the vicinity, used optical/near-infrared colors to select system members, and put constraints on the morphology of the spatially extended emission. The system is characterized by (1) a population of compact, low-luminosity ({approx}0.1 L*) sources-17 primarily young, small (R{sub e} Almost-Equal-To 1-2 kpc), disky galaxies including an obscured active galactic nucleus-that are all substantially offset ({approx}>20 kpc) from the line-emitting nebula; (2) the lack of a central galaxy at or near the peak of the Ly{alpha} emission; and (3) several nearly coincident, spatially extended emission components-Ly{alpha}, He II, and UV continuum-that are extremely smooth. These morphological findings are difficult to reconcile with theoretical models that invoke outflows, cold flows, or resonant scattering, suggesting that while all of these physical phenomena may be occurring, they are not sufficient to explain the powering and large extent of Ly{alpha} nebulae. In addition, although the compact galaxies within the system are irrelevant as power sources, the region is significantly overdense relative to the field galaxy population (by at least a factor of four). These observations provide the first estimate of the luminosity function of galaxies within an individual Ly{alpha} nebula system and suggest that large Ly{alpha} nebulae may be the seeds of galaxy groups or low-mass clusters.

  14. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    SciTech Connect

    Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit; Anthony-Twarog, Barbara J. E-mail: holtz@nmsu.edu

    2015-06-15

    We present stellar metallicities in Leo I, Leo II, IC 1613, and Phoenix dwarf galaxies derived from medium (F390M) and broad (F555W, F814W) band photometry using the Wide Field Camera 3 instrument on board the Hubble Space Telescope. We measured metallicity distribution functions (MDFs) in two ways, (1) matching stars to isochrones in color–color diagrams and (2) solving for the best linear combination of synthetic populations to match the observed color–color diagram. The synthetic technique reduces the effect of photometric scatter and produces MDFs 30%–50% narrower than the MDFs produced from individually matched stars. We fit the synthetic and individual MDFs to analytical chemical evolution models (CEMs) to quantify the enrichment and the effect of gas flows within the galaxies. Additionally, we measure stellar metallicity gradients in Leo I and II. For IC 1613 and Phoenix our data do not have the radial extent to confirm a metallicity gradient for either galaxy. We find the MDF of Leo I (dwarf spheroidal) to be very peaked with a steep metal-rich cutoff and an extended metal-poor tail, while Leo II (dwarf spheroidal), Phoenix (dwarf transition), and IC 1613 (dwarf irregular) have wider, less peaked MDFs than Leo I. A simple CEM is not the best fit for any of our galaxies; therefore we also fit the “Best Accretion Model” of Lynden-Bell. For Leo II, IC 1613, and Phoenix we find similar accretion parameters for the CEM even though they all have different effective yields, masses, star formation histories, and morphologies. We suggest that the dynamical history of a galaxy is reflected in the MDF, where broad MDFs are seen in galaxies that have chemically evolved in relative isolation and narrowly peaked MDFs are seen in galaxies that have experienced more complicated dynamical interactions concurrent with their chemical evolution.

  15. DETECTION OF MOLECULAR GAS IN VOID GALAXIES: IMPLICATIONS FOR STAR FORMATION IN ISOLATED ENVIRONMENTS

    SciTech Connect

    Das, M.; Honey, M.; Saito, T.; Iono, D.; Ramya, S.

    2015-12-10

    We present the detection of molecular gas from galaxies located in nearby voids using the CO(1–0) line emission as a tracer. The observations were performed using the 45 m single dish radio telescope of the Nobeyama Radio Observatory. Void galaxies lie in the most underdense parts of our universe and a significant fraction of them are gas rich, late-type spiral galaxies. Although isolated, they have ongoing star formation but appear to be slowly evolving compared to galaxies in denser environments. Not much is known about their star formation properties or cold gas content. In this study, we searched for molecular gas in five void galaxies. The galaxies were selected based on their relatively high IRAS fluxes or Hα line luminosities, both of which signify ongoing star formation. All five galaxies appear to be isolated and two lie within the Bootes void. We detected CO(1–0) emission from four of the five galaxies in our sample and their molecular gas masses lie between 10{sup 8} and 10{sup 9} M{sub ⊙}. We conducted follow-up Hα imaging observations of three detected galaxies using the Himalayan Chandra Telescope and determined their star formation rates (SFRs) from their Hα fluxes. The SFR varies from 0.2 to 1 M{sub ⊙} yr{sup −1}; which is similar to that observed in local galaxies. Our study indicates that although void galaxies reside in underdense regions, their disks contain molecular gas and have SFRs similar to galaxies in denser environments. We discuss the implications of our results.

  16. EVOLUTION OF GROUP GALAXIES FROM THE FIRST RED-SEQUENCE CLUSTER SURVEY

    SciTech Connect

    Li, I. H.; Yee, H. K. C.; Hsieh, B. C.; Gladders, M. E-mail: hyee@astro.utoronto.ca E-mail: gladders@oddjob.uchicago.edu

    2012-04-20

    We study the evolution of the red-galaxy fraction (f{sub red}) in 905 galaxy groups with 0.15 {<=} z < 0.52. The galaxy groups are identified by the 'probability friends-of-friends' algorithm from the first Red-Sequence Cluster Survey (RCS1) photometric-redshift sample. There is a high degree of uniformity in the properties of the red sequence of the group galaxies, indicating that the luminous red-sequence galaxies in the groups are already in place by z {approx} 0.5 and that they have a formation epoch of z {approx}> 2. In general, groups at lower redshifts exhibit larger f{sub red} than those at higher redshifts, showing a group Butcher-Oemler effect. We investigate the evolution of f{sub red} by examining its dependence on four parameters, one of which can be classified as intrinsic and three of which can be classified as environmental: galaxy stellar mass (M{sub *}), total group stellar mass (M{sub *,grp}, a proxy for group halo mass), normalized group-centric radius (r{sub grp}), and local galaxy density ({Sigma}{sub 5}). We find that M{sub *} is the dominant parameter such that there is a strong correlation between f{sub red} and galaxy stellar mass. Furthermore, the dependence of f{sub red} on the environmental parameters is also a strong function of M{sub *}. Massive galaxies (M{sub *} {approx}> 10{sup 11} M{sub Sun }) show little dependence of f{sub red} on r{sub grp}, M{sub *,grp}, and {Sigma}{sub 5} over the redshift range. The dependence of f{sub red} on these parameters is primarily seen for galaxies with lower masses, especially for M{sub *} {approx}< 10{sup 10.6} M{sub Sun }. We observe an apparent 'group down-sizing' effect, in that galaxies in lower-mass halos, after controlling for galaxy stellar mass, have lower f{sub red}. We find a dependence of f{sub red} on both r{sub grp} and {Sigma}{sub 5} after the other parameters are controlled. At a fixed r{sub grp}, there is a significant dependence of f{sub red} on {Sigma}{sub 5}, while r{sub grp

  17. Galaxy triplets in Sloan Digital Sky Survey Data Release 7 - II. A connection with compact groups?

    NASA Astrophysics Data System (ADS)

    Duplancic, Fernanda; O'Mill, Ana Laura; Lambas, Diego G.; Sodré, Laerte; Alonso, Sol

    2013-08-01

    We analyse a sample of 71 triplets of luminous galaxies derived from the work of O'Mill et al. We compare the properties of triplets and their members with those of control samples of compact groups, the 10 brightest members of rich clusters and galaxies in pairs. The triplets are restricted to have members with spectroscopic redshifts in the range 0.01 ≤ z ≤ 0.14 and absolute r-band luminosities brighter than Mr = -20.5. For these member galaxies, we analyse the stellar mass content, the star formation rates, the Dn(4000) parameter and (Mg - Mr) colour index. Since galaxies in triplets may finally merge in a single system, we analyse different global properties of these systems. We calculate the probability that the properties of galaxies in triplets are strongly correlated. We also study total star formation activity and global colours, and define the triplet compactness as a measure of the percentage of the system total area that is filled by the light of member galaxies. We concentrate in the comparison of our results with those of compact groups to assess how the triplets are a natural extension of these compact systems. Our analysis suggests that triplet galaxy members behave similarly to compact group members and galaxies in rich clusters. We also find that systems comprising three blue, star-forming, young stellar population galaxies (blue triplets) are most probably real systems and not a chance configuration of interloping galaxies. The same holds for triplets composed of three red, non-star-forming galaxies, showing the correlation of galaxy properties in these systems. From the analysis of the triplet as a whole, we conclude that, at a given total stellar mass content, triplets show a total star formation activity and global colours similar to compact groups. However, blue triplets show a high total star formation activity with a lower stellar mass content. From an analysis of the compactness parameter of the systems we find that light is even more

  18. The GEEC2 spectroscopic survey of Galaxy groups at 0.8 < z < 1

    NASA Astrophysics Data System (ADS)

    Balogh, Michael L.; McGee, Sean L.; Mok, Angus; Wilman, David J.; Finoguenov, Alexis; Bower, Richard G.; Mulchaey, John S.; Parker, Laura C.; Tanaka, Masayuki

    2014-09-01

    We present the data release of the Gemini-South GMOS spectroscopy in the fields of 11 galaxy groups at 0.8 < z < 1, within the COSMOS field. This forms the basis of the Galaxy Environment Evolution Collaboration 2 (GEEC2) project to study galaxy evolution in haloes with M ˜ 1013 M⊙ across cosmic time. The final sample includes 162 spectroscopically confirmed members with R < 24.75, and is >50 per cent complete for galaxies within the virial radius, and with stellar mass Mstar > 1010.3 M⊙. Including galaxies with photometric redshifts, we have an effective sample size of ˜400 galaxies within the virial radii of these groups. We present group velocity dispersions, dynamical and stellar masses. Combining with the GCLASS sample of more massive clusters at the same redshift, we find the total stellar mass is strongly correlated with the dynamical mass, with log M200 = 1.20(log Mstar - 12) + 14.07. This stellar fraction of ˜1 per cent is lower than predicted by some halo occupation distribution models, though the weak dependence on halo mass is in good agreement. Most groups have an easily identifiable most massive galaxy (MMG) near the centre of the galaxy distribution, and we present the spectroscopic properties and surface brightness fits to these galaxies. The total stellar mass distribution in the groups, excluding the MMG, compares well with an NFW (Navarro Frenk & White) profile with concentration 4, for galaxies beyond ˜0.2R200. This is more concentrated than the number density distribution, demonstrating that there is some mass segregation.

  19. The HST Snapshot Survey of Nearby Dwarf Galaxy Candidates. III. Resolved Dwarf Galaxies In and Beyond the Local Group

    NASA Astrophysics Data System (ADS)

    Grebel, E. K.; Seitzer, P.; Dolphin, A. E.; Geisler, D.; Guhathakurta, P.; Hodge, P. W.; Karachentsev, I. D.; Karachentseva, V. E.; Sarajedini, A.; Sharina, M. E.

    1999-12-01

    We present results for several nearby, resolved dwarf galaxies imaged with WFPC2 in the framework of our HST snapshot survey of nearby dwarf galaxy candidates (Seitzer et al., paper I in this series). All data presented here were analyzed with the automated photometry package HSTPHOT (Dolphin et al., paper IV in this series). Our closest target is the recently discovered Cassiopeia dwarf spheroidal (dSph) galaxy (Karachentsev & Karachentseva 1999, A&A, 341, 355), a new Local Group member and companion of M31 (Grebel & Guhathakurta 1999, ApJ, 511, 101). Our WFPC2 snapshot data reveal a pronounced red horizontal branch in Cas dSph. IC 5152 is a dwarf irregular (dIrr) just beyond the Local Group. Our data show a significant intermediate-age population with a strongly tilted asymptotic giant branch (AGB), a substantial young population, and a wide giant branch. Other nearby galaxies to be discussed include NGC 1560, ESO 471-G006, ESO 470-G018, and KK 035. Most of these galaxies are being resolved into stars for the first time. We describe their properties in detail and derive distances for all dwarfs with a well-defined tip of the red giant branch. Membership of these galaxies in nearby groups is discussed. Support for this work was provided by NASA through grant GO-08192.97A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. EKG acknowledges support by NASA through grant HF-01108.01-98A from the Space Telescope Science Institute. EKG and IDK are supported by the Henri Chrétien International Research Grant administered by the American Astronomical Society. PG is an Alfred P. Sloan Research Fellow.

  20. The Evolution of Galaxy Number Density at z > 8 and Its Implications

    NASA Astrophysics Data System (ADS)

    Conselice, Christopher J.; Wilkinson, Aaron; Duncan, Kenneth; Mortlock, Alice

    2016-10-01

    The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However, there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z ∼ 8 to determine how the number densities of galaxies change as a function of time and mass limit. We show that the increase in the total number density of galaxies (ϕ T), more massive than M * = 106 M ⊙, decreases as ϕ T ∼ t ‑1, where t is the age of the universe. We further show that this evolution turns over and rather increases with time at higher mass lower limits of M * > 107 M ⊙. By using the M * = 106 M ⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is {2.0}-0.6+0.7× {10}12 (2 trillion), almost a factor of 10 higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.

  1. Resolving the stellar halos of six massive disk galaxies beyond the Local Group

    NASA Astrophysics Data System (ADS)

    Monachesi, Antonela; Bell, Eric F.; Radburn-Smith, David J.; de Jong, Roelof S.; Bailin, Jeremy; Holwerda, Benne; Streich, David

    2016-08-01

    Models of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies' merger histories. Currently, only few detailed observations of stellar halos are available, mainly for the Milky Way and M31. We present the stellar halo color/metallicity and density profiles of red giant branch stars out to ~60 kpc along the minor axis of six massive nearby Milky Way-like galaxies beyond the Local Group from the Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey. This enlargement of the sample of galaxies with observations of stellar halo properties is needed to understand the range of possible halo properties, i.e. not only the mean properties but also the halo-to-halo scatter, what a `typical' halo looks like, and how similar the Milky Way halo is to other halos beyond the Local Group.

  2. The ultraviolet and infrared star formation rates of compact group galaxies: an expanded sample

    NASA Astrophysics Data System (ADS)

    Lenkić, Laura; Tzanavaris, Panayiotis; Gallagher, Sarah C.; Desjardins, Tyler D.; Walker, Lisa May; Johnson, Kelsey E.; Fedotov, Konstantin; Charlton, Jane; Hornschemeier, Ann E.; Durrell, Pat R.; Gronwall, Caryl

    2016-07-01

    Compact groups of galaxies provide insight into the role of low-mass, dense environments in galaxy evolution because the low velocity dispersions and close proximity of galaxy members result in frequent interactions that take place over extended time-scales. We expand the census of star formation in compact group galaxies by Tzanavaris et al. (2010) and collaborators with Swift UVOT, Spitzer IRAC and MIPS 24 μm photometry of a sample of 183 galaxies in 46 compact groups. After correcting luminosities for the contribution from old stellar populations, we estimate the dust-unobscured star formation rate (SFRUV) using the UVOT uvw2 photometry. Similarly, we use the MIPS 24 μm photometry to estimate the component of the SFR that is obscured by dust (SFRIR). We find that galaxies which are MIR-active (MIR-`red'), also have bluer UV colours, higher specific SFRs, and tend to lie in H I-rich groups, while galaxies that are MIR-inactive (MIR-`blue') have redder UV colours, lower specific SFRs, and tend to lie in H I-poor groups. We find the SFRs to be continuously distributed with a peak at about 1 M⊙ yr-1, indicating this might be the most common value in compact groups. In contrast, the specific SFR distribution is bimodal, and there is a clear distinction between star-forming and quiescent galaxies. Overall, our results suggest that the specific SFR is the best tracer of gas depletion and galaxy evolution in compact groups.

  3. THE EPOCH OF ASSEMBLY OF TWO GALAXY GROUPS: A COMPARATIVE STUDY

    SciTech Connect

    Nichols, Matthew; Bland-Hawthorn, Joss

    2013-10-01

    Nearby galaxy groups of comparable mass to the Local Group show global variations that reflect differences in their evolutionary history. Satellite galaxies in groups have higher levels of gas deficiency as the distance to their host decreases. The well established gas-deficiency profile of the Local Group reflects an epoch of assembly starting at z ∼< 10. We investigate whether this gas-deficiency profile can be used to determine the epoch of assembly for other nearby groups. We choose the M81 group as this has the most complete inventory, both in terms of membership and multi-wavelength observations. We expand our earlier evolutionary model of satellite dwarf galaxies to not only confirm this result for the Local Group but also show that the more gas-rich M81 group is likely to have assembled at a later time (z ∼< 1-3) than the Local Group.

  4. NGC 5291: Implications for the Formation of Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Malphrus, Benjamin K.; Simpson, Caroline E.; Gottesman, S. T.; Hawarden, Timothy G.

    1997-01-01

    The possible formation and evolution of dwarf irregular galaxies from material derived from perturbed evolved galaxies is addressed via an H I study of a likely example, the peculiar system NGC 5291. This system, located in the western outskirts of the cluster Abell 3574, contains the lenticular galaxy NGC 5291 which is in close proximity to a disturbed companion and is flanked by an extensive complex of numerous knots extending roughly 4 min north and 4 min south of the galaxy. In an initial optical and radio study, Longmore et al. (1979, MNRAS, 188, 285) showed that these knots have the spectra of vigorous star-forming regions, and suggested that some may in fact be young dwarf irregular galaxies. High resolution 21-cm line observations taken with the VLA are presented here and reveal that the H I distribution associated with this system encompasses not only the entire N-S complex of optical knots, but also forms an incomplete ring or tail that extends approximately 3 min to the west. The H I associated with NGC 5291 itself shows a high velocity range; the Seashell is not detected. The formation mechanism for this unusual system is unclear and two models - a large, low-luminosity ram-swept disk, and a ram-swept interaction-are discussed. The H I in the system contains numerous concentrations, mostly along the N-S arc of the star-forming complexes, which generally coincide with one or more optical knots; the larger H I features contain several x 10(exp 9) solar mass of gas. Each of the knots is compared to a set of criteria designed to determine if these objects are bound against their own internal kinetic energy and are tidally stable relative to the host galaxy. An analysis of the properties of the H I concentrations surrounding the optical star-forming complexes indicates that at least the largest of these is a bound system; it also possesses a stellar component. It is suggested that this object is a genuinely young dwarf irregular galaxy that has evolved from

  5. Star formation and environmental quenching of GEEC2 group galaxies at z ˜ 1

    NASA Astrophysics Data System (ADS)

    Mok, Angus; Balogh, Michael L.; McGee, Sean L.; Wilman, David J.; Finoguenov, Alexis; Tanaka, Masayuki; Bower, Richard G.; Hou, Annie; Mulchaey, John S.; Parker, Laura C.

    2014-03-01

    We present new analysis from the Group Environment Evolution Collaboration 2 (GEEC2) spectroscopic survey of galaxy groups at 0.8 < z < 1. Our previous work revealed an intermediate population between the star-forming and quiescent sequences and a strong environmental dependence in the fraction of quiescent galaxies. Only ˜5 per cent of star-forming galaxies in both the group and field sample show a significant enhancement in star formation, which suggests that quenching is the primary process in the transition from the star-forming to the quiescent state. To model the environmental quenching scenario, we have tested the use of different exponential quenching time-scales and delays between satellite accretion and the onset of quenching. We find that with no delay, the quenching time-scale needs to be long in order to match the observed quiescent fraction, but then this model produces too many intermediate galaxies. Fixing a delay time of 3 Gyr, as suggested from the local Universe, produces too few quiescent galaxies. The observed fractions are best matched with a model that includes a delay that is proportional to the dynamical time and a rapid quenching time-scale (˜0.25 Gyr), but this model also predicts intermediate galaxies Hδ strength higher than that observed. Using stellar synthesis models, we have tested other scenarios, such as the rejuvenation of star formation in early-type galaxies and a portion of quenched galaxies possessing residual star formation. If environment quenching plays a role in the GEEC2 sample, then our work suggests that only a fraction of intermediate galaxies may be undergoing this transition and that quenching occurs quite rapidly in satellite galaxies (≲0.25 Gyr).

  6. The Star Formation Histories of Local Group Dwarf Galaxies. III. Characterizing Quenching in Low-mass Galaxies

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2015-05-01

    We explore the quenching of low-mass galaxies (104 ≲ {{M}\\star } ≲ 108 {{M}⊙ }) as a function of lookback time using the star formation histories (SFHs) of 38 Local Group dwarf galaxies. The SFHs were derived by analyzing color-magnitude diagrams of resolved stellar populations in archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. We find: (1) lower-mass galaxies quench earlier than higher-mass galaxies; (2) inside of Rvirial there is no correlation between a satellite’s current proximity to a massive host and its quenching epoch; and (3) there are hints of systematic differences in the quenching times of M31 and Milky Way (MW) satellites, although the sample size and uncertainties in the SFHs of M31 dwarfs prohibit definitive conclusions. Combined with results from the literature, we qualitatively consider the redshift evolution (z = 0-1) of the quenched galaxy fraction over ˜7 dex in stellar mass (104 ≲ {{M}\\star } ≲ 1011.5 {{M}⊙ }). The quenched fraction of all galaxies generally increases toward the present, with both the lowest and highest-mass systems exhibiting the largest quenched fractions at all redshifts. In contrast, galaxies between {{M}\\star } ˜ 108-1010 {{M}⊙ } have the lowest quenched fractions. We suggest that such intermediate-mass galaxies are the least efficient at quenching. Finally, we compare our quenching times with predictions for infall times for low-mass galaxies associated with the MW. We find that some of the lowest-mass satellites (e.g., CVn II, Leo IV) may have been quenched before infall, while higher-mass satellites (e.g., Leo I, Fornax) typically quench ˜1-4 Gyr after infall. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA constract NAS 5-26555.

  7. INTRAGROUP AND GALAXY-LINKED DIFFUSE X-RAY EMISSION IN HICKSON COMPACT GROUPS

    SciTech Connect

    Desjardins, Tyler D.; Gallagher, Sarah C.; Tzanavaris, Panayiotis; Hornschemeier, Ann E.; Brandt, William N.; Charlton, Jane C.; Garmire, Gordon P.; Gronwall, Caryl; Konstantopoulos, Iraklis S.; Johnson, Kelsey E.; Zabludoff, Ann I.

    2013-02-15

    Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L{sub X} -T relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L{sub X} -{sigma} relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L{sub X} increases with decreasing group H I to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on H I morphology whereby systems with intragroup H I indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L{sub X} of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.

  8. Intragroup and Galaxy-linked Diffuse X-ray Emission In Hickson Compact Groups

    NASA Technical Reports Server (NTRS)

    Desjardins, Tyler D.; Gallagher, Sarah C.; Tzanavaris, Panayiotis; Mulchaey, John S.; Brandt, William N.; Charlton, Jane C.; Garmire, Gordon P.; Gronwall, Caryl; Cardiff, Ann; Johnson, Kelsey E.; Konstantopoulos, Iraklis, S.; Zabludoff, Ann I.

    2013-01-01

    Isolated compact groups (CGs) of galaxies present a range of dynamical states, group velocity dispersions, and galaxy morphologies with which to study galaxy evolution, particularly the properties of gas both within the galaxies and in the intragroup medium. As part of a large, multiwavelength examination of CGs, we present an archival study of diffuse X-ray emission in a subset of nine Hickson compact groups (HCGs) observed with the Chandra X-Ray Observatory. We find that seven of the groups in our sample exhibit detectable diffuse emission. However, unlike large-scale emission in galaxy clusters, the diffuse features in the majority of the detected groups are linked to the individual galaxies, in the form of both plumes and halos likely as a result of vigourous star formation or activity in the galaxy nucleus, as well as in emission from tidal features. Unlike previous studies from earlier X-ray missions, HCGs 31, 42, 59, and 92 are found to be consistent with the L(sub X-Tau) relationship from clusters within the errors, while HCGs 16 and 31 are consistent with the cluster L(sub X-sigma) relation, though this is likely coincidental given that the hot gas in these two systems is largely due to star formation. We find that L(sub X) increases with decreasing group Hi to dynamical-mass ratio with tentative evidence for a dependence in X-ray luminosity on Hi morphology whereby systems with intragroup Hi indicative of strong interactions are considerably more X-ray luminous than passively evolving groups. We also find a gap in the L(sub X) of groups as a function of the total group specific star formation rate. Our findings suggest that the hot gas in these groups is not in hydrostatic equilibrium and these systems are not low-mass analogs of rich groups or clusters, with the possible exception of HCG 62.

  9. Properties of 34 massive galaxy groups within 0.012 < z < 0.027

    NASA Astrophysics Data System (ADS)

    Kopylova, F. G.; Kopylov, A. I.

    2015-04-01

    In order to extend the relationship between the infrared luminosity of groups and clusters of galaxies and their dynamic mass to the 1-5 × 1013 M ⊙ mass region, we selected from the study of Ramella et al. (2004) certain galaxy groups in the region of 0.012 < z < 0.027. Based on the archive data from the SDSS, NED, and 2MASX, for these 34 galaxy groups we determined the dynamic and photometric characteristics. Overall, the sample has the following median characteristics: z = 0.0226, M 200 = 0.58 × 1014 M ⊙, L K = 1.26 × 1012 L ⊙, and N( M K < -21m) = 22. Having this sample added to the earlier prepared sample of 148 groups and clusters of galaxies, we found the following relationships between the dynamic mass M 200, infrared (IR) luminosity, and the number of galaxies within the R 200 radius: L K ( M K < -21m) ∝ M 0.77, N( M K < -21m) ∝ M 0.82, and M/L K ∝ L K/0.22. Practically all the members of the studied sample show a good agreement between the dynamic mass of groups M 200 and IR luminosity of galaxies, and eventually their stellar mass (only the group MKW12 deviates more than 2 σ in all the dependencies).

  10. Behavior of Neutral Hydrogen in the NGC 877/6 Galaxy Group

    NASA Astrophysics Data System (ADS)

    Manning Hall, Porter; Minchin, Robert F.; Taylor, Rhys

    2015-01-01

    We observed a 5 square degree area centered on -02:17:31, 14:32:00 at 21-cm as part of the Arecibo Galaxy Environment Survey (AGES) with the NGC 877/6 galaxy group at a velocity of 4000 km/s as the primary target. Our observations covered the redshift range -5,000 < cz < 20,000 km/s allowing for a large volume in front and behind the complex to be analyzed. The NGC 877/6 group contains 8 galaxies inside a common HI envelope with a total neutral hydrogen mass of LogMHI = 10.73. HI is detected outside of the optically-identified galaxies and there are a number of tidal features within the complex. These include AGC 749170, a possible tidal remnant identified by ALFALFA and whose detection we confirm here. Another, smaller group associated with UGC 1742 (LogMHI = 9.95; cz = 6900 km/s) was identified as showing signs of galaxy interaction as well as the possibility of a tidal formation not catalogued in NED as a galaxy. Of the 44 HI sources identified in the data cube, 12 (27%) were not previously recorded in the NED database as galaxies. We will continue our analysis with data from the Mock spectrometers which will extend the redshift range to 45000 km/s.

  11. Friends-of-friends galaxy group finder with membership refinement. Application to the local Universe

    NASA Astrophysics Data System (ADS)

    Tempel, E.; Kipper, R.; Tamm, A.; Gramann, M.; Einasto, M.; Sepp, T.; Tuvikene, T.

    2016-04-01

    Context. Groups form the most abundant class of galaxy systems. They act as the principal drivers of galaxy evolution and can be used as tracers of the large-scale structure and the underlying cosmology. However, the detection of galaxy groups from galaxy redshift survey data is hampered by several observational limitations. Aims: We improve the widely used friends-of-friends (FoF) group finding algorithm with membership refinement procedures and apply the method to a combined dataset of galaxies in the local Universe. A major aim of the refinement is to detect subgroups within the FoF groups, enabling a more reliable suppression of the fingers-of-God effect. Methods: The FoF algorithm is often suspected of leaving subsystems of groups and clusters undetected. We used a galaxy sample built of the 2MRS, CF2, and 2M++ survey data comprising nearly 80 000 galaxies within the local volume of 430 Mpc radius to detect FoF groups. We conducted a multimodality check on the detected groups in search for subgroups. We furthermore refined group membership using the group virial radius and escape velocity to expose unbound galaxies. We used the virial theorem to estimate group masses. Results: The analysis results in a catalogue of 6282 galaxy groups in the 2MRS sample with two or more members, together with their mass estimates. About half of the initial FoF groups with ten or more members were split into smaller systems with the multimodality check. An interesting comparison to our detected groups is provided by another group catalogue that is based on similar data but a completely different methodology. Two thirds of the groups are identical or very similar. Differences mostly concern the smallest and largest of these other groups, the former sometimes missing and the latter being divided into subsystems in our catalogue. The catalogues are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc

  12. Evidence for Multiple Mergers among Ultraluminous Infrared Galaxies: Remnants of Compact Groups?

    PubMed

    Borne; Bushouse; Lucas; Colina

    2000-02-01

    In a large sample of ultraluminous infrared galaxies (ULIRGs) imaged with the Hubble Space Telescope, we have identified a significant subsample that shows evidence for multiple mergers. The evidence is seen among two classes of ULIRGs: (1) those with multiple remnant nuclei in their core, sometimes accompanied by a complex system of tidal tails, and (2) those that are in fact dense groupings of interacting (soon-to-merge) galaxies. We conservatively estimate that, in the redshift range 0.05groups of galaxies (see Hickson). An evolutionary progression is consistent with the results: from compact groups to pairs to ULIRGs to elliptical galaxies. The last step follows the blowout of gas and dust from the ULIRG. PMID:10622759

  13. AGN feedback in groups of galaxies: a joint X-ray/low-frequency radio study

    NASA Astrophysics Data System (ADS)

    Giacintucci, S.; O'Sullivan, E.; Vrtilek, J. M.; Raychaudhury, S.; David, L. P.; Venturi, T.; Athreya, R.; Gitti, M.

    2010-07-01

    We present an ongoing, low-frequency radio/X-ray study of 18 nearby galaxy groups, chosen for the evidence, either in the X-ray or radio images, of AGN/intragroup gas interaction. We have obtained radio observations at 235 MHz and 610 MHz with the Giant Metrewave Radio Telescope (GMRT) for all the groups, and 327 MHz and 150 MHz for a few. We present results of the recent Chandra/GMRT study of the interesting case of AWM 4, a relaxed poor cluster of galaxies with no evidence of a large cool core and no X-ray cavities associated with the central radio galaxy. Our analysis shows how joining low-frequency radio data (to track the history of AGN outbursts) with X-ray data (to determine the state of the hot gas, its disturbances, heating and cooling) can provide a unique insight into the nature of the feedback mechanism in galaxy groups.

  14. MCG 06-45-001 - Not a local group galaxy

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Sage, Leslie J.

    1990-01-01

    Observations of (C-12)O and (C-13)O J = 1 to 0 for MCG 06-45-001 are examined. It is argued that two features of CO emission with velocities of 1 and 10 km/s indicate that the object is similar to the Galactic molecular clouds in the immediate vicinity, and not to a spiral galaxy as suggested previously. It is considered that CO emission cannot arise from a spiral galaxy at a distance of 2-5 Mpc and that the object is unlikely to be a nearby dwarf. The feature at 10 km/s is considered to arise from a molecular cloud associated with an H II region, which produces the observed IRAS flux.

  15. CHEMICAL ABUNDANCES OF SEVEN IRREGULAR AND THREE TIDAL DWARF GALAXIES IN THE M81 GROUP

    SciTech Connect

    Croxall, Kevin V.; Van Zee, Liese; Lee, Henry; Miller, Bryan W.; Skillman, Evan D.; Lee, Janice C.; Cote, Stephanie; Kennicutt, Robert C. E-mail: vanzee@astro.indiana.ed E-mail: skillman@astro.umn.ed E-mail: stephanie.cote@nrc-cnrc.gc.c E-mail: bmiller@gemini.ed

    2009-11-01

    We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H II regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H II region had a detection of the temperature sensitive [O III] lambda4363 line, allowing a 'direct' determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies, and the observed oxygen abundances are typically in agreement with the well-known metallicity-luminosity relation. However, three candidate 'tidal dwarf' galaxies lie well off this relation: UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sight as the M81 tidal debris field. We propose that these H II regions formed from previously enriched gas which was stripped from nearby massive galaxies (e.g., NGC 3077 and M81) during a recent tidal interaction.

  16. The frequency and properties of young tidal dwarf galaxies in nearby gas-rich groups

    NASA Astrophysics Data System (ADS)

    Lee-Waddell, K.; Spekkens, K.; Chandra, P.; Patra, N.; Cuillandre, J.-C.; Wang, J.; Haynes, M. P.; Cannon, J.; Stierwalt, S.; Sick, J.; Giovanelli, R.

    2016-08-01

    We present high-resolution Giant Metrewave Radio Telescope (GMRT) H I observations and deep Canada-France-Hawaii Telescope (CFHT) optical imaging of two galaxy groups: NGC 4725/47 and NGC 3166/9. These data are part of a multi-wavelength unbiased survey of the gas-rich dwarf galaxy populations in three nearby interacting galaxy groups. The NGC 4725/47 group hosts two tidal knots and one dwarf irregular galaxy (dIrr). Both tidal knots are located within a prominent H I tidal tail, appear to have sufficient mass (Mgas ≈ 108 M⊙) to evolve into long-lived tidal dwarf galaxies (TDGs) and are fairly young in age. The NGC 3166/9 group contains a TDG candidate, AGC 208457, at least three dIrrs and four H I knots. Deep CFHT imaging confirms that the optical component of AGC 208457 is bluer - with a 0.28 mag g - r colour - and a few Gyr younger than its purported parent galaxies. Combining the results for these groups with those from the NGC 871/6/7 group reported earlier, we find that the H I properties, estimated stellar ages and baryonic content of the gas-rich dwarfs clearly distinguish tidal features from their classical counterparts. We optimistically identify four potentially long-lived tidal objects associated with three separate pairs of interacting galaxies, implying that TDGs are not readily produced during interaction events as suggested by some recent simulations. The tidal objects examined in this survey also appear to have a wider variety of properties than TDGs of similar mass formed in current simulations of interacting galaxies, which could be the result of pre- or post-formation environmental influences.

  17. The Formation of Dust Lanes: Implications for Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Dalcanton, Julianne J.; Yoachim, Peter; Bernstein, Rebecca A.

    2004-06-01

    From a survey of edge-on disks, we find that disk galaxies show a sharp, mass-dependent transition in the structure of their dusty ISM. In more massive, rapidly rotating disks with Vc>120kms-1, we see the well-defined dust lanes traditionally associated with edge-on galaxies. However, in more slowly rotating, lower mass galaxies with Vc<120kms-1, we find no dust lanes. Instead, the distribution of dust in these galaxies has a much larger scale height and thus appears more diffuse. Evidence suggests that the change in scale height is due primarily to changes in the turbulent velocities supporting the gas layer rather than to sharp changes in the gas surface density. A detailed analysis of our sample reveals that the decrease in the dust scale height is associated with the onset of disk instabilities, evaluated for a mixed star+gas disk. Specifically, we find that all of the high-mass galaxies with dust lanes are gravitationally unstable and thus are prone to fragmentation and gravitational collapse along spiral arms. Empirically, our data imply that turbulence has lower characteristic velocities in the presence of disk instabilities, leading to smaller gas scale heights and the appearance of narrow dust lanes. The drop in velocity dispersion may be due either to a switch in the driving mechanism for turbulence from supernovae to gravitational instabilities or to a change in the response of the ISM to supernovae after the ISM has collapsed to a dense layer. We hypothesize that the drop in gas scale height may lead to significant increases in the star formation rate when disk instabilities are present. First, the collapse of the gas layer increases the typical gas density, reducing the star formation timescale. Second, the star formation efficiency increases because of lower turbulent velocities. These two effects can combine to produce a sharp increase in the star formation rate with little change in the gas surface density and may therefore provide an explanation

  18. A COMPACT GROUP OF GALAXIES AT Z = 2.48 HOSTING AN AGN-DRIVEN OUTFLOW

    SciTech Connect

    Shih, Hsin-Yi; Stockton, Alan E-mail: stockton@ifa.hawaii.edu

    2015-12-10

    We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 10{sup 11}M{sub ⊙} and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass–metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow.

  19. A 3D analysis of the metal distribution in the compact group of galaxies HCG 31

    NASA Astrophysics Data System (ADS)

    Torres-Flores, Sergio; Mendes de Oliveira, Claudia; Alfaro-Cuello, Mayte; Rodrigo Carrasco, Eleazar; de Mello, Duilia; Amram, Philippe

    2015-02-01

    We present new Gemini/GMOS integral field unit observations of the central region of the merging compact group of galaxies HCG 31. Using this data set, we derive the oxygen abundances for the merging galaxies HCG 31A and HCG 31C. We found a smooth metallicity gradient between the nuclei of these galaxies, suggesting a mixing of metals between these objects. These results are confirmed by high-resolution Fabry-Perot data, from which we infer that gas is flowing between HCG 31A and HCG 31C.

  20. Studying structure formation and evolution with strong-lensing galaxy groups

    NASA Astrophysics Data System (ADS)

    Foëx, Gaël; Motta, Veronica; Limousin, Marceau; Verdugo, Tomas; Gastaldello, Fabio

    2016-10-01

    We present the analysis of a sample of strong-lensing galaxy group candidates. Our main findings are: confirmation of group-scale systems, complex light distributions, presence of large-scale structures in their surroundings, and evidence of a strong-lensing bias in the mass-concentration relation. We also report the detection of the first 'Bullet group'.

  1. THE RELATION BETWEEN MORPHOLOGY AND DYNAMICS OF POOR GROUPS OF GALAXIES

    SciTech Connect

    Tovmassian, Hrant M.; Plionis, M. E-mail: mplionis@astro.noa.gr

    2009-05-10

    We investigate the relation between the projected morphology and the velocity dispersion of groups of galaxies using two recently compiled group catalogs, one based on the Two Micron All Sky Survey redshift survey (Crook et al.) and the other on the Sloan Digital Sky Survey Data Release 5 galaxy catalog (Tago et al.). We analyze a suitable subsample of groups from each catalog selected such that it minimizes possible systematic effects. We find that the velocity dispersion of groups is strongly correlated with the group-projected shape and size, with elongated and larger groups having a lower velocity dispersion. Such a correlation could be attributed to the dynamical evolution of groups, with groups in the initial stages of formation, before virialization is complete, having small velocity dispersion, a large size, and an elongated shape that reflects the anisotropic accretion of galaxies along filamentary structures. However, we show that the same sort of correlations could also be reproduced in prolatelike groups, irrespective of their dynamical state, if the net galaxy motion is preferentially along the group elongation, since then the groups oriented close to the line of sight will appear more spherical, will have a small projected size and high-velocity dispersion, while groups oriented close to the sky plane will appear larger in projection, more elongated, and will have smaller velocity dispersion. Although both factors must play a role in shaping the observed correlations, we attempt to disentangle them by performing tests that relate only to the dynamical evolution of groups (i.e., calculating the fraction of early-type galaxies in groups and the projected group compactness). Indeed we find a strong positive (negative) correlation between the group velocity dispersion (group-projected major axis) with the fraction of early-type galaxy members. We conclude that (1) the observed dependences of the group velocity dispersion on the group-projected size and

  2. SLOSHING COLD FRONTS IN GALAXY GROUPS AND THEIR PERTURBING DISK GALAXIES: AN X-RAY, OPTICAL, AND RADIO CASE STUDY

    SciTech Connect

    Gastaldello, Fabio; Di Gesu, Laura; Ghizzardi, Simona; Rossetti, Mariachiara; Giacintucci, Simona; Girardi, Marisa; Roediger, Elke; Brighenti, Fabrizio; Buote, David A.; Humphrey, Philip J.; Eckert, Dominique; Ettori, Stefano; Mathews, William G.

    2013-06-10

    We present a combined X-ray, optical, and radio analysis of the galaxy group IC 1860 using the currently available Chandra and XMM data, multi-object spectroscopy data from the literature, and Giant Metrewave Radio Telescope (GMRT) data. The Chandra and XMM imaging and spectroscopy reveal two surface brightness discontinuities at 45 and 76 kpc shown to be consistent with a pair of cold fronts. These features are interpreted as due to sloshing of the central gas induced by an off-axis minor merger with a perturber. This scenario is further supported by the presence of a peculiar velocity of the central galaxy IC 1860 and the identification of a possible perturber in the optically disturbed spiral galaxy IC 1859. The identification of the perturber is consistent with the comparison with numerical simulations of sloshing. The GMRT observation at 325 MHz shows faint, extended radio emission contained within the inner cold front, as seen in some galaxy clusters hosting diffuse radio mini-halos. However, unlike mini-halos, no particle reacceleration is needed to explain the extended radio emission, which is consistent with aged radio plasma redistributed by the sloshing. There is a strong analogy between the X-ray and optical phenomenology of the IC 1860 group and that of two other groups, NGC 5044 and NGC 5846, showing cold fronts. The evidence presented in this paper is among the strongest supporting the currently favored model of cold-front formation in relaxed objects and establishes the group scale as a chief environment for studying this phenomenon.

  3. Tracing the evolution within nearby galaxy groups: a multi-wavelength approach

    NASA Astrophysics Data System (ADS)

    Bettoni, Daniela; Marino, Antonina; Rampazzo, Roberto; Plana, Henri; Rosado, Margarita; Galletta, Giuseppe; Mazzei, Paola; Bianchi, Luciana; Buson, Lucio M.; Ambrocio-Cruz, Patricia; Gabbasov, Ruslan

    2015-03-01

    Evolutionary scenarios suggest that several mechanisms (from inner secular evolution to accretion/merging) may transform galaxy members, driving groups from an active star forming phase to a more passive, typical of dense environments. We are investigating this transition in a nearby group sample, designed to cover a wide range of properties (see also Marino et al. (2010), Bettoni et al. (2011) and Marino et al. (2012)). We study two groups, USGC U268 and USGC U376 located in different regions of the Leo cloud, through a photometric and kinematic characterization of their member galaxies. We revisit the group membership, using results from recent red-shift surveys, and we investigate their substructures. U268, composed of 10 catalogued members and 11 new added members, has a small fraction (~24%) of early-type galaxies (ETGs). U376 has 16 plus 8 new added members, with ~38% of ETGs. We find the significant substructuring in both groups suggesting that they are likely accreting galaxies. U268 is located in a more loose environment than U376. For each member galaxy, broad band integrated and surface photometry have been obtained in far-UV (FUV) and near-UV (NUV) with GALEX, and in u, g, r, i, z (SDSS) bands. Hα imaging and 2D high resolution kinematical data have been obtained using PUMA Scanning Fabry-Perot interferometer at the 2.12 m telescope in San Pedro Mártir (Baja California, México). We improved the galaxy classification and we detected morphological and kinematical distortions that may be connected to either on-going and/or past interaction/accretion events or environmental induced secular evolution. U268 appears more active than U376, with a large fraction of galaxies showing interaction signatures (60% vs. 13%). The presence of bars among late-type galaxies is ~10% in U268 and 29% in U376. The cumulative distribution of (FUV - NUV) colors of galaxies in U268 is significantly different (bluer) than that of U376's galaxies. Most (80%) of the early

  4. Galaxies in X-Ray Groups. I. Robust Membership Assignment and the Impact of Group Environments on Quenching

    NASA Astrophysics Data System (ADS)

    George, Matthew R.; Leauthaud, Alexie; Bundy, Kevin; Finoguenov, Alexis; Tinker, Jeremy; Lin, Yen-Ting; Mei, Simona; Kneib, Jean-Paul; Aussel, Hervé; Behroozi, Peter S.; Busha, Michael T.; Capak, Peter; Coccato, Lodovico; Covone, Giovanni; Faure, Cecile; Fiorenza, Stephanie L.; Ilbert, Olivier; Le Floc'h, Emeric; Koekemoer, Anton M.; Tanaka, Masayuki; Wechsler, Risa H.; Wolk, Melody

    2011-12-01

    Understanding the mechanisms that lead dense environments to host galaxies with redder colors, more spheroidal morphologies, and lower star formation rates than field populations remains an important problem. As most candidate processes ultimately depend on host halo mass, accurate characterizations of the local environment, ideally tied to halo mass estimates and spanning a range in halo mass and redshift, are needed. In this work, we present and test a rigorous, probabilistic method for assigning galaxies to groups based on precise photometric redshifts and X-ray-selected groups drawn from the COSMOS field. The groups have masses in the range 1013 <~ M 200c/M ⊙ <~ 1014 and span redshifts 0 < z < 1. We characterize our selection algorithm via tests on spectroscopic subsamples, including new data obtained at the Very Large Telescope, and by applying our method to detailed mock catalogs. We find that our group member galaxy sample has a purity of 84% and completeness of 92% within 0.5{R_{200c}}. We measure the impact of uncertainties in redshifts and group centering on the quality of the member selection with simulations based on current data as well as future imaging and spectroscopic surveys. As a first application of our new group member catalog which will be made publicly available, we show that member galaxies exhibit a higher quenched fraction compared to the field at fixed stellar mass out to z ~ 1, indicating a significant relationship between star formation and environment at group scales. We also address the suggestion that dusty star-forming galaxies in such groups may impact the high-l power spectrum of the cosmic microwave background and find that such a population cannot explain the low power seen in recent Sunyaev-Zel'dovich measurements.

  5. Direct observational evidence for a large transient galaxy population in groups at 0.85 < z < 1

    NASA Astrophysics Data System (ADS)

    Balogh, Michael L.; McGee, Sean L.; Wilman, David J.; Finoguenov, Alexis; Parker, Laura C.; Connelly, Jennifer L.; Mulchaey, John S.; Bower, Richard G.; Tanaka, Masayuki; Giodini, Stefania

    2011-04-01

    We introduce our survey of galaxy groups at 0.85 < z < 1, as an extension of the Group Environment and Evolution Collaboration. Here we present the first results, based on Gemini GMOS-S nod-and-shuffle spectroscopy of seven galaxy groups selected from spectroscopically confirmed, extended XMM detections in COSMOS. We use photometric redshifts to select potential group members for spectroscopy, and target galaxies with r < 24.75. In total, we have over 100 confirmed group members, and four of the groups have >15 members. The dynamical mass estimates are in good agreement with the masses estimated from the X-ray luminosity, with most of the groups having 13 < log Mdyn/M⊙ < 14. We compute stellar masses by template-fitting the spectral energy distributions; our spectroscopic sample is statistically complete for all galaxies with Mstar≳ 1010.1 M⊙, and for blue galaxies we sample masses as low as Mstar˜ 108.8 M⊙. The fraction of total mass in galaxy starlight spans a range of 0.25-3 per cent, for the six groups with reliable mass determinations. Like lower redshift groups, these systems are dominated by red galaxies, at all stellar masses Mstar > 1010.1 M⊙. A few group galaxies inhabit the 'blue cloud' that dominates the surrounding field; instead, we find a large and possibly distinct population of galaxies with intermediate colours. The 'green valley' that exists at low redshift is instead well populated in these groups, containing ˜30 per cent of the galaxies. These do not appear to be exceptionally dusty galaxies, and about half show prominent Balmer absorption lines. Furthermore, their Hubble Space Telescope morphologies appear to be intermediate between those of red-sequence and blue-cloud galaxies of the same stellar mass. Unlike red-sequence galaxies, most of the green galaxies have a disc component, but one that is smaller and less structured than discs found in the blue cloud. We postulate that these are a transient population, migrating from the

  6. VizieR Online Data Catalog: Hickson's Compact groups of Galaxies (Hickson+ 1982-1994)

    NASA Astrophysics Data System (ADS)

    Hickson, P.

    1999-06-01

    The catalog of groups (file "groups.dat") is a list of 100 compact groups of galaxies identified by a systematic search of the Palomar Observatory Sky Survey red prints. Each group contains four or more galaxies, has an estimated mean surface brightness brighter than 26.0 magnitude per arcsec2 and satisfies an isolation criterion. Dynamical parameters were derived for 92 of the 100 groups, which are listed in file "dynamics.dat"; the Hubble constant was assumed to be Ho=100km/s/Mpc. Data about individual galaxies in these groups are merged into the "galaxies.dat" file; these data include photometric parameters, morphology, redshifts and absolute magnitudes originally published in four different papers. They result from CCD observations at CFHT (Canada-France-Hawaii Telescope) in 1983-1985. Redshifts were observed at the 1.5m telescope of the F.L. Whipple Observatory on Mt. Hopkins, Arizona, over the period 1984-1986, in wavelength range 470-710nm; the remaining fainter galaxies were observed with the CFHT. (4 data files).

  7. EXTERNAL MASS ACCUMULATION ONTO CORE POTENTIALS: IMPLICATIONS FOR STAR CLUSTERS, GALAXIES, AND GALAXY CLUSTERS

    SciTech Connect

    Naiman, J. P.; Ramirez-Ruiz, E.; Lin, D. N. C.

    2011-07-01

    Accretion studies have been focused on the flow around bodies with point mass gravitational potentials, but few general results are available for non-point mass distributions. Here, we study the accretion flow onto non-divergent, core potentials moving through a background medium. We use Plummer and Hernquist potentials as examples to study gas accretion onto star clusters, dwarf and large galaxy halos, and galaxy clusters in a variety of astrophysical environments. The general conditions required for a core potential to collectively accrete large quantities of gas from the external medium are derived using both simulations and analytic results. The consequences of large mass accumulation in galaxy nuclei, dwarf galaxies, and star clusters are twofold. First, if the gas cools effectively star formation can be triggered, generating new stellar members in the system. Second, if the collective potential of the system is able to alter the ambient gas properties before the gas is accreted onto the individual core members, the augmented mass supply rates could significantly alter the state of the various accreting stellar populations and result in an enhanced central black hole accretion luminosity.

  8. X-RAY GROUPS OF GALAXIES IN THE AEGIS DEEP AND WIDE FIELDS

    SciTech Connect

    Erfanianfar, G.; Lerchster, M.; Nandra, K.; Connelly, J. L.; Mirkazemi, M.; Finoguenov, A.; Tanaka, M.; Laird, E.; Bielby, R.; Faber, S. M.; Kocevski, D.; Jeltema, T.; Newman, J. A.; Coil, A. L.; Brimioulle, F.; Davis, M.; McCracken, H. J.; Willmer, C.; Gerke, B.; and others

    2013-03-10

    We present the results of a search for extended X-ray sources and their corresponding galaxy groups from 800 ks Chandra coverage of the All-wavelength Extended Groth Strip International Survey (AEGIS). This yields one of the largest X-ray-selected galaxy group catalogs from a blind survey to date. The red-sequence technique and spectroscopic redshifts allow us to identify 100% of reliable sources, leading to a catalog of 52 galaxy groups. These groups span the redshift range z {approx} 0.066-1.544 and virial mass range M{sub 200} {approx} 1.34 Multiplication-Sign 10{sup 13}-1.33 Multiplication-Sign 10{sup 14} M{sub Sun }. For the 49 extended sources that lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we identify spectroscopic counterparts and determine velocity dispersions. We select member galaxies by applying different cuts along the line of sight or in projected spatial coordinates. A constant cut along the line of sight can cause a large scatter in scaling relations in low-mass or high-mass systems depending on the size of the cut. A velocity-dispersion-based virial radius can cause a larger overestimation of velocity dispersion in comparison to an X-ray-based virial radius for low-mass systems. There is no significant difference between these two radial cuts for more massive systems. Independent of radial cut, an overestimation of velocity dispersion can be created in the case of the existence of significant substructure and compactness in X-ray emission, which mostly occur in low-mass systems. We also present a comparison between X-ray galaxy groups and optical galaxy groups detected using the Voronoi-Delaunay method for DEEP2 data in this field.

  9. A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.

    PubMed

    Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J; Greene, Jenny E; Blakeslee, John P; Janish, Ryan

    2016-04-21

    Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes. PMID:27049949

  10. A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.

    PubMed

    Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J; Greene, Jenny E; Blakeslee, John P; Janish, Ryan

    2016-04-21

    Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

  11. Percolation galaxy groups and clusters in the sdss redshift survey: identification, catalogs, and the multiplicity function

    SciTech Connect

    Berlind, Andreas A.; Frieman, Joshua A.; Weinberg, David H.; Blanton, Michael R.; Warren, Michael S.; Abazajian, Kevork; Scranton, Ryan; Hogg, David W.; Scoccimarro, Roman; Bahcall, Neta A.; Brinkmann, J.; Gott, J.Richard, III; Kleinman, S.J.; Krzesinski, J.; Lee, Brian C.; Miller, Christopher J.; Nitta, Atsuko; Schneider, Donald P.; Tucker, Douglas L.; Zehavi, Idit; /CCPP, New York /Chicago U., Astron. Astrophys. Ctr. /Ohio State U., Dept. Astron. /Los Alamos /Pittsburgh U. /Princeton U. /Subaru Telescope /Apache Point Observ. /Mt. Suhora Observ., Cracow /LBL, Berkeley /Cerro-Tololo InterAmerican Obs. /Penn State U., Astron. Astrophys. /Fermilab /Arizona U., Astron. Dept. - Steward Observ. /Case Western Reserve U.

    2006-01-01

    We identify galaxy groups and clusters in volume-limited samples of the SDSS redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribution, and velocity dispersion. We adopt a linking length combination that yields, for galaxy groups with ten or more members: a group multiplicity function that is unbiased with respect to the true halo multiplicity function; an unbiased median relation between the multiplicities of groups and their associated halos; a spurious group fraction of less than {approx}1%; a halo completeness of more than {approx}97%; the correct projected size distribution as a function of multiplicity; and a velocity dispersion distribution that is {approx}20% too low at all multiplicities. These results hold over a range of mock catalogs that use different input recipes of populating halos with galaxies. We apply our group-finding algorithm to the SDSS data and obtain three group and cluster catalogs for three volume-limited samples that cover 3495.1 square degrees on the sky. We correct for incompleteness caused by fiber collisions and survey edges, and obtain measurements of the group multiplicity function, with errors calculated from realistic mock catalogs. These multiplicity function measurements provide a key constraint on the relation between galaxy populations and dark matter halos.

  12. Chandra and XMM View Galaxy Groups: New Details from Sharper Images

    NASA Astrophysics Data System (ADS)

    Vrtilek, J. M.; Ponman, T. J.; O'Sullivan, E. J.; David, L. P.; Harris, D. E.; Forman, W.; Jones, C.; Lane, W. M.; Kassim, N. E.

    2004-08-01

    Groups and poor clusters are the locus of most galaxies in the present-day Universe and the building blocks from which clusters form. They accordingly occupy a significant place in the continuum of structure between isolated galaxies and rich clusters. Owing to the lower temperature of their intracluster gas, X-ray emission from groups produces strong lines from a broader range of elements than do hotter clusters. Here we show results from an examination of several X-ray bright groups, mostly from the Hickson, AWM, and MKW lists, relevant to issues of current interest in the study of both groups and clusters: the distribution of heavy elements, the presence and nature of X-ray cavities and their relation to radio observations, the presence of cooling cores, and X-ray signatures of recent galaxy interactions. This work was supported in part by NASA grants GO2-3186X and GO4-5154X.

  13. Individual QSOs, Groups, & Clusters of High Redshift QSOs Associated with Low Redshift Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Burbidge, Geoffrey; Napier, W.

    2009-01-01

    Starting more than forty years ago it was found by Arp and others that many high redshift QSOs lie very close to comparatively nearby spiral galaxies. As time has gone on the implication of these results have been ignored. Implicitly they have been assumed to be accidental configurations. By now there are so many data, sometimes involving clusters of high z QSOs, that the data requires re-examination. We have done this using conservative statistical methods. We have concluded that the physical associations are real and thus it appears that QSOs are being ejected from spiral galaxies which often show other aspects of activity. Some examples of these phenomena will be described. Thus despite the fact that most investigators continue to use QSOs for cosmological investigations, the results are doomed to failure. Even more important the nature of the high redshifts of QSOs (but not the redshifts of normal galaxies) remains a puzzle yet to be solved.

  14. The lack of star formation gradients in galaxy groups up to z ˜ 1.6

    NASA Astrophysics Data System (ADS)

    Ziparo, F.; Popesso, P.; Biviano, A.; Finoguenov, A.; Wuyts, S.; Wilman, D.; Salvato, M.; Tanaka, M.; Ilbert, O.; Nandra, K.; Lutz, D.; Elbaz, D.; Dickinson, M.; Altieri, B.; Aussel, H.; Berta, S.; Cimatti, A.; Fadda, D.; Genzel, R.; Le Flo'ch, E.; Magnelli, B.; Nordon, R.; Poglitsch, A.; Pozzi, F.; Portal, M. Sanchez; Tacconi, L.; Bauer, F. E.; Brandt, W. N.; Cappelluti, N.; Cooper, M. C.; Mulchaey, J. S.

    2013-10-01

    In the local Universe, galaxy properties show a strong dependence on environment. In cluster cores, early-type galaxies dominate, whereas star-forming galaxies are more and more common in the outskirts. At higher redshifts and in somewhat less dense environments (e.g. galaxy groups), the situation is less clear. One open issue is that of whether and how the star formation rate (SFR) of galaxies in groups depends on the distance from the centre of mass. To shed light on this topic, we have built a sample of X-ray selected galaxy groups at 0 < z < 1.6 in various blank fields [Extended Chandra Deep Field South (ECDFS), Cosmological Evolution Survey (COSMOS), Great Observatories Origin Deep Survey (GOODS)]. We use a sample of spectroscopically confirmed group members with stellar mass M⋆ > 1010.3 M⊙ in order to have a high spectroscopic completeness. As we use only spectroscopic redshifts, our results are not affected by uncertainties due to projection effects. We use several SFR indicators to link the star formation (SF) activity to the galaxy environment. Taking advantage of the extremely deep mid-infrared Spitzer MIPS and far-infrared Herschel1 PACS observations, we have an accurate, broad-band measure of the SFR for the bulk of the star-forming galaxies. We use multi-wavelength Spectral Energy Distribution (SED) fitting techniques to estimate the stellar masses of all objects and the SFR of the MIPS and PACS undetected galaxies. We analyse the dependence of the SF activity, stellar mass and specific SFR on the group-centric distance, up to z ˜ 1.6, for the first time. We do not find any correlation between the mean SFR and group-centric distance at any redshift. We do not observe any strong mass segregation either, in agreement with predictions from simulations. Our results suggest that either groups have a much smaller spread in accretion times with respect to the clusters and that the relaxation time is longer than the group crossing time.

  15. Examining the Center: Positions, Dominance, and Star Formation Rates of Most Massive Group Galaxies at Intermediate Redshift

    NASA Astrophysics Data System (ADS)

    Connelly, Jennifer L.; Parker, Laura C.; McGee, Sean; Mulchaey, John S.; Finoguenov, Alexis; Balogh, Michael; Wilman, David; Group Environment Evolution Collaboration

    2015-01-01

    The group environment is believed to be the stage for many galaxy transformations, helping evolve blue star-forming galaxies to red passive ones. In local studies of galaxy clusters, the central member is usually a single dominant giant galaxy at the center of the potential with little star formation thought to be the result of galaxy mergers. In nearby groups, a range of morphologies and star formation rates are observed and the formation history is less clear. Further, the position and dominance of the central galaxy cannot be assumed in groups, which are less massive and evolved than clusters. To understand the connections between global group properties and properties of the central group galaxy at intermediate redshift, we examine galaxy groups from the Group Environment and Evolution Collaboration (GEEC) catalog, including both optically- and X-ray-selected groups at redshift z~0.4. The sample is diverse, containing a range in overall mass and evolutionary state. The number of groups is significant, membership is notably complete, and measurements span the IR to the UV allowing the properties of the members to be connected to those of the host groups. Having investigated trends in the global group properties previously, including mass and velocity substructure, we turn our attention now to the galaxy populations, focusing on the central regions of these systems. The most massive and second most massive group galaxies are identified by their stellar mass. The positions of the most massive galaxies (MMGs) are determined with respect to both the luminosity-weighted and X-ray center. Star formation rates are used to explore the fraction of passive/quiescent versus star-forming MMGs and the dominance of the MMGs in our group sample is also tested. Determinations of these characteristics and trends constitute the important first steps toward a detailed understanding of the relationships between the properties of host groups and their most massive galaxies and the

  16. Deep Optical Imaging of a Compact Group of Galaxies: Seyfert's Sextet

    NASA Astrophysics Data System (ADS)

    Nishiura, Shingo; Murayama, Takashi; Shimada, Masashi; Sato, Yasunori; Nagao, Tohru; Molikawa, Kohji; Taniguchi, Yoshiaki; Sanders, D. B.

    2000-11-01

    To investigate the dynamical status of Seyfert's Sextet (SS), we have obtained a deep optical (VR+I) image of this group. Our image shows that a faint envelope, down to a surface brightness μoptical(AB)~=27 mag arcsec-2, surrounds the member galaxies. This envelope is irregular in shape. It is likely that this shape is attributed either to recent-past or to ongoing galaxy interactions in SS. If the member galaxies have experienced a number of mutual interactions over a long timescale, the shape of the envelope should be rounder. Therefore, the irregularly shaped morphology suggests that SS is in an early phase of dynamical interaction among the member galaxies. It is interesting to note that the soft X-ray image obtained with ROSAT (Pildis, Bregman, & Evrard) is significantly similar in morphology. We discuss the possible future evolution of SS briefly.

  17. Measurable Relationship between Bright Galaxies and Their Faint Companions in WHL J085910.0+294957, a Galaxy Cluster at z = 0.30: Vestiges of Infallen Groups?

    NASA Astrophysics Data System (ADS)

    Lee, Joon Hyeop; Lee, Hye-Ran; Kim, Minjin; Seon, Kwang-Il; Kim, Sang Chul; Yang, Soung-Chul; Ree, Chang Hee; Lee, Jong Chul; Jeong, Hyunjin; Ko, Jongwan; Choi, Changsu

    2014-08-01

    The properties of satellite galaxies are closely related to their host galaxies in galaxy groups. In cluster environments, on the other hand, the interaction between close neighbors is known to be limited. Our goal is to examine the relationships between host and satellite galaxies in the harsh environment of a galaxy cluster. To achieve this goal, we study a galaxy cluster WHL J085910.0+294957 at z = 0.30 using deep images obtained with CQUEAN CCD camera mounted on the 2.1 m Otto Struve Telescope. After member selection based on the scaling relations of photometric and structural parameters, we investigate the relationship between bright (Mi <= -18) galaxies and their faint (-18 < Mi <= -15) companions. The weighted mean color of faint companion galaxies shows no significant dependence (<1σ to bootstrap uncertainties) on cluster-centric distance and local luminosity density as well as the luminosity and concentration of an adjacent bright galaxy. However, the weighted mean color shows marginal dependence (~2.2σ) on the color of an adjacent bright galaxy when the sample is limited to bright galaxies with at least two faint companions. By using a permutation test, we confirm that the correlation in color between bright galaxies and their faint companions in this cluster is statistically significant with a confidence level of 98.7%. The statistical significance increases if we additionally remove non-members using the Sloan Digital Sky Survey photometric redshift information (~2.6σ and 99.3%). Our results suggest three possible scenarios: (1) vestiges of infallen groups, (2) dwarf capturing, and (3) tidal tearing of bright galaxies.

  18. Measurable relationship between bright galaxies and their faint companions in WHL J085910.0+294957, a galaxy cluster at z = 0.30: vestiges of infallen groups?

    SciTech Connect

    Lee, Joon Hyeop; Lee, Hye-Ran; Kim, Minjin; Seon, Kwang-Il; Kim, Sang Chul; Yang, Soung-Chul; Ree, Chang Hee; Lee, Jong Chul; Jeong, Hyunjin; Ko, Jongwan; Choi, Changsu

    2014-08-20

    The properties of satellite galaxies are closely related to their host galaxies in galaxy groups. In cluster environments, on the other hand, the interaction between close neighbors is known to be limited. Our goal is to examine the relationships between host and satellite galaxies in the harsh environment of a galaxy cluster. To achieve this goal, we study a galaxy cluster WHL J085910.0+294957 at z = 0.30 using deep images obtained with CQUEAN CCD camera mounted on the 2.1 m Otto Struve Telescope. After member selection based on the scaling relations of photometric and structural parameters, we investigate the relationship between bright (M{sub i} ≤ –18) galaxies and their faint (–18 < M{sub i} ≤ –15) companions. The weighted mean color of faint companion galaxies shows no significant dependence (<1σ to bootstrap uncertainties) on cluster-centric distance and local luminosity density as well as the luminosity and concentration of an adjacent bright galaxy. However, the weighted mean color shows marginal dependence (∼2.2σ) on the color of an adjacent bright galaxy when the sample is limited to bright galaxies with at least two faint companions. By using a permutation test, we confirm that the correlation in color between bright galaxies and their faint companions in this cluster is statistically significant with a confidence level of 98.7%. The statistical significance increases if we additionally remove non-members using the Sloan Digital Sky Survey photometric redshift information (∼2.6σ and 99.3%). Our results suggest three possible scenarios: (1) vestiges of infallen groups, (2) dwarf capturing, and (3) tidal tearing of bright galaxies.

  19. Carnegie-Spitzer-IMACS Survey: The Rise of Galaxy Groups Since z=1

    NASA Astrophysics Data System (ADS)

    Williams, Rik J.; Kelson, D.; Dressler, A.; McCarthy, P.; Mulchaey, J.; Oemler, A., Jr.; Shectman, S.

    2012-01-01

    We present the first measurements of the evolution of the group stellar mass function (GSMF) since z=1 from the Carnegie-Spitzer-IMACS (CSI) Survey. CSI combines robust mass selection through Spitzer 3.6-micron photometry with low-resolution spectroscopy over a 15 deg2 area, allowing the detailed study of large group (and group/field galaxy) samples over the expected epoch of group formation. From the initial 36,000 CSI galaxy redshifts over 5 deg2, we select groups using a standard friends-of-friends algorithm in angular and redshift space, constructing the GSMF in 3 redshift bins. These mass functions agree well with GSMFs from SDSS at z=0, and with X-ray-selected cluster mass functions at higher masses and redshifts. At all masses the GSMF evolves strongly from z=0.5-1, but only weak evolution is seen in low-mass (log M* ˜ 12.0) groups since z=0.5, indicating that most of these were in place at that epoch. As the majority of low-redshift galaxies reside in groups, the group environment may therefore play an important role in the decline in star formation and evolution of galaxy structures since z=1.

  20. THE ZURICH ENVIRONMENTAL STUDY (ZENS) OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. II. GALAXY STRUCTURAL MEASUREMENTS AND THE CONCENTRATION OF MORPHOLOGICALLY CLASSIFIED SATELLITES IN DIVERSE ENVIRONMENTS

    SciTech Connect

    Cibinel, A.; Carollo, C. M.; Lilly, S. J.; Miniati, F.; Cameron, E.; Peng, Y.; Pipino, A.; Rudick, C. S.; Silverman, J. D.; Van Gorkom, J. H.; Finoguenov, A.; Norberg, P. E-mail: marcella@phys.ethz.ch

    2013-10-20

    We present structural measurements for the galaxies in the 0.05 < z < 0.0585 groups of the Zurich Environmental Study, aimed at establishing how galaxy properties depend on four environmental parameters: group halo mass (M{sub GROUP}), group-centric distance (R/R{sub 200}), ranking into central or satellite, and large-scale structure density (δ{sub LSS}). Global galaxy structure is quantified both parametrically and non-parametrically. We correct all these measurements for observational biases due to point-spread function blurring and surface brightness effects as a function of galaxy size, magnitude, steepness of light profile, and ellipticity. Structural parameters are derived also for bulges, disks, and bars. We use the galaxy bulge-to-total ratios (B/T) together with the calibrated non-parametric structural estimators to implement a quantitative morphological classification that maximizes purity in the resulting morphological samples. We investigate how the concentration C of satellite galaxies depends on galaxy mass for each Hubble type and on M{sub GROUP}, R/R{sub 200}, and δ{sub LSS}. At galaxy masses M ≥ 10{sup 10} M{sub ☉}, the concentration of disk satellites increases with increasing stellar mass separately within each morphological bin of B/T. The known increase in concentration with stellar mass for disk satellites is thus due, at least in part, to an increase in galaxy central stellar density at constant B/T. The correlation between concentration and galaxy stellar mass becomes progressively steeper for later morphological types. The concentration of disk satellites shows a barely significant dependence on δ{sub LSS} or R/R{sub 200}. The strongest environmental effect is found with group mass for >10{sup 10} M{sub ☉} disk-dominated satellites, which are ∼10% more concentrated in high mass groups than in lower mass groups.

  1. The HI Content of Galaxies in Groups and Clusters as Measured by ALFALFA

    NASA Astrophysics Data System (ADS)

    Odekon, Mary Crone; Koopmann, Rebecca A.; Haynes, Martha P.; Finn, Rose A.; McGowan, Christopher; Micula, Adina; Reed, Lyle; Giovanelli, Riccardo; Hallenbeck, Gregory

    2016-06-01

    We present the HI content of galaxies in nearby groups and clusters as measured by the 70% complete Arecibo Legacy Fast-ALFA (ALFALFA) survey, including constraints from ALFALFA detection limits. Our sample includes 22 systems at distances between 70 and 160 Mpc over the mass range 12.5<' {log} M/{M}⊙ < 15.0, for a total of 1986 late-type galaxies. We find that late-type galaxies in the centers of groups lack HI at fixed stellar mass relative to the regions surrounding them. Larger groups show evidence of a stronger dependence of HI properties on environment, despite a similar dependence of color on environment at fixed stellar mass. We compare several environment variables to determine which is the best predictor of galaxy properties; group-centric distance r and r/{R}200 are similarly effective predictors, while local density is slightly more effective and group size and halo mass are slightly less effective. While both central and satellite galaxies in the blue cloud exhibit a significant dependence of HI content on local density, only centrals show a strong dependence on stellar mass, and only satellites show a strong dependence on halo mass. Finally, we see evidence that HI is deficient for blue cloud galaxies in denser environments even when both stellar mass and color are fixed. This is consistent with a picture where HI is removed or destroyed, followed by reddening within the blue cloud. Our results support the existence of pre-processing in isolated groups, along with an additional rapid mechanism for gas removal within larger groups and clusters, perhaps ram-pressure stripping.

  2. Compact Groups of Galaxies with Complete Spectroscopic Redshifts in the Local Universe

    NASA Astrophysics Data System (ADS)

    Sohn, Jubee; Hwang, Ho Seong; Geller, Margaret J.; Diaferio, Antonaldo; Rines, Kenneth J.; Lee, Myung Gyoon; Lee, Gwang-Ho

    2015-12-01

    Dynamical analysis of compact groups provides important tests of models of compact group formation and evolution. By compiling 2066 redshifts from FLWO/FAST, from the literature, and from SDSS DR12 in the fields of compact groups in tet{McC09}, we construct the largest sample of compact groups with complete spectroscopic redshifts in the redshift range 0.01 < z < 0.22. This large redshift sample shows that the interloper fraction in the tet{McC09} compact group candidates is ˜ 42%. A secure sample of 332 compact groups includes 192 groups with four or more member galaxies and 140 groups with three members. The fraction of early-type galaxies in these compact groups is 62%, higher than for the original Hickson compact groups. The velocity dispersions of early- and late-type galaxies in compact groups change little with groupcentric radius; the radii sampled are less than 100 h^{-1} kpc, smaller than the radii typically sampled by members of massive clusters of galaxies. The physical properties of our sample compact groups include size, number density, velocity dispersion, and local environment; these properties slightly differ from those derived for the original Hickson compact groups and for the DPOSS II compact groups. Differences result from subtle differences in the way the group candidates were originally selected. The abundance of the compact groups changes little with redshift over the range covered by this sample. The approximate constancy of the abundance for this sample is a potential constraint on the evolution of compact groups on a few Gigayear timescale.

  3. Sunyaev-Zel'dovich Effects from Quasars in Galaxies and Groups

    NASA Astrophysics Data System (ADS)

    Lapi, A.; Cavaliere, A.; De Zotti, G.

    2003-11-01

    The energy fed by active galactic nuclei to the surrounding diffuse baryons changes their amount, temperature, and distribution; so in groups and in member galaxies it affects the X-ray luminosity and also the Sunyaev-Zel'dovich effect. Here we compute how the latter is enhanced by the transient blast wave driven by an active quasar and is depressed when the equilibrium is recovered with a depleted density. We constrain such depressions and enhancements with the masses of relic black holes in galaxies and the X-ray luminosities in groups. We discuss how all these linked observables can tell the quasar contribution to the thermal history of the baryons pervading galaxies and groups.

  4. K-Band Properties of Well-Sampled Groups of Galaxies

    NASA Astrophysics Data System (ADS)

    Ramella, Massimo; Boschin, Walter; Geller, Margaret J.; Mahdavi, Andisheh; Rines, Kenneth

    2004-11-01

    We use a sample of 55 groups and six clusters of galaxies ranging in mass from 7×1011 to 1.5×1015 Msolar to examine the correlation of the Ks-band luminosity with mass discovered by Lin and coauthors in 2003. We use the Two-Micron All-Sky Survey catalog and published redshifts to construct complete magnitude-limited redshift surveys of the groups. From these surveys we explore the IR photometric properties of groups members, including their IR color distribution and luminosity function. Although we find no significant difference between the group Ks luminosity function and the general field, there is a difference between the color distribution of luminous group members and their counterparts (generally background) in the field. There is a significant population of luminous galaxies with H-Ks>~0.35, which are rarely, if ever, members of the groups in our sample. The most luminous galaxies that populate the groups have a very narrow range of IR color. Over the entire mass range covered by our sample, the Ks luminosity increases with mass as LKs~M0.64+/-0.06, implying that the mass-to-light ratio in the Ks band increases with mass. The agreement between this result and earlier investigations of essentially nonoverlapping sets of systems shows that this window in galaxy formation and evolution is insensitive to the selection of the systems and to the details of the mass and luminosity computations.

  5. Stellar content of nearby galaxies. III - The local group spiral galaxy M33

    NASA Technical Reports Server (NTRS)

    Wilson, Christine D.; Madore, Barry F.; Freedman, Wendy L.

    1990-01-01

    BVRI CCD photometry is presented for stars brighter than V = 21 mag in four fields in the nearby spiral galaxy M33. V vs (B - V) and I vs (V - I) color-magnitude diagrams clearly show both a young stellar population (as indicated by the blue main sequence and red supergiant plumes) as well as an intermediate-age population of asymptotic giant branch stars. Deep photometry in the outer field (where crowding is less severe) reveals a population consistent in color and magnitude with the tip of the first red giant branch. The M33 distance modulus, 24.6 + or - 0.3 mag, derived from this Population II component is consistent with a recent redetermination of the distance modulus found from Population I Cepheid variables. Finally, some evidence is presented for a radial gradient in the average internal reddening for the fields in M33 reported here.

  6. Searching for intermediate groups of galaxies with Suzaku in Bootes field

    NASA Astrophysics Data System (ADS)

    Mitsuishi, Ikuyuki; Maejima, Masato; Kobayashi, Hiroaki; Babazaki, Yasunori; Matsumoto, Hironori; Tawara, Yuzuru; Miller, Eric D.

    2015-08-01

    To investigate redshift evolution of groups of galaxies is significant also in terms of galaxy evolution. Recent observational studies show that an AGN fraction and a magnitude gap between the first and the second brightest group galaxies increase in group environments at lower redshifts (Oh et al. 2014 & Gozaliasl et al. 2014). Thus, comprehension for the evolution of the systems will bring us to hints on both morphological evolution of galaxies and galaxy-galaxy interactions. However, observational samples of groups of galaxies at higher redshifts are limited due to its low flux and surface brightness. Thus, we aimed at searching for new samples using both X-ray and optical data. To identify the group systems at higher redshifts, deep optical imaging and spectroscopic data are needed. Bootes field is one of the best regions for this purpose because there are up to 17 bands of data available per source from infrared, optical, UV, and X-ray (e.g., Kenter et al. 2005, Chung et al. 2014). XBootes survey was conducted in 2003 using Chandra (Murray et al. 2005) and X-ray extended sources were detected around intermediate optically-identified groups of galaxies even though Chandra could not reveal their origins due to poor photon statistics. Thus, we conducted X-ray follow-up observations using Suzaku which has low and stable background and thus is optimum for such low surface brightness sources for brightest 6 group candidates with redshifts of 0.15-0.42. Consequently, Suzaku detected excess emissions from all the targets in their images and spectral analysis reveals that 4 sources are originated from group- or poor-cluster-scale halos with temperatures, abundances and luminosities of 1.6-3.0 keV, <0.3 solar and ~1044 erg s-1, respectively while no significant emissions from diffuse sources were found from the other two targets. In this conference, we will report on the details of our analysis and results using multiwavelength data such as radio, optical and X-ray to

  7. Searching for intermediate groups of galaxies with Suzaku in Bootes field

    NASA Astrophysics Data System (ADS)

    Tawara, Yuzuru; Mitsuishi, Ikuyuki

    2016-07-01

    To investigate redshift evolution of groups of galaxies is significant also in terms of galaxy evolution. Recent observational studies show that an AGN fraction and a magnitude gap between the first and the second brightest group galaxies increase in group environments at lower redshifts (Oh et al. 2014 & Gozaliasl et al. 2014). Thus, comprehension for the evolution of the systems will bring us to hints on both morphological evolution of galaxies and galaxy-galaxy interactions. However, observational samples of groups of galaxies at higher redshifts are limited due to its low flux and surface brightness. Thus, we aimed at searching for new samples using both X-ray and optical data. To identify the group systems at higher redshifts, deep optical imaging and spectroscopic data are needed. Bootes field is one of the best regions for this purpose because there are up to 17 bands of data available per source from infrared, optical, UV, and X-ray (e.g., Kenter et al. 2005, Chung et al. 2014). XBootes survey was conducted in 2003 using Chandra (Murray et al. 2005) and X-ray extended sources were detected around intermediate optically-identified groups of galaxies even though Chandra could not reveal their origins due to poor photon statistics. Thus, we conducted X-ray follow-up observations using Suzaku which has low and stable background and thus is optimum for such low surface brightness sources for brightest 6 group candidates with redshifts of 0.15-0.42. Consequently, Suzaku detected excess emissions from all the targets in their images and spectral analysis reveals that 6 sources are originated from group- or poor-cluster-scale halos with temperatures, abundances and luminosities of 1.6-3.0 keV, <0.3 solar and ~1044 erg s-1, respectively. In this conference, we will report on the details of our analysis and results using multiwavelength data such as radio, optical and X-ray to examine the AGN fractions and magnitude gaps in our samples and discuss the redshift

  8. What have we learned from the XMM-Newton surveys of Local Group Galaxies?

    NASA Astrophysics Data System (ADS)

    Haberl, F.

    2016-06-01

    The study of X-ray source populations and diffuse X-ray emission in nearby galaxies is of major importance in understanding the X-ray output of more distant galaxies as well as learning about processes that occur on interstellar scales within our own Galaxy. Depending on the star formation history of the galaxies different types of X-ray sources dominate the total X-ray emission. With modern observatories like XMM-Newton the various classes of X-ray sources (high and low mass X-ray binaries, supernova remnants, super-soft sources) can be studied to the faintest end of their luminosity distribution in Local Group galaxies. XMM-Newton successfully surveyed the large spiral galaxies M31 and M33 and the star forming, irregular Magellanic Clouds. I'll summarise the most important results we have obtained from older populations like low mass X-ray binaries and classical novae in M31 to the younger populations of high mass X-ray binaries and supernova remnants in the Magellanic Clouds. I'll discuss still open questions in this field of research which can be addressed using the high sensitivity of the XMM-Newton instruments.

  9. The Reddening law outside the local group galaxies: The case of NGC 7552 and NGC 5236

    NASA Technical Reports Server (NTRS)

    Kinney, Anne L.; Calzetti, Daniela; Bica, Eduardo; Storchi-Bergmann, Thaisa

    1994-01-01

    The dust reddening law from the UV to the near-IR for the extended regions of galaxies is here derived from the spectral distributions of the starburst spiral galaxies NGC 7552 and NGC 5236. The centers of these galaxies have similar absorption and emission line spectra, differing only if the strength of their interstellar lines and in the continuum distribution, with NGC 7552 appearing more reddened than NGC 5236. The disk of NGC 7552 is more inclined, and there is evidence that its center is observed through additional foreground dust and gas clouds, as compared to the center of NGC 5236. While the galaxies can be expected to have similar dust content, they are known to have different dust path lengths to our line of sight. Therefore, differences in the shape of the spectra can be attributed mainly to the effects of dust, allowing us to probe for the first time the properties of the reddening law outside the local group of galaxies. We derive the reddening law based on the optical depth of the emission line of H Alpha and H Beta and also based on the continuum distribtuion. We find that the optical depth from the emission line regions are about twice the optical depth of the continuum regions. Thus, dereddening a starburst galaxy by scaling the Milky Way reddening laws to optical depths obtained from the H Alpha/H Beta line ratio overcompensates for the effect of dust.

  10. H I IN LOCAL GROUP DWARF GALAXIES AND STRIPPING BY THE GALACTIC HALO

    SciTech Connect

    Grcevich, Jana; Putman, Mary E E-mail: mputman@astro.columbia.edu

    2009-05-01

    We examine the H I content and environment of all of the Local Group dwarf galaxies (M {sub tot} < 10{sup 10} M {sub sun}), including the numerous newly discovered satellites of the Milky Way and M31. All of the new dwarfs, with the exception of Leo T, have no detected H I. The majority of dwarf galaxies within {approx}270 kpc of the Milky Way or Andromeda are undetected in H I (<10{sup 4} M {sub sun} for Milky Way dwarfs), while those further than {approx}270 kpc are predominantly detected with masses {approx}10{sup 5} to 10{sup 8} M {sub sun}. Analytical ram-pressure arguments combined with velocities obtained via proper motion studies allow for an estimate of the halo density of the Milky Way at several distances. This halo density is constrained to be greater than 2x 10{sup -4}-3 x 10{sup -4} cm{sup -3} out to distances of at least 70 kpc. This is broadly consistent with theoretical models of the diffuse gas in a Milky Way-like halo and is consistent with this component hosting a large fraction of a galaxy's baryons. Accounting for completeness in the dwarf galaxy count, gasless dwarf galaxies could have provided at most 2.1 x 10{sup 8} M {sub sun} of H I gas to the Milky Way, which suggests that most of our Galaxy's star formation fuel does not come from accreted small satellites in the current era.

  11. X-Ray-selected Galaxy Groups in Boötes

    NASA Astrophysics Data System (ADS)

    Vajgel, Bruna; Jones, Christine; Lopes, Paulo A. A.; Forman, William R.; Murray, Stephen S.; Goulding, Andrew; Andrade-Santos, Felipe

    2014-10-01

    We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. We used follow-up Chandra observations to better define the group sample and their X-ray properties. Group redshifts were measured from the AGN and Galaxy Evolution Survey spectroscopic data. We used photometric data from the NOAO Deep Wide Field Survey to estimate the group richness (N gals) and the optical luminosity (L opt). Our final sample comprises 32 systems at z < 1.75 with 14 below z = 0.35. For these 14 systems, we estimate velocity dispersions (σ gr ) and perform a virial analysis to obtain the radii (R 200 and R 500) and total masses (M 200 and M 500) for groups with at least 5 galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (LX ). We examine the performance of the group properties σgr, L opt, and LX , as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the LX -M 500 relation at approximately M 500 = 5 × 1013 M ⊙ (for M 500 > 5 × 1013 M ⊙, M500 \\propto L_X0.61+/- 0.02, while for M 500 <= 5 × 1013 M ⊙, M500 \\propto L_X0.44+/- 0.05). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions, and projection effects that reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group luminosity function estimates, eROSITA will identify ~1800 groups (LX = 1041-1043 erg s-1) within a distance of 200 Mpc. Since groups lie in large

  12. Merger Histories of Galaxy Halos and Implications for Disk Survival

    SciTech Connect

    Stewart, Kyle R.; Bullock, James S.; Wechsler, Risa H.; Maller, Ariyeh H.; Zentner, Andrew R.

    2008-05-16

    The authors study the merger histories of galaxy dark matter halos using a high resolution {Lambda}CDM N-body simulation. The merger trees follow {approx} 17,000 halos with masses M{sub 0} = (10{sup 11} - 10{sup 13})h{sup -1}M{sub {circle_dot}} at z = 0 and track accretion events involving objects as small as m {approx_equal} 10{sup 10} h{sup -1}M{sub {circle_dot}}. They find that mass assembly is remarkably self-similar in m/M{sub 0}, and dominated by mergers that are {approx}10% of the final halo mass. While very large mergers, m {approx}> 0.4 M{sub 0}, are quite rare, sizeable accretion events, m {approx} 0.1 M{sub 0}, are common. Over the last {approx} 10 Gyr, an overwhelming majority ({approx} 95%) of Milky Way-sized halos with M{sub 0} = 10{sup 12} h{sup -1}M{sub {circle_dot}} have accreted at least one object with greater total mass than the Milky Way disk (m > 5 x 10{sup 10} h{sup -1}M{sub {circle_dot}}), and approximately 70% have accreted an object with more than twice that mass (m > 10{sup 11} h{sup -1}M{sub {circle_dot}}). The results raise serious concerns about the survival of thin-disk dominated galaxies within the current paradigm for galaxy formation in a {Lambda}CDM universe. in order to achieve a {approx} 70% disk-dominated fraction in Milky Way-sized {Lambda}CDM halos, mergers involving m {approx_equal} 2 x 10{sup 11} h{sup -1}M{sub {circle_dot}} objects must not destroy disks. Considering that most thick disks and bulges contain old stellar populations, the situation is even more restrictive: these mergers must not heat disks or drive gas into their centers to create young bulges.

  13. The Local Group as a time machine: studying the high-redshift Universe with nearby galaxies

    NASA Astrophysics Data System (ADS)

    Boylan-Kolchin, Michael; Weisz, Daniel R.; Johnson, Benjamin D.; Bullock, James S.; Conroy, Charlie; Fitts, Alex

    2015-10-01

    We infer the UV luminosities of Local Group galaxies at early cosmic times (z ˜ 2 and z ˜ 7) by combining stellar population synthesis modelling with star formation histories derived from deep colour-magnitude diagrams constructed from Hubble Space Telescope (HST) observations. Our analysis provides a basis for understanding high-z galaxies - including those that may be unobservable even with the James Webb Space Telescope (JWST) - in the context of familiar, well-studied objects in the very low-z Universe. We find that, at the epoch of reionization, all Local Group dwarfs were less luminous than the faintest galaxies detectable in deep HST observations of blank fields. We predict that JWST will observe z ˜ 7 progenitors of galaxies similar to the Large Magellanic Cloud today; however, the HST Frontier Fields initiative may already be observing such galaxies, highlighting the power of gravitational lensing. Consensus reionization models require an extrapolation of the observed blank-field luminosity function (LF) at z ≈ 7 by at least 2 orders of magnitude in order to maintain reionization. This scenario requires the progenitors of the Fornax and Sagittarius dwarf spheroidal galaxies to be contributors to the ionizing background at z ˜ 7. Combined with numerical simulations, our results argue for a break in the UV LF from a faint-end slope of α ˜ -2 at MUV ≲ -13 to α ˜ -1.2 at lower luminosities. Applied to photometric samples at lower redshifts, our analysis suggests that HST observations in lensing fields at z ˜ 2 are capable of probing galaxies with luminosities comparable to the expected progenitor of Fornax.

  14. X-ray analysis of the galaxy group UGC 03957 beyond R200 with Suzaku

    NASA Astrophysics Data System (ADS)

    Thölken, Sophia; Lovisari, Lorenzo; Reiprich, Thomas H.; Hasenbusch, Jan

    2016-07-01

    Context. In the last few years, the outskirts of galaxy clusters have been studied in detail and the analyses have brought up interesting results such as indications of possible gas clumping and the breakdown of hydrostatic, thermal, and ionization equilibrium. These phenomena affect the entropy profiles of clusters, which often show deviations from the self-similar prediction around R200. However, significant uncertainties remain for groups of galaxies. In particular the question, of whether entropy profiles are similar to those of galaxy clusters. Aims: We investigated the gas properties of the galaxy group UGC 03957 up to 1.4 R200 ≈ 1.4 Mpc in four azimuthal directions with the Suzaku satellite. We checked for azimuthal symmetry and obtained temperature, entropy, density, and gas mass profiles. Previous studies point to deviations from equilibrium states at the outskirts of groups and clusters and so we studied the hydrodynamical status of the gas at these large radii. Methods: We performed a spectral analysis of five Suzaku observations of UGC 03957 with ~138 ks good exposure time in total and five Chandra snapshot observations for point source detection. We investigated systematic effects such as point spread function and uncertainties in the different background components, and performed a deprojection of the density and temperature profile. Results: We found a temperature drop of a factor of ~3 from the center to the outskirts that is consistent with previous results for galaxy clusters. The metal abundance profile shows a flat behavior towards large radii, which is a hint for galactic winds as the primary ICM enrichment process. The entropy profile is consistent with numerical simulations after applying a gas mass fraction correction. Feedback processes and AGN activity might be one explanation for entropy modification, imprinting out to larger radii in galaxy groups than in galaxy clusters. Previous analyses for clusters and groups often showed an

  15. A catalog of compact groups of galaxies in the RSDSS commissioning data

    SciTech Connect

    Lee, Brian C.; Allam, Sahar S.; Tucker, Douglas L.; Annis, James; Blanton, Michael R.; Johnston, David E.; Scranton, Ryan; Acebo, Yamina; Bahcall, Neta A.; Bartelmann, Matthias; Bohringer, Hans; Ellman, Nancy; Grebel, Eva K.; Infante, Leopoldo; Loveday, Jon; McKay, Timothy A.; Prada, Francisco; Schneider, Donald P.; Stoughton, Chris; Szalay, Alexander S.; Vogeley, Michael S.; Voges, Wolfgang; Yanny, Brian

    2003-11-18

    Compact groups (CGs) of galaxies--relatively poor groups of galaxies in which the typical separations between members is of the order of a galaxy diameter--offer an exceptional laboratory for the study of dense galaxian environments with short (<1Gyr) dynamical time-scales. In this paper, we present an objectively defined catalog of CGs in 153 sq deg of the Sloan Digital Sky Survey Early Data Release (SDSS EDR). To identify CGs, we applied a modified version of Hickson's (1982) criteria aimed at finding the highest density CGs and thus reducing the number of chance alignments. Our catalog contains 175 CGs down to a limiting galaxy magnitude of r* = 21. The resulting catalog has a median depth of approximately z = 0.13, substantially deeper than previous CG catalogs. Since the SDSS will eventually image up to one quarter of the celestial sphere, we expect our final catalog, based upon the completed SDSS, will contain on the order of 5,000-10,000 CGs. This catalog will be useful for conducting studies of the general characteristics of CGs, their environments, and their component galaxies.

  16. Status of The Dynamical Census of Galaxies and Groups in the RESOLVE Survey

    NASA Astrophysics Data System (ADS)

    Eckert, Kathleen D.; Kannappan, Sheila; Hall, Kirsten; Moffett, Amanda J.; Norris, Mark A.; Stark, David; Hoversten, Erik A.; Snyder, Elaine M.; Bittner, Ashley; Norman, Dara J.; Naluminsa, Elizabeth; Crawford, Steve; Vaisanen, Petri; Baker, Ashley; Berlind, Andreas A.; Rosenberg, Daniel; Beauchemin, Ryan William; Bonfield, Charles; RESOLVE Team

    2016-01-01

    The REsolved Spectroscopy of a Local VolumE (RESOLVE) survey is measuring either velocity dispersions or rotation velocities for ~1500 galaxies and ~200 multi-galaxy groups within >50,000 cubic Mpc of the z~0 universe, above a galaxy baryonic mass limit of ~10^9 Msun. Our kinematic census combines multi-slit, IFU, Fabry-Perot, long-slit, and radio linewidth data from the SOAR, SALT, Gemini, AAT, GBT, and Arecibo telescopes, with telescope/instrument combinations optimized for individual galaxy properties. We present a status update of the data taken, particularly focusing on the RESOLVE Early Science region overlapping Stripe 82. We also discuss challenges for dynamical measurements including measuring galaxy inclinations, determining the mix of support from rotational and random motions, and measuring dynamical masses for groups with few members. Finally, we conclude with a preliminary velocity function for the RESOLVE Early Science region. This work has been supported by the NSF through grants AST-0955368 and OCI-1156614, the NC Space Grant Graduate Research Fellowship Program, and a UNC Royster Society of Fellows Dissertation Completion Fellowship.

  17. Catalogs of Compact Groups of Galaxies from the Enhanced SDSS DR12

    NASA Astrophysics Data System (ADS)

    Sohn, Jubee; Geller, Margaret J.; Hwang, Ho Seong; Zahid, H. Jabran; Lee, Myung Gyoon

    2016-08-01

    We apply a friends-of-friends algorithm to an enhanced SDSS DR12 spectroscopic catalog, including redshift from the literature to construct a catalog of 1588 N≥slant 3 compact groups of galaxies containing 5178 member galaxies and covering the redshift range 0.01 < z < 0.19. This catalog contains 18 times as many systems and reaches 3 times the depth of the similar catalog of Barton et al. We construct catalogs from both magnitude-limited and volume-limited galaxy samples. Like Barton et al. we omit the frequently applied isolation criterion in the compact group selection algorithm. Thus the groups selected by fixed projected spatial and rest-frame line-of-sight velocity separation produce a catalog of groups with a redshift-independent median size. In contrast to previous catalogs, the enhanced SDSS DR12 catalog (including galaxies with r < 14.5) includes many systems with z ≲ 0.05. The volume-limited samples are unique to this study. The compact group candidates in these samples have a median stellar mass independent of redshift. Groups with velocity dispersion ≲100 {km} {{{s}}}-1 show abundant evidence for ongoing dynamical interactions among the members. The number density of the volume-limited catalogs agrees with previous catalogs at the lowest redshifts but decreases as the redshift increases. The SDSS fiber placement constraints limit the catalog’s completeness. In spite of this issue, the volume-limited catalogs provide a promising basis for detailed spatially resolved probes of the impact of galaxy–galaxy interactions within similar dense systems over a broad redshift range.

  18. Star Formation Suppression in Compact Group Galaxies: A New Path to Quenching?

    NASA Astrophysics Data System (ADS)

    Alatalo, K.; Appleton, P. N.; Lisenfeld, U.; Bitsakis, T.; Lanz, L.; Lacy, M.; Charmandaris, V.; Cluver, M.; Dopita, M. A.; Guillard, P.; Jarrett, T.; Kewley, L. J.; Nyland, K.; Ogle, P. M.; Rasmussen, J.; Rich, J. A.; Verdes-Montenegro, L.; Xu, C. K.; Yun, M.

    2015-10-01

    We present CO(1-0) maps of 12 warm H2-selected Hickson Compact Groups (HCGs), covering 14 individually imaged warm H2 bright galaxies, with the Combined Array for Research in Millimeter Astronomy. We found a variety of molecular gas distributions within the HCGs, including regularly rotating disks, bars, rings, tidal tails, and possibly nuclear outflows, though the molecular gas morphologies are more consistent with spirals and early-type galaxies than mergers and interacting systems. Our CO-imaged HCG galaxies, when plotted on the Kennicutt-Schmidt relation, shows star formation (SF) suppression of < {S} > =10+/- 5, distributed bimodally, with five objects exhibiting suppressions of {S} ≳ 10 and depletion timescales ≳10 Gyr. This SF inefficiency is also seen in the efficiency per freefall time of Krumholz et al. We investigate the gas-to-dust ratios of these galaxies to determine if an incorrect LCO-M(H2) conversion caused the apparent suppression and find that HCGs have normal gas-to-dust ratios. It is likely that the cause of the apparent suppression in these objects is associated with shocks injecting turbulence into the molecular gas, supported by the fact that the required turbulent injection luminosity is consistent with the bright H2 luminosity reported by Cluver et al. Galaxies with high SF suppression ({S} ≳ 10) also appear to be those in the most advanced stages of transition across both optical and infrared color space. This supports the idea that at least some galaxies in HCGs are transitioning objects, where a disruption of the existing molecular gas in the system suppresses SF by inhibiting the molecular gas from collapsing and forming stars efficiently. These observations, combined with recent work on poststarburst galaxies with molecular reservoirs, indicates that galaxies do not need to expel their molecular reservoirs prior to quenching SF and transitioning from blue spirals to red early-type galaxies. This may imply that SF quenching can

  19. ANCIENT STARS BEYOND THE LOCAL GROUP: RR LYRAE VARIABLES AND BLUE HORIZONTAL BRANCH STARS IN SCULPTOR GROUP DWARF GALAXIES

    SciTech Connect

    Da Costa, G. S.; Jerjen, H.; Rejkuba, M.; Grebel, E. K.

    2010-01-10

    We have used Hubble Space Telescope Advanced Camera for Surveys images to generate color-magnitude diagrams that reach below the magnitude of the horizontal branch in the Sculptor Group dwarf galaxies ESO294-010 and ESO410-005. In both diagrams, blue horizontal branch stars are unambiguously present, a signature of the existence of an ancient stellar population whose age is comparable to that of the Galactic halo globular clusters. The result is reinforced by the discovery of numerous RR Lyrae variables in both galaxies. The occurrence of these stars is the first direct confirmation of the existence of ancient stellar populations beyond the Local Group and indicates that star formation can occur at the earliest epochs even in low-density environments.

  20. On the recovery of the local group motion from galaxy redshift surveys

    SciTech Connect

    Nusser, Adi; Davis, Marc; Branchini, Enzo E-mail: mdavis@berkeley.edu

    2014-06-20

    There is an ∼150 km s{sup –1} discrepancy between the measured motion of the Local Group (LG) of galaxies with respect to the cosmic microwave background and the linear theory prediction based on the gravitational force field of the large-scale structure in full-sky redshift surveys. We perform a variety of tests which show that the LG motion cannot be recovered to better than 150-200 km s{sup –1} in amplitude and within ≈10° in direction. The tests rely on catalogs of mock galaxies identified in the Millennium simulation using semi-analytic galaxy formation models. We compare these results to the K{sub s} = 11.75 Two-Mass Galaxy Redshift Survey, which provides the deepest and most complete all-sky spatial distribution of galaxies with spectroscopic redshifts available thus far. In our analysis, we use a new concise relation for deriving the LG motion and bulk flow from the true distribution of galaxies in redshift space. Our results show that the main source of uncertainty is the small effective depth of surveys like the Two-Mass Redshift Survey (2MRS), which prevents a proper sampling of the large-scale structure beyond ∼100 h {sup –1} Mpc. Deeper redshift surveys are needed to reach the 'convergence scale' of ≈250 h {sup –1} Mpc in a ΛCDM universe. Deeper surveys would also mitigate the impact of the 'Kaiser rocket' which, in a survey like 2MRS, remains a significant source of uncertainty. Thanks to the quiet and moderate density environment of the LG, purely dynamical uncertainties of the linear predictions are subdominant at the level of ∼90 km s{sup –1}. Finally, we show that deviations from linear galaxy biasing and shot noise errors provide a minor contribution to the total error budget.

  1. A 17-billion-solar-mass black hole in a group galaxy with a diffuse core

    NASA Astrophysics Data System (ADS)

    Thomas, Jens; Ma, Chung-Pei; McConnell, Nicholas J.; Greene, Jenny E.; Blakeslee, John P.; Janish, Ryan

    2016-04-01

    Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day ‘dormant’ descendants of this population of ‘active’ black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall—the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600—a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

  2. Observations of dwarfs in nearby voids: implications for galaxy formation and evolution

    NASA Astrophysics Data System (ADS)

    Pustilnik, Simon A.

    2016-10-01

    The intermediate results of the ongoing study of deep samples of ~200 galaxies residing in nearby voids, are presented. Their properties are probed via optical spectroscopy, ugri surface photometry, and HI 21-cm line measurements, with emphasis on their evolutionary status. We derive directly the hydrogen mass M(HI), the ratio M(HI)/LB and the evolutionary parameter gas-phase O/H. Their luminosities and integrated colours are used to derive stellar mass M* and the second evolutionary parameter - gas mass-fraction f g). The colours of the outer parts, typically representative of the galaxy oldest stellar population, are used to estimate the upper limits on time since the beginning of the main SF episode. We compare properties of void galaxies with those of the similar late-type galaxies in denser environments. Most of void galaxies show smaller O/H for their luminosity, in average by ~30\\%, indicating slower evolution. Besides, the fraction of ~10\\% of the whole void sample or ~30\\% of the least luminous void LSB dwarfs show the oxygen deficiency by a factor of 2-5. The majority of this group appear very gas-rich, with f g ~(95-99)%, while their outer parts appear rather blue, indicating the time of onset of the main star-formation episode of less than 1-4 Gyr. Such unevolved LSBD galaxies appear not rare among the smallest void objects, but turned out practically missed to date due to the strong observational selection effects. Our results evidense for unusual evolutionary properties of the sizable fraction of void galaxies, and thus, pose the task of better modelling of dwarf galaxy formation and evolution in voids.

  3. LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626

    SciTech Connect

    Sil'chenko, O. K.; Shulga, A. P.; Moiseev, A. V. E-mail: alina.shulga@gmail.co

    2010-11-15

    We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of three-dimensional spectroscopy, long-slit spectroscopy, and imaging, with the aim of identifying the epoch and mechanisms of their transformation from spirals. Both galaxies have appeared to bear complex features obviously resulting from minor merging: decoupled gas kinematics, nuclear star-forming rings, and multi-tiered oval large-scale stellar disks. The weak emission line nucleus of NGC 3599 bears all signs of Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. We conclude that the transformation of these lenticular galaxies took place about 1-2 Gyr ago, through gravitational mechanisms unrelated to the hot intragroup medium of Leo II.

  4. Studying high redshift galaxy groups with the Athena Wide-Field-Imager

    NASA Astrophysics Data System (ADS)

    Pacaud, Florian; Reiprich, Thomas; Ramos Ceja, Miriam Elizabeth; Lovisari, Lorenzo

    2016-07-01

    In this contribution, we will discuss the potential of Athena to study high redshift galaxy groups (1groups in Athena WFI observations and our ability to identify them as extended sources among the numerous active galactic nuclei (AGN) at similar fluxes. Our analysis also includes the determination of the physical properties of these galaxy groups (average gas temperature, luminosity). Based on these tools, we discuss the science achievable with such systems thanks to Athena and its dependance on the final instrumental set-up. In particular, we investigate the impact of different levels of contamination by AGNs and assumptions on the luminosity of the groups as a function of their mass.

  5. The Role of Star Formation in Radio-Loud Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Herbst, Hanna; Wilcots, E.; Hess, K.

    2010-01-01

    X-ray observations have shown that additional non-gravitational processes are required to explain the heating of the intergalactic medium in galaxy groups. The two most likely processes are galactic outflows from starbursts and feedback from AGN. Here, we look at star formation as a possible additional heating mechanism in X-ray luminous groups such as NGC 741, NGC 1052, NGC 524, and NGC 1587. We report on the results of optical imaging of these groups carried out using the WIYN 3.5m telescope with a specific emphasis on measuring the star formation rates of the resident galaxies in each group and estimating the impact of that star formation on the thermodynamics of the intragroup medium.

  6. X-ray Emission from Early-Type Galaxies in Groups and Poor Clusters

    NASA Astrophysics Data System (ADS)

    Paolillo, M.

    2002-04-01

    We present the study of three bright Early-Type galaxies hosted in groups or poor clusters: NGC 1399, NGC 1404 and NGC 507. We used ROSAT HRI, PSPC and, when available, higher resolution Chandra data to study the structure of the X-ray halo. The halo center of NGC 1399 and NGC 507 is dominated by a bright emission peak coincident with the position of the optical galaxy. This central peak is not explained by cooling flow models and is likely to be produced by kinetically heated stellar material. Within the effective radius, the hot gas distribution is tracing the galactic potential due to luminous matter. At larger distances the halo dynamics is dominated by dark matter extending on group and cluster scales. The NGC 1399 complex morphology further requires that the dark matter distribution has a hierarchical structure or that environmental effects are producing departures from hydrostatic equilibrium. We found significant density fluctuations in the hot gas distribution of both NGC 1399 and NGC 507, some of which are explained by the interaction of the radio-emitting plasma with the surrounding ISM. The remaining structures may be the result of galaxy-galaxy encounters, wakes produced by the motion of the galaxy through the ICM or may reflect the inhomogeneity of the cooling process invoked by many authors to explain the failure of the standard cooling-flow models. NGC 1404 represents a puzzling case since, despite its similarity with dominant cluster members, significant differences are found in the hot gas properties. These conflicting evidences can be explained by environmental effects, such as stifling of galactic winds by the ICM. Finally, we studied the population of discrete sources found in proximity of the two dominant galaxies.

  7. Gender and Leadership: The Implications of Small Group Research.

    ERIC Educational Resources Information Center

    Gale, Linda Lyman

    1988-01-01

    Reviews selected literature from the small group communication research on gender and leadership emergence and suggests implications of this research for women seeking administrative positions. Hopes that, as men and women become sensitive to effects of sex-role stereotypes on group dynamics and leadership behaviors, there will be increase in…

  8. Ultra-compact high velocity clouds in the ALFALFA HI survey: Candidate Local Group galaxies?

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth Ann Kovenz

    The increased sensitivity and spatial resolution of the ALFALFA HI survey has resulted in the detection of ultra-compact high velocity clouds (UCHVCs). These objects are good candidates to represent low mass gas-rich galaxies in the Local Group and Local Volume with stellar populations that are too faint to be detected in extant optical surveys. This idea is referred to as the "minihalo hypothesis". We identify the UCHVCs within the ALFALFA dataset via the use of a 3D matched filtering signal identification algorithm. UCHVCs are selected based on a compact size (< 30'), separation from Galactic HI (|upsilon LSR| > 120 km s-1) and isolation. Within the 40% complete ALFALFA survey (alpha.40), 59 UCHVCs are identified; 19 are in a most-isolated subset and are the best galaxy candidates. Due to the presence of large HVC complexes in the fall sky, most notably the Magellanic Stream, the association of UCHVCs with existing structure cannot be ruled out. In the spring sky, the spatial and kinematic distribution of the UCHVCs is consistent with simulations of dark matter halos within the Local Group. In addition, the HI properties of the UCHVCs (if placed at 1 Mpc) are consistent with both theoretical and observational predictions for low mass gas-rich galaxies. Importantly, the HI properties of the UCHVCs are consistent with those of two recently discovered low mass gas-rich galaxies in the Local Group and Local Volume, Leo T and Leo P. Detailed follow-up observations are key for addressing the minihalo hypothesis. High resolution HI observations can constrain the environment of a UCHVC and offer evidence for a hosting dark matter halo through evidence of rotation support and comparison to theoretical models. Observations of one UCHVC at high resolution (15'') reveal the presence of a clumpy HI distribution, similar to both low mass galaxies and circumgalactic compact HVCs. An extended envelope containing ˜50% of the HI flux is resolved out by the array configuration

  9. Steepened inner density profiles of group galaxies via interactions: an N-body analysis

    NASA Astrophysics Data System (ADS)

    Dobke, Benjamin M.; King, Lindsay J.; Fellhauer, Michael

    2007-06-01

    We continue to see a range of values for the Hubble constant obtained from gravitationally lensed multiple image time-delays when assuming an isothermal lens despite a robust value from the Hubble Space Telescope (HST) key project (72 +/- 8 kms-1 Mpc-1). One explanation is that there is a variation in Hubble constant values due to a fundamental heterogeneity in lens galaxies present in groups, that is, central galaxies with a high dark matter surface density, and satellite galaxies with a possibly stripped halo, low dark matter surface density, and a more centrally concentrated matter distribution. Our goal is to see if a variety of group interactions between the most-massive group members can result in significant changes in the galaxy density profiles over the scale probed by strong lensing (<~15 kpc). While stripping of the outer parts of the halo can be expected, the impact on inner regions where the luminous component is important is less clear in the context of lensing, though still crucial, as a steepened density profile within this inner region allows these lens systems to be consistent with current HST/Wilkinson Microwave Anisotropy Probe (WMAP) estimates on H0. We employ the particle-mesh code SUPERBOX to carry out the group interaction simulations. An important advantage of using such a code is that it implements a fast, low-storage fast Fourier transform (FFT) algorithm allowing simulations with millions of particles on desk-top machines. We simulate interactions between group members, comparing the density profile for the satellite before and after interaction for the mass range of 1011 to 1013Msolar. Our investigations show a significant steepening of the density profile in the region of ~5-20 kpc, i.e. that which dominates strong lensing in lens galaxies. This effect is independent of the initial mass-to-light ratio. Additionally, the steepening in the inner region is transient in nature, with consecutive interactions returning the profile to an

  10. Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

    NASA Astrophysics Data System (ADS)

    Villaescusa-Navarro, Francisco; Planelles, Susana; Borgani, Stefano; Viel, Matteo; Rasia, Elena; Murante, Giuseppe; Dolag, Klaus; Steinborn, Lisa K.; Biffi, Veronica; Beck, Alexander M.; Ragone-Figueroa, Cinthia

    2016-03-01

    By means of zoom-in hydrodynamic simulations, we quantify the amount of neutral hydrogen (H I) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics, include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split into two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analysed to account for H I self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter haloes monotonically increases with the halo mass and can be well described by a power law of the form M_{H I}(M,z)∝ M^{3/4}. Our results point out that AGN feedback reduces both the total halo mass and its H I mass, although it is more efficient in removing H I. We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by ˜50 per cent, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within haloes is also affected by AGN feedback, whose effect is to decrease the fraction of H I that resides in the halo inner regions. By extrapolating our results to haloes not resolved in our simulations, we derive astrophysical implications from the measurements of Ω _{H I}(z): haloes with circular velocities larger than ˜25 km s-1 are needed to host H I in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of Ω _{H I}b_{H I} derived from available 21 cm intensity mapping observations.

  11. Detailed photometric analysis of young star groups in the galaxy NGC 300

    NASA Astrophysics Data System (ADS)

    Rodríguez, M. J.; Baume, G.; Feinstein, C.

    2016-10-01

    Aims: The purpose of this work is to understand the global characteristics of the stellar populations in NGC 300. In particular, we focused our attention on searching young star groups and study their hierarchical organization. The proximity and orientation of this Sculptor Group galaxy make it an ideal candidate for this study. Methods: The research was conducted using archival point spread function (PSF) fitting photometry measured from images in multiple bands obtained with the Advanced Camera for Surveys of the Hubble Space Telescope (ACS/HST). Using the path linkage criterion (PLC), we cataloged young star groups and analyzed them from the observation of individual stars in the galaxy NGC 300. We also built stellar density maps from the bluest stars and applied the SExtractor code to identify overdensities. This method provided an additional tool for the detection of young stellar structures. By plotting isocontours over the density maps and comparing the two methods, we could infer and delineate the hierarchical structure of the blue population in the galaxy. For each region of a detected young star group, we estimated the size and derived the radial surface density profiles for stellar populations of different color (blue and red). A statistical decontamination of field stars was performed for each region. In this way it was possible to build the color-magnitude diagrams (CMD) and compare them with theoretical evolutionary models. We also constrained the present-day mass function (PDMF) per group by estimating a value for its slope. Results: The blue population distribution in NGC 300 clearly follows the spiral arms of the galaxy, showing a hierarchical behavior in which the larger and loosely distributed structures split into more compact and denser ones over several density levels. We created a catalog of 1147 young star groups in six fields of the galaxy NGC 300, in which we present their fundamental characteristics. The mean and the mode radius values

  12. GALAXY INTERACTIONS IN COMPACT GROUPS. I. THE GALACTIC WINDS OF HCG16

    SciTech Connect

    Vogt, Frederic P. A.; Dopita, Michael A.; Kewley, Lisa J.

    2013-05-10

    Using the WiFeS integral field spectrograph, we have undertaken a series of observations of star-forming galaxies in compact groups. In this first paper dedicated to the project, we present the analysis of the spiral galaxy NGC 838, a member of the Hickson Compact Group 16, and of its galactic wind. Our observations reveal that the wind forms an asymmetric, bipolar, rotating structure, powered by a nuclear starburst. Emission line ratio diagnostics indicate that photoionization is the dominant excitation mechanism at the base of the wind. Mixing from slow shocks (up to 20%) increases further out along the outflow axis. The asymmetry of the wind is most likely caused by one of the two lobes of the wind bubble bursting out of its H I envelope, as indicated by line ratios and radial velocity maps. The characteristics of this galactic wind suggest that it is caught early (a few Myr) in the wind evolution sequence. The wind is also quite different from the galactic wind in the partner galaxy NGC 839 which contains a symmetric, shock-excited wind. Assuming that both galaxies have similar interaction histories, the two different winds must be a consequence of the intrinsic properties of NGC 838 and NGC 839 and their starbursts.

  13. AGN Feedback in Galaxy Groups: A Joint GMRT/X-ray Study

    NASA Astrophysics Data System (ADS)

    Giacintucci, S.; Vrtilek, J. M.; O'Sullivan, E.; Raychaudhury, S.; David, L. P.; Venturi, T.; Athreya, R.; Gitti, M.

    2009-12-01

    We present an ongoing study of 18 nearby galaxy groups, chosen for the availability of Chandra and/or XMM-Newton data and evidence for AGN/hot intragroup gas interaction. We have obtained 235 and 610 MHz observations at the GMRT for all the groups, and 327 and 150 MHz for a few. We discuss two interesting cases-NGC 5044 and AWM 4-which exhibit different kinds of AGN/hot gas interaction. With the help of these examples we show how joining low-frequency radio data (to track the history of AGN outbursts through emission from aged electron populations) with X-ray data (to determine the state of hot gas, its disturbances, heating and cooling) can provide a unique insight into the nature of the feedback mechanism in galaxy groups.

  14. Intragroup diffuse light in compact groups of galaxies: HCG 79, 88 and 95

    NASA Astrophysics Data System (ADS)

    Da Rocha, C.; Mendes de Oliveira, C.

    2005-12-01

    Deep B and R images of three Hickson Compact Groups, HCG 79, 88 and 95, have been analysed using a new wavelet technique to measure possible intragroup diffuse light present in these systems. The method used, OV_WAV, is a wavelet technique particularly suitable for detecting low surface brightness extended structures, down to a signal-to-noise ratio (S/N) = 0.1 per pixel, which corresponds to a 5σ detection level in wavelet space. The three groups studied are in different evolutionary stages, as can be judged by their very different fractions of the total light contained in their intragroup haloes: 46 +/- 11 per cent for HCG 79 and 11 +/- 26 per cent for HCG 95, in the B band, and HCG 88 had no component detected down to a limiting surface brightness of 29.1B mag arcsec-2. For HCG 95, the intragroup light (IGL) is red, similar to the mean colours of the group galaxies themselves, suggesting that it is formed by an old population with no significant ongoing star formation. For HCG 79, however, the intragroup material has a significantly bluer colour than the mean colour of the group galaxies, suggesting that the diffuse light may, at least in part, come from stripping of dwarf galaxies which dissolved into the group potential well.

  15. Local dark energy: HST evidence from the vicinity of the M81/M82 galaxy group

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Karachentsev, I. D.; Kashibadze, O. G.; Makarov, D. I.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.

    2007-10-01

    The Hubble Space Telescope observations of the nearby galaxy group M81/M82 and its vicinity indicate that the dynamics of the expansion outflow around the group is dominated by the antigravity of the dark energy background. The local density of dark energy in the area is estimated to be near the global dark energy density or perhaps exactly equal to it. This conclusion agrees well with our previous results for the Local Group vicinity and the vicinity of the Cen A/M83 group.

  16. SARCS strong-lensing galaxy groups. II. Mass-concentration relation and strong-lensing bias

    NASA Astrophysics Data System (ADS)

    Foëx, G.; Motta, V.; Jullo, E.; Limousin, M.; Verdugo, T.

    2014-12-01

    Aims: Various studies have shown a lensing bias in the mass-concentration relation of cluster-scale structures that is the result of an alignment of the major axis and the line of sight. In this paper, we aim to study this lensing bias through the mass-concentration relation of galaxy groups, thus extending observational constraints to dark matter haloes of mass ~1013-1014 M⊙. Methods: Our work is based on the stacked weak-lensing analysis of a sample of 80 strong-lensing galaxy groups. By combining several lenses, we significantly increase the signal-to-noise ratio of the lensing signal, thus providing constraints on the mass profile that cannot be obtained for individual objects. The resulting shear profiles were fitted with various mass models, among them the Navarro-Frank-White (NFW) profile, which provides an estimate of the total mass and of the concentration of the composite galaxy groups. Results: The main results of our analysis are the following: (i) the lensing signal does not allow us to firmly distinguish between a simple singular isothermal sphere mass distribution and the expected NFW mass profile; (ii) we obtain an average concentration c200 = 8.6-1.3+2.1 that is much higher than the value expected from numerical simulations for the corresponding average mass M200 = 0.73-0.10+0.11 × 1014 M⊙; (iii) the combination of our results with those at larger mass scales gives a mass-concentration relation c(M) of more than two decades in mass, whose slope disagrees with predictions from numerical simulations using unbiased populations of dark matter haloes; (iv) our combined c(M) relation matches results from simulations that only used haloes with a large strong-lensing cross-section, that is, elongated with a major axis close to the line of sight; (v) for the simplest case of prolate haloes, we estimate a lower limit on the minor-to-major axis ratio a/c = 0.5 for the average SARCS galaxy group with a toy model. Conclusions: Our analysis based on galaxy

  17. Weak lensing calibrated M-T scaling relation of galaxy groups in the cosmos field

    SciTech Connect

    Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.

    2013-11-20

    The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute{sup 2}, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48{sub −0.09}{sup +0.13}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV.

  18. The redshift-space neighborhoods of 36 loose groups of galaxies. 1: The data

    NASA Technical Reports Server (NTRS)

    Ramella, Massimo; Geller, Margaret J.; Hurchra, John P.; Thorstensen, John R.

    1995-01-01

    We have selected 36 loose groups of galaxies (RGH89) with at least five members, and with mean redshift average value of CZ is greater than 3200 km/s. These groups all lie within the first two slices of the CfA redshift survey 8(sup h) less than or equal to alpha less than or equal to 17(sup h) and 26.5 deg less than or equal to delta less than or equal to 38.5 deg). For each of these groups, we define the redshift-space neighborhood as a region centered on the group coordinates and delimited by a circle of projected radius R(sub cir) = 1.5/h Mpc on the sky, and by a velocity interval delta (sub cz) = 3000 km/s. Here we give the redshifts of 334 galaxies in these redshift-space neighborhoods. For completeness, we also give the redshifts of the 232 original members. These data include 199 new redshifts. We demonstrate that these samples of fainter galaxies significantly increase the number of members.

  19. Implications of a variable IMF for the interpretation of observations of galaxy populations

    NASA Astrophysics Data System (ADS)

    Clauwens, Bart; Schaye, Joop; Franx, Marijn

    2016-11-01

    We investigate the effect of a metallicity-dependent stellar initial mass function (IMF), as deduced observationally by Martín-Navarro et al., on the inferred stellar masses and star formation rates (SFRs) of a representative sample of 186 886 SDSS galaxies. Relative to a Chabrier IMF, for which we show the implied masses to be close to minimal, the inferred masses increase in both the low- and high-metallicity regimes due to the addition of stellar remnants and dwarf stars, respectively. The resulting galaxy stellar mass function (GSMF) shifts towards higher masses by 0.5 dex, without affecting the high-mass slope (and thus the need for effective quenching). The implied low-redshift SFR density increases by an order of magnitude. However, these results depend strongly on the assumed IMF parametrization, which is not directly constrained by the observations. Varying the low-end IMF slope instead of the high-end IMF slope, while maintaining the same dwarf-to-giant ratio, results in a much more modest GSMF shift of 0.2 dex and a 10 per cent increase in the SFR density relative to the Chabrier IMF. A bottom-heavy IMF during the late, metal-rich evolutionary stage of a galaxy would help explain the rapid quenching and the bimodality in the galaxy population by on the one hand making galaxies less quenched (due to the continued formation of dwarf stars) and on the other hand reducing the gas consumption time-scale. We conclude that the implications of the observational evidence for a variable IMF could vary from absolutely dramatic to mild but significant.

  20. A Compact Group of Galaxies at z = 2.48 Hosting an AGN-driven Outflow

    NASA Astrophysics Data System (ADS)

    Shih, Hsin-Yi; Stockton, Alan

    2015-12-01

    We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 1011M⊙ and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass-metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The work is also based, in part, on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  1. Neutral Hydrogen Clouds Near Early-Type Dwarf Galaxies of the Local Group

    NASA Astrophysics Data System (ADS)

    Bouchard, Antoine; Carignan, Claude; Staveley-Smith, Lister

    2006-06-01

    Parkes neutral hydrogen 21 cm line (H I) observations of the surroundings of nine early-type Local Group dwarfs are presented. We detected numerous H I clouds in the general direction of those dwarfs, and these clouds are often offset from the optical center of the galaxies. Although all the observed dwarfs, except Antlia, occupy phase-space regions where the high-velocity cloud (HVC) density is well above average, the measured offsets are smaller than one would expect from a fully random cloud distribution. Possible association is detected for 11 of the 16 investigated clouds, while for two galaxies, Sextans and Leo I, no H I was detected. The galaxies in which H I clouds were found not to coincide with the optical yet have a significant probability of being associated are the Sculptor dwarf, Tucana, LGS 3, Cetus, and Fornax. If the clouds are indeed associated, these galaxies have H I masses of MHI=2×105, 2×106, 7×105, 7×105, and 1×105 Msolar, respectively. However, neither ram pressure nor tidal stripping can easily explain the offsets. In some cases, large offsets are found where ram pressure should be the least effective.

  2. X-ray-selected galaxy groups in Boötes

    SciTech Connect

    Vajgel, Bruna; Lopes, Paulo A. A.; Jones, Christine; Forman, William R.; Murray, Stephen S.; Goulding, Andrew; Andrade-Santos, Felipe

    2014-10-10

    We present the X-ray and optical properties of the galaxy groups selected in the Chandra X-Boötes survey. We used follow-up Chandra observations to better define the group sample and their X-ray properties. Group redshifts were measured from the AGN and Galaxy Evolution Survey spectroscopic data. We used photometric data from the NOAO Deep Wide Field Survey to estimate the group richness (N {sub gals}) and the optical luminosity (L {sub opt}). Our final sample comprises 32 systems at z < 1.75 with 14 below z = 0.35. For these 14 systems, we estimate velocity dispersions (σ {sub gr}) and perform a virial analysis to obtain the radii (R {sub 200} and R {sub 500}) and total masses (M {sub 200} and M {sub 500}) for groups with at least 5 galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (L{sub X} ). We examine the performance of the group properties σ{sub gr}, L {sub opt}, and L{sub X} , as proxies for the group mass. Understanding how well these observables measure the total mass is important to estimate how precisely the cluster/group mass function is determined. Exploring the scaling relations built with the X-Boötes sample and comparing these with samples from the literature, we find a break in the L{sub X} -M {sub 500} relation at approximately M {sub 500} = 5 × 10{sup 13} M {sub ☉} (for M {sub 500} > 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.61±0.02}, while for M {sub 500} ≤ 5 × 10{sup 13} M {sub ☉}, M{sub 500}∝L{sub X}{sup 0.44±0.05}). Thus, the mass-luminosity relation for galaxy groups cannot be described by the same power law as galaxy clusters. A possible explanation for this break is the dynamical friction, tidal interactions, and projection effects that reduce the velocity dispersion values of the galaxy groups. By extending the cluster luminosity function to the group regime, we predict the number of groups that new X-ray surveys, particularly eROSITA, will detect. Based on our cluster/group

  3. Properties of galaxy groups in the Sloan Digital Sky Survey - II. Active galactic nucleus feedback and star formation truncation

    NASA Astrophysics Data System (ADS)

    Weinmann, Simone M.; van den Bosch, Frank C.; Yang, Xiaohu; Mo, H. J.; Croton, Darren J.; Moore, Ben

    2006-11-01

    Successfully reproducing the galaxy luminosity function (LF) and the bimodality in the galaxy distribution requires a mechanism that can truncate star formation in massive haloes. Current models of galaxy formation consider two such truncation mechanisms: strangulation, which acts on satellite galaxies, and active galactic nucleus (AGN) feedback, which predominantly affects central galaxies. The efficiencies of these processes set the blue fraction of galaxies, fblue(L, M), as a function of galaxy luminosity, L, and halo mass, M. In this paper, we use a galaxy group catalogue extracted from the Sloan Digital Sky Survey (SDSS) to determine fblue(L, M). To demonstrate the potential power of these data as a benchmark for galaxy formation models, we compare the results to the semi-analytical model for galaxy formation of Croton et al. Although this model accurately fits the global statistics of the galaxy population, as well as the shape of the conditional LF, there are significant discrepancies when the blue fraction of galaxies as a function of mass and luminosity is compared between the observations and the model. In particular, the model predicts (i) too many faint satellites in massive haloes, (ii) a blue fraction of satellites that is much too low, and (iii) a blue fraction of centrals that is too high and with an inverted luminosity dependence. In the same order, we argue that these discrepancies owe to (i) the neglect of tidal stripping in the semi-analytical model, (ii) the oversimplified treatment of strangulation, and (iii) improper modelling of dust extinction and/or AGN feedback. The data presented here will prove useful to test and calibrate future models of galaxy formation and, in particular, to discriminate between various models for AGN feedback and other star formation truncation mechanisms.

  4. Redshift-Space Distortions and f(z) from Group-Galaxy Correlations

    NASA Astrophysics Data System (ADS)

    Mohammad, F. G.; de la Torre, S.; Guzzo, L.; Bianchi, D.; Peacock, J. A.

    2016-10-01

    We investigate the accuracy achievable on measurements of the the growth rate of structure f(z) using redshift-space distortions (RSD), when (a) these are measured on the group-galaxy cross correlation function; (b) the latter is expanded over a modified version of the conventional spherical armonics, ``truncated multipole moments''. Simulation results give first indications that this combination can push systematic errors on f(z) below 3%, using scales r >= 10h -1 Mpc.

  5. Project Galaxy - Sustianable Resource Supply and Environmental Implications

    SciTech Connect

    Downing, Mark; Wimmer, Robert

    2012-03-01

    Understanding what it takes to move from a corn-based liquid fuels industry to one that is cellulosic-based requires a complex transition over time. This transition implies, among other things, a shift from annual cropping systems considered under United States Department of Agriculture (USDA) policy as commodity crops, to perennial lignocellulosic crops that are herbaceous and wood-based. Because of changes in land use as well as biomass and other crop supplies, land-based environmental amenities such as water quality, soil health and tilth, air quality, and animal and avian species populations and their diversity change also. Environmental effects are measured as magnitudes (how much they are impacted), and direction of the impact (either positive or negative). By developing a series of quantitative and qualitative metrics, the larger issue of defining relative sustainability may be addressed, and this can be done at a finer detail of regional (scale) and environmental amenity-specific impacts. Although much literature exists about research relevant to specific environmental variables, there is no published, documented, nor research literature on direct application of environmental over-compliance with regards a 'biorefinery.' Our three goals were to (1) understand and quantify bioenergy sustainability and some key environmental effects in a generic set of examples; (2) explain the effort and means to define and quantify specific qualitative environmental measures, and to determine a way to understand changes in these measures over time and what their implications might be; and (3) use these outcomes to evaluate potential sites in any geographic area. This would permit assessment of candidate locations, combined with an understanding of co-production of fuels, chemicals, and electric power, to interpret sustainability measures and the relationship between environmental sustainability and economic sustainability. The process of determining environmental

  6. An Observational Limit on the Dwarf Galaxy Population of the Local Group

    NASA Astrophysics Data System (ADS)

    Whiting, Alan B.; Hau, George K. T.; Irwin, Mike; Verdugo, Miguel

    2007-02-01

    We present the results of an all-sky, deep optical survey for faint Local Group dwarf galaxies. Candidate objects were selected from the second Palomar Observatory Sky Survey and ESO/Science Research Council survey plates, and follow-up observations were performed to determine whether they were indeed overlooked members of the Local Group. Only two galaxies (Antlia and Cetus) were discovered this way out of 206 candidates. Based on internal and external comparisons, we estimate that our visual survey is more than 77% complete for objects larger than 1' in size and with a surface brightness greater than an extremely faint limit over the 72% of the sky not obstructed by the Milky Way. Our limit of sensitivity cannot be calculated exactly, but it is certainly fainter than 25 mag arcsec-2 in R, probably 25.5 and possibly approaching 26. We conclude that there are at most one or two Local Group dwarf galaxies fitting our observational criteria still undiscovered in the clear part of the sky, and roughly a dozen hidden behind the Milky Way. Our work places the ``missing satellite problem'' on a firm quantitative observational basis. We present detailed data on all our candidates, including surface brightness measurements.

  7. Exploring the Dependence of Galaxy Properties on Group Halo Environment in RESOLVE

    NASA Astrophysics Data System (ADS)

    Baker, Ashley; Berlind, A. A.; Kannappan, S.; Moffett, A. J.; RESOLVE Team

    2014-01-01

    We discuss the development of a new halo mass metric based on group dynamics for the RESOLVE survey as well as its application to understanding the dependence of galaxy properties on environment. Methods and parameters for group finding and calculating dynamical mass are optimized on a mock catalog with similar redshift range to RESOLVE. We also develop additional metrics of the evolutionary state of the group. These methods are applied to a sample of galaxies in the B-semester footprint of the RESOLVE survey, which overlaps with SDSS Stripe 82, as well as the ECO catalog, a larger volume-limited survey that encloses the A-semester footprint of RESOLVE. Using both dynamical halo mass and halo evolutionary state to quantify environment, we study its influence on galaxy properties such as color, gas content, and star formation history. We acknowledge REU funding support to Vanderbilt under NSF grant PHY-1263045 and to the RESOLVE survey at UNC Chapel Hill under AST-0955368.

  8. VizieR Online Data Catalog: Galaxy groups in the VIMOS-VLT Deep Survey (Cucciati+, 2010)

    NASA Astrophysics Data System (ADS)

    Cucciati, O.; Marinoni, C.; Iovino, A.; Bardelli, S.; Adami, C.; Mazure, A.; Scodeggio, M.; Maccagni, D.; Temporin, S.; Zucca, E.; de, Lucia G.; Blaizot, J.; Garilli, B.; Meneux, B.; Zamorani, G.; Le Fevre, O.; Cappi, A.; Guzzo, L.; Bottini, D.; Le Brun, V.; Tresse, L.; Vettolani, G.; Zanichelli, A.; Arnouts, S.; Bolzonella, M.; Charlot, S.; Ciliegi, P.; Contini, T.; Foucaud, S.; Franzetti, P.; Gavignaud, I.; Ilbert, O.; Lamareille, F.; McCracken, H. J.; Marano, B.; Merighi, R.; Paltani, S.; Pella, R.; Pollo, A.; Pozzetti, L.; Vergani, D.; Perez-Montero, E.

    2010-08-01

    We have compiled a homogeneous catalogue of optical galaxy groups identified in the VVDS-02h field (0.7x0.7deg2^) by means of the VDM algorithm, in the range 0.2<=z<=1.0. We give the coordinates (RA, DE and z) and a few properties (velocity dispersion, number of galaxy members) of the so-found groups. We also list the galaxies that belong to these groups (ID, RA, DE, z, quality of redshift measurement). (2 data files).

  9. The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic High-Velocity Clouds.

    PubMed

    Zwaan; Briggs

    2000-02-20

    The Arecibo H i Strip Survey probed the halos of approximately 300 cataloged galaxies and the environments of approximately 14 groups with sensitivity to neutral hydrogen masses >/=107 M middle dot in circle. The survey detected no objects with properties resembling the high-velocity clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHi=107.5 M middle dot in circle objects distributed throughout groups and galaxy halos at distances of approximately 1 Mpc, the survey should have made approximately 70 HVC detections in groups and approximately 250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of galaxies or group barycenters. If the clouds are in virial equilibrium, their average dark matter fraction must be 98% or higher.

  10. Identifying Local Group field galaxies that have interacted with the Milky Way

    NASA Astrophysics Data System (ADS)

    Teyssier, Maureen; Johnston, Kathryn V.; Kuhlen, Michael

    2012-11-01

    We distinguish between Local Group field galaxies that may have passed through the virial volume of the Milky Way, and those that have not, via a statistical comparison against populations of dark matter haloes in the Via Lactea II (VLII) simulation with known orbital histories. Analysis of VLII provides expectations for this escaped population: they contribute 13 per cent of the galactic population between 300 and 1500 kpc from the Milky Way, and hence we anticipate that about 7 of the 54 known Local Group galaxies in that distance range are likely to be Milky Way escapees. These objects can be of any mass below that of the Milky Way, and they are expected to have positive radial velocities with respect to the Milky Way. Comparison of the radius-velocity distributions of VLII populations and measurements of Local Group galaxies presents a strong likelihood that Tucana, Cetus, NGC 3109, Sextans A, Sextans B, Antlia, NGC 6822, Phoenix, Leo T and NGC 185 have passed through the Milky Way. Most of these dwarfs have a lower H I mass fraction than the majority of dwarfs lying at similar distances to either the Milky Way or M31. Indeed, several of these galaxies - especially those with lower masses - contain signatures in their morphology, star formation history and/or gas content indicative of evolution seen in simulations of satellite/parent galactic interactions. Our results offer strong support for scenarios in which dwarfs of different types form a sequence in morphology and gas content, with evolution along the sequence being driven by interaction history.

  11. Evolution in the H I Gas Content of Galaxy Groups: Pre-processing and Mass Assembly in the Current Epoch

    NASA Astrophysics Data System (ADS)

    Hess, Kelley M.; Wilcots, Eric M.

    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.

  12. Star Formation as a Function of Neutral Hydrogen Gas Density in Local Group Galaxies

    NASA Astrophysics Data System (ADS)

    Carlson, Erika K.; Madore, Barry F.; Freedman, Wendy L.

    2016-06-01

    We present a study of the efficiency and timescales of star formation as a function of local neutral hydrogen gas density in four Local Group galaxies: M33, NGC 6822, the LMC, and the SMC. In this work, we conceptualize the process of star formation as a cycle of two major phases - (1) a gas dynamics phase in which neutral hydrogen gas coalesces into clouds, and (2) a stellar phase in which stars have formed and interrupt further gas coalescence during their active lifetimes. By examining the spatial distribution and number densities of stars on maps of neutral hydrogen, we estimate the timescale of the gas coalescence phase relative to the timescale of the stellar phase and infer an efficiency of star formation as a function of neutral hydrogen gas density. From these timescales and efficiencies, we will calculate star formation rates as a function of neutral hydrogen gas density in these galaxies.

  13. THE EFFECT OF ENVIRONMENT ON MILKY-WAY-MASS GALAXIES IN A CONSTRAINED SIMULATION OF THE LOCAL GROUP

    SciTech Connect

    Creasey, Peter; Scannapieco, Cecilia; Nuza, Sebastián E.; Gottlöber, Stefan; Steinmetz, Matthias; Yepes, Gustavo

    2015-02-10

    In this Letter, we present, for the first time, a study of star formation rate (SFR), gas fraction, and galaxy morphology of a constrained simulation of the Milky Way (MW) and Andromeda (M31) galaxies compared to other MW-mass galaxies. By combining with unconstrained simulations, we cover a sufficient volume to compare these galaxies’ environmental densities ranging from the field to that of the Local Group (LG). This is particularly relevant as it has been shown that, quite generally, galaxy properties depend intimately upon their environment, most prominently when galaxies in clusters are compared to those in the field. For galaxies in loose groups such as the LG, however, environmental effects have been less clear. We consider the galaxy’s environmental density in spheres of 1200 kpc (comoving) and find that while environment does not appear to directly affect morphology, there is a positive trend with SFRs. This enhancement in star formation occurs systematically for galaxies in higher density environments, regardless whether they are part of the LG or in filaments. Our simulations suggest that the richer environment at megaparsec scales may help replenish the star-forming gas, allowing higher specific SFRs in galaxies such as the MW.

  14. The Properties of Local Barred Disks in the Field and Dense Environments: Implications for Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Marinova, I.; Jogee, S.; Barazza, F. D.; Heiderman, A.; Gray, M. E.; Barden, M.; Wolf, C.; Peng, C. Y.; Bacon, D.; Balogh, M.; Bell, E. F.; Böhm, A.; Caldwell, J. A. R.; Häußler, B.; Heymans, C.; Jahnke, K.; van Kampen, E.; Lane, K.; McIntosh, D. H.; Meisenheimer, K.; Sánchez, S. F.; Sommerville, R. S.; Taylor, A.; Wisotzki, L.; Zheng, X.

    2009-12-01

    Stellar bars are the most efficient internal drivers of disk evolution because they redistribute material and angular momentum within the galaxy and dark matter halo. Mounting evidence suggests that processes other than major mergers, such as minor mergers, secular processes driven by bars, and clump coalescence, as well as smooth accretion, play an important role in galaxy evolution since z = 2. As a key step toward characterizing this evolution and constraining theoretical models, we determine the frequency and properties of bars in the local Universe in both field and cluster environment, based on three of our studies: Marinova & Jogee (2007), Barazza, Jogee, & Marinova (2008) and Marinova et al. (2009). Among field spirals of intermediate Hubble types in the OSU survey, we find using ellipse fitting that the bar fraction is 44% in the optical and 60% in the NIR, giving an extinction correction factor of approximately 1.4 at z ˜ 0. Using data from the Abell 901/902 cluster system at z ˜ 0.165 from the HST ACS survey STAGES, we find that the optical bar fraction is a strong trend of both absolute magnitude and host bulge-to-total ratio, increasing for galaxies that are brighter and/or more disk-dominated. The latter trend is also found in the field from SDSS. For bright early types and faint late types the optical bar fraction in the cluster is similar to that in the field. We find that between the core region and the virial radii of the clusters the optical bar fraction is not a strong function of local environment density. We discuss the implications of our results in the context of theoretical models of the impact of bars on galaxy evolution.

  15. Probing the dusty inhabitants of the Local Group Galaxies: JWST/MIRI colors of infrared stellar populations

    NASA Astrophysics Data System (ADS)

    Jones, Olivia; Meixner, Margaret

    2016-01-01

    The assembly of galaxies involves the life cycle of mass, metal enrichment and dust that JWST will probe. Detailed studies of nearby galaxies provides guidance for interpreting the more distant forming galaxies. JWST/MIRI will enable stellar population studies akin to work done with HST on the Local Group galaxies but over a new wavelength range. MIRI's imaging capability over nine photometric bands from 5 to 28 microns is particularly suited to survey stars with an infrared excess and to detangle the extinction or thermal emission from various species of dust. These dusty stellar populations include young stellar objects, evolved stars and supernovae that are bright in the infrared. Using the rich Spitzer-IRS spectroscopic dataset and spectral classifications from the Surveying the Agents of Galaxy Evolution (SAGE)-Spectroscopic survey of over a thousand objects in the Magellanic Clouds, we calculate the expected flux -densities and colors in the MIRI broadband filters for these prominent infrared sources. We uses these fluxes to illustrate what JWST will see in stellar population studies for other Local Group galaxies. JWST/MIRI observations of infrared sources in Local Group Galaxies will constrain the life cycle of galaxies through their dust emission. For example, how much of the interstellar dust is supplied by dying stars? Do the number of young stellar objects agree with star formation diagnostic for the galaxy? We discuss the locations of the post- and pre-main-sequence populations in MIRI color-color and color-magnitude space and examine which filters are best for identifying populations of sources. We connect these results to existing galaxies with HST data for instance Andromeda and M33.

  16. Intragroup diffuse light in compact groups of galaxies - II. HCG 15, 35 and 51

    NASA Astrophysics Data System (ADS)

    Da Rocha, C.; Ziegler, B. L.; Mendes de Oliveira, C.

    2008-08-01

    This continuing study of intragroup light in compact groups of galaxies aims to establish new constraints to models of formation and evolution of galaxy groups, specially of compact groups, which are a key part in the evolution of larger structures, such as clusters. In this paper we present three additional groups (HCG 15, 35 and 51) using deep wide-field B- and R-band images observed with the LAICA camera at the 3.5-m telescope at the Calar Alto observatory (CAHA). This instrument provides us with very stable flat-fielding, a mandatory condition for reliably measuring intragroup diffuse light. The images were analysed with the OV_WAV package, a wavelet technique that allows us to uncover the intragroup component in an unprecedented way. We have detected that 19, 15 and 26 per cent of the total light of HCG 15, 35 and 51, respectively, are in the diffuse component, with colours that are compatible with old stellar populations and with mean surface brightness that can be as low as 28.4 B mag arcsec-2. Dynamical masses, crossing times and mass-to-light ratios were recalculated using the new group parameters. Also tidal features were analysed using the wavelet technique.

  17. The early chemical enrichment histories of two Sculptor group dwarf galaxies as revealed by RR lyrae variables

    SciTech Connect

    Yang, Soung-Chul; Kim, Sang Chul; Kyeong, Jaemann; Wagner-Kaiser, Rachel; Sarajedini, Ata

    2014-03-20

    We present the results of our analysis of the RR Lyrae (RRL) variable stars detected in two transition-type dwarf galaxies (dTrans), ESO294-G010 and ESO410-G005 in the Sculptor group, which is known to be one of the closest neighboring galaxy groups to our Local Group. Using deep archival images from the Advanced Camera for Surveys on board the Hubble Space Telescope, we have identified a sample of RRL candidates in both dTrans galaxies (219 RRab (RR0) and 13 RRc (RR1) variables in ESO294-G010; 225 RRab and 44 RRc stars in ESO410-G005). The metallicities of the individual RRab stars are calculated via the period-amplitude-[Fe/H] relation derived by Alcock et al. This yields mean metallicities of ([Fe/H]){sub ESO294} = –1.77 ± 0.03 and ([Fe/H]){sub ESO410} = –1.64 ± 0.03. The RRL metallicity distribution functions (MDFs) are investigated further via simple chemical evolution models; these reveal the relics of the early chemical enrichment processes for these two dTrans galaxies. In the case of both galaxies, the shapes of the RRL MDFs are well described by pre-enrichment models. This suggests two possible channels for the early chemical evolution for these Sculptor group dTrans galaxies: (1) the ancient stellar populations of our target dwarf galaxies might have formed from the star forming gas which was already enriched through 'prompt initial enrichment' or an 'initial nucleosynthetic spike' from the very first massive stars, or (2) this pre-enrichment state might have been achieved by the end products from more evolved systems of their nearest neighbor, NGC 55. We also study the environmental effects of the formation and evolution of our target dTrans galaxies by comparing their properties with those of 79 volume limited (D {sub ☉} < 2 Mpc) dwarf galaxy samples in terms of the luminosity-metallicity relation and the H I gas content. The presence of these RRL stars strongly supports the idea that although the Sculptor Group galaxies have a considerably

  18. Comparison of the properties of two fossil groups of galaxies with the normal group NGC 6034 based on multiband imaging and optical spectroscopy

    NASA Astrophysics Data System (ADS)

    Adami, C.; Jouvel, S.; Guennou, L.; Le Brun, V.; Durret, F.; Clement, B.; Clerc, N.; Comerón, S.; Ilbert, O.; Lin, Y.; Russeil, D.; Seemann, U.

    2012-04-01

    Context. Fossil groups are dominated by a bright galaxy, and their luminosity functions show an absence within half the virial radius of galaxies brighter than the central galaxy magnitude +2. They are nevertheless massive with an extended X-ray halo. The formation and evolution of these structures is still widely debated. Aims: To better understand the origin of these structures, it is crucial to study their faint galaxy population, as well as their large-scale environment, to determine in particular whether they are isolated or not. Methods: We collected multiband imaging and spectroscopy for two fossil groups (RX J1119.7+2126 and 1RXS J235814.4+150524) and one normal group (associated with NGC 6034). We computed photometric redshifts in the central zones of each group, combining previous data with the SDSS five-band data. For each group we investigated the red sequence (RS) of the color-magnitude relation and computed the luminosity functions, stellar population ages and distributions of the group members. Spectroscopy allowed us to investigate the large-scale surroundings of these groups and the substructure levels in 1RXS J235814.4+150524 and NGC 6034. Results: The large-scale environment of 1RXS J235814.4+150524 is poor, though its galaxy density map shows a clear signature of the surrounding cosmic web. RX J1119.7+2126 appears to be very isolated, while the cosmic environment of NGC 6034 is very rich. At the group scale, 1RXS J235814.4+150524 shows no substructure. Galaxies with recent stellar populations seem preferentially located in the group outskirts. A red sequence is discernable for all three groups in a color-magnitude diagram. The luminosity functions based on photometric redshift selection and on statistical background subtraction have comparable shapes, and agree with the few points obtained from spectroscopic redshifts. These luminosity functions show the expected dip between first and second brightest galaxies for the fossil groups only. Their

  19. The star formation histories of local group dwarf galaxies. II. Searching for signatures of reionization

    SciTech Connect

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-07-10

    We search for signatures of reionization in the star formation histories (SFHs) of 38 Local Group dwarf galaxies (10{sup 4} < M{sub *} < 10{sup 9} M{sub ☉}). The SFHs are derived from color-magnitude diagrams using archival Hubble Space Telescope/Wide Field Planetary Camera 2 imaging. Only five quenched galaxies (And V, And VI, And XIII, Leo IV, and Hercules) are consistent with forming the bulk of their stars before reionization, when full uncertainties are considered. Observations of 13 of the predicted 'true fossils' identified by Bovill and Ricotti show that only two (Hercules and Leo IV) indicate star formation quenched by reionization. However, both are within the virial radius of the Milky Way and evidence of tidal disturbance complicates this interpretation. We argue that the late-time gas capture scenario posited by Ricotti for the low mass, gas-rich, and star-forming fossil candidate Leo T is observationally indistinguishable from simple gas retention. Given the ambiguity between environmental effects and reionization, the best reionization fossil candidates are quenched low mass field galaxies (e.g., KKR 25).

  20. Ionized gas in the circumgalactic vicinity of the M81 galaxy group

    NASA Astrophysics Data System (ADS)

    Al Najm, M. N.; Polikarpova, O. L.; Shchekinov, Yu. A.

    2016-04-01

    The dynamics of the dust and gas in the tidal region of the M81 galaxy group have been analyzed, and the drift of the dust relative to the gas has been estimated, including the drift due to the action of radiation pressure from stars in M81. It is concluded that a large fraction of the gas in the tidal region is in the form of ionized hydrogen HII that shields the observedHI gas from the extragalactic Lyman continuum: the observed atomic gas could be only 10% of the total mass of gas. Only then it is possible to satisfactorily explain the excess dust abundance, which exceeds the Galactic value by a factor of six. By analogy, extended HI disks in galaxies with sizes appreciably larger than the stellar disks could be surrounded by HII envelopes with a comparable or greater mass. Such disks could play an important role in supporting prolonged star formation in galaxies with extended HI disks. Associated observational manifestations are discussed. Such HII envelopes outside HI disks could be detectable in absorption in Ly α and lines of ions of heavy elements.

  1. HIERARCHICAL STELLAR STRUCTURES IN THE LOCAL GROUP DWARF GALAXY NGC 6822

    SciTech Connect

    Gouliermis, Dimitrios A.; Walter, Fabian; Schmeja, Stefan; Klessen, Ralf S.; De Blok, W. J. G. E-mail: walter@mpia-hd.mpg.d E-mail: rklessen@ita.uni-heidelberg.d

    2010-12-20

    We present a comprehensive study of the star cluster population and the hierarchical structure in the clustering of blue stars with ages {approx}<500 Myr in the Local Group dwarf irregular galaxy NGC 6822. Our observational material comprises the most complete optical stellar catalog of the galaxy from imaging with the Suprime-Cam at the 8.2 m Subaru Telescope. We identify 47 distinct star clusters with the application of the nearest-neighbor density method to this catalog for a detection threshold of 3{sigma} above the average stellar density. The size distribution of the detected clusters can be very well approximated by a Gaussian with a peak at {approx}68 pc. The total stellar masses of the clusters are estimated by extrapolating the cumulative observed stellar mass function of all clusters to be in the range 10{sup 3}-10{sup 4} M{sub sun}. Their number distribution is fitted very well by a power law with index {alpha} {approx} 1.5 {+-} 0.7, which is consistent with the cluster mass functions of other Local Group galaxies and the cluster initial mass function. In addition to the detected star clusters of the galaxy, the application of the nearest-neighbor density method for various density thresholds, other than 3{sigma}, enabled the identification of stellar concentrations in various lengthscales. The stellar density maps constructed with this technique provide a direct proof of hierarchically structured stellar concentrations in NGC 6822, in the sense that smaller dense stellar concentrations are located inside larger and looser ones. We illustrate this hierarchy by the so-called dendrogram, or structure tree of the detected stellar structures, which demonstrates that most of the detected structures split up into several substructures over at least three levels. We quantify the hierarchy of these structures with the use of the minimum spanning tree method. We find that structures detected at 1, 2, and 3{sigma} density thresholds are hierarchically constructed

  2. The masses of satellites in GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

    NASA Astrophysics Data System (ADS)

    Sifón, Cristóbal; Cacciato, Marcello; Hoekstra, Henk; Brouwer, Margot; van Uitert, Edo; Viola, Massimo; Baldry, Ivan; Brough, Sarah; Brown, Michael J. I.; Choi, Ami; Driver, Simon P.; Erben, Thomas; Grado, Aniello; Heymans, Catherine; Hildebrandt, Hendrik; Joachimi, Benjamin; de Jong, Jelte T. A.; Kuijken, Konrad; McFarland, John; Miller, Lance; Nakajima, Reiko; Napolitano, Nicola; Norberg, Peder; Robotham, Aaron S. G.; Schneider, Peter; Kleijn, Gijs Verdoes

    2015-12-01

    We use the first 100 deg2 of overlap between the Kilo-Degree Survey and the Galaxy And Mass Assembly survey to determine the average galaxy halo mass of ˜10 000 spectroscopically confirmed satellite galaxies in massive (M > 1013 h-1 M⊙) galaxy groups. Separating the sample as a function of projected distance to the group centre, we jointly model the satellites and their host groups with Navarro-Frenk-White density profiles, fully accounting for the data covariance. The probed satellite galaxies in these groups have total masses log ≈ 11.7-12.2 consistent across group-centric distance within the errorbars. Given their typical stellar masses, log ˜ 10.5, such total masses imply stellar mass fractions of / ≈ 0.04 h-1. The average subhalo hosting these satellite galaxies has a mass Msub ˜ 0.015Mhost independent of host halo mass, in broad agreement with the expectations of structure formation in a Λ cold dark matter universe.

  3. Stellar and Gas Phase Metallicity of Low Surface Brighness Galaxies: Implication on Star Formation Process within Young Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kim, Ji Hoon

    2015-08-01

    Low surface brightness (LSB) galaxies, whose central surface brightness, μB, is fainter than 23 mag/arcsec2 in the B-band, have been one of the most intriguing galaxy populations. Their unique characteristics, such as blue colors in optical and near-infrared light, low metallicity, low stellar and gas surface densities, low dust content, and high gas mass fraction (up to 90%), resemble physical conditions of young galaxies of the early Universe whose interstellar medium (ISM) has not been enriched before major star formation activities initiated and should provide a testbed for star formation process at the exremly low surface density regime. Given that their star formation histories are still poorly constrained, LSB galaxies are known to have large specific star formation rates (sSFRs) with large gas fractions. There is also a correlation between their sSFRs and gas fractions. One of plausible scenarios is that the star formation efficiency may be an increasing funtion of time, perhaps due in part to the slow build up of metals and dust. Moreover, it is suspected that, being located in low number density area in terms of galaxy environment, LSB galaxies may receive additional gas to fuel their star formation activity via sporadic cold gas accretion, especially toward their outskirt regions analogous to extended ultraviolet disks. Due to their relatively isolated nature without having endured much interactions, LSB galaxies can mimic star formation processes of disk galaxies of the early Universe within their interstellar media (ISM). We present preliminary results based on stellar and gas phase metallicity of LSB galaxies along with their environment parameters to show how star-forming ISM of young disk galaxies before metal enrichment.

  4. H I Studies of the Sculptor Group Galaxies. V - NGC 253

    NASA Astrophysics Data System (ADS)

    Puche, D.; Carignan, C.; van Gorkom, J. H.

    1995-07-01

    A VLA HI map was made of NGC 253. In this study, there is a continuum map (ngc0253.con), an HI data cube (ngc0253.cub), and moment maps (ngc0253.m0 = total HI, ngc0253.m1 = velocity field, and ngc0253.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  5. H I Studies of the Sculptor Group Galaxies. II - NGC 7793

    NASA Astrophysics Data System (ADS)

    Carignan, C.; Puche, D.

    1995-08-01

    A VLA HI map was made of NGC 7793. In this study, there is a continuum map (ngc7793.con), an HI data cube (ngc7793.cub), and moment maps (ngc7793.m0 = total HI, ngc7793.m1 = velocity field, and ngc7793.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  6. H I Studies of the Sculptor Group Galaxies. IV - NGC 247

    NASA Astrophysics Data System (ADS)

    Carignan, C.; Puche, D.

    1995-07-01

    A VLA HI map was made of NGC 247. In this study, there is a continuum map (ngc0247.con), an HI data cube (ngc0247.cub), and moment maps (ngc0247.m0 = total HI, ngc0247.m1 = velocity field, and ngc0247.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  7. H I Studies of the Sculptor Group Galaxies. VI - NGC 300

    NASA Astrophysics Data System (ADS)

    Puche, D.; Carignan, C.; Bosma, A.

    1995-07-01

    A VLA HI map was made of NGC 300. In this study, there is a continuum map (ngc0300.con), an HI data cube (ngc0300.cub), and moment maps (ngc0300.m0 = total HI, ngc0300.m1 = velocity field, and ngc0300.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  8. H I Studies of the Sculptor Group Galaxies. III - NGC 55

    NASA Astrophysics Data System (ADS)

    Puche, Daniel; Carignan, Claude; Wainscoat, Richard J.

    1995-07-01

    A VLA HI map was made of NGC 55. In this study, there is a continuum map (ngc0055.con), an HI data cube (ngc0055.cub), and moment maps (ngc0055.m0 = total HI, ngc0055.m1 = velocity field, and ngc0055.m2 = second moment). These maps have been used in an extensive dynamical and kinematical study of the Sculptor Group galaxies. The images and related TeX file come from the NRAO CDROM "Images From the Radio Universe" (c. 1992 National Radio Astronomy Observatory, used with permission).

  9. First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group

    NASA Astrophysics Data System (ADS)

    2003-05-01

    First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a

  10. Mass-to-Light-Ratios of the galaxy clusters and groups observed with Suzaku

    NASA Astrophysics Data System (ADS)

    Sasaki, T.; Matsushita, K.; Sato, K.; Abe, Y.; Akamatsu, H.; Fujita, Y.; Kanno, Y.; Simionescu, A.; Tamura, T.; Werner, N.

    2016-06-01

    We analyzed 15 nearby (z < 0.06 ) clusters and groups observed with Suzaku out to ˜ 2 r_{500}. We derived Fe abundance profiles in the ICM, electron density, cumulative gas mass and Fe mass. We also collected K-band luminosities of galaxies and calculated the ratio of the cumulative gas mass and Fe mass in the ICM to the K-band luminosity (gas-mass-to-light ratio and iron-mass-to-light ratio, respectively). The Coma, Perseus, and medium systems have relatively flat radial profiles of the metal abundances at 0.3 solar within 0.5-1 r_{500}, and ˜ 0.2 solar beyond r_{500}. The gas-mass-to-light-ratios and iron-mass-to-light-ratios ratios increase with radius out to r_{500} and become flatter beyond the radius. The weighted average of the iron-mass-to-light ratios of the clusters at 1.6 r_{500} agrees with the expectation with the Salpeter initial-mass-function of stars, and we do not need a top-heavy slope. In contrast, groups and poor clusters have lower gas-mass-to-light ratios and lower iron-mass-to-light ratios than that of rich systems, with the higher entropy excess. Above these results, we discuss an early metal enrichment in galaxy clusters and groups.

  11. The far-ultraviolet signature of the 'missing' baryons in the Local Group of galaxies.

    PubMed

    Nicastro, Fabrizio; Zezas, Andreas; Elvis, Martin; Mathur, Smita; Fiore, Fabrizio; Cecchi-Pestellini, Cesare; Burke, Douglas; Drake, Jeremy; Casella, Piergiorgio

    2003-02-13

    The number of baryons detected in the low-redshift (z < 1) Universe is far smaller than the number detected in corresponding volumes at higher redshifts. Simulations of the formation of structure in the Universe show that up to two-thirds of the 'missing' baryons may have escaped detection because of their high temperature and low density. One of the few ways to detect this matter directly is to look for its signature in the form of ultraviolet absorption lines in the spectra of background sources such as quasars. Here we show that the amplitude of the average velocity vector of 'high velocity' O vi (O5+) absorption clouds detected in a survey of ultraviolet emission from active galactic nuclei decreases significantly when the vector is transformed to the frames of the Galactic Standard of Rest and the Local Group of galaxies. At least 82 per cent of these absorbers are not associated with any 'high velocity' atomic hydrogen complex in our Galaxy, and are therefore likely to result from a primordial warm-hot intergalactic medium pervading an extended corona around the Milky Way or the Local Group. The total mass of baryons in this medium is estimated to be up to approximately 10(12) solar masses, which is of the order of the mass required to dynamically stabilize the Local Group.

  12. VizieR Online Data Catalog: GEEC2 spectroscopic survey of Galaxy groups (Balogh+, 2014)

    NASA Astrophysics Data System (ADS)

    Balogh, M. L.; McGee, S. L.; Mok, A.; Wilman, D. J.; Finoguenov, A.; Bower, R. G.; Mulchaey, J. S.; Parker, L. C.; Tanaka, M.

    2015-04-01

    GEEC2 is a spectroscopic survey of galaxies in 11 groups, one of which was serendipitously discovered in the background of the target, within the COSMOS field. The spectroscopy was obtained with GMOS-South over two semesters (2010A and 2011A). The original goal of the survey was to observe ~20 groups, with 3-4 spectroscopic masks each, to allow an investigation of the intrinsic scatter within group populations. However, repeated attempts to complete the programme have been thwarted by bad weather, scheduling conflicts at Gemini, and variance in ranking from semester to semester. Following the lack of any time awarded in 2012B, attempts to extend the sample have been abandoned for the moment. Details of the target selection and spectroscopic observations have been presented in Papers I-III. (4 data files).

  13. The Star Formation History of the Local Group Dwarf Elliptical Galaxy NGC 185. I. Stellar Content

    NASA Astrophysics Data System (ADS)

    Martínez-Delgado, D.; Aparicio, A.

    1998-04-01

    We present VI CCD photometry of ~16,000 stars in a 7.2‧ x 7.2‧ field of the Local Group dwarf elliptical galaxy NGC 185. The resulting VI color-magnitude diagram reveals a dominant red giant branch population, an important number of luminous red stars located above the tip of the red giant branch, and a number of blue and yellow stars. Besides the nucleus, our field also covers a large, less crowded area of the galaxy. We show color-magnitude diagrams at six different distances from the nucleus. The red giant branch becomes substantially narrower at larger distances from the nucleus, while the photometry gets deeper. In this paper, we concentrate on investigating the contribution of the observational effects (mainly crowding) to this observed gradient. Although we cannot rule out here the possibility that this trend partially originates in a gradient of the characteristics of the stellar populations of the galaxy with radius, we show that a strong radial gradient exists in the observational effects that can mimic a gradient in the real properties (e.g., age, metallicity) of the stellar population. A distance modulus of m - M = 23.95 +/- 0.10 has been obtained from the tip of the red giant branch, in good agreement with previous estimates. The average stellar metallicity is estimated to be [Fe/H] = -1.43 +/- 0.15, and decreases for increasing galactocentric distance. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  14. Galaxy evolution in nearby loose groups - II. Photometric and kinematic characterization of USGC U268 and USGC U376 group members in the Leo cloud

    NASA Astrophysics Data System (ADS)

    Marino, A.; Plana, H.; Rampazzo, R.; Bianchi, L.; Rosado, M.; Bettoni, D.; Galletta, G.; Mazzei, P.; Buson, L.; Ambrocio-Cruz, P.; Gabbasov, R. F.

    2013-01-01

    This paper is the second of a series of papers in which we are exploring the coevolution of galaxies and groups in the local Universe, by adopting a multiwavelength approach. Here, we present the photometric and kinematic characterization of two groups, USGC U268 and USGC U376 (U268 and U376 hereafter), which are located in different regions of the Leo cloud. We revisit the group membership, using results from recent redshift surveys, and we investigate their substructures. U268, which is composed of 10 catalogued members and 11 new added members, has a small fraction (≈24 per cent) of early-type galaxies (ETGs). U376 has 16 catalogued members plus eight new added members, with ≈38 per cent of ETGs. We find that there are significant substructures in both groups, which suggests that they are likely to be accreting galaxies. U268 is located in a more loose environment than U376. For each member galaxy, broad-band integrated and surface photometry have been obtained in far-ultraviolet (FUV) and near-ultraviolet (NUV) with the Galaxy Evolution Explorer (GALEX), and in the u, g, r, i and z (Sloan Digital Sky Survey) bands. Hα imaging and two-dimensional high-resolution kinematical data have been obtained using the scanning Fabry-Pérot interferometer (PUMA) at the 2.12-m telescope at San Pedro Mártir (Baja California, Mexico). We have improved the galaxy classification and we have detected morphological and kinematical distortions that might be connected either to ongoing and/or past interaction/accretion events or to environmental-induced secular evolution. U268 appears to be more active than U376, with a large fraction of galaxies showing interaction signatures (60 per cent versus 13 per cent). The presence of bars among late-type galaxies is ≈10 per cent in U268 and ≈29 per cent in U376. The cumulative distribution of the FUV-NUV colours of galaxies in U268 is significantly different from that in U376, with galaxies in U268 being bluer than those in U376

  15. A Dynamically Driven, Universal Thermal Profile of Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Reiss, Ido; Keshet, Uri

    2015-09-01

    Large scale structures such as groups and clusters of galaxies show a universal, nearly linear entropy radial profile K(r). Using deprojected 16 clusters and 12 groups from the literature, we find that K\\propto {r}0.96+/- 0.01, consistent with the mean power-law index (0.9–1.1) of previous studies. A similarly good fit is given by a τ \\propto {r}0.72+/- 0.01 ratio between cooling and free-fall times. Both profiles slightly flatten at small radii, as τ becomes of order unity. The entropy profile is usually attributed to self-similar shock accretion (shown to be inconsistent with the data), to non-standard heat conduction, or to turbulent heating. We argue that a dynamical mechanism is needed to sustain such a universal profile, oblivious to the temperature peak at the edge of the core and to the virial shock at the outskirts, and robust to the presence of ongoing cooling, merger, and active galactic nucleus activity. In particular, we show that such a profile can be naturally obtained in a spiral flow, which is likely to underlie most galaxy aggregates according to the ubiquitous spiral patterns and cold fronts observed. Generalizing a two-phase spiral flow model out to the virial radius surprisingly reproduces the thermal profile. A generalized Schwarzschild criterion indicates that observed spiral patterns must involve a convective layer, which may regulate the thermal profile.

  16. Stellar Content and Recent Star Formation History of the Local Group Dwarf Irregular Galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Bernard, Edouard J.; Aparicio, Antonio; Gallart, Carme; Padilla-Torres, Carmen P.; Panniello, Maurizio

    2007-09-01

    We present resolved-star VI photometry of the Local Group dwarf irregular galaxy IC 1613 reaching I ~ 23.5, obtained with the wide-field camera at the 2.5 m Isaac Newton Telescope. A fit to the stellar density distribution shows an exponential profile of scale length 2.9' ± 0.1' and gives a central surface brightness μV,0 = 22.7 ± 0.6. The significant number of red giant branch (RGB) stars present in the outer part of our images (r > 16.5') indicates that the galaxy is actually more extended than previously estimated. A comparison of the color-magnitude diagrams (CMDs) as a function of galactocentric distance shows a clear gradient in the age of its population, the scale length increasing with age, while we find no evidence of a metallicity gradient from the width of the RGB. We present quantitative results of the recent star formation history from a synthetic CMD analysis using IAC-STAR. We find a mean star formation rate of (1.6 ± 0.8) × 10-3 Modot yr-1 kpc-2 in the central r lesssim 2.5' for the last 300 Myr. Based on observations made with the Isaac Newton Telescope, operated on the island of La Palma by the Isaac Newton Group, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

  17. Galaxy evolution through resolved stellar populations in the nearby Centaurus A group .

    NASA Astrophysics Data System (ADS)

    Crnojević, D.; Grebel, E. K.; Ferguson, A. M. N.; Koch, A.; Rejkuba, M.; Da Costa, G.; Jerjen, H.; Irwin, M. J.; Bernard, E. J.; Arimoto, N.; Jablonka, P.; Kobayashi, C.

    The CenA group is a nearby dense complex (˜4 Mpc) dominated by an active elliptical galaxy, hosting more than 60 dwarf companions with a variety of morphological types and stellar contents. We study the resolved stellar populations of a sample of dwarfs using optical and near-infrared data from ACS/HST and ISAAC/VLT. We characterize their recent star formation histories and metallicity content, and compare them to what is known for Local Group dwarfs, underlining similarities and differences. Our results probe the fu ndamental interplay between nature and nurture in the evolution of dwarfs in such a dense environment. We further present the results of the first deep survey of resolved stellar populations in the remote outer halo of our nearest giant elliptical, CenA (VIMOS/VLT optical data). Tracing its halo structure (radial profile, extent and metallicity) out to a remarkable ˜85 kpc and comparing the halo stellar populations to those of CenA's dwarf companions enables us to constrain the mechanisms that contributed to the build-up of CenA in the context of cosmological galaxy formation models.

  18. AGN Feedback in Galaxy Groups: The Two Interesting Cases of AWM 4 and NGC 5044

    NASA Astrophysics Data System (ADS)

    Gastaldello, Fabio; Buote, David A.; Brighenti, Fabrizio; Mathews, William G.; Temi, Pasquale; Ettori, Stefano

    2009-12-01

    We present AGN feedback in the interesting cases of two groups: AWM 4 and NGC 5044. AWM 4 is characterized by a combination of properties which seems to defy the paradigm for AGN heating in cluster cores: a flat inner temperature profile indicative of a past, major heating episode which completely erased the cool core, as testified by the high central cooling time (>3 Gyrs) and by the high central entropy level (~50 keV cm2), and yet an active central radio galaxy with extended radio lobes out to 100 kpc, revealing recent feeding of the central massive black hole. A recent Chandra observation has revealed the presence of a compact cool corona associated with the BCG, solving the puzzle of the apparent lack of low entropy gas surrounding a bright radio source, but opening the question of its origin. NGC 5044 shows in the inner 10 kpc a pair of cavities together with a set of bright filaments. The cavities are consistent with a recent AGN outburst as also indicated by the extent of dust and Hα emission even though the absence of extended 1.4 GHz emission remains to be explained. The soft X-ray filaments coincident with Hα and dust emission are cooler than those which do not correlate with optical and infrared emission, suggesting that dust-aided cooling can contribute to the overall cooling. For the first time sloshing cold fronts at the scale of a galaxy group have been observed in this object.

  19. Chemo-dynamical evolution of the Local Group dwarf galaxies: The origin of r-process elements

    NASA Astrophysics Data System (ADS)

    Hirai, Y.; Ishimaru, Y.; Saitoh, T. R.; Fujii, M. S.; Hidaka, J.; Kajino, T.

    2016-06-01

    The r-process elements such as Au, Eu, and U are observed in the extremely metal-poor stars in the Milky Way halo and the Local Group dwarf galaxies. However, the origin of r-process elements has not yet been identified. The abundance of r-process elements of stars in the Local Group galaxies provides clues to clarify early evolutionary history of galaxies. It is important to understand the chemical evolution of the Local Group dwarf galaxies which would be building blocks of the Milky Way. In this study, we perform a series of N-body/smoothed particle hydrodynamic simulations of dwarf galaxies. We show that neutron star mergers can reproduce the observation of r-process elements. We find that the effects of gas mixing processes including metals in the star-forming region of a typical scale of giant molecular clouds ¥sim 10-100 pc play significant roles in the early chemical enrichment of dwarf galaxies. We also find that the star formation rate of ˜ 10^{-3} M_{⊙}yr^{-1} in early epoch (<1 Gyr) of galactic halo evolution is necessary for these results. Our results suggest that neutron star mergers are a major site of r-process.

  20. First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group

    NASA Astrophysics Data System (ADS)

    2003-05-01

    First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a

  1. Galaxy And Mass Assembly (GAMA): The absence of stellar mass segregation in galaxy groups and consistent predictions from GALFORM and EAGLE simulations

    NASA Astrophysics Data System (ADS)

    Kafle, P. R.; Robotham, A. S. G.; Lagos, C. del P.; Davies, L. J.; Moffett, A. J.; Driver, S. P.; Andrews, S. K.; Baldry, I. K.; Bland-Hawthorn, J.; Brough, S.; Cortese, L.; Drinkwater, M. J.; Finnegan, R.; Hopkins, A. M.; Loveday, J.

    2016-09-01

    We investigate the contentious issue of the presence, or lack thereof, of satellites mass segregation in galaxy groups using the Galaxy And Mass Assembly (GAMA) survey, the GALFORM semi-analytic and the EAGLE cosmological hydrodynamical simulation catalogues of galaxy groups. We select groups with halo mass 12 ≤ log (Mhalo/h-1M⊙) < 14.5 and redshift z ≤ 0.32 and probe the radial distribution of stellar mass out to twice the group virial radius. All the samples are carefully constructed to be complete in stellar mass at each redshift range and efforts are made to regularise the analysis for all the data. Our study shows negligible mass segregation in galaxy group environments with absolute gradients of ≲ 0.08 dex and also shows a lack of any redshift evolution. Moreover, we find that our results at least for the GAMA data are robust to different halo mass and group centre estimates. Furthermore, the EAGLE data allows us to probe much fainter luminosities (r-band magnitude of 22) as well as investigate the three-dimensional spatial distribution with intrinsic halo properties, beyond what the current observational data can offer. In both cases we find that the fainter EAGLE data show a very mild spatial mass segregation at z ≤ 0.22, which is again not apparent at higher redshift. Interestingly, our results are in contrast to some earlier findings using the Sloan Digital Sky Survey. We investigate the source of the disagreement and suggest that subtle differences between the group finding algorithms could be the root cause.

  2. HST Imaging of the Local Volume Dwarf Galaxies Pisces A and B: Prototypes for Local Group Dwarfs

    NASA Astrophysics Data System (ADS)

    Tollerud, Erik J.; Geha, Marla C.; Grcevich, Jana; Putman, Mary E.; Weisz, Daniel R.; Dolphin, Andrew E.

    2016-08-01

    We present observations of the Pisces A and B galaxies with the Advanced Camera for Surveys on the Hubble Space Telescope. Photometry from these images clearly resolves a red giant branch (RGB) for both objects, demonstrating that they are nearby dwarf galaxies. We describe a Bayesian inferential approach to determining the distance to these galaxies using the magnitude of the tip of the RGB, and then apply this approach to these galaxies. This reveals the distance to these galaxies as {5.64}-0.15+0.13 {{Mpc}} and {8.89}-0.85+0.75 {{Mpc}} for Pisces A and B, respectively, placing both within the Local Volume but not the Local Group (LG). We estimate the star formation histories of these galaxies, which suggests that they have recently undergone an increase in their star formation rates. Together these yield luminosities for Pisces A and B of {M}V=-{11.57}-0.05+0.06 and -12.9 ± 0.2, respectively, and estimated stellar masses of {log}({M}* /{M}⊙ )={7.0}-1.7+0.4 and {7.5}-1.8+0.3. We further show that these galaxies are likely at the boundary between nearby voids and higher-density filamentary structure. This suggests that they are entering a higher-density region from voids, where they would have experienced delayed evolution, consistent with their recent increased star formation rates. If this is indeed the case, they are useful for study as proxies of the galaxies that later evolved into typical LG satellite galaxies.

  3. Hot versus cold: The dichotomy in spherical accretion of cooling flows onto supermassive black holes in elliptical galaxies, galaxy groups, and clusters

    SciTech Connect

    Guo, Fulai; Mathews, William G.

    2014-01-10

    Feedback heating from active galactic nuclei (AGNs) has been commonly invoked to suppress cooling flows predicted in hot gas in elliptical galaxies, galaxy groups, and clusters. Previous studies have focused on if and how AGN feedback heats the gas but have little paid attention to its triggering mechanism. Using spherically symmetric simulations, we investigate how large-scale cooling flows are accreted by central supermassive black holes (SMBHs) in eight well-observed systems and find an interesting dichotomy. In massive clusters, the gas develops a central cooling catastrophe within about the cooling time (typically ∼100-300 Myr), resulting in cold-mode accretion onto SMBHs. However, in our four simulated systems on group and galaxy scales at a low metallicity Z = 0.3 Z {sub ☉}, the gas quickly settles into a long-term state that has a cuspy central temperature profile extending to several tens to about 100 pc. At the more realistic solar metallicity, two groups (with R {sub e} ∼ 4 kpc) still host the long-term, hot-mode accretion. Both accretion modes naturally appear in our idealized calculations where only cooling, gas inflow, and compressional heating are considered. The long-term, hot-mode accretion is maintained by the quickly established closeness between the timescales of these processes, preferably in systems with low gas densities, low gas metallicities, and importantly, compact central galaxies, which result in strong gravitational acceleration and compressional heating at the intermediate radii. Our calculations predict that central cuspy temperature profiles appear more often in smaller systems than galaxy clusters, which instead often host significant cold gas and star formation.

  4. Weak Lensing Calibrated M-T Scaling Relation of Galaxy Groups in the COSMOS Fieldsstarf

    NASA Astrophysics Data System (ADS)

    Kettula, K.; Finoguenov, A.; Massey, R.; Rhodes, J.; Hoekstra, H.; Taylor, J. E.; Spinelli, P. F.; Tanaka, M.; Ilbert, O.; Capak, P.; McCracken, H. J.; Koekemoer, A.

    2013-11-01

    The scaling between X-ray observables and mass for galaxy clusters and groups is instrumental for cluster-based cosmology and an important probe for the thermodynamics of the intracluster gas. We calibrate a scaling relation between the weak lensing mass and X-ray spectroscopic temperature for 10 galaxy groups in the COSMOS field, combined with 55 higher-mass clusters from the literature. The COSMOS data includes Hubble Space Telescope imaging and redshift measurements of 46 source galaxies per arcminute2, enabling us to perform unique weak lensing measurements of low-mass systems. Our sample extends the mass range of the lensing calibrated M-T relation an order of magnitude lower than any previous study, resulting in a power-law slope of 1.48^{+0.13}_{-0.09}. The slope is consistent with the self-similar model, predictions from simulations, and observations of clusters. However, X-ray observations relying on mass measurements derived under the assumption of hydrostatic equilibrium have indicated that masses at group scales are lower than expected. Both simulations and observations suggest that hydrostatic mass measurements can be biased low. Our external weak lensing masses provide the first observational support for hydrostatic mass bias at group level, showing an increasing bias with decreasing temperature and reaching a level of 30%-50% at 1 keV. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc., under NASA contract NAS 5-26555. Also based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA; the European Southern Observatory under Large Program 175.A-0839, Chile; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which

  5. WISE Discovery of Hyper Luminous Galaxies at z=2-4 and Their Implications for Galaxy and AGN Evolution

    NASA Technical Reports Server (NTRS)

    Tsai, Chao Wei; Eisenhardt, Peter; Wu, Jingwen; Bridge, Carrie; Assef, Roberto; Benford, Dominic; Blain, Andrew; Cutri, Roc; Griffith, Robert L.; Jarrett, Thomas; Lonsdale, Carol; Petty, Sara; Sayers, Jack; Stanford, Adam; Stern, Daniel; Wright, Edward L.; Yan, Lin

    2014-01-01

    On behalf of the WISE Science team, we present the discovery of a class of distant dust-enshrouded galaxies with extremely high luminosity. These galaxies are selected to have extreme red colors in the mid-IR using NASA's Wide-field Infrared Survey Explorer (WISE). They are faint in the optical and near-IR, predominantly at zeta = 2-4, and with IR luminosity > 10(exp 13) Solar Luminosity, making them Hyper-Luminous Infrared Galaxies (HyLIRGs). SEDs incorporating the WISE, Spitzer, and Herschel PACS and SPIRE photometry indicate hot dust dominates the bolometric luminosity, presumably powered by AGN. Preliminary multi-wavelength follow-up suggests that they are different from normal populations in the local M-sigma relation. Their low source density implies that these objects are either intrinsically rare, or a short-lived phase in a more numerous population. If the latter is the case, these hot, dust-enshrouded galaxies may be an early stage in the interplay between AGN and galaxies.

  6. X-ray emission from clusters and groups of galaxies

    PubMed Central

    Mushotzky, Richard

    1998-01-01

    Recent major advances in x-ray imaging and spectroscopy of clusters have allowed the determination of their mass and mass profile out to ≈1/2 the virial radius. In rich clusters, most of the baryonic mass is in the gas phase, and the ratio of mass in gas/stars varies by a factor of 2–4. The baryonic fractions vary by a factor of ≈3 from cluster to cluster and almost always exceed 0.09 h50−[3/2] and thus are in fundamental conflict with the assumption of Ω = 1 and the results of big bang nucleosynthesis. The derived Fe abundances are 0.2–0.45 solar, and the abundances of O and Si for low redshift systems are 0.6–1.0 solar. This distribution is consistent with an origin in pure type II supernova. The amount of light and energy produced by these supernovae is very large, indicating their importance in influencing the formation of clusters and galaxies. The lack of evolution of Fe to a redshift of z ≈ 0.4 argues for very early enrichment of the cluster gas. Groups show a wide range of abundances, 0.1–0.5 solar. The results of an x-ray survey indicate that the contribution of groups to the mass density of the universe is likely to be larger than 0.1 h50−2. Many of the very poor groups have large x-ray halos and are filled with small galaxies whose velocity dispersion is a good match to the x-ray temperatures. PMID:9419327

  7. Properties of Galaxy Groups Selected from Chandra X-ray Observations of the Boötes Field

    NASA Astrophysics Data System (ADS)

    Vajgel, B.; Lopes, P. A. A.; Jones, C.; Forman, W. R.; Murray, S. S.

    2014-10-01

    Galaxy groups are not simply scaled down versions of rich clusters (e.g. Mulchaey 2000, Voit 2005). Due to a group's shallow gravitational potential, feedback processes play an important role in the group's evolution. It is important to understand galaxy groups since, in hierarchical clustering, they are the building blocks of large scale structure. Thus, in addition to determining the characteristics of groups, it is important to determine the mass function over the range that includes poor clusters and groups. We present the properties of the galaxy groups selected in the Chandra X-Boötes survey (Kenter et al. 2005). Group redshifts are measured from the AGES (Kochanek et al. 2012) spectroscopic data. We use photometric data from the NOAO Deep Wide Field Survey (NDWFS) (Jannuzi & Dey 1999) to estimate the group richness (N_{gals}) and the optical luminosity (L_{opt}). Our final sample comprises 32 systems at z < 0.80, with 14 below z = 0.35. For these systems we estimate velocity dispersions (σ_{gr}) and perform a virial analysis to obtain the radius (R_{200} and R_{500}) and mass (M_{200} and M_{500}) for groups with at least five galaxy members. We use the Chandra X-ray observations to derive the X-ray luminosity (L_{X}). We examine the performance of the group properties σ_{gr}, L_{opt} and L_{X}, as proxies for the group mass. Understanding how these observables measure the total mass is important to estimate how well the cluster/group mass function is determined. By extending the mass function to the group regime, we predict the number of groups that new X-ray surveys, eROSITA, will detect.

  8. Galaxies in x-ray selected clusters and groups in Dark Energy Survey data. I. Stellar mass growth of bright central galaxies since z ~ 1.2

    DOE PAGES

    Zhang, Y.; Miller, C.; McKay, T.; Rooney, P.; Evrard, A. E.; Romer, A. K.; R. Perfecto; Song, J.; Desai, S.; Mohr, J.; et al

    2016-01-14

    Here, using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z ~ 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift.

  9. From Individuals to Groups and Back: The Evolutionary Implications of Group Phenotypic Composition

    PubMed Central

    Farine, Damien R.; Montiglio, Pierre-Olivier; Spiegel, Orr

    2015-01-01

    There is increasing interest in understanding the processes that maintain phenotypic variation in groups, populations, or communities. Recent studies have investigated how the phenotypic composition of groups or aggregations (e.g., its average phenotype or phenotypic variance) affects ecological and social processes, and how multi-level selection can drive phenotypic covariance among interacting individuals. However, we argue that these questions are rarely studied together. We present a unified framework to address this gap, and discuss how group phenotypic composition (GPC) can impact on processes ranging from individual fitness to population demography. By emphasising the breadth of topics affected, we hope to motivate more integrated empirical studies of the ecological and evolutionary implications of GPC. PMID:26411618

  10. MODELING OF THE HERMES SUBMILLIMETER SOURCE LENSED BY A DARK MATTER DOMINATED FOREGROUND GROUP OF GALAXIES

    SciTech Connect

    Gavazzi, R.; Cooray, A.; Conley, A.; Aguirre, J. E.; Amblard, A.; Auld, R.; Beelen, A.; Blain, A.; Bock, J.; Bradford, C. M.; Bridge, C.; Djorgovski, S. G.; Blundell, R.; Brisbin, D.; Burgarella, D.; Chanial, P.; Christopher, N.; Clements, D. L.; Cox, P.

    2011-09-10

    We present the results of a gravitational lensing analysis of the bright z{sub s} = 2.957 submillimeter galaxy (SMG) HERMES found in the Herschel/SPIRE science demonstration phase data from the Herschel Multi-tiered Extragalactic Survey (HerMES) project. The high-resolution imaging available in optical and near-IR channels, along with CO emission obtained with the Plateau de Bure Interferometer, allows us to precisely estimate the intrinsic source extension and hence estimate the total lensing magnification to be {mu} = 10.9 {+-} 0.7. We measure the half-light radius R{sub eff} of the source in the rest-frame near-UV and V bands that characterize the unobscured light coming from stars and find R{sub eff,*} = [2.0 {+-} 0.1] kpc, in good agreement with recent studies on the SMG population. This lens model is also used to estimate the size of the gas distribution (R{sub eff,gas} = [1.1 {+-} 0.5] kpc) by mapping back in the source plane the CO (J = 5 {yields} 4) transition line emission. The lens modeling yields a relatively large Einstein radius R{sub Ein} = 4.''10 {+-} 0.''02, corresponding to a deflector velocity dispersion of [483 {+-} 16] km s{sup -1}. This shows that HERMES is lensed by a galaxy group-size dark matter halo at redshift z{sub l} {approx} 0.6. The projected dark matter contribution largely dominates the mass budget within the Einstein radius with f{sub dm}(< R{sub Ein}) {approx} 80%. This fraction reduces to f{sub dm}(< R{sub eff,G1} {approx_equal} 4.5 kpc) {approx} 47% within the effective radius of the main deflecting galaxy of stellar mass M{sub *,G1} = [8.5 {+-} 1.6] x 10{sup 11} M{sub sun}. At this smaller scale the dark matter fraction is consistent with results already found for massive lensing ellipticals at z {approx} 0.2 from the Sloan Lens ACS Survey.

  11. Chandra Observations of the Galaxy Group AWM 5: Cool Core Reheating and Thermal Conduction Suppression

    NASA Astrophysics Data System (ADS)

    Baldi, A.; Forman, W.; Jones, C.; Nulsen, P.; David, L.; Kraft, R.; Simionescu, A.

    2009-03-01

    We present an analysis of a 40 ks Chandra observation of the galaxy group AWM 5. It has a small (~8 kpc) dense cool core with a temperature of ~1.2 keV and the temperature profile decreases at larger radii, from ~3.5 keV just outside the core to ~2 keV at ~300 kpc from the center. The abundance distribution shows a "hole" in the central ~10 kpc, where the temperature declines sharply. An abundance of at least a few times solar is observed ~15-20 kpc from the center. The deprojected electron density profile shows a break in slope at ~13 kpc and can be fit by two β models, with β = 0.72+0.16 -0.11 and rc = 5.7+1.8 -1.5 kpc, for the inner part, and β = 0.34 ± 0.01 and rc = 31.3+5.8 -5.5 kpc, for the outer part. The mass fraction of hot gas is fairly flat in the center and increases for r > 30 kpc up to a maximum of ~6.5% at r ~ 380 kpc. The gas cooling time within the central 30 kpc is smaller than a Hubble time, although the temperature only declines in the central ~8 kpc region. This discrepancy suggests that an existing cooling core has been partially reheated. In particular, thermal conduction could have been a significant source of reheating. In order for heating due to conduction to balance cooling due to emission of X-rays, conductivity must be suppressed by a large factor (at least ~100). Past active galactic nuclei activity (still visible as a radio source in the center of the group) is, however, the most likely source that reheated the central regions of AWM 5. We also studied the properties of the ram pressure stripped tail in the group member NGC 6265. This galaxy is moving at M ≈ 3.4+0.5 -0.6 (v ~ 2300 km s-1) through the hot group gas. The physical length of the tail is ~42 kpc and its mass is 2.1 ± 0.2 × 109 M sun.

  12. Evolved stars in the Local Group galaxies - I. AGB evolution and dust production in IC 1613

    NASA Astrophysics Data System (ADS)

    Dell'Agli, F.; Di Criscienzo, M.; Boyer, M. L.; García-Hernández, D. A.

    2016-08-01

    We used models of thermally pulsing asymptotic giant branch (AGB) stars, which also describe the dust-formation process in the wind, to interpret the combination of near- and mid-infrared photometric data of the dwarf galaxy IC 1613. This is the first time that this approach is extended to an environment different from the Milky Way and the Magellanic Clouds (MCs). Our analysis, based on synthetic population techniques, shows nice agreement between the observations and the expected distribution of stars in the colour-magnitude diagrams obtained with JHK and Spitzer bands. This allows a characterization of the individual stars in the AGB sample in terms of mass, chemical composition and formation epoch of the progenitors. We identify the stars exhibiting the largest degree of obscuration as carbon stars evolving through the final AGB phases, descending from 1-1.25 M⊙ objects of metallicity Z = 10-3 and from 1.5-2.5 M⊙ stars with Z = 2 × 10-3. Oxygen-rich stars constitute the majority of the sample (˜65 per cent), mainly low-mass stars (<2 M⊙) that produce a negligible amount of dust (≤10-7 M⊙ yr-1). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be ˜6 × 10-7 M⊙ yr-1 with an uncertainty of 30 per cent. The capability of the current generation of models to interpret the AGB population in an environment different from the MCs opens the possibility to extend this kind of analysis to other Local Group galaxies.

  13. The Local Group Galaxy IC 1613 and its asymptotic giant branch variables

    NASA Astrophysics Data System (ADS)

    Menzies, John W.; Whitelock, Patricia A.; Feast, Michael W.

    2015-09-01

    JHKS photometry is presented from a 3-yr survey of the central regions of the Local Group dwarf irregular galaxy IC 1613. The morphologies of the colour-magnitude and colour-colour diagrams are discussed with particular reference to the supergiants and M- and C-type asymptotic giant branch (AGB) stars. Mean JHKS magnitudes, amplitudes and periods are given for five O-rich and nine C-rich Mira variables for which bolometric magnitudes are also estimated. A distance of 750 kpc ((m - M)0 = 24.37 ± 0.08 mag) is derived for IC 1613 by fitting a period-luminosity (PL) relation to the C-rich Miras. This is in agreement with values from the literature. The AGB stars exhibit a range of ages. A comparison with theoretical isochrones suggests that four luminous O-rich Miras are as young as 2 × 108 yr. One of these has a lithium absorption line in its spectrum, demonstrating that it is undergoing hot bottom burning (HBB). This supports the idea that HBB is the cause of the high luminosity of these AGB stars, which puts them above the fundamental PL relation. Further studies of similar stars, selected from their positions in the PL diagram, could provide insight into HBB. A much fainter, presumed O-rich, Mira is similar to those found in Galactic globular clusters. The C Miras are of intermediate age. The O-rich variables are not all recognized as O-rich, or even as AGB stars, on the basis of their J - KS colour. It is important to appreciate this when using near-infrared surveys to classify AGB stars in more distant galaxies.

  14. Physically detached 'compact groups'

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    A small fraction of galaxies appear to reside in dense compact groups, whose inferred crossing times are much shorter than a Hubble time. These short crossing times have led to considerable disagreement among researchers attempting to deduce the dynamical state of these systems. In this paper, we suggest that many of the observed groups are not physically bound but are chance projections of galaxies well separated along the line of sight. Unlike earlier similar proposals, ours does not require that the galaxies in the compact group be members of a more diffuse, but physically bound entity. The probability of physically separated galaxies projecting into an apparent compact group is nonnegligible if most galaxies are distributed in thin filaments. We illustrate this general point with a specific example: a simulation of a cold dark matter universe, in which hydrodynamic effects are included to identify galaxies. The simulated galaxy distribution is filamentary and end-on views of these filaments produce apparent galaxy associations that have sizes and velocity dispersions similar to those of observed compact groups. The frequency of such projections is sufficient, in principle, to explain the observed space density of groups in the Hickson catalog. We discuss the implications of our proposal for the formation and evolution of groups and elliptical galaxies. The proposal can be tested by using redshift-independent distance estimators to measure the line-of-sight spatial extent of nearby compact groups.

  15. Spectroscopic Confirmation of the Dwarf Spheroidal Galaxy d0994+71 as a Member of the M81 Group of Galaxies

    NASA Astrophysics Data System (ADS)

    Toloba, Elisa; Sand, David; Guhathakurta, Puragra; Chiboucas, Kristin; Crnojević, Denija; Simon, Joshua D.

    2016-10-01

    We use Keck/DEIMOS spectroscopy to measure the first velocity and metallicity of a dwarf spheroidal (dSph) galaxy beyond the Local Group using resolved stars. Our target, d0944+71, is a faint dSph found in the halo of the massive spiral galaxy M81 by Chiboucas et al. We coadd the spectra of 27 individual stars and measure a heliocentric radial velocity of ‑38 ± 10 km s‑1. This velocity is consistent with d0944+71 being gravitationally bound to M81. We coadd the spectra of the 23 stars that are consistent with being red giant branch stars and measure an overall metallicity of [Fe/H] = ‑1.3 ± 0.3 based on the calcium triplet lines. This metallicity is consistent with d0944+71 following the metallicity‑luminosity relation for Local Group dSphs. We investigate several potential sources of observational bias but find that our sample of targeted stars is representative of the metallicity distribution function of d0944+71 and any stellar contamination due to seeing effects is negligible. The low ellipticity of the galaxy and its position in the metallicity‑luminosity relation suggest that d0944+71 has not been affected by strong tidal stripping.

  16. Stellar Populations in Compact Galaxy Groups: a Multi-wavelength Study of HCGs 16, 22, and 42, Their Star Clusters, and Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Fedotov, K.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Desjardins, T. D.; Gallagher, S. C.; Walker, L. M.; Johnson, K. E.; Tzanavaris, Panayiotis; Gronwall, C.

    2013-01-01

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy.We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 "associates" (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  17. STELLAR POPULATIONS IN COMPACT GALAXY GROUPS: A MULTI-WAVELENGTH STUDY OF HCGs 16, 22, AND 42, THEIR STAR CLUSTERS, AND DWARF GALAXIES

    SciTech Connect

    Konstantopoulos, I. S.; Maybhate, A.; Charlton, J. C.; Gronwall, C.; Fedotov, K.; Desjardins, T. D.; Gallagher, S. C.; Durrell, P. R.; Mulchaey, J. S.; English, J.; Walker, L. M.; Johnson, K. E.; Tzanavaris, P.

    2013-06-20

    We present a multi-wavelength analysis of three compact galaxy groups, Hickson compact groups (HCGs) 16, 22, and 42, which describe a sequence in terms of gas richness, from space- (Swift, Hubble Space Telescope (HST), and Spitzer) and ground-based (Las Campanas Observatory and Cerro Tololo Inter-American Observatory) imaging and spectroscopy. We study various signs of past interactions including a faint, dusty tidal feature about HCG 16A, which we tentatively age-date at <1 Gyr. This represents the possible detection of a tidal feature at the end of its phase of optical observability. Our HST images also resolve what were thought to be double nuclei in HCG 16C and D into multiple, distinct sources, likely to be star clusters. Beyond our phenomenological treatment, we focus primarily on contrasting the stellar populations across these three groups. The star clusters show a remarkable intermediate-age population in HCG 22, and identify the time at which star formation was quenched in HCG 42. We also search for dwarf galaxies at accordant redshifts. The inclusion of 33 members and 27 ''associates'' (possible members) radically changes group dynamical masses, which in turn may affect previous evolutionary classifications. The extended membership paints a picture of relative isolation in HCGs 16 and 22, but shows HCG 42 to be part of a larger structure, following a dichotomy expected from recent studies. We conclude that (1) star cluster populations provide an excellent metric of evolutionary state, as they can age-date the past epochs of star formation; and (2) the extended dwarf galaxy population must be considered in assessing the dynamical state of a compact group.

  18. Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters

    NASA Astrophysics Data System (ADS)

    Kundert, A.; Gastaldello, F.; D'Onghia, E.; Girardi, M.; Aguerri, J. A. L.; Barrena, R.; Corsini, E. M.; De Grandi, S.; Jiménez-Bailón, E.; Lozada-Muñoz, M.; Méndez-Abreu, J.; Sánchez-Janssen, R.; Wilcots, E.; Zarattini, S.

    2015-11-01

    We present the first pointed X-ray observations of 10 candidate fossil galaxy groups and clusters. With these Suzaku observations, we determine global temperatures and bolometric X-ray luminosities of the intracluster medium (ICM) out to r500 for six systems in our sample. The remaining four systems show signs of significant contamination from non-ICM sources. For the six objects with successfully determined r500 properties, we measure global temperatures in the range 2.8 ≤ TX ≤ 5.3 keV, bolometric X-ray luminosities of 0.8 × 1044 ≤ LX, bol ≤ 7.7 × 1044 erg s-1, and estimate masses, as derived from TX, of M500 ≳ 1014 M⊙. Fossil cluster scaling relations are constructed for a sample that combines our Suzaku observed fossils with fossils in the literature. Using measurements of global X-ray luminosity, temperature, optical luminosity, and velocity dispersion, scaling relations for the fossil sample are then compared with a control sample of non-fossil systems. We find the fits of our fossil cluster scaling relations are consistent with the relations for normal groups and clusters, indicating fossil clusters have global ICM X-ray properties similar to those of comparable mass non-fossil systems.

  19. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    SciTech Connect

    Gaspari, M.; Brighenti, F.; Temi, P.

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  20. Cosmic ray electrons, positrons and the synchrotron emission of the Galaxy: consistent analysis and implications

    SciTech Connect

    Bernardo, Giuseppe Di; Evoli, Carmelo; Gaggero, Daniele; Grasso, Dario; Maccione, Luca E-mail: carmelo.evoli@desy.de E-mail: dario.grasso@pi.infn.it

    2013-03-01

    A multichannel analysis of cosmic ray electron and positron spectra and of the diffuse synchrotron emission of the Galaxy is performed by using the DRAGON code. This study is aimed at probing the interstellar electron source spectrum down to E ∼< 1GeV and at constraining several propagation parameters. We find that above 4GeV the e{sup −} source spectrum is compatible with a power-law of index ∼ 2.5. Below 4GeV instead it must be significantly suppressed and the total lepton spectrum is dominated by secondary particles. The positron spectrum and fraction measured below a few GeV are consistently reproduced only within low reacceleration models. We also constrain the scale-height z{sub t} of the cosmic-ray distribution using three independent (and, in two cases, original) arguments, showing that values of z{sub t} ∼< 2kpc are excluded. This result may have strong implications for particle dark matter searches.

  1. The Abundances of the Fe Group Elements in Early B Stars in the Magellanic Clouds and Our Galaxy

    NASA Astrophysics Data System (ADS)

    Peters, Geraldine Joan; Adelman, Saul Joseph

    2015-08-01

    The abundances of the Fe-peak elements (Ti, V, Cr, Mn, Fe, Co, and Ni) are of interest as they are important for assessing opacities for stellar evolution calculations, confirming theoretical calculations of explosive nucleosynthesis, and inferring the past history of supernova activity in a galaxy. FUSE FUV spectra of early B stars in the LMC and SMC and HST/STIS FUV/NUV spectra of nearby B stars in our galaxy are analyzed with the Hubeny/Lanz programs TLUSTY/SYNSPEC to determine abundance for the Fe group elements and produce a map of these abundances in the Magellanic Clouds (MC) and Magellanic Bridge (MB). Except for four weak multiplets of Fe III there are no measurable lines from the Fe group in the optical region. The Fe group species found in the FUV spectra of early B stars are primarily in the second stage of ionization. The best set of lines in the FUSE spectral region are Fe III (UV1), V III 1150 Å, and Cr III 1137 Å. Analysis of the galactic B stars provides a good assessment of the reliability of the atomic parameters that are used for the MC calculations. Twenty-two early B stars in the MC and MB and five in our galaxy were analyzed. In general the Fe group abundances range from solar to slightly below solar in our region of the galaxy. But in the MCs the abundances of V, Cr, and Fe tend to be significantly lower than the mean metal abundances for the galaxy. Maps of the Fe group abundances and their variations in the LMC and SMC, tracers of recent enrichment of the ISM from supernova activity, are shown. Support from NASA grants NAG5-13212, NNX10AD66G, STScI HST-GO-13346.22, and USC’s Women in Science and Engineering (WiSE) program is greatly appreciated.

  2. Observations of Environmental Quenching in Groups in the 11 GYR Since z = 2.5: Different Quenching For Central and Satellite Galaxies

    NASA Technical Reports Server (NTRS)

    Tal, Tomer; Dekel, Avishai; Marchesini, Danilo; Momcheva, Ivelina; Nelson, Erica J.; Patel, Shannon G.; Quadri, Ryan F.; Rix, Hans-Walter; Skelton, Rosalind E.; Wake, David A.; Whitaker, Katherine E.; Oesch, Pascal; Muzzin, Adam; Brammer, Gabriel B.; vanDokkum, Peter G.; Franx, Marijn; Illingworth, Garth D.; Leja, Joel; Magee, Daniel

    2014-01-01

    We present direct observational evidence for star formation quenching in galaxy groups in the redshift range 0 less than z less than 2.5. We utilize a large sample of nearly 6000 groups, selected by fixed cumulative number density from three photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over roughly 11 Gyr. At z approximately 0, central galaxies in our sample range in stellar mass from Milky Way/M31 analogs (M=6.5x10(exp 10) M/solar mass) to nearby massive ellipticals (M=1.5x10(exp 11) M/solar mass). Satellite galaxies in the same groups reach masses as low as twice that of the Large Magellanic Cloud (M=6.5x10(exp 9) M/solar mass). Using statistical background subtraction, we measure the average rest-frame colors of galaxies in our groups and calculate the evolving quiescent fractions of centrals and satellites over seven redshift bins. Our analysis shows clear evidence for star formation quenching in group halos, with a different quenching onset for centrals and their satellite galaxies. Using halo mass estimates for our central galaxies, we find that star formation shuts off in centrals when typical halo masses reach between 10(exp 12) and 10(exp 13) M/solar mass, consistent with predictions from the halo quenching model. In contrast, satellite galaxies in the same groups most likely undergo quenching by environmental processes, whose onset is delayed with respect to their central galaxy. Although star formation is suppressed in all galaxies over time, the processes that govern quenching are different for centrals and satellites. While mass plays an important role in determining the star formation activity of central galaxies, quenching in satellite galaxies is dominated by the environment in which they reside.

  3. Observations of environmental quenching in groups in the 11 Gyr since z = 2.5: Different quenching for central and satellite galaxies

    SciTech Connect

    Tal, Tomer; Illingworth, Garth D.; Magee, Daniel; Oesch, Pascal; Van Dokkum, Pieter G.; Leja, Joel; Momcheva, Ivelina; Nelson, Erica J.; Muzzin, Adam; Franx, Marijn; Brammer, Gabriel B.; Marchesini, Danilo; Patel, Shannon G.; Quadri, Ryan F.; Rix, Hans-Walter; Skelton, Rosalind E.; Wake, David A.; Whitaker, Katherine E.

    2014-07-10

    We present direct observational evidence for star formation quenching in galaxy groups in the redshift range 0 < z < 2.5. We utilize a large sample of nearly 6000 groups, selected by fixed cumulative number density from three photometric catalogs, to follow the evolving quiescent fractions of central and satellite galaxies over roughly 11 Gyr. At z ∼ 0, central galaxies in our sample range in stellar mass from Milky Way/M31 analogs (M{sub *}/M{sub ☉} = 6.5 × 10{sup 10}) to nearby massive ellipticals (M{sub *}/M{sub ☉} = 1.5 × 10{sup 11}). Satellite galaxies in the same groups reach masses as low as twice that of the Large Magellanic Cloud (M{sub *}/M{sub ☉} = 6.5 × 10{sup 9}). Using statistical background subtraction, we measure the average rest-frame colors of galaxies in our groups and calculate the evolving quiescent fractions of centrals and satellites over seven redshift bins. Our analysis shows clear evidence for star formation quenching in group halos, with a different quenching onset for centrals and their satellite galaxies. Using halo mass estimates for our central galaxies, we find that star formation shuts off in centrals when typical halo masses reach between 10{sup 12} and 10{sup 13} M{sub ☉}, consistent with predictions from the halo quenching model. In contrast, satellite galaxies in the same groups most likely undergo quenching by environmental processes, whose onset is delayed with respect to their central galaxy. Although star formation is suppressed in all galaxies over time, the processes that govern quenching are different for centrals and satellites. While mass plays an important role in determining the star formation activity of central galaxies, quenching in satellite galaxies is dominated by the environment in which they reside.

  4. Studying the evolution of galaxies in compact groups over the past 3 Gyr - II. The importance of environment in the suppression of star formation

    NASA Astrophysics Data System (ADS)

    Bitsakis, T.; Dultzin, D.; Ciesla, L.; Díaz-Santos, T.; Appleton, P. N.; Charmandaris, V.; Krongold, Y.; Guillard, P.; Alatalo, K.; Zezas, A.; González, J.; Lanz, L.

    2016-06-01

    We present an in depth study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multiwavelength sample to-date, comprised 1770 groups (containing 7417 galaxies), in the redshift range of 0.01 < z < 0.23. To derive the physical properties of the galaxies, we rely on ultraviolet (UV)-to-infrared spectral energy distribution modelling, using CIGALE. Our results suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3 to 10 times). Moreover, their star formation histories as well as their UV-optical and mid-infrared colours are significantly different from those of field and cluster galaxies, indicating that compact group galaxies spend more time transitioning through the green valley. The morphological transformation from late-type spirals to early-type galaxies occurs in the mid-infrared transition zone rather than in the UV-optical green valley. We find evidence of shocks in the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence. Our results suggest that in addition to gas stripping, turbulence and shocks might play an important role in suppressing the star formation in compact group galaxies.

  5. Chemical history of isolated dwarf galaxies of the Local Group - I. dSphs: Cetus and Tucana

    NASA Astrophysics Data System (ADS)

    Avila-Vergara, N.; Carigi, L.; Hidalgo, S. L.; Durazo, R.

    2016-04-01

    For the first time, we obtain chemical evolution models (CEMs) for Tucana and Cetus, two isolated dwarf spheroidal galaxies of the Local Group. The CEMs have been built from the star formation histories (SFHs) and the metallicity histories, both obtained independently by the Local Cosmology from Isolated Dwarfs (LCID) project from deep colour-magnitude diagrams. Based on our models, we find that the chemical histories were complex and can be divided into different epochs and scenarios. In particular, during 75 per cent of the SFH, the galaxies behaved as closed boxes and, during the remaining 25 per cent, either received a lot of primordial gas by accretion or they lost metals through metal-rich winds. In order to discriminate between these two scenarios, abundances ratios in old stars are needed. At t ˜ 4.5 Gyr, the galaxies lost most of their gas due to a short-strong, well-mixed wind. We obtain very similar CEMs for both galaxies, although Cetus is twice as massive as Tucana. We conclude that the star formation in both galaxies began with only 1.5 per cent of the baryonic mass fraction predicted by Λ cold dark matter.

  6. QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES

    SciTech Connect

    Pan, Zhizheng; Lin, Weipeng; Li, Jinrong; Kong, Xu; Wang, Jing E-mail: linwp@shao.ac.cn

    2014-09-01

    In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u – r colors of early-type galaxies (ETGs) are flat out to R {sub 90}, while the colors monotonously turn blue when r > 0.5 R {sub 50} for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV – r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R {sub 90}. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ∼50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable ''blue-cores'' and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.

  7. Quenching Depends on Morphologies: Implications from the Ultraviolet-Optical Radial Color Distributions in Green Valley Galaxies

    NASA Astrophysics Data System (ADS)

    Pan, Zhizheng; Li, Jinrong; Lin, Weipeng; Wang, Jing; Kong, Xu

    2014-09-01

    In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u - r colors of early-type galaxies (ETGs) are flat out to R 90, while the colors monotonously turn blue when r > 0.5 R 50 for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV - r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R 90. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ~50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cores" and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.

  8. The XXL Survey. X. K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Ziparo, F.; Smith, G. P.; Mulroy, S. L.; Lieu, M.; Willis, J. P.; Hudelot, P.; McGee, S. L.; Fotopoulou, S.; Lidman, C.; Lavoie, S.; Pierre, M.; Adami, C.; Chiappetti, L.; Clerc, N.; Giles, P.; Maughan, B.; Pacaud, F.; Sadibekova, T.

    2016-06-01

    Galaxy clusters and groups are important cosmological probes and giant cosmic laboratories for studying galaxy evolution. Much effort has been devoted to understanding how and when baryonic matter cools at the centre of potential wells. However, a clear picture of the efficiency with which baryons are converted into stars is still missing. We present the K-band luminosity-halo mass relation, LK,500-M500,WL, for a subsample of 20 of the 100 brightest clusters in the XXL Survey observed with WIRCam at the Canada-France-Hawaii Telescope (CFHT). For the first time, we have measured this relation via weak-lensing analysis down to M500,WL = 3.5 × 1013 M⊙. This allows us to investigate whether the slope of the LK-M relation is different for groups and clusters, as seen in other works. The clusters in our sample span a wide range in mass, M500,WL = 0.35-12.10 × 1014 M⊙, at 0 < z < 0.6. The K-band luminosity scales as log 10(LK,500/ 1012 L⊙) ∝ βlog 10(M500,WL/ 1014 M⊙) with β = 0.85+0.35-0.27 and an intrinsic scatter of σlnLK|M = 0.37+0.19-0.17. Combining our sample with some clusters in the Local Cluster Substructure Survey (LoCuSS) present in the literature, we obtain a slope of 1.05+0.16-0.14 and an intrinsic scatter of 0.14+0.09-0.07. The flattening in the LK-M seen in previous works is not seen here and might be a result of a bias in the mass measurement due to assumptions on the dynamical state of the systems. We also study the richness-mass relation and find that group-sized halos have more galaxies per unit halo mass than massive clusters. However, the brightest cluster galaxy (BCG) in low-mass systems contributes a greater fraction to the total cluster light than BCGs do in massive clusters; the luminosity gap between the two brightest galaxies is more prominent for group-sized halos. This result is a natural outcome of the hierarchical growth of structures, where massive galaxies form and gain mass within low-mass groups and are ultimately accreted

  9. Populations of High-Luminosity Density-Bounded HII Regions in Spiral Galaxies? Evidence and Implications

    NASA Technical Reports Server (NTRS)

    Beckman, J. E.; Rozas, M.; Zurita, A.; Watson, R. A.; Knapen, J. H.

    2000-01-01

    In this paper we present evidence that the H II regions of high luminosity in disk galaxies may be density bounded, so that a significant fraction of the ionizing photons emitted by their exciting OB stars escape from the regions. The key piece of evidence is the presence, in the Ha luminosity functions (LFs) of the populations of H iI regions, of glitches, local sharp peaks at an apparently invariant luminosity, defined as the Stromgren luminosity Lstr), LH(sub alpha) = Lstr = 10(sup 38.6) (+/- 10(sup 0.1)) erg/ s (no other peaks are found in any of the LFs) accompanying a steepening of slope for LH(sub alpha) greater than Lstr This behavior is readily explicable via a physical model whose basic premises are: (a) the transition at LH(sub alpha) = Lstr marks a change from essentially ionization bounding at low luminosities to density bounding at higher values, (b) for this to occur the law relating stellar mass in massive star-forming clouds to the mass of the placental cloud must be such that the ionizing photon flux produced within the cloud is a function which rises more steeply than the mass of the cloud. Supporting evidence for the hypothesis of this transition is also presented: measurements of the central surface brightnesses of H II regions for LH(sub alpha) less than Lstr are proportional to L(sup 1/3, sub H(sub alpha)), expected for ionization bounding, but show a sharp trend to a steeper dependence for LH(sub alpha) greater than Lstr, and the observed relation between the internal turbulence velocity parameter, sigma, and the luminosity, L, at high luminosities, can be well explained if these regions are density bounded. If confirmed, the density-bounding hypothesis would have a number of interesting implications. It would imply that the density-bounded regions were the main sources of the photons which ionize the diffuse gas in disk galaxies. Our estimates, based on the hypothesis, indicate that these regions emit sufficient Lyman continuum not only to

  10. Intrinsic alignment of simulated galaxies in the cosmic web: implications for weak lensing surveys

    NASA Astrophysics Data System (ADS)

    Codis, S.; Gavazzi, R.; Dubois, Y.; Pichon, C.; Benabed, K.; Desjacques, V.; Pogosyan, D.; Devriendt, J.; Slyz, A.

    2015-04-01

    The intrinsic alignment of galaxy shapes (by means of their angular momentum) and their cross-correlation with the surrounding dark matter tidal field are investigated using the 160 000, z = 1.2 synthetic galaxies extracted from the high-resolution cosmological hydrodynamical simulation HORIZON-AGN. One- and two-point statistics of the spin of the stellar component are measured as a function of mass and colour. For the low-mass galaxies, this spin is locally aligned with the tidal field `filamentary' direction while, for the high-mass galaxies, it is perpendicular to both filaments and walls. The bluest galaxies of our synthetic catalogue are more strongly correlated with the surrounding tidal field than the reddest galaxies, and this correlation extends up to ˜10 h- 1 Mpc comoving distance. We also report a correlation of the projected ellipticities of blue, intermediate-mass galaxies on a similar scale at a level of 10-4 which could be a concern for cosmic shear measurements. We do not report any measurable intrinsic alignments of the reddest galaxies of our sample. This work is a first step towards the use of very realistic catalogue of synthetic galaxies to evaluate the contamination of weak lensing measurement by the intrinsic galactic alignments.

  11. The large scale structure of the Universe revealed with high redshift emission-line galaxies: implications for future surveys

    NASA Astrophysics Data System (ADS)

    Antonino Orsi, Alvaro

    2015-08-01

    Nebular emission in galaxies trace their star-formation activity within the last 10 Myr or so. Hence, these objects are typically found in the outskirts of massive clusters, where otherwise environmental effects can effectively stop the star formation process. In this talk I discuss the nature of emission-line galaxies (ELGs) and its implications for their clustering properties. To account for the relevant physical ingredients that produce nebular emission, I combine semi-analytical models of galaxy formation with a radiative transfer code of Ly-alpha photons, and the photoionzation and shock code MAPPINGS-III. As a result, the clustering strength of ELGs is found to correlate weakly with the line luminosities. Also, their 2-d clustering displays a weak finger-of-god effect, and the clustering in linear scales is affected by assembly bias. I review the impact of the nature of this galaxy population for future spectroscopic large surveys targeting ELGs to extract cosmological results. In particular, I present forecasts for the ELG population in J-PAS, an 8000 deg^2 survey with 54 narrow-band filters covering the optical range, expected to start in 2016.

  12. GAS SLOSHING AND RADIO GALAXY DYNAMICS IN THE CORE OF THE 3C 449 GROUP

    SciTech Connect

    Lal, Dharam V.; Kraft, Ralph P.; Randall, Scott W.; Forman, William R.; Nulsen, Paul E. J.; Jones, Christine; Roediger, Elke; ZuHone, John A.; Hardcastle, Martin J.; Croston, Judith H.

    2013-02-10

    We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a 'sloshing' cold front due to a merger within the last {approx}<1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge. We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.

  13. Gas Sloshing and Radio Galaxy Dynamics in the Core of the 3C 449 Group

    NASA Technical Reports Server (NTRS)

    Lal, Dharam V.; Kraft, Ralph P.; Randall, Scott W.; Forman, William R.; Nulsen, Paul E.; Roediger, Elke; ZuHone, John A.; Hardcastle, Martin J.; Jones, Christine; Croston, Judith H.

    2013-01-01

    We present results from a 140 ks Chandra/ACIS-S observation of the hot gas around the canonical FR I radio galaxy 3C 449. An earlier, shorter 30 ks Chandra observation of the group gas showed an unusual entropy distribution and a surface brightness edge in the gas that could be a strong shock around the inner radio lobes. In our deeper data we find no evidence for a temperature increase inside of the brightness edge, but a temperature decrease across part of the edge. This suggests that the edge is a "sloshing" cold front due to a merger within the last 1.3-1.6 Gyr. Both the northern and southern inner jets are bent slightly to the west in projection as they enter their respective lobes, suggesting that the sloshing core is moving to the east. The straight inner jet flares at approximately the position where it crosses the contact edge, suggesting that the jet is entraining and thermalizing some of the hot gas as it crosses the edge.We also detect filaments of X-ray emission around the southern inner radio jet and lobe which we attribute to low entropy entrained gas. The lobe flaring and gas entrainment were originally predicted in simulations of Loken et al. and are confirmed in our deep observation.

  14. The Araucaria Project: The Distance to the Sculptor Group Galaxy NGC 55 from a Newly Discovered Abundant Cepheid Population

    NASA Astrophysics Data System (ADS)

    Pietrzyński, Grzegorz; Gieren, Wolfgang; Soszyński, Igor; Udalski, Andrzej; Bresolin, Fabio; Kudritzki, Rolf-Peter; Mennickent, Ronald; Walker, Alistair; Garcia, Alejandro; Szewczyk, Olaf; Szymański, MichaŁ; Kubiak, Marcin; Wyrzykowski, Łukasz

    2006-12-01

    We have detected, for the first time, Cepheid variables in the Sculptor Group SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods ranging from 5.6 to 175.9 days; 133 of these objects have periods longer than 10 days, making NGC 55 to date the galaxy with the largest known number of long-period Cepheids in the Sculptor Group. We construct period-luminosity relations from our data and obtain distance moduli corrected for the small foreground reddening to NGC 55 of 26.79+/-0.04 mag (internal error) in V, 26.66+/-0.03 mag in I, and 26.40+/-0.05 mag in the reddening-independent V-I Wesenheit index. The trend of increasing distance moduli with shorter wavelength hints at the existence of significant reddening intrinsic to NGC 55, which affects the measured Cepheid magnitudes. From our data we determine the intrinsic mean reddening of the Cepheids in NGC 55 as E(B-V)=0.102 mag, which brings the distance determinations from the different bands into excellent agreement. Our best distance estimate for NGC 55 from the present optical Cepheid photometry is 26.40+/-0.05 (internal error) +/-0.09 mag (systematic error). This value is tied to an assumed LMC distance of 18.50 mag. Our quoted systematic error of the present NGC 55 Cepheid distance does not take into account the current uncertainty in the distance of the fiducial LMC galaxy itself. Within the small respective uncertainties, the Sculptor Group galaxies NGC 55 and NGC 300 are at the same distance of 1.9 Mpc, strengthening the case for a physical association of these galaxies. Based on observations obtained with the 1.3 m Warsaw telescope at Las Campanas Observatory, Chile.

  15. Chemical abundances in low surface brightness galaxies: Implications for their evolution

    NASA Technical Reports Server (NTRS)

    Mcgaugh, S. S.; Bothun, G. D.

    1993-01-01

    Low Surface Brightness (LSB) galaxies are an important but often neglected part of the galaxy content of the universe. Their importance stems both from the selection effects which cause them to be under-represented in galaxy catalogs, and from what they can tell us about the physical processes of galaxy evolution that has resulted in something other than the traditional Hubble sequence of spirals. An important constraint for any evolutionary model is the present day chemical abundances of LSB disks. Towards this end, spectra for a sample of 75 H 2 regions distributed in 20 LSB disks galaxies were obtained. Structurally, this sample is defined as having B(0) fainter than 23.0 mag arcsec(sup -2) and scale lengths that cluster either around 3 kpc or 10 kpc. In fact, structurally, these galaxies are very similar to the high surface brightness spirals which define the Hubble sequence. Thus, our sample galaxies are not dwarf galaxies but instead have masses comparable to or in excess of the Milky Way. The basic results from these observations are summarized.

  16. A new window of exploration in the mass spectrum: strong lensing by galaxy groups in the SL2S

    NASA Astrophysics Data System (ADS)

    Limousin, M.; Cabanac, R.; Gavazzi, R.; Kneib, J.-P.; Motta, V.; Richard, J.; Thanjavur, K.; Foex, G.; Pello, R.; Crampton, D.; Faure, C.; Fort, B.; Jullo, E.; Marshall, P.; Mellier, Y.; More, A.; Soucail, G.; Suyu, S.; Swinbank, M.; Sygnet, J.-F.; Tu, H.; Valls-Gabaud, D.; Verdugo, T.; Willis, J.

    2009-08-01

    The existence of strong lensing systems with Einstein radii covering the full mass spectrum, from ˜ 1-2 arcsec (produced by galaxy scale dark matter haloes) to >10 arcsec (produced by galaxy cluster scale haloes) have long been predicted. Many lenses with Einstein radii around 1-2 arcsec and above 10 arcsec have been reported but very few in between. In this article, we present a sample of 13 strong lensing systems with Einstein radii in the range 3 arcsec-8 arcsec (or image separations in the range 6 arcsec-16 arcsec), i.e. systems produced by galaxy group scale dark matter haloes. This group sample spans a redshift range from 0.3 to 0.8. This opens a new window of exploration in the mass spectrum, around 1013-1014 M⊙, a crucial range for understanding the transition between galaxies and galaxy clusters, and a range that have not been extensively probed with lensing techniques. These systems constitute a subsample of the Strong Lensing Legacy Survey (SL2S), which aims to discover strong lensing systems in the Canada France Hawaii Telescope Legacy Survey (CFHTLS). The sample is based on a search over 100 square degrees, implying a number density of ~0.13 groups per square degree. Our analysis is based on multi-colour CFHTLS images complemented with Hubble Space Telescope imaging and ground based spectroscopy. Large scale properties are derived from both the light distribution of elliptical galaxies group members and weak lensing of the faint background galaxy population. On small scales, the strong lensing analysis yields Einstein radii between 2.5 arcsec and 8 arcsec. On larger scales, strong lens centres coincide with peaks of light distribution, suggesting that light traces mass. Most of the luminosity maps have complicated shapes, implying that these intermediate mass structures may be dynamically young. A weak lensing signal is detected for 6 groups and upper limits are provided for 6 others. Fitting the reduced shear with a Singular Isothermal Sphere, we

  17. The Local Group Census: planetary nebulae in the spheroidal galaxies NGC 147, NGC 185 and NGC 205

    NASA Astrophysics Data System (ADS)

    Corradi, R. L. M.; Magrini, L.; Greimel, R.; Irwin, M.; Leisy, P.; Lennon, D. J.; Mampaso, A.; Perinotto, M.; Pollacco, D. L.; Walsh, J. R.; Walton, N. A.; Zijlstra, A. A.

    2005-02-01

    In the framework of our narrow-band survey of Local Group galaxies, we present the results of the search for planetary nebulae (PNe) in three spheroidal companions to the Andromeda galaxy. We find 9 candidate PNe in NGC 147, 5 in NGC 185, and 75 in the ˜0.4 square degree area searched around NGC 205, increasing the number of PNe known in these galaxies. It is shown that in the crowded regions of these galaxies continuum-subtracted images are more effective in detecting PNe than colour-colour diagrams obtained via automatic photometry. For NGC 205, the degree of contamination of PNe belonging to the halo of M 31 is estimated; taking it into account, 35 PNe within 1.5 tidal radii from the centre of NGC 205 have been used to build its PN luminosity function. Candidate PNe in NGC 185 are systematically brighter than those in NGC 147. Considering that star formation is thought to have been much stronger in NGC 185 than in NGC 147 in the last 3 Gyr, this might suggest that the bright end of the PN luminosity function is populated by relatively massive stars, as predicted by some recent theoretical models. This result, however, has to be taken with some caution, given the small PN population size of these galaxies and a rather incomplete knowledge of their star formation history. Based on observations obtained at the 2.5m INT telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias.

  18. The spatial clustering of radio sources in NVSS and FIRST; implications for galaxy clustering evolution

    NASA Astrophysics Data System (ADS)

    Overzier, R. A.; Röttgering, H. J. A.; Rengelink, R. B.; Wilman, R. J.

    2003-07-01

    We have measured the angular correlation function, w(theta ), of radio sources in the 1.4 GHz NVSS and FIRST radio surveys. Below ~ 6arcmin the signal is dominated by the size distribution of classical double radio galaxies, an effect underestimated in some previous studies. We model the physical size distribution of FRII radio galaxies to account for this excess signal in w(theta ). The amplitude of the true cosmological clustering of radio sources is roughly constant at A =~ 1*E-3 for flux limits of 3-40 mJy, but has increased to A =~ 7*E-3 at 200 mJy. This can be explained if powerful (FRII) radio galaxies probe significantly more massive structures compared to radio galaxies of average power at z ~ 1. This is consistent with powerful high-redshift radio galaxies generally having massive (forming) elliptical hosts in rich (proto-)cluster environments. For FRIIs we derive a spatial (comoving) correlation length of r0=14+/-3 h-1 Mpc. This is remarkably close to that measured for extremely red objects (EROs) associated with a population of old elliptical galaxies at z ~ 1 by \\citet{daddi01}. Based on their similar clustering properties, we propose that EROs and powerful radio galaxies may be the same systems seen at different evolutionary stages. Their r0 is ~ 2x higher than that of QSOs at a similar redshift, and comparable to that of bright ellipticals locally. This suggests that r0 (comoving) of these galaxies has changed little from z ~ 1 to z=0, in agreement with current Lambda CDM hierarchical merging models for the clustering evolution of massive early-type galaxies. Alternatively, the clustering of radio galaxies can be explained by the galaxy conservation model. This then implies that radio galaxies of average power are the progenitors of the local field population of early-types, while the most powerful radio galaxies will evolve into a present-day population with r0 comparable to that of local rich clusters.

  19. VizieR Online Data Catalog: ZENS: galaxies in groups along the cosmic web. I. (Carollo+, 2013)

    NASA Astrophysics Data System (ADS)

    Carollo, C. M.; Cibinel, A.; Lilly, S. J.; Miniati, F.; Norberg, P.; Silverman, J. D.; van Gorkom, J.; Cameron, E.; Finoguenov, A.; Peng, Y.; Pipino, A.; Rudick, C. S.

    2015-03-01

    The entire ZENS sample of 141 galaxy groups was selected from the 2PIGG catalog (Eke et al. 2004, J/MNRAS/348/866), which is based on a friends-of-friends (FOF; Huchra & Geller 1982, VII/86) percolation algorithm thoroughly tested on realistic mock galaxy catalogs generated from cosmological N-body simulations. The 2PIGG catalog covers 1500deg2 of the 2dFGRS (Colless+, 2001, VII/250). The data were taken in several observing runs over the period 2005-2009. Following a pilot-project time allocation in 2005, most of the observations were carried out as service-mode observations in the context of the ESO Large Program 177.A-0680. Paper II (Cibinel+, 2013ApJ...776...72C) provides details of the observing runs, the raw data properties, the data reduction procedures, and the photometric calibration for WFI data of the ZENS groups. (2 data files).

  20. Tidal Interactions at the Edge of the Local Group: New Evidence for Tidal Features in the Antlia Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    Penny, Samantha J.; Pimbblet, Kevin A.; Conselice, Christopher J.; Brown, Michael J. I.; Grützbauch, Ruth; Floyd, David J. E.

    2012-10-01

    Using deep B-band imaging down to ~μ B = 26 mag arcsec-2, we present evidence for tidal tails in the Antlia Dwarf galaxy, one of the most distant members of the Local Group. This elongation is in the direction of Antlia's nearest neighbor, the Magellanic-type NGC 3109. The tail is offset by <10° from a vector linking the centers of the two galaxies, indicative of interactions between the pair. Combined with the warped disk previously identified in NGC 3109, Antlia and NGC 3109 must be at a small separation for tidal features to be present in Antlia. We calculate that Antlia cannot be completely disrupted by NGC 3109 in a single interaction unless its orbit pericenter is <6 kpc; however, multiple interactions could significantly alter its morphology. Therefore despite being located right at the edge of the Local Group, environmental effects are playing an important role in Antlia's evolution.

  1. TIDAL INTERACTIONS AT THE EDGE OF THE LOCAL GROUP: NEW EVIDENCE FOR TIDAL FEATURES IN THE ANTLIA DWARF GALAXY

    SciTech Connect

    Penny, Samantha J.; Pimbblet, Kevin A.; Brown, Michael J. I.; Floyd, David J. E.; Conselice, Christopher J.; Gruetzbauch, Ruth

    2012-10-20

    Using deep B-band imaging down to {approx}{mu}{sub B} = 26 mag arcsec{sup -2}, we present evidence for tidal tails in the Antlia Dwarf galaxy, one of the most distant members of the Local Group. This elongation is in the direction of Antlia's nearest neighbor, the Magellanic-type NGC 3109. The tail is offset by <10 Degree-Sign from a vector linking the centers of the two galaxies, indicative of interactions between the pair. Combined with the warped disk previously identified in NGC 3109, Antlia and NGC 3109 must be at a small separation for tidal features to be present in Antlia. We calculate that Antlia cannot be completely disrupted by NGC 3109 in a single interaction unless its orbit pericenter is <6 kpc; however, multiple interactions could significantly alter its morphology. Therefore despite being located right at the edge of the Local Group, environmental effects are playing an important role in Antlia's evolution.

  2. Molecular gas content of H I monsters and implications to cold gas content evolution in galaxies

    NASA Astrophysics Data System (ADS)

    Lee, Cheoljong; Chung, Aeree; Yun, Min S.; Cybulski, Ryan; Narayanan, G.; Erickson, N.

    2014-06-01

    We present 12CO (J = 1 → 0) observations of a sample of local galaxies (0.04 < z < 0.08) with a large neutral hydrogen reservoir, or `H I monsters'. The data were obtained using the redshift search receiver on the five college radio astronomy observatory (FCRAO) 14 m telescope. The sample consists of 20 H I-massive galaxies with MH I > 3 × 1010 M⊙ from the Arecibo Legacy Fast ALFA (ALFALFA) survey and 8 low surface brightness galaxies (LSBs) with a comparable MH I(>1.5 × 1010 M⊙). Our sample selection is purely based on the amount of neutral hydrogen, thereby providing a chance to study how atomic and molecular gas relate to each other in these H I-massive systems. We have detected CO in 15 out of 20 ALFALFA selected galaxies and 4 out of 8 LSBs with molecular gas mass MH2 of (1-11)× 109 M⊙. Their total cold gas masses of (2-7) × 1010 M⊙ make them some of the most gas-massive galaxies identified to date in the Local Universe. Observed trends associated with H I, H2, and stellar properties of the H I massive galaxies and the field comparison sample are analysed in the context of theoretical models of galaxy cold gas content and evolution, and the importance of total gas content and improved recipes for handling spatially differentiated behaviours of disc and halo gas are identified as potential areas of improvement for the modelling.

  3. Dark matter halo properties of GAMA galaxy groups from 100 square degrees of KiDS weak lensing data

    NASA Astrophysics Data System (ADS)

    Viola, M.; Cacciato, M.; Brouwer, M.; Kuijken, K.; Hoekstra, H.; Norberg, P.; Robotham, A. S. G.; van Uitert, E.; Alpaslan, M.; Baldry, I. K.; Choi, A.; de Jong, J. T. A.; Driver, S. P.; Erben, T.; Grado, A.; Graham, Alister W.; Heymans, C.; Hildebrandt, H.; Hopkins, A. M.; Irisarri, N.; Joachimi, B.; Loveday, J.; Miller, L.; Nakajima, R.; Schneider, P.; Sifón, C.; Verdoes Kleijn, G.

    2015-10-01

    The Kilo-Degree Survey is an optical wide-field survey designed to map the matter distribution in the Universe using weak gravitational lensing. In this paper, we use these data to measure the density profiles and masses of a sample of ˜1400 spectroscopically identified galaxy groups and clusters from the Galaxy And Mass Assembly survey. We detect a highly significant signal (signal-to-noise-ratio ˜120), allowing us to study the properties of dark matter haloes over one and a half order of magnitude in mass, from M ˜ 1013-1014.5 h-1 M⊙. We interpret the results for various subsamples of groups using a halo model framework which accounts for the mis-centring of the brightest cluster galaxy (used as the tracer of the group centre) with respect to the centre of the group's dark matter halo. We find that the density profiles of the haloes are well described by an NFW profile with concentrations that agree with predictions from numerical simulations. In addition, we constrain scaling relations between the mass and a number of observable group properties. We find that the mass scales with the total r-band luminosity as a power law with slope 1.16 ± 0.13 (1σ) and with the group velocity dispersion as a power law with slope 1.89 ± 0.27 (1σ). Finally, we demonstrate the potential of weak lensing studies of groups to discriminate between models of baryonic feedback at group scales by comparing our results with the predictions from the Cosmo-OverWhelmingly Large Simulations project, ruling out models without AGN feedback.

  4. Metal distributions out to 0.5 r {sub 180} in the intracluster medium of four galaxy groups observed with Suzaku

    SciTech Connect

    Sasaki, Toru; Matsushita, Kyoko; Sato, Kosuke E-mail: matusita@rs.kagu.tus.ac.jp

    2014-01-20

    We studied the distributions of metal abundances and metal-mass-to-light ratios in the intracluster medium (ICM) of four galaxy groups, MKW 4, HCG 62, the NGC 1550 group, and the NGC 5044 group, out to ∼0.5 r {sub 180} observed with Suzaku. The iron abundance decreases with radius and is about 0.2-0.4 solar beyond 0.1 r {sub 180}. At a given radius in units of r {sub 180}, the iron abundance in the ICM of the four galaxy groups was consistent with or smaller than those of clusters of galaxies. The Mg/Fe and Si/Fe ratios in the ICM are nearly constant at the solar ratio out to 0.5 r {sub 180}. We also studied systematic uncertainties in the derived metal abundances, comparing the results from two versions of atomic data for astrophysicists (ATOMDB) and single- and two-temperature model fits. Since the metals have been synthesized in galaxies, we collected K-band luminosities of galaxies from the Two Micron All Sky Survey catalog and calculated the integrated iron-mass-to-light-ratios (IMLR), or the ratios of the iron mass in the ICM to light from stars in galaxies. The groups with smaller gas-mass-to-light ratios have smaller IMLR values and the IMLR is inversely correlated with the entropy excess. Based on these abundance features, we discussed the past history of metal enrichment processes in groups of galaxies.

  5. On the spin bias of satellite galaxies in the local group-like environment

    SciTech Connect

    Lee, Jounghun; Lemson, Gerard E-mail: lemson@mpa-garching.mpg.de

    2013-05-01

    We utilize the Millennium-II simulation databases to study the spin bias of dark subhalos in the Local Group-like systems which have two prominent satellites with comparable masses. Selecting the group-size halos with total mass similar to that of the Local Group (LG) from the friends-of-friends halo catalog and locating their subhalos from the substructure catalog, we determine the most massive (main) and second to the most massive (submain) ones among the subhalos hosted by each selected halo. When the dimensionless spin parameter (λ) of each subhalo is derived from its specific angular momentum and circular velocity at virial radius, a signal of correlation is detected between the spin parameters of the subhalos and the main-to-submain mass ratios of their host halos at z = 0: the higher main-to-submain mass ratio a host halo has, the higher mean spin parameter its subhalos have. It is also found that the correlations exist even for the subhalo progenitors at z = 0.5 and 1. Our interpretation of this result is that the subhalo spin bias is not a transient effect but an intrinsic property of a LG-like system with higher main-to- submain mass ratio, caused by stronger anisotropic stress in the region. A cosmological implication of our result is also discussed.

  6. Promotional Perspectives of Reference Group Influence: Advertising Implications

    ERIC Educational Resources Information Center

    Lessig, V. Parker; Park, C. Whan

    1978-01-01

    Examines the role of reference groups and promotional appeals in satisfying consumer motivations. Emphasizes three motivational reference group functions: informational, utilitarian, and value-expressive. (RL)

  7. An X-Ray Flux-Limited Sample of Galaxy Clusters: Physical Properties and Cosmological Implications

    NASA Astrophysics Data System (ADS)

    Reiprich, Thomas H.

    2001-07-01

    An X-ray selected and X-ray flux-limited sample comprising the 63 X-ray brightest galaxy clusters in the sky (excluding the galactic band, called HIFLUGCS) has been constructed based on the ROSAT All-Sky Survey. The flux limit has been set at 2x10^-11 erg/s/cm^2 in the energy band 0.1-2.4 keV. It has been shown that a high completeness is indicated by several tests. Due to the high flux limit this sample can be used for a variety of applications requiring a statistical cluster sample without any corrections to the effective survey volume. Mainly high quality pointed observations have been used to determine fluxes and physical cluster parameters. It has been shown that a tight correlation exists between the X-ray luminosity and the gravitational mass using HIFLUGCS and an extended sample of 106 galaxy clusters. The relation and its scatter have been quantified using different fitting methods. A comparison to theoretical and numerical predictions shows an overall agreement. This relation may be directly applied in large X-ray cluster surveys or dark matter simulations for conversions between X-ray luminosity and gravitating mass. Data from the performance verification phase of the recently launched X-ray satellite observatory XMM-Newton on the galaxy cluster Abell 1835 has been analyzed, in order to test the assumption of isothermality of the cluster gas in the outer parts applied throughout the work. It has been found that the measured outer temperature profile is consistent with being isothermal. In the inner regions a clear drop of the temperature by a factor of two has been found. Physical properties of the cluster sample have been studied by analyzing relations between different cluster parameters. The overall properties are well understood but in detail deviations from simple expectations have been found. It has been found that the gas mass fraction (fgas) does not vary as a function of intracluster gas temperature. For galaxy groups (kTx < 2 keV), however, a

  8. The star formation histories of local group dwarf galaxies. I. Hubble space telescope/wide field planetary camera 2 observations

    SciTech Connect

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-07-10

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ∼ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ∼ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10{sup 5} M{sub ☉} to 30% for galaxies with M > 10{sup 7} M{sub ☉}) and is largely explained by environment; (5) the distinction between 'ultra-faint' and 'classical' dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.

  9. The Star Formation Histories of Local Group Dwarf Galaxies. I. Hubble Space Telescope/Wide Field Planetary Camera 2 Observations

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel R.; Dolphin, Andrew E.; Skillman, Evan D.; Holtzman, Jon; Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F.

    2014-07-01

    We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with τ ~ 5 Gyr (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH (τ ~ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 105 M ⊙ to 30% for galaxies with M > 107 M ⊙) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  10. Implications of the ISO LWS spectrum of the prototypical ultraluminous galaxy: ARP 220

    NASA Technical Reports Server (NTRS)

    Fischer, J.; Satyapal, S.; Luhman, M. L.; Melnick, G.; Cox, P.; Cernicharo, J.; Stacey, G. J.; Smith, H. A.; Lord, S. D.; Greenhouse, M. A.

    1997-01-01

    The low resolution far infrared spectrum of the galaxy Arp 220, obtained with the low wavelength spectrometer (LWS) onboard the Infrared Space Observatory (ISO), is presented. The spectrum is dominated by the OH, H2O, CH, NH3 and O I absorption lines. The upper limits on the far infrared fine structure lines indicate a softer radiation in Arp 220 than in starburst galaxies.

  11. Extended Light in E/S0 Galaxies and Implications for Disk Rebirth

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda J.; Kannappan, S. J.; Laine, S.; Wei, L. H.; Baker, A. J.; Impey, C. D.

    2010-01-01

    The recent discovery of extended ultraviolet (XUV) disks around a large fraction of late-type galaxies provides evidence for unexpectedly large-scale disk building at recent epochs. Combining GALEX UV observations with deep optical and Spitzer IR imaging, we search for XUV disks in a sample of nearby low-to-intermediate mass E/S0 galaxies to explore evidence for disk rebuilding after mergers. Preliminary visual classification yields ten XUV-disk candidates from the full sample of 30, intriguingly similar to the 30% frequency for late-type galaxies. These XUV candidates occur at a wide range of masses and on both the red and blue sequences in color vs. stellar mass, indicating a possible association with processes like gas accretion and/or galaxy interactions that would affect the galaxy population broadly. We go on to apply the quantitative Type 1 and Type 2 XUV-disk definitions to this sample and identify multiple Type 1 XUVs, i.e., galaxies with UV structure beyond the expected star formation threshold. We also find several galaxies that come close to satisfying the Type 2 definition, but that definition proves problematic to apply to this sample: the NUV-derived star formation threshold radii for our E/S0s often lie inside the 80% Ks-band light (K80) radii, violating an implicit assumption of the Type 2 definition, or lie outside but not as far as the definition requires. Nonetheless, we identify otherwise Type 2-like galaxies ("modified Type 2 XUVs") that have higher star formation rates and bluer FUV - NUV colors than Type 1 XUVs in the sample. We propose that Type 1 XUVs may reflect early or inefficient stages of star formation, while modified Type 2 XUVs perhaps reflect inside-out disk regrowth.

  12. Extended Light in E/S0 Galaxies and Implications for Disk Rebirth

    NASA Astrophysics Data System (ADS)

    Moffett, A. J.; Kannappan, S. J.; Laine, S.; Wei, L. H.; Baker, A. J.; Impey, C. D.

    2010-06-01

    The recent discovery of extended ultraviolet (XUV) disks around a large fraction of late-type galaxies provides evidence for unexpectedly large-scale disk building at recent epochs. Combining GALEX UV observations with deep optical and Spitzer IR imaging, we search for XUV disks in a sample of nearby low-to-intermediate mass E/S0 galaxies to explore evidence for disk rebuilding after mergers. Preliminary visual classification yields ten XUV-disk candidates from the full sample of 30, intriguingly similar to the ˜30% frequency for late-type galaxies. These XUV candidates occur at a wide range of masses and on both the red and blue sequences in color vs. stellar mass, indicating a possible association with processes like gas accretion and/or galaxy interactions that would affect the galaxy population broadly. We go on to apply the quantitative Type 1 and Type 2 XUV-disk definitions to a nine-galaxy subsample analyzed in detail. For this subsample, six of the nine are Type 1 XUVs, i.e., galaxies with UV structure beyond the expected star formation threshold. The other three come close to satisfying the Type 2 definition, but that definition proves problematic to apply to this sample: the NUV-derived star formation threshold radii for our E/S0s often lie inside the 80% Ks-band light (K80) radii, violating an implicit assumption of the Type 2 definition, or lie outside but not as far as the definition requires. Nonetheless, the three otherwise Type 2-like galaxies ("modified Type 2 XUVs") have higher star formation rates and bluer FUV - NUV colors than the Type 1 XUVs in the sample. We propose that Type 1 XUVs may reflect early or inefficient stages of star formation, while modified Type 2 XUVs perhaps reflect inside-out disk regrowth.

  13. RADIO DETECTION OF GREEN PEAS: IMPLICATIONS FOR MAGNETIC FIELDS IN YOUNG GALAXIES

    SciTech Connect

    Chakraborti, Sayan; Yadav, Naveen; Ray, Alak; Cardamone, Carolin

    2012-02-10

    Green Peas are a new class of young, emission line galaxies that were discovered by citizen volunteers in the Galaxy Zoo project. Their low stellar mass, low metallicity, and very high star formation rates make Green Peas the nearby (z {approx} 0.2) analogs of the Lyman break galaxies which account for the bulk of the star formation in the early universe (z {approx} 2-5). They thus provide accessible laboratories in the nearby universe for understanding star formation, supernova feedback, particle acceleration, and magnetic field amplification in early galaxies. We report the first direct radio detection of Green Peas with low frequency Giant Metrewave Radio Telescope observations and our stacking detection with archival Very Large Array FIRST data. We show that the radio emission implies that these extremely young galaxies already have magnetic fields ({approx}> 30 {mu}G) even larger than that of the Milky Way. This is at odds with the present understanding of magnetic field growth based on amplification of seed fields by dynamo action over a galaxy's lifetime. Our observations strongly favor models with pregalactic magnetic fields at {mu}G levels.

  14. Gas retention and accumulation in stellar clusters and galaxies: Implications for star formation and black hole accretion

    NASA Astrophysics Data System (ADS)

    Naiman, Jill

    Star formation cannot proceed without the existence of an extensive gas reservoir. In particular, the supply of gas to form stars in dwarf galaxies and star clusters requires overcoming a variety of difficulties - namely, the effectiveness of different feedback mechanisms in removing gas from these shallow gravitational potentials. In addition, the supply of external gas to these systems is determined by the large scale galactic structure in which they reside. This thesis employs computational hydrodynamics coupled with physically realistic subgrid feedback prescriptions to resolve the interplay between the small scale feedback mechanisms and larger scale gas flows to determine the amount of gas a shallow potential can accumulate. First, we consider the flow of gas external to dwarf galaxies and star clusters into their cores as a generalized accretion process. Second, we explore the enhancement of gas accretion rates onto the compact members of young star clusters when the flow of external gas into the cluster cores is large. Third, we discuss how external gas flows initiated by the presence of a massive nuclear star cluster can enhance central massive black hole accretion rates during galaxy mergers. Fourth, we change our focus to exploring internal stellar wind retention in proto-globular clusters as a mechanism to supply gas for multiple episodes of star formation. Finally, the implications of stellar wind retention on the current gas reservoir in globular clusters is discussed.

  15. The mass distribution and the law of gravity in the Local Group dwarf irregular galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Lake, George; Skillman, Evan D.

    1989-10-01

    Results are presented on the H I spectral-line distribution and velocity field of the Local Group dwarf galaxy IC 1613, which were obtained using VLA of the NRAO. The rotation curve of IC 1613 was determined, and Newtonian and non-Newtonian mass models were built. It was found that the H I is lumpy in the inner parts, but H I contours in the outer parts of the galaxy are smooth. The velocity field is regular, and the line of nodes is coincident with the major axis of the gas distribution. The rotation curve of IC 1613 shows evidence of dark matter in the outer parts. However, the maximum density of a dark halo that can be tolerated is an order of magnitude lower than that needed to explain the velocity dispersions of the extreme dwarf spheroidals.

  16. VizieR Online Data Catalog: Galaxy groups and clouds in the local universe (Makarov+, 2011)

    NASA Astrophysics Data System (ADS)

    Makarov, D.; Karachentsev, I.

    2014-10-01

    We use the HyperLEDA (Paturel et al., 2003, http://atlas.obs-hp.fr/hyperleda/) and the NED (http://ned.ipac.caltech.edu) data bases as the main sources of data on radial velocities, apparent magnitudes, morphological types and other parameters of galaxies. (1 data file).

  17. Dust In Hell: Discovery Of Dust In Hot Gas Around Group-Centered Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Temi, Pasquale; Brighenti, F.; Mathews, W. G.

    2007-05-01

    Observations with the Spitzer infrared telescope reveal extended internally produced dust in the hot gas (KT 1 KeV) atmospheres surrounding two optically normal galaxies, NGC 5044 and NGC 4636. We interpret this as a dusty buoyant outflow resulting from energy released by gas accretion onto supermassive black holes in the galaxy cores. Both galaxies have highly disturbed, transient activities in the hot gas and contain strong dust emission at 70 and 160 microns in excess of what expected from normal stellar mass loss. The 70 micron image is clearly extended. The lifetime of dust in hot (KT=1KeV) interstellar gas to destruction by sputtering (ion impacts), 10 million years, establishes the time when the dust first entered the hot gas. Remarkably, in NGC 5044 we observe interstellar PAH dust-molecular emission at 8 microns out to about 5 Kpc that is spatially coincident with extended Halpha+[NII] emission from warm gas. We propose that this dust comes from the destruction and heating of dusty disks in the nuclei of these galaxies, followed by buoyant transport. A simple calculation shows that dust-assisted cooling in outflowing buoyant gas in NGC 5044 can cool the gas within a few Kpc in about 10 million years, explaining the optical line emission observed.

  18. Focus Group Evidence: Implications for Design and Analysis

    ERIC Educational Resources Information Center

    Ryan, Katherine E.; Gandha, Tysza; Culbertson, Michael J.; Carlson, Crystal

    2014-01-01

    In evaluation and applied social research, focus groups may be used to gather different kinds of evidence (e.g., opinion, tacit knowledge). In this article, we argue that making focus group design choices explicitly in relation to the type of evidence required would enhance the empirical value and rigor associated with focus group utilization. We…

  19. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    NASA Technical Reports Server (NTRS)

    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.

  20. Early-type Galaxies at z = 1.3. I. The Lynx Supercluster: Cluster and Groups at z = 1.3. Morphology and Color-Magnitude Relation

    NASA Astrophysics Data System (ADS)

    Mei, Simona; Stanford, S. Adam; Holden, Brad P.; Raichoor, Anand; Postman, Marc; Nakata, Fumiaki; Finoguenov, Alexis; Ford, Holland C.; Illingworth, Garth D.; Kodama, Tadayuki; Rosati, Piero; Tanaka, Masayuki; Huertas-Company, Marc; Rettura, Alessandro; Shankar, Francesco; Carrasco, Eleazar R.; Demarco, Ricardo; Eisenhardt, Peter; Jee, Myungkook J.; Koyama, Yusei; White, Richard L.

    2012-08-01

    We confirm the detection of three groups in the Lynx supercluster, at z ≈ 1.3, through spectroscopic follow-up and X-ray imaging, and we give estimates for their redshifts and masses. We study the properties of the group galaxies compared to the two central clusters, RX J0849+4452 and RX J0848+4453. Using spectroscopic follow-up and multi-wavelength photometric redshifts, we select 89 galaxies in the clusters, of which 41 are spectroscopically confirmed, and 74 galaxies in the groups, of which 25 are spectroscopically confirmed. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30%-40% level by simple automated classification methods (e.g., based on Sérsic index). In luminosity-selected samples, both clusters and groups show high fractions of bulge-dominated galaxies with a diffuse component that we visually identified as a disk and which we classified as bulge-dominated spirals, e.g., Sas. The ETG fractions never rise above ≈50% in the clusters, which is low compared to the fractions observed in other massive clusters at z ≈ 1. In the groups, ETG fractions never exceed ≈25%. However, overall bulge-dominated galaxy fractions (ETG plus Sas) are similar to those observed for ETGs in clusters at z ~ 1. Bulge-dominated galaxies visually classified as spirals might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples of galaxies with masses M > 1010.6 M ⊙ within Σ > 500 Mpc-2, the ETG and overall bulge-dominated galaxy fractions show no significant evolution with respect to local clusters, suggesting that morphological transformations might occur at lower masses

  1. Galaxies at High Redshift

    NASA Astrophysics Data System (ADS)

    Pérez-Fournon, I.; Balcells, M.; Moreno-Insertis, F.; Sánchez, F.

    2010-08-01

    Participants; Group photograph; Preface; Acknowledgements; 1. Galaxy formation and evolution: recent progress R. Ellis; 2. Galaxies at high redshift M. Dickinson; 3. High-redshift galaxies: the far-infrared and sub-millimeter view A. Franceschini; 4. Quasar absorption lines J. Bechtold; 5. Stellar population synthesis models at low and high redshift G. Bruzual A.; 6. Elliptical galaxies K. C. Freeman; 7. Disk galaxies K. C. Freeman; 8. Dark matter in disk galaxies K. C. Freeman.

  2. Chemo-dynamical evolution model: Enrichment of r-process elements in the Local Group dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Hirai, Yutaka; Ishimaru, Yuhri; Saitoh, Takayuki R.; Fujii, Michiko S.; Hidaka, Jun; Kajino, Toshitaka

    2016-08-01

    Neutron star mergers are one of the candidate astrophysical site(s) of r-process. Several chemical evolution studies however pointed out that the observed abundance of r-process is difficult to reproduce by neutron star mergers. In this study, we aim to clarify the enrichment of r-process elements in the Local Group dwarf galaxies. We carry out numerical simulations of galactic chemo-dynamical evolution using an N-body/smoothed particle hydrodynamics code, ASURA. We construct a chemo-dynamical evolution model for dwarf galaxies assuming that neutron star mergers are the major source of r-process elements. Our models reproduce the observed dispersion in [Eu/Fe] as a function of [Fe/H] with neutron star mergers with a merger time of 100 Myr. We find that star formation efficiency and metal mixing processes during the first <~ 300 Myr of galaxy evolution are important to reproduce the observations. This study supports that neutron star mergers are a major site of r-process.

  3. The Personalities of Group Leaders: Implications for Selection and Training.

    ERIC Educational Resources Information Center

    MacLennan, Beryce W.

    This paper discusses the growing recognition that the personalities and life experiences of group leaders are important factors in their effectiveness. Leaders should be warm, empathetic, responsive, understand individual and group behavior, give feedback, be trusted and accepted. Life experiences and personal development are important for the…

  4. The Luminosities, Sizes, and Velocity Dispersions of Brightest Cluster Galaxies: Implications for Formation History

    NASA Astrophysics Data System (ADS)

    Bernardi, Mariangela; Hyde, Joseph B.; Sheth, Ravi K.; Miller, Chris J.; Nichol, Robert C.

    2007-04-01

    The size-luminosity relation of early-type brightest cluster galaxies (BCGs), Re ~ L0.88, is steeper than that for the bulk of the early-type galaxy population, for which Re ~ L0.68. This is true if quantities derived from either de Vaucouleurs or Sérsic fits to the surface brightness profiles are used. Contamination from an intracluster light component centered on the BCG, with parameters similar to what has been seen in some recent studies, is not able to account for this difference. In addition, although BCGs are hardly offset from the fundamental plane defined by the bulk of the early-type population, they show considerably smaller scatter. The larger than expected sizes of BCGs, and the increased homogeneity, are qualitatively consistent with models that seek to explain the colors of the most massive galaxies by invoking dry dissipationless mergers, since dissipation tends to reduce the sizes of galaxies, and wet mergers that result in star formation would tend to increase the scatter in luminosity at a fixed size and velocity dispersion. Furthermore, BCGs define the same g - r color-magnitude relation as the bulk of the early-type population. If BCGs formed from dry mergers, then BCG progenitors must have been red for their magnitudes, suggesting that they hosted older stellar populations than is typical for their luminosities. Our findings have two other consequences. First, the Re-L relation of the early-type galaxy population as a whole (i.e., normal plus BCG) exhibits some curvature: the most luminous galaxies tend to have larger sizes than is expected from the Re ~ L0.68 scaling—some of this curvature must be a consequence of the fact that an increasing fraction of the most luminous galaxies are BCGs. The second consequence is suggested by the fact that, despite following a steeper size-luminosity relation, BCGs tend to define a tight relation between dynamical mass Reσ2/G and luminosity. Although this relation is slightly different than that defined

  5. A Bound Violation on the Galaxy Group Scale: The Turn-around Radius of NGC 5353/4

    NASA Astrophysics Data System (ADS)

    Lee, Jounghun; Kim, Suk; Rey, Soo-Chang

    2015-12-01

    The first observational evidence for the violation of the maximum turn-around radius on the galaxy group scale is presented. The NGC 5353/4 group is chosen as an ideal target for our investigation of the bound-violation because of its proximity, low-density environment, optimal mass scale, and the existence of a nearby thin straight filament. Using the observational data on the line-of-sight velocities and three-dimensional distances of the filament galaxies located in the bound zone of the NGC 5353/4 group, we construct their radial velocity profile as a function of separation distance from the group center and then compare it to the analytic formula obtained empirically by Falco et al. to find the best-fit value of an adjustable parameter with the help of the maximum likelihood method. The turn-around radius of NGC 5353/4 is determined to be the separation distance where the adjusted analytic formula for the radial velocity profile yields zero. The estimated turn-around radius of NGC 5353/4 turned out to substantially exceed the upper limit predicted by the spherical model based on the ΛCDM cosmology. Even when the restrictive condition of spherical symmetry is released, the estimated value is found to be only marginally consistent with the ΛCDM expectation.

  6. Non-parametric star formation histories for four dwarf spheroidal galaxies of the Local Group

    NASA Astrophysics Data System (ADS)

    Hernandez, X.; Gilmore, Gerard; Valls-Gabaud, David

    2000-10-01

    We use recent Hubble Space Telescope colour-magnitude diagrams of the resolved stellar populations of a sample of local dSph galaxies (Carina, Leo I, Leo II and Ursa Minor) to infer the star formation histories of these systems, SFR(t). Applying a new variational calculus maximum likelihood method, which includes a full Bayesian analysis and allows a non-parametric estimate of the function one is solving for, we infer the star formation histories of the systems studied. This method has the advantage of yielding an objective answer, as one need not assume a priori the form of the function one is trying to recover. The results are checked independently using Saha's W statistic. The total luminosities of the systems are used to normalize the results into physical units and derive SN type II rates. We derive the luminosity-weighted mean star formation history of this sample of galaxies.

  7. The masses of local group dwarf spheroidal galaxies: The death of the universal mass profile

    SciTech Connect

    Collins, Michelle L. M.; Martin, Nicolas F.; Chapman, Scott C.; Irwin, Michael J.; Rich, R. M.; Ibata, Rodrigo A.; Bate, Nicholas F.; Lewis, Geraint F.; Peñarrubia, Jorge; Casey, Caitlin M.; Ferguson, Annette M. N.; Koch, Andreas; McConnachie, Alan W.; Tanvir, Nial

    2014-03-01

    We investigate the claim that all dwarf spheroidal galaxies (dSphs) reside within halos that share a common, universal mass profile as has been derived for dSphs of the galaxy. By folding in kinematic information for 25 Andromeda dSphs, more than doubling the previous sample size, we find that a singular mass profile cannot be found to fit all of the observations well. Further, the best-fit dark matter density profile measured solely for the Milky Way dSphs is marginally discrepant with that of the Andromeda dSphs (at just beyond the 1σ level), where a profile with lower maximum circular velocity, and hence mass, is preferred. The agreement is significantly better when three extreme Andromeda outliers, And XIX, XXI, and XXV, all of which have large half-light radii (≳ 600 pc) and low-velocity dispersions (σ {sub v} < 5 km s{sup –1}), are omitted from the sample. We argue that the unusual properties of these outliers are likely caused by tidal interactions with the host galaxy.

  8. LOCAL GROUP DWARF ELLIPTICAL GALAXIES. II. STELLAR KINEMATICS TO LARGE RADII IN NGC 147 AND NGC 185

    SciTech Connect

    Geha, M.; Van der Marel, R. P.; Kalirai, J.; Guhathakurta, P.; Kirby, E. N.

    2010-03-01

    We present kinematic and metallicity profiles for the M 31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radial coverage for any dE galaxy, extending to a projected distance of 8 half-light radii (8r{sub eff} {approx} 14'). We achieve this coverage via Keck/DEIMOS multislit spectroscopic observations of 520 and 442 member red giant branch stars in NGC 147 and NGC 185, respectively. In contrast to previous studies, we find that both dEs have significant internal rotation. We measure a maximum rotational velocity of 17 +- 2 km s{sup -1} for NGC 147 and 15 +- 5 km s{sup -1} for NGC 185. While both rotation profiles suggest a flattening in the outer regions, there is no indication that we have reached the radius of maximum rotation velocity. The velocity dispersions decrease gently with radius with average dispersions of 16 +- 1 km s{sup -1} and 24 +- 1 km s{sup -1} for NGC 147 and NGC 185, respectively. The average metallicities for NGC 147 and NGC 185 are [Fe/H] = -1.1 +- 0.1 and [Fe/H] = -1.3 +- 0.1, respectively; both dEs have internal metallicity dispersions of 0.5 dex, but show no evidence for a radial metallicity gradient. We construct two-{integral} axisymmetric dynamical models and find that the observed kinematical profiles cannot be explained without modest amounts of non-baryonic dark matter. We measure central mass-to-light ratios of M/L{sub V} = 4.2 +- 0.6 and M/L{sub V} = 4.6 +- 0.6 for NGC 147 and NGC 185, respectively. Both dE galaxies are consistent with being primarily flattened by their rotational motions, although some anisotropic velocity dispersion is needed to fully explain their observed shapes. The velocity profiles of all three Local Group dEs (NGC 147, NGC 185, and NGC 205) suggest that rotation is more prevalent in the dE galaxy class than previously assumed, but often manifests only at several times the effective radius. Since all dEs outside the Local Group have been

  9. The active galactic nucleus population in X-ray-selected galaxy groups at 0.5 < Z < 1.1

    SciTech Connect

    Oh, Semyeong; Woo, Jong-Hak; Matsuoka, Kenta; Mulchaey, John S.; Finoguenov, Alexis; Tanaka, Masayuki; Cooper, Michael C.; Ziparo, Felicia; Bauer, Franz E.

    2014-07-20

    We use Chandra data to study the incidence and properties of active galactic nuclei (AGNs) in 16 intermediate redshift (0.5 < z < 1.1) X-ray-selected galaxy groups in the Chandra Deep Field-South. We measure an AGN fraction of f(L{sub X,H}>10{sup 42};M{sub R}<−20)=8.0{sub −2.3}{sup +3.0}% at z-bar ∼0.74, approximately a factor of two higher than the AGN fraction found for rich clusters at comparable redshift. This extends the trend found at low redshift for groups to have higher AGN fractions than clusters. Our estimate of the AGN fraction is also more than a factor of three higher than that of low redshift X-ray-selected groups. Using optical spectra from various surveys, we also constrain the properties of emission-line selected AGNs in these groups. In contrast to the large population of X-ray AGNs (N(L{sub X,{sub H}} > 10{sup 41} erg s{sup –1}) = 25), we find only four emission-line AGNs, three of which are also X-ray bright. Furthermore, most of the X-ray AGNs in our groups are optically dull (i.e., lack strong emission-lines), similar to those found in low redshift X-ray groups and clusters of galaxies. This contrasts with the AGN population found in low redshift optically selected groups which are dominated by emission-line AGNs. The differences between the optically and X-ray-selected AGNs populations in groups are consistent with a scenario where most AGNs in the densest environments are currently in a low accretion state.

  10. Evolution of public cooperation in a monitored society with implicated punishment and within-group enforcement.

    PubMed

    Chen, Xiaojie; Sasaki, Tatsuya; Perc, Matjaž

    2015-01-01

    Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite well-mixed populations. We also show that the addition of within-group enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that group-size effects and within-group enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental group-size effects that facilitate prosocial collective action. PMID:26597333

  11. Evolution of public cooperation in a monitored society with implicated punishment and within-group enforcement

    PubMed Central

    Chen, Xiaojie; Sasaki, Tatsuya; Perc, Matjaž

    2015-01-01

    Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite well-mixed populations. We also show that the addition of within-group enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that group-size effects and within-group enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental group-size effects that facilitate prosocial collective action. PMID:26597333

  12. Evolution of public cooperation in a monitored society with implicated punishment and within-group enforcement

    NASA Astrophysics Data System (ADS)

    Chen, Xiaojie; Sasaki, Tatsuya; Perc, Matjaž

    2015-11-01

    Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite well-mixed populations. We also show that the addition of within-group enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that group-size effects and within-group enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental group-size effects that facilitate prosocial collective action.

  13. Evolution of public cooperation in a monitored society with implicated punishment and within-group enforcement.

    PubMed

    Chen, Xiaojie; Sasaki, Tatsuya; Perc, Matjaž

    2015-11-24

    Monitoring with implicated punishment is common in human societies to avert freeriding on common goods. But is it effective in promoting public cooperation? We show that the introduction of monitoring and implicated punishment is indeed effective, as it transforms the public goods game to a coordination game, thus rendering cooperation viable in infinite and finite well-mixed populations. We also show that the addition of within-group enforcement further promotes the evolution of public cooperation. However, although the group size in this context has nonlinear effects on collective action, an intermediate group size is least conductive to cooperative behaviour. This contradicts recent field observations, where an intermediate group size was declared optimal with the conjecture that group-size effects and within-group enforcement are responsible. Our theoretical research thus clarifies key aspects of monitoring with implicated punishment in human societies, and additionally, it reveals fundamental group-size effects that facilitate prosocial collective action.

  14. THE EFFECT OF ENVIRONMENT ON THE FORMATION OF H{alpha} FILAMENTS AND COOL CORES IN GALAXY GROUPS AND CLUSTERS

    SciTech Connect

    McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard E-mail: veilleux@astro.umd.edu

    2011-04-10

    We present the results of a combined X-ray and H{alpha} study of 10 galaxy groups and 17 galaxy clusters using the Chandra X-ray Observatory and the Maryland Magellan Tunable Filter. We find no difference in the morphology or detection frequency of H{alpha} filaments in groups versus clusters over the mass range 10{sup 13} < M{sub 500} < 10{sup 15} M{sub sun}. The detection frequency of H{alpha} emission is shown to be only weakly dependent on the total mass of the system at the 52% confidence level. In contrast, we find that the presence of H{alpha} filaments is strongly correlated with both the global (89% confidence level) and core (84%) intracluster medium (ICM) entropy, as well as the X-ray cooling rate (72%). The H{alpha} filaments are therefore an excellent proxy for the cooling ICM. The H{alpha} filaments are more strongly correlated with the cooling properties of the ICM than with the radio properties of the brightest cluster galaxy; this further supports the scenario where these filaments are directly associated with a thermally unstable, rapidly cooling ICM, rather than radio bubbles. The ICM cooling efficiency, defined as the X-ray cooling rate per unit gas mass, is shown to correlate with the total system mass, indicating that groups are more efficient at cooling than clusters. This result implies that, in systems with cool cores, active galactic nucleus feedback scales with the total mass of the system, in agreement with earlier suggestions.

  15. The 60-μm extragalactic background radiation intensity, dust-enshrouded active galactic nuclei and the assembly of groups and clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Blain, A. W.; Phillips, T. G.

    2002-06-01

    Submillimetre- (submm-) wave observations have revealed a cosmologically significant population of high-redshift dust-enshrouded galaxies. The form of evolution inferred for this population can be reconciled easily with COBE FIRAS and DIRBE measurements of the cosmic background radiation (CBR) intensity at wavelengths longer than ~100μm. At shorter wavelengths, however, the 60-μm CBR intensity reported by Finkbeiner, Davis & Schlegel is less easily accounted for. Lagache et al. have proposed that this excess CBR emission is a warm Galactic component, and the detection of the highest-energy γ-rays from blazars limits the CBR intensity at these wavelengths, but here we investigate possible sources of this excess CBR emission, assuming that it has a genuine extragalactic origin. We propose and test three explanations, each involving additional populations of luminous, evolving galaxies not readily detected in existing submm-wave surveys. First, an additional population of dust-enshrouded galaxies with hot dust temperatures, perhaps dust-enshrouded, Compton-thick active galactic nuclei (AGN) as suggested by recent deep Chandra surveys. Secondly, a population of dusty galaxies with temperatures more typical of the existing submm-selected galaxies, but at relatively low redshifts. These could plausibly be associated with the assembly of groups and clusters of galaxies. Thirdly, a population of low-luminosity, cool, quiescent spiral galaxies. Hot AGN sources and the assembly of galaxy groups can account for the excess 60-μm background. There are significant problems with the cluster assembly scenario, in which too many bright 60-μm IRAS sources are predicted. Spiral galaxies have the wrong spectral energy distributions to account for the excess. Future wide-field far-infrared (IR) surveys at wavelengths of 70 and 250μm using the SIRTF and Herschel space missions will sample representative volumes of the distant Universe, allowing any hot population of dusty AGNs and

  16. The Halo Merger Rate in the Millennium Simulation and Implications for Observed Galaxy Merger Fractions

    NASA Astrophysics Data System (ADS)

    Genel, Shy; Genzel, Reinhard; Bouché, Nicolas; Naab, Thorsten; Sternberg, Amiel

    2009-08-01

    We have developed a new method to extract halo merger rates from the Millennium Simulation. First, by removing superfluous mergers that are artifacts of the standard friends-of-friends (FOF) halo identification algorithm, we find a lower merger rate compared to previous work. The reductions are more significant at lower redshifts and lower halo masses, and especially for minor mergers. Our new approach results in a better agreement with predictions from the extended Press-Schechter model. Second, we find that the FOF halo finder overestimates the halo mass by up to 50% for halos that are about to merge, which leads to an additional ≈20% overestimate of the merger rate. Therefore, we define halo masses by including only particles that are gravitationally bound to their FOF groups. We provide new best-fitting parameters for a global formula to account for these improvements. In addition, we extract the merger rate per progenitor halo, as well as per descendant halo. The merger rate per progenitor halo is the quantity that should be related to observed galaxy merger fractions when they are measured via pair counting. At low-mass/redshift, the merger rate increases moderately with mass and steeply with redshift. At high enough mass/redshift (for the rarest halos with masses a few times the "knee" of the mass function), these trends break down, and the merger rate per progenitor halo decreases with mass and increases only moderately with redshift. Defining the merger rate per progenitor halo also allows us to quantify the rate at which halos are being accreted onto larger halos, in addition to the minor and major merger rates. We provide an analytic formula that converts any given merger rate per descendant halo into a merger rate per progenitor halo. Finally, we perform a direct comparison between observed merger fractions and the fraction of halos in the Millennium Simulation that have undergone a major merger during the recent dynamical friction time, and find a

  17. INTEGRAL Spectroscopy of IRAS 17208-0014: Implications for the Evolutionary Scenarios of Ultraluminous Infrared Galaxies

    NASA Astrophysics Data System (ADS)

    Arribas, Santiago; Colina, Luis

    2003-07-01

    New integral field optical fiber spectroscopy obtained with the INTEGRAL system, together with archival HST WFPC2 and NICMOS images, has been used to investigate the ultraluminous infrared galaxy (ULIRG) IRAS 17208-0014, one of the coldest and most luminous objects in the IRAS 1 Jy sample. We have found that the optical nucleus is not coincident with the true (near-IR and dynamical) nucleus, but that it is displaced by 1.3 kpc (1.5") from it. As a consequence, the previous optical spectral classifications for the nucleus of this galaxy have to be changed from H II to LINER. The ionized gas emission is concentrated around the optical nucleus, where a young (5-6 Myr), massive [(3+/-1)×108 Msolar], and luminous [(6+/-2)×1010 Lsolar] starburst is detected. Contrary to what is found in dynamically young ULIRGs, no strong line emission tracing star-forming regions, or tidal dwarf galaxies, is detected in the inner parts of the tidal tails. The two-dimensional gas velocity field identifies the optically faint K-band nucleus as the dynamical nucleus of the galaxy and shows that the 3 kpc, tilted (i~35deg) disk is rotating at Δvsini=250 km s-1. Radial motions of gas are found along the minor kinematic axis, which, according to the geometry of the system, are well interpreted as inflows perpendicular to the inner disk. The existence of such inflows supports the idea that, as a consequence of the merging process, gas is channeling from the external regions, several kiloparsecs away, into the nuclear regions where the massive starburst reported above is taking place. The kinematical, morphological, and photometric evidence presented here supports the idea that in IRAS 17208-0014 we are witnessing a luminous, cool ULIRG that is at the final coalescence phase of a system composed of two spiral galaxies with m<=m* and a mass ratio of ~2:1, each consisting of a disk+bulge internal structure, that have been involved in a prograde encounter. This system will most likely evolve

  18. Other-Regulation in Collaborative Groups: Implications for Regulation Quality

    ERIC Educational Resources Information Center

    Rogat, Toni Kempler; Adams-Wiggins, Karlyn R.

    2014-01-01

    The current study examines variation in other-regulation, conceptualized as efforts by one student to regulate their group's work. This study extends research which has conceptualized other-regulation as temporarily guiding others' conceptual understanding and skill development by broadening the spectrum of other-regulation to include…

  19. Galaxy-galaxy(-galaxy) lensing as a sensitive probe of galaxy evolution

    NASA Astrophysics Data System (ADS)

    Saghiha, H.; Hilbert, S.; Schneider, P.; Simon, P.

    2012-11-01

    Context. The gravitational lensing effect provides various ways to study the mass environment of galaxies. Aims: We investigate how galaxy-galaxy(-galaxy) lensing can be used to test models of galaxy formation and evolution. Methods: We consider two semi-analytic galaxy formation models based on the Millennium Run N-body simulation: the Durham model by Bower et al. (2006, MNRAS, 370, 645) and the Garching model by Guo et al. (2011, MNRAS, 413, 101). We generate mock lensing observations for the two models, and then employ Fast Fourier Transform methods to compute second- and third-order aperture statistics in the simulated fields for various galaxy samples. Results: We find that both models predict qualitatively similar aperture signals, but there are large quantitative differences. The Durham model predicts larger amplitudes in general. In both models, red galaxies exhibit stronger aperture signals than blue galaxies. Using these aperture measurements and assuming a linear deterministic bias model, we measure relative bias ratios of red and blue galaxy samples. We find that a linear deterministic bias is insufficient to describe the relative clustering of model galaxies below ten arcmin angular scales. Dividing galaxies into luminosity bins, the aperture signals decrease with decreasing luminosity for brighter galaxies, but increase again for fainter galaxies. This increase is likely an artifact due to too many faint satellite galaxies in massive group and cluster halos predicted by the models. Conclusions: Our study shows that galaxy-galaxy(-galaxy) lensing is a sensitive probe of galaxy evolution.

  20. Luminous and Dark Matter Profiles from Galaxies to Clusters: Bridging the Gap with Group-scale Lenses

    NASA Astrophysics Data System (ADS)

    Newman, Andrew B.; Ellis, Richard S.; Treu, Tommaso

    2015-11-01

    Observations of strong gravitational lensing, stellar kinematics, and larger-scale tracers enable accurate measures of the distribution of dark matter (DM) and baryons in massive early-type galaxies (ETGs). While such techniques have been applied to galaxy-scale and cluster-scale lenses, the paucity of intermediate-mass systems with high-quality data has precluded a uniform analysis of mass-dependent trends. With the aim of bridging this gap, we present new observations and analyses of 10 group-scale lenses at < z> =0.36, characterized by Einstein radii {θ }{{Ein}}=2\\buildrel{\\prime\\prime}\\over{.} 5-5\\buildrel{\\prime\\prime}\\over{.} 1 and a mean halo mass of {M}200={10}14.0 {M}⊙ . We measure a mean concentration c200 = 5.0 ± 0.8 consistent with unmodified cold dark matter halos. By combining our data with other lens samples, we analyze the mass structure of ETGs in 1013 {M}⊙ -1015 {M}⊙ halos using homogeneous techniques. We show that the slope of the total density profile γtot within the effective radius depends on the stellar surface density, as demonstrated previously, but also on the halo mass. We analyze these trends using halo occupation models and resolved stellar kinematics with the goal of testing the universality of the DM profile. Whereas the central galaxies of clusters require a shallow inner DM density profile, group-scale lenses are consistent with a Navarro-Frenk-White profile or one that is slightly contracted. The largest uncertainties arise from the sample size and likely radial gradients in stellar populations. We conclude that the net effect of baryons on the DM distribution may not be universal, but more likely varies with halo mass due to underlying trends in star formation efficiency and assembly history.

  1. THE ZURICH ENVIRONMENTAL STUDY (ZENS) OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. V. PROPERTIES AND FREQUENCY OF MERGING SATELLITES AND CENTRALS IN DIFFERENT ENVIRONMENTS

    SciTech Connect

    Pipino, A.; Cibinel, A.; Tacchella, S.; Carollo, C. M.; Lilly, S. J.; Miniati, F.; Silverman, J. D.; Van Gorkom, J. H.; Finoguenov, A.

    2014-12-20

    We use the Zurich Environmental Study database to investigate the environmental dependence of the merger fraction Γ and merging galaxy properties in a sample of ∼1300 group galaxies with M > 10{sup 9.2} M {sub ☉} and 0.05 < z < 0.0585. In all galaxy mass bins investigated in our study, we find that Γ decreases by a factor of ∼2-3 in groups with halo masses M {sub HALO} > 10{sup 13.5} M {sub ☉} relative to less massive systems, indicating a suppression of merger activity in large potential wells. In the fiducial case of relaxed groups only, we measure a variation of ΔΓ/Δlog (M {sub HALO}) ∼ –0.07 dex{sup –1}, which is almost independent of galaxy mass and merger stage. At galaxy masses >10{sup 10.2} M {sub ☉}, most mergers are dry accretions of quenched satellites onto quenched centrals, leading to a strong increase of Γ with decreasing group-centric distance at these mass scales. Both satellite and central galaxies in these high-mass mergers do not differ in color and structural properties from a control sample of nonmerging galaxies of equal mass and rank. At galaxy masses of <10{sup 10.2} M {sub ☉} where we mostly probe satellite-satellite pairs and mergers between star-forming systems close pairs (projected distance <10-20 kpc) show instead ∼2 × enhanced (specific) star formation rates and ∼1.5 × larger sizes than similar mass, nonmerging satellites. The increase in both size and star formation rate leads to similar surface star formation densities in the merging and control-sample satellite populations.

  2. Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution

    NASA Astrophysics Data System (ADS)

    Esteban, C.; García-Rojas, J.; Carigi, L.; Peimbert, M.; Bresolin, F.; López-Sánchez, A. R.; Mesa-Delgado, A.

    2014-09-01

    We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2-10, Mrk 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253-0312, Tol 1457-262, Tol 1924-416 and the H II region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10420 Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C2+ and/or O2+ from faint pure recombination lines in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O versus O/H, C/O versus N/O and C/N versus O/H relations for Galactic and extragalactic H II regions and comparing with results for Galactic halo stars and damped Lyα systems. We find that H II regions in star-forming dwarf galaxies occupy a different locus in the C/O versus O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H II regions should have the same origin than in halo stars. The comparison between the C/O ratios in H II regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H II regions and that this coupling breaks in very low metallicity objects.

  3. Some astrophysical implication of gas profiles in a new galaxy clusters model

    NASA Astrophysics Data System (ADS)

    Piedipalumbo, Ester; Cardone, V. F.; Tortora, C.

    2004-12-01

    The structure of the dark matter and the thermodynamical status of the hot gas in galaxy clusters is an interesting and widely discussed topic in modern astrophysics. Recently, Rasia et al. (2004) have proposed a new dynamical model of clusters of galaxies, which describes both the dark matter halo and the hot intracluster gas. We analyze the influence of the gas density and temperature profiles on the properties of the X-emission and the comptonization parameter that determines the CMBR temperature decrement due to the Sunyaev - Zel’dovich effect† .A complete traetment of this topic is found in Cardone V.F., Piedipalumbo E., Tortora C., 2005, A&A, 429, 49

  4. CARBON-RICH DUST PRODUCTION IN METAL-POOR GALAXIES IN THE LOCAL GROUP

    SciTech Connect

    Sloan, G. C.; Matsuura, M.; Lagadec, E.; Van Loon, J. Th.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Bernard-Salas, J.

    2012-06-20

    We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a star's lifetime on the asymptotic giant branch.

  5. Extragalactic H 2 regions in the UV: Implications for primeval galaxies and quasars

    NASA Technical Reports Server (NTRS)

    Meier, D. L.; Kellogg, W. K.; Terlevich, R.

    1980-01-01

    Three extragalactic regions of rapid star formation with red shifts great enough to separate the L alpha region from geocoronal L alpha were observed with the IUE satellite. Only the low metal abundance object had detectable L alpha emission. L alpha is therefore expected to be weak or absent in collapsed primeval galaxies. The detected object has a L alpha H beta identical to that of quasars.

  6. The Jeans modeling of the Milky Way galaxy: implications of the kinematics of the stellar halo

    NASA Astrophysics Data System (ADS)

    Samurović, S.; Lalović, A.

    2011-07-01

    Aims: We investigate the predictions of Newtonian dynamics and the MOND theory related to the Milky Way galaxy using the Jeans equation. Methods: We used the measurements of the radial velocities of the blue horizontal branch (BHB) halo stars to test the predictions of Newtonian gravity and to also extend our study to different MOND models, taking orbital anisotropies that we calculate into account. Results: The halo stars of the Galaxy were used as a tracer of the Galaxy's gravitational potential. The Jeans equation was calculated for both the Newtonian and the MOND approaches. We assumed spherical symmetry and calculated the Jeans equation by taking orbital anisotropies into account. Circular velocities for both approaches were also analyzed. Conclusions: We solved the Jeans equation in spherical approximation and confirm that the Newtonian model without dark matter cannot fit the observed velocity dispersion profile and that the truncated flat model with dark matter can provide a good fit to the observed velocity dispersion. For the MOND models, from the Jeans modeling and the models of the circular velocity curves, we found that two models can provide a fit to the data without significant anisotropies whereas two other tested models need various anisotropies to obtain the same result.

  7. Group Leader Reflections on Their Training and Experience: Implications for Group Counselor Educators and Supervisors

    ERIC Educational Resources Information Center

    Ohrt, Jonathan H.; Ener, Elizabeth; Porter, Jessica; Young, Tabitha L.

    2014-01-01

    Effective group leaders possess specialized counseling skills and abilities; however, attention to group leadership training appears to be lagging behind that of individual counseling. In this phenomenological study we explored group leaders' perceptions of their training and experience. Twenty-two professional counselors participated in…

  8. Group Decisions in Biodiversity Conservation: Implications from Game Theory

    PubMed Central

    Frank, David M.; Sarkar, Sahotra

    2010-01-01

    Background Decision analysis and game theory [1], [2] have proved useful tools in various biodiversity conservation planning and modeling contexts [3]–[5]. This paper shows how game theory may be used to inform group decisions in biodiversity conservation scenarios by modeling conflicts between stakeholders to identify Pareto–inefficient Nash equilibria. These are cases in which each agent pursuing individual self–interest leads to a worse outcome for all, relative to other feasible outcomes. Three case studies from biodiversity conservation contexts showing this feature are modeled to demonstrate how game–theoretical representation can inform group decision-making. Methodology and Principal Findings The mathematical theory of games is used to model three biodiversity conservation scenarios with Pareto–inefficient Nash equilibria: (i) a two–agent case involving wild dogs in South Africa; (ii) a three–agent raptor and grouse conservation scenario from the United Kingdom; and (iii) an n–agent fish and coral conservation scenario from the Philippines. In each case there is reason to believe that traditional mechanism–design solutions that appeal to material incentives may be inadequate, and the game–theoretical analysis recommends a resumption of further deliberation between agents and the initiation of trust—and confidence—building measures. Conclusions and Significance Game theory can and should be used as a normative tool in biodiversity conservation contexts: identifying scenarios with Pareto–inefficient Nash equilibria enables constructive action in order to achieve (closer to) optimal conservation outcomes, whether by policy solutions based on mechanism design or otherwise. However, there is mounting evidence [6] that formal mechanism–design solutions may backfire in certain cases. Such scenarios demand a return to group deliberation and the creation of reciprocal relationships of trust. PMID:20523732

  9. Implications of poikilitic textures in LL-group chondrites

    NASA Technical Reports Server (NTRS)

    Fodor, R. V.; Keil, K.

    1975-01-01

    Five lithic fragments with poikilitic textures in five LL-group chondrites are examined by microscope and electron microprobe to determine whether the textures have resulted from processes related to impact events, such as thermal metamorphism or partial melting. The bulk and pyroxene compositions of the fragments are determined. The compositional characteristics of minerals in certain fragments are found to indicate an apparent melt origin. It is concluded that impact processes produced the poikilitic textures and that complete melting, partial melting, and solid-state recrystallization all have had some part in producing the textures.

  10. XMM-Newton and Chandra Observations of the Galaxy Group NGC 5044. 1; Evidence for Limited Multiphase Hot Gas

    NASA Technical Reports Server (NTRS)

    Buote, David A.; Lewis, Aaron D.; Brighenti, Fabrizio; Mathews, William G.

    2003-01-01

    Using new XMM and Chandra observations, we present an analysis of the temperature structure of the hot gas within a radius of 100 kpc of the bright nearby galaxy group NGC 5044. A spectral deprojection analysis of data extracted from circular annuli reveals that a two-temperature model (2T) of the hot gas is favored over single-phase or cooling flow (M = 4.5 +/- 0.2 solar mass/yr) models within the central approx.30 kpc. Alternatively, the data can be fitted equally well if the temperature within each spherical shell varies continuously from approx.T(sub h) to T(sub c) approx. T(sub h)/2, but no lower. The high spatial resolution of the Chandra data allows us to determine that the temperature excursion T(sub h) approaches T(sub c) required in each shell exceeds the temperature range between the boundaries of the same shell in the best-fitting single-phase model. This is strong evidence for a multiphase gas having a limited temperature range. We do not find any evidence that azimuthal temperature variations within each annulus on the sky can account for the range in temperatures within each shell. We provide a detailed investigation of the systematic errors on the derived spectral models considering the effects of calibration, plasma codes, bandwidth, variable NH, and background rate. We find that the RGS gratings and the EPIC and ACIS CCDs give fully consistent results when the same models are fitted over the same energy ranges for each instrument. The cooler component of the 2T model has a temperature (T(sub c) approx. 0.7 keV) similar to the kinetic temperature of the stars. The hot phase has a temperature (T(sub h) approx. 1.4 keV) characteristic of the virial temperature of the solar mass halo expected in the NGC 5044 group. However, in view of the morphological disturbances and X-ray holes visible in the Chandra image within R approx. equals 10 kpc, bubbles of gas heated to approx.T(sub h) in this region may be formed by intermittent AGN feedback. Some

  11. Implications of the Kidd blood group system in renal transplantation.

    PubMed

    Rourk, A; Squires, J E

    2012-01-01

    The association of the Kidd blood group system with hemolytic transfusion reactions and hemolytic disease of the newborn is well known. The Kidd antigens, which are localized to the HUT/UT-B urea transport protein, are found on red blood cells and the endothelial cells of the blood vessels of the medulla of the kidney. Recently it has been suggested that these antigens might play a role as minor histocompatibility antigens in renal transplantation. In the current case, the appearance of an anti-Jk(b) 10 years after renal transplantation associated with early renal allograft rejection further supports the potential importance of these antigens in renal transplantation and allograft rejection. PMID:23286555

  12. Large-scale gas dynamics in the adhesion model: implications for the two-phase massive galaxy formation scenario

    NASA Astrophysics Data System (ADS)

    Domínguez-Tenreiro, R.; Oñorbe, J.; Martínez-Serrano, F.; Serna, A.

    2011-06-01

    implications for diffuse or shocked mass elements), as well as on their possible observational implications, these patterns have been confronted with some generic properties of singular flows as described by the adhesion model (i.e. potential character of the velocity field, singular versus regular points, dressing, locality when a spectrum of perturbations is implemented). We have found that the common patterns the simulations show can be interpreted as a natural consequence of flow properties that, moreover, could explain different generic observational results from massive galaxies or their samples. We briefly discuss some of them.

  13. Galaxies in X-Ray Selected Clusters and Groups in Dark Energy Survey Data. I. Stellar Mass Growth of Bright Central Galaxies since z~1.2

    NASA Astrophysics Data System (ADS)

    Zhang, Y.; Miller, C.; McKay, T.; Rooney, P.; Evrard, A. E.; Romer, A. K.; Perfecto, R.; Song, J.; Desai, S.; Mohr, J.; Wilcox, H.; Bermeo-Hernandez, A.; Jeltema, T.; Hollowood, D.; Bacon, D.; Capozzi, D.; Collins, C.; Das, R.; Gerdes, D.; Hennig, C.; Hilton, M.; Hoyle, B.; Kay, S.; Liddle, A.; Mann, R. G.; Mehrtens, N.; Nichol, R. C.; Papovich, C.; Sahlén, M.; Soares-Santos, M.; Stott, J.; Viana, P. T.; Abbott, T.; Abdalla, F. B.; Banerji, M.; Bauer, A. H.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Carnero Rosell, A.; Castander, F. J.; Diehl, H. T.; Doel, P.; Cunha, C. E.; Eifler, T. F.; Fausti Neto, A.; Fernandez, E.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gaztanaga, E.; Gruen, D.; Gruendl, R. A.; Honscheid, K.; James, D.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Maia, M. A. G.; Makler, M.; Marshall, J. L.; Martini, Paul; Miquel, R.; Ogando, R.; Plazas, A. A.; Roodman, A.; Rykoff, E. S.; Sako, M.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla, I.; Smith, R. C.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Tucker, D.; Vikram, V.; da Costa, L. N.

    2016-01-01

    Using the science verification data of the Dark Energy Survey for a new sample of 106 X-ray selected clusters and groups, we study the stellar mass growth of bright central galaxies (BCGs) since redshift z ~ 1.2. Compared with the expectation in a semi-analytical model applied to the Millennium Simulation, the observed BCGs become under-massive/under-luminous with decreasing redshift. We incorporate the uncertainties associated with cluster mass, redshift, and BCG stellar mass measurements into an analysis of a redshift-dependent BCG-cluster mass relation, {m}*\\propto {≤ft(\\frac{{M}200}{1.5× {10}14{M}⊙ }\\right)}0.24+/- 0.08{(1+z)}-0.19+/- 0.34, and compare the observed relation to the model prediction. We estimate the average growth rate since z = 1.0 for BCGs hosted by clusters of M200,z = 1013.8 M⊙ at z = 1.0: m*,BCG appears to have grown by 0.13 ± 0.11 dex, in tension at the ˜2.5σ significance level with the 0.40 dex growth rate expected from the semi-analytic model. We show that the build-up of extended intracluster light after z = 1.0 may alleviate this tension in BCG growth rates.

  14. Galaxy NGC 55

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the 'local group' of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy.

  15. VizieR Online Data Catalog: Compact groups of galaxies in SDSS DR7 (Mendel+, 2011)

    NASA Astrophysics Data System (ADS)

    Mendel, J. T.; Ellison, S. L.; Simard, L.; Patton, D. R.; McConnachie, A. W.

    2012-07-01

    In Paper III (Cat. J/MNRAS/395/255) we describe the photometric selection of CGs from the SDSS Data Release 6 (Adelman-McCarthy et al., 2008, Cat. II/282/), which included imaging of the entire SDSS-II Legacy Survey area. Since that paper, SDSS Data Release 7 (DR7; Abazajian et al., 2009ApJS..182..543A) has provided an additional ~1200deg2 of spectroscopic data, completing spectroscopic observations of the SDSS-II Legacy Survey footprint. In what follows we use galaxy catalogues drawn from SDSS DR7 and, where available, supplement the CG samples in Paper III with updated spectroscopic information. (2 data files).

  16. The X-ray Zurich environmental study (X-zens). I. Chandra and XMM-Newton observations of active galactic nuclei in galaxies in nearby groups

    SciTech Connect

    Silverman, J. D.; Miniati, F.; Carollo, C. M.; Cibinel, A.; Lilly, S. J.; Schawinski, K.; Finoguenov, A.

    2014-01-01

    We describe X-ray observations with Chandra and XMM-Newton of 18 M {sub group} ∼ 1-6 × 10{sup 13} M {sub ☉}, z ∼ 0.05 galaxy groups from the Zurich ENvironmental Study. The X-ray data aim at establishing the frequency and properties, unaffected by host galaxy dilution and obscuration, of active galactic nuclei (AGNs) in central and satellite galaxies, also as a function of halo-centric distance. X-ray point-source detections are reported for 22 of the 177 galaxies, down to a sensitivity level of f {sub 0.5} {sub –} {sub 8} {sub keV} ∼ 5 × 10{sup –15} erg cm{sup –2} s{sup –1}, corresponding to a limiting luminosity of L {sub 0.5} {sub –} {sub 8} {sub keV} ∼ 3 × 10{sup 40} erg s{sup –1}. With the majority of the X-ray sources attributed to AGNs of low-to-moderate levels (L/L {sub Edd} ≳ 10{sup –4}), we discuss the detection rate in the context of the occupation of AGNs to halos of this mass scale and redshift and compare the structural and morphological properties between AGN-active and non-active galaxies. At galaxy mass scales <10{sup 11} M {sub ☉}, central galaxies appear to be a factor of ∼4 more likely to host AGNs than satellite galaxies of similar mass. This effect, coupled with the tendency for AGNs to be hosted by massive galaxies, explains the (weak) trend for AGNs to be preferentially found in the inner parts of group halos, with no detectable trend with halo-centric distance in the frequency of AGNs within the satellite population. Finally, our data indicate that the rate of decline with redshift of AGN activity in galaxy groups matches that of the global AGN population, indicating that either AGN activity occurs preferentially in group halos or that the evolution rate is independent of halo mass.

  17. Childhood Memories and Receptivity to Corrective Feedback in Group Supervision: Implications for Group Work

    ERIC Educational Resources Information Center

    Alexander, Angela; Hulse-Killacky, Diana

    2005-01-01

    This article presents findings from an exploration into supervisees' perspectives on childhood memories and receptivity to corrective feedback in group supervision. Historically, students' receptivity to corrective feedback has not been explored relative to their childhood memories. Ten graduate students from four practicum groups participated in…

  18. A Robust Test of the Unified Model for Seyfert Galaxies with Implications for the Starburst Phenomenon

    NASA Technical Reports Server (NTRS)

    Weaver, Kimberly A.

    1997-01-01

    My research involves detailed analysis of X-ray emission from Active Galactic Nuclei (AGN). For over a decade, the paradigm for AGN has rested soundly on the unified model hypothesis, which posits that the only difference between broad-line objects (e.g., Type 1 Seyfert galaxies) and narrow-line objects (e.g., Type 2 Seyferts) is that in the former case our line of sight evades toroidal obscuration surrounding the nucleus, while in the latter, our line of sight is blocked by the optically thick torus. It is well established that some Seyfert 2s contain Seyfert I nuclei (i.e., a hidden broad line region), but whether or not all Seyfert 2s contain obscured Seyfert 1 nuclei or whether some Seyfert 2s are intrinsically Seyfert 2s is not known. Optical, IR, and UV surveys are not appropriate to examine this hypothesis because such emissions are either anisotropic or subject to the effects of obscuration, and thus depend strongly on viewing angle. Hard X-rays, on the other hand, can penetrate gas with column densities as high as 10( exp 24.5) cm(-2) and thus provide reliable, direct probes of the cores of heavily obscured AGN. Combining NASA archival data from the Advanced Satellite of Cosmology and Astrophysics (ASCA), the Rossi X-ray Timing Explorer (RXTE), and Rosat, I am accumulating X-ray data between 0.1 and 60 keV to produce a catalog of the broad-band X-ray spectral properties of Seyfert galaxies. These data will be used to perform concrete tests of the unified model, and (compared with similar data on Starbursts) to examine a possible evolutionary connection between Seyfert and Starburst galaxies.

  19. Double Exponential Disks in Irregular Galaxies and Implications for Star Formation Thresholds

    NASA Astrophysics Data System (ADS)

    Hunter, D. A.; Elmegreen, B. G.; Anderson, E.

    2005-12-01

    V-band imaging as part of a large multi-wavelength survey of irregular (Im), Magellanic-``spiral'' (Sm), and Blue Compact Dwarf (BCD) galaxies reveals that 28% of the Im and Sm systems have complex surface brightness profiles: an exponential decline of starlight with a break followed by, usually, a steeper exponential in the outer parts. Ultra-deep imaging of two of these systems shows that the outer exponential continues without end to our detection limit of 29 mag of 1 arcsec2. Breaks like this have also been seen in the outer disks of spirals, but the breaks occur at smaller radii in Im galaxies. We reproduce the double exponential profiles with a new model of star formation that combines the Toomre large-scale gravitational instability criterion of the gas with local compression mechanisms. The inner exponential covers the regime where the average gas density is large enough for gravitational instabilities to dominate. The outer exponential occurs where the average gas density drops below the critical threshold for gravitational instabilities, but a low level of turbulence and other local processes occassionally form clouds. Star formation sputters along out there in a patchy fashion that results in a star-forming gradient that is somewhat exponential but steeper than that in the inner disk. This model also predicts that the break radius should be higher in spirals than in Im galaxies, as observed, because spirals have a larger unstable disk. Funding for this work was provided by the Lowell Research Fund and by the National Science Foundation through grants AST-0204922 to DAH and AST-0205097 to BGE.

  20. Redshift Distributions of Galaxies in the DES Science Verification Shear Catalogue and Implications for Weak Lensing

    SciTech Connect

    Bonnett, C.

    2015-07-21

    We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based photometric redshift methods { annz2, bpz calibrated against BCC-U fig simulations, skynet, and tpz { are analysed. For training, calibration, and testing of these methods, we also construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evalu-ated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-zs. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ±0.01 over the range 0:3 < z < 1:3, we construct three tomographic bins with means of z = {0.45; 0.67,1.00g}. These bins each have systematic uncertainties δz ≲ 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of σ8 of approx. 3%. This shift is within the one sigma statistical errors on σ8 for the DES SV shear catalog. We also found that further study of the potential impact of systematic differences on the critical surface density, Σcrit, contained levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0:05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.

  1. An X-Ray, Optical, and Radio Search for Supernova Remnants in the Nearby Sculptor Group Sd Galaxy NGC 7793

    NASA Astrophysics Data System (ADS)

    Pannuti, Thomas G.; Duric, Nebojsa; Lacey, Christina K.; Ferguson, Annette M. N.; Magnor, Marcus A.; Mendelowitz, Caylin

    2002-02-01

    This paper is the second in a series devoted to examining the multiwavelength properties of supernova remnants (SNRs) located in nearby galaxies. We consider here the resident SNRs in the nearby Sculptor group Sd galaxy NGC 7793. Using our own Very Large Array (VLA) radio observations at 6 and 20 cm, as well as archived ROSAT X-ray data, previously published optical results, and our own Hα image, we have searched for X-ray and radio counterparts to previously known optically identified SNRs and for new previously unidentified SNRs at these two wavelength regimes. Consistent with our prior results for NGC 300, only a tiny minority of the optically identified SNRs have been found at another wavelength. The most noteworthy source in our study is N7793-S26, which is the only SNR in this galaxy that is detected at all three wavelengths (X-ray, optical, and radio). It features a long (~450 pc) filamentary morphology that is clearly seen in both the optical and the radio images. N7793-S26's radio luminosity exceeds that of the Galactic SNR Cas A, and based on equipartition calculations we determine that an energy of at least 1052 ergs is required to maintain this source. Such a result argues for the source being created by multiple supernova explosions rather than by a single supernova event. A second optically identified SNR, N7793-S11, has detectable radio emission but no detectable X-ray emission. A radio-selected sample of candidate SNRs has also been prepared by searching for coincidences between nonthermal radio sources and regions of Hα emission in this galaxy. This search has produced five new candidate radio SNRs to be added to the 28 SNRs that have already been detected by optical methods. A complementary search for new candidate X-ray SNRs has also been conducted by searching for soft-spectrum sources (kT<1 keV) that are coincident with regions of Hα emission. That search has yielded a candidate X-ray SNR that is coincident with one (and possibly two) of the

  2. Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton

    NASA Astrophysics Data System (ADS)

    Sanders, J. S.; Fabian, A. C.; Smith, R. K.

    2011-01-01

    Using the width of emission lines in XMM-Newton Reflection Grating Spectrometer spectra, we place direct constraints on the turbulent velocities of the X-ray emitting medium in the cores of 62 galaxy clusters, groups and elliptical galaxies. We find five objects where we can place an upper limit on the line-of-sight broadening of 500 km s-1 (90 per cent confidence level), using a single thermal component model. Two other objects are lower than this limit when two thermal components are used. Half of the objects examined have an upper limit on the velocity broadening of less than 700 km s-1. To look for objects which have significant turbulent broadening, we use Chandra spectral maps to compute the expected broadening caused by the spatial extent of the source. Comparing these with our observed results, we find that Klemola 44 has extra broadening at the level of 1500 km s-1. RX J1347.5-1145 shows weak evidence for turbulent velocities at 800 km s-1. In addition we obtain limits on turbulence for Zw 3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less than 200 km s-1. After subtraction of the spatial contribution and including a 50 km s-1 systematic uncertainty, we find at least 15 sources with less than 20 per cent of the thermal energy density in turbulence.

  3. Velocity width measurements of the coolest X-ray emitting material in the cores of clusters, groups and elliptical galaxies

    NASA Astrophysics Data System (ADS)

    Sanders, J. S.; Fabian, A. C.

    2013-03-01

    We examine the velocity width of cool X-ray emitting material using XMM-Newton Reflection Grating Spectrometer (RGS) spectra of a sample of clusters and group of galaxies and elliptical galaxies. Improving on our previous analyses, we apply a spectral model which accounts for broadening due to the spatial extent of the source. With both conventional and Markov Chain Monte Carlo approaches we obtain limits, or in a few cases measurements, of the velocity broadening of the coolest X-ray material. In our sample, we include new observations targeting objects with compact, bright, line-rich cores. One of these, MACS J2229.7-2755, gives a velocity limit of 280 km s^{-1} at the 90 per cent confidence level. Other systems with limits close to 300 km s^{-1} include A 1835, NGC 4261 and NGC 4472. For more than a third of the targets we find limits better than 500 km s^{-1} . HCG 62, NGC 1399 and A 3112 show evidence for {˜ } 400 km s^{-1} velocity broadening. For a smaller sample of objects, we use continuum-subtracted emission line surface brightness profiles to account for the spatial broadening. Although there are significant systematic errors associated with the technique ({˜ } 150 km s^{-1} ), we find broadening at the level of 280 to 500 km s^{-1} in A 3112, NGC 1399 and NGC 4636.

  4. VizieR Online Data Catalog: Mass and luminosity of maxBCG galaxies groups (Proctor+, 2015)

    NASA Astrophysics Data System (ADS)

    Proctor, R. N.; Mendes de Oliveira, C.; Azanha, L.; Dupke, R.; Overzier, R.

    2015-11-01

    Our sample was selected from groups identified in the maxBCG catalogue of Koester et al. (2007, Cat. J/ApJ/660/239). This catalogue was constructed from the SDSS photometric survey using a cluster finding algorithm based on three well-defined properties of galaxies in clusters: spatial clustering, the presence of a "red-sequence" and the presence of a brightest cluster galaxy(BCG) at the centre of the cluster (Koester et al., 2007ApJ...660..221K). Using this method, Koester et al. (2007, Cat. J/ApJ/660/239) identify more than 13000 clusters. Using DR9 of the SDSS-III (Ahn et al., 2012ApJS..203...21A, Cat. V/139), we then selected all the clusters from the maxBCG catalogue that have a BCG with a spectroscopic redshift in the redshift interval z=0.05-0.16 and possessing six or more spectroscopically confirmed members. (1 data file).

  5. THE GALAXY-HALO/SUBHALO CONNECTION: MASS RELATIONS AND IMPLICATIONS FOR SOME SATELLITE OCCUPATIONAL DISTRIBUTIONS

    SciTech Connect

    Rodriguez-Puebla, A.; Avila-Reese, V.; Drory, N.

    2013-04-10

    We infer the local stellar-to-halo/subhalo mass relations (MRs) for central and satellite galaxies separately. Our statistical method is an extension of the abundance matching, halo occupation distribution, and conditional stellar mass function formalisms. We constrain the model using several combinations of observational data, consisting of the total galaxy stellar mass function (GSMF), its decomposition into centrals and satellites, and the projected two-point correlation functions (2PCFs) measured in different stellar mass (M{sub *}) bins. In addition, we use the {Lambda}CDM halo and subhalo mass functions. The differences among the resulting MRs are within the model-fit uncertainties (which are very small, smaller than the intrinsic scatter between galaxy and halo mass), no matter what combination of data are used. This shows that matching abundances or occupational numbers is equivalent, and that the GSMFs and 2PCFs are tightly connected. We also constrain the values of the intrinsic scatter around the central-halo (CH) and satellite-subhalo (SS) MRs assuming them to be constant: {sigma}{sub c} = 0.168 {+-} 0.051 dex and {sigma}{sub s} = 0.172 {+-} 0.057 dex, respectively. The CH and SS MRs are actually different, in particular when we take the subhalo mass at the present-day epoch instead of at their accretion time. When using the MRs for studying the satellite population (e.g., in the Milky Way, MW), the SS MR should be chosen instead of the average one. Our model allows one to calculate several population statistics. We find that the central galaxy M{sub *} is not on average within the mass distribution of the most massive satellite, even for cluster-sized halos, i.e., centrals are not a mere realization of the high end of the satellite mass function; however for >3 Multiplication-Sign 10{sup 13} M{sub Sun} halos, {approx}15% of centrals could be. We also find that the probabilities of MW-sized halos of having N Magellanic Cloud (MC) sized satellites agree

  6. Chandra and XMM Observations of Galaxy Groups: The Influence of Central AGN at the Low End of the Cluster Mass Scale

    NASA Astrophysics Data System (ADS)

    Vrtilek, J. M.; O'Sullivan, E. J.; David, L. P.

    2007-05-01

    Groups and poor clusters are the locus of most galaxies in the present-day Universe; they shape the environment in which the bulk of galaxies evolve and constitute the building blocks from which clusters form. Hot X-ray emitting gas in galaxy groups, especially those dominated by ellipticals, is both a significant constituent of the total mass and an active participant in the group evolution. Chandra and XMM, offering between them high angular resolution, substantial collecting area, and spatially-resolved spectroscopy at good spectral resolution, have given us the means to discover hitherto unanticipated phenomena, in groups as in clusters, and to explore a new set of issues that bring us closer to understanding the evolution of groups and their constituent galaxies: the distribution of heavy elements, the presence of X-ray cavities and their relation to radio observations, the nature of cooling cores, and X-ray signatures of recent galaxy interactions. We here show Chandra and XMM data selected to illustrate recent results regarding some of these themes. Examples include: • Two 2keV poor clusters initially selected for XMM observations owing to their regular and relaxed appearance, MKW 4 and AWM 4, are revealed to be very different: MKW 4 seems quiescent and has developed a cool core, unlike AWM 4, which is disturbed in temperature and abundance distribution, a difference traceable to AGN activity at the center of AWM 4. • NGC 4636 exhibits a plume of high-abundance gas extending from the galaxy, likely the result of an AGN outburst producing significant gas mixing. • The temperature profile of NGC 3411 is that of a normal group with a cooling core except at the very center, where a sharp rise suggests recent AGN reheating.

  7. Some Like it Hot: Linking Diffuse X-Ray Luminosity, Baryonic Mass, and Star Formation Rate in Compact Groups of Galaxies

    NASA Technical Reports Server (NTRS)

    Desjardins, Tyler D.; Gallagher, Sarah C.; Hornschemeier, Ann E.; Mulchaey, John S.; Walker, Lisa May; Brandt, Willian N.; Charlton, Jane C.; Johnson, Kelsey E.; Tzanavaris, Panayiotis

    2014-01-01

    We present an analysis of the diffuse X-ray emission in 19 compact groups (CGs) of galaxies observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in L(x-T) and (L(x-sigma), even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify Hickson CGs 19, 22, 40, and 42, and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and Hi masses are great than or equal to 10(sup (11.3) solar mass are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 micron star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due togas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies.

  8. Some like it hot: Linking diffuse X-ray luminosity, baryonic mass, and star formation rate in compact groups of galaxies

    SciTech Connect

    Desjardins, Tyler D.; Gallagher, Sarah C.; Hornschemeier, Ann E.; Tzanavaris, Panayiotis; Walker, Lisa May; Johnson, Kelsey E.; Brandt, William N.; Charlton, Jane C.

    2014-08-01

    We present an analysis of the diffuse X-ray emission in 19 compact groups (CGs) of galaxies observed with Chandra. The hottest, most X-ray luminous CGs agree well with the galaxy cluster X-ray scaling relations in L{sub X} -T and L{sub X} -σ, even in CGs where the hot gas is associated with only the brightest galaxy. Using Spitzer photometry, we compute stellar masses and classify Hickson CGs 19, 22, 40, and 42, and RSCGs 32, 44, and 86 as fossil groups using a new definition for fossil systems that includes a broader range of masses. We find that CGs with total stellar and H I masses ≳ 10{sup 11.3} M{sub ☉} are often X-ray luminous, while lower-mass CGs only sometimes exhibit faint, localized X-ray emission. Additionally, we compare the diffuse X-ray luminosity against both the total UV and 24 μm star formation rates of each CG and optical colors of the most massive galaxy in each of the CGs. The most X-ray luminous CGs have the lowest star formation rates, likely because there is no cold gas available for star formation, either because the majority of the baryons in these CGs are in stars or the X-ray halo, or due to gas stripping from the galaxies in CGs with hot halos. Finally, the optical colors that trace recent star formation histories of the most massive group galaxies do not correlate with the X-ray luminosities of the CGs, indicating that perhaps the current state of the X-ray halos is independent of the recent history of stellar mass assembly in the most massive galaxies.

  9. Variable stars in Local Group Galaxies - II. Sculptor dSph

    NASA Astrophysics Data System (ADS)

    Martínez-Vázquez, C. E.; Stetson, P. B.; Monelli, M.; Bernard, E. J.; Fiorentino, G.; Gallart, C.; Bono, G.; Cassisi, S.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Walker, A. R.

    2016-08-01

    We present the identification of 634 variable stars in the Milky Way dSph satellite Sculptor based on archival ground-based optical observations spanning ˜24 years and covering ˜ 2.5 deg2. We employed the same methodologies as the "Homogeneous Photometry" series published by Stetson. In particular, we have identified and characterized the largest (536) RR Lyrae sample so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally we identify 37 Long Period Variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (˜1.5M⊙) and SX Phoenicis stars (˜1M⊙). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.

  10. RR LYRAE VARIABLES IN THE LOCAL GROUP DWARF GALAXY NGC 147

    SciTech Connect

    Yang, S-C.; Sarajedini, Ata E-mail: ata@astro.ufl.ed

    2010-01-01

    We investigate the RR Lyrae (RRL) population in NGC 147, a dwarf satellite galaxy of M31 (Andromeda). We used both Thuan-Gunn g-band ground-based photometry from the literature and Hubble Space Telescope Wide Field Planetary Camera 2 archival data in the F555W and F814W passbands to investigate the pulsation properties of RRL variable candidates in NGC 147. These data sets represent the two extreme cases often found in RRL studies with respect to the phase coverage of the observations and the quality of the photometric measurements. Extensive artificial variable star tests for both cases were performed. We conclude that neither data set is sufficient to confidently determine the pulsation properties of the NGC 147 RRLs. Thus, while we can assert that NGC 147 contains RRL variables, and therefore a population older than approx10 Gyr, it is not possible at this time to use the pulsation properties of these RRLs to study other aspects of this old population. Our results provide a good reference for gauging the completeness of RRL variable detection in future studies.

  11. Stellar populations in local group dwarf elliptical galaxies. I - NGC 147

    NASA Technical Reports Server (NTRS)

    Mould, J. R.; Kristian, J.; Da Costa, G. S.

    1983-01-01

    A color-magnitude diagram of NGC 147 to an I magnitude of 23 is presented. The stellar population in the outer parts of this elliptical galaxy resembles that of the globular clusters of the Milky Way. Quantitative comparison of the giant branch with those of globular clusters yields a mean metallicity of -1.2 + or - 0.2, making NGC 147 a part of the general correlation between mass and metallicity seen in ellipticals. The giant branch appears to be broad, which suggests a metallicity dispersion. The absence of asymptotic giant branch stars at luminosities above that of the red giant branch tip sets an upper limit of 10 percent for the fraction of stars in this NGC 147 field that have ages less than 12 Gyr. This result contrasts with the situation in some of the related, but less massive, dwarf spheroidal systems. If the choice is made to assume, rather than determine the stellar content of NGC 147, a distance of 630 + or - 50 kpc is derived, similar to that of M31.

  12. Variable stars in Local Group Galaxies - II. Sculptor dSph

    NASA Astrophysics Data System (ADS)

    Martínez-Vázquez, C. E.; Stetson, P. B.; Monelli, M.; Bernard, E. J.; Fiorentino, G.; Gallart, C.; Bono, G.; Cassisi, S.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Walker, A. R.

    2016-11-01

    We present the identification of 634 variable stars in the Milky Way dwarf spheroidal (dSph) satellite Sculptor based on archival ground-based optical observations spanning ˜24 yr and covering ˜2.5 deg2. We employed the same methodologies as the `Homogeneous Photometry' series published by Stetson. In particular, we have identified and characterized one of the largest (536) RR Lyrae samples so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally, we identify 37 long period variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (˜1.5 M⊙) and SX Phoenicis stars (˜1 M⊙). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.

  13. J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

    NASA Astrophysics Data System (ADS)

    Schirmer, M.; Suyu, S.; Schrabback, T.; Hildebrandt, H.; Erben, T.; Halkola, A.

    2010-05-01

    Aims: We have discovered a strong lensing fossil group (J0454) projected near the well-studied cluster MS0451-0305. Using the large amount of available archival data, we compare J0454 to normal groups and clusters. A highly asymmetric image configuration of the strong lens enables us to study the substructure of the system. Methods: We used multicolour Subaru/Suprime-Cam and CFHT/Megaprime imaging, together with Keck spectroscopy to identify member galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the brightest elliptical and the lensed arc. Using HST/ACS images, we determined the group's weak lensing signal and modelled the strong lens system. This is the first time that a fossil group is analysed with lensing methods. The X-ray luminosity and temperature were derived from XMM-Newton data. Results: J0454 is located at z = 0.26, with a gap of 2.5 mag between the brightest and second brightest galaxies within half the virial radius. Outside a radius of 1.5 Mpc, we find two filaments extending over 4 Mpc, and within we identify 31 members spectroscopically and 33 via the red sequence with i < 22 mag. They segregate into spirals (σ_v = 590 km s-1) and a central concentration of ellipticals (σ_v = 480 km s-1), establishing a morphology-density relation. Weak lensing and cluster richness relations yield consistent values of r200 = 810-850 kpc and M200 = (0.75-0.90) × 1014 M_⊙. The brightest group galaxy (BGG) is inconsistent with the dynamic centre of J0454. It strongly lenses a galaxy at z = 2.1 ± 0.3, and we model the lens with a pseudo-isothermal elliptical mass distribution. A high external shear, and a discrepancy between the Einstein radius and the weak lensing velocity dispersion requires that the BGG must be offset from J0454's dark halo centre by at least 90-130 kpc. The X-ray halo is offset by 24 ± 16 kpc from the BGG, shows no signs of a cooling flow and can be fit by a single β-model. With LX = (1.4 ± 0.2) × 1043 erg s-1 J0454

  14. Hot Gaseous Atmospheres in Galaxy Groups and Clusters Are Both Heated and Cooled by X-Ray Cavities

    NASA Astrophysics Data System (ADS)

    Brighenti, Fabrizio; Mathews, William G.; Temi, Pasquale

    2015-04-01

    Expanding X-ray cavities observed in hot gas atmospheres of many galaxy groups and clusters generate shock waves and turbulence that are primary heating mechanisms required to avoid uninhibited radiatively cooling flows which are not observed. However, we show here that the evolution of buoyant cavities also stimulates radiative cooling of observable masses of low-temperature gas. During their early evolution, radiative cooling occurs in the wakes of buoyant cavities in two locations: in thin radial filaments parallel to the buoyant velocity and more broadly in gas compressed beneath rising cavities. Radiation from these sustained compressions removes entropy from the hot gas. Gas experiencing the largest entropy loss cools first, followed by gas with progressively less entropy loss. Most cooling occurs at late times, ˜ 108-109 yr, long after the X-ray cavities have disrupted and are impossible to detect. During these late times, slightly denser low entropy gas sinks slowly toward the centers of the hot atmospheres where it cools intermittently, forming clouds near the cluster center. Single cavities of energy 1057-1058 ergs in the atmosphere of the NGC 5044 group create 108-109 M⊙ of cooled gas, exceeding the mass of extended molecular gas currently observed in that group. The cooled gas clouds we compute share many attributes with molecular clouds recently observed in NGC 5044 with ALMA: self-gravitationally unbound, dust-free, quasi-randomly distributed within a few kiloparsecs around the group center.

  15. VizieR Online Data Catalog: Choirs, HI galaxy groups (Sweet+, 2013)

    NASA Astrophysics Data System (ADS)

    Sweet, S. M.; Meurer, G.; Drinkwater, M. J.; Kilborn, V.; Denes, H.; Bekki, K.; Hanish, D.; Ferguson, H.; Knezek, P.; Bland-Hawthorn, J.; Dopita, M.; Doyle-Pegg, M. T.; Elson, E.; Freeman, K.; Heckman, T.; Kennicutt, R.; Kim, J. H.; Koribalski, B.; Meyer, M.; Putman, M.; Ryan-Weber, E.; Smith, C.; Staveley-Smith, L.; Wong, O. I.; Webster, R.; Werk, J.; Zwaan, M.

    2014-07-01

    Our sample is drawn from the 292 HiPASS targets observed for SINGG. HI measurements are all from the HiPASS HI catalogue HICAT (Meyer et al. 2004MNRAS.350.1195M, Cat. VIII/73), except for two groups (HiPASS J0443-05 and J1059-09). After noticing an anomalous HI mass for one group, we manually remeasured the HI mass of every Choir group. (2 data files).

  16. CLUSTERING OF SLOAN DIGITAL SKY SURVEY III PHOTOMETRIC LUMINOUS GALAXIES: THE MEASUREMENT, SYSTEMATICS, AND COSMOLOGICAL IMPLICATIONS

    SciTech Connect

    Ho, Shirley; White, Martin; Schlegel, David J.; Seljak, Uros; Reid, Beth; Cuesta, Antonio; Padmanabhan, Nikhil; Seo, Hee-Jong; De Putter, Roland; Ross, Ashley J.; Percival, Will J.; Saito, Shun; Schlafly, Eddie; Hernandez-Monteagudo, Carlos; Sanchez, Ariel G.; Blanton, Michael; Skibba, Ramin; Schneider, Don; Mena, Olga; Viel, Matteo; and others

    2012-12-10

    The Sloan Digital Sky Survey (SDSS) surveyed 14,555 deg{sup 2}, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between z = 0.45 and z = 0.65, constructed from the SDSS using methods described in Ross et al. This data set spans 11,000 deg{sup 2} and probes a volume of 3 h {sup -3} Gpc{sup 3}, making it the largest volume ever used for galaxy clustering measurements. We describe in detail the construction of the survey window function and various systematics affecting our measurement. With such a large volume, high-precision cosmological constraints can be obtained given careful control and understanding of the observational systematics. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at four redshift slices with an accuracy of {approx}15%, with a bin size of {delta}{sub l} = 10 on scales of the baryon acoustic oscillations (BAOs; at l {approx} 40-400). We also apply corrections to the power spectra due to systematics and derive cosmological constraints using the full shape of the power spectra. For a flat {Lambda}CDM model, when combined with cosmic microwave background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H{sub 0} constraints from using 600 Cepheids observed by Wide Field Camera 3 (WFC3; HST), we find {Omega}{sub {Lambda}} = 0.73 {+-} 0.019 and H{sub 0} to be 70.5 {+-} 1.6 s{sup -1} Mpc{sup -1} km. For an open {Lambda}CDM model, when combined with WMAP7 + HST, we find {Omega}{sub K} = 0.0035 {+-} 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 {+-} 0.078, and H{sub 0} to be 71.3 {+-} 1.7 s{sup -1} Mpc{sup -1} km, which is competitive with the latest large-scale structure constraints from large spectroscopic

  17. Clustering of Sloan Digital Sky Survey III Photometric Luminous Galaxies: The Measurement, Systematics, and Cosmological Implications

    NASA Astrophysics Data System (ADS)

    Ho, Shirley; Cuesta, Antonio; Seo, Hee-Jong; de Putter, Roland; Ross, Ashley J.; White, Martin; Padmanabhan, Nikhil; Saito, Shun; Schlegel, David J.; Schlafly, Eddie; Seljak, Uros; Hernández-Monteagudo, Carlos; Sánchez, Ariel G.; Percival, Will J.; Blanton, Michael; Skibba, Ramin; Schneider, Don; Reid, Beth; Mena, Olga; Viel, Matteo; Eisenstein, Daniel J.; Prada, Francisco; Weaver, Benjamin A.; Bahcall, Neta; Bizyaev, Dimitry; Brewinton, Howard; Brinkman, Jon; Nicolaci da Costa, Luiz; Gott, John R.; Malanushenko, Elena; Malanushenko, Viktor; Nichol, Bob; Oravetz, Daniel; Pan, Kaike; Palanque-Delabrouille, Nathalie; Ross, Nicholas P.; Simmons, Audrey; de Simoni, Fernando; Snedden, Stephanie; Yeche, Christophe

    2012-12-01

    The Sloan Digital Sky Survey (SDSS) surveyed 14,555 deg2, and delivered over a trillion pixels of imaging data. We present a study of galaxy clustering using 900,000 luminous galaxies with photometric redshifts, spanning between z = 0.45 and z = 0.65, constructed from the SDSS using methods described in Ross et al. This data set spans 11,000 deg2 and probes a volume of 3 h -3 Gpc3, making it the largest volume ever used for galaxy clustering measurements. We describe in detail the construction of the survey window function and various systematics affecting our measurement. With such a large volume, high-precision cosmological constraints can be obtained given careful control and understanding of the observational systematics. We present a novel treatment of the observational systematics and its applications to the clustering signals from the data set. In this paper, we measure the angular clustering using an optimal quadratic estimator at four redshift slices with an accuracy of ~15%, with a bin size of δ l = 10 on scales of the baryon acoustic oscillations (BAOs; at l ~ 40-400). We also apply corrections to the power spectra due to systematics and derive cosmological constraints using the full shape of the power spectra. For a flat ΛCDM model, when combined with cosmic microwave background Wilkinson Microwave Anisotropy Probe 7 (WMAP7) and H 0 constraints from using 600 Cepheids observed by Wide Field Camera 3 (WFC3; HST), we find ΩΛ = 0.73 ± 0.019 and H 0 to be 70.5 ± 1.6 s-1 Mpc-1 km. For an open ΛCDM model, when combined with WMAP7 + HST, we find Ω K = 0.0035 ± 0.0054, improved over WMAP7+HST alone by 40%. For a wCDM model, when combined with WMAP7+HST+SN, we find w = -1.071 ± 0.078, and H 0 to be 71.3 ± 1.7 s-1 Mpc-1 km, which is competitive with the latest large-scale structure constraints from large spectroscopic surveys such as the SDSS Data Release 7 (DR7) and WiggleZ. We also find that systematic-corrected power spectra give consistent

  18. EARLY-TYPE GALAXIES AT z = 1.3. I. THE LYNX SUPERCLUSTER: CLUSTER AND GROUPS AT z = 1.3. MORPHOLOGY AND COLOR-MAGNITUDE RELATION

    SciTech Connect

    Mei, Simona; Raichoor, Anand; Huertas-Company, Marc; Adam Stanford, S.; Rettura, Alessandro; Jee, Myungkook J.; Holden, Brad P.; Illingworth, Garth D.; Nakata, Fumiaki; Kodama, Tadayuki; Finoguenov, Alexis; Ford, Holland C.; Rosati, Piero; Tanaka, Masayuki; Koyama, Yusei; Shankar, Francesco; Carrasco, Eleazar R.; Demarco, Ricardo; Eisenhardt, Peter; and others

    2012-08-01

    We confirm the detection of three groups in the Lynx supercluster, at z Almost-Equal-To 1.3, through spectroscopic follow-up and X-ray imaging, and we give estimates for their redshifts and masses. We study the properties of the group galaxies compared to the two central clusters, RX J0849+4452 and RX J0848+4453. Using spectroscopic follow-up and multi-wavelength photometric redshifts, we select 89 galaxies in the clusters, of which 41 are spectroscopically confirmed, and 74 galaxies in the groups, of which 25 are spectroscopically confirmed. We morphologically classify galaxies by visual inspection, noting that our early-type galaxy (ETG) sample would have been contaminated at the 30%-40% level by simple automated classification methods (e.g., based on Sersic index). In luminosity-selected samples, both clusters and groups show high fractions of bulge-dominated galaxies with a diffuse component that we visually identified as a disk and which we classified as bulge-dominated spirals, e.g., Sas. The ETG fractions never rise above Almost-Equal-To 50% in the clusters, which is low compared to the fractions observed in other massive clusters at z Almost-Equal-To 1. In the groups, ETG fractions never exceed Almost-Equal-To 25%. However, overall bulge-dominated galaxy fractions (ETG plus Sas) are similar to those observed for ETGs in clusters at z {approx} 1. Bulge-dominated galaxies visually classified as spirals might also be ETGs with tidal features or merger remnants. They are mainly red and passive, and span a large range in luminosity. Their star formation seems to have been quenched before experiencing a morphological transformation. Because their fraction is smaller at lower redshifts, they might be the spiral population that evolves into ETGs. For mass-selected samples of galaxies with masses M > 10{sup 10.6} M{sub Sun} within {Sigma} > 500 Mpc{sup -2}, the ETG and overall bulge-dominated galaxy fractions show no significant evolution with respect to local

  19. VERY STRONG EMISSION-LINE GALAXIES IN THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY AND IMPLICATIONS FOR HIGH-REDSHIFT GALAXIES

    SciTech Connect

    Atek, H.; Colbert, J.; Shim, H.; Siana, B.; Bridge, C.; Scarlata, C.; Malkan, M.; Ross, N. R.; McCarthy, P.; Dressler, A.; Hathi, N. P.; Teplitz, H.; Henry, A.; Martin, C.; Bunker, A. J.; Fosbury, R. A. E.

    2011-12-20

    The WFC3 Infrared Spectroscopic Parallel Survey uses the Hubble Space Telescope (HST) infrared grism capabilities to obtain slitless spectra of thousands of galaxies over a wide redshift range including the peak of star formation history of the universe. We select a population of very strong emission-line galaxies with rest-frame equivalent widths (EWs) higher than 200 A. A total of 176 objects are found over the redshift range 0.35 < z < 2.3 in the 180 arcmin{sup 2} area that we have analyzed so far. This population consists of young and low-mass starbursts with high specific star formation rates (sSFR). After spectroscopic follow-up of one of these galaxies with Keck/Low Resolution Imaging Spectrometer, we report the detection at z = 0.7 of an extremely metal-poor galaxy with 12 + log(O/H) =7.47 {+-} 0.11. After estimating the active galactic nucleus fraction in the sample, we show that the high-EW galaxies have higher sSFR than normal star-forming galaxies at any redshift. We find that the nebular emission lines can substantially affect the total broadband flux density with a median brightening of 0.3 mag, with some examples of line contamination producing brightening of up to 1 mag. We show that the presence of strong emission lines in low-z galaxies can mimic the color-selection criteria used in the z {approx} 8 dropout surveys. In order to effectively remove low-redshift interlopers, deep optical imaging is needed, at least 1 mag deeper than the bands in which the objects are detected. Without deep optical data, most of the interlopers cannot be ruled out in the wide shallow HST imaging surveys. Finally, we empirically demonstrate that strong nebular lines can lead to an overestimation of the mass and the age of galaxies derived from fitting of their spectral energy distribution (SED). Without removing emission lines, the age and the stellar mass estimates are overestimated by a factor of 2 on average and up to a factor of 10 for the high-EW galaxies

  20. A revised catalog of CfA galaxy groups in the Virgo/Great Attractor flow field

    NASA Technical Reports Server (NTRS)

    Nolthenius, Richard

    1993-01-01

    A new identification of groups and clusters in the CfAl Catalog of Huchra, et al. (1983) is presented, using a percolation algorithm to identify density enhancements. The procedure differs from that of the original Geller and Huchra (1983; GH) catalog in several important respects; galaxy distances are calculated from the Virgo-Great Attractor flow model of Faber and Burnstein (1988), the adopted distance linkage criteria is only approx. 1/4 as large as in the Geller and Huchra catalog, the sky link relation is taken from Nolthenius and White (1987), correction for interstellar extinction is included, and 'by-hand' adjustments to group memberships are made in the complex regions of Virgo/Coma I/Ursa Major and Coma/A1367 (to allow for varying group velocity dispersions and to trim unphysical 'spider arms'). Since flow model distances are poorly determined in these same regions, available distances from the IR Tully-Fisher planetary nebula luminosity function and surface brightness resolution methods are adopted if possible.

  1. A peculiar Of star in the Local Group galaxy IC 1613

    NASA Astrophysics Data System (ADS)

    Herrero, A.; Garcia, M.; Puls, J.; Uytterhoeven, K.; Najarro, F.; Lennon, D. J.; Rivero-González, J. G.

    2012-07-01

    Context. Results from the theory of radiatively driven winds are nowadays incorporated in stellar evolutionary and population synthesis models, and are used in our interpretation of the observations of the deep Universe. Yet, the theory has been confirmed only until Small Magellanic Cloud metallicities. Observations and analyses of O-stars at lower metallicities are difficult, but much needed to prove the theory. Aims: We have observed GHV-62024, an O6.5 IIIf star in the low-metallicity galaxy IC 1613 (Z ≈ 0.15 Z⊙) to study its evolution and wind. According to a previous preliminary analysis that was subject to significant restrictions this star could challenge the radiatively driven wind theory at low metallicities. Here we present a complete analysis of this star. Methods: Our observations were obtained with VIMOS at VLT, at R ≈ 2000 and covered approximately between 4000 and 7000 Å. The observations were analysed using the latest version of the model atmosphere code FASTWIND, which includes the possibility of calculating the N iii spectrum. Results: We obtain the stellar parameters and conclude that the star follows the average wind momentum-luminosity relationship (WLR) expected for its metallicity, but with a high value for the exponent of the wind velocity law, β. Comparing this with values of other stars in the literature, we suggest that this high value may be reached because GHV-62024 could be a fast rotator seen at a low inclination angle. We also suggest that this could favour the appearance of the spectral "f"-characterictics. While the derived β value does not change by adopting a lower wind terminal velocity, we show that a wrong V∞ has a clear impact on the position of the star in the WLR diagram. The N and He abundances are very high, consistent with strong CNO mixing that could have been caused by the fast rotation, although we cannot discard a different origin with present data. Stellar evolutionary model predictions are consistent with

  2. A CATALOG OF ULTRA-COMPACT HIGH VELOCITY CLOUDS FROM THE ALFALFA SURVEY: LOCAL GROUP GALAXY CANDIDATES?

    SciTech Connect

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P. E-mail: riccardo@astro.cornell.edu

    2013-05-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s{sup -1}, median angular diameters of 10', and median velocity widths of 23 km s{sup -1}. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of {approx}1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of {approx}10{sup 5}-10{sup 6} M{sub Sun }, H I diameters of {approx}2-3 kpc, and indicative dynamical masses within the H I extent of {approx}10{sup 7}-10{sup 8} M{sub Sun }, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  3. Shocks and Cavities from Multiple Outbursts in the Galaxy Group NGC 5813: A Window to Active Galactic Nucleus Feedback

    NASA Astrophysics Data System (ADS)

    Randall, S. W.; Forman, W. R.; Giacintucci, S.; Nulsen, P. E. J.; Sun, M.; Jones, C.; Churazov, E.; David, L. P.; Kraft, R.; Donahue, M.; Blanton, E. L.; Simionescu, A.; Werner, N.

    2011-01-01

    We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. The system shows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc from the central source, from three distinct outbursts of the central active galactic nucleus (AGN), which occurred 3 × 106, 2 × 107, and 9 × 107 yr ago. The Hα and X-ray observations reveal filaments of cool gas that has been uplifted by the X-ray cavities. The inner two cavity pairs are filled with radio-emitting plasma, and each pair is associated with an elliptical surface brightness edge, which we unambiguously identify as shocks (with measured temperature jumps) with Mach numbers of M ≈ 1.7 and M ≈ 1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise dynamically relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts differs by a factor of six, from (1.5-10)×1042 erg s-1, indicating that the mean jet power changes significantly over long (~107 yr) timescales. The total energy output of the most recent outburst is also more than an order of magnitude less than the total energy of the previous outburst (1.5 × 1056 erg versus 4 × 1057 erg), which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. The outburst interval implied by both the shock and cavity ages (~107 yr) indicates that, in this system, shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the intracluster medium and the central supermassive black hole.

  4. A Catalog of Ultra-compact High Velocity Clouds from the ALFALFA Survey: Local Group Galaxy Candidates?

    NASA Astrophysics Data System (ADS)

    Adams, Elizabeth A. K.; Giovanelli, Riccardo; Haynes, Martha P.

    2013-05-01

    We present a catalog of 59 ultra-compact high velocity clouds (UCHVCs) extracted from the 40% complete ALFALFA HI-line survey. The ALFALFA UCHVCs have median flux densities of 1.34 Jy km s-1, median angular diameters of 10', and median velocity widths of 23 km s-1. We show that the full UCHVC population cannot easily be associated with known populations of high velocity clouds. Of the 59 clouds presented here, only 11 are also present in the compact cloud catalog extracted from the commensal GALFA-HI survey, demonstrating the utility of this separate dataset and analysis. Based on their sky distribution and observed properties, we infer that the ALFALFA UCHVCs are consistent with the hypothesis that they may be very low mass galaxies within the Local Volume. In that case, most of their baryons would be in the form of gas, and because of their low stellar content, they remain unidentified by extant optical surveys. At distances of ~1 Mpc, the UCHVCs have neutral hydrogen (H I) masses of ~105-106 M ⊙, H I diameters of ~2-3 kpc, and indicative dynamical masses within the H I extent of ~107-108 M ⊙, similar to the Local Group ultra-faint dwarf Leo T. The recent ALFALFA discovery of the star-forming, metal-poor, low mass galaxy Leo P demonstrates that this hypothesis is true in at least one case. In the case of the individual UCHVCs presented here, confirmation of their extragalactic nature will require further work, such as the identification of an optical counterpart to constrain their distance.

  5. Writing Groups: History, Theory, and Implications: Studies in Writing and Rhetoric.

    ERIC Educational Resources Information Center

    Gere, Anne Ruggles

    Drawing on previously unpublished archival materials as well as historical accounts of American education and the self-help tradition of education in the United States, this book examines the origins, theoretical bases, and implications of writing groups. Following an introduction that points out the varied circumstances under which writing groups…

  6. THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. III. GALAXY PHOTOMETRIC MEASUREMENTS AND THE SPATIALLY RESOLVED COLOR PROPERTIES OF EARLY- AND LATE-TYPE SATELLITES IN DIVERSE ENVIRONMENTS

    SciTech Connect

    Cibinel, A.; Carollo, C. M.; Lilly, S. J.; Miniati, F.; Pipino, A.; Cameron, E.; Peng, Y.; Rudick, C. S.; Bonoli, S.; Silverman, J. D.; Van Gorkom, J. H.; Finoguenov, A.; Norberg, P. E-mail: marcella@phys.ethz.ch

    2013-11-10

    We present photometric measurements for the galaxies—and when possible their bulges and disks—in the 0.05 < z < 0.0585 groups of the Zurich Environmental Study (ZENS); these measurements include (B – I) colors, color gradients and maps, color dispersions, as well as stellar masses and star formation rates. The ZENS galaxies are classified into quenched, moderately star-forming, and strongly star-forming using a combination of spectral features and far-UV-to-optical colors; this approach optimally distinguishes quenched systems from dust-reddened star-forming galaxies. The latter contribute up to 50% to the (B – I) 'red sequence' at ∼10{sup 10} M{sub ☉}. At fixed morphological or spectral type, we find that galaxy stellar masses are largely independent of environment, and especially of halo mass. As a first utilization of our photometric database, we study, at fixed stellar mass and Hubble type, how (B – I) colors, color gradients, and color dispersion of disk satellites depend on group mass M{sub GROUP}, group-centric distance R/R{sub 200}, and large-scale structure overdensity δ{sub LSS}. The strongest environmental trend is found for disk-dominated satellites with M{sub GROUP} and R/R{sub 200}. At M ∼< 10{sup 10} M{sub ☉}, disk-dominated satellites are redder in the inner regions of the groups than in the outer parts. At M ∼> 10{sup 10} M{sub ☉}, these satellites have shallower color gradients in higher mass groups and in the cores of groups compared with lower mass groups and the outskirts of groups. Stellar population analyses and semi-analytic models suggest that disk-dominated satellites undergo quenching of star formation in their outer disks, on timescales τ{sub quench} ∼ 2 Gyr, as they progressively move inside the group potential.

  7. Confining hot spots in 3C 196 - Implications for QSO-companion galaxies

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Broderick, J. J.; Mitchell, K. J.

    1986-01-01

    VLBI observations of the extremely compact hot spot in the northern radio lobe of the QSO 3C 196 reveal the angular size of its smallest substructure to be 0.065 arcsec x 0.045 arcsec or about 300 pc at the redshift distance. The morphology of the hot spot and its orientation relative to the more diffuse radio emission suggest that it is formed by an oblique interaction between the nuclear QSO jet and circum-QSO cloud. The inferred density in this cloud, together with its apparent size, imply that the cloud contains a galactic mass, greater than a billion solar masses of gas. The effect of the jet will be to hasten gravitational collapse of the cloud. If many QSOs such as 3C 196 are formed or found in gas-rich environments, the QSO radio phase may commonly stimulate the metamorphosis of circum-QSO gas to QSO-companion galaxies or it may play a significant part in catalyzing star formation in existing companions.

  8. Confining hot spots in 3C 196 - implications for QSO-companion galaxies

    SciTech Connect

    Brown, R.L.; Broderick, J.J.; Mitchell, K.J.

    1986-07-01

    VLBI observations of the extremely compact hot spot in the northern radio lobe of the QSO 3C 196 reveal the angular size of its smallest substructure to be 0.065 arcsec x 0.045 arcsec or about 300 pc at the redshift distance. The morphology of the hot spot and its orientation relative to the more diffuse radio emission suggest that it is formed by an oblique interaction between the nuclear QSO jet and circum-QSO cloud. The inferred density in this cloud, together with its apparent size, imply that the cloud contains a galactic mass, greater than a billion solar masses of gas. The effect of the jet will be to hasten gravitational collapse of the cloud. If many QSOs such as 3C 196 are formed or found in gas-rich environments, the QSO radio phase may commonly stimulate the metamorphosis of circum-QSO gas to QSO-companion galaxies or it may play a significant part in catalyzing star formation in existing companions. 30 references.

  9. A determination of the thick disk chemical abundance distribution: Implications for galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gilmore, Gerard; Wyse, Rosemary F. G.; Jones, Bryn J.

    1995-01-01

    We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15 less than or approximately = V less than or approximately = 18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000 pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7 dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or greater than or approximately = 12 Gyr, and are consistent with a spread to older ages.

  10. A Measurement of Large-Scale Peculiar Velocities of Clusters of Galaxies: Results and Cosmological Implications

    NASA Astrophysics Data System (ADS)

    Kashlinsky, A.; Atrio-Barandela, F.; Kocevski, D.; Ebeling, H.

    2008-10-01

    Peculiar velocities of clusters of galaxies can be measured by studying the fluctuations in the cosmic microwave background (CMB) generated by the scattering of the microwave photons by the hot X-ray-emitting gas inside clusters. While for individual clusters such measurements result in large errors, a large statistical sample of clusters allows one to study cumulative quantities dominated by the overall bulk flow of the sample with the statistical errors integrating down. We present results from such a measurement using the largest all-sky X-ray cluster catalog combined to date and the 3 yr WMAP CMB data. We find a strong and coherent bulk flow on scales out to at least gsim300 h-1 Mpc, the limit of our catalog. This flow is difficult to explain by gravitational evolution within the framework of the concordance ΛCDM model and may be indicative of the tilt exerted across the entire current horizon by far-away pre-inflationary inhomogeneities.

  11. ENTROPY AT THE OUTSKIRTS OF GALAXY CLUSTERS AS IMPLICATIONS FOR COSMOLOGICAL COSMIC-RAY ACCELERATION

    SciTech Connect

    Fujita, Yutaka; Ohira, Yutaka; Yamazaki, Ryo

    2013-04-10

    Recently, gas entropy at the outskirts of galaxy clusters has attracted much attention. We propose that the entropy profiles could be used to study cosmic-ray (CR) acceleration around the clusters. If the CRs are effectively accelerated at the formation of clusters, the kinetic energy of infalling gas is consumed by the acceleration and the gas entropy should decrease. As a result, the entropy profiles become flat at the outskirts. If the acceleration is not efficient, the entropy should continue to increase outward. By comparing model predictions with X-ray observations with Suzaku, which show flat entropy profiles, we find that the CRs have carried {approx}< 7% of the kinetic energy of the gas away from the clusters. Moreover, the CR pressure at the outskirts can be {approx}< 40% of the total pressure. On the other hand, if the entropy profiles are not flat at the outskirts, as indicated by combined Plank and ROSAT observations, the carried energy and the CR pressure should be much smaller than the above estimations.

  12. The BL-Lacertae gamma-ray blazar PKS 1424+240 associated with a group of galaxies at z = 0.6010

    NASA Astrophysics Data System (ADS)

    Rovero, A. C.; Muriel, H.; Donzelli, C.; Pichel, A.

    2016-05-01

    Context. PKS 1424+240 is a BL-Lac blazar with unknown redshift that was detected at high-energy gamma rays by Fermi-LAT with a hard spectrum. At very high energy (VHE), it was first detected by VERITAS and later confirmed by MAGIC. Its spectral energy distribution is highly attenuated at VHE gamma rays, which is coherent with distant sources. Several estimations enabled the redshift to be constrained to the range 0.6 group of galaxies. Methods: Elliptical galaxies are associated with groups, and BL-Lac objects are typically hosted by them, so we decided to search for the host group of the blazar. For this, we performed optical spectroscopic observations of thirty objects in the field of view of PKS 1424+240 using the Gemini Multi-Object Spectrograph. After analysing the data for groups, we evaluated the probability of finding groups of galaxies by chance around the position of PKS 1424+240, using a deep catalogue of groups. We also used photometric data from the SDSS catalogue to analyse the red sequence of the proposed blazar host group Results: We found a new group of galaxies with eight members at z = 0.6010 ± 0.003, a virial radius of Rvir = 1.53 Mpc, and a velocity dispersion of σv = 813 ± 187 km s-1. The photometric study indicates that more members are probably populating this previously uncatalogued group of galaxies. The probability of PKS 1424+240 being a member of this group was found to be ≳98%. Conclusions: The new group of galaxies found at z = 0.6010 ± 0.003 is very likely

  13. VizieR Online Data Catalog: HCG and RSCG compact group galaxies with WISE (Zucker+, 2016)

    NASA Astrophysics Data System (ADS)

    Zucker, C.; Walker, L. M.; Johnson, K.; Gallagher, S.; Alatalo, K.; Tzanavaris, P.

    2016-07-01

    For this study, we draw our sample from groups in the HCG catalog (Hickson 1982, VII/213) and the Redshift Survey Compact Group catalog (RSCG; Barton et al. 1996AJ....112..871B). We utilize new ALLWISE coadds from Lang (unWISE; 2014AJ....147..108L), which preserve the native resolution of the raw frames (~6.1", 6.4", 6.5" and 12.0" for bands W1, W2, W3, and W4). (1 data file).

  14. Observations of asymmetric velocity fields and gas cooling in the NGC 4636 galaxy group X-ray halo

    NASA Astrophysics Data System (ADS)

    Ahoranta, Jussi; Finoguenov, Alexis; Pinto, Ciro; Sanders, Jeremy; Kaastra, Jelle; de Plaa, Jelle; Fabian, Andrew

    2016-08-01

    Aims: This study aims to probe the thermodynamic properties of the hot intragroup medium (IGM) plasma in the core regions of the NGC 4636 galaxy group by detailed measurements of several emission lines and their relative intensities. Methods: We analyzed deep XMM-Newton Reflection Grating Spectrometer (RGS) data in five adjacent spectral regions in the central parts of the NGC 4636 galaxy group. We examined the suppression of the Fe xvii resonance line (15.01 Å) as compared to the forbidden lines of the same ion (17.05 Å and 17.10 Å). The presence and radial dependence of the cooling flow was investigated through spectral modeling. Parallel analysis with deep Chandra Advances CCD Imaging Spectrometer (ACIS) data was conducted to gain additional information about the thermodynamical properties of the IGM. Results: The plasma at the group center to the north shows efficient Fe xvii ion resonant scattering, yielding (Iλ17.05 + Iλ17.10) /Iλ15.01 line ratios up to 2.9 ± 0.4, corresponding toabout twice the predicted line ratio. In contrast, no resonant scattering was detected at the south side. The regions featuring resonant scattering coincide with those embodying large amounts of cool (kT ≲ 0.4 keV) gas phases, and the spectral imprints of cooling gas with a total mass deposition rate of ~0.8 M⊙ yr-1 within the examined region of 2.4' × 5.0'. Conclusions: We interpret the results as possible evidence of asymmetric turbulence distribution in the NGC 4636 IGM: turbulence dominates the gas dynamics to the south, while collective gas motions characterize the dynamics to the north. X-ray images show imprints of energetic AGN at both sides, yet we find evidence of turbulence heating at the south and gas cooling at the north of the core. We infer that the observed asymmetry may be the result of the specific observation angle to the source, or arise from the turbulence driven by core sloshing at south side.

  15. Population gradients and photometric metallicities in early- and transition-type dwarf galaxies: Clues from the Sculptor group

    NASA Astrophysics Data System (ADS)

    Lianou, S.; Grebel, E. K.; Da Costa, G. S.; Rejkuba, M.; Jerjen, H.; Koch, A.

    2013-02-01

    Aims: We focus on the resolved stellar populations of one early-type and four transition-type dwarf galaxies in the Sculptor group, with the aim to examine the potential presence of population gradients and place constraints on their mean metallicities. Methods: We use deep Hubble Space Telescope images to construct color-magnitude diagrams, from which we select stellar populations that trace different evolutionary phases in order to constrain their range of ages and metallicities, as well as to examine their spatial distribution. In addition, we use the resolved stars in the red giant branch in order to derive photometric metallicities. Results: All studied dwarfs contain intermediate-age stars with ages of ~1 Gyr and older as traced by the luminous asymptotic giant branch and red clump stars, while the transition-type dwarfs contain also stars younger than ~1 Gyr as traced by a young main sequence and vertical red clump stars. Moreover, the spatial distribution of the stars that trace different evolutionary phases shows a population gradient in all transition-type dwarfs. The derived error-weighted mean metallicities, assuming purely old stellar populations, range from -1.5 dex for ESO294-G010 to -1.9 dex for Scl-dE1, and should be considered as lower limits to their true metallicities. Assuming intermediate-age stellar populations to dominate the dwarfs, we derive upper limits for the metallicities that are 0.3 to 0.2 dex higher than the metallicities derived assuming purely old populations. We discuss how photometric metallicity gradients are affected by the age-metallicity degeneracy, which prevents strong conclusions regarding their actual presence. Finally, the transition-type dwarfs lie beyond the virial radius of their closest bright galaxy, as also observed for the Local Group transition-type dwarfs. Scl-dE1 is the only dwarf spheroidal in our sample and is an outlier in a potential morphology-distance relation, similar as the two isolated dwarf

  16. The X-Ray Zurich Environmental Study (X-ZENS). II. X-Ray Observations of the Diffuse Intragroup Medium in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Miniati, Francesco; Finoguenov, Alexis; Silverman, John D.; Carollo, Marcella; Cibinel, Anna; Lilly, Simon J.; Schawinski, Kevin

    2016-03-01

    We present the results of a pilot XMM-Newton and Chandra program aimed at studying the diffuse intragroup medium (IGM) of optically selected nearby groups from the Zurich ENvironmental Study (ZENS) catalog. The groups are in a narrow mass range about {10}13 {M}⊙ , a mass scale at which the interplay between the IGM and the group member galaxies is still largely unprobed. X-ray emission from the IGM is detected in the energy band 0.5-2 keV with flux ≤slant {10}-13 erg s-1 cm-2, which is one order of magnitude fainter than for typical ROSAT groups (RASS). For many groups, we set upper limits on the X-ray luminosity, indicating that the detections are likely probing the upper envelope of the X-ray emitting groups. We find that weighting the group halo mass by the fraction of the total stellar mass locked in the bulge galaxy components might reduce the bias of mass estimates based on the total optical luminosity with respect to the X-ray mass estimates, (consistent with Andreon, at larger mass scales). We measure a stellar mass fraction with a median value of about 1%, with a contribution from the most massive galaxies between 30% and 50%. Optical and X-ray data often give complementary answers concerning the dynamical state of the groups, and are essential for a complete picture of the group system. Extending this pilot program to a larger sample of groups is necessary to unveil any imprint of interaction between member galaxies and IGM in halo potentials of key importance for environmentally driven galactic evolution.

  17. SERENDIPITOUS DISCOVERY OF A MASSIVE cD GALAXY AT z = 1.096: IMPLICATIONS FOR THE EARLY FORMATION AND LATE EVOLUTION OF cD GALAXIES

    SciTech Connect

    Liu, F. S.; Guo Yicheng; Koo, David C.; Trump, Jonathan R.; Barro, Guillermo; Yesuf, Hassen; Faber, S. M.; Cheung, Edmond; Cassata, P.; Koekemoer, A. M.; Grogin, Norman A.; Pentericci, L.; Castellano, M.; Mao, Shude; Xia, X. Y.; Hathi, Nimish P.; Huang, Kuang-Han; Kocevski, Dale; McGrath, Elizabeth J.; and others

    2013-06-01

    We have made a serendipitous discovery of a massive ({approx}5 Multiplication-Sign 10{sup 11} M{sub Sun }) cD galaxy at z = 1.096 in a candidate-rich cluster in the Hubble Ultra Deep Field (HUDF) area of GOODS-South. This brightest cluster galaxy (BCG) is the most distant cD galaxy confirmed to date. Ultra-deep HST/WFC3 images reveal an extended envelope starting from {approx}10 kpc and reaching {approx}70 kpc in radius along the semimajor axis. The spectral energy distributions indicate that both its inner component and outer envelope are composed of an old, passively evolving (specific star formation rate <10{sup -4} Gyr{sup -1}) stellar population. The cD galaxy lies on the same mass-size relation as the bulk of quiescent galaxies at similar redshifts. The cD galaxy has a higher stellar mass surface density ({approx}M{sub *}/R{sub 50}{sup 2}) but a similar velocity dispersion ({approx}{radical}(M{sub *}/R{sub 50})) to those of more massive, nearby cDs. If the cD galaxy is one of the progenitors of today's more massive cDs, its size (R{sub 50}) and stellar mass have had to increase on average by factors of 3.4 {+-} 1.1 and 3.3 {+-} 1.3 over the past {approx}8 Gyr, respectively. Such increases in size and stellar mass without being accompanied by significant increases in velocity dispersion are consistent with evolutionary scenarios driven by both major and minor dissipationless (dry) mergers. If such cD envelopes originate from dry mergers, our discovery of even one example proves that some BCGs entered the dry merger phase at epochs earlier than z = 1. Our data match theoretical models which predict that the continuance of dry mergers at z < 1 can result in structures similar to those of massive cD galaxies seen today. Moreover, our discovery is a surprise given that the extreme depth of the HUDF is essential to reveal such an extended cD envelope at z > 1 and, yet, the HUDF covers only a minuscule region of sky ({approx}3.1 Multiplication-Sign 10{sup -8

  18. Implications of Spikes in the Redshift Distribution of Z ~ 3 Galaxies

    NASA Astrophysics Data System (ADS)

    Wechsler, Risa H.; Gross, Michael A. K.; Primack, Joel R.; Blumenthal, George R.; Dekel, Avishai

    1998-10-01

    We address the high peaks found by Steidel and coworkers in the redshift distribution of ``Lyman-break'' objects (LBOs) at redshift z ~= 3. The highest spike represents a relative overdensity of 2.6 in the distribution of LBOs in pixels of comoving size ~10 h-1 Mpc. We examine the likelihood of such a spike in the redshift distribution within a suite of models for the evolution of structure in the universe, including models with Ω = 1 (a standard cold dark matter [SCDM] and a cold plus hot dark matter model [CHDM]) and with Ω0 = 0.4-0.5 (a flat cold dark matter model with a nonzero cosmological constant Λ [ΛCDM] and an open cold dark matter model [OCDM]). Using high-resolution dissipationless N-body simulations, we analyze deep pencil-beam surveys from these models in the same way that they are actually observed, identifying LBOs with the most massive dark matter halos. We find that all the models (with SCDM as a marginal exception) have a substantial probability of producing spikes similar to those observed, because the massive halos are much more clumped than the underlying matter; i.e., they are biased. Therefore, the likelihood of such a spike is not a good discriminator among these models. We find in these models that the mean biasing parameter b of LBOs with respect to dark matter varies within a range b ~= 2-5 on a scale of ~10 h-1 Mpc. However, all models show considerable dispersion in their biasing, with the local biasing parameter reaching values as high as ten. We also compute the two-body correlation functions of LBOs predicted in these models. The LBO correlation functions are less steep than galaxies today (γ ~ -1.4) but show similar or slightly longer correlation lengths.

  19. ON THE INTERMEDIATE-REDSHIFT CENTRAL STELLAR MASS-HALO MASS RELATION, AND IMPLICATIONS FOR THE EVOLUTION OF THE MOST MASSIVE GALAXIES SINCE z ∼ 1

    SciTech Connect

    Shankar, Francesco; Buchan, Stewart; Guo, Hong; Zheng, Zheng; Bouillot, Vincent; Rettura, Alessandro; Meert, Alan; Bernardi, Mariangela; Sheth, Ravi; Vikram, Vinu; Kravtsov, Andrey; Marchesini, Danilo; Behroozi, Peter; Maraston, Claudia; Capozzi, Diego; Ascaso, Begoña; Huertas-Company, Marc; Lemaux, Brian C.; Gal, Roy R.; Lubin, Lori M.; and others

    2014-12-20

    The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z ∼ 1 for stellar masses M {sub star} ≳ 2 × 10{sup 11} M {sub ☉}. Specifically, we find significant evidence for a high-mass end slope of β ≳ 0.35-0.70 instead of the usual β ≲ 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (≲ 0.15 dex) in stellar mass at fixed halo mass, in the redshift range z < 0.8 and for M {sub star} > 3 × 10{sup 11} M {sub ☉}, suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z ∼ 1.

  20. THE SPACE DENSITY OF EXTENDED ULTRAVIOLET (XUV) DISKS IN THE LOCAL UNIVERSE AND IMPLICATIONS FOR GAS ACCRETION ONTO GALAXIES

    SciTech Connect

    Lemonias, Jenna J.; Schiminovich, David; Thilker, David; Bianchi, Luciana; Wyder, Ted K.; Martin, D. Christopher; Seibert, Mark; Madore, Barry F.; Treyer, Marie A.; Heckman, Timothy M.; Rich, R. Michael

    2011-06-01

    We present results of the first unbiased search for extended ultraviolet (XUV)-disk galaxies undertaken to determine the space density of such galaxies. Our sample contains 561 local (0.001 < z < 0.05) galaxies that lie in the intersection of available Galaxy Evolution Explorer (GALEX) deep imaging (exposure time >1.5 x 10{sup 4} s) and Sloan Digital Sky Survey DR7 footprints. We explore modifications to the standard classification scheme for our sample that includes both disk- and bulge-dominated galaxies. Visual classification of each galaxy in the sample reveals an XUV-disk frequency of up to 20% for the most nearby portion of our sample. On average over the entire sample (out to z = 0.05) the frequency ranges from a hard limit of 4%-14%. The GALEX imaging allows us to detect XUV disks beyond 100 Mpc. The XUV regions around XUV-disk galaxies are consistently bluer than the main bodies. We find a surprisingly high frequency of XUV emission around luminous red (NUV-r > 5) and green valley (3 < NUV-r < 5) galaxies. The XUV-disk space density in the local universe is >(1.5-4.2) x 10{sup -3} Mpc{sup -3}. Using the XUV emission as an indicator of recent gas accretion, we estimate that the cold gas accretion rate onto these galaxies is >(1.7-4.6) x 10{sup -3} M{sub sun} Mpc{sup -3} yr{sup -1}. The number of XUV disks in the green valley and the estimated accretion rate onto such galaxies points to the intriguing possibility that 7%-18% of galaxies in this population are transitioning away from the red sequence.

  1. Einstein observations of the Hydra A cluster and the efficiency of galaxy formation in groups and clusters

    NASA Technical Reports Server (NTRS)

    David, L. P.; Arnaud, K. A.; Forman, W.; Jones, C.

    1990-01-01

    The Einstein imaging proportional counter observations of the poor cluster of galaxies centered on the radio galaxy Hydra A are examined. From the surface brightness profile, it is found that the X-ray-emitting gas in the Hydra A cluster must be condensing out of the intracluster medium at a rate of 600 solar masses/yr. This is one of the largest mass deposition rates observed in a cluster of galaxies. The ratio of gas mass to stellar mass is compared for a variety of systems, showing that this ratio correlates with the gas temperature.

  2. Spectra of High-Ionization Seyfert 1 Galaxies: Implications for the Narrow-Line Region

    NASA Technical Reports Server (NTRS)

    Moore, David; Cohen, Ross D.; Marcy, Geoffrey W.

    1996-01-01

    We present line profiles and profile parameters for the Narrow-Line Regions (NLRs) of six Seyfert 1 galaxies with high-ionization lines: MCG 8-11-11, Mrk 79, Mrk 704, Mrk 841, NGC 4151, and NGC 5548. The sample was chosen primarily with the goal of obtaining high-quality [Fe VII] lambda6087 and, when possible, [Fe X] lambda6374 profiles to determine if these lines are more likely formed in a physically distinct 'coronal line region' or are formed throughout the NLR along with lines of lower critical density (n(sub cr)) and/or Ionization Potential (IP). We discuss correlations of velocity shift and width with n(sub cr) and IP. In some objects, lines of high IP and/or n(sub cr) are systematically broader than those of low IP/n(sub cr). Of particular interest, however, are objects that show no correlations of line width with either IP or n(sub cr). In these objects, lines of high and low IP/n(sub cr), are remarkably similar, which is difficult to reconcile with the classical picture of the NLR, in which lines of high and low IP/n(sub cr) are formed in physically distinct regions. We argue for similar spatial extents for the flux in lines with similar profiles. Here, as well as in a modeling-oriented companion paper, we develop further an idea suggested by Moore & Cohen that objects that do and do not show line width correlations with IP/n(sub cr) can both be explained in terms of a single NLR model with only a small difference in the cloud column density distinguishing the two types of object. Overall, our objects do not show correlations between the Full Width at Half-Maximum (FWHM) and IP and/or n(sub cr). The width must be defined by a parameter that is sensitive to extended profile wings in order for the correlations to result. We present models in which FWHM correlations with IP and/or n(sub cr) result only after simulating the lower spectral resolution used in previous observational studies. The models that simulate the higher spectral resolution of our

  3. A pair of O VI and broad Ly α absorbers probing warm gas in a galaxy group environment at z ˜ 0.4

    NASA Astrophysics Data System (ADS)

    Pachat, Sachin; Narayanan, Anand; Muzahid, Sowgat; Khaire, Vikram; Srianand, Raghunathan; Wakker, Bart P.; Savage, Blair D.

    2016-05-01

    We report the detection of two O VI absorbers at z = 0.416 14 and 0.419 50 (|Δv| = 710 km s-1), towards SBS 0957+599. Both absorbers are multiphase systems tracing substantial reservoirs of warm baryons. The low- and intermediate-ionization metals in the z = 0.416 14 absorber are consistent with an origin in photoionized gas. O VI has a velocity structure different from other metal species. Ly α shows the presence of a broad feature. The linewidths for O VI and the broad Ly α suggest T = 7.1 × 105 K. This warm medium is probing a baryonic column, which is an order of magnitude more than the total hydrogen in the cooler photoionized gas. The second absorber is detected only in H I and O VI. Here a temperature of 4.6 × 104 K supports O VI originating in a low-density photoionized gas. A broad component is seen in Ly α, offset from O VI. The temperature in the broad Ly α is T ≲ 2.1 × 105 K. The absorbers reside in a galaxy overdensity region with seven spectroscopically identified galaxies within ˜10 Mpc and Δv ˜ 1000 km s-1 of the z = 0.416 14 absorber, and two galaxies inside a similar separation from the z = 0.419 50 absorber. The distribution of galaxies relative to the absorbers suggests that the line of sight could be intercepting a large-scale filament connecting galaxy groups, or the extended halo of a sub-L* galaxy. Though kinematically proximate, the two absorbers reaffirm the diversity in the physical conditions of low red-shift O VI systems and the galactic environments they inhabit.

  4. A spectroscopic sample of massive, quiescent z ∼ 2 galaxies: implications for the evolution of the mass-size relation

    SciTech Connect

    Krogager, J.-K.; Zirm, A. W.; Toft, S.; Man, A.; Brammer, G.

    2014-12-10

    We present deep, near-infrared Hubble Space Telescope/Wide Field Camera 3 grism spectroscopy and imaging for a sample of 14 galaxies at z ≈ 2 selected from a mass-complete photometric catalog in the COSMOS field. By combining the grism observations with photometry in 30 bands, we derive accurate constraints on their redshifts, stellar masses, ages, dust extinction, and formation redshifts. We show that the slope and scatter of the z ∼ 2 mass-size relation of quiescent galaxies is consistent with the local relation, and confirm previous findings that the sizes for a given mass are smaller by a factor of two to three. Finally, we show that the observed evolution of the mass-size relation of quiescent galaxies between z = 2 and 0 can be explained by the quenching of increasingly larger star forming galaxies at a rate dictated by the increase in the number density of quiescent galaxies with decreasing redshift. However, we find that the scatter in the mass-size relation should increase in the quenching-driven scenario in contrast to what is seen in the data. This suggests that merging is not needed to explain the evolution of the median mass-size relation of massive galaxies, but may still be required to tighten its scatter, and explain the size growth of individual z = 2 galaxies quiescent galaxies.

  5. The Roadmap for Unification in Galaxy Group Selection. I. A Search for Extended X-ray Emission in the CNOC2 Survey

    NASA Astrophysics Data System (ADS)

    Finoguenov, A.; Connelly, J. L.; Parker, L. C.; Wilman, D. J.; Mulchaey, J. S.; Saglia, R. P.; Balogh, M. L.; Bower, R. G.; McGee, S. L.

    2009-10-01

    X-ray properties of galaxy groups can unlock some of the most challenging research topics in modern extragalactic astronomy: the growth of structure and its influence on galaxy formation. Only with the advent of the Chandra and XMM-Newton facilities have X-ray observations reached the depths required to address these questions in a satisfactory manner. Here we present an X-ray imaging study of two patches from the CNOC2 spectroscopic galaxy survey using combined Chandra and XMM-Newton data. A state of the art extended source finding algorithm has been applied, and the resultant source catalog, including redshifts from a spectroscopic follow-up program, is presented. The total number of spectroscopically identified groups is 25 spanning a redshift range 0.04-0.79. Approximately 50% of CNOC2 spectroscopically selected groups in the deeper X-ray (RA14h) field are likely X-ray detections, compared to 20% in the shallower (RA21h) field. Statistical modeling shows that this is consistent with expectations, assuming an expected evolution of the LX -M relation. A significant detection of a stacked shear signal for both spectroscopic and X-ray groups indicates that both samples contain real groups of about the expected mass. We conclude that the current area and depth of X-ray and spectroscopic facilities provide a unique window of opportunity at z ~ 0.4 to test the X-ray appearance of galaxy groups selected in various ways. There is at present no evidence that the correlation between X-ray luminosity and velocity dispersion evolves significantly with redshift, which implies that catalogs based on either method can be fairly compared and modeled. Based on observations with the ESA/NASA XMM-Newton science mission; the European Southern Observatory, Chile; NASA/ESA Chandra X-ray Observatory.

  6. Chandra and VLA Observations of Supermassive Black Hole Outbursts in M87 and Implications for Feedback in Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Forman, William R.; Churazov, E.; Jones, C.

    2013-04-01

    We discuss the effects of supermassive black hole (SMBH) outbursts on the hot atmospheres surrounding massive galaxies as observed with X-ray and radio observations. We initially focus on a detailed study of outbursts from the supermassive black hole in M87 using Chandra and VLA observations. We model the outburst that created the classical Mach 1.2 shock seen in Chandra images and derive the characteristic energy (5x1057 ergs), duration (2 Myrs), and age (12 Myrs) of the outburst from numerical models. We review the outburst history of the SMBH in M87 over the past ~100 Myr. We discuss the implications of the outbursts for feedback in typical early-type galaxy atmospheres.

  7. Comparative Genomics of the Bacterial Genus Streptococcus Illuminates Evolutionary Implications of Species Groups

    PubMed Central

    Gao, Xiao-Yang; Zhi, Xiao-Yang; Li, Hong-Wei; Klenk, Hans-Peter; Li, Wen-Jun

    2014-01-01

    Members of the genus Streptococcus within the phylum Firmicutes are among the most diverse and significant zoonotic pathogens. This genus has gone through considerable taxonomic revision due to increasing improvements of chemotaxonomic approaches, DNA hybridization and 16S rRNA gene sequencing. It is proposed to place the majority of streptococci into “species groups”. However, the evolutionary implications of species groups are not clear presently. We use comparative genomic approaches to yield a better understanding of the evolution of Streptococcus through genome dynamics, population structure, phylogenies and virulence factor distribution of species groups. Genome dynamics analyses indicate that the pan-genome size increases with the addition of newly sequenced strains, while the core genome size decreases with sequential addition at the genus level and species group level. Population structure analysis reveals two distinct lineages, one including Pyogenic, Bovis, Mutans and Salivarius groups, and the other including Mitis, Anginosus and Unknown groups. Phylogenetic dendrograms show that species within the same species group cluster together, and infer two main clades in accordance with population structure analysis. Distribution of streptococcal virulence factors has no obvious patterns among the species groups; however, the evolution of some common virulence factors is congruous with the evolution of species groups, according to phylogenetic inference. We suggest that the proposed streptococcal species groups are reasonable from the viewpoints of comparative genomics; evolution of the genus is congruent with the individual evolutionary trajectories of different species groups. PMID:24977706

  8. Kinematically-Decoupled Cores in Dwarf Ellipticals in the Virgo Cluster: Implications for Infallen Groups in Clusters

    NASA Astrophysics Data System (ADS)

    Toloba, Elisa; Guhathakurta, P.; van de Ven, G.; Boselli, A.; Lisker, T.; Peletier, R.; SMAKCED Collaboration

    2014-01-01

    A small fraction 8%) of elliptical galaxies contain kinematically-decoupled cores (KDCs), where the kinematical properties of the central region of the galaxy are distinct from those of the main body of the galaxy. KDCs are difficult to detect in dwarf elliptical (dE) galaxies because of their low central surface brightnesses. There was only one statistically robust detection of a KDC in a dE prior to our study. We present spectroscopic evidence for KDCs in two Virgo cluster dEs, VCC 1183 and VCC 1453, that were studied as part of the SMAKCED project. These KDCs have radii of 1.8$''$ (0.14 kpc) and 4.2$''$ (0.33 kpc), respectively. They are distinct from the main body of the galaxy is three ways: (1) inverted sense of rotation; (2) younger and more metal-rich stellar population; and (3) rounder isophotal shape. The frequency of occurence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs and for dEs in general. The fact that dEs represent the most common galaxy class in clusters and have never been seen in isolation suggests that they are products of environmental processes that transformed their progenitors. However, it is unclear which types of galaxies are dE progenitors and which environmental processes are the most important. These KDCs provide new clues. Dwarf-dwarf wet mergers and gas accretion are argued to be the only mechanisms that can simultaneously explain all of the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a small relative velocity. Thus, we conclude that KDCs in cluster dEs were formed in galaxy pairs residing in poor groups or in isolation whose subsequent infall into the cluster quenched their star formation. This research was supported by a Fulbright fellowship and by a grant from the National Science Foundation.

  9. Distant FR I radio galaxies in the Hubble Deep Field: implications for the cosmological evolution of radio-loud AGN

    NASA Astrophysics Data System (ADS)

    Snellen, I. A. G.; Best, P. N.

    2001-12-01

    Deep and high-resolution radio observations of the Hubble Deep Field and flanking fields have shown the presence of two distant edge-darkened FRI radio galaxies, allowing for the first time an estimate of their high-redshift space density. If it is assumed that the space density of FRI radio galaxies at z>1 is similar to that found in the local Universe, then the chance of finding two FRI radio galaxies at these high radio powers in such a small area of sky is <1 per cent. This suggests that these objects were significantly more abundant at z>1 than at present, effectively ruling out the possibility that FRI radio sources undergo no cosmological evolution. We suggest that FRI and FRII radio galaxies should not be treated as intrinsically distinct classes of objects, but that the cosmological evolution is simply a function of radio power with FRI and FRII radio galaxies of similar radio powers undergoing similar cosmological evolutions. Since low-power radio galaxies have mainly FRI morphologies and high-power radio galaxies have mainly FRII morphologies, this results in a generally stronger cosmological evolution for the FRIIs than the FRIs. We believe that additional support from the V/Vmax test for evolving and non-evolving population of FRIIs and FRIs respectively is irrelevant, since this test is sensitive over very different redshift ranges for the two classes.

  10. Galaxy NGC 300

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the nearby spiral galaxy NGC 300 was taken by Galaxy Evolution Explorer in a single orbit exposure of 27 minutes on October 10, 2003. NGC 300 lies 7 million light years from our Milky Way galaxy and is one of a group of galaxies in the constellation Sculptor. NGC 300 is often used as a prototype of a spiral galaxy because in optical images it displays flowing spiral arms and a bright central region of older (and thus redder) stars. The Galaxy Evolution Explorer image taken in ultraviolet light shows us that NGC 300 is an efficient star-forming galaxy. The bright blue regions in the Galaxy Evolution Explorer image reveal new stars forming all the way into the nucleus of NGC 300.

  11. Absorption-line detections of 10{sup 5}-10{sup 6} K gas in spiral-rich groups of galaxies

    SciTech Connect

    Stocke, John T.; Keeney, Brian A.; Danforth, Charles W.; Syphers, David; Yamamoto, H.; Shull, J. Michael; Green, James C.; Froning, Cynthia; Savage, Blair D.; Wakker, Bart; Kim, Tae-Sun; Ryan-Weber, Emma V.; Kacprzak, Glenn G.

    2014-08-20

    Using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope, the COS Science Team has conducted a high signal-to-noise survey of 14 bright QSOs. In a previous paper, these far-UV spectra were used to discover 14 'warm' (T ≥ 10{sup 5} K) absorbers using a combination of broad Lyα and broad O VI absorptions. A reanalysis of a few of this new class of absorbers using slightly relaxed fitting criteria finds as many as 20 warm absorbers could be present in this sample. A shallow, wide spectroscopic galaxy redshift survey has been conducted around these sight lines to investigate the warm absorber environment, which is found to be spiral-rich groups or cluster outskirts with radial velocity dispersions σ = 250-750 km s{sup –1}. While 2σ evidence is presented favoring the hypothesis that these absorptions are associated with the galaxy groups and not with the individual, nearest galaxies, this evidence has considerable systematic uncertainties and is based on a small sample size so it is not entirely conclusive. If the associations are with galaxy groups, the observed frequency of warm absorbers (dN/dz = 3.5-5 per unit redshift) requires them to be very extended as an ensemble on the sky (∼1 Mpc in radius at high covering factor). Most likely these warm absorbers are interface gas clouds whose presence implies the existence of a hotter (T ∼ 10{sup 6.5} K), diffuse, and probably very massive (>10{sup 11} M {sub ☉}) intra-group medium which has yet to be detected directly.

  12. Evolution of Hot Gas in Elliptical Galaxies

    NASA Technical Reports Server (NTRS)

    Mathews, William G.

    2004-01-01

    This theory grant was awarded to study the curious nature, origin and evolution of hot gas in elliptical galaxies and their surrounding groups. Understanding the properties of this X-ray emitting gas has profound implications over the broad landscape of modern astrophysics: cosmology, galaxy formation, star formation, cosmic metal enrichment, galactic structure and dynamics, and the physics of hot gases containing dust and magnetic fields. One of our principal specific objectives was to interpret the marvelous new observations from the XMM and Chandru satellite X-ray telescopes.

  13. THE M81 GROUP DWARF IRREGULAR GALAXY DDO 165. II. CONNECTING RECENT STAR FORMATION WITH INTERSTELLAR MEDIUM STRUCTURES AND KINEMATICS

    SciTech Connect

    Cannon, John M.; Most, Hans P.; Skillman, Evan D.; Weisz, Daniel R.; Warren, Steven R. E-mail: hmost@macalester.edu E-mail: dweisz@astro.umn.edu

    2011-07-01

    We compare the stellar populations and complex neutral gas dynamics of the M81 group dIrr galaxy DDO 165 using data from the Hubble Space Telescope and the Very Large Array. Cannon et al. in Paper I of this series identified two kinematically distinct H I components, multiple localized high velocity gas features, and eight H I holes and shells (the largest of which spans {approx}2.2 x 1.1 kpc). Using the spatial and temporal information from the stellar populations in DDO 165, we compare the patterns of star formation (SF) over the past 500 Myr with the H I dynamics. We extract localized star formation histories within 6 of the 8 H I holes identified in Paper I, as well as 23 other regions that sample a range of stellar densities and neutral gas properties. From population synthesis modeling, we derive the energy outputs (from stellar winds and supernovae) of the stellar populations within these regions over the last 100 Myr, and compare with refined estimates of the energies required to create the H I holes. In all cases, we find that 'feedback' is energetically capable of creating the observed structures in the interstellar medium (ISM). Numerous regions with significant energy inputs from feedback lack coherent H I structures but show prominent localized high velocity gas features; this feedback signature is a natural product of temporally and spatially distributed SF. In DDO 165, the extended period of heightened SF activity (lasting more than 1 Gyr) is energetically capable of creating the observed holes and high velocity gas features in the neutral ISM.

  14. The Unexpected Past of a Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    1996-08-01

    understood by Knut Lundmark and P.J. Melotte. The designation WLM is shorthand of Wolf-Lundmark-Melotte. More recent investigations have fixed its distance at about 2.9 million light years, somewhat farther away than the Andromeda galaxy (2 million light years) and placing it at the very edge of the region occupied by the Local Group. WLM is one of the most isolated members; its nearest neighbour dwarf galaxy, IC 1613, is more 1 million light years away. A halo around WLM The ESO astronomers recently obtained deep CCD images of WLM with the 3.5-m ESO New Technology Telescope (NTT) and the ESO Multi-Mode Instrument (EMMI). With the excellent imaging capabilities of this facility, they were able to see large numbers of individual stars in this galaxy. A mosaic of two of these images is reproduced as ESO Press Photo 34/96 that accompanies this Press Release. WLM appears to be quite elongated, and surprisingly, its largest extension is about 8000 light years or more than twice as large as thought before. Nevertheless, this is still 12 times smaller than the Milky Way galaxy. There is a clear excess of very faint stars that extends to the edge of the sky field covered by the NTT exposures. Some of these are probably foreground stars inside the Milky Way, but there are many more than expected, and their numbers increase closer to WLM . These stars look quite different from the ones in the central region of that galaxy: they are much redder and relatively faint; this is a strong indication that they are much older. The distant stars thus appear to belong to an old halo around this dwarf galaxy. This shows that WLM must be very old, perhaps as old as the Milky Way, and in any case much older than indicated by the ages of the stars near its centre. The present discovery furthermore proves that a halo may also form around a dwarf galaxy, and it is not a feature exclusively reserved for large spiral galaxies. Implications of this discovery WLM is so isolated that it has most probably

  15. The ACS LCID Project. XI. On the Early Time Resolution of SFHs of Local Group Dwarf Galaxies: Comparing the Effects of Reionization in Models with Observations

    NASA Astrophysics Data System (ADS)

    Aparicio, Antonio; Hidalgo, Sebastian L.; Skillman, Evan; Cassisi, Santi; Mayer, Lucio; Navarro, Julio; Cole, Andrew; Gallart, Carme; Monelli, Matteo; Weisz, Daniel; Bernard, Edouard; Dolphin, Andrew; Stetson, Peter

    2016-05-01

    The analysis of the early star formation history (SFH) of nearby galaxies, obtained from their resolved stellar populations, is relevant as a test for cosmological models. However, the early time resolution of observationally derived SFHs is limited by several factors. Thus, direct comparison of observationally derived SFHs with those derived from theoretical models of galaxy formation is potentially biased. Here we investigate and quantify this effect. For this purpose, we analyze the duration of the early star formation activity in a sample of four Local Group dwarf galaxies and test whether they are consistent with being true fossils of the pre-reionization era; i.e., if the quenching of their star formation occurred before cosmic reionization by UV photons was completed. Two classical dSph (Cetus and Tucana) and two dTrans (LGS-3 and Phoenix) isolated galaxies with total stellar masses between 1.3× {10}6 and 7.2× {10}6 {M}⊙ have been studied. Accounting for time resolution effects, the SFHs peak as much as 1.25 Gyr earlier than the optimal solutions. Thus, this effect is important for a proper comparison of model and observed SFHs. It is also shown that none of the analyzed galaxies can be considered a true fossil of the pre-reionization era, although it is possible that the outer regions of Cetus and Tucana are consistent with quenching by reionization. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #10505.

  16. The ACS LCID Project. XI. On the Early Time Resolution of SFHs of Local Group Dwarf Galaxies: Comparing the Effects of Reionization in Models with Observations

    NASA Astrophysics Data System (ADS)

    Aparicio, Antonio; Hidalgo, Sebastian L.; Skillman, Evan; Cassisi, Santi; Mayer, Lucio; Navarro, Julio; Cole, Andrew; Gallart, Carme; Monelli, Matteo; Weisz, Daniel; Bernard, Edouard; Dolphin, Andrew; Stetson, Peter

    2016-05-01

    The analysis of the early star formation history (SFH) of nearby galaxies, obtained from their resolved stellar populations, is relevant as a test for cosmological models. However, the early time resolution of observationally derived SFHs is limited by several factors. Thus, direct comparison of observationally derived SFHs with those derived from theoretical models of galaxy formation is potentially biased. Here we investigate and quantify this effect. For this purpose, we analyze the duration of the early star formation activity in a sample of four Local Group dwarf galaxies and test whether they are consistent with being true fossils of the pre-reionization era; i.e., if the quenching of their star formation occurred before cosmic reionization by UV photons was completed. Two classical dSph (Cetus and Tucana) and two dTrans (LGS-3 and Phoenix) isolated galaxies with total stellar masses between 1.3× {10}6 and 7.2× {10}6 {M}ȯ have been studied. Accounting for time resolution effects, the SFHs peak as much as 1.25 Gyr earlier than the optimal solutions. Thus, this effect is important for a proper comparison of model and observed SFHs. It is also shown that none of the analyzed galaxies can be considered a true fossil of the pre-reionization era, although it is possible that the outer regions of Cetus and Tucana are consistent with quenching by reionization. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #10505.

  17. The galaxy luminosity function in groups and clusters: the faint-end upturn and the connection to the field luminosity function

    NASA Astrophysics Data System (ADS)

    Lan, Ting-Wen; Ménard, Brice; Mo, Houjun

    2016-07-01

    We characterize the luminosity functions of galaxies residing in z ˜ 0 groups and clusters over the broadest ranges of luminosity and mass reachable by the Sloan Digital Sky Survey. Our measurements cover four orders of magnitude in luminosity, down to about Mr = -12 mag or L = 107 L⊙, and three orders of magnitude in halo mass, from 1012 to 1015 M⊙. We find a characteristic scale, Mr ˜ -18 mag or L ˜ 109 L⊙, below which the slope of the luminosity function becomes systematically steeper. This trend is present for all halo masses and originates mostly from red satellites. This ubiquitous faint-end upturn suggests that it is formation, rather than halo-specific environmental effect, that plays a major role in regulating the stellar masses of faint satellites. We show that the satellite luminosity functions can be described in a simple manner by a double Schechter function with amplitudes scaling with halo mass over the entire range of observables. Combining these conditional luminosity functions with the dark matter halo mass function, we accurately recover the entire field luminosity function over 10 visual magnitudes and reveal that satellite galaxies dominate the field luminosity function at magnitudes fainter than -17. We find that the luminosity functions of blue and red satellite galaxies show distinct shapes and we present estimates of the stellar mass fraction as a function of halo mass and galaxy type. Finally, using a simple model, we demonstrate that the abundances and the faint-end slopes of blue and red satellite galaxies can be interpreted in terms of their formation history, with two distinct modes separated by some characteristic time.

  18. THE ATACAMA COSMOLOGY TELESCOPE: DETECTION OF SUNYAEV-ZEL'DOVICH DECREMENT IN GROUPS AND CLUSTERS ASSOCIATED WITH LUMINOUS RED GALAXIES

    SciTech Connect

    Hand, Nick; Das, Sudeep; Dunkley, Joanna; Hajian, Amir; Appel, John W.; Essinger-Hileman, Thomas; Fowler, Joseph W.; Hincks, Adam D.; Battaglia, Nick; Richard Bond, J.; Devlin, Mark J.; Klein, Jeff; Duenner, Rolando; Halpern, Mark; Hasselfield, Matthew; Hilton, Matt; Hlozek, Renee; Hughes, John P.; Irwin, Kent D.; Kosowsky, Arthur

    2011-07-20

    We present a detection of the Sunyaev-Zel'dovich (SZ) decrement associated with the luminous red galaxy (LRG) sample of the Sloan Digital Sky Survey. The SZ data come from 148 GHz maps of the equatorial region made by the Atacama Cosmology Telescope. The LRG sample is divided by luminosity into four bins, and estimates for the central SZ temperature decrement are calculated through a stacking process. We detect and account for a bias of the SZ signal due to weak radio sources. We use numerical simulations to relate the observed decrement to Y{sub 200} and clustering properties to relate the galaxy luminosity to halo mass. We also use a relation between brightest cluster galaxy luminosity and cluster mass based on stacked gravitational lensing measurements to estimate the characteristic halo masses. The masses are found to be around 10{sup 14} M{sub sun}.

  19. An extremely dense group of massive galaxies at the centre of the protocluster at z = 3.09 in the SSA22 field

    NASA Astrophysics Data System (ADS)

    Kubo, M.; Yamada, T.; Ichikawa, T.; Kajisawa, M.; Matsuda, Y.; Tanaka, I.; Umehata, H.

    2016-01-01

    We report the discovery of an extremely dense group of massive galaxies at the centre of the protocluster at z = 3.09 in the SSA22 field from near-infrared spectroscopy conducted with the multi-object infrared camera and spectrograph (MOIRCS) on the Subaru Telecope. The newly discovered group comprises seven galaxies confirmed at zspec ≈ 3.09 within 180 kpc, including five massive objects with the stellar masses larger than 1010.5 M⊙ and is associated with a bright submillimetre source SSA22-AzTEC14. The dynamical mass of the group estimated from the line-of-sight velocity dispersion of the members is Mdyn ˜ 1.6 ± 0.3 × 1013 M⊙. Such a dense group is expected to be very rare at high redshift, as we have found only a few comparable systems in large-volume cosmological simulations. Such rare groups in simulations are hosted in collapsed haloes with Mvir = 1013.4-1014.0 M⊙ and evolve into the brightest cluster galaxies (BCGs) of the most massive clusters at present. The observed AzTEC14 group at z = 3.09 is therefore very likely to be a proto-BCG in the multiple merger phase. The observed total stellar mass of the group is 5.8^{+5.1}_{-2.0}× 10^{11} M_{⊙}, which suggests that over half the stellar mass of its descendant had been formed by z = 3. Moreover, we have identified over two members for each of the four Lyα blobs (LABs) using our new spectroscopic data. This verifies our previous argument that many of the LABs in the SSA22 protocluster associated with multiple developed stellar components.

  20. MOND implications for spectral line profiles of shell galaxies: shell formation history and mass-velocity scaling relations

    NASA Astrophysics Data System (ADS)

    Bílek, M.; Jungwiert, B.; Ebrová, I.; Bartošková, K.

    2015-03-01

    Context. Many ellipticals are surrounded by round stellar shells probably stemming from minor mergers. A new method for constraining gravitational potential in elliptical galaxies has recently been suggested. It uses the spectral line profiles of these shells to measure the circular velocity at the edge of the shell and the expansion velocity of the shell itself. MOND is an alternative to the dark matter framework aiming to solve the missing mass problem. Aims: We study how the circular and expansion velocities behave in MOND for large shells. Methods: The asymptotic behavior for infinitely large shells is derived analytically. The applicability of the asymptotic results for finitely sized shells is studied numerically on a grid of galaxies modeled with Sérsic spheres. Results: Circular velocity settles asymptotically at a value determined by the baryonic mass of the galaxy forming the baryonic Tully-Fisher relation known for disk galaxies. Shell expansion velocity also becomes asymptotically constant. The expansion velocities of large shells form a multibranched analogy to the baryonic Tully-Fisher relation, together with the galactic baryonic masses. For many - but not all - shell galaxies, the asymptotic values of these two types of velocities are reached under the effective radius. If MOND is assumed to work in ellipticals, then the shell spectra allow many details of the history to be revealed about the formation of the shell system, including its age. The results pertaining to circular velocities apply to all elliptical galaxies, not only those with shells.

  1. The gap of stellar mass in galaxy groups: another perspective of the too-big-to-fail problem in the Milky Way

    NASA Astrophysics Data System (ADS)

    Kang, Xi; Wang, Lei; Luo, Yu

    2016-08-01

    The Milky Way (MW) presents the too-big-to-fail (TBTF) problem that there are two observed satellite galaxies with maximum circular velocity larger than 55 km s-1, and others have velocity less than 25 km s-1, but the cold dark matter (CDM) model predicts that there should be more than 10 subhaloes with velocity larger than 25 km s-1. Those massive subhaloes with 25 km s-1 < Vmax < 55 km s-1 should not have failed to form stars. The TBTF problem severely challenges the CDM model. Most efforts are seeking the effects of baryonic feedback, decreasing the mass of the MW, changing the properties of dark matter, so as to assign the observed low-velocity satellites into the massive subhaloes found in simulations. However, the TBTF problem can be avoided if the MW has not accreted subhaloes with velocity within 25 < Vmax < 55 km s-1 although the probability of such a gap is lower as ˜1 per cent and cannot be tested against observations. In this work, we study the gap in stellar mass of satellite galaxies using the Sloan Digital Sky Survey group catalogue and a semi-analytical model. We find that there are 1-2 per cent of galaxy groups with a large gap in the stellar mass of their satellites. These `big gap' groups have accreted less massive subhaloes in their formation history and naturally display a gap between their satellite galaxies. If extrapolating our results to the MW is appropriate, we conclude that it is very likely that our MW has not accreted enough massive subhaloes to host those low-velocity satellites, and the TBTF problem is naturally avoided.

  2. A Deep Search for Extended Radio Continuum Emission from Dwarf Spheroidal Galaxies: Implications for Particle Dark Matter

    NASA Astrophysics Data System (ADS)

    Spekkens, Kristine; Mason, Brian S.; Aguirre, James E.; Nhan, Bang

    2013-08-01

    We present deep radio observations of four nearby dwarf spheroidal (dSph) galaxies, designed to detect extended synchrotron emission resulting from weakly interacting massive particle (WIMP) dark matter annihilations in their halos. Models by Colafrancesco et al. (CPU07) predict the existence of angularly large, smoothly distributed radio halos in such systems, which stem from electron and positron annihilation products spiraling in a turbulent magnetic field. We map a total of 40.5 deg2 around the Draco, Ursa Major II, Coma Berenices, and Willman 1 dSphs with the Green Bank Telescope (GBT) at 1.4 GHz to detect this annihilation signature, greatly reducing discrete-source confusion using the NVSS catalog. We achieve a sensitivity of σsub <~ 7 mJy beam-1 in our discrete source-subtracted maps, implying that the NVSS is highly effective at removing background sources from GBT maps. For Draco we obtained approximately concurrent Very Large Array observations to quantify the variability of the discrete source background, and find it to have a negligible effect on our results. We construct radial surface brightness profiles from each of the subtracted maps, and jackknife the data to quantify the significance of the features therein. At the ~10' resolution of our observations, foregrounds contribute a standard deviation of 1.8 mJy beam-1 <= σast <= 5.7 mJy beam-1 to our high-latitude maps, with the emission in Draco and Coma dominated by foregrounds. On the other hand, we find no significant emission in the Ursa Major II and Willman 1 fields, and explore the implications of non-detections in these fields for particle dark matter using the fiducial models of CPU07. For a WIMP mass M χ = 100 GeV annihilating into b\\bar{b} final states and B = 1 μG, upper limits on the annihilation cross-section for Ursa Major II and Willman I are log (langσvrangχ, cm3 s-1) <~ -25 for the preferred set of charged particle propagation parameters adopted by CPU07; this is comparable to

  3. New redshift z ≃ 9 galaxies in the Hubble Frontier Fields: implications for early evolution of the UV luminosity density

    NASA Astrophysics Data System (ADS)

    McLeod, D. J.; McLure, R. J.; Dunlop, J. S.; Robertson, B. E.; Ellis, R. S.; Targett, T. A.

    2015-07-01

    We present the results of a new search for galaxies at redshift z ≃ 9 in the first two Hubble Frontier Fields with completed HST WFC3/IR and ACS imaging. To ensure robust photometric redshift solutions, and to minimize incompleteness, we confine our search to objects with H160 < 28.6 (AB mag), consider only image regions with an rms noise σ160 > 30 mag (within a 0.5-arcsec diameter aperture), and insist on detections in both H160 and J140. The result is a survey covering an effective area (after accounting for magnification) of 10.9 arcmin2, which yields 12 galaxies at 8.4 < z < 9.5. Within the Abell-2744 cluster and parallel fields, we confirm the three brightest objects reported by Ishigaki et al., but recover only one of the four z > 8.4 sources reported by Zheng et al. In the MACSJ0416.1-240 cluster field, we report five objects, and explain why each of these eluded detection or classification as z ≃ 9 galaxies in the published searches of the shallower CLASH data. Finally, we uncover four z ≃ 9 galaxies from the MACSJ0416.1-240 parallel field. Based on the published magnification maps, we find that only one of these 12 galaxies is likely boosted by more than a factor of 2 by gravitational lensing. Consequently, we are able to perform a fairly straightforward reanalysis of the normalization of the z ≃ 9 UV galaxy luminosity function as explored previously in the HUDF12 programme. We conclude that the new data strengthen the evidence for a continued smooth decline in UV luminosity density (and hence star formation rate density) from z ≃ 8 to 9, contrary to recent reports of a marked drop-off at these redshifts. This provides further support for the scenario in which early galaxy evolution is sufficiently extended to explain cosmic reionization.

  4. How Do Galaxies Grow?

    NASA Astrophysics Data System (ADS)

    2008-08-01

    Astronomers have caught multiple massive galaxies in the act of merging about 4 billion years ago. This discovery, made possible by combining the power of the best ground- and space-based telescopes, uniquely supports the favoured theory of how galaxies form. ESO PR Photo 24/08 ESO PR Photo 24/08 Merging Galaxies in Groups How do galaxies form? The most widely accepted answer to this fundamental question is the model of 'hierarchical formation', a step-wise process in which small galaxies merge to build larger ones. One can think of the galaxies forming in a similar way to how streams merge to form rivers, and how these rivers, in turn, merge to form an even larger river. This theoretical model predicts that massive galaxies grow through many merging events in their lifetime. But when did their cosmological growth spurts finish? When did the most massive galaxies get most of their mass? To answer these questions, astronomers study massive galaxies in clusters, the cosmological equivalent of cities filled with galaxies. "Whether the brightest galaxies in clusters grew substantially in the last few billion years is intensely debated. Our observations show that in this time, these galaxies have increased their mass by 50%," says Kim-Vy Tran from the University of Zürich, Switzerland, who led the research. The astronomers made use of a large ensemble of telescopes and instruments, including ESO's Very Large Telescope (VLT) and the Hubble Space Telescope, to study in great detail galaxies located 4 billion light-years away. These galaxies lie in an extraordinary system made of four galaxy groups that will assemble into a cluster. In particular, the team took images with VIMOS and spectra with FORS2, both instruments on the VLT. From these and other observations, the astronomers could identify a total of 198 galaxies belonging to these four groups. The brightest galaxies in each group contain between 100 and 1000 billion of stars, a property that makes them comparable

  5. THE COLORS OF CENTRAL AND SATELLITE GALAXIES IN zCOSMOS OUT TO z {approx_equal} 0.8 AND IMPLICATIONS FOR QUENCHING

    SciTech Connect

    Knobel, C.; Lilly, S. J.; Kovac, K.; Peng, Y.; Bschorr, T. J.; Carollo, C. M.; Caputi, K.; Contini, T.; Kneib, J.-P.; Le Fevre, O.; Renzini, A.; Scodeggio, M.; Zamorani, G.; Bardelli, S.; Bolzonella, M.; Bongiorno, A.; Cucciati, O.; De la Torre, S.; De Ravel, L.; and others

    2013-05-20

    We examine the red fraction of central and satellite galaxies in the large zCOSMOS group catalog out to z {approx_equal} 0.8, correcting for both the incompleteness in stellar mass and for the less than perfect purities of the central and satellite samples. We show that at all masses and at all redshifts, the fraction of satellite galaxies that have been quenched, i.e., that are red, is systematically higher than that of centrals, as seen locally in the Sloan Digital Sky Survey (SDSS). The satellite quenching efficiency, which is the probability that a satellite is quenched because it is a satellite rather than a central, is, as locally, independent of stellar mass. Furthermore, the average value is about 0.5, which is also very similar to that seen in the SDSS. We also construct the mass functions of blue and red centrals and satellites and show that these broadly follow the predictions of the Peng et al. analysis of the SDSS groups. Together, these results indicate that the effect of the group environment in quenching satellite galaxies was very similar to what it is today when the universe was about half its present age.

  6. The MUSE view of QSO PG 1307+085: an elliptical galaxy on the MBH-σ* relation interacting with its group environment

    NASA Astrophysics Data System (ADS)

    Husemann, B.; Bennert, V. N.; Scharwächter, J.; Woo, J.-H.; Choudhury, O. S.

    2016-01-01

    We report deep optical integral-field spectroscopy with the Multi-Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope of the luminous radio-quiet quasi-stellar object (QSO) PG 1307+085 obtained during commissioning. Given the high sensitivity and spatial resolution delivered by MUSE, we are able to resolve the compact (re ˜ 1.3 arcsec) elliptical host galaxy. After spectroscopic deblending of the QSO and host galaxy emission, we infer a stellar velocity dispersion of σ* = 155 ± 19 km s-1. This places PG 1307+085 on the local MBH-σ* relation within its intrinsic scatter but offset towards a higher black hole mass with respect to the mean relation. The MUSE observations reveal a large extended narrow-line region (ENLR) around PG 1307+085 reaching out to ˜30 kpc. In addition, we detect a faint ionized gas bridge towards the most massive galaxy of the galaxy group at 50 kpc distance. The ionized gas kinematics does not show any evidence for gas outflows on kpc scales despite the high QSO luminosity of Lbol > 1046 erg s-1. Based on the ionized gas distribution, kinematics and metallicity we discuss the origin of the ENLR with respect to its group environments including minor mergers, ram-pressure stripping or gas accretion as the likely scenarios. We conclude that PG 1307+085 is a normal elliptical host in terms of the scaling relations, but that the gas is likely affected by the environment through gravity or ambient pressure. It is possible that the interaction with the environment, seen in the ionized gas, might be responsible for driving sufficient gas to the black hole.

  7. Radio Galaxies.

    ERIC Educational Resources Information Center

    Downes, Ann

    1986-01-01

    Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

  8. THE ORIGIN OF DUST IN EARLY-TYPE GALAXIES AND IMPLICATIONS FOR ACCRETION ONTO SUPERMASSIVE BLACK HOLES

    SciTech Connect

    Martini, Paul; Dicken, Daniel; Storchi-Bergmann, Thaisa

    2013-04-01

    We have conducted an archival Spitzer study of 38 early-type galaxies in order to determine the origin of the dust in approximately half of this population. Our sample galaxies generally have good wavelength coverage from 3.6 {mu}m to 160 {mu}m, as well as visible-wavelength Hubble Space Telescope (HST) images. We use the Spitzer data to estimate dust masses, or establish upper limits, and find that all of the early-type galaxies with dust lanes in the HST data are detected in all of the Spitzer bands and have dust masses of {approx}10{sup 5}-10{sup 6.5} M{sub Sun }, while galaxies without dust lanes are not detected at 70 {mu}m and 160 {mu}m and typically have <10{sup 5} M{sub Sun} of dust. The apparently dust-free galaxies do have 24 {mu}m emission that scales with the shorter-wavelength flux, yet substantially exceeds the expectations of photospheric emission by approximately a factor of three. We conclude this emission is dominated by hot, circumstellar dust around evolved stars that does not survive to form a substantial interstellar component. The order-of-magnitude variations in dust masses between galaxies with similar stellar populations rule out a substantial contribution from continual, internal production in spite of the clear evidence for circumstellar dust. We demonstrate that the interstellar dust is not due to purely external accretion, unless the product of the merger rate of dusty satellites and the dust lifetime is at least an order of magnitude higher than expected. We propose that dust in early-type galaxies is seeded by external accretion, yet the accreted dust is maintained by continued growth in externally accreted cold gas beyond the nominal lifetime of individual grains. The several Gyr depletion time of the cold gas is long enough to reconcile the fraction of dusty early-type galaxies with the merger rate of gas-rich satellites. As the majority of dusty early-type galaxies are also low-luminosity active galactic nuclei and likely fueled

  9. Local Group

    NASA Astrophysics Data System (ADS)

    Mateo, M.; Murdin, P.

    2000-11-01

    Not long after EDWIN HUBBLE established that galaxies are `island universes' similar to our home galaxy, the MILKY WAY, he realized that a few of these external galaxies are considerably closer to us than any others. In 1936 he first coined the term `Local Group' in his famous book The Realm of the Nebulae to identify our nearest galactic neighbors. More than 60 yr later, the galaxies of the Loca...

  10. Shakhbazian compact galaxy groups. III. Photometric and spectroscopic study of ShCG 181, ShCG 344,ShCG 361, and ShCG 362

    NASA Astrophysics Data System (ADS)

    Tovmassian, H. M.; Tiersch, H.; Navarro, S. G.; Chavushyan, V. H.; Tovmassian, G. H.; Neizvestny, S.

    2004-03-01

    In 1995 we commenced a detailed spectral and photometric study of Shakhbazian compact groups. In this paper the results on groups ShCG 181, ShCG 344, ShCG 361, and ShCG 362 are presented. The redshifts of member galaxies in groups and the radial velocity dispersions, the results of the surface photometry in BVR, the profiles of the surface brightness versus semi-major axis a (or a1/4) and the twisting position angle versus semi-major axis of galaxies, virial masses, luminosities and mass-to-luminosity ratios, and the crossing times of groups are given. It is shown that some members of groups are in the process of interaction. On the basis of the results obtained in this and previous works, the general properties of thirteen ShCGs are discussed. Figures 2, 3, 5, 6, 8, 9, 11, 12 and Table 2 are only available in electronic form at http://www.edpsciences.org

  11. Satellite dwarf galaxies in a hierarchical universe: the prevalence of dwarf-dwarf major mergers

    SciTech Connect

    Deason, Alis; Wetzel, Andrew; Garrison-Kimmel, Shea

    2014-10-20

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ∼10% of satellite dwarf galaxies with M {sub star} > 10{sup 6} M {sub ☉} that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased toward larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger fraction doubles for dwarf galaxies outside of the host virial radius, so the most distant dwarf galaxies in the Local Group are the most likely to have experienced a recent major merger. We discuss the implications of these results on observable dwarf merger remnants, their star formation histories, the gas content of mergers, and massive black holes in dwarf galaxies.

  12. The Globular Cluster System of the Spiral Galaxy NGC 7814

    NASA Astrophysics Data System (ADS)

    Rhode, Katherine L.; Zepf, Stephen E.

    2003-11-01

    We present the results of a wide-field photometric study of the globular cluster (GC) system of the edge-on Sab spiral NGC 7814. This is the first spiral to be fully analyzed from our survey of the GC systems of a large sample of galaxies beyond the Local Group. NGC 7814 is of particular interest because a previous study estimated that it has 500-1000 GCs, giving it the largest specific frequency (SN) known for a spiral. Understanding this galaxy's GC system is important in terms of our understanding of the GC populations of spirals in general and has implications for the formation of massive galaxies. We observed the galaxy in BVR filters with the WIYN 3.5 m telescope and used image classification and three-color photometry to select GC candidates. We also analyzed archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of NGC 7814, both to help quantify the contamination level of the WIYN GC candidate list and to detect GCs in the inner part of the galaxy halo. Combining HST data with high-quality ground-based images allows us to trace the entire radial extent of this galaxy's GC system and determine the total number of GCs directly through observation. We find that rather than being an especially high-SN spiral, NGC 7814 has <~200 GCs and SN~1, making it comparable to the two most well-studied spiral galaxies, the Milky Way and M31. We explore the implications of these results for models of the formation of galaxies and their GC systems. The initial results from our survey suggest that the GC systems of typical elliptical galaxies can be accounted for by the merger of two or more spirals, but that for highly luminous elliptical galaxies, additional physical processes may be needed.

  13. Identification of dusty massive stars in star-forming dwarf irregular galaxies in the Local Group with mid-IR photometry

    NASA Astrophysics Data System (ADS)

    Britavskiy, N. E.; Bonanos, A. Z.; Mehner, A.; Boyer, M. L.; McQuinn, K. B. W.

    2015-12-01

    Context. Increasing the statistics of spectroscopically confirmed evolved massive stars in the Local Group enables the investigation of the mass loss phenomena that occur in these stars in the late stages of their evolution. Aims: We aim to complete the census of luminous mid-IR sources in star-forming dwarf irregular (dIrr) galaxies of the Local Group. To achieve this we employed mid-IR photometric selection criteria to identify evolved massive stars, such as red supergiants (RSGs) and luminous blue variables (LBVs), by using the fact that these types of stars have infrared excess due to dust. Methods: The method is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies. We applied our criteria to four dIrr galaxies: Pegasus, Phoenix, Sextans A, and WLM, selecting 79 point sources that we observed with the VLT/FORS2 spectrograph in multi-object spectroscopy mode. Results: We identified 13 RSGs, of which 6 are new discoveries, as well as two new emission line stars, and one candidate yellow supergiant. Among the other observed objects we identified carbon stars, foreground giants, and background objects, such as a quasar and an early-type galaxy that contaminate our survey. We use the results of our spectroscopic survey to revise the mid-IR and optical selection criteria for identifying RSGs from photometric measurements. The optical selection criteria are more efficient in separating extragalactic RSGs from foreground giants than mid-IR selection criteria, but the mid-IR selection criteria are useful for identifying dusty stars in the Local Group. This work serves as a basis for further investigation of the newly discovered dusty massive stars and their host galaxies. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 090.D-0009 and 091.D-0010.Appendix A is available in electronic form at http://www.aanda.org

  14. Comparative internal kinematics of the H II regions in interacting and isolated galaxies: implications for massive star formation modes

    NASA Astrophysics Data System (ADS)

    Zaragoza-Cardiel, Javier; Beckman, John E.; Font, Joan; García-Lorenzo, Begoña; Camps-Fariña, Artemi; Fathi, Kambiz; James, Philip A.; Erroz-Ferrer, Santiago; Barrera-Ballesteros, Jorge; Cisternas, Mauricio

    2015-08-01

    We have observed 12 interacting galaxy pairs using the Fabry-Perot interferometer GH αFaS (Galaxy H α Fabry-Perot system) on the 4.2-m William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma. We present here the Hα surface brightness, velocity and velocity dispersion maps for the 10 systems we have not previously observed using this technique, as well as the physical properties (sizes, Hα luminosities and velocity dispersion) of 1259 H II regions from the full sample. We also derive the physical properties of 1054 H II regions in a sample of 28 isolated galaxies observed with the same instrument in order to compare the two populations of H II regions. We find a population of the brightest H II regions for which the scaling relations, for example the relation between the Hα luminosity and the radius, are clearly distinct from the relations for the regions of lower luminosity. The regions in this bright population are more frequent in the interacting galaxies. We find that the turbulence, and also the star formation rate (SFR), are enhanced in the H II regions in the interacting galaxies. We have also extracted the Hα equivalent widths for the H II regions of both samples, and we have found that the distribution of H II region ages coincides for the two samples of galaxies. We suggest that the SFR enhancement is brought about by gas flows induced by the interactions, which give rise to gravitationally bound gas clouds which grow further by accretion from the flowing gas, producing conditions favourable to star formation.

  15. The Atacama Cosmology Telescope: Detection or Sunyaev-Zel'Dovich Decrement in Groups and Clusters Associated with Luminous Red Galaxies

    NASA Technical Reports Server (NTRS)

    Hand, Nick; Appel, John William; Battaglia, Nick; Bond, J. Richard; Das, Sudeep; Devlin, Mark J.; Dunkley, Joanna; Dunner, Rolando; Essinger-Hileman, Thomas; Fowler, Joseph W.; Hajian, Amir; Halpern, Mark; Hasselfield, Matthew; Hilton, Matt; Hincks, Adam D.; Hlozek, Renee; Hughes, John P.; Irwin, Kent D.; Klein, Jeff; Kosowsky, Arthur; Lin, Yen-Ting; Marriage, Tobias A.; Marsden, Danica; McLaren, Mike; Wollack, Ed

    2010-01-01

    We present a detection of the Sunyaev-Zel'dovich (SZ) decrement associated with the Luminous Red Galaxy (LRG) sample of the Sloan Digital Sky Survey. The SZ data come from 148 GHz maps of the equatorial region made by the Atacama Cosmology Telescope (ACT). The LRG sample is divided by luminosity into four bins, and estimates for the central Sunyaev-Zel'dovich temperature decrement are calculated through a stacking process. We detect and account for a bias of the SZ signal due to weak radio sources. We use numerical simulations to relate the observed decrement to Y(sub 200) and clustering properties to relate the galaxy luminosity bins to mass. We also use a relation between BCG luminosity and cluster mass based on stacked gravitational lensing measurements to estimate the characteristic halo masses. The masses are found to be in the range approx.10(exp 13) - 10(exp 14)/h Stellar Mass, a lower range than has been previously probed.

  16. Whirlpool Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Scientists are seeing unprecedented detail of the spiral arms and dust clouds in the nearby Whirlpool galaxy, thanks to a new Hubble Space Telescope image, available at http://www.jpl.nasa.gov/pictures/wfpc/wfpc.html. The image uses data collected January 15 and 24, 1995, and July 21, 1999, by Hubble's Wide Field and Planetary Camera 2, designed and built by JPL. Using the image, a research group led by Dr. Nick Scoville of the California Institute of Technology, Pasadena, clearly defined the structure of the galaxy's cold dust clouds and hot hydrogen, and they linked star clusters within the galaxy to their parent dust clouds.

    The Whirlpool galaxy is one of the most photogenic galaxies. This celestial beauty is easily seen and photographed with smaller telescopes and studied extensively from large ground- and space-based observatories. The new composite image shows visible starlight and light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms.

    The galaxy is having a close encounter with a nearby companion galaxy, NGC 5195, just off the upper edge of the image. The companion's gravitational pull is triggering star formation in the main galaxy, lit up by numerous clusters of young and energetic stars in brilliant detail. Luminous clusters are highlighted in red by their associated emission from glowing hydrogen gas.

    This image was composed by the Hubble Heritage Team from Hubble archive data and was superimposed onto data taken by Dr. Travis Rector of the National Optical Astronomy Observatory at the .9-meter (35-inch) telescope at the National Science Foundation's Kitt Peak National Observatory, Tucson, Ariz. Scoville's team includes M. Polletta of the University of Geneva, Switzerland; S. Ewald and S. Stolovy of Caltech; and R. Thompson and M. Rieke of the University of Arizona, Tucson.

    The Space Telescope Science Institute, Baltimore, Md., manages space operations for the Hubble Space

  17. A DIRECT MEASUREMENT OF THE BARYONIC MASS FUNCTION OF GALAXIES AND IMPLICATIONS FOR THE GALACTIC BARYON FRACTION

    SciTech Connect

    Papastergis, Emmanouil; Huang, Shan; Giovanelli, Riccardo; Haynes, Martha P.; Cattaneo, Andrea E-mail: shan@astro.cornell.edu E-mail: haynes@astro.cornell.edu

    2012-11-10

    We use both an H I-selected and an optically selected galaxy sample to directly measure the abundance of galaxies as a function of their 'baryonic' mass (stars + atomic gas). Stellar masses are calculated based on optical data from the Sloan Digital Sky Survey and atomic gas masses are calculated using atomic hydrogen (H I) emission line data from the Arecibo Legacy Fast ALFA survey. By using the technique of abundance matching, we combine the measured baryonic function of galaxies with the dark matter halo mass function in a {Lambda}CDM universe, in order to determine the galactic baryon fraction as a function of host halo mass. We find that the baryon fraction of low-mass halos is much smaller than the cosmic value, even when atomic gas is taken into account. We find that the galactic baryon deficit increases monotonically with decreasing halo mass, in contrast with previous studies which suggested an approximately constant baryon fraction at the low-mass end. We argue that the observed baryon fractions of low-mass halos cannot be explained by reionization heating alone, and that additional feedback mechanisms (e.g., supernova blowout) must be invoked. However, the outflow rates needed to reproduce our result are not easily accommodated in the standard picture of galaxy formation in a {Lambda}CDM universe.

  18. Fe-Group Elements in the Metal-Poor Star HD 84937: Abundances and their Implications

    NASA Astrophysics Data System (ADS)

    Sneden, Chris; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth; Wood, Michael P.

    2016-01-01

    We have derived accurate relative abundances of the Fe-group elements Sc through Zn in the very metal-poor main-sequence turnoff star HD 84937. For this study we analyzed high resolution, high signal-to-noise HST/STIS and VLT/UVES spectra over a total wavelength range 2300-7000 Å. We employed only recent or newly-applied reliable laboratory transition data for all species. Abundances from more than 600 lines of non-Fe species were combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. From parallel analyses of solar photospheric spectra we also derived new solar abundances of these elements. This in turn yielded internally-consistent relative HD 84937 abundances with respect to the Sun. For seven of the ten Fe-group elements the HD 84937 abundances were from both neutral and ionized transitions. In all of these cases the neutral and ionized species yield the same abundances within the measurement uncertainties. Therefore standard Saha ionization balance appears to hold in the HD 84937 atmosphere. We derived metallicity [Fe/H] = -2.32 with sample standard deviation of 0.06. Solid evidence is seen for departures from the solar abundance mix in HD 84937, for example [Co/Fe] = +0.14, [Cu/Fe] = -0.83, and <[Sc,Ti,V/Fe]> = +0.31. Combining our Sc, Ti, and V abundances for this star with those from large-sample spectroscopic surveys suggests that these elements are positively correlated in stars with [Fe/H] < -2. HD 84937 is unusually enriched in Sc, Ti, and V. Our analysis strongly suggests that different types of supernovae with a large scatter of explosion energies and asymmetries contributed to the creation of the Fe-group elements early in the Galaxy's history.This work has been supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grants AST-1211055 (J.E.L.), AST-1211585 (C.S.), PHY-1430152 (through JINA, J.J.C. and M.P.), EU MIRGCT-2006-046520 (M.P.), and by the ``Lendlet-2014'' Programme of the Hungarian Academy of

  19. Classic Galaxy with Glamour

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This color composite image of nearby NGC 300 combines the visible-light pictures from Carnegie Institution of Washington's 100-inch telescope at Las Campanas Observatory (colored red and yellow), with ultraviolet views from NASA's Galaxy Evolution Explorer. Galaxy Evolution Explorer detectors image far ultraviolet light (colored blue).

    This composite image traces star formation in progress. Young hot blue stars dominate the outer spiral arms of the galaxy, while the older stars congregate in the nuclear regions which appear yellow-green. Gases heated by hot young stars and shocks due to winds from massive stars and supernova explosions appear in pink, as revealed by the visible-light image of the galaxy.

    Located nearly 7 million light years away, NGC 300 is a member of a nearby group of galaxies known as the Sculptor Group. It is a spiral galaxy like our own Milky Way.

  20. SIMULTANEOUS MODELING OF THE STELLAR AND DUST EMISSION IN DISTANT GALAXIES: IMPLICATIONS FOR STAR FORMATION RATE MEASUREMENTS

    SciTech Connect

    Utomo, Dyas; Kriek, Mariska; Labbé, Ivo; Fumagalli, Mattia; Conroy, Charlie

    2014-03-10

    We have used near-ultraviolet (NUV) to mid-infrared (MIR) composite spectral energy distributions (SEDs) to simultaneously model the attenuated stellar and dust emission of 0.5 ≲ z ≲ 2.0 galaxies. These composite SEDs were previously constructed from the photometric catalogs of the NEWFIRM Medium-Band Survey by stacking the observed photometry of galaxies that have similar rest-frame NUV-to-NIR SEDs. In this work, we include a stacked MIPS 24 μm measurement for each SED type to extend the SEDs to rest-frame MIR wavelengths. Consistent with previous studies, the observed MIR emission for most SED types is higher than expected from only the attenuated stellar emission. We fit the NUV-to-MIR composite SEDs with the Flexible Stellar Population Synthesis (FSPS) models, which include both stellar and dust emission. We compare the best-fit star formation rates (SFRs) to the SFRs based on simple UV+IR estimators. Interestingly, the UV and IR luminosities overestimate SFRs—compared to the model SFRs—by more than ∼1 dex for quiescent galaxies, while for the highest star-forming galaxies in our sample the two SFRs are broadly consistent. The difference in specific SFRs also shows a gradually increasing trend with declining specific SFR, implying that quiescent galaxies have even lower specific SFRs than previously found. Contributions from evolved stellar populations to both the UV and the MIR SEDs most likely explain the discrepancy. Based on this work, we conclude that SFRs should be determined from modeling the attenuated stellar and dust emission simultaneously, instead of employing simple UV+IR-based SFR estimators.

  1. A sclerite-bearing stem group entoproct from the early Cambrian and its implications

    PubMed Central

    Zhang, Zhifei; Holmer, Lars E.; Skovsted, Christian B.; Brock, Glenn A.; Budd, Graham E.; Fu, Dongjing; Zhang, Xingliang; Shu, Degan; Han, Jian; Liu, Jianni; Wang, Haizhou; Butler, Aodhán; Li, Guoxiang

    2013-01-01

    The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans. PMID:23336066

  2. A sclerite-bearing stem group entoproct from the early Cambrian and its implications.

    PubMed

    Zhang, Zhifei; Holmer, Lars E; Skovsted, Christian B; Brock, Glenn A; Budd, Graham E; Fu, Dongjing; Zhang, Xingliang; Shu, Degan; Han, Jian; Liu, Jianni; Wang, Haizhou; Butler, Aodhán; Li, Guoxiang

    2013-01-01

    The Lophotrochozoa includes disparate tentacle-bearing sessile protostome animals, which apparently appeared in the Cambrian explosion, but lack an uncontested fossil record. Here we describe abundant well preserved material of Cotyledion tylodes Luo et Hu, 1999, from the Cambrian (Series 2) Chengjiang deposits, reinterpreted here as a stem-group entoproct. The entoproct affinity is supported by the sessile body plan and interior soft anatomy. The body consists of an upper calyx and a lower elongate stalk with a distal holdfast. The soft anatomy includes a U-shaped gut with a mouth and aboral anus ringed by retractable marginal tentacles. Cotyledion differs from extant entoprocts in being larger, and having the calyx and the stalk covered by numerous loosely-spaced external sclerites. The description of entoprocts from the Chengjiang biota traces the ancestry of yet another lophotrochozoan phylum back to the Cambrian radiation, and has important implications for the earliest evolution of lophotrochozoans. PMID:23336066

  3. Cosmological implications of interacting group field theory models: Cyclic universe and accelerated expansion

    NASA Astrophysics Data System (ADS)

    de Cesare, Marco; Pithis, Andreas G. A.; Sakellariadou, Mairi

    2016-09-01

    We study the cosmological implications of interactions between spacetime quanta in the group field theory (GFT) approach to quantum gravity from a phenomenological perspective. Our work represents a first step towards understanding early Universe cosmology by studying the dynamics of the emergent continuum spacetime, as obtained from a fundamentally discrete microscopic theory. In particular, we show how GFT interactions lead to a recollapse of the Universe while preserving the bounce replacing the initial singularity, which has already been shown to occur in the free case. It is remarkable that cyclic cosmologies are thus obtained in this framework without any a priori assumption on the geometry of spatial sections of the emergent spacetime. Furthermore, we show how interactions make it possible to have an early epoch of accelerated expansion, which can be made to last for an arbitrarily large number of e -folds, without the need to introduce an ad hoc potential for the scalar field.

  4. Constraining the role of Type IA and Type II supernovae in galaxy groups by spatially resolved analysis of ROSAT and ASCA observations

    NASA Astrophysics Data System (ADS)

    Finoguenov, A.; Ponman, T. J.

    1999-04-01

    We present the results of modelling the distribution of gas properties in the galaxy groups HCG 51, HCG 62 and NGC 5044, and in the poor cluster AWM 7, using both ASCA SIS and ROSAT data. The spectral quality of the ASCA data allows the radial distribution in the abundances of several elements to be resolved. In all systems apart from HCG 51, we see both central cooling flows and a general decline in metal abundances with radius. The ratio of iron to alpha-element abundances varies significantly, and, in comparison with theoretical supernova yields, indicates a significant contribution to the metal abundance of the intergalactic medium from Type Ia supernovae. This is seen both within the groups and throughout much of the cluster AWM 7. The total energy input into the IGM from supernovae can be calculated from our results, and is typically 20-40 per cent of the thermal energy of the gas, mostly from Type II supernovae. Our results support the idea that the SN II ejecta have been more widely distributed in the IGM, probably owing to the action of galaxy winds, and the lower iron mass-to-light ratio in groups suggests that some of this enriched gas has been lost altogether from the shallower potential wells of the smaller systems.

  5. A COMBINED LOW-RADIO FREQUENCY/X-RAY STUDY OF GALAXY GROUPS. I. GIANT METREWAVE RADIO TELESCOPE OBSERVATIONS AT 235 MHz AND 610 MHz

    SciTech Connect

    Giacintucci, Simona; O'Sullivan, Ewan; Vrtilek, Jan; David, Laurence P.; Mazzotta, Pasquale; Gitti, Myriam; Jones, Christine; Forman, William R.; Raychaudhury, Somak; Ponman, Trevor; Venturi, Tiziana; Athreya, Ramana M.; Clarke, Tracy E.; Murgia, Matteo; Ishwara-Chandra, C. H.

    2011-05-10

    We present new Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz of 18 X-ray bright galaxy groups. These observations are part of an extended project, presented here and in future papers, which combines low-frequency radio and X-ray data to investigate the interaction between central active galactic nuclei (AGNs) and the intra-group medium (IGM). The radio images show a very diverse population of group-central radio sources, varying widely in size, power, morphology, and spectral index. Comparison of the radio images with Chandra and XMM-Newton X-ray images shows that groups with significant substructure in the X-ray band and marginal radio emission at {approx}>1 GHz host low-frequency radio structures that correlate with substructures in IGM. Radio-filled X-ray cavities, the most evident form of AGN/IGM interaction in our sample, are found in half of the systems and are typically associated with small, low-, or mid-power double radio sources. Two systems, NGC5044 and NGC4636, possess multiple cavities, which are isotropically distributed around the group center, possibly due to group weather. In other systems the radio/X-ray correlations are less evident. However, the AGN/IGM interaction can manifest itself through the effects of the high-pressure medium on the morphology, spectral properties, and evolution of the radio-emitting plasma. In particular, the IGM can confine fading radio lobes in old/dying radio galaxies and prevent them from dissipating quickly. Evidence for radio emission produced by former outbursts that co-exist with current activity is found in six groups of the sample.

  6. The Araucaria Project: the Distance to the Sculptor Group Galaxy NGC 247 from Cepheid Variables Discovered in a Wide-Field Imaging Survey

    NASA Astrophysics Data System (ADS)

    García-Varela, Alejandro; Pietrzyński, Grzegorz; Gieren, Wolfgang; Udalski, Andrzej; Soszyński, Igor; Walker, Alistair; Bresolin, Fabio; Kudritzki, Rolf-Peter; Szewczyk, Olaf; Szymański, Michał; Kubiak, Marcin; Wyrzykowski, Łukasz

    2008-11-01

    We report on the discovery of a Cepheid population in the Sculptor Group spiral galaxy NGC 247 for the first time. On the basis of wide-field images collected in photometric surveys in V and I bands that were conducted with three different telescopes and cameras, 23 Cepheid variables were discovered with periods ranging from 17 to 131 days. We have constructed the period-luminosity relations from these data and obtained distance moduli to NGC 247 of 28.20 ± 0.05 mag (internal error) in V, 28.04 ± 0.06 mag in I, and 27.80 ± 0.09 mag in the reddening-independent Wesenheit index. From our optical data we have determined the total mean reddening of the Cepheids in NGC 247 to be E(B - V) = 0.13 mag, which brings the true distance modulus determinations from the V and I bands into excellent agreement with the distance determination in the Wesenheit index. The best estimate for the true distance modulus of NGC 247 from our optical Cepheid photometry is 27.80 ± 0.09 (internal error) ±0.09 mag (systematic error), which is in excellent agreement with other recent distance determinations for NGC 247 from the tip of the red giant branch method and from the Tully-Fisher relation. The distance for NGC 247 places this galaxy at twice the distance of two other Sculptor Group galaxies, NGC 300 and NGC 55, yielding supporting evidence for the filament-like structure of this group of galaxies. The reported distance value is tied to an assumed Large Magellanic Cloud distance modulus of 18.50 mag. Based on observations obtained with the 1.3 m telescope at the Las Campanas Observatory, the 2.2 m ESO/MPI telescope at the European Southern Observatory for Large Programme 171.D-0004, and the 4.0 m Blanco telescope at the Cerro Tololo Inter-American Observatory. This work is part of the PhD thesis of A.G.V.

  7. MEASUREMENT OF A METALLICITY GRADIENT IN A z = 2 GALAXY: IMPLICATIONS FOR INSIDE-OUT ASSEMBLY HISTORIES

    SciTech Connect

    Jones, Tucker; Ellis, Richard; Jullo, Eric; Richard, Johan

    2010-12-20

    We present near-infrared imaging spectroscopy of the strongly lensed z = 2.00 galaxy SDSS J120601.69+514227.8 ('the Clone arc'). Using OSIRIS on the Keck 2 telescope with laser guide star adaptive optics, we achieve resolved spectroscopy with 0.20 arcsec FWHM resolution in the diagnostic emission lines [O III], H{alpha}, and [N II]. The lensing magnification allows us to map the velocity and star formation from H{alpha} emission at a physical resolution of {approx_equal}300 pc in the galaxy source plane. With an integrated star formation rate of {approx_equal}50 M{sub sun} yr{sup -1}, the galaxy is typical of sources similarly studied at this epoch. It is dispersion dominated with a velocity gradient of {approx_equal}{+-}80 km s{sup -1} and average dispersion {sigma}r-bar=85 km s{sup -1}; the dynamical mass is 2.4 x 10{sup 10} M{sub sun} within a half-light radius of 2.9 kpc. Robust detection of [N II] emission across the entire OSIRIS field of view enables us to trace the gas phase metallicity distribution with 500 pc resolution. We find a strong radial gradient in both the [N II]/H{alpha} and [O III]/H{alpha} ratios indicating a metallicity gradient of -0.27 {+-} 0.05 dex kpc{sup -1} with central metallicity close to solar. We demonstrate that the gradient is seen independently in two multiple images. While the physical gradient is considerably steeper than that observed in local galaxies, in terms of the effective radius at that epoch, the gradient is similar. This suggests that subsequent growth occurs in an inside-out manner with the inner metallicity gradient diminished over time due to radial mixing and enrichment from star formation.

  8. Measurement of a Metallicity Gradient in a z = 2 Galaxy: Implications for Inside-out Assembly Histories

    NASA Astrophysics Data System (ADS)

    Jones, Tucker; Ellis, Richard; Jullo, Eric; Richard, Johan

    2010-12-01

    We present near-infrared imaging spectroscopy of the strongly lensed z = 2.00 galaxy SDSS J120601.69+514227.8 ("the Clone arc"). Using OSIRIS on the Keck 2 telescope with laser guide star adaptive optics, we achieve resolved spectroscopy with 0.20 arcsec FWHM resolution in the diagnostic emission lines [O III], Hα, and [N II]. The lensing magnification allows us to map the velocity and star formation from Hα emission at a physical resolution of sime300 pc in the galaxy source plane. With an integrated star formation rate of sime50 M sun yr-1, the galaxy is typical of sources similarly studied at this epoch. It is dispersion dominated with a velocity gradient of sime±80 km s-1 and average dispersion \\bar{σ} = 85 km s-1 the dynamical mass is 2.4 × 1010 M sun within a half-light radius of 2.9 kpc. Robust detection of [N II] emission across the entire OSIRIS field of view enables us to trace the gas phase metallicity distribution with 500 pc resolution. We find a strong radial gradient in both the [N II]/Hα and [O III]/Hα ratios indicating a metallicity gradient of -0.27 ± 0.05 dex kpc-1 with central metallicity close to solar. We demonstrate that the gradient is seen independently in two multiple images. While the physical gradient is considerably steeper than that observed in local galaxies, in terms of the effective radius at that epoch, the gradient is similar. This suggests that subsequent growth occurs in an inside-out manner with the inner metallicity gradient diminished over time due to radial mixing and enrichment from star formation.

  9. Galaxies in the First Billion Years: Implications for Reionization and the Star Formation History at z>6

    NASA Astrophysics Data System (ADS)

    Bunker, A. J.; Stanway, E. R.; Ellis, R. S.; Lacy, M.; Stark, D. P.; Chie, K.; McMahon, R. G.; Eyles, L. P.

    2008-10-01

    Redshift 6, one billion years after the Big Bang, marks the end of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionization. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images (Stanway et al. 2003; Bunker et al. 2004).

  10. Implications of the Group Model of Supervision and Consultation in Forensic Training.

    PubMed

    Frierson, Richard L; Joshi, Kaustubh G

    2016-09-01

    The clinical case conference has been a hallmark of undergraduate and graduate medical education for decades and affords attendees the opportunity to hear about interesting and difficult cases and to learn from a discussion of the complexities of diagnosis and treatment. In forensic psychiatry, the complexities in a case conference also extend to the formation of a forensic opinion. The application of the clinical case conference to forensic psychiatry has not been described in the literature, although many fellowship programs engage in this activity. In the forensic arena, special ethics concerns may arise regarding confidentiality, dual agency, and conflicts of interest. In this commentary, we discuss the implications of using the group approach to supervision and consultation outlined by Buchanan et al., as it relates to professional development and understanding of ethics among forensic psychiatry trainees. We also discuss the usefulness of this type of group consultation in faculty development, including the satisfaction of the Accreditation Council of Graduate Medical Education's (ACGME) Common Program Requirements and, potentially, one part of the Maintenance of Certification requirements of the American Board of Psychiatry and Neurology, Inc. PMID:27644863

  11. THE FORNAX DWARF GALAXY AS A REMNANT OF RECENT DWARF-DWARF MERGING IN THE LOCAL GROUP

    SciTech Connect

    Yozin, C.; Bekki, K.

    2012-09-01

    We present results from the first numerical analysis to support the hypothesis, first proposed in Coleman et al., that the Fornax dwarf galaxy was formed from the minor merging of two dwarfs about 2 Gyr ago. Using orbits for the Fornax dwarf that are consistent with the latest proper motion measurements, our dynamical evolution models show that the observed asymmetric shell-like substructures can be formed from the remnant of a smaller dwarf during minor merging. These models also predict the formation of diffuse stellar streams. We discuss how these stellar substructures depend on model parameters of dwarf-dwarf merging, and how the intermediate-age subpopulations found in the vicinity of these substructures may be formed from gas accretion in past merger events. We also suggest that one of Fornax's globular clusters originates from a merged dwarf companion, and demonstrate where as yet undetected tidal streams or H I gas formed from the dwarf merging may be found in the outer halo of the Galaxy.

  12. A Comparison of the Galaxy Populations in the Coma and Distant Clusters: The Evolution of k+a Galaxies and the Role of the Intracluster Medium

    NASA Astrophysics Data System (ADS)

    Poggianti, Bianca M.; Bridges, Terry J.; Komiyama, Y.; Yagi, M.; Carter, Dave; Mobasher, Bahram; Okamura, S.; Kashikawa, N.

    2004-01-01

    The spectroscopic properties of galaxies in the Coma Cluster are compared with those of galaxies in rich clusters at z~0.5, to investigate the evolution of the star formation history in clusters. Luminous galaxies with MV<=-20 and poststarburst/post-star-forming (k+a) spectra that constitute a significant fraction of galaxies in distant cluster samples are absent in Coma, where spectacular cases of k+a spectra are found instead at MV>-18.5 and represent a significant proportion of the cluster dwarf galaxy population. A simple inspection of their positions on the sky indicates that this type of galaxy does not show a preferential location within the cluster, but the bluest and strongest lined group of k+a galaxies lie in projection toward the central 1.4 Mpc of Coma and have radial velocities significantly higher than the cluster mean. We find a striking correlation between the positions of these young and strong poststarburst galaxies and substructure in the hot intracluster medium (ICM) identified from XMM-Newton data, with these galaxies lying close to the edges of two infalling substructures. This result strongly suggests that the interaction with the dense ICM could be responsible for the quenching of the star formation (thus creating the k+a spectrum) and, possibly, for any previous starburst. The evolution with redshift of the luminosity distribution of k+a galaxies can be explained by a ``downsizing effect,'' with the maximum luminosity/mass of actively star-forming galaxies infalling onto clusters decreasing at lower redshift. We discuss the possible physical origin of this downsizing effect and the implications of our results for current scenarios of environmental effects on the star formation in galaxies. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

  13. Galaxy NGC5474

    NASA Technical Reports Server (NTRS)

    2003-01-01

    NASA's Galaxy Evolution Explorer took this ultraviolet color image of the galaxy NGC5474 on June 7, 2003. NGC5474 is located 20 million light-years from Earth and is within a group of galaxies dominated by the Messier 101 galaxy. Star formation in this galaxy shows some evidence of a disturbed spiral pattern, which may have been induced by tidal interactions with Messier 101.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  14. Interplay of the scaling limit and the renormalization group: Implications for symmetry restoration

    NASA Astrophysics Data System (ADS)

    Konik, Robert M.; Saleur, Hubert; Ludwig, Andreas W.

    2002-08-01

    Symmetry restoration is usually understood as a renormalization-group induced phenomenon. In this context, the issue of whether one-loop renormalization-group equations can be trusted in predicting symmetry restoration has recently been the subject of much debate. Here we advocate a more pragmatic point of view and expand the definition of symmetry restoration to encompass all situations where the physical properties have only a weak dependence upon an anisotropy in the bare couplings. Moreover we concentrate on universal properties, and so take a scaling limit where the physics is well described by a field theory. In this context, we find a large variety of models that exhibit, for all practical purposes, symmetry restoration: even if symmetry is not restored in a strict sense, physical properties are surprisingly insensitive to the remaining anisotropy. Although we have adopted an expanded notion of symmetry restoration, we nonetheless emphasize that the scaling limit also has implications for symmetry restoration as a renormalization-group induced phenomenon. In all the models we considered, the scaling limit turns out only to permit bare couplings which are nearly isotropic and small. Then the one-loop β function should contain all the physics and higher loop orders can be neglected. We suggest that this feature generalizes to more complex models. We exhibit a large class of theories with current-current perturbations [of which the SO(8) model of interest in two-leg Hubbard ladders and armchair carbon nanotubes is one] where the one-loop β functions indicate symmetry restoration; thus we argue that these results can be trusted within the scaling limit.

  15. Luminosity function for galaxy clusters

    NASA Astrophysics Data System (ADS)

    Bajan, K.; Biernacka, M.; Flin, P.; Godłowski, W.; Panko, E.; Popiela, J.

    2016-10-01

    We constructed and studied the luminosity function of 6188 galaxyclusters. This was performed by counting brightness of galaxiesbelonging to clusters in the PF catalogue, taking galaxy data fromMRSS. Our result shows that the investigated structures arecharacterized by a luminosity function different from that ofoptical galaxies and radiogalaxies (Machalski & Godłowski2000). The implications of this result for theoriesof galaxy formation are briefly discussed.

  16. THE M81 GROUP DWARF IRREGULAR GALAXY DDO 165. I. HIGH-VELOCITY NEUTRAL GAS IN A POST-STARBURST SYSTEM

    SciTech Connect

    Cannon, John M.; Most, Hans P.; Skillman, Evan D.; Weisz, Daniel R.; Warren, Steven R.; Cook, David; Dolphin, Andrew E.; Kennicutt, Robert C.; Lee, Janice; Seth, Anil; Walter, Fabian E-mail: skillman@astro.umn.edu E-mail: warren@astro.umn.edu E-mail: adolphin@raytheon.com E-mail: jlee@obs.carnegiescience.edu E-mail: walter@mpia.de

    2011-07-01

    We present new multi-configuration Very Large Array H I spectral line observations of the M81 group dwarf irregular post-starburst galaxy DDO 165. The H I morphology is complex, with multiple column density peaks surrounding a large region of very low H I surface density that is offset from the center of the stellar distribution. The bulk of the neutral gas is associated with the southern section of the galaxy; a secondary peak in the north contains {approx}15% of the total H I mass. These components appear to be kinematically distinct, suggesting that either tidal processes or large-scale blowout have recently shaped the interstellar medium (ISM) of DDO 165. Using spatially resolved position-velocity maps, we find multiple localized high-velocity gas features. Cross-correlating with radius-velocity analyses, we identify eight shell/hole structures in the ISM with a range of sizes ({approx}400-900 pc) and expansion velocities ({approx}7-11 km s{sup -1}). These structures are compared with narrow- and broadband imaging from the Kitt Peak National Observatory and the Hubble Space Telescope (HST). Using the latter data, recent works have shown that DDO 165's previous 'burst' phase was extended temporally ({approx}>1 Gyr). We thus interpret the high-velocity gas features, H I holes, and kinematically distinct components of the galaxy in the context of the immediate effects of 'feedback' from recent star formation (SF). In addition to creating H I holes and shells, extended SF events are capable of creating localized high-velocity motion of the surrounding interstellar material. A companion paper connects the energetics from the H I and HST data.

  17. Non-axisymmetric structure in the satellite dwarf galaxy NGC 2976: Implications for its dark/bright mass distribution and evolution

    SciTech Connect

    Valenzuela, Octavio; Hernandez-Toledo, Hector; Cano, Mariana; Pichardo, Bárbara; Puerari, Ivanio; Buta, Ronald; Groess, Robert

    2014-02-01

    We present the result of an extensive search for non-axisymmetric structures in the dwarf satellite galaxy of M81, NGC 2976, using multiwavelength archival observations. The galaxy is known to present kinematic evidence for a bisymmetric distortion; however, the stellar bar presence is controversial. This controversy motivated the possible interpretation of NGC 2976 as presenting an elliptical disk triggered by a prolate dark matter halo. We applied diagnostics used in spiral galaxies in order to detect stellar bars or spiral arms. The m = 2 Fourier phase has a jump around 60 arcsec, consistent with a central bar and bisymmetric arms. The CO, 3.6 μm surface brightness, and the dust lanes are consistent with a gas-rich central bar and possibly with gaseous spiral arms. The bar-like feature is offset close to 20° from the disk position angle, in agreement with kinematic estimations. The kinematic jumps related to the dust lanes suggest that the bar perturbation in the disk kinematics is non-negligible and the reported non-circular motions, the central gas excess, and the nuclear X-ray source (active galactic nucleus/starburst) might be produced by the central bar. Smoothed particle hydrodynamics simulations of disks inside triaxial dark halos suggest that the two symmetric spots at 130 arcsec and the narrow arms may be produced by gas at turning points in an elliptical disk, or, alternatively, the potential ellipticity can be produced by a tidally induced strong stellar bar/arms; in both cases the rotation curve interpretation is, importantly, biased. The M81 group is a natural candidate to trigger the bisymmetric distortion and the related evolution as suggested by the H I tidal bridge detected by Chynoweth et al. We conclude that both mechanisms, the gas-rich bar and spiral arms triggered by the environment (tidal stirring) and primordial halo triaxiality, can explain most of the NGC 2976 non-circular motions, mass redistribution, and nuclear activity

  18. Redshift distributions of galaxies in the Dark Energy Survey Science Verification shear catalogue and implications for weak lensing

    NASA Astrophysics Data System (ADS)

    Bonnett, C.; Troxel, M. A.; Hartley, W.; Amara, A.; Leistedt, B.; Becker, M. R.; Bernstein, G. M.; Bridle, S. L.; Bruderer, C.; Busha, M. T.; Carrasco Kind, M.; Childress, M. J.; Castander, F. J.; Chang, C.; Crocce, M.; Davis, T. M.; Eifler, T. F.; Frieman, J.; Gangkofner, C.; Gaztanaga, E.; Glazebrook, K.; Gruen, D.; Kacprzak, T.; King, A.; Kwan, J.; Lahav, O.; Lewis, G.; Lidman, C.; Lin, H.; MacCrann, N.; Miquel, R.; O'Neill, C. R.; Palmese, A.; Peiris, H. V.; Refregier, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sánchez, C.; Sheldon, E.; Uddin, S.; Wechsler, R. H.; Zuntz, J.; Abbott, T.; Abdalla, F. B.; Allam, S.; Armstrong, R.; Banerji, M.; Bauer, A. H.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carretero, J.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Doel, P.; Fausti Neto, A.; Fernandez, E.; Flaugher, B.; Fosalba, P.; Gerdes, D. W.; Gruendl, R. A.; Honscheid, K.; Jain, B.; James, D. J.; Jarvis, M.; Kim, A. G.; Kuehn, K.; Kuropatkin, N.; Li, T. S.; Lima, M.; Maia, M. A. G.; March, M.; Marshall, J. L.; Martini, P.; Melchior, P.; Miller, C. J.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sako, M.; Sanchez, E.; Santiago, B.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Vikram, V.; Walker, A. R.; Dark Energy Survey Collaboration

    2016-08-01

    We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based photometric redshift methods—annz2, bpz calibrated against BCC-Ufig simulations, skynet, and tpz—are analyzed. For training, calibration, and testing of these methods, we construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-z 's. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 ±0.01 over the range 0.3

  19. Chemo-dynamical evolution model: Enrichment of r-process elements in the Local Group dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Hirai, Yutaka; Ishimaru, Yuhri; Saitoh, Takayuki R.; Fujii, Michiko S.; Hidaka, Jun; Kajino, Toshitaka

    2015-08-01

    Enrichment of the r-process elements is expected to provide a critical clue to understand the formation history of galactic halos. Recent astronomical high dispersion observations of metal-poor stars have shown large dispersions in relative abundance ratios of r-process elements such as [Eu/Fe] in stars with [Fe/H] < -2.5. Astrophysical site(s) of r-process has, however, not been identified yet. Promising site(s) of r-process are core-collapse supernovae (CCSNe) and neutron-star mergers (NSMs). Recent nucleosynthesis studies have shown that r-process elements heavier than 110 of mass nu