Science.gov

Sample records for local group galaxy

  1. The dynamics of isolated Local Group galaxies

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Bullock, James S.; Boylan-Kolchin, Michael; Kaplinghat, Manoj; Cohen, Judith G.

    2014-03-01

    We measured velocities of 862 individual red giant stars in seven isolated dwarf galaxies in the Local Group: NGC 6822, IC 1613, VV 124 (UGC 4879), the Pegasus dwarf irregular galaxy (DDO 216), Leo A, Cetus and Aquarius (DDO 210). We also computed velocity dispersions, taking into account the measurement uncertainties on individual stars. None of the isolated galaxies is denser than the densest Local Group satellite galaxy. Furthermore, the isolated dwarf galaxies have no obvious distinction in the velocity dispersion-half-light radius plane from the satellite galaxies of the Milky Way and M31. The similarity of the isolated and satellite galaxies' dynamics and structural parameters imposes limitations on environmental solutions to the `too big to fail' problem, wherein there are fewer dense dwarf satellite galaxies than would be expected from cold dark matter simulations. This data set also has many other applications for dwarf galaxy evolution, including the transformation of dwarf irregular into dwarf spheroidal galaxies. We intend to explore these issues in future work.

  2. 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.

  3. 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

  4. 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.

  5. Chemical evolution models of Local Group galaxies

    NASA Astrophysics Data System (ADS)

    Tosi, Monica

    Status quo and perspectives of standard chemical evolution models of Local Group galaxies are summarized, and what we have learned from them is discussed, as well as what we have not learned yet, and what I think will be learned in the near future. Galactic chemical evolution models have shown that: I) stringent constraints on primordial nucleosynthesis can be derived from the observed Galactic abundances of the light elements; II) the Milky Way has been accreting external gas from early epochs to the present time; and III) the vast majority of Galactic halo stars have formed quite rapidly at early epochs. Chemical evolution models for the closest dwarf galaxies, although still uncertain, are expected to become extremely reliable in the immediate future, thanks to the quality of new generation photometric and spectroscopic data which are currently being acquired.

  6. 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.

  7. Constraining the Mass of the Local Group through Proper Motion Measurements of Local Group Galaxies

    NASA Astrophysics Data System (ADS)

    Sohn, S. Tony; van der Marel, R.; Anderson, J.

    2012-01-01

    The Local Group and its two dominant spiral galaxies have been the benchmark for testing many aspects of cosmological and galaxy formation theories. This includes, e.g., dark halo profiles and shapes, substructure and the "missing satellite" problem, and the minimum mass for galaxy formation. But despite the extensive work in all of these areas, our knowledge of the mass of the Milky Way and M31, and thus the total mass of the Local Group remains one of the most poorly established astronomical parameters (uncertain by a factor of 4). One important reason for this problem is the lack of information in tangential motions of galaxies, which can be only obtained through proper motion measurements. In this study, we introduce our projects for measuring absolute proper motions of (1) the dwarf spheroidal galaxy Leo I, (2) M31, and (3) the 4 dwarf galaxies near the edge of the Local Group (Cetus, Leo A, Tucana, and Sag DIG). Results from these three independent measurements will provide important clues to the mass of the Milky Way, M31, and the Local Group as a whole, respectively. We also present our proper motion measurement technique that uses compact background galaxies as astrometric reference sources.

  8. HII regions in dwarf irregular galaxies of the local group

    NASA Technical Reports Server (NTRS)

    Hodge, Paul; Lee, Myung Gyoon

    1990-01-01

    Deep, narrowband H alpha Charge Coupled Device (CCD) surveys of HII regions were carried out in several dwarf irregular galaxies in and near the local group. Data are now complete for these galaxies: NGC 6822, GR 8, IC 10, IC 1613, Sextans A, Sextans B, and Sag Irr. Observations are complete for DDO 47, 53, 167, 168 and 187. Details of some of the results for the surveys completed so far are discussed. For NGC 6822, CCD survey at H alpha resulted in the detection of 145 HII regions in the local group irregular galaxy NGC 6822. Most of them are newly detected, faint surface-brightness objects. Positions, maps and dimensions are being published elsewhere. For GR 8, a deep narrowband H alpha imaging of the nearby dwarf irregular galaxy GR 8 revealed a total of 32 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies, except for size of sample effects. Most HII regions detected are at the very low luminosity end of the general luminosity function. For IC 10, a deep CCD narrowband H alpha imaging of the local group dwarf irregular galaxy IC 10 revealed a total of 144 HII regions. Positions, H alpha luminosities, and sizes of these objects were determined. The H alpha luminosity function has the same shape as that for more luminous galaxies.

  9. Dust Production in Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Zijlstra, Albert; Sloan, Greg; Bernard-Salas, Jeronimo; Blommaert, Joris A. D. L.; Cioni, Maria-Rosa; Devost, Daniel; Feast, Michael W.; Groenewegen, Martin A. T.; Habing, Harm; Hony, Sacha; Lagadec, Eric; Loup, Cecile; Matsuura, Mikako; Menzies, John W.; Sloan, Greg C.; Waters, L. B. F. M.; Whitelock, Patricia A.; Wood, Peter R.; van Loon, Jacco Th.

    2006-05-01

    The superwind phase on the Asymptotic Giant Branch is a crucial ingredient of stellar and galactic evolution. The superwind ejecta are responsible for much of the interstellar hydrogen of evolved galaxies, and are a dominant contributor to the dust input into the ISM. The superwind determines the final mass of stellar remnants, and therefore affects, e.g., the type-I supernova rate. The characteristics of the superwind are still very poorly known, especially at non-solar metallicities. Spitzer has contributed a large and invaluable dataset on Magellanic Cloud stars, measuring dust, molecular bands and allowing accurate mass-loss measurements. We now propose to extend the (age, metallicity) parameter range by observing a number of other Milky Way satellites. The carbon stars in these galaxies trace an older population than the Magellanic Clouds, and extend to much lower metallicities. They are therefore crucial to allow us to extrapolate the Magellanic Cloud measurements to metal-poor environments. We propose to acquire low-resolution spectra of stars in the Sagittarius dwarf galaxy, Carina, Sculptor and Fornax. The selected stars range in metallicity from -0.55 to -2.0, and in age from 5-8 Gyr. Two low-metallicity planetary nebulae in these galaxies are also included. We will study the dust continuum, dust minerals (SiC, MgS) and gas-phase molecular bands (especially acetylene). Mass loss rates will be determined using our dust models, and we will measure the fractional abundances of amorphous carbon dust and SiC grains. Only Spitzer can provide these crucial measurements of extra-galactic AGB stars. The result will be our first knowledge of mass loss efficiency, dust formation, and dust abundances, at low to very low metallicities. These data are necessary to obtain reliable models of mass loss and of stellar evolution.

  10. 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.

  11. Local Group galaxies in a ΛCDM Universe

    NASA Astrophysics Data System (ADS)

    Li, Yang-Shyang

    2009-01-01

    This thesis focuses on the galaxies in the Local Group including the Milky Way and its satellites and the Andromeda galaxy. I start with the analyses of satellites in a dark matter halo presumably similar to that of the Milky Way (Chapter 2). One of the goals is to establish the relation between the dark matter satellites seen in the simulations and the satellites (and especially their dark matter haloes) we see around the Milky Way. For example, do the simulated satellites have similar properties in terms of spatial distribution and kinematics to those of the Milky Way? I then take a further step to combine these dark matter simulations with phenomenological recipes to follow the evolution of the baryons that may be associated to the satellites (Chapter 3). The essential questions that I address here are: why there are only approximately 20 satellites around the Milky Way while many more are predicted in the simulations? What physical processes have affected the satellites and led them to have the variety of properties we observe today? In Chapter 4, I delve into the dynamical properties of the model satellites and compare the mass content in the innermost regions with the recent observational constraints for the Milky Way dwarfs. In Chapter 5, I estimate the masses of the Local Group and the Milky Way using a novel simulation of the Universe.

  12. Dwarf Galaxies in the Local Group and in the Local Volume (Invited Talk)

    NASA Astrophysics Data System (ADS)

    Grebel, E. K.

    After summarizing the characteristics of different types of dwarf galaxies I briefly review our current state of knowledge of dwarf galaxy evolution in the Local Group, for which we now have a fairly detailed although by no means comprehensive picture. All Local Group dwarfs studied to date contain an old population, though its fraction varies considerably. The majority of the dwarf companions of the Milky Way shows evidence for a common epoch of ancient star formation. Spatial variations in star formation are frequently observed in many dwarf galaxies in the Local Group and beyond. These spatial variations range from a seemingly stochastic distribution of star-forming regions in gas-rich, high-mass dwarfs to radial gradients in low-mass dwarfs. The global mode of star formation may be either continuous with amplitude variations or episodic. High-mass dwarf galaxies tend to form stars over a Hubble time, whereas low-mass dwarfs eventually cease to form stars, possibly aided by environmental effects. Much less is known about the content and properties of dwarf galaxies in the Local Volume, which we are trying to remedy through a large observational effort. Dwarf galaxies in the Local Volume follow a similar trend with absolute magnitude, mean metallicity, and central surface brightness as the Local Group dwarfs do, and appear to be subject to morphological segregation.

  13. Planetary nebulae in galaxies beyond the Local Group.

    NASA Astrophysics Data System (ADS)

    Ford, H. C.; Ciardullo, R.; Jacoby, G. H.; Hui, X.

    Planetary nebulae can be used to estimate the distances to galaxies and to measure stellar dynamics in faint halos. The authors discuss surveys which have netted a total of 665 candidate planetary nebulae in NGC 5128 (Cen A), NGC 5102, NGC 3031 (M81), NGC 3115, three galaxies in the Leo Group (NGC 3379, NGC 3384, NGC 3377), NGC 5866, and finally, in NGC 4486 (M87). The highly consistent distances derived from the brightnesses of the jth nebula and the median nebula in different fields in the same galaxy and from different galaxies in the same group lend strong support to the suggestion that planetaries are an accurate standard candle in old stellar populations. Comparison of theoretical luminosity functions to be observed PNLFs shows that there is a very small dispersion in the central star masses.

  14. Dwarf Galaxies in the Leo I Group: the Group Luminosity Function beyond the Local Group (Oral Contribution)

    NASA Astrophysics Data System (ADS)

    Flint, K.; Bolte, M.; Mendes de Oliveira, C.

    We present first results of a survey of the Leo I group at 10 Mpc for M_R < -10 dwarf galaxies. This is part of a larger program to measure the faint end of the galaxy luminosity function in nearby poor groups. Our method is optimized to find Local-Group-like dwarfs down to dwarf spheroidal surface brightnesses, but we also find very large LSB dwarfs in Leo I with no Local Group counterpart. A preliminary measurement of the luminosity function yields a slope consistent with that measured in the Local Group.

  15. 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.

  16. Observational Evidence for Galaxy Evolution in the Local Group (Invited Talk)

    NASA Astrophysics Data System (ADS)

    Tolstoy, E.

    This review aims to give a summary of our understanding of galaxy evolution as infered from studies of nearby galaxies; how observations made with the Hubble Space Telescope have contributed significantly to our detailed understanding of the older stellar populations in Local Group dwarf galaxies. Recent results from VLT are also promising interesting future prospects for the study of resolved stellar populations in nearby dwarf galaxies.

  17. A redshift survey of IRAS galaxies. V - The acceleration on the Local Group

    NASA Technical Reports Server (NTRS)

    Strauss, Michael A.; Yahil, Amos; Davis, Marc; Huchra, John P.; Fisher, Karl

    1992-01-01

    The acceleration on the Local Group is calculated based on a full-sky redshift survey of 5288 galaxies detected by IRAS. A formalism is developed to compute the distribution function of the IRAS acceleration for a given power spectrum of initial perturbations. The computed acceleration on the Local Group points 18-28 deg from the direction of the Local Group peculiar velocity vector. The data suggest that the CMB dipole is indeed due to the motion of the Local Group, that this motion is gravitationally induced, and that the distribution of IRAS galaxies on large scales is related to that of dark matter by a simple linear biasing model.

  18. 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.

  19. 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.

  20. Chemical substructure and inhomogeneous mixing in Local Group dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Venn, K. A.

    Evidence for inhomogeneous mixing in the Carina, Draco, and Sculptor dwarf galaxies is examined from chemical abundance patterns. Inhomogeneous mixing at early times is indicated in the classical dwarf galaxies, though cannot be ascertained in ultra faint dwarfs. Mixing efficiencies can affect the early metallicity distribution function, the pre-enrichment levels in globular clusters, and also have an impact on the structure of dwarf systems at early times. Numerical models that include chemical evolution explicitly do a better job in reproducing the observations, and make interesting predictions for the nature of dwarf galaxies and their first stars at the earliest times.

  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 STELLAR-TO-HALO MASS RELATION FOR LOCAL GROUP GALAXIES

    SciTech Connect

    Brook, C. B.; Cintio, A. Di; Knebe, A.; Yepes, G.; Gottlöber, S.; Hoffman, Y.; Garrison-Kimmel, S.

    2014-03-20

    We contend that a single power-law halo mass distribution is appropriate for direct matching to the stellar masses of observed Local Group dwarf galaxies, allowing the determination of the slope of the stellar mass-halo mass relation for low-mass galaxies. Errors in halo masses are well defined as the Poisson noise of simulated Local Group realizations, which we determine using local volume simulations. For the stellar mass range 10{sup 7} M {sub ☉}galaxies, we find that the stellar mass-halo mass relation follows a power law with slope of 3.1, significantly steeper than most values in the literature. This steep relation between stellar and halo masses would indicate that Local Group dwarf galaxies are hosted by dark matter halos with a small range of mass. Our methodology is robust down to the stellar mass to which the census of observed Local Group galaxies is complete, but the significant uncertainty in the currently measured slope of the stellar-to-halo mass relation will decrease dramatically if the Local Group completeness limit was 10{sup 6.5} M {sub ☉} or below, highlighting the importance of pushing such limit to lower masses and larger volumes.

  3. Local group irregular galaxies LGS 3 and Pegasus

    SciTech Connect

    Christian, C.A.; Tully, R.B.

    1983-07-01

    The Galileo/IFA 500 x 500 CCD camera was used to resolve red giant stars in the gas-rich dwarf galaxy LGS 3 at magnitudes fainter than V = 21.8. Depending on whether these stars are >10/sup 9/ yr old or 10/sup 8/--10/sup 9/ yr old, the distance of the galaxy is 0.7--1.2 Mpc. Although H I gas has been detected in this system, there has been no significant star formation for at least the last 7 x 10/sup 7/ yr. The CM diagram of LGS 3 is compared with the CM diagrams of the Pegasus irregular galaxy discussed by Hoessel and Mould. A distance of 1.3 Mpc is suggested for Pegasus, rather than the larger distance preferred by Hoessel and Mould or the very much larger distance offered by Sandage and Tammann.

  4. Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Tully, R. Brent

    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}12}{{M}⊙ } 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}matter}˜ 0.15 in a flat topology, with a 68% probability of being less than 0.44.

  5. 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.

  6. Metallicity Distribution Functions of Four Local Group Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Ross, Teresa L.; Holtzman, Jon; Saha, Abhijit; Anthony-Twarog, Barbara J.

    2015-06-01

    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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is

  7. 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.

  8. Estimated number of field stars toward Galactic globular clusters and Local Group Galaxies

    NASA Technical Reports Server (NTRS)

    Ratnatunga, K. U.; Bahcall, J. N.

    1985-01-01

    Field star densities are estimated for 89 fields with /b/ greater than 10 degrees based on the Galaxy model of Bahcall and Soneira (1980, 1984; Bahcall et al. 1985). Calculated tables are presented for 76 of the fields toward Galactic globular clusters, and 16 Local Group Galaxies in 13 fields. The estimates can be used as an initial guide for planning both ground-based and Space Telescope observations of globular clusters at intermediate-to-high Galactic latitudes.

  9. The Local Group Dwarf Irregular Galaxy NGC 6822: new insight on its star formation history .

    NASA Astrophysics Data System (ADS)

    Fusco, F.; Buonanno, R.; Bono, G.; Cassisi, S.; Monelli, M.; Pietrinferni, A.; Hidalgo, S. L.; Aparicio, A.

    We present a new photometric analysis of the Local Group Dwarf Irregular Galaxy NGC 6822 based on archival Hubble Space Telescope Advanced Camera for Surveys images. The data correspond to three fields covering the south-east region of the galaxy; for each field F475W and F814W HST bands are available. For each field an accurate color magnitude diagram (F814W, F475W-F814W) has been obtained. Preliminary hints on the galaxy star formation history are presented based on the comparison with isochrones from "A Bag of Stellar Tracks and Isochrones" (BaSTI) database.

  10. 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

  11. 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.

  12. Mass of the Local Group from Proper Motions of Distant Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    van der Marel, Roeland

    2010-09-01

    The Local Group and its two dominant spirals, the Milky Way and M31, have become the benchmark for testing many aspects of cosmological and galaxy formation theories, due to many exciting new discoveries in the past decade. However, it is difficult to put results in a proper cosmological context, because our knowledge of the mass M of the Local Group remains uncertain by a factor 4. In units of 10^{12} solar masses, a spherical infall model for the zero-velocity surface gives M 1.3; the sum of estimates for the Milky Way and M31 masses gives M 2.6; and the Local Group Timing argument for the M31 orbit gives M 5.6. It is possible to discriminate between the proposed masses by calculating the orbits of galaxies at the edge of the Local Group, which requires knowledge of transverse velocity components. We therefore propose to use ACS/WFC to determine the proper motions of the 4 dwarf galaxies near the edge of the Local Group {Cetus, Leo A, Tucana, Sag DIG} for which deep first epoch data {with 5-7 year time baselines} already exist in the HST Archive. Our team has extensive expertise with HST astrometric science, and our past/ongoing work for, e.g., Omega Cen, LMC/SMC and M31 show that the necessary astrometric accuracy is within the reach of HST's demonstrated capabilities. We have developed, tested, and published a new technique that uses compact background galaxies as astrometric reference sources, and we have already reduced the first epoch data. The final predicted transverse velocity accuracy, 36 km/s when averaged over the sample, will be sufficient to discriminate between each of the proposed Local Group masses at 2-sigma significance {4-sigma between the most extreme values}. Our project will yield the most accurate Local Group mass determination to date, and only HST can achieve the required accuracy.

  13. 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.

  14. 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.

  15. 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.

  16. Radio properties of galaxy groups in the Local Universe (<80 Mpc)

    NASA Astrophysics Data System (ADS)

    Kolokythas, K.

    2013-09-01

    The most likely source of energy injection into the intergalactic medium of galaxy groups is AGN (Active Galactic Nuclei) feedback. Since >50% of galaxies in the local Universe reside in groups and many of them host radiative cooling gas halos, which can fuel a central SMBH, they are probably the key environment for the study of AGN/hot gas interactions. Using a complete, optically selected sample of groups -the Complete Local-Volume Groups Sample (CLoGS) project- observed in both radio and Xray bands, I examine the radio properties of AGN in nearby galaxy groups. My work targets to the characterization of the AGN population in groups, and examination of their impact on the intra-group gas and member galaxies. By focusing on low-frequency radio emission (240 MHz and 610 MHz ), past as well as current AGN activity can be identified with the combination of good spatial resolution at 610 MHz and the sensitivity to older electron populations at 235 MHz. The combination then of radio with optical and X-ray bands reveals the complex interactions with their environment and the physical processes that govern galaxy transformations. Results from our new GMRT observations at 235 and 610 MHz will be presented here for the first time for the systems of 4261, 5982, 1060 and 5903. These systems are good examples of the wide variety of radio properties: from groups dominated by a single powerful central source (4261), through weak AGN and star-formation dominated systems (1060, 5982) to diffuse, merger-related sources (5903). These are all important for the investigation of the IGM/AGN connection and the understanding of the physical mechanisms of the energy injection.

  17. 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.

  18. 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}ȯ )={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.

  19. 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.

  20. 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.

  1. 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.

  2. The luminosities of backsplash galaxies in constrained simulations of the Local Group

    NASA Astrophysics Data System (ADS)

    Knebe, Alexander; Libeskind, Noam I.; Knollmann, Steffen R.; Martinez-Vaquero, Luis A.; Yepes, Gustavo; Gottlöber, Stefan; Hoffman, Yehuda

    2011-03-01

    We study the differences and similarities in the luminosities of bound, infalling and the so-called backsplash galaxies of the Milky Way and M31 using a hydrodynamical simulation performed within the Constrained Local UniversE Simulation (CLUES) project. The simulation models the formation of the Local Group within a self-consistent cosmological framework. We find that even though backsplash galaxies passed through the virial radius of their host halo and hence may have lost a (significant) fraction of their mass, their stellar populations are hardly affected. This leaves us with comparable luminosity functions for infalling and backsplash galaxies and hence little hope to decipher their past (and different) formation and evolutionary histories by luminosity measurements alone. Nevertheless, due to the tidal stripping of dark matter we find that the mass-to-light ratios have changed when comparing the various populations against each other: they are highest for the infalling galaxies and lowest for the bound satellites with the backsplash galaxies in between.

  3. 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.

  4. 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.

  5. 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.

  6. Dark energy in the two-body problem: The local group of galaxies

    NASA Astrophysics Data System (ADS)

    Emelyanov, N. V.; Kovalyov, M. Yu.; Chernin, A. D.

    2015-06-01

    The two-body problem of classical mechanics can be extended in a natural way by introducing a universal dark-energy background, which acts as a third dynamical factor. For real systems of galaxies, the corresponding additional acceleration is described by general relativity in the Newtonian limit, in which deviations from the Minkowski metric are very small. It is shown that this acceleration has the same form in different inertial and non-inertial reference frames. The invariance of the acceleration produced by dark energy reflects the fact that, according to its mechanical properties, dark energy is a vacuum that is comoving with any motion. In this generalized formulation, as in the classical case, the two-body problem with a dark-energy background reduces to the motion of a single body in a central field. Two problems of this kind are considered for the Local Group of galaxies. The first, "internal," problem concerns the binary system formed by the main bodies of the Local Group: our galaxy and M31. The subject of the second, "external," problem is the binary system formed by the Local Group as a whole and its closest neighbor, the Virgo Cluster. In the internal problem, the effect of the dark energy is that the binary system is not bound if its mass does not exceed 3 × 1012 M⊙, which is allowed by the observational data. The external problem demonstrates the possibility of an evolutionary scenario in which a group could initially be located in the volume of a cluster, but then leave it and, moving away with an acceleration created by dark energy, arrive at the observed distance from the cluster.

  7. 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.

  8. 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).

  9. 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.

  10. 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

  11. 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

  12. 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.

  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. 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, that 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 a 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 1-1.25Msun objects of metallicity Z=0.001 and from 1.5-2.5Msun stars with Z=0.002. Oxygen-rich stars constitute the majority of the sample (65%), mainly low mass stars (<2Msun) that produce a negligible amount of dust (<10^{-7}Msun/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be 6x10^{-7}Msun/yr with an uncertainty of 30%. 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.

  15. 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.

    2016-05-01

    We used models of thermally-pulsing asymptotic giant branch (AGB) stars, that 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 a 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 - 1.25M⊙ objects of metallicity Z = 10-3 and from 1.5 - 2.5M⊙ stars with Z = 2 × 10-3. Oxygen-rich stars constitute the majority of the sample (˜65%), mainly low mass stars (<2M⊙) that produce a negligible amount of dust (≤10-7M⊙/yr). We predict the overall dust-production rate from IC 1613, mostly determined by carbon stars, to be ˜6 × 10-7M⊙/yr with an uncertainty of 30%. 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.

  16. 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.

  17. 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.

  18. Going out with a bang or a whimper? Star formation and quenching in the Local Group's satellite galaxies

    NASA Astrophysics Data System (ADS)

    Benson, Andrew

    2014-10-01

    HST observations of the Milky Way and M31's satellite galaxies show that those galaxies have an incredible diversity of star-formation histories, yet with the exception of the Magellanic Clouds, NGC205, and NGC185, none have active star formation or cold gas at the present. What accounts for the variation in star-formation histories, and what turns off star formation? We propose to use the publicly available Galacticus semi-analytic modeling code to explore the mechanisms for star formation and quenching of Local Group dwarf galaxies, comparing the satellite galaxies of the Milky Way and M31 with the star-forming "field" galaxies of the Local Group. We will create new modules for Galacticus to incorporate physical processes necessary to follow star formation and quenching {e.g., ram- pressure and tidal stripping and compression of gas}, and perform a Markov Chain Monte Carlo analysis of the HST-derived star-formation histories to determine the best-fit physical model and degeneracies of parameters for star formation in the Local Group. These new modules and the Markov chains will be publicly released via the Galacticus web server. With this study, we can determine to what extent the star-formation histories and quenching of Local Group dwarfs are governed by physical processes that depend on properties of the Milky Way and M31's dark and gas halos versus other "external" {e.g., reionization-induced photoionization} or "internal" {e.g., supernova feedback} processes. This study will be a window into the broader question of star formation in dwarf galaxies.

  19. Chemical analysis of carbon stars in the Local Group. II. The Carina dwarf spheroidal galaxy

    NASA Astrophysics Data System (ADS)

    Abia, C.; de Laverny, P.; Wahlin, R.

    2008-04-01

    Aims:We present new results of our ongoing chemical study of carbon stars in Local Group galaxies to test the critical dependence of s-process nucleosynthesis on the stellar metallicity. Methods: We collected optical spectra with the VLT/UVES instrument of two carbon stars found in the Carina Dwarf Spheroidal (dSph) galaxy, namely ALW-C6 and ALW-C7. We performed a full chemical analysis using the new generation of hydrostatic, spherically symmetric carbon-rich model atmospheres and the spectral synthesis method in LTE. Results: The luminosities, atmosphere parameters and chemical composition of ALW-C6 and ALW-C7 are compatible with these stars being in the TP-AGB phase undergoing third dredge-up episodes, although their extrinsic nature (external pollution in a binary stellar system) cannot be definitively excluded. Our chemical analysis shows that the metallicity of both stars agree with the average metallicity ([Fe/H] -1.8 dex) previously derived for this satellite galaxy from the analysis of both low resolution spectra of RGB stars and the observed colour magnitude diagrams. ALW-C6 and ALW-C7 present strong s-element enhancements, [ s/Fe] = +1.6, +1.5, respectively. These enhancements and the derived s-process indexes [ ls/Fe] , [ hs/Fe] and [ hs/ls] are compatible with theoretical s-process nucleosynthesis predictions in low mass AGB stars ( 1.5 M_⊙) on the basis that the 13C(α,n)16O is the main source of neutrons. Furthermore, the analysis of C2 and CN bands reveals a large carbon enhancement (C/O 7 and 5, respectively), much larger than the values typically found in galactic AGB carbon stars (C/O 1{-}2). This is also in agreement with the theoretical prediction that AGB carbon stars are formed more easily through third dredge-up episodes as the initial stellar metallicity drops. However, theoretical low-mass AGB models apparently fail to simultaneously fit the observed s-element and carbon enhancements. On the other hand, Zr is found to be less enhanced in

  20. 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.

  1. 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.

  2. X-ray Source Population Study of the Local Group Galaxy M 31

    NASA Astrophysics Data System (ADS)

    Stiele, Holger

    2010-11-01

    This dissertation presents the analysis of a large and deep XMM-Newton survey of the second large Local Group spiral galaxy M31. The survey observations, taken between June 2006 and February 2008, together with re-analysed archival observations from June 2000 to July 2004 cover, for the first time, the whole D25 ellipse of M 31 with XMM-Newton down to a limiting luminosity of ˜10^35 erg s-1 in the 0.2-4.5 keV band. The main goal of the thesis was a study of the different source populations of M 31 that can be observed in X-rays. Therefore a catalogue was created, which contains all 1 948 sources detected in the 0.2 - 12.0 keV range. 961 of these sources were detected in X-rays for the first time. Source classification and identification was based on X-ray hardness ratios, spatial extent of the sources, and by cross correlating with catalogues in the X-ray, optical, infrared and radio wavelengths. An additional classification criterion was the long-term temporal variability of the sources in X-rays. This variability allows us to distinguish between X-ray binaries and active galactic nuclei. Furthermore, supernova remnant classifications of previous studies that did not use long-term variability as a classification criterion, could be validated. Including previous Chandra and ROSAT observations in the long-term variability study allowed me to detect additional transient or at least highly variable sources, which are good candidates for being X-ray binaries. Fourteen of the 40 supersoft source (SSS) candidates correlated with optical novae and therefore can be considered the supersoft emission of the optical novae. Among them is the first nova/SSS detected in a globular cluster of M 31. Correlations with previous ROSAT and Chandra studies revealed that only three SSSs are visible for at least one decade. This result underlines the strong long-term variability found for the class of SSSs. In addition the correlations demonstrated that strict selection criteria have to

  3. The Local Group: Our Galactic Neighborhood.

    ERIC Educational Resources Information Center

    Hodge, Paul

    1987-01-01

    Presents information on the properties and largest spirals of the Local Group galaxies. Explains the three categories of galaxies, identifies the brightest members of the Local Group, and discusses recent discoveries within the group. (ML)

  4. Local Universe Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Carignan, Claude

    2015-08-01

    One of the outstanding problems in cosmology is addressing the "small-scale crisis" and understanding structure formation at the smallest scales. Standard Lambda Cold Dark Matter cosmological simulations of Milky Way-size DM halos predict many more DM sub-halos than the number of dwarf galaxies observed. This is the so-called Missing Satellites Problem. The most popular interpretation of the Missing Satellites Problem is that the smallest dark matter halos in the universe are extremely inefficient at forming stars. The virialized extent of the Milky Way's halo should contain ~500 satellites, while only ˜100 satellites and dwarfs are observed in the whole Local Group. Despite the large amount of theoretical work and new optical observations, the discrepancy, even if reduced, still persists between observations and hierarchical models, regardless of the model parameters. It may be possible to find those isolated ultra-faint missing dwarf galaxies via their neutral gas component, which is one of the goals we are pursuing with the SKA precursor KAT-7 in South Africa, and soon with the SKA pathfinder MeerKAT.

  5. The Nearest Group of Galaxies

    NASA Astrophysics Data System (ADS)

    van den Bergh, Sidney

    1999-06-01

    The small Antlia-Sextans clustering of galaxies is located at a distance of only 1.36 Mpc from the Sun and 1.72 Mpc from the adopted barycenter of the Local Group. The latter value is significantly greater than the radius of the zero-velocity surface of the Local Group that, for an assumed age of 14 Gyr, has R0=1.18+/-0.15 Mpc. This, together with the observation that the members of the Ant-Sex group have a mean redshift of 114+/-12 km s-1 relative to the centroid of the Local Group, suggests that the Antlia-Sextans group is not bound to our Local Group and that it is expanding with the Hubble flow. If this conclusion is correct, then Antlia-Sextans may be the nearest external clustering of galaxies. The total galactic population of the Ant-Sex group is ~1/5 that of the Local Group. However, the integrated luminosity of Ant-Sex is 2 orders of magnitude lower than that of the Local Group.

  6. LOCAL TADPOLE GALAXIES

    SciTech Connect

    Elmegreen, Debra Meloy; Putko, Joseph; Dewberry, Janosz; Elmegreen, Bruce G.; Sanchez Almeida, Jorge; Munoz-Tunon, Casiana

    2012-05-10

    Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use Sloan Digital Sky Survey data to determine the ages, masses, and surface densities of the heads and tails in 14 local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with rest-frame galaxy luminosity, ranging from {approx}10{sup 5} M{sub Sun} at galaxy absolute magnitude U = -13 mag to 10{sup 9} M{sub Sun} at U = -20 mag. The corresponding head surface density increases from several M {sub Sun} pc{sup -2} locally to 10-100 M{sub Sun} pc{sup -2} at high redshift, and the star formation rate (SFR) per unit area in the head increases from {approx}0.01 M{sub Sun} yr{sup -1} kpc{sup -2} locally to {approx}1 M{sub Sun} yr{sup -1} kpc{sup -2} at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological SFRs, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far-outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size.

  7. Planetary nebulae: the universal mass-metallicity relation for Local Group dwarf galaxies and the chemistry of NGC 205

    NASA Astrophysics Data System (ADS)

    Gonçalves, Denise R.; Magrini, Laura; Teodorescu, Ana M.; Carneiro, Carolina M.

    2014-10-01

    Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC 205 by using Gemini Multi-Object Spectrographs (GMOS@Gemini) spectra to derive their physical and chemical parameters. The chemical patterns and evolutionary tracks for 14 of our PNe suggest that there are no type I PNe among them. These PNe have an average oxygen abundance of 12+log(O/H) = 8.08 ± 0.28 and progenitor masses of 2-2.5 M⊙ and thus were born ˜1.0-1.7 Gyr ago. Our results are in good agreement with previous PN studies of NGC 205. The present 12+log(O/H) is combined with our previous work and results in the literature to study the PN metallicity trends of Local Group (LG) dwarf galaxies, in an effort to establish the PN luminosity-metallicity and mass-metallicity relations (LZR and MZR) for LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous attempts to obtain such relations failed to provide correct conclusions because they were based on limited samples. As far as we are able to compare stellar with nebular metallicities, our MZR is in very good agreement with the slope of the MZR recently obtained for LG dwarf galaxies using spectroscopic stellar metallicities by Kirby and coauthors. In fact, we found that both dIrr and dSph galaxies follow the same MZR, at variance with the differences claimed in the past. Moreover, our MZR is also consistent with the global MZR of star-forming galaxies, which span a wider stellar mass range (˜106-1011 M⊙).

  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. Local normal galaxies

    NASA Technical Reports Server (NTRS)

    Fichtel, Carl E.

    1990-01-01

    In the near future, high energy (E greater than 20 MeV) gamma ray astronomy offers the promise of a new means of examining the closest galaxies. Two and possibly three local galaxies, the Small and Large Magellanic Clouds and M31, should be visible to the high energy gamma ray telescope on the Gamma Ray Observatory, and the first should be seen by GAMMA-1. With the assumptions of adequate cosmic ray production and reasonable magnetic field strengths, both of which should likely be satisfied, specific predictions of the gamma ray emission can be made separating the concepts of the galactic and universal nature of cosmic rays. A study of the synchrotron radiation from the Large Magellanic Cloud (LMC) suggests that the cosmic ray density is similar to that in the local region of our galaxy, but not uniform. It is hoped the measurements will be able to verify this independent of assumptions about the magnetic fields in the LMC.

  10. 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.

  11. VizieR Online Data Catalog: Dwarf galaxy planes in Local Group (Pawlowski+, 2013)

    NASA Astrophysics Data System (ADS)

    Pawlowski, M. S.; Kroupa, P.; Jerjen, H.

    2014-09-01

    The analysis presented in the following is based on the catalogue of nearby galaxies as compiled by McConnachie (2012AJ....144....4M, Cat. J/AJ/144/4) (see also Mateo, 1998ARA&A..36..435M). It includes information on all known galaxies within 3Mpc from the Sun, which have distance estimates based on resolved stellar populations. We use the galaxy positions, radial distances and line-of-sight velocities of the LG galaxies as provided by the most recent online version of the tables by McConnachie (2012AJ....144....4M, https://www.astrosci.ca/users/alan/NearbyDwarfsDatabase.html, Version 2013/Jun/17). To this we add the recently published line-of-sight velocity for Andromeda XXIX (Tollerud et al., 2013ApJ...768...50T) for which no velocities are provided in the catalogue yet. (1 data file).

  12. 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.

  13. First OB-stars in the iron-poor local group galaxy Sextans A

    NASA Astrophysics Data System (ADS)

    Camacho, I.; García, M.; Herrero, A.

    2015-05-01

    Massive stars are crucial to understand the chemical and dynamical evolution of the Universe. Our knowledge of their physics at sub-SMC metallicities, dominant in the early Universe, is still in its infancy, due to the lack of proper observations and analyses. We have started a programme to observe stars in nearby galaxies with metallicities below that of the SMC. For this purpose, we have developed photometric criteria which allowed us to set a list of blue massive candidates in Sextans A, a galaxy with a metallicity of [Fe/H]= -1.85. We have secured OSIRIS@GTC spectra of these candidates and have discovered six O-type and seven early-B stars, which constitutes the first atlas of blue massive stars in this galaxy. Using FASTWIND model atmospheres, we have obtained the main physical parameters of the O-type stars (effective temperature, gravity, wind strength and He content).This is the lowest metallicity for which an observational temperature scale of O-stars has been stablished. This work is part of the PhD of I. Camacho aimed at the identification, classification and analysis of massive OB stars in low metallicity galaxies.

  14. Local Group Cosmology

    NASA Astrophysics Data System (ADS)

    Martínez-Delgado, David

    2013-11-01

    List of contributors; List of participants; Preface; Acknowledgments; Abbreviations; 1. The formation of the Milky Way in the CDM paradigm Ken Freeman; 2. Dark matter content and tidal effects in Local Group dwarf galaxies Steven R. Majewski; 3. Notes on the missing satellites problem James Bullock; 4. The Milky Way satellite galaxies Pavel Kroupa; 5. Stellar tidal streams Rodrigo Ibata; 6. Tutorial: the analysis of colour-magnitude diagrams David Valls-Gabaud; 7. Tutorial: modeling tidal streams using N-body simulations Jorge Peñarrubia.

  15. 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.

  16. THE ACS LCID PROJECT. IV. DETECTION OF THE RED GIANT BRANCH BUMP IN ISOLATED GALAXIES OF THE LOCAL GROUP

    SciTech Connect

    Monelli, M.; Hidalgo, S. L; Aparicio, A.; Gallart, C.; Cassisi, S.; Bernard, E. J.; Skillman, E. D. E-mail: carme@iac.e E-mail: shidalgo@iac.e E-mail: ejb@roe.ac.u

    2010-08-01

    We report the detection and analysis of the red giant branch (RGB) luminosity function bump in a sample of isolated dwarf galaxies in the Local Group. We have designed a new analysis approach comparing the observed color-magnitude diagrams (CMDs) with theoretical best-fit CMDs derived from precise estimates of the star formation histories of each galaxy. This analysis is based on studying the difference between the V magnitude of the RGB bump and the horizontal branch at the level of the RR Lyrae instability strip ({Delta}V {sup bump}{sub HB}) and we discuss here a technique for reliably measuring this quantity in complex stellar systems. By using this approach, we find that the difference between the observed and predicted values of {Delta}V {sup bump}{sub HB} is +0.13 {+-} 0.14 mag. This is smaller, by about a factor of 2, than the well-known discrepancy between theory and observation at low metallicity commonly derived for Galactic globular clusters (GCs). This result is confirmed by a comparison between the adopted theoretical framework and empirical estimates of the {Delta}V {sup bump}{sub HB} parameter for both a large database of Galactic GCs and for four other dwarf spheroidal galaxies for which this estimate is available in the literature. We also investigate the strength of the RGB bump feature (R{sub bump}), and find very good agreement between the observed and theoretically predicted R{sub bump} values. This agreement supports the reliability of the evolutionary lifetimes predicted by theoretical models of the evolution of low-mass stars.

  17. Stellar populations in local group dwarf elliptical galaxies. II - NGC 205

    NASA Technical Reports Server (NTRS)

    Mould, J.; Kristian, J.; Da Costa, G. S.

    1984-01-01

    NGC 205, a dwarf elliptical companion of M31, was studied using deep CCD photometry on the VRI system. Consideration is given to a comparison between the giant branch and the Galactic globular clusters, the degree of chemical enrichment in the outer parts of NGC 204, and the setting of constraints on the stellar population of NGC 205. Should the distance of the galaxy be that of M31, this field's stellar population is extremely old. If star formation in NGC 205 is a recurring phenomenon, it is confined to the interior of the galaxy. Should the stellar population of NGC 205 be as old as Galactic globular clusters, its distance modulus is 24.3 + or - 0.2. The giant branch location corresponds to a mean metallicity greater than or equal to -0.9 + or - 0.2, and a metallicity dispersion is determined to be sigma greater than or equal to 0.5 dex. Also noted is that the color distribution at a given luminosity appears to be positively skewed.

  18. 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.

  19. The Araucaria Project: The Distance to the Local Group Galaxy IC 1613 from Near-Infrared Photometry of Cepheid Variables

    NASA Astrophysics Data System (ADS)

    Pietrzyński, Grzegorz; Gieren, Wolfgang; Soszyński, Igor; Bresolin, Fabio; Kudritzki, Rolf-Peter; Dall'Ora, Massimo; Storm, Jesper; Bono, Giuseppe

    2006-05-01

    We have measured accurate near-infrared magnitudes in the J and K bands of 39 Cepheid variables in the irregular Local Group galaxy IC 1613 with well-determined periods and optical VI light curves. Using the template light curve approach of Soszyński, Gieren, & Pietrzyński, accurate mean magnitudes were obtained from these data, which allowed us to determine the distance to IC 1613 relative to the LMC from a multiwavelength period-luminosity solution in the optical VI and near-IR JK bands with an unprecedented accuracy. Our result for the IC 1613 distance is (m-M)0=24.291+/-0.035 (random error) mag, with an additional systematic uncertainty smaller than 2%. From our multiwavelength approach, we find for the total (average) reddening to the IC 1613 Cepheids E(B-V)=0.090+/-0.019 mag, which is significantly higher than the foreground reddening of about 0.03 mag, showing the presence of appreciable dust extinction inside the galaxy. Our data suggest that the extinction law in IC 1613 is very similar to the Galactic one. Our distance result agrees, within the uncertainties, with two earlier infrared Cepheid studies in this galaxy, of Macri et al. (from HST data on 4 Cepheids) and McAlary et al. (from ground-based H-band photometry of 10 Cepheids), but our result has reduced the total uncertainty on the distance to IC 1613 (relative to the LMC) to less than 3%. With distances to nearby galaxies from Cepheid infrared photometry at this level of accuracy, which are currently being obtained in our Araucaria Project, it seems possible to significantly reduce the systematic uncertainty of the Hubble constant, as derived from the HST Key Project approach, by improving the calibration of the metallicity effect on PL relation zero points and by improving the distance determination to the LMC. Based on observations obtained with the New Technology Telescope (NNT) at ESO La Silla for programs 074.D-0318(B) and 074.D-0505(B).

  20. Probing the Dark Matter Content of Local Group Dwarf Spheroidal Galaxies with FLAMES

    NASA Astrophysics Data System (ADS)

    Wilkinson, Mark I.; Kleyna, Jan T.; Gilmore, Gerard F.; Evans, N. Wyn; Koch, Andreas; Grebel, Eva K.; Wyse, Rosemary F. G.; Harbeck, Daniel R.

    2006-06-01

    We present preliminary kinematic results from our VLT programme of spectroscopic observations in the Carina dwarf spheroidal galaxy using the FLAMES multi-object spectrograph. These new data suggest that the dark matter halo of this galaxy has a uniform density core. The implications for our understanding of the nature of the dark matter are discussed. Z% Aaronson M. 1983, ApJ 266, L11 Belokurov V. et al. 2006, ApJL, submitted, astro-ph/0604355 Goerdt T. et al. 2006, MNNRAS 368, 1073 Harbeck D. et al. 2001, AJ 122, 3092 Kleyna J. T. et al. 2001, ApJ 564, L115 Kleyna J. T. et al. 2003, ApJ 588, L21 Koch A. et al. 2006a, The Messenger 123, 38 Koch A. et al. 2006b, AJ 131, 895 Majewski S. R. et al. 2005, AJ 130, 2677 Martin N. et al. 2006, MNRAS 367, L69 Mateo M. et al. 1993, AJ 105, 510 Mateo M. 1997, ASP Conf. Ser. 116, 259 Mateo M. et al. 1998, AJ 116, 2315 Monelli M. et al. 2003, AJ 126, 218 Munoz R. R. et al. 2005, ApJ 631, L137 Shetrone M. D. et al. 2001, ApJ 548, 592 Tolstoy E. et al. 2006, The Messenger 123, 33 Wilkinson M. I. et al. 2002, MNRAS 330, 778 Wilkinson M. I. et al. 2004, MNRAS 611, L21 Wilkinson M. I. et al. 2006, in proceedings of XXIst IAP meeting, EDP sciences, astro-ph/0602186 Willman B. et al. 2005, ApJ 626, L85 Wyse R. F. G. et al. 2006, ApJ 639, L13 Zucker D. B. et al. 2006, ApJ 643, L103

  1. 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.

  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. 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.

  4. 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.

  5. Isolated galaxies, pairs, and groups of galaxies

    NASA Technical Reports Server (NTRS)

    Kuneva, I.; Kalinkov, M.

    1990-01-01

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

  6. The Assembly of Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Ponman, Trevor

    2001-09-01

    The most interesting phase in the evolution of a galaxy group is the virialisation stage, at which the infall velocities of the galaxies are randomised and the interstellar gas compressed and heated. The violently fluctuating environment experienced by galaxies during this phase may have long-lasting effects on their properties. Such virialising groups appear to be quite rare, since the phase is transient, but we have identified three strong candidates from an extensive study of groups with ROSAT. We propose to obtain high quality spectral images of these with ACIS in order to study the way in which the intergalactic medium is heated, and the effects of strong interactions on galaxy properties.

  7. 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

  8. Angular momentum in the Local Group

    SciTech Connect

    Dunn, A.; Laflamme, R.

    1994-04-01

    We briefly review models for the Local Group and the acquisition of its angular momentum. We describe early attempts to understand the origin of the spin of the galaxies discussing the hypothesis that the Local Group has little angular momentum. Finally we show that using Peebles` least action principle there should be a rather large amount of orbital angular momentum compared to the magnitude of the spin of its galaxies. Therefore the Local Group cannot be thought as tidally isolated. Using Peebles` trajectories we give a possible set of trajectories for Local Group galaxies which would predict their spin.

  9. Tidal Dwarf Galaxies In Gas-rich Interacting Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Eigenthaler, Paul

    2014-01-01

    Galaxy-galaxy interactions in gas-rich galaxy groups or pairs can form tidal bridges and tails. These tidal arms can contain kinematically decoupled structures with active star formation in the same mass range as dwarf galaxies, so-called tidal dwarf galaxies (TDGs). They differ from ordinary dwarf galaxies by their lack of dark matter and higher metallicity content. Compact groups of galaxies are an ideal environment to study the origin and evolution of TDGs since the high spatial volume density of member galaxies allows for frequent and efficient interactions between galaxies forming tidal tails. Hunsberger et al. (1996) identified 47 TDG candidates in Hickson compact groups (HCGs) and estimated that more than 50% of all dwarf galaxies in compact groups are former TDGs. Statistical considerations based on observations of interacting galaxies illustrate that a significant fraction of today's dwarf galaxies could have had a tidal origin. In their early evolution, TDGs can easily be distinguished from classical dwarf galaxies as they are still embedded in large tidal structures and show ongoing star formation, identified via strong Hα emission in these aggregates. Simulations of interacting galaxies, and of TDGs in particular, have shown that TDGs can survive their first starburst event and turn into long-lived dwarf sized objects. Preliminary results from deep Hα imaging with the SOAR telescope to detect new TDGs in a sample of 10 Hickson compact groups will be presented.

  10. 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

  11. A TREASURY STUDY OF STAR-FORMING REGIONS IN THE LOCAL GROUP. I. HST PHOTOMETRY OF YOUNG POPULATIONS IN SIX DWARF GALAXIES

    SciTech Connect

    Bianchi, Luciana; Efremova, Boryana; Hodge, Paul; Massey, Philip; Olsen, K. A. G.

    2012-03-15

    We present a comprehensive study of young stellar populations in six dwarf galaxies in or near the Local Group: Phoenix, Pegasus, Sextans A, Sextans B, WLM, and NGC 6822. Their star-forming regions, selected from GALEX wide-field far-UV imaging, were imaged (at sub-pc resolution) with the WFPC2 camera on board the Hubble Space Telescope (HST) in six bandpasses from far-UV to I to detect and characterize their hot massive star content. This study is part of HST treasury survey program HST-GO-11079; the general data characteristics and reduction procedures are detailed in this paper and results are presented for the first six galaxies. From a total of 180 HST images, we provide catalogs of the multi-band stellar photometry and derive the physical parameters of massive stars by analyzing it with model-atmosphere colors. We use the results to infer ages, number of massive stars, extinction, and spatial characteristics of the young stellar populations. The hot massive star content varies largely across our galaxy sample, from an inconspicuous presence in Phoenix and Pegasus to the highest relative abundance of young massive stars in Sextans A and WLM. Albeit to a largely varying extent, most galaxies show a very young population (a few Myrs, except for Phoenix), and older ones (a few 10{sup 7} years in Sextans A, Sextans B, NGC 6822, and WLM, {approx}10{sup 8}yr in Phoenix and Pegasus), suggesting discrete bursts of recent star formation in the mapped regions. The hot massive star content (indicative of the young populations) broadly correlates with the total galaxy stellar mass represented by the integrated optical magnitude, although it varies by a factor of {approx}3 between Sextans A, WLM, and Sextans B, which have similar M{sub V}. Extinction properties are also derived.

  12. 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.

  13. Observing Dwarf Galaxies in the Local Universe

    NASA Astrophysics Data System (ADS)

    Simon, Joshua

    2016-03-01

    Dwarf galaxies in the Local Group are key probes of both dark matter and galaxy formation. They are the smallest, oldest, most dark matter-dominated, and least chemically enriched stellar systems currently known. However, despite two decades of major computational, theoretical, and observational advances in this field, we are still working toward a complete understanding of star and galaxy formation at the faint end of the galaxy luminosity function. In the last year, large sky surveys such as the Dark Energy Survey and Pan-STARRS have made an unprecedented series of discoveries, nearly doubling the population of Milky Way satellite galaxies that was known at the start of 2015. This increase in the number of nearby dwarfs may significantly improve the sensitivity of searches for dark matter annihilation radiation. Many of these new dwarfs are likely to have originated as satellites of the Magellanic Clouds, providing a unique opportunity to study the effect of galactic environment on the formation of the faintest dwarfs. I will provide an overview of recent discoveries and how they fit in to the previously known population of nearby dwarf galaxies, highlighting a few of the most interesting objects from the perspective of dark matter and stellar nucleosynthesis.

  14. Fossils of reionization in the local group

    SciTech Connect

    Gnedin, Nickolay Y.; Kravtsov, Andrey V.; /KICP, Chicago /Chicago U., EFI /Chicago U., Astron. Astrophys. Ctr.

    2006-01-01

    We use a combination of high-resolution gas dynamics simulations of high-redshift dwarf galaxies and dissipationless simulations of a Milky Way sized halo to estimate the expected abundance and spatial distribution of the dwarf satellite galaxies that formed most of their stars around z {approx} 8 and evolved only little since then. Such galaxies can be considered as fossils of the reionization era, and studying their properties could provide a direct window into the early, pre-reionization stages of galaxy formation. We show that 5-15% of the objects existing at z {approx} 8 do indeed survive until the present in the MW like environment without significant evolution. This implies that it is plausible that the fossil dwarf galaxies do exist in the Local Group. Because such galaxies form their stellar systems early during the period of active merging and accretion, they should have spheroidal morphology regardless of their current distance from the host galaxy. We show that both the expected luminosity function and spatial distribution of dark matter halos which are likely to host fossil galaxies agree reasonably well with the observed distributions of the luminous (L{sub V} > 10{sup 6} Lsun) Local Group fossil candidates near the host galaxy (d<200 kpc). However, the predicted abundance is substantially larger (by a factor of 2-3) for fainter galaxies (L{sub V} < 10{sup 6} Lsun) at larger distances (d>300 kpc). We discuss several possible explanations for this discrepancy.

  15. Comparing galaxy populations in compact and loose groups of galaxies. II. Brightest group galaxies

    NASA Astrophysics Data System (ADS)

    Martínez, Héctor J.; Coenda, Valeria; Muriel, Hernán

    2013-09-01

    Aims: The properties of the brightest galaxies (BCGs) are studied in both compact and loose groups of galaxies in order to better understand the physical mechanisms influencing galaxy evolution in different environments. Methods: Samples of BCGs are selected in compact and loose groups of galaxies previously identified in the Sloan Digital Sky Survey. The following physical properties of the BCGs in compact groups and in sub-samples of loose groups are compared, defined by their mass and total luminosity: absolute magnitude, colour, size, surface brightness, stellar mass, concentration and morphological information from the Galaxy Zoo. The fraction of BCGs classified as red and/or early-type as a function of galaxy luminosity is studied. The fraction of the group's total luminosity contained in the BCG and the difference in luminosity between the BCG and the second-ranked galaxy, are also analysed. Results: Some properties of BCGs in compact and loose groups are comparable. However, BCGs in compact groups are systematically more concentrated and have larger surface brightness than their counterparts in both, high- and low-mass loose groups. The fractions of red and early-type BCGs in compact groups are consistent with those of high-mass loose groups. Comparing BCGs in sub-samples of compact and loose groups selected for their similar luminosities, BCGs in compact groups are found to be, on average, brighter, more massive, larger, redder and more frequently classified as elliptical. In compact groups, the BCG contains a larger fraction of the system's total luminosity and differs more in absolute magnitude from the second-ranked galaxy. Using a simple model, which dry-merges the BCG in loose groups with a random choice among the 2nd, 3rd and 4th-ranked galaxies in the group, and allowing for some star loss in the process, we show that the absolute magnitude distributions of BCGs in compact and loose groups of similar luminosities can be made more alike. Conclusions

  16. 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.

  17. Mapping Hydrogen in the Galaxy, Galactic Halo, and Local Group with ALFA: The GALFA-H I Survey Starting with TOGS

    NASA Astrophysics Data System (ADS)

    Gibson, S. J.; Douglas, K. A.; Heiles, C.; Korpela, E. J.; Peek, J. E. G.; Putman, M. E.; Stanimirović, S.

    2008-08-01

    Radio observations of gas in the Milky Way and Local Group are vital for understanding how galaxies function as systems. The unique sensitivity of Arecibo's 305 m dish, coupled with the 7-beam Arecibo L-Band Feed Array (ALFA), provides an unparalleled tool for investigating the full range of interstellar phenomena traced by the H I 21 cm line. The GALFA (Galactic ALFA) H I Survey is mapping the entire Arecibo sky over a velocity range of -700 to +700 km s-1 with 0.2 km s-1 velocity channels and an angular resolution of 3.4'. We present highlights from the TOGS (Turn On GALFA Survey) portion of GALFA-H I, which is covering thousands of square degrees in commensal drift scan observations with the ALFALFA and AGES extragalactic ALFA surveys. This work is supported in part by the National Astronomy and Ionosphere Center, operated by Cornell University under cooperative agreement with the National Science Foundation.

  18. 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.

  19. 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.

  20. Is the misalignment of the Local Group velocity and the dipole generated by the 2MASS Redshift Survey typical in {lambda} cold dark matter and the halo model of galaxies?

    SciTech Connect

    Erdogdu, Pirin; Lahav, Ofer

    2009-08-15

    We predict the acceleration of the Local Group generated by the 2MASS Redshift Survey within the framework of {lambda} cold dark matter and the halo model of galaxies. We show that as the galaxy fluctuations derived from the halo model have more power on small scales compared with the mass fluctuations, the misalignment angle between the CMB velocity vector and the 2MASS Redshift Survey dipole is in reasonable agreement with the observed 21 deg. This statistical analysis suggests that it is not necessary to invoke a hypothetical nearby galaxy or a distant cluster to explain this misalignment.

  1. Observational properties of compact groups of galaxies

    NASA Technical Reports Server (NTRS)

    Hickson, Paul

    1990-01-01

    Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

  2. Morphology transformation in pairs of galaxies - the local sample

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; de Mello, D. F.; Infante, L.

    1998-04-01

    We present photometric analysis of a local sample of 14 isolated pairs of galaxies. The photometric properties analyzed in the local pairs are: colors, morphology, tidal effects and activity. We verify that close pairs have an excess of early-type galaxies and many elliptical galaxies in this pairs are, in fact, lenticular galaxies. Many late-pairs in our sample show strong tidal damage and blue star formation regions. We conclude that pairs of different morphologies may have passed through different evolution processes which violently transformed their morphology. Pairs with at least one early-type component may be descendents of groups of galaxies. However, late-type pairs are probably long-lived showing clearly signs of interaction. Some of them could be seen as an early stage of mergers. These photometric databases will be used for future comparison with more distant pairs in order to study galaxy evolution.

  3. CORRELATION BETWEEN GROUP LOCAL DENSITY AND GROUP LUMINOSITY

    SciTech Connect

    Deng Xinfa; Yu Guisheng

    2012-11-10

    In this study, we investigate the correlation between group local number density and total luminosity of groups. In four volume-limited group catalogs, we can conclude that groups with high luminosity exist preferentially in high-density regions, while groups with low luminosity are located preferentially in low-density regions, and that in a volume-limited group sample with absolute magnitude limit M{sub r} = -18, the correlation between group local number density and total luminosity of groups is the weakest. These results basically are consistent with the environmental dependence of galaxy luminosity.

  4. ROSAT observations of compact groups of galaxies

    NASA Technical Reports Server (NTRS)

    Pildis, Rachel A.; Bregman, Joel N.; Evrard, August E.

    1995-01-01

    We have systematically analyzed a sample of 13 new and archival ROSAT Position Sensitive Proportional Counter (PSPC) observations of compact groups of galaxies: 12 Hickson compact groups plus the NCG 2300 group. We find that approximately two-thirds of the groups have extended X-ray emission and, in four of these, the emission is resolved into diffuse emission from gas at a temperature of kT approximately 1 keV in the group potential. All but one of the groups with extended emission have a spiral fraction of less than 50%. The baryon fraction of groups with diffuse emission is 5%-19%, similar to the values in clusters of galaxies. However, with a single exception (HCG 62), the gas-to-stellar mass ratio in our groups has a median value near 5%, somewhat greater than the values for individual early-type galaxies and two orders of magnitude than in clusters of galaxies. The X-ray luminosities of individual group galaxies are comparable to those of similar field galaxies, although the L(sub X)-L(sub B) relation for early-type galaxies may be flatter in compact groups than in the field.

  5. 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.

  6. The chemical evolution of galaxies in the local volume

    NASA Astrophysics Data System (ADS)

    Croxall, Kevin V.

    2010-12-01

    The composition of the universe has greatly changed since the first matter condensed from the primordial soup of the Big Bang. As galaxies have grown and evolved over the past Hubble time, massive luminous galaxies have built up more heavy elements than their low mass counterparts. While sundry physical mechanisms have been proposed to account for this observed trend, the physical connection between galaxy mass and metallicity has evaded the understanding of astronomers for several decades. In order to gain a greater understanding of this metallicity-luminosity relation and the physical drivers behind the chemical evolution of galaxies, we have performed a detailed study of galaxies in both isolated and non-isolated environments: namely, galaxies in the local volume (D ≤ 5 Mpc) and galaxy members belonging to the M81 group. Our results from studying the M81 group imply that recent interactions among the central galaxies in this group, rather than mechanisms intrinsic to the galaxies, are likely responsible for the anomalously high abundances in three cluster members. While tidal interactions can alter the chemical make up the galaxies involved, the well established metallicity-luminosity relation indicates a more universal chemical evolution. To further explore this idea, we analyze galaxy abundances, stellar & gas distributions, and kinematics from both new and archival observations of forty-five low mass galaxies within 5 Mpc of the Milky Way. Our results indicate that these galaxies occupy a different mass-to-light ratio parameter space than their larger counter parts. Our study of the local volume explores the effects of various galaxy attributes such as mass, star formation rate, gas mass fraction, and the mass distribution that offer more concrete connections with the evolution of the system. We show that none of the attributes measured in this study exhibit more correlation with metallicity (measured via nebular oxygen abundances) than does the luminosity

  7. 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.

  8. 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.

  9. Neutral hydrogen in compact groups of galaxies

    SciTech Connect

    Williams, B.A.; Rood, H.J.

    1987-02-01

    Integrated H I profiles were detected for 34 of 51 Hickson compact groups (HCGs) of galaxies, and sensitive upper limits to the H I flux density were measured for the other 17. About 60 percent of the galaxies within compact groups are spirals, and a significant tendency exists for the fraction of elliptical galaxies to increase with group surface brightness. The amount of dark matter within the compact group region is negligibly small. An HCG on average contains half as much neutral hydrogen as a loose group with a similar spectrum of galaxy luminosities and morphological types, implying that compact groups are independent dynamical entities and not transient or projected configurations of loose groups. The observed fraction of galaxies which are luminous enough to be possible merger products of compact groups is small compared with the fraction required by the theory of dynamical friction. A clear discrepancy thus exists between solid empirical evidence and a straightforward prediction of Newtonian dynamical theory in a setting which does not permit a dark matter explanation. 44 references.

  10. Nearby Clumpy, Gas Rich, Star-forming Galaxies: Local Analogs of High-redshift Clumpy Galaxies

    NASA Astrophysics Data System (ADS)

    Garland, C. A.; Pisano, D. J.; Mac Low, M.-M.; Kreckel, K.; Rabidoux, K.; Guzmán, R.

    2015-07-01

    Luminous compact blue galaxies (LCBGs) have enhanced star formation rates (SFRs) and compact morphologies. We combine Sloan Digital Sky Survey data with H i data of 29 LCBGs at redshift z ∼ 0 to understand their nature. We find that local LCBGs have high atomic gas fractions (∼50%) and SFRs per stellar mass consistent with some high-redshift star-forming galaxies (SFGs). Many local LCBGs also have clumpy morphologies, with clumps distributed across their disks. Although rare, these galaxies appear to be similar to the clumpy SFGs commonly observed at z ∼ 1–3. Local LCBGs separate into three groups: (1) interacting galaxies (∼20%) (2) clumpy spirals (∼40%) and (3) non-clumpy, non-spirals with regular shapes and smaller effective radii and stellar masses (∼40%). It seems that the method of building up a high gas fraction, which then triggers star formation, is not the same for all local LCBGs. This may lead to a dichotomy in galaxy characteristics. We consider possible gas delivery scenarios and suggest that clumpy spirals, preferentially located in clusters and with companions, are smoothly accreting gas from tidally disrupted companions and/or intracluster gas enriched by stripped satellites. Conversely, as non-clumpy galaxies are preferentially located in the field and tend to be isolated, we suggest clumpy, cold streams, which destroy galaxy disks and prevent clump formation, as a likely gas delivery mechanism for these systems. Other possibilities include smooth cold streams, a series of minor mergers, or major interactions.

  11. CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP

    SciTech Connect

    Chiboucas, Kristin; Jacobs, Bradley A.; Tully, R. Brent; Karachentsev, Igor D. E-mail: bjacobs@ifa.hawaii.edu E-mail: ikar@luna.sao.ru

    2013-11-01

    We have followed up on the results of a 65 deg{sup 2} CFHT/MegaCam imaging survey of the nearby M81 Group searching for faint and ultra-faint dwarf galaxies. The original survey turned up 22 faint candidate dwarf members. Based on two-color HST ACS/WFC and WFPC2 photometry, we now confirm 14 of these as dwarf galaxy members of the group. Distances and stellar population characteristics are discussed for each. To a completeness limit of M{sub r{sup '}}= -10, we find a galaxy luminosity function slope of –1.27 ± 0.04 for the M81 Group. In this region, there are now 36 M81 Group members known, including 4 blue compact dwarfs; 8 other late types including the interacting giants M81, NGC 3077, and M82; 19 early type dwarfs; and at least 5 potential tidal dwarf galaxies. We find that the dSph galaxies in M81 appear to lie in a flattened distribution, similar to that found for the Milky Way and M31. One of the newly discovered dSph galaxies has properties similar to the ultra-faint dwarfs being found in the Local Group with a size R{sub e} ∼ 100 pc and total magnitude estimates M{sub r{sup '}}= -6.8 and M{sub I} ∼ –9.1.

  12. 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.

  13. SUPERDENSE MASSIVE GALAXIES IN WINGS LOCAL CLUSTERS

    SciTech Connect

    Valentinuzzi, T.; D'Onofrio, M.; Fritz, J.; Poggianti, B. M.; Bettoni, D.; Fasano, G.; Moretti, A.; Omizzolo, A.; Varela, J.; Cava, A.; Couch, W. J.; Dressler, A.; Moles, M.; Kjaergaard, P.; Vanzella, E.

    2010-03-20

    Massive quiescent galaxies at z > 1 have been found to have small physical sizes, and hence to be superdense. Several mechanisms, including minor mergers, have been proposed for increasing galaxy sizes from high- to low-z. We search for superdense massive galaxies in the WIde-field Nearby Galaxy-cluster Survey (WINGS) of X-ray selected galaxy clusters at 0.04 < z < 0.07. We discover a significant population of superdense massive galaxies with masses and sizes comparable to those observed at high redshift. They approximately represent 22% of all cluster galaxies more massive than 3 x 10{sup 10} M{sub sun}, are mostly S0 galaxies, have a median effective radius (R{sub e} ) = 1.61 +- 0.29 kpc, a median Sersic index (n) = 3.0 +- 0.6, and very old stellar populations with a median mass-weighted age of 12.1 +- 1.3 Gyr. We calculate a number density of 2.9 x 10{sup -2} Mpc{sup -3} for superdense galaxies in local clusters, and a hard lower limit of 1.3 x 10{sup -5} Mpc{sup -3} in the whole comoving volume between z = 0.04 and z = 0.07. We find a relation between mass, effective radius, and luminosity-weighted age in our cluster galaxies, which can mimic the claimed evolution of the radius with redshift, if not properly taken into account. We compare our data with spectroscopic high-z surveys and find that-when stellar masses are considered-there is consistency with the local WINGS galaxy sizes out to z {approx} 2, while a discrepancy of a factor of 3 exists with the only spectroscopic z > 2 study. In contrast, there is strong evidence for a large evolution in radius for the most massive galaxies with M{sub *} > 4 x 10{sup 11} M{sub sun} compared to similarly massive galaxies in WINGS, i.e., the brightest cluster galaxies.

  14. Evolution of local luminous compact blue galaxies

    NASA Astrophysics Data System (ADS)

    Rabidoux, Katherine; Pisano, Daniel J.

    2015-01-01

    Luminous compact blue galaxies (LCBGs) are a type of very blue, very compact star-forming galaxy that was common at z~1 but is rare in the local universe. While it is clear from this discrepancy that LCBGs must be a rapidly-evolving class of galaxy, it is not clear what type(s) of galaxy they become. Fortunately, since they are bright and nearby, the rare examples of z~0 LCBGs are easily studied across a large range of wavelengths. We have conducted a study of z~0 analogs to the z~1 LCBGs to investigate their galaxy-wide internal properties in order to determine what is triggering their current episode of star formation, for how long the star formation can continue, and what the galaxies may become once their star formation rates decrease from current levels. We have taken resolved H I observations of nine LCBGs and unresolved radio continuum observations of 35 LCBGs and combined this data with archival broad-band data to probe their global properties. We conclude that LCBGs are rotationally-supported, star-forming disk galaxies that, while they may be forming small central bulges or bars, are highly unlikely to evolve into dwarf elliptical, dwarf spheroidal, or elliptical galaxies on their own due to their masses and rotation velocities. LCBGs will likely fade to be spiral galaxies with lower surface brightnesses once their current episodes of star formation conclude. In addition, we have modeled the SEDs of the LCBGs in our sample to determine whether LCBGs' star formation is ramping up or winding down, and for how much longer their current active phase of star formation will last. We have begun to put together a picture of the current evolutionary stage of this class of galaxies, and have better constrained their future evolutionary paths.

  15. Red Supergiants in the Local Group

    NASA Astrophysics Data System (ADS)

    Levesque, E. M.

    2013-05-01

    Galaxies in the Local Group span a factor of 15 in metallicity, ranging from the super-solar M 31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the lowest-metallicity (0.1 Z⊙) Local Group galaxy currently forming stars. Studies of massive star populations across this broad range of environments have revealed important metal-licity-dependent evolutionary trends, allowing us to test the accuracy of stellar evolutionary tracks at these metallicities for the first time. The RSG population is particularly valuable as a key mass-losing phase of moderately massive stars and a source of core-collapse supernova progenitors. By reviewing recent work on the RSG populations in the Local Group, we are able to quantify limits on these stars' effective temperatures and masses and probe the relationship between RSG mass loss behaviors and host environments. Extragalactic surveys of RSGs have also revealed several unusual RSGs that display signs of unusual spectral variability and dust production, traits that may potentially also correlate with the stars' host environments. I will present some of the latest work that has advanced our understanding of RSGs in the Local Group, and consider the many new questions posed by our ever-evolving picture of these stars.

  16. Are groups of galaxies virialized systems?

    NASA Technical Reports Server (NTRS)

    Diaferio, Antonaldo; Ramella, Massimo; Geller, Margaret J.; Ferrari, Attilio

    1993-01-01

    Groups are systems of galaxies with crossing times t(cr) much smaller than the Hubble time. Most of them have t(cr) less than 0.1/H0. The usual interpretation is that they are in virial equilibrium. We compare the data of the group catalog selected from the CfA redshift survey extension with different N-body models. We show that the distributions of kinematic and dynamical quantities of the groups in the CfA catalog can be reproduced by a single collapsing group observed along different line of sights. This result shows that (1) projection effects dominate the statistics of these systems, and (2) observed groups of galaxies are probably still in the collapse phase.

  17. The Next Generation Virgo Cluster Survey. VII. The Intrinsic Shapes of Low-luminosity Galaxies in the Core of the Virgo Cluster, and a Comparison with the Local Group

    NASA Astrophysics Data System (ADS)

    Sánchez-Janssen, Rubén; Ferrarese, Laura; MacArthur, Lauren A.; Côté, Patrick; Blakeslee, John P.; Cuillandre, Jean-Charles; Duc, Pierre-Alain; Durrell, Patrick; Gwyn, Stephen; McConnacchie, Alan W.; Boselli, Alessandro; Courteau, Stéphane; Emsellem, Eric; Mei, Simona; Peng, Eric; Puzia, Thomas H.; Roediger, Joel; Simard, Luc; Boyer, Fred; Santos, Matthew

    2016-03-01

    We investigate the intrinsic shapes of low-luminosity galaxies in the central 300 kpc of the Virgo Cluster using deep imaging obtained as part of the Next Generation Virgo Cluster Survey (NGVS). We build a sample of nearly 300 red-sequence cluster members in the yet-unexplored -14 < Mg < -8 mag range, and we measure their apparent axis ratios, q, through Sérsic fits to their two-dimensional light distribution, which is well described by a constant ellipticity parameter. The resulting distribution of apparent axis ratios is then fit by families of triaxial models with normally distributed intrinsic ellipticities, E = 1 - C/A, and triaxialities, T = (A2 - B2)/(A2 - C2). We develop a Bayesian framework to explore the posterior distribution of the model parameters, which allows us to work directly on discrete data, and to account for individual, surface-brightness-dependent axis ratio uncertainties. For this population we infer a mean intrinsic ellipticity \\bar{E} = {0.43}-0.02+0.02 and a mean triaxiality \\bar{T} = {0.16}-0.06+0.07. This implies that faint Virgo galaxies are best described as a family of thick, nearly oblate spheroids with mean intrinsic axis ratios 1:0.94:0.57. The core of Virgo lacks highly elongated low-luminosity galaxies, with 95% of the population having q > 0.45. We additionally attempt a study of the intrinsic shapes of Local Group (LG) satellites of similar luminosities. For the LG population we infer a slightly larger mean intrinsic ellipticity \\bar{E} = {0.51}-0.06+0.07, and the paucity of objects with round apparent shapes translates into more triaxial mean shapes, 1:0.76:0.49. Numerical studies that follow the tidal evolution of satellites within LG-sized halos are in good agreement with the inferred shape distributions, but the mismatch for faint galaxies in Virgo highlights the need for more adequate simulations of this population in the cluster environment. We finally compare the intrinsic shapes of NGVS low-mass galaxies with

  18. 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.

  19. 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.

  20. LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

    SciTech Connect

    Sanchez Almeida, J.; Munoz-Tunon, C.; Mendez-Abreu, J.; Elmegreen, D. M.; Elmegreen, B. G. E-mail: cmt@iac.es E-mail: elmegreen@vassar.edu

    2013-04-10

    Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure H{alpha} velocity curves of seven local tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation ({approx}70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the tadpole head (three out of five cases). The size and velocity dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] {lambda}6583/H{alpha} often shows significant spatial variations across the galaxies ({approx}0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation as a sign of external gas accretion (cold-flows) onto the head of the tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas.

  1. 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

  2. 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

  3. 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.

  4. Scaling Relations of Galaxy Groups and PoorClusters

    NASA Astrophysics Data System (ADS)

    Sun, Ming

    Galaxy groups and poor clusters are ideal systems to study baryonic physics, which is important for both using clusters for precision cosmology and understanding galaxy formation and evolution. Over the last decade, our understanding of the ICM properties of galaxy groups and poor clusters has greatly improved. However, there are still many unresolved problems. We propose to study the X-ray scaling relations of galaxy groups and poor clusters with XMM data in the archive. The study of a large sample is important to address significant systematic uncertainties. The rich XMM archive on low-mass systems is of great value, as they are selected by the cluster, galaxy, and AGN panels with different effective selection functions. Our sample includes about 100 groups and poor clusters with sufficient XMM data. The state-of-the-art method to model the local X-ray background will be applied, which is key for deriving X-ray gas properties at low surface brightness. The important scaling relations including M-T, M-Y_X, f_gas-T, entropy-M, L-T, L-Y_X, L-M and abundance-M will be derived. The scatter of in these relations will also be examined, as well as their connection to other group properties. This project represents a significant improvement over previous work. The final results will greatly improve our understanding of baryon physics in clusters and groups, especially when combined with the active efforts in simulation and analytic theory which are currently ongoing.

  5. 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.

  6. The global warming of group satellite galaxies

    NASA Astrophysics Data System (ADS)

    Yozin, C.; Bekki, K.

    2016-05-01

    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.

  7. 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.

  8. The global warming of group satellite galaxies

    NASA Astrophysics Data System (ADS)

    Yozin, C.; Bekki, K.

    2016-08-01

    Recent studies adopting $\\lambda_{\\rm Re}$, a proxy for specific angular momentum, have highlighted how early-type galaxies (ETGs) are composed of two kinematic classes for which distinct formation mechanisms can be inferred. With upcoming surveys expected to obtain $\\lambda_{\\rm Re}$ from a broad range of environments (e.g. SAMI, MaNGA), we investigate in this numerical study how the $\\lambda_{\\rm Re}$-$\\epsilon_{\\rm e}$ distribution of fast-rotating dwarf satellite galaxies reflects their evolutionary state. By combining N-body/SPH simulations of progenitor disc galaxies (stellar mass $\\simeq$10$^{\\rm 9}$ M$_{\\odot}$), 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 $\\lambda_{\\rm Re}$-$\\epsilon_{\\rm e}$ distribution at $z<0.1$ reproduces its observational counterpart from the ATLAS$^{\\rm 3D}$/SAURON projects. We predict therefore how the observed $\\lambda_{\\rm Re}$-$\\epsilon_{\\rm e}$ distribution of a group evolves according to these ensemble tidal interactions.

  9. 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

  10. MAGNIFICATION BY GALAXY GROUP DARK MATTER HALOS

    SciTech Connect

    Ford, Jes; Hildebrandt, Hendrik; Van Waerbeke, Ludovic; Leauthaud, Alexie; Tanaka, Masayuki; Capak, Peter; Finoguenov, Alexis; George, Matthew R.; Rhodes, Jason

    2012-08-01

    We report on the detection of gravitational lensing magnification by a population of galaxy groups, at a significance level of 4.9{sigma}. Using X-ray-selected groups in the COSMOS 1.64 deg{sup 2} field, and high-redshift Lyman break galaxies as sources, we measure a lensing-induced angular cross-correlation between the samples. After satisfying consistency checks that demonstrate we have indeed detected a magnification signal, and are not suffering from contamination by physical overlap of samples, we proceed to implement an optimally weighted cross-correlation function to further boost the signal to noise of the measurement. Interpreting this optimally weighted measurement allows us to study properties of the lensing groups. We model the full distribution of group masses using a composite-halo approach, considering both the singular isothermal sphere and Navarro-Frenk-White profiles, and find our best-fit values to be consistent with those recovered using the weak-lensing shear technique. We argue that future weak-lensing studies will need to incorporate magnification along with shear, both to reduce residual systematics and to make full use of all available source information, in an effort to maximize scientific yield of the observations.

  11. Environmentally driven star formation during a super galaxy group merger

    NASA Astrophysics Data System (ADS)

    Monroe, Jonathan; Tran, Kim-Vy; Gonzalez, Anthony H.

    2016-01-01

    We find evidence for outside-in growth of galaxies within a merging super galaxy group at a redshift of z~0.37. We utilize Hubble Space Telescope imaging in rest-frame UV and visual to measure color gradients across the super group and internally within 138 individual galaxies that are spectroscopically confirmed members. The group members show enhanced star formation at intermediate environmental densities. The high resolution imaging shows that the group galaxies have bluer disks, i.e. most of the new stars are forming in the disk which supports outside-in growth. These disk-dominated galaxies will likely fade to become S0 members.

  12. 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.

  13. What is the number of spiral galaxies in compact groups

    NASA Technical Reports Server (NTRS)

    Tikhonov, N. A.

    1990-01-01

    The distribution of morphological types of galaxies in compact groups is studied on plates from the 6 m telescope. In compact groups there are 57 percent galaxies of late morphological types (S + Irr), 23 percent lenticulars (SO) and 20 percent elliptical galaxies. The morphological content of compact groups is very nearly the same as in loose groups. There is no dependence of galaxy morphology on density in all compact groups (and possibly in loose groups). Genuine compact groups form only 60 percent of Hickson's list.

  14. Structural properties of central galaxies in groups and clusters

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng; McIntosh, Daniel H.; Mo, H. J.; Katz, Neal; van den Bosch, Frank C.; Weinberg, Martin; Weinmann, Simone M.; Pasquali, Anna; Yang, Xiaohu

    2009-09-01

    Using a statistically representative sample of 911 central galaxies (CENs) from the Sloan Digital Sky Survey (SDSS) Data Release 4 group catalogue, we study how the structure (shape and size) of the first rank (by stellar mass) group and cluster members depends on (1) galaxy stellar mass (Mstar), (2) the global environment defined by the dark matter halo mass (Mhalo) of the host group and (3) the local environment defined by their special halocentric position. We quantify the structure of SDSS galaxies with a GALFIT-based pipeline that fits two-dimensional Sérsic models to the r-band image data. Through tests with simulated and real galaxy images, we demonstrate that our pipeline can recover Sérsic parameters without significant bias. We find that the fitting results are most sensitive to the background sky level determination, and we strongly recommend using the SDSS global value. We also find that uncertainties in the background sky level translate into a strong covariance between the total magnitude, the half-light radius (r50) and the Sérsic index (n), especially for bright/massive galaxies. Applying our pipeline to the CEN sample, we find that n of CENs depends strongly on Mstar, but only weakly or not at all on Mhalo. The n-Mstar relation holds for CENs over the full range of halo masses that we consider. Less massive CENs tend to be disc like and high-mass systems are typically spheroids, with a considerable scatter in n at all galaxy masses. Similarly, CEN sizes depend on galaxy stellar mass and luminosity, with early- and late-type galaxies exhibiting different slopes for the size-luminosity (r50-L) and the size-stellar mass (r50-Mstar) scaling relations. Moreover, to test the impact of local environment on CENs, we compare the structure of CENs with that satellite galaxies (SATs) of comparable Mstar. We find that low-mass (<1010.75h-2Msolar) SATs have somewhat larger median Sérsic indices than CENs of a similar Mstar. Furthermore, low-mass, late

  15. 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.

  16. 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.

  17. Tidal effects on the spatial structure of the Local Group

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Chiosi, C.

    2009-05-01

    Aims: The spatial distribution of galaxies in the Local Group (LG) is the footprint of its formation mechanism and the gravitational interactions among its members and the external massive galaxies or galaxy groups. Using a 3D-geometrical description of the spatial distribution of all the members of the LG (not only the satellites of the MW and M 31) based on present-day data of positions and distances, we found in our previous study that all galaxies (MW, M 31, their satellites, and even the most distant objects) are confined within a slab of about 200 kpc thickness. Examining how external galaxies or groups would gravitationally affect (and eventually alter) the planar structure (and its temporal evolution) of the LG, they found that the external force field acts parallel to the plane determined by geometry and studied this with the Least Action Principle. Methods: In this paper, we thoroughly investigated the role played by the tidal forces exerted by external galaxies or galaxy groups on the LG galaxies (the most distant dwarfs in particular) in shaping their large-scale distribution. We studied in particular an idea based on the well-known effect of tidal interactions, according to which a system of mass-points can undergo not only tidal stripping but also tidal compression and thus become flatter. Results: Excluding the dwarf galaxies tightly bound to the MW and M 31, the same tidal forces can account for the planar distribution of the remaining dwarf galaxies. We analytically recover our previous results and prove that a planar distribution of the LG dwarf galaxies is compatible with the external force field. We also highlight the physical cause of this result.

  18. 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.

  19. 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.

  20. 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.

  1. The Milky Way, the Local Group & the IR Tully-Fisher Diagram

    NASA Technical Reports Server (NTRS)

    Malhotra, S.; Spergel, D.; Rhoads, J.; Li, J.

    1996-01-01

    Using the near infrared fluxes of local group galaxies derived from Cosmic Background Explorer/Diffuse Infrared Background Experiment band maps and published Cepheid distances, we construct Tully-Fisher diagrams for the Local Group.

  2. 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

  3. 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⊙.

  4. Magnetic fields in Local Group dwarf irregulars

    NASA Astrophysics Data System (ADS)

    Chyży, K. T.; Weżgowiec, M.; Beck, R.; Bomans, D. J.

    2011-05-01

    Aims: We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods: We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m Effelsberg telescope at 2.64 GHz. Three galaxies were detected. A higher frequency (4.85 GHz) was used to search for polarized emission in five dwarfs that are the most luminous ones in the infrared domain, of which three were detected. Results: Magnetic fields in LG dwarfs are weak, with a mean value of the total field strength of <4.2 ± 1.8 μG, three times lower than in the normal spirals. The strongest field among all LG dwarfs of 10 μG (at 2.64 GHz) is observed in the starburst dwarf IC 10. The production of total magnetic fields in dwarf systems appears to be regulated mainly by the star-formation surface density (with the power-law exponent of 0.30 ± 0.04) or by the gas surface density (with the exponent 0.47 ± 0.09). In addition, we find systematically stronger fields in objects of higher global star-formation rate. The dwarf galaxies follow a similar far-infrared relationship (with a slope of 0.91 ± 0.08) to that determined for high surface brightness spiral galaxies. The magnetic field strength in dwarf galaxies does not correlate with their maximum rotational velocity, indicating that a small-scale rather than a large-scale dynamo process is responsible for producting magnetic fields in dwarfs. If magnetization of the Universe by galactic outflows is coeval with its metal enrichment, we show that more massive objects (such as Lyman break galaxies) can efficiently magnetize the intergalactic medium with a magnetic field strength of about 0.8 nG out to a distance of 160-530 kpc at redshifts 5-3, respectively. Magnetic fields that are several times weaker and shorter magnetization

  5. 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.

  6. An Imaging Survey of Late-Type Galaxies: Local Benchmarks of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Taylor, V. A.

    2005-12-01

    Nearby (z ˜ 0) irregular, peculiar, and merging galaxies resemble the majority of galaxy types observed at high redshift. Since optical observations of galaxies at high redshift cover their rest-frame ultraviolet emission, imaging of local late-type galaxies in the ultraviolet and optical will provide a necessary basis for understanding high-redshift galaxies and their implications for galaxy formation and evolution. For this purpose, I present an analysis of a unique, panchromatic sample of 199 mostly late-type, irregular, peculiar, and merging nearby galaxies observed in a combination of 10 different pass-bands from the far ultraviolet through the infrared. I first present results of a study of the color gradients of these galaxies. I find that although elliptical through mid-type spiral galaxies are redder in their centers than their outskirts, most late-type spirals, irregular, and merging galaxies are bluer in their centers, becoming increasingly redder at larger radii. This indicates that late-type galaxies have a significant halo or thick disk of older stars, while young UV-bright stars dominate their inner regions. These results are consistent with models of hierarchical galaxy formation. I also present measurements of the concentration, asymmetry, and clumpiness ("CAS") parameters of these galaxies. These fundamental galaxy parameters can be used for galaxy classification, and studying and identifying merging and perturbed galaxies. The dependence of these parameters on wavelength yields a quantitative measure of the "morphological k-correction," which describes how the appearance of a galaxy changes with rest-frame wavelength. I find that the CAS parameters depend on galaxy type, and vary significantly with rest-frame wavelength, especially short-ward of the Balmer break. Galaxies generally become less concentrated and more asymmetric and clumpy at shorter wavelengths. Funded by NASA grants GO-8645.01-A, GO-9124.01-A and GO-9824.01-A, GALEXGI04

  7. The extended structure of the dwarf irregular galaxies Sextans A and Sextans B. Signatures of tidal distortion in the outskirts of the Local Group

    NASA Astrophysics Data System (ADS)

    Bellazzini, M.; Beccari, G.; Fraternali, F.; Oosterloo, T. A.; Sollima, A.; Testa, V.; Galleti, S.; Perina, S.; Faccini, M.; Cusano, F.

    2014-06-01

    We present a detailed study of the stellar and H i structure of the dwarf irregular galaxies Sextans A and Sextans B, members of the NGC 3109 association. We use newly obtained deep (r ≃ 26.5) and wide-field g and r photometry to extend the surface brightness (SB) profiles of the two galaxies down to μV ≃ 31.0 mag/arcsec2. We find that both galaxies are significantly more extended than previously traced with surface photometry, out to ~4 kpc from their centres along their major axes. Older stars are found to have more extended distribution than younger populations. We obtain the first estimate of the mean metallicity for the old stars in Sex B, from the colour distribution of the red giant branch, ⟨[Fe/H]⟩ = -1.6. The SB profiles show significant changes of slope and cannot be fitted with a single Sérsic model. Both galaxies have HI discs as massive as their respective stellar components. In both cases the H i discs display solid-body rotation with maximum amplitude of ~50 km s-1 (albeit with significant uncertainty due to the poorly constrained inclination), implying a dynamical mass ~109 M⊙, a mass-to-light ratio M / LV ~ 25, and a dark-to-baryonic mass ratio of ~10. The distribution of the stellar components is more extended than the gaseous disc in both galaxies. We find that the main, approximately round, stellar body of Sex A is surrounded by an elongated low-SB stellar halo that can be interpreted as a tidal tail, similar to that found in another member of the same association (Antlia). We discuss these, as well as other evidence of tidal disturbance, in the framework of a past passage of the NGC 3109 association close to the Milky Way, which has been hypothesised by several authors and is also supported by the recently discovered filamentary configuration of the association itself. Appendices are available in electronic form at http://www.aanda.orgTable of stellar photometry is only available at the CDS via anonymous ftp to http

  8. 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.

  9. 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.

  10. The coronal parameters of local Seyfert galaxies

    NASA Astrophysics Data System (ADS)

    Marinucci, A.; Tortosa, A.; NuSTAR AGN Physics Working Group

    2016-05-01

    One of the open problems for AGN is the nature of the primary X-ray emission: It is likely due to Comptonization of soft UV photons, but the optical depth and temperature of the emitting corona were largely unknown before the launch of the Nuclear Spectroscopic Telescope Array (NuSTAR). It is the first focusing hard X-ray telescope on orbit, ∼ 100 times more sensitive in the 10-79 keV band compared to previous observatories, enabling the study of AGN at high energies with high precision. We present and discuss the results on the hot corona parameters of active galactic nuclei that have been recently measured with NuSTAR (often in coordination with XMM-Newton, Suzaku, or wift) with unprecedented accuracy, in a number of local Seyfert galaxies.

  11. TWO LOCAL VOLUME DWARF GALAXIES DISCOVERED IN 21 cm EMISSION: PISCES A AND B

    SciTech Connect

    Tollerud, Erik J.; Geha, Marla C.; Grcevich, Jana; Putman, Mary E.; Stern, Daniel E-mail: marla.geha@yale.edu E-mail: mputman@astro.columbia.edu

    2015-01-01

    We report the discovery of two dwarf galaxies, Pisces A and B, from a blind 21 cm H I search. These were the only two galaxies found via optical imaging and spectroscopy of 22 H I clouds identified in the GALFA-H I survey as dwarf galaxy candidates. They have properties consistent with being in the Local Volume (<10 Mpc), and one has resolved stellar populations such that it may be on the outer edge of the Local Group (∼1 Mpc from M31). While the distance uncertainty makes interpretation ambiguous, these may be among the faintest star-forming galaxies known. Additionally, rough estimates comparing these galaxies to ΛCDM dark matter simulations suggest consistency in number density, implying that the dark matter halos likely to host these galaxies are primarily H I-rich. The galaxies may thus be indicative of a large population of dwarfs at the limit of detectability that are comparable to the faint satellites of the Local Group. Because they are outside the influence of a large dark matter halo to alter their evolution, these galaxies can provide critical anchors to dwarf galaxy formation models.

  12. 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

  13. The star formation histories of Hickson compact group galaxies

    NASA Astrophysics Data System (ADS)

    Plauchu-Frayn, I.; Del Olmo, A.; Coziol, R.; Torres-Papaqui, J. P.

    2012-10-01

    Aims: We study the star formation fistory (SFH) of 210 galaxy members of 55 Hickson compact groups (HCG) and 309 galaxies from the Catalog of Isolated Galaxies (CIG). The SFH traces the variation of star formation over the lifetime of a galaxy, and consequently yields a snapshot picture of its formation. Comparing the SFHs in these extremes in galaxy density allows us to determine the main effects of compact groups (CG) on the formation of galaxies. Methods: We fit our spectra using the spectral synthesis code STARLIGHT and obtained the stellar population contents and mean stellar ages of HCG and CIG galaxies in three different morphological classes: early-type galaxies (EtG), early-type spirals (EtS), and late-type spirals (LtS). Results: We find that EtG and EtS galaxies in HCG show higher contents of old and intermediate stellar populations as well as an important deficit of the young stellar population, which clearly implies an older average stellar age in early galaxies in HCG. For LtS galaxies we find similar mean values for the stellar content and age in the two samples. However, we note that LtS can be split into two subclasses, namely old and young LtS. In HCG we find a higher fraction of young LtS than in the CIG sample, in addition, most of these galaxies belong to groups in which most of the galaxies are also young and actively forming stars. The specific star formation rate (SSFR) of spiral galaxies in the two samples differ. The EtS in HCG show lower SSFR values, while LtS peak at higher values compared with their counterparts in isolation. We also measured the shorter star formation time scale (SFTS) in HCG galaxies, which indicates that they have a shorter star formation activity than CIG galaxies. We take these observations as evidence that galaxies in CG have evolved more rapidly than galaxies in isolation, regardless of their morphology. Our observations are consistent with the hierarchical galaxy formation model, which states that CGs are

  14. Midlife Crises in Dwarf Galaxies in the NGC 5353/4 Group

    NASA Astrophysics Data System (ADS)

    Tully, R. Brent; Trentham, Neil

    2008-04-01

    This third paper in a series about the dwarf galaxy populations in groups within the Local Supercluster concerns the intermediate mass (2.1 × 1013 M sun) NGC 5353/4 Group with a core dominated by S0 systems and a periphery of mostly spiral systems. Dwarf galaxies are strongly concentrated toward the core. The mass-to-light ratio M/LR = 105 M sun/L sun is a factor of 3 lower than for the two groups studied earlier in the series. The properties of the group suggest it is much less dynamically evolved than those two groups of early-type galaxies. By comparison, the NGC 5353/4 Group lacks superluminous systems but has a large fraction of intermediate-luminosity galaxies; or equivalently, a luminosity function with a flatter faint-end slope. The luminosity function for the NGC 5353/4 Group should steepen as the intermediate-luminosity galaxies merge. Evidence for the ongoing collapse of the group is provided by the unusually large incidence of star-formation activity in small galaxies with early morphological types. The pattern in the distribution of galaxies with activity suggests a succession of infall events. Residual gas in dwarfs that enter the group is used up in sputtering events. The resolution of midlife crises is exhaustion.

  15. The XMM view of the outskirts of galaxy groups

    NASA Astrophysics Data System (ADS)

    Gastaldello, F.

    2016-06-01

    I will present the results of XMM observations on the outskirts of the bright galaxy group NGC 5044 addressing mass, entropy and metal abundances. I will discuss the results that XMM can achieve by exploring the outskirts of groups providing a complementary and fundamental piece of informations to the scenario emerging for the more massive clusters of galaxies.

  16. The Hα kinematics of interacting galaxies in 12 compact groups

    NASA Astrophysics Data System (ADS)

    Torres-Flores, S.; Amram, P.; Mendes de Oliveira, C.; Plana, H.; Balkowski, C.; Marcelin, M.; Olave-Rojas, D.

    2014-08-01

    We present new Fabry-Perot observations for a sample of 42 galaxies located in 12 compact groups of galaxies: HCG 1, HCG 14, HCG 25, HCG 44, HCG 53, HCG 57, HCG 61, HCG 69, HCG 93, VV 304, LGG 455 and Arp 314. From the 42 observed galaxies, a total of 26 objects are spiral galaxies, which range from Sa to Im morphological types. The remaining 16 objects are E, S0 and S0a galaxies. Using these observations, we have derived velocity maps, monochromatic and velocity dispersion maps for 24 galaxies, where 18 are spiral, three are S0a, two are S0 and one is an Im galaxy. From the 24 velocity fields obtained, we could derive rotation curves for 15 galaxies; only two of them exhibit rotation curves without any clear signature of interactions. Based on kinematic information, we have evaluated the evolutionary stage of the different groups of the current sample. We identify groups that range from having no Hα emission to displaying an extremely complex kinematics, where their members display strongly perturbed velocity fields and rotation curves. In the case of galaxies with no Hα emission, we suggest that past galaxy interactions removed their gaseous components, thereby quenching their star formation. However, we cannot discard that the lack of Hα emission is linked with the detection limit for some of our observations.

  17. 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.

  18. The luminosity function of galaxies in compact groups

    NASA Technical Reports Server (NTRS)

    Ribeiro, A. L. B.; De Carvalho, R. R.; Zepf, S. E.

    1994-01-01

    We use counts of faint galaxies in the regions of compact groups to extend the study of the luminosity function of galaxies in compact groups to absolute magnitudes as faint as M(sub B) = -14.5 + 5 log h. We find a slope of the faint end of the luminosity function of approximately alpha = -0.8, with a formal uncertainty of 0.15. This slope is not significantly different from that found for galaxies in other environments. Our results do not support previous suggestions of a dramatic underabundance of intrinsically faint galaxies in compact groups, which were based on extrapolations from fits at brighter magnitudes. The normal faint-end slope of the luminosity function in compact groups is in agreement with previous evidence that most galaxies in compact groups have not been dramatically affected by recent merging.

  19. Mechanisms for Galaxy Transformation in the Complex Environment of SuperGroup Abell 1882

    NASA Astrophysics Data System (ADS)

    Sengupta, Aparajita; Keel, W. C.; Morrison, G. E.; Windhorst, R. A.; Smith, B.

    2013-01-01

    We present our results from a multi-wavelength study of galaxy transformations in the outskirts of SuperGroup Abell 1882, a highly filamentary and clumpy structure caught in the early stages of coalescing into a Coma-like cluster. Our data have been drawn from MMT, GMOS, WIYN, SDSS, SARA, CFHT, GALEX, Spitzer and Chandra. Clusters grow by accretion through filaments, and these accreted galaxies undergo transformations due to environmental effects. Radial locations of these transformations in cluster outskirts can be mapped to a time sequence. In relaxed clusters, several evolutionary mechanisms take effect on similar spatial and temporal scales, thus making it almost impossible to disentangle different local and global mechanisms. A SuperGroup, on the other hand, has 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. We have studied transformations in Specific Star Formation Rate, birth rate parameter, color and morphological properties of 342 spectroscopically confirmed member galaxies of Abell 1882, as they make their journey through the feeding filaments into the high density core of the structure, as a function of their local galaxy density and structure-centric distance. Our results show that significant transformations in galaxies begin to occur much before the galaxies reach the X-ray gas environments of the dense groups. This indicates that ram pressure stripping is unlikely driver of early galaxy transformations in proto-clusters.

  20. The Fossils of the First Galaxies in the Local Universe

    NASA Astrophysics Data System (ADS)

    Bovill, Mia Sauda

    We argue that, at least a fraction of the newly discovered population of ultra-faint dwarfs in the Local Group constitute the fossil relics of a once ubiquitous population of dwarf galaxies formed before reionization with maximum circular velocities, vmax < 20 km s -1, where vmax ˜ M 1/3. To follow the evolution and distribution of the fossils of the first galaxies on Local Volume, 5 - 10 Mpc, scales, we have developed a new method for generating initial conditions for ΛCDM N-body simulations which provides the necessary dynamic range. The initial distribution of particles represents the position, velocity and mass distribution of the dark and luminous ha- los extracted from pre-reionization simulations. We find that ultra-faint dwarfs have properties compatible with well preserved fossils of the first galaxies and are able to reproduce the observed luminosity-metallicity relation. However, because the brightest pre-reionization dwarfs form preferentially in overdense regions, they have merged into non-fossil halos with vmax > 20-30 km s-1. Hence, we find a luminosity threshold of true-fossils of 106 Lsolar, casting doubts on the classification of some classical dSphs as fossils. We also argue that the ultra-faints at R < 50 kpc, have had their stellar properties significantly modified by tides, and that a large population of fossils remains undetected due to log(Sigma V) < -1.4. Next, we show that fossils of the first galaxies have galactocentric distributions and cumulative luminosity func- tions consistent with observations. We predict there are ˜ 300 luminous satellites orbiting within Rvir of the Milky Way, ˜ 50-70% of which are fossils. Despite our multidimensional agreement at low luminosities, our primordial model produces an overabundance of bright dwarf satellites (LV > 105 Lsolar), with this "bright satellite problem" most evident in the outer parts of the Milky Way. We estimate that, although relatively bright (LV > 105 Lsolar), these ghostly

  1. Environment of Seyfert 2 galaxies: the group of galaxies around NGC5252.

    NASA Astrophysics Data System (ADS)

    Freudling, W.; Prieto, M. Almudena

    1996-02-01

    The relatively large neutral hydrogen contents and enhanced density of companion galaxies around Seyfert 2 galaxies suggests that tidal interaction could play a major role in the evolution of Seyfert 2 galaxies. Recent observations of the distribution of neutral hydrogen in the active S0 galaxy NGC5252 have shown a disturbed morphology which suggests that the HI in this galaxy could have been acquired through interaction with neighboring galaxies (Prieto & Freudling 1993 and 1995). We have searched for other HI rich galaxies within a radius of 25 arcmin and a redshift range of +/-600km/s around the center location and redshift of NGC5252. A total of five galaxies were found, four of them are cataloged galaxies with no previous redshifts available. These five galaxies were mapped with the VLA in order to search for signs of recent tidal interactions. The maps and derived HI parameters are presented and compared to the one of NGC5252, the sixth member of the group. Two of the galaxies (UGC 8635) are an interacting pair. No signs of other recent interactions were found. Using the Arecibo telescope, we also searched for intergalactic neutral hydrogen between the group members as another potential source of gas for NGC5252. Upper limits on intergroup gas are given for three positions. The lack of evidence for interaction among the galaxies could be interpreted in two different ways. Either interaction occurred in the distant past and triggered activity in this galaxy over a long period of time. Alternatively, factors other than the gas supply might be responsible for the observation that Seyfert 2 galaxies tend to be surrounded by a region of enhanced galaxy density.

  2. Unveiling the Effects of Environment on Star Formation in Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Rieke, George; Bai, Lei; Marcillac, Delphine; Momcheva, Ivelina; Mulchaey, John; Rieke, Marcia; Tyler, Krystal; Zabludoff, Ann

    2008-03-01

    As galaxies evolve, they are subject to a menagerie of violent events that can disrupt or entirely subdue ongoing star formation. Nowhere is this more apparent than in high-density environments. Clustering due to hierarchical formation results in interactions between galaxies and the intracluster medium, leading to the demise of star formation and the rise of red sequence galaxies. However, correlations between local density and galaxy properties like morphology, star formation rate, and color exist from the largest clusters down to the poorest groups. It is likely, since the majority of galaxies lie in groups, that global trends in fundamental properties are driven by this environment. That is, the strong observed decline in star formation rate from z ~ 1 is likely to be directly related to processes affecting group galaxies. Despite this, groups are rarely studied, especially compared to the massive amounts of data available for clusters. Indeed, if we wish to study the effect of density on galaxy evolution, we need to focus on all densities. We propose to observe 48 groups of galaxies at intermediate redshifts (0.12 < z < 0.82), the era where strong evolution and transformation are expected for groups, with MIPS at 24-microns. This waveband is ideal for studying obscured star formation in galaxies, which is especially useful for our intermediate redshift range, where other star formation indicators, such as H-alpha and [OII] emission lines, become difficult to acquire and/or correct for obscuration. We will combine our groups with additional data for nearby groups and those at z ~ 1, as well as data for clusters at similar redshifts, to study the effects of a wide variety of densities on galaxy evolution from z ~ 1 to the present.

  3. VizieR Online Data Catalog: Friends-of-friends galaxy group finder (Tempel+, 2016)

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    To delineate galaxy groups in the local Universe, we used galaxy data from the extragalactic distance database (EDD2; Tully et al., 2009AJ....138..323T). The sample encompasses three datasets. As the main source, we used the Two Micron All Sky Survey (Skrutskie et al. 2006AJ....131.1163S, Cat. VII/233) Redshift Survey (2MRS) galaxies brighter than 11.75 mag in the Ks band (for a description of the catalogue, see Huchra et al., 2012, Cat. J/ApJS/199/26). We only used galaxies that are securely off the Galactic plane: Galactic latitude |b|>5°. Since the galaxy sample becomes extremely sparse farther away, we only used galaxies with a cosmic microwave background (CMB) corrected redshift z=0...0.1 (up to 430Mpc). This selection restricts our 2MRS sample to 43480 galaxies. For our analysis, we complemented the main 2MRS sample with two other sources. From the CosmicFlows-2 survey that contains 8198 galaxies with redshift-independent distance estimates (CF2; Tully et al., 2013, Cat. J/AJ/146/86), we added 3627 (of these, 2799 galaxies do not have a measured Ks magnitude). In addition, we made use of the 2M++ catalogue Lavaux & Hudson (2011, Cat. J/MNRAS/416/2840), which combines elements from the 2MRS, the 6DF Galaxy Survey (Jones et al. 2009MNRAS.399..683J, Cat. VII/259), and the Sloan Digital Sky Survey (York et al., 2000AJ....120.1579Y). Of the 64745 galaxies of the 2M++, we added 31271 galaxies down to Ks<12.54, which extends the sample well beyond the 2MRS magnitude limit. Our final galaxy dataset includes 78378 galaxies. (4 data files).

  4. Groups of galaxies in the ROSAT north ecliptic pole survey

    NASA Technical Reports Server (NTRS)

    Henry, J. Patrick

    1994-01-01

    The X-ray properties of groups of galaxies are presented. Their distribution of luminosity and temperature appears to be associated with the extrapolation of these distributions from rich clusters of galaxies. The properties of the ensemble of groups of galaxies are almost totally unknown. Only a few X-ray observations of groups that were selected by optical methods were published so far. A sample of eight groups with 'z' inferior to 0.04, of which three have 'z' inferior to 0.03 was investigated. The temperature and the luminosity functions at one point were determined.

  5. 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

  6. Environmental quantification and Halpha characterisation of the most isolated galaxies in the local Universe

    NASA Astrophysics Data System (ADS)

    Verley, Simon

    2005-12-01

    The role of the environment on galaxy evolution is still not fully understood. In order to quantify and set limits on the role of nurture one must identify and study a sample of isolated galaxies. The AMIGA project "Analysis of the Interstellar Medium of Isolated Galaxies" is doing a multi-wavelength study of a large sample of isolated galaxies in order to examine their interstellar medium and star formation activity. We processed 950 galaxies from the Catalogue of Isolated Galaxies (Karachentseva, 1973) and evaluated their isolation using an automated star-galaxy classification procedure (down to M_B = 17.5) on large digitised POSS-I fields surrounding each isolated galaxy. We defined, compared and discussed various criteria to quantify the degree of isolation for these galaxies: e.g. Karachentseva's revised criterion, local surface density computations, estimation of the external tidal force affecting each isolated galaxy. We find galaxies violating Karachentseva's original criterion, and we define various subsamples of galaxies according to their degree of isolation. Additionally, we sought for the redshifts of the primary and companion galaxies to access the radial dimension and have an accurate three dimensional picture of the surroundings. Finally, we applied our pipeline to triplets, compact groups and clusters and interpret the isolated galaxy population in light of these control samples. The star formation is known to be affected by the local environment of the galaxies, but the star formation rate also highly depends on the intrinsic interstellar medium features. Disentangling these two effects is still a challenging subject. To address this issue, we observed and gathered photometric data (Halpha narrow- & r Gunn broad-band filters) for 200 spiral galaxies from the Catalogue of Isolated Galaxies which are, by definition, in low-density regions. We subsequently studied the Halpha morphological aspect of the 45 biggest and less inclined galaxies. Using

  7. An infrared imaging study of galaxies in the local universe

    NASA Technical Reports Server (NTRS)

    Grauer, Albert D.; Rieke, Marcia J.; Mcleod, Kim K.

    1995-01-01

    This poster was a preliminary report on a survey of galaxies in the local universe at J and K using a NICMOS3 256 x 256 infrared photometric camera attached to the 61 inch telescope on Mt. Bigelow. Deep images are being obtained for a representative sample of galaxies in the Uppsala General Catalogue. Structural and color parameters are determined for a wide variety of galactic types. These data should prove to be valuable in characterizing stellar populations within disks and bulges, determining if IR-active galaxies have unusual global as well as- nuclear properties, and understanding the effects of evolution and redshift dimming in distant galaxies.

  8. Our Milky Way structure in the context of local galaxies

    NASA Astrophysics Data System (ADS)

    Shen, Juntai

    2015-08-01

    The Milky Way is the closest galaxy to us, and has been studied extensively due to its proximity. Understanding its structure and dynamics will help us understand spiral galaxies in general. I will review the latest research progress in the structure, kinematics, and dynamics of the Milky Way in the context of local galaxies. I will cover most structural components (the bulge/bar, disk, and spiral structures) and discuss the implications of some new results on the formation history of our home galaxy.

  9. 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.

  10. DISTRIBUTION OF SATELLITE GALAXIES IN HIGH-REDSHIFT GROUPS

    SciTech Connect

    Wang Yougang; Chen Xuelei; Park, Changbom; Hwang, Ho Seong

    2010-08-01

    We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great Observatories Origins Deep Survey to study the color-morphological properties of satellite galaxies and investigate possible alignment between the distribution of the satellites and the orientation of their central galaxy. We confirm the bimodal color and morphological-type distribution for satellite galaxies at this redshift range: the red and blue classes correspond to the early and late morphological types, respectively, and the early-type satellites are on average brighter than the late-type ones. Furthermore, there is a morphological conformity between the central and satellite galaxies: the fraction of early-type satellites in groups with an early-type central is higher than those with a late-type central galaxy. This effect is stronger at smaller separations from the central galaxy. We find a marginally significant signal of alignment between the major axis of the early-type central galaxy and its satellite system, while for the late-type centrals no significant alignment signal is found. We discuss the alignment signal in the context of shape evolution of groups.

  11. 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.

  12. HSTPROMO and the Dynamics of the Local Group

    NASA Astrophysics Data System (ADS)

    Besla, Gurtina

    2016-05-01

    Our understanding of the dynamics of our Local Group of galaxies has changed dramatically over the past few years owing to significant advancements in astrometry and our theoretical understanding of galaxy structure. I will provide an overview of key contributions by the Hubble Space Telescope to this evolving picture. In particular, I will highlight the HSTPROMO team’s proper motion measurements of key players in the Local Group, such as the fastest (Leo I) and most massive (LMC and SMC) satellites of the Milky Way and the first ever direct proper motion measurement of M31. These results have met with controversy, challenging preconceived notions of the orbital dynamics of key components of the Local Group. I will further highlight the importance of HST’s continued role in this field in the era of Gaia.

  13. Isolated elliptical galaxies in the local Universe

    NASA Astrophysics Data System (ADS)

    Lacerna, I.; Hernández-Toledo, H. M.; Avila-Reese, V.; Abonza-Sane, J.; del Olmo, A.

    2016-04-01

    Context. We have studied a sample of 89 very isolated, elliptical galaxies at z < 0.08 and compared their properties with elliptical galaxies located in a high-density environment such as the Coma supercluster. Aims: Our aim is to probe the role of environment on the morphological transformation and quenching of elliptical galaxies as a function of mass. In addition, we elucidate the nature of a particular set of blue and star-forming isolated ellipticals identified here. Methods: We studied physical properties of ellipticals, such as color, specific star formation rate, galaxy size, and stellar age, as a function of stellar mass and environment based on SDSS data. We analyzed the blue and star-forming isolated ellipticals in more detail, through photometric characterization using GALFIT, and infer their star formation history using STARLIGHT. Results: Among the isolated ellipticals ≈20% are blue, ≲8% are star forming, and ≈10% are recently quenched, while among the Coma ellipticals ≈8% are blue and just ≲1% are star forming or recently quenched. There are four isolated galaxies (≈4.5%) that are blue and star forming at the same time. These galaxies, with masses between 7 × 109 and 2 × 1010 h-2 M⊙, are also the youngest galaxies with light-weighted stellar ages ≲1 Gyr and exhibit bluer colors toward the galaxy center. Around 30-60% of their present-day luminosity, but only <5% of their present-day mass, is due to star formation in the last 1 Gyr. Conclusions: The processes of morphological transformation and quenching seem to be in general independent of environment since most of elliptical galaxies are "red and dead", although the transition to the red sequence should be faster for isolated ellipticals. In some cases, the isolated environment seems to propitiate the rejuvenation of ellipticals by recent (<1 Gyr) cold gas accretion.

  14. 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).

  15. The APOSTLE simulations: solutions to the Local Group's cosmic puzzles

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Frenk, Carlos S.; Fattahi, Azadeh; Navarro, Julio F.; Bower, Richard G.; Crain, Robert A.; Dalla Vecchia, Claudio; Furlong, Michelle; Helly, John. C.; Jenkins, Adrian; Oman, Kyle A.; Schaller, Matthieu; Schaye, Joop; Theuns, Tom; Trayford, James; White, Simon D. M.

    2016-04-01

    The Local Group galaxies offer some of the most discriminating tests of models of cosmic structure formation. For example, observations of the Milky Way (MW) and Andromeda satellite populations appear to be in disagreement with N-body simulations of the `lambda cold dark matter' (ΛCDM) model: there are far fewer satellite galaxies than substructures in CDM haloes (the `missing satellites' problem); dwarf galaxies seem to avoid the most massive substructures (the `too-big-to-fail' problem); and the brightest satellites appear to orbit their host galaxies on a thin plane (the `planes of satellites' problem). Here we present results from APOSTLE (A Project Of Simulating The Local Environment), a suite of cosmological hydrodynamic simulations of 12 volumes selected to match the kinematics of the Local Group (LG) members. Applying the EAGLE code to the LG environment, we find that our simulations match the observed abundance of LG galaxies, including the satellite galaxies of the MW and Andromeda. Due to changes to the structure of haloes and the evolution in the LG environment, the simulations reproduce the observed relation between stellar mass and velocity dispersion of individual dwarf spheroidal galaxies without necessitating the formation of cores in their dark matter profiles. Satellite systems form with a range of spatial anisotropies, including one similar to the MWs, confirming that such a configuration is not unexpected in ΛCDM. Finally, based on the observed velocity dispersion, size, and stellar mass, we provide estimates of the maximum circular velocity for the haloes of nine MW dwarf spheroidals.

  16. Fossil Groups in the Local Universe

    NASA Technical Reports Server (NTRS)

    OSullivan, Ewan

    2005-01-01

    The two galaxies observed as part of this project were originally selected as fossil group candidates because of their isolation from other galaxies and their apparent high X-ray luminosity and extended X-ray emission. However, the X-ray data available was minimal, being drawn from the ROSAT All-Sky Survey. We have performed an initial analysis of the XMM data from both galaxies and found that their gaseous halos are smaller, cooler, and less luminous than expected. In the case of NGC 57, the RASS estimate of extent and luminosity was biased because of a previously unidentified background group which is visible in the XMM data to one side of the galaxy. In the case of IC 153 1, the contribution from background point sources near the galaxy appears to be to blame. This suggests that both galaxies should be reclassified as isolated ellipticals. Such systems are very rare, and currently poorly understood; for comparison, there are now 6-10 known fossil groups, but only one isolated elliptical with useful X-ray data. We are currently re-analyzing the data for the two galaxies to take advantage of the calibration improvements of SAS 6.1, and to include calculations of the mass profiles of the two systems. A paper is currently in preparation dealing with the X-ray properties and environment of the galaxies, and we expect to submit this to the Astrophysical Journal within the next two months. Multi-band optical imaging of the field surrounding NGC 57 has been acquired to confirm its isolated status and provide more information on the background group. IC 1531 was accepted as a target in Chandra cycle 6 as part of a related proposal, and we intend to add this new observation to our XMM data when it becomes available. A second paper is planned to include the results of this combined analysis.

  17. The Relation between Galaxy Morphology and Environment in the Local Universe: An RC3-SDSS Picture

    NASA Astrophysics Data System (ADS)

    Wilman, David J.; Erwin, Peter

    2012-02-01

    We present results of an analysis of the local (z ~ 0) morphology-environment relation for 911 bright (MB < -19) galaxies, based on matching classical RC3 morphologies with the Sloan Digital Sky Survey based group catalog of Yang et al., which includes halo mass estimates. This allows us to study how the relative fractions of spirals, lenticulars, and ellipticals depend on halo mass over a range of 1011.7-1014.8 h -1 M ⊙, from isolated single-galaxy halos to massive groups and low-mass clusters. We pay particular attention to how morphology relates to central versus satellite status (where "central" galaxies are the most massive within their halo). The fraction of galaxies which are elliptical is a strong function of stellar mass; it is also a strong function of halo mass, but only for central galaxies. We interpret this as evidence for a scenario where elliptical galaxies are always formed, probably via mergers, as central galaxies within their halos, with satellite ellipticals being previously central galaxies accreted onto a larger halo. The overall fraction of galaxies which are S0 increases strongly with halo mass, from ~10% to ~70%. Here, too, we find striking differences between the central and satellite populations. 20% ± 2% of central galaxies with stellar masses M * > 1010.5 M ⊙ are S0 regardless of halo mass, but satellite S0 galaxies are only found in massive (>1013 h -1 M ⊙) halos, where they are 69% ± 4% of the M * > 1010.5 M ⊙ satellite population. This suggests two channels for forming S0 galaxies: one which operates for central galaxies and another which transforms lower-mass ( M * <~ 1011 M ⊙) accreted spirals into satellite S0 galaxies in massive halos. Analysis of finer morphological structure (bars and rings in disk galaxies) shows some trends with stellar mass, but none with halo mass; this is consistent with other recent studies which indicate that bars are not strongly influenced by galaxy environment. Radio sources in high

  18. Stellar populations in local star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Perez-Gonzalez, P. G.

    2003-11-01

    The main goal of this thesis work is studying the main properties of the stellar populations embedded in a statistically complete sample of local active star-forming galaxies: the Universidad Complutense de Madrid (UCM) Survey of emission-line galaxies. This sample contains 191 local star-forming galaxies at an average redshift of 0.026. The survey was carried out using an objective-prism technique centered at the wavelength of the Halpha nebular emission-line (a common tracer of recent star formation). (continues)

  19. MASS DISTRIBUTION IN HICKSON COMPACT GROUPS OF GALAXIES

    SciTech Connect

    Plana, H.; Amram, P.; De Oliveira, C. Mendes; Balkowski, C.

    2010-01-15

    This study presents the mass distribution for a sample of 18 late-type galaxies in nine Hickson compact groups. We used H{alpha} rotation curves (RCs) from high-resolution two-dimensional velocity fields of Fabry-Perot observations and the J-band photometry from the Two Micron All Sky Survey, in order to determine the dark halo and the visible matter distributions. The study compares two halo density profiles, an isothermal core-like distribution, and a cuspy one. We also compare their visible and dark matter distributions with those of galaxies belonging to cluster and field galaxies coming from two samples: 40 cluster galaxies of Barnes et al. and 35 field galaxies of Spano et al. The central halo surface density is found to be constant with respect to the total absolute magnitude similar to what is found for the isolated galaxies. This suggests that the halo density is independent of galaxy type and environment. We have found that core-like density profiles better fit the RCs than cuspy-like ones. No major differences have been found between field, cluster, and compact group galaxies with respect to their dark halo density profiles.

  20. A New Method to Estimate Halo Mass of Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Lu, Yi; Yang, Xiaohu; Shen, Shiyin

    2015-08-01

    Reliable halo mass estimation for a given galaxy system plays an important role both in cosmology and galaxy formation studies. Here we set out to find the way that can improve the halo mass estimation for those galaxy systems with limited brightest member galaxies been observed. Using four mock galaxy samples constructed from semi-analytical formation models, the subhalo abundance matching method and the conditional luminosity functions, respectively, we find that the luminosity gap between the brightest and the subsequent brightest member galaxies in a halo (group) can be used to significantly reduce the scatter in the halo mass estimation based on the luminosity of the brightest galaxy alone. Tests show that these corrections can significantly reduce the scatter in the halo mass estimations by $\\sim 50\\%$ to $\\sim 70\\%$ in massive halos depending on which member galaxies are considered. Comparing to the traditional ranking method, we find that this method works better for groups with less than five members, or in observations with very bright magnitude cut.

  1. THE CONNECTION BETWEEN GALAXIES AND DARK MATTER STRUCTURES IN THE LOCAL UNIVERSE

    SciTech Connect

    Reddick, Rachel M.; Wechsler, Risa H.; Behroozi, Peter S.; Tinker, Jeremy L. E-mail: rwechsler@stanford.edu

    2013-07-01

    We provide new constraints on the connection between galaxies in the local universe, identified by the Sloan Digital Sky Survey, and dark matter halos and their constituent substructures in the {Lambda}-cold dark matter model using WMAP7 cosmological parameters. Predictions for the abundance and clustering properties of dark matter halos, and the relationship between dark matter hosts and substructures, are based on a high-resolution cosmological simulation, the Bolshoi simulation. We associate galaxies with dark matter halos and subhalos using subhalo abundance matching, and perform a comprehensive analysis which investigates the underlying assumptions of this technique including (1) which halo property is most closely associated with galaxy stellar masses and luminosities, (2) how much scatter is in this relationship, and (3) how much subhalos can be stripped before their galaxies are destroyed. The models are jointly constrained by new measurements of the projected two-point galaxy clustering and the observed conditional stellar mass function of galaxies in groups. We find that an abundance matching model that associates galaxies with the peak circular velocity of their halos is in good agreement with the data, when scatter of 0.20 {+-} 0.03 dex in stellar mass at a given peak velocity is included. This confirms the theoretical expectation that the stellar mass of galaxies is tightly correlated with the potential wells of their dark matter halos before they are impacted by larger structures. The data put tight constraints on the satellite fraction of galaxies as a function of galaxy stellar mass and on the scatter between halo and galaxy properties, and rule out several alternative abundance matching models that have been considered. This will yield important constraints for galaxy formation models, and also provides encouraging indications that the galaxy-halo connection can be modeled with sufficient fidelity for future precision studies of the dark universe.

  2. The Connection between Galaxies and Dark Matter Structures in the Local Universe

    SciTech Connect

    Reddick, Rachel M.; Wechsler, Risa H.; Tinker, Jeremy L.; Behroozi, Peter S.

    2012-07-11

    We provide new constraints on the connection between galaxies in the local Universe, identified by the Sloan Digital Sky Survey (SDSS), and dark matter halos and their constituent substructures in the {Lambda}CDM model using WMAP7 cosmological parameters. Predictions for the abundance and clustering properties of dark matter halos, and the relationship between dark matter hosts and substructures, are based on a high-resolution cosmological simulation, the Bolshoi simulation. We associate galaxies with dark matter halos and subhalos using subhalo abundance matching, and perform a comprehensive analysis which investigates the underlying assumptions of this technique including (a) which halo property is most closely associated with galaxy stellar masses and luminosities, (b) how much scatter is in this relationship, and (c) how much subhalos can be stripped before their galaxies are destroyed. The models are jointly constrained by new measurements of the projected two-point galaxy clustering and the observed conditional stellar mass function of galaxies in groups. We find that an abundance matching model that associates galaxies with the peak circular velocity of their halos is in good agreement with the data, when scatter of 0.20 {+-} 0.03 dex in stellar mass at a given peak velocity is included. This confirms the theoretical expectation that the stellar mass of galaxies is tightly correlated with the potential wells of their dark matter halos before they are impacted by larger structures. The data put tight constraints on the satellite fraction of galaxies as a function of galaxy stellar mass and on the scatter between halo and galaxy properties, and rule out several alternative abundance matching models that have been considered. This will yield important constraints for galaxy formation models, and also provides encouraging indications that the galaxy - halo connection can be modeled with sufficient fidelity for future precision studies of the dark Universe.

  3. Exploring Evolution Through the Effects of Galaxy-Galaxy and Group Interactions on Gas Content

    NASA Astrophysics Data System (ADS)

    Fertig, Derek; Rosenberg, J. L.; Patton, D. R.; Ellison, S. L.

    2014-01-01

    Galaxy-galaxy interactions are a driving force in galaxy evolution, producing changes in color, morphology, metallicity and enhancing star formation. Many factors contributing to these changes have been well studied such as environment and orientation of the interaction, however studies of the gas content have been limited. To address the question of how interactions affect the gas content of galaxy pairs, we present results from two studies taking different approaches to the question. We present results from a combined optical and HI 21 cm study of 102 galaxy pairs with projected separations up to 120 kpc and velocity differences less than 500 km/s. These pairs were selected from the SDSS spectroscopic survey and were also observed by the ALFALFA HI 21 cm survey. We use these data to study how interactions effect the SFE and HI gas content of these systems. From the second study we present initial results from VLA D-array observations of a galaxy group in which interactions appear to be removing much of the cold gas from the galaxies creating a large reservoir in the inter-group medium. We investigate how this removal of gas and subsequent reservoir impact the evolution of the galaxies within the group, particularly two systems which are transitioning through the green valley. This work has been supported by NSF grant AST-000167932 and a George Mason University Presidential Fellowship.

  4. The fraction of BL Lacertae objects in groups of galaxies

    NASA Astrophysics Data System (ADS)

    Muriel, H.

    2016-06-01

    Context. BL Lac objects are a rare class of active galactic nuclei that typically show featureless optical spectra that make it difficult to estimate the redshift. A novel method for estimating the redshift of BL Lac objects has recently been proposed which assumes that these objects typically reside in groups of galaxies. Aims: The aim of this work is to estimate the fraction of BL Lac objects that reside in groups of galaxies. Methods: We use a sample of groups (M12 catalogue) selected by applying a friends-of-friends algorithm in the SDSS DR12. Galaxies in the M12 sample were cross-correlated with the sample of blazars in the BZCAT. We found that 121 galaxies in the M12 catalogue are blazars in the BZCAT sample, all but one are BL Lac objects, and a large fraction are classified as BL Lac-galaxy dominated. Results: Analysing the fraction of galaxies in groups as a function of redshift we have estimated a correction factor that takes into account the typical incompleteness of the catalogues based on the friends-of-friends algorithm. Once this factor was applied to the sample of BL Lac objects with a counterpart in the M12 catalogue, we found that the percentage of BL Lac objects in groups is ≳ 67 ± 8%. Conclusions: The high rate of BL Lac objects in groups found in this work strongly supports a recent method that has successfully estimated the redshift of BL Lac objects with featureless spectra.

  5. Dark energy domination in the local flow of giant galaxies

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.

    2015-05-01

    A dozen of the most luminous galaxies, at distances of up to 10 Mpc from the Local Group, move away from the group, forming the local expansion flow of giants. We use recent Hubble Space Telescope data on local giants and their numerous fainter companions to study the dynamical structure and evolutionary trends of the flow. An N-body computer model, which reproduces the observed kinematics of the flow, is constructed under the assumption that the flow is embedded in the universal dark energy background. In the model, the motions of the flow members are controlled by their mutual attraction force and the repulsion force produced by the dark energy. It is found that the dark energy repulsion dominates the force field of the flow. Because of this, the flow expands with acceleration. The dark energy domination is enhanced by the environment effect of the low mean matter density on the spatial scale of 50 Mpc in the local Universe. The dark energy domination increases with time and introduces to the flow an asymptotically linear velocity-distance relation with the universal time-rate that depends on the dark energy density only.

  6. 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⊙.

  7. 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).

  8. MAGGIE: Models and Algorithms for Galaxy Groups, Interlopers and Environment

    NASA Astrophysics Data System (ADS)

    Duarte, Manuel; Mamon, Gary A.

    2015-11-01

    Combining our knowledge of halo structure and internal kinematics from cosmological dark matter simulations and the distribution of halo interlopers in projected phase space measured in cosmological galaxy simulations, we develop MAGGIE, a prior- and halo-based, probabilistic, abundance matching (AM) grouping algorithm for doubly complete subsamples (in distance and luminosity) of flux-limited samples. We test MAGGIE-L and MAGGIE-M (in which group masses are derived from AM applied to the group luminosities and stellar masses, respectively) on groups of at least three galaxies extracted from a mock Sloan Digital Sky Survey Legacy redshift survey, incorporating realistic observational errors on galaxy luminosities and stellar masses. In comparison with the optimal Friends-of-Friends (FoF) group finder, groups extracted with MAGGIE are much less likely to be secondary fragments of true groups; in primary fragments, its galaxy memberships (relative to the virial sphere of the real-space group) are much more complete and usually more reliable, and its masses are much less biased and usually with less scatter, as are its group luminosities and stellar masses (computed in MAGGIE using the membership probabilities as weights). FoF outperforms MAGGIE only for high-mass clusters: for the reliability of the galaxy population and the dispersion of its total mass. In comparison with our implementation of the Yang et al. group finder, MAGGIE reaches much higher completeness and slightly lower group fragmentation and dispersion on group total masses, luminosities and stellar masses, but slightly greater bias in the latter two and lower reliabilities. MAGGIE should therefore lead to sharper trends of environmental effects on galaxies and more accurate mass-orbit modelling.

  9. On optical mass estimation methods for galaxy groups

    NASA Astrophysics Data System (ADS)

    Pearson, R. J.; Ponman, T. J.; Norberg, P.; Robotham, A. S. G.; Farr, W. M.

    2015-05-01

    We examine the performance of a variety of different estimators for the mass of galaxy groups, based on their galaxy distribution alone. We draw galaxies from the Sloan Digital Sky Survey for a set of groups and clusters for which hydrostatic mass estimates based on high-quality Chandra X-ray data are available. These are used to calibrate the galaxy-based mass proxies, and to test their performance. Richness, luminosity, galaxy overdensity, rms radius and dynamical mass proxies are all explored. These different mass indicators all have their merits, and we argue that using them in combination can provide protection against being misled by the effects of dynamical disturbance or variations in star formation efficiency. Using them in this way leads us to infer the presence of significant non-statistical scatter in the X-ray based mass estimates we employ. We apply a similar analysis to a set of mock groups derived from applying a semi-analytic galaxy formation code to the Millennium dark matter simulation. The relations between halo mass and the mass proxies differ significantly in some cases from those seen in the observational groups, and we discuss possible reasons for this.

  10. ASKAP H I imaging of the galaxy group IC 1459

    NASA Astrophysics Data System (ADS)

    Serra, P.; Koribalski, B.; Kilborn, V.; Allison, J. R.; Amy, S. W.; Ball, L.; Bannister, K.; Bell, M. E.; Bock, D. C.-J.; Bolton, R.; Bowen, M.; Boyle, B.; Broadhurst, S.; Brodrick, D.; Brothers, M.; Bunton, J. D.; Chapman, J.; Cheng, W.; Chippendale, A. P.; Chung, Y.; Cooray, F.; Cornwell, T.; DeBoer, D.; Diamond, P.; Forsyth, R.; Gough, R.; Gupta, N.; Hampson, G. A.; Harvey-Smith, L.; Hay, S.; Hayman, D. B.; Heywood, I.; Hotan, A. W.; Hoyle, S.; Humphreys, B.; Indermuehle, B.; Jacka, C.; Jackson, C. A.; Jackson, S.; Jeganathan, K.; Johnston, S.; Joseph, J.; Kamphuis, P.; Leach, M.; Lenc, E.; Lensson, E.; Mackay, S.; Marquarding, M.; Marvil, J.; McClure-Griffiths, N.; McConnell, D.; Meyer, M.; Mirtschin, P.; Neuhold, S.; Ng, A.; Norris, R. P.; O'Sullivan, J.; Pathikulangara, J.; Pearce, S.; Phillips, C.; Popping, A.; Qiao, R. Y.; Reynolds, J. E.; Roberts, P.; Sault, R. J.; Schinckel, A. E. T.; Shaw, R.; Shimwell, T. W.; Staveley-Smith, L.; Storey, M.; Sweetnam, A. W.; Troup, E.; Tzioumis, A.; Voronkov, M. A.; Westmeier, T.; Whiting, M.; Wilson, C.; Wong, O. I.; Wu, X.

    2015-09-01

    We present H I imaging of the galaxy group IC 1459 carried out with six antennas of the Australian Square Kilometre Array Pathfinder equipped with phased-array feeds. We detect and resolve H I in 11 galaxies down to a column density of ˜1020 cm-2 inside a ˜6 deg2 field and with a resolution of ˜1 arcmin on the sky and ˜8 km s-1 in velocity. We present H I images, velocity fields and integrated spectra of all detections, and highlight the discovery of three H I clouds - two in the proximity of the galaxy IC 5270 and one close to NGC 7418. Each cloud has an H I mass of ˜109 M⊙ and accounts for ˜15 per cent of the H I associated with its host galaxy. Available images at ultraviolet, optical and infrared wavelengths do not reveal any clear stellar counterpart of any of the clouds, suggesting that they are not gas-rich dwarf neighbours of IC 5270 and NGC 7418. Using Parkes data, we find evidence of additional extended, low-column-density H I emission around IC 5270, indicating that the clouds are the tip of the iceberg of a larger system of gas surrounding this galaxy. This result adds to the body of evidence on the presence of intragroup gas within the IC 1459 group. Altogether, the H I found outside galaxies in this group amounts to several times 109 M⊙, at least 10 per cent of the H I contained inside galaxies. This suggests a substantial flow of gas in and out of galaxies during the several billion years of the group's evolution.

  11. The formation of compact groups of galaxies. I: Optical properties

    NASA Technical Reports Server (NTRS)

    Diaferio, Antonaldo; Geller, Margaret J.; Ramella, Massimo

    1994-01-01

    The small crossing time of compact groups of galaxies (t(sub cr)H(sub 0) approximately less than 0.02) makes it hard to understand why they are observable at all. Our dissipationless N-body simulations show that within a single rich collapsing group compact groups of galaxies continually form. The mean lifetime of a particular compact configuration if approximately 1 Gyr. On this time scale, members may merge and/or other galaxies in the loose group may join the compact configuration. In other words, compact configurations are continually replaced by new systems. The frequency of this process explains the observability of compact groups. Our model produces compact configurations (compact groups (CG's) with optical properties remarkably similar to Hickson's (1982) compact groups (HCG's): (1) CG's have a frequency distribution of members similar to that of HCG's; (2) CG's are approximately equals 10 times as dense as loose groups; (3) CG's have dynamical properties remarkably similar to those of HCG's; (4) most of the galaxy members of CG's are not merger remnants. The crucial aspect of the model is the relationship between CG's and the surrounding rich loose group. Our model predicts the frequency of occurrence of CG's. A preliminary analysis of 18 rich loose groups is consistent with the model prediction. We suggest further observational tests of the model.

  12. Dynamical history of the Local Group in ΛCDM

    NASA Astrophysics Data System (ADS)

    Banik, Indranil; Zhao, Hongsheng

    2016-06-01

    The positions and velocities of galaxies in the Local Group (LG) measure the gravitational field within it. This is mostly due to the Milky Way (MW) and Andromeda (M31). We constrain their masses using distance and radial velocity (RV) measurements of 32 LG galaxies. To do this, we follow the trajectories of many simulated particles starting on a pure Hubble flow at redshift 9. For each observed galaxy, we obtain a trajectory which today is at the same position. Its final velocity is the model prediction for the velocity of that galaxy. Unlike previous simulations based on spherical symmetry, ours are axisymmetric and include gravity from Centaurus A. We find the total LG mass is {4.33^{+0.37}_{-0.32}× {10}^{12} M_{⊙}}, with 0.14 ± 0.07 of this being in the MW. We approximately account for IC 342, M81, the Great Attractor and the Large Magellanic Cloud. No plausible set of initial conditions yields a good match to the RVs of our sample of LG galaxies. Observed RVs systematically exceed those predicted by the best-fitting Lambda Cold Dark Matter (ΛCDM) model, with a typical disagreement of {45.1^{+7.0}_{-5.7}} km s-1 and a maximum of 110 ± 13 km s-1 for DDO 99. Interactions between LG dwarf galaxies cannot easily explain this. One possibility is a past close flyby of the MW and M31. This arises in some modified gravity theories but not in ΛCDM. Gravitational slingshot encounters of material in the LG with either of these massive fast-moving galaxies could plausibly explain why some non-satellite LG galaxies are moving away from us even faster than a pure Hubble flow.

  13. 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

  14. Effects of AGN feedback in galaxy groups and Intergalactic Medium

    NASA Astrophysics Data System (ADS)

    Lagos, C.; Padilla, N.; Cora, S.

    2009-05-01

    The combination of Cosmological numerical simulations and semi-analytical models of galaxy formation is a very appropriate method to study how different phenomena influence the galaxy and galaxy cluster formation. The main advantage of this combination consists in the fact that N-body simulations do not need to be rerun every time a change in the assumptions about baryonic processes is made since these are included in the semi-analytical models which run on the final N-Body simulation output. The Semi-analytic model takes into account radiative cooling of gas, stellar formation and different types of SN contribution, which eject energy and metals to the interstellar medium, allowing the chemical enrichment of the intergalactic medium. In this project we use the semi-analytic hybrid model by Cora (2006, MNRAS, 368, 1540) and implement the AGN feedback, in two modes, the QSO mode (which takes into account mergers and galactic disk instabilities), and the Radio mode, which modifies the cooling in the galaxies These two processes allow to suppress the super flows in the hybrid model, and allows the study of QSOs in galaxy groups. This new implementation opens different possibles studies including the QSO luminosity function, the anti-hierarchical evolution of Mass Function, the BH mass and bulge mass relation, Color-Magnitude diagrams, TF relation, the galaxy luminosity function, the effects of AGN in neighbor galaxies and the behavior of QSOs in the sub-millimeter window.

  15. IGM Heating and AGN activity in Fossil Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Miraghaei, H.; Khosroshahi, H. G.; Klöckner, H.-R.; Ponman, T. J.; Jetha, N. N.; Raychaudhury, S.

    2014-07-01

    Fossil galaxy groups are energetically and morphologically ideal environments to study the intergalactic medium (IGM) heating, because their inter-galactic gas is undisturbed due to the lack of recent group scale mergers. We study the role of active galactic nuclei (AGN) in heating the IGM in a sample of five fossil galaxy groups by employing properties at 610 MHz and 1.4 GHz. We find that two of the dominant galaxies in fossil groups, ESO 3060170 and RX J1416.4+2315, are associated with the radio lobes. We evaluate the PdV work of the radio lobes and their corresponding heating power and compare to the X-ray emission loss within cooling radius. Our results show that the power due to mechanical heating is not sufficiently high to suppress the cooling.

  16. The Tully-Fisher relations for Hickson compact group galaxies

    NASA Astrophysics Data System (ADS)

    Torres-Flores, S.; Mendes de Oliveira, C.; Plana, H.; Amram, P.; Epinat, B.

    2013-07-01

    We used K-band photometry, maximum rotational velocities derived from Fabry-Perot data and H I observed and predicted masses to study, for the first time, the K band, stellar and baryonic Tully-Fisher relations for galaxies in Hickson compact groups. We compared these relations with the ones defined for galaxies in less dense environments from the Gassendi HAlpha survey of Spirals and from a sample of gas-rich galaxies. We find that most of the Hickson compact group galaxies lie on the K-band Tully-Fisher relation defined by field galaxies with a few low-mass outliers, namely HCG 49b and HCG 96c, which appear to have had strong recent burst of star formation. The stellar Tully-Fisher relation for compact group galaxies presents a similar dispersion to that of the K-band relation, and it has no significant outliers when a proper computation of the stellar mass is done for the strongly star-forming galaxies. The scatter in these relations can be reduced if the gaseous component is taken into account, i.e. if a baryonic Tully-Fisher relation is considered. In order to explain the positions of the galaxies off the K-band Tully-Fisher relation, we favour a scenario in which their luminosities are brightened due to strong star formation or AGN activity. We argue that strong bursts of star formation can affect the B- and K-band luminosities of HCG 49b and HCG 96c and in the case of the latter also AGN activity may affect the K-band magnitude considerably, without affecting their total masses.

  17. Local expansion flows of galaxies: quantifying acceleration effect of dark energy

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Teerikorpi, P.

    2013-08-01

    The nearest expansion flow of galaxies observed around the Local group is studied as an archetypical example of the newly discovered local expansion flows around groups and clusters of galaxies in the nearby Universe. The flow is accelerating due to the antigravity produced by the universal dark energy background. We introduce a new acceleration measure of the flow which is the dimensionless ``acceleration parameter" Q (x) = x - x-2 depending on the normalized distance x only. The parameter is zero at the zero-gravity distance x = 1, and Q(x) ∝ x, when x ≫ 1. At the distance x = 3, the parameter Q = 2.9. Since the expansion flows have a self-similar structure in normalized variables, we expect that the result is valid as well for all the other expansion flows around groups and clusters of galaxies on the spatial scales from ˜ 1 to ˜ 10 Mpc everywhere in the Universe.

  18. Comparing the clustering of galaxies and galaxy group by using the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Wang, Yiran; Brunner, R. J.

    2014-01-01

    By using the angular two-point correlation function, we measure the clustering strength of a clean sample of galaxies (explored in Wang, Brunner, & Dolence 2013) for the Sloan Digital Sky Survey Data Release Seven. By using these same data, we first find isolated pairs, triplets, quads, and larger groups of galaxies, and subsequently measure the clustering of these subsamples. We find the clustering strength increases with groups size, which supports the halo model of galaxy clustering and demonstrates the efficacy of our isolated group catalog for general studies such as the galaxy merger rate. Finally, we explore the effects of galaxy spectral type and photometric redshift on the clustering behavior of these galaxy group samples. References: Blake, C., Collister, A., Lahav, O. 2008, MNRAS, 385, 1257 Hickson, P. 1982, ApJ, 255, 382 Ross, A. J., Brunner, R. J. 2009, MNRAS, 399, 878 Wang Y., Brunner R. J., Dolence J. C. 2013, MNRAS, 432, 1961 Zehavi, I., et al. 2004, ApJ, 608, 16

  19. 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.

  20. 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

  1. 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.

  2. 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

  3. Tracer populations in the Local Group

    NASA Astrophysics Data System (ADS)

    Watkins, Laura L.

    2011-04-01

    So often in astronomy, an object is not considered for its individual merits, but for what we may learn from its properties regarding some larger population. The existence of dark matter is a prime example of this; we cannot see it directly but we can infer its presence by noting its effects on the stars orbiting within its potential. This thesis describes how various sets of tracer populations can be used to probe the properties of a variety of galaxies in the Local Group. I begin by describing the extraction of a variable catalogue from the Sloan Digital Sky Survey Stripe 82 dataset and then use the catalogue to select a high-quality set of RR Lyrae stars. Analysing the distribution of the RR Lyraes reveals three significant substructures in the Milky Way halo: the Hercules-Aquila Cloud and the Sagittarius Stream, which were already known to exist, and the Pisces Overdensity, which was previously undetected. It is a faint, extended structure found at ~80 kpc and is of unknown origin. Altogether, I find that nearly 80% of the RR Lyraes are associated with substructures, consistent with the theory that galaxy halos are predominantly, or even entirely, made up from disrupted satellites. I also investigate the density distribution of RR Lyraes in the halo, finding that it is best fit by a broken-power-law model, in good agreement with previous work. I go on to develop a set of tracer mass estimators that build on previous work which make use of actual (and not projected) distance and proper motion data, reflecting the amount and quality of data now available to us. I show that proper motion data is, in theory, very useful and can greatly increase the accuracy of the mass estimates; in practice, however, current analysis is hampered by the large errors inherent in the proper motion data. The results are also subject to mass-anisotropy degeneracy, which current data is not yet able to break. Nevertheless, I am able to estimate the mass of the Milky Way to be M = 2.7±0

  4. Galaxy interactions in the Hickson Compact Group 88

    NASA Astrophysics Data System (ADS)

    Brosch, Noah

    2015-12-01

    I present observations of the Hickson Compact Group 88 (HCG88) obtained during the commissioning of a new 28-inch telescope at the Wise Observatory. This galaxy group was advertized to be non-interacting, or to be in a very early interaction stage, but this is not the case. The observations reported here were done using a `luminance' filter, essentially a very broad R filter, reaching a low surface brightness level of ≈26 mag arcsec-2. Additional observations were obtained in a narrow spectral band approximately centred on the rest-frame H α line from the group. Contrary to previous studies, my observations show that at least two of the major galaxies have had significant interactions in the past, although probably not between themselves. I report the discovery of a faint extended tail emerging from the brightest of the group galaxies, severe isophote twisting and possible outer shells around another galaxy, and map the H II regions in all the galaxies.

  5. 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.

  6. Nebular metallicities in two isolated local void dwarf galaxies

    SciTech Connect

    Nicholls, David C.; Jerjen, Helmut; Dopita, Michael A.; Basurah, Hassan

    2014-01-01

    Isolated dwarf galaxies, especially those situated in voids, may provide insight into primordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H II regions in such galaxies is key to investigating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these objects. The first object has a single low luminosity H II region, while the second is in a more vigorous star forming phase with several bright H II regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

  7. STRUCTURES OF LOCAL GALAXIES COMPARED TO HIGH-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Petty, Sara M.; De Mello, DuIlia F.; Gallagher, John S.; Gardner, Jonathan P.; Lotz, Jennifer M.; Matt Mountain, C.; Smith, Linda J.

    2009-08-15

    The rest-frame far-ultraviolet morphologies of eight nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, and NGC 7673) are compared with 54 galaxies at z {approx} 1.5 and 46 galaxies at z {approx} 4 observed in the Great Observatories Origins Deep Survey (GOODS) taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. The nearby sample is artificially redshifted to z {approx} 1.5 and 4 by applying luminosity and size scaling. We compare the simulated galaxy morphologies to real z {approx} 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M {sub 20}), and the Sersic index (n). We explore the use of nonparametric methods with two-dimensional profile fitting and find the combination of M {sub 20} with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M {sub 20} 20/30% of real/simulated galaxies at z {approx} 1.5 and 37/12% at z {approx} 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z {approx} 1.5 and z {approx} 4 real galaxies are exponential disks or bulge-like with n>0.8, and {approx} 30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with {approx} 35% bulge or exponential at z {approx} 1.5 and 4. Therefore, {approx} 20%-30% of Lyman-break galaxies have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n < 0.8 and M {sub 20}> - 1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z {approx} 1.5 and 4.

  8. 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 H i 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\\lt {log} M/{M}ȯ \\lt 15.0, for a total of 1986 late-type galaxies. We find that late-type galaxies in the centers of groups lack H i at fixed stellar mass relative to the regions surrounding them. Larger groups show evidence of a stronger dependence of H i 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 H i 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 H i 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 H i 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.

  9. 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.

  10. Morphological classification of local luminous infrared galaxies

    NASA Astrophysics Data System (ADS)

    Psychogyios, A.; Charmandaris, V.; Diaz-Santos, T.; Armus, L.; Haan, S.; Howell, J.; Le Floc'h, E.; Petty, S. M.; Evans, A. S.

    2016-06-01

    We present analysis of the morphological classification of 89 luminous infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey (GOALS) sample, using non-parametric coefficients and compare their morphology as a function of wavelength. We rely on images that were obtained in the optical (B- and I-band) as well as in the infrared (H-band and 5.8 μm). Our classification is based on the calculation of Gini and the second order of light (M20) non-parametric coefficients, which we explore as a function of stellar mass (M⋆), infrared luminosity (LIR), and star formation rate (SFR). We investigate the relation between M20, the specific SFR (sSFR) and the dust temperature (Tdust) in our galaxy sample. We find that M20 is a better morphological tracer than Gini, as it allows us to distinguish systems that were formed by double systems from isolated and post-merger LIRGs. The effectiveness of M20 as a morphological tracer increases with increasing wavelength, from the B to H band. In fact, the multi-wavelength analysis allows us to identify a region in the Gini-M20 parameter space where ongoing mergers reside, regardless of the band used to calculate the coefficients. In particular, when measured in the H band, a region that can be used to identify ongoing mergers, with minimal contamination from LIRGs in other stages. We also find that, while the sSFR is positively correlated with M20 when measured in the mid-infrared, i.e. star-bursting galaxies show more compact emission, it is anti-correlated with the B-band-based M20. We interpret this as the spatial decoupling between obscured and unobscured star formation, whereby the ultraviolet/optical size of an LIRG experience an intense dust-enshrouded central starburst that is larger that in the mid-infrared since the contrast between the nuclear to the extended disk emission is smaller in the mid-infrared. This has important implications for high redshift surveys of dusty sources, where sizes of galaxies

  11. 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

    shape, should be attributed mostly to the dynamical state of groups, and (2) groups of galaxies in the local universe do not constitute a family of objects in dynamical equilibrium, but rather a family of cosmic structures that are presently at various stages of their virialization process.

  12. Red Galaxy Structures Toward a Large Quasar Group Field

    NASA Astrophysics Data System (ADS)

    Williger, Gerard M.; Feil, E. C.; Haberzettl, L.; Clowes, R.; Campusano, L.; Haines, C. P.; Valls-Gabaud, D.; Lehnert, M.; Nesvadba, N.; LQG Team

    2014-01-01

    We present data from deep FUV-NUV-griz images toward a 2 sq degree region in the Clowes-Campusano Large Quasar Group field, which contains structures of quasars on the >100 Mpc scale at 0.8 and 1.2. Large Quasar Groups may be the signal posts for galaxy structures analogous to superclusters at high redshift. Using the six band photometry, we calculate photometric redshifts for red-selected galaxies to identify supercluster-size structures, and compare their locations with the quasars in the field.

  13. X-ray and optical properties of groups of galaxies

    NASA Technical Reports Server (NTRS)

    Dell'antonio, Ian P.; Geller, Margaret J.; Fabricant, Daniel G.

    1994-01-01

    We have measured 125 redshifts in 31 groups of galaxies observed with Einstein, and have compiled an additional 543 redshifts from the literature. There is a correlation between galaxy surface density and group velocity dispersion, with mu is proportional to sigma(exp 1.6 +/- 0.6), but the scatter about this relation is large. We examine the relationship between the group x-ray luminosity in the 0.3-3.5 keV band and the measured velocity dispersion. Richer groups follow the same relation as rich clusters (1982) with L(sub X) proportional to sigma(exp 4.0 +/- 0.6), but the relation flattens for lower luminosity systems which have velocity dispersions below 300 km/s. We suggest that the L(sub x)-sigma relation arises from a combination of extended cluster emission and emission associated with individual galaxies. The x-ray emission for the richer groups is dominated by emission from the intragroup medium, as for the richer clusters; emission from the poorer clusters is dominated by less extended emission associated with the individual group galaxies.

  14. 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

  15. Effect of Halo Mass on HI Gas Content of Galaxies in Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Yoon, Ilsang; Rosenberg, J. L.

    2014-01-01

    We combine the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA (ALFALFA) Survey to study the distribution of cold atomic gas fraction of galaxies that reside in groups and clusters in local Universe. A careful cross-matching between galaxies in SDSS, ALFALFA, and SDSS halo group catalog produces a sample of galaxies with decent statistics in the stellar mass range 108.4 M⊙ ≦ M* ≦ 1010.6 M⊙ and the halo mass range 1012.5 h-1 M⊙ ≦ Mh ≦ 1015.0 h-1 M⊙ for a range of projected distance from the group center 0.04 ≦ r/rvir ≦ 2.0. In order to limit our study to group and cluster interaction processes (not tidal stripping in pairs), we remove close pairs that may be undergoing tidal interactions from the sample. We construct a comparison sample from the isolated field galaxies and investigate the radial distribution of the gas-to-stellar mass ratio for galaxies in groups and clusters relative to the comparison samples with similar stellar mass and redshift. We find that the gas-to-stellar mass ratio decreases toward the centers of groups with halo mass greater than ≈ 1013.8 h-1 M⊙ but find no such trend for galaxies in small halo mass groups. This halo mass dependent effect suggests that there is a threshold for efficient gas stripping due to interaction between galaxies and intracluster medium (ICM). This trend together with the HI line profile properties of our sample galaxies in groups and clusters is consistent with the ram pressure stripping. In particular, the observed relationship between stripping and halo mass is predicted by the classical Gunn-Gott ram pressure stripping criterion modified by scaling relations for galaxies and dark matter halo, which indicates that there is a threshold halo mass for efficient ram pressure stripping for given galaxy stellar mass and ICM temperature. This study was funded by NSF grant AST-000167932.

  16. The birthplace of compact groups of galaxies

    NASA Technical Reports Server (NTRS)

    Ramella, Massimo; Diaferio, Antonaldo; Geller, Margaret J.; Huchra, John P.

    1994-01-01

    We use complete redshift surveys to study the redshift neighborhoods of 38 Hickson compact groups (HCGs). Twenty-nine of these HCGs (76%) are embedded in rich looser systems which we call HCG associations. Analysis of the redshift neighborhood of HCGs outside the CfA survey suggests that most HCGs are embedded in more extended physical systems. Rich loose groups extracted from the CfA survey (Ramella et al. (1994)) have physical properties similar to those of the HCG associations. These rich loose groups often contain compact configurations. N-body experiments (Diaferio (1994)) suggest that compact configurations analogous to HCGs form continually during the collapse of rich loose groups. These observational and numerical results suggest that rich loose groups are the birthplace of HCGs.

  17. Exploring the Escape of Hydrogen Ionizing Photons from Local Galaxies

    NASA Astrophysics Data System (ADS)

    Davis, Jesse A.; Rosenberg, Jessica L.; Venkatesan, Aparna; Cannon, John M.; Salzer, John Joseph

    2016-01-01

    role of dwarf galaxies in the ionization of the local IGM and cosmic reionization.

  18. STELLAR POPULATIONS OF ELLIPTICAL GALAXIES IN THE LOCAL UNIVERSE

    SciTech Connect

    Zhu Guangtun; Blanton, Michael R.; Moustakas, John E-mail: michael.blanton@nyu.ed

    2010-10-10

    We study the stellar populations of 1923 elliptical galaxies at z < 0.05 selected from the Sloan Digital Sky Survey as a function of velocity dispersion, {sigma}, and environment. Our sample constitutes among the largest high-fidelity samples of elliptical galaxies with uniform imaging and optical spectroscopy assembled to date. Confirming previous studies, we find that elliptical galaxies dominate at high luminosities ({approx}>L*), and that the highest-{sigma} ellipticals favor high-density environments. We construct average, high signal-to-noise spectra in bins of {sigma} and environment and find the following: (1) lower-{sigma} galaxies have a bluer optical continuum and stronger (but still weak) emission lines; (2) at fixed {sigma}, field ellipticals have a slightly bluer stellar continuum, especially at wavelengths {approx}<4000 A, and have stronger (but still weak) emission lines compared with their group counterparts, although this environmental dependence is strongest for low-{sigma} ellipticals and the highest-{sigma} ellipticals are much less affected. Based on Lick indices measured from both the individual and average spectra, we find that (1) at a given {sigma}, elliptical galaxies in groups have systematically weaker Balmer absorption than their field counterparts, although this environmental dependence is most pronounced at low {sigma}; (2) there is no clear environmental dependence of (Fe), while the {alpha}-element absorption indices such as Mg b are only slightly stronger in galaxies belonging to rich groups. An analysis based on simple stellar populations (SSPs) reveals that more massive elliptical galaxies are older, more metal-rich, and more strongly {alpha}-enhanced. We also find that (1) the SSP-equivalent ages of galaxies in rich groups are, on average, {approx}1 Gyr older than in the field, although once again this effect is strongest at low {sigma}; (2) galaxies in rich groups have slightly lower [Fe/H] and are marginally more strongly

  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. FREQUENT SPIN REORIENTATION OF GALAXIES DUE TO LOCAL INTERACTIONS

    SciTech Connect

    Cen, Renyue

    2014-04-10

    We study the evolution of angular momenta of M {sub *} = 10{sup 10}-10{sup 12} M {sub ☉} galaxies utilizing large-scale ultra-high resolution cosmological hydrodynamic simulations and find that the spin of the stellar component changes direction frequently because of interactions with nearby systems, such as major mergers, minor mergers, significant gas inflows, and torques. The rate and nature of change of spin direction cannot be accounted for by large-scale tidal torques, because the rates of the latter fall short by orders of magnitude and because the apparent random swings of the spin direction are inconsistent with the alignment by linear density field. The implications for galaxy formation as well as the intrinsic alignment of galaxies are profound. Assuming the large-scale tidal field is the sole alignment agent, a new picture emerging is that intrinsic alignment of galaxies would be a balance between slow large-scale coherent torquing and fast spin reorientation by local interactions. What is still open is whether other processes, such as feeding galaxies with gas and stars along filaments or sheets, introduce coherence for spin directions of galaxies along the respective structures.

  1. The evolution of star formation activity in galaxy groups

    NASA Astrophysics Data System (ADS)

    Erfanianfar, G.; Popesso, P.; Finoguenov, A.; Wuyts, S.; Wilman, D.; Biviano, A.; Ziparo, F.; Salvato, M.; Nandra, K.; Lutz, D.; Elbaz, D.; Dickinson, M.; Tanaka, M.; Mirkazemi, M.; Balogh, M. L.; Altieri, M. B.; Aussel, H.; Bauer, F.; Berta, S.; Bielby, R. M.; Brandt, N.; Cappelluti, N.; Cimatti, A.; Cooper, M.; Fadda, D.; Ilbert, O.; Le Floch, E.; Magnelli, B.; Mulchaey, J. S.; Nordon, R.; Newman, J. A.; Poglitsch, A.; Pozzi, F.

    2014-12-01

    We study the evolution of the total star formation (SF) activity, total stellar mass (ΣM*) and halo occupation distribution (HOD) in massive haloes by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of star formation rate (SFR) for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from spectral energy distribution (SED) fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high-redshift groups (0.5 < z < 1.1) is higher with respect to the low-redshift (0.15 < z < 0.5) sample at any mass by 0.8 ± 0.12 dex. A milder difference (0.35 ± 0.1 dex) is observed between the low-redshift bin and the groups at z ˜ 0. We show that the level of SF activity is declining more rapidly in the more massive haloes than in the more common lower mass haloes. We do not observe any evolution in the HOD and total stellar mass-halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass haloes, consistently with a `halo downsizing' scenario.

  2. 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

  3. Properties of Galaxies and Groups at z < 1.4

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    In this work, we analyze a sample of galaxy groups constructed from the fourth data release of the Deep Extragalactic Evolutionary Probe 2 (DEEP2) including the Extended Groth Strip (EGS). This sample was obtained by Gerke et al. (2012) using the Voronoi-Delaunay Method. We selected 105 galaxy groups with at least 8 members in a radius of 4 Mpc. For each group we estimated its properties such as velocity dispersion (σ), physical radius (R_{200}) and mass (M_{200}). We also classify the groups as Gaussian and non-Gaussian (dynamic evolved or not) based on their galaxy velocity distributions. This classification is based on the following statistical tests: Anderson-Darling, Kolmogorov-Smirnov, Shapiro-Wilk, Jarque-Bera, Cramer-von Mises, D'Agostino and Dip test. When the Dip test confirms the hypothesis of the unimodality and all other tests prove the normality of the system, the group is classified as Gaussian. The behavior of gaussianity was checked varying the distance to the center of the group in 2-4 times its physical radius. Our results show that the number of systems classified as non-Gaussian groups grows with the increase of the physical radius.

  4. The Properties of Poor Groups of Galaxies. III. The Galaxy Luminosity Function

    NASA Astrophysics Data System (ADS)

    Zabludoff, Ann I.; Mulchaey, John S.

    2000-08-01

    The form of the galaxy luminosity function (GLF) in poor groups-regions of intermediate galaxy density that are common environments for galaxies-is not well understood. Multiobject spectroscopy and wide-field CCD imaging now allow us to measure the GLF of bound group members directly (i.e., without statistical background subtraction) and to compare the group GLF with the GLFs of the field and of rich clusters. We use R-band images in 1.5×1.5 degree2 mosaics to obtain photometry for galaxies in the fields of six nearby (2800groups for which we have extensive spectroscopic data, including 328 new galaxy velocities. For the five groups with luminous X-ray halos, the composite group GLF for group members with -23+5loghgroup center is fit adequately by a Schechter function with M*R=-21.6+/-0.4+5log h and α=-1.3+/-0.1. We also find that (1) the ratio of dwarfs (-17+5logh>=MR>-19+5logh) to giants (MR<=-19+5logh) is significantly larger for the five groups with luminous X-ray halos than for the one marginally X-ray-detected group; (2) the composite GLF for the luminous X-ray groups is consistent in shape with two measures of the composite R-band GLF for rich clusters (Trentham; Driver et al.) and flatter at the faint end than another (α~-1.5 Smith et al.); (3) the composite group GLF rises more steeply at the faint end than the R-band GLF of the Las Campanas Redshift Survey (LCRS; α=-0.7 from Lin et al.), a large volume survey dominated by galaxies in environments more rarefied than luminous X-ray groups; (4) the shape difference between the LCRS field and composite group GLFs results mostly from the population of non-emission line galaxies (EW [O II]<5 Å), whose dwarf-to-giant ratio is larger in the denser group environment than in the field (cf. Ferguson & Sandage; Bromley et al.); and (5) the non-emission line dwarfs are more concentrated about the group center than the non

  5. 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

  6. 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.

  7. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows ‑0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z˜ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  8. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows ‑0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z∼ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  9. Applying Social Networking and Clustering Algorithms to Galaxy Groups in ALFALFA

    NASA Astrophysics Data System (ADS)

    Bramson, Ali; Wilcots, E. M.

    2012-01-01

    Because most galaxies live in groups, and the environment in which it resides affects the evolution of a galaxy, it is crucial to develop tools to understand how galaxies are distributed within groups. At the same time we must understand how groups are distributed and connected in the larger scale structure of the Universe. I have applied a variety of networking techniques to assess the substructure of galaxy groups, including distance matrices, agglomerative hierarchical clustering algorithms and dendrograms. We use distance matrices to locate groupings spatially in 3-D. Dendrograms created from agglomerative hierarchical clustering results allow us to quantify connections between galaxies and galaxy groups. The shape of the dendrogram reveals if the group is spatially homogenous or clumpy. These techniques are giving us new insight into the structure and dynamical state of galaxy groups and large scale structure. We specifically apply these techniques to the ALFALFA survey of the Coma-Abell 1367 supercluster and its resident galaxy groups.

  10. A model for the formation of the Local Group

    SciTech Connect

    Peebles, P.J.E.; Melott, A.L.; Holmes, M.R.; Jiang, L.R. Kansas Univ., Lawrence )

    1989-10-01

    Observational tests of a model for the formation of the Local Group are presented and analyzed in which the mass concentration grows by gravitational accretion of local-pressure matter onto two seed masses in an otherwise homogeneous initial mass distribution. The evolution of the mass distribution is studied in an analytic approximation and a numerical computation. The initial seed mass and separation are adjusted to produce the observed present separation and relative velocity of the Andromeda Nebula and the Galaxy. If H(0) is adjusted to about 80 km/s/Mpc with density parameter Omega = 1, then the model gives a good fit to the motions of the outer members of the Local Group. The same model gives particle orbits at radius of about 100 kpc that reasonably approximate the observed distribution of redshifts of the Galactic satellites. 47 refs.

  11. 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

  12. Dark matter searches with Cherenkov telescopes: nearby dwarf galaxies or local galaxy clusters?

    NASA Astrophysics Data System (ADS)

    Sánchez-Conde, Miguel A.; Cannoni, Mirco; Zandanel, Fabio; Gómez, Mario E.; Prada, Francisco

    2011-12-01

    In this paper, we compare dwarf galaxies and galaxy clusters in order to elucidate which object class is the best target for gamma-ray DM searches with imaging atmospheric Cherenkov telescopes (IACTs). We have built a mixed dwarfs+clusters sample containing some of the most promising nearby dwarf galaxies (Draco, Ursa Minor, Wilman 1 and Segue 1) and local galaxy clusters (Perseus, Coma, Ophiuchus, Virgo, Fornax, NGC 5813 and NGC 5846), and then compute their DM annihilation flux profiles by making use of the latest modeling of their DM density profiles. We also include in our calculations the effect of DM substructure. Willman 1 appears as the best candidate in the sample. However, its mass modeling is still rather uncertain, so probably other candidates with less uncertainties and quite similar fluxes, namely Ursa Minor and Segue 1, might be better options. As for galaxy clusters, Virgo represents the one with the highest flux. However, its large spatial extension can be a serious handicap for IACT observations and posterior data analysis. Yet, other local galaxy cluster candidates with more moderate emission regions, such as Perseus, may represent good alternatives. After comparing dwarfs and clusters, we found that the former exhibit annihilation flux profiles that, at the center, are roughly one order of magnitude higher than those of clusters, although galaxy clusters can yield similar, or even higher, integrated fluxes for the whole object once substructure is taken into account. Even when any of these objects are strictly point-like according to the properties of their annihilation signals, we conclude that dwarf galaxies are best suited for observational strategies based on the search of point-like sources, while galaxy clusters represent best targets for analyses that can deal with rather extended emissions. Finally, we study the detection prospects for present and future IACTs in the framework of the constrained minimal supersymmetric standard model. We

  13. Dark Matter Searches with Cherenkov Telescopes: Nearby Dwarf Galaxies or Local Galaxy Clusters?

    SciTech Connect

    Sanchez-Conde, Miguel A.; Cannoni, Mirco; Zandanel, Fabio; Gomez, Mario E.; Prada, Francisco; /IAA, Granada

    2012-06-06

    In this paper, we compare dwarf galaxies and galaxy clusters in order to elucidate which object class is the best target for gamma-ray DM searches with imaging atmospheric Cherenkov telescopes (IACTs). We have built a mixed dwarfs+clusters sample containing some of the most promising nearby dwarf galaxies (Draco, Ursa Minor, Wilman 1 and Segue 1) and local galaxy clusters (Perseus, Coma, Ophiuchus, Virgo, Fornax, NGC 5813 and NGC 5846), and then compute their DM annihilation flux profiles by making use of the latest modeling of their DM density profiles. We also include in our calculations the effect of DM substructure. Willman 1 appears as the best candidate in the sample. However, its mass modeling is still rather uncertain, so probably other candidates with less uncertainties and quite similar fluxes, namely Ursa Minor and Segue 1, might be better options. As for galaxy clusters, Virgo represents the one with the highest flux. However, its large spatial extension can be a serious handicap for IACT observations and posterior data analysis. Yet, other local galaxy cluster candidates with more moderate emission regions, such as Perseus, may represent good alternatives. After comparing dwarfs and clusters, we found that the former exhibit annihilation flux profiles that, at the center, are roughly one order of magnitude higher than those of clusters, although galaxy clusters can yield similar, or even higher, integrated fluxes for the whole object once substructure is taken into account. Even when any of these objects are strictly point-like according to the properties of their annihilation signals, we conclude that dwarf galaxies are best suited for observational strategies based on the search of point-like sources, while galaxy clusters represent best targets for analyses that can deal with rather extended emissions. Finally, we study the detection prospects for present and future IACTs in the framework of the constrained minimal supersymmetric standard model. We

  14. 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

  15. Finding Galaxy Groups in the Fields of Lensed Quasars

    NASA Astrophysics Data System (ADS)

    Grant, Catherine E.; Bautz, M. W.

    2006-09-01

    Gravitationally lensed quasars can be used as an invaluable cosmological tool, however, the asymmetry observed in many lensed systems requires models of the lens to include a strong external shear component in addition to the lensing galaxy. The lensing galaxy may be a member of a group or cluster which could provide sufficient shear to account for the lensed image configuration. We are searching for X-ray emission from groups and clusters of galaxies in the fields of multiply-imaged quasars using Chandra's resolving power to separate the faint diffuse emission from the much brighter quasar images. We have analyzed all observations of gravitationally lensed quasars available in the Chandra archive from launch through the end of 2005 to search for this diffuse emission. We present a catalog of cluster and group properties for those fields with significant diffuse emission, and upper limits on group properties in fields where no diffuse emission is detected. These measurements are compared with optical data, where available, and with quasar lensing models. This research was supported by NASA contracts NAS-8-38252 and NAS-8-37716.

  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. Dust-obscured galaxies in the local universe

    SciTech Connect

    Hwang, Ho Seong; Geller, Margaret J. E-mail: mgeller@cfa.harvard.edu

    2013-06-01

    We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy Evolution Explorer (GALEX) data to select local analogs of high-redshift (z ∼ 2) dust obscured galaxies (DOGs). We identify 47 local DOGs with S {sub 12μm}/S {sub 0.22μm} ≥ 892 and S {sub 12μm} > 20 mJy at 0.05 < z < 0.08 in the Sloan Digital Sky Survey data release 7. The infrared (IR) luminosities of these DOGs are in the range 3.4 × 10{sup 10} (L {sub ☉}) ≲ L {sub IR} ≲ 7.0 × 10{sup 11} (L {sub ☉}) with a median L {sub IR} of 2.1 × 10{sup 11} (L {sub ☉}). We compare the physical properties of local DOGs with a control sample of galaxies that have lower S {sub 12μm}/S {sub 0.22μm} but have similar redshift, IR luminosity, and stellar mass distributions. Both WISE 12 μm and GALEX near-ultraviolet (NUV) flux densities of DOGs differ from the control sample of galaxies, but the difference is much larger in the NUV. Among the 47 DOGs, 36% ± 7% have small axis ratios in the optical (i.e., b/a < 0.6), larger than the fraction among the control sample (17% ± 3%). There is no obvious sign of interaction for many local DOGs. No local DOGs have companions with comparable optical magnitudes closer than ∼50 kpc. The large- and small-scale environments of DOGs are similar to the control sample. Many physical properties of local DOGs are similar to those of high-z DOGs, even though the IR luminosities of local objects are an order of magnitude lower than for the high-z objects: the presence of two classes (active galactic nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV rather than extreme brightness in the mid-IR, and diverse optical morphology. These results suggest a common underlying physical origin of local and high-z DOGs. Both seem to represent the high-end tail of the dust obscuration distribution resulting from various physical mechanisms rather than a unique phase of galaxy evolution.

  18. The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf Galaxies as Revealed by RR Lyrae Variables

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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 lang[Fe/H]rangESO294 = -1.77 ± 0.03 and lang[Fe/H]rangESO410 = -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 ⊙ < 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 different

  19. 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

  20. PN populations in the local group and distant stellar populations

    NASA Astrophysics Data System (ADS)

    Reid, Warren

    2016-08-01

    Our understanding of galactic structure and evolution is far from complete. Within the past twelve months we have learnt that the Milky Way is about 50% wider than was previously thought. As a consequence, new models are being developed that force us to reassess the kinematic structure of our Galaxy. Similarly, we need to take a fresh look at the halo structure of external galaxies in our Local Group. Studies of stellar populations, star-forming regions, clusters, the interstellar medium, elemental abundances and late stellar evolution are all required in order to understand how galactic assembly has occurred as we see it. PNe play an important role in this investigation by providing a measure of stellar age, mass, abundances, morphology, kinematics and synthesized matter that is returned to the interstellar medium (ISM). Through a method of chemical tagging, halo PNe can reveal evidence of stellar migration and galactic mergers. This is an outline of the advances that have been made towards uncovering the full number of PNe in our Local Group galaxies and beyond. Current numbers are presented and compared to total population estimates based on galactic mass and luminosity. A near complete census of PNe is crucial to understanding the initial-to-final mass relation for stars with mass >1 to <8 times the mass of the sun. It also allows us to extract more evolutionary information from luminosity functions and compare dust-to-gas ratios from PNe in different galactic locations. With new data provided by the Gaia satellite, space-based telescopes and the rise of giant and extra-large telescopes, we are on the verge of observing and understanding objects such as PNe in distant galaxies with the same detail we expected from Galactic observations only a decade ago.

  1. Groups of galaxies. III. the CfA survey

    SciTech Connect

    Geller, M.J.; Huchra, J.P.

    1983-06-01

    We present a statistically homogeneous group catalog (CfA) based on the CfA redshift survey (Huchra et al.). Groups in the catalog are all density enhancements in redshift space of a factor greater than 20. Group members are identified according to the procedure described in our previous study (Huchra and Geller) of a shallower whole-sky sample. All groups contain at least three members. Of the 176 groups in the CfA catalog, 102 have been identified in one or more previous studies. Because our algorithm searches for volume rather than surface density enhancements, the groups in a given region generally change only through the addition of fainter members when the magnitude limit of the galaxy catalog increases. In the region of overlap, agreement between our shallow catalog and the CfA catalog is excellent.

  2. RR Lyrae variables in the Andromeda group galaxies

    NASA Astrophysics Data System (ADS)

    Yang, Soung-Chul

    2011-08-01

    /H ]AndXI = -1.75; [Fe/H] AndXIII = --1.74) are consistent with the values calculated from the RGB slope indicating that our measurements are not significantly affected by the evolutionary effects of RRL stars. The distance to each galaxy was calculated using the absolute V magnitudes of the RRab stars. We obtained (m -- M)0, V = 24.54 for And XI and this value becomes (m -- M)0,V = 24.71 for And XIII. We discuss the origins of And XI and And XIII based on a comparative analysis of the luminosity-metallicity (L-M) relation of Local Group dwarf galaxies.

  3. Studying AGN Feedback in Galaxy Clusters and Groups with Athena

    NASA Astrophysics Data System (ADS)

    Sanders, Jeremy; Athena Topical PanelAGN Feedback in Clusters; Groups

    2015-09-01

    In the centres of clusters of galaxies and groups the central active galactic nuclei are playing a vital role in preventing the rapid cooling of the surrounding hot atmosphere. Important scientific questions remain unanswered, however. These include (1) What is the mechanism by which the energy from jets is dissipated and distributed through intracluster or intragroup medium? (2) How is the AGN fuelling regulated? (3) What is the cumulative impact of powerful radio galaxies on baryons over cosmic time? With its high spectral resolution, good spatial resolution and large effective area, Athena promises to make important progress in answering these questions. For the first time it will measure both the spatially-resolved velocity distribution and thermodynamics of the cluster core region, allowing us to measure all the energetic contributions to feedback and cooling in the hot plasma. We describe how Athena will address these areas, as described in our supporting paper for the Athena mission proposal on AGN feedback in galaxy clusters and groups.

  4. Fossil group origins. VII. Galaxy substructures in fossil systems

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Context. Fossil groups (FG) are expected to be the final product of galaxy merging within galaxy groups. In simulations, they are predicted to assemble their mass at high redshift. This early formation allows for the innermost M∗ galaxies to merge into a massive central galaxy. Then, they are expected to maintain their fossil status because of the few interactions with the large-scale structure. In this context, the magnitude gap between the two brightest galaxies of the system is considered a good indicator of its dynamical status. As a consequence, the systems with the largest gaps should be dynamically relaxed. Aims: In order to examine the dynamical status of these systems, we systematically analyze, for the first time, the presence of galaxy substructures in a sample of 12 spectroscopically-confirmed fossil systems with redshift z ≤ 0.25. Methods: We apply a number of tests to investigate the substructure in fossil systems in the two-dimensional space of projected positions out to R200. Moreover, for a subsample of five systems with at least 30 spectroscopically-confirmed members we also analyze the substructure in the velocity and in the three-dimensional velocity-position spaces. Additionally, we look for signs of recent mergers in the regions around the central galaxies. Results: We find that an important fraction of fossil systems show substructure. The fraction depends critically on the adopted test, since each test is more sensitive to a particular type of substructure. Conclusions: Our interpretation of the results is that fossil systems are not, in general, as relaxed as expected from simulations. Our sample of 12 spectroscopically-confirmed fossil systems need to be extended to compute an accurate fraction, but our conclusion is that this fraction is similar to the fraction of substructure detected in nonfossil clusters. This result points out that the magnitude gap alone is not a good indicator of the dynamical status of a system. However, the

  5. Searching for Wolf-Rayet Stars in the Local Group

    NASA Astrophysics Data System (ADS)

    Shara, M. M.; Zurek, D.; Kanarek, G.; Faherty, J.

    2012-12-01

    Tony Moffat has been inspiring the hunt for new Wolf-Rayet stars for over 40 years. These extraordinary objects offer critical tests of stellar evolution theory, and are predicted to be progenitors of type Ib and Ic supernovae. We're only going to know if that prediction is correct (in our lifetimes) by locating and spectrographically confirming of order 10 000 WR stars - a daunting but increasingly doable task. Our 2009 prediction that roughly 6 500 Wolf-Rayet stars live in our Galaxy has been followed by demonstrations in the past few years that, via narrowband infrared imaging and spectroscopy, we can find and confirm almost all Galactic WR stars. The rest of the Local Group is unlikely to contain more than 1 000 WR stars, so the Milky Way is THE place to search exhaustively for them. I briefly describe how we hunt and gather WR stars and give a current (mid-2011) Local Group census of them.

  6. Dwarf spheroidal satellite formation in a reionized Local Group

    NASA Astrophysics Data System (ADS)

    Milosavljević, Miloš; Bromm, Volker

    2014-05-01

    Dwarf spheroidal satellite galaxies have emerged a powerful probe of small-scale dark matter clustering and of cosmic reionization. They exhibit structural and chemical continuity with dwarf irregular galaxies in the field and with spheroidal galaxies in high-density environments. By combining empirical constraints derived for star formation at low gas column densities and metallicities in the local Universe with a model for dark matter and baryonic mass assembly, we provide an analytical description of how the dwarf spheroidals acquired their stellar content. Their progenitors formed stars until the gas content, initially reduced from the cosmic average by the thermal pressure of the reionized intergalactic medium, was finally ram pressure stripped during the progenitors' accretion on to the host galaxy. Dwarf spheroidal satellites of differing luminosities seem to share very similar most massive progenitor histories that reach thresholds for gas cooling by atomic line emission at epochs at which the Lagrangian volume of the Local Group should have been reionized. We hypothesize that dwarf spheroidals formed the bulk of their stars in partially rotationally supported H I discs in a reionized universe. This model provides an explanation for the `common mass scale' relation and reproduces the empirical luminosity-size and luminosity-metallicity relations. Explosive feedback phenomena, such as outflows driven by the concerted action of supernovae, need not have been significant in the dwarf spheroidals' formation. We further speculate that the true pre-reionization fossils should exhibit a structure distinct from that of the dwarf spheroidals, e.g. in the form of dense isolated or nuclear star clusters.

  7. 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.

  8. A WISE VIEW OF STAR FORMATION IN LOCAL GALAXY CLUSTERS

    SciTech Connect

    Chung, Sun Mi; Gonzalez, Anthony H.; Eisenhardt, Peter R.; Stern, Daniel; Stanford, Spencer A.; Brodwin, Mark; Jarrett, Thomas

    2011-12-10

    We present results from a systematic study of star formation in local galaxy clusters using 22 {mu}m data from the Wide-field Infrared Survey Explorer (WISE). The 69 systems in our sample are drawn from the Cluster Infall Regions Survey, and all have robust mass determinations. The all-sky WISE data enable us to quantify the amount of star formation, as traced by 22 {mu}m, as a function of radius well beyond R{sub 200}, and investigate the dependence of total star formation rate upon cluster mass. We find that the fraction of star-forming galaxies increases with cluster radius but remains below the field value even at 3R{sub 200}. We also find that there is no strong correlation between the mass-normalized total specific star formation rate and cluster mass, indicating that the mass of the host cluster does not strongly influence the total star formation rate of cluster members.

  9. Dwarfs and Giants in the local flows of galaxies.

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Emelyanov, N. V.; Karachentsev, I. D.

    We use recent Hubble Space Telescope data on nearby dwarf and giant galaxies to study the dynamical structure and evolutionary trends of the local expansion flows of galaxies. It is found that antigravity of dark energy dominates the force field of the flows and makes them expand with acceleration. It also cools the flows and introduces to them the nearly linear velocity-distance relation with the time-rate close to the global Hubble's factor. There are grounds to expect that this is the universal physical regularity that is common not only for the nearby flows we studied here, but also for all the expansion flows of various spatial scales from the 1 Mpc scale and up to the scale of the global cosmological expansion.

  10. A Census of Baryons in Galaxy Clusters and Groups

    NASA Astrophysics Data System (ADS)

    Gonzalez, Anthony H.; Zaritsky, Dennis; Zabludoff, Ann I.

    2007-09-01

    We determine the contribution of stars in galaxies, intracluster stars, and the intracluster medium to the total baryon budget in nearby galaxy clusters and groups. We find that the baryon mass fraction (fb≡Ωb/Ωm) within r500 is constant for systems with M500 between 6×1013 and 1×1015 Msolar. Although fb is lower than the WMAP value, the shortfall is on the order of both the observational systematic uncertainties and the depletion of baryons within r500 that is predicted by simulations. The data therefore provide no compelling evidence for undetected baryonic components, particularly any that would be expected to vary in importance with cluster mass. A unique feature of the current analysis is direct inclusion of the contribution of intracluster light (ICL) in the baryon budget. With the addition of the ICL to the stellar mass in galaxies, the increase in X-ray gas mass fraction with increasing total mass is entirely accounted for by a decrease in the total stellar mass fraction, supporting the argument that the behavior of both the stellar and X-ray gas components is dominated by a decrease in star formation efficiency in more massive environments. Within just the stellar component, the fraction of the total stellar luminosity in the central, giant brightest cluster galaxy (BCG) and ICL (hereafter the BCG+ICL component) decreases as velocity dispersion (σ) increases for systems with 145 km s-1<=σ<=1026 km s-1, suggesting that the BCG+ICL component, and in particular the dominant ICL component, grows less efficiently in higher mass environments. The degree to which this behavior arises from our sample selection, which favored systems with central, giant elliptical galaxies, remains unclear. A more robust result is the identification of low-mass groups with large BCG+ICL components, demonstrating that the creation of ``intracluster'' stars does not require a massive cluster environment. Within r500 and r200, the BCG+ICL contributes on average 40% and 33% of