WorldWideScience

Sample records for dwarf elliptical galaxies

  1. Constraining Galaxy Formation Models with Dwarf Ellipticals in Clusters

    CERN Document Server

    Conselice, C J

    2005-01-01

    Recent observations demonstrate that dwarf elliptical (dE) galaxies in clusters, despite their faintness, are likely a critical galaxy type for understanding the processes behind galaxy formation. Dwarf ellipticals are the most common galaxy type, and are particularly abundant in rich galaxy clusters. The dwarf to giant ratio is in fact highest in rich clusters of galaxies, suggesting that cluster dEs do not form in groups that later merge to form clusters. Dwarf ellipticals are potentially the only galaxy type whose formation is sensitive to global, rather than local, environment. The dominant idea for explaining the formation of these systems, through Cold Dark Matter models, is that dEs form early and within their present environments. Recent results suggest that some dwarfs appear in clusters after the bulk of massive galaxies form, a scenario not predicted in standard hierarchical structure formation models. Many dEs have younger and more metal rich stellar populations than dwarfs in lower density enviro...

  2. Nucleated Dwarf Elliptical Galaxies in the Coma Cluster

    NARCIS (Netherlands)

    Matkovic, Ana; Ferguson, H. C.; Peng, E.; den Brok, M.

    2010-01-01

    Recent studies show that most dwarf elliptical galaxies (dE) in nearby clusters possess nuclear star clusters. Earlier studies used photographic plates and frequently missed the faint nuclei in dEs. For the first time, we are able to identify nuclei in a large number of dE galaxies in the Coma clust

  3. IC3328 a "dwarf elliptical galaxy" with spiral structure

    CERN Document Server

    Jerjen, H; Binggeli, B; Jerjen, Helmut; Kalnajs, Agris; Binggeli, Bruno

    2000-01-01

    We present the 2-D photometric decomposition of the Virgo galaxy IC3328. The analysis of the global light distribution of this morphologically classified nucleated dwarf elliptical galaxy (dE1,N) reveals a tightly wound, bi-symmetric spiral structure with a diameter of 4.5 kpc, precisely centered on the nucleus of the dwarf. The amplitude of the spiral is only three percent of the dwarf's surface brightness making it the faintest and smallest spiral ever found in a galaxy. In terms of pitch angle and arm winding the spiral is similar to the intermediate-type galaxy M51, but it lacks the dust and prominent HII regions which signal the presence of gas. The visual evidence of a spiral pattern in an early-type dwarf galaxy reopens the question on whether these dwarfs are genuine rotationally supported or anisotropic stellar systems. In the case of IC3328, we argue for a nearly face-on disk (dS0) galaxy with an estimated maximum rotation velocity of v_c,max = 55kms-1. The faintness of the spiral and the small moti...

  4. On the unification of dwarf and giant elliptical galaxies

    CERN Document Server

    Graham, Alister W

    2008-01-01

    The near orthogonal distributions of dwarf elliptical (dE) and giant elliptical (E) galaxies in the mu_e-Mag and mu_e-log(R_e) diagrams have been interpreted as evidence for two distinct galaxy formation processes. However, continuous, linear relationships across the alleged dE/E boundary at M_B = -18 mag - such as those between central surface brightness (mu_0) and (i) galaxy magnitude and (ii) light-profile shape (n) - suggest a similar, governing formation mechanism. Here we explain how these latter two linear trends necessitate a different behavior for dE and E galaxies, exactly as observed, in diagrams involving mu_e (and also _e). A natural consequence is that the distribution of dEs and Es in Fundamental Plane type analyses that use the associated intensity I_e, or _e, are expected to appear different. Together with other linear trends across the alleged dE/E boundary, such as those between luminosity and color, metallicity, and velocity dispersion, it appears that the dEs form a continuous extension t...

  5. Made-to-Measure Dark Matter Haloes, Elliptical Galaxies and Dwarf Galaxies in Action Coordinates

    CERN Document Server

    Williams, A A

    2014-01-01

    We provide a family of action-based distribution functions (DFs) for the double-power law family of densities often used to model galaxies. The DF itself is a double-power law in combinations of the actions, and reduces to the known limits in the case of a pure power-law at small and large radii. Our method enables the velocity anisotropy of the model to be tuned, and so the anisotropy in the inner and outer parts can be specified for the application in hand. We provide self-consistent DFs for the Hernquist and Jaffe models - both with everywhere isotropic velocity dispersions, and with kinematics that gradually becomes more radially anisotropic on moving outwards. We also carry out this exercise for a cored dark-matter model. These are tailored to represent dark haloes and elliptical galaxies respectively with kinematic properties inferred from simulations or observational data. Finally, we relax a cored luminous component within a dark matter halo to provide a self-consistent model of a dwarf spheroidal emb...

  6. The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei and Stellar Halos

    OpenAIRE

    Lotz, Jennifer M.; Miller, Bryan W.; Ferguson, Henry C.

    2004-01-01

    We present the results of a Hubble Space Telescope WFPC2 F555W and F814W survey of 69 dwarf elliptical galaxies (dEs) in the Virgo and Fornax Clusters and Leo Group. The $V-I$ colors of the dE globular clusters, nuclei, and underlying field star populations are used to trace the dE star-formation histories. We find that the dE globular cluster candidates are as blue as the metal-poor globular clusters of the Milky Way. The observed correlation of the dE globular cluster systems' $V-I$ color w...

  7. Surface Photometry of the Dwarf Elliptical Galaxies NGC 185 and NGC 205

    CERN Document Server

    Kim, S C; Kim, Sang Chul; Lee, Myung Gyoon

    1998-01-01

    We present BVRI CCD surface photometry for the central (6'.35 X 6'.35) regions of the dwarf elliptical galaxies NGC 185 and NGC 205 in the Local Group. Surface brightness profiles of NGC 185 (R = 25". The colors of NGC 205 get bluer inward at 1" < R < 50", and remain flat outside. Our photometry, supplemented by the photometry based on the far-ultraviolet and visual images of the HST archive data, shows that there is an inversion of color at the very nucleus region (at about 1"). The implications of the redder color of the core part of the nucleus compared with neighboring regions are discussed. The amount of the excess components in the central regions of these galaxies is estimated to be ~10^5 solar luminosity. Distributions of dust clouds in the central regions of the two galaxies are also investigated.

  8. Dwarf Elliptical Galaxies Structure, Star Formation, and Color-Magnitude Diagrams

    CERN Document Server

    Carraro, G; Girardi, L; Lia, C

    2001-01-01

    The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N-body/hydro-dynamical simulations that include star formation, feed-back and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old episode to a series of bursts over most of the Hubble time. We start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities. We predict the final structure of dwarf spheroidal galaxies, their kinemati...

  9. The intrinsic ellipticity of dwarf spheroidal galaxies: constraints from the Andromeda system

    CERN Document Server

    Salomon, Jean-Baptiste; Martin, Nicolas; Famaey, Benoit

    2015-01-01

    We present a study of the intrinsic deprojected ellipticity distribution of the satellite dwarf galaxies of the Andromeda galaxy, assuming that their visible components have a prolate shape, which is a natural outcome of simulations. Different possibilities for the orientation of the major axis of the prolate dwarf galaxies are tested, pointing either as close as possible to the radial direction towards the centre of Andromeda, or tangential to the radial direction, or with a random angle in the plane that contains the major axis and the observer. We find that the mean intrinsic axis ratio is ~ 1/2, with small differences depending on the assumed orientation of the population. Our deprojections also suggest that a significant fraction of the satellites, ~ 10%, are tidally disrupted remnants. We find that there is no evidence of any obvious difference in the morphology and major axis orientation between satellites that belong to the vast thin plane of co-rotating galaxies around Andromeda and those that do not...

  10. Stellar Populations in Galaxies: Progress on The Milky Way, on Dwarf Irregulars, and on Elliptical Galaxies

    Directory of Open Access Journals (Sweden)

    Dante Minniti

    2001-01-01

    Full Text Available I discuss specific topics of stellar populations where major progress is occurring. Large surveys like the MACHO Project are contributing to our understanding of the inner structure of our Galaxy. Towards these inner regions , different components (bulge, inner halo, and inner thin and thick disks overlap. We can learn much about these stellar populations using the MACHO database. We expect major progress in the study of the outer Milky Way halo in following years from the SDSS database. Very distant BHB stars located in the outskirts of the halo would be identified. I also describe recent observations of nearby dwarf irregular galaxies, and discuss what they tell us about their stellar content, and about the way these galaxies form. It is now possible to construct deep luminosity functions and color-magnitude diagrams for galaxies beyond the Local Group. I finally review recent work on the resolved stellar populations of the giant early type galaxy NGC~5128.

  11. The Globular Cluster System of the Virgo Dwarf Elliptical Galaxy VCC 1087

    CERN Document Server

    Beasley, M A; Brodie, J P; Cenarro, A J; Geha, M; Beasley, Michael A.; Strader, Jay; Brodie, Jean P.

    2005-01-01

    We have analysed the globular cluster (GC) system of the nucleated dwarf elliptical galaxy VCC 1087 in the Virgo cluster, based on Keck/LRIS spectroscopy and archival HST/ACS imaging. We estimate VCC 1087 hosts a total population of 77+/-19 GCs, which corresponds to a relatively high V-band specific frequency of 5.8+/-1.4. The g-z color distribution of the GCs shows a blue (metal-poor) peak with a tail of redder (metal-rich) clusters similar in color to those seen in luminous ellipticals. Spectroscopy of a subsample of 12 GCs suggests that the GC system is old and coeval (~10 Gyr), with a fairly broad metallicity distribution (-1.81. A compilation of the kinematics of the GC systems of 9 early-type galaxies shows surprising diversity in the v/sigma parameter for GC systems. In this context, the GC system of VCC 1087 exhibits the most significant rotation to velocity dispersion signature. Modeling the velocity dispersion profile of the GCs and galaxy stars suggest fairly constant mass-to-light ratios of ~3 out...

  12. HST/ACS Direct Ages of the Dwarf Elliptical Galaxies NGC 147 and NGC 185

    CERN Document Server

    Geha, M; Grocholski, A; Dolphin, A; van der Marel, R P; Guhathakurta, P

    2015-01-01

    We present the deepest optical photometry for any dwarf elliptical (dE) galaxy based on Hubble Space Telescope ACS observations of the Local Group dE galaxies NGC 147 and NGC 185. The resulting F606W and F814W color-magnitude diagrams are the first to reach below the main sequence turnoff in a dE galaxy, allowing us to determine full star formation histories in these systems. The ACS fields are located ~1.5 effective radii from the galaxy center to avoid photometric crowding. While our ACS pointings in both dEs show unambiguous evidence for old and intermediate age stars, the mean age in NGC 147 is ~ 4 Gyr younger as compared to NGC 185. In NGC 147, only 40% of stars were in place 12.5 Gyrs ago (z~5), with the bulk of the remaining stellar population forming between 5 to 7 Gyr. In contrast, 70% of stars were formed in NGC 185 field more than12.5 Gyr ago with the majority of the remaining population forming between 8 to 10 Gyr. Star formation ceased in both ACS fields at least 3 Gyr ago. Previous observations ...

  13. Abundance ratios and IMF slope in the dwarf elliptical galaxy NGC~1396 with MUSE

    CERN Document Server

    Mentz, J J; Peletier, R F; Falcón-Barroso, J; Lisker, T; van de Ven, G; Loubser, S I; Hilker, M; Sánchez-Janssen, R; Napolitano, N; Cantiello, M; Capaccioli, M; Norris, M; Paolillo, M; Smith, R; Beasley, M A; Lyubenova, M; Munoz, R; Puzia, T

    2016-01-01

    Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (M$_V = -16.60$, Mass $\\sim 4\\times10^8$ M$_\\odot$), located in the Fornax cluster, have been performed with the VLT/ MUSE spectrograph in the wavelength region from $4750-9350$ \\AA{}. In this paper we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galacto-centric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of $\\sim$ 6 Gyr and a metallicity [Fe/H]$\\sim$ $-0.4$, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe] $\\sim +0.1$, and under-abundant Sodium, with [Na/Fe] values around $-0.1$, while [Mg/Fe] is overabundant at all radii, increasing from $\\sim+0.1$ in the centre to $\\sim +0.2$ dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1...

  14. Investigating Dwarf Spiral Galaxies

    Science.gov (United States)

    Weerasooriya, Sachithra; Dunn, Jacqueline M.

    2017-01-01

    Several studies have proposed that dwarf elliptical / spheroidal galaxies form through the transformation of dwarf irregular galaxies. Early and late type dwarfs resemble each other in terms of their observed colors and light distributions (each can often be represented by exponential disks), providing reason to propose an evolutionary link between the two types. The existence of dwarf spirals has been largely debated. However, more and more recent studies are using the designation of dwarf spiral to describe their targets of interest. This project seeks to explore where dwarf spirals fit into the above mentioned evolutionary sequence, if at all. Optical colors will be compared between a sample of dwarf irregular, dwarf elliptical, and dwarf spiral galaxies. The dwarf irregular and dwarf elliptical samples have previously been found to overlap in both optical color and surface brightness profile shape when limiting the samples to their fainter members. A preliminary comparison including the dwarf spiral sample will be presented here, along with a comparison of available ultraviolet and near-infrared data. Initial results indicate a potential evolutionary link that merits further investigation.

  15. The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

    CERN Document Server

    Michielsen, D; Conselice, C J; Toloba, E; Whiley, I M; Aragón-Salamanca, A; Balcells, M; Cardiel, N; Cenarro, A J; Gorgas, J; Peletier, R F; Vazdekis, A

    2007-01-01

    Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby Universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research and Training Network embarked on a study of dwarf galaxies named MAGPOP-ITP (Peletier et al., 2007). In this paper, we present the analysis of a sample of 24 dwarf elliptical galaxies (dEs) in the Virgo Cluster and in the field, using optical long-slit spectroscopy. We examine their stellar populations in combination with their light distribution and environment. We confirm and strengthen previous results that dEs are, on average, younger and more metal-poor than normal elliptical galaxies, and that their [alpha/Fe] abundance ratios scatter around solar. This is in accordance with the downsizing picture of galaxy formation where mass is the main driver for the star formation history. We also find new correlations be...

  16. HST/ACS Direct Ages of the Dwarf Elliptical Galaxies NGC 147 and NGC 185

    Science.gov (United States)

    Geha, M.; Weisz, D.; Grocholski, A.; Dolphin, A.; van der Marel, R. P.; Guhathakurta, P.

    2015-10-01

    We present the deepest optical photometry for any dwarf elliptical (dE) galaxy based on Hubble Space Telescope Advanced Camera for Surveys (ACS) observations of the Local Group dE galaxies NGC 147 and NGC 185. Our F606W and F814W color-magnitude diagrams are the first to reach below the oldest main sequence turnoff in a dE galaxy, allowing us to determine full star formation histories in these systems. The ACS fields are located roughly ˜1.5 effective radii from the galaxy center to avoid photometric crowding. While both ACS fields show unambiguous evidence for old and intermediate age stars, the mean age of NGC 147 is ˜4-5 Gyr younger as compared to NGC 185. In NGC 147, only 40% of stars were in place 12.5 Gyr ago (z ˜ 5), with the bulk of the remaining stellar population forming between 5 to 7 Gyr. In contrast, 70% of stars were formed in NGC 185 prior to 12.5 Gyr ago with the majority of the remaining population forming between 8 to 10 Gyr ago. Star formation has ceased in both ACS fields for at least 3 Gyr. Previous observations in the central regions of NGC 185 show evidence for star formation as recent as 100 Myr ago, and a strong metallicity gradient with radius. This implies a lack of radial mixing between the center of NGC 185 and our ACS field. The lack of radial gradients in NGC 147 suggests that our inferred SFHs are more representative of its global history. We interpret the inferred differences in star formation histories to imply an earlier infall time into the M31 environment for NGC 185 as compared to NGC 147.

  17. NGC 5044-N50: a link between blue compact galaxies and dwarf ellipticals

    Science.gov (United States)

    Cellone, Sergio A.; Buzzoni, Alberto

    We present new optical observations of the dwarf galaxy N50 in the NGC 5044 Group, showing that this object is probably at an intermediate BCD→dE evolutionary stage, after a realtively recent burst of star formation.

  18. Surface brightness and color distributions in blue compact dwarf galaxies. I - Haro 2, an extreme example of a star-forming young elliptical galaxy

    Science.gov (United States)

    Loose, Hans-Hermann; Thuan, Trinh X.

    1986-01-01

    The first results of a large-scale program to study the morphology and structure of blue compact dwarf galaxies from CCD observations are presented. The observations and reduction procedures are described, and surface brightness and color profiles are shown. The results are used to discuss the morphological type of Haro 2 and its stellar populations. It is found that Haro 2 appears to be an extreme example of an elliptical galaxy undergoing intense star formation in its central regions, and that the oldest stars it contains were made only about four million yr ago. The 'missing' mass problem of Haro 2 is also discussed.

  19. The relation between stellar populations, structure and environment for dwarf elliptical galaxies from the MAGPOP-ITP

    NARCIS (Netherlands)

    Michielsen, D.; Boselli, A.; Conselice, C. J.; Toloba, E.; Whiley, I. M.; Aragon-Salamanca, A.; Balcells, M.; Cardiel, N.; Cenarro, A. J.; Gorgas, J.; Peletier, R. F.; Vazdekis, A.

    2008-01-01

    Dwarf galaxies, as the most numerous type of galaxy, offer the potential to study galaxy formation and evolution in detail in the nearby universe. Although they seem to be simple systems at first view, they remain poorly understood. In an attempt to alleviate this situation, the MAGPOP EU Research a

  20. Morphological Mutations of Dwarf Galaxies

    CERN Document Server

    Hensler, Gerhard

    2012-01-01

    Dwarf galaxies (DGs) are extremely challenging objects in extragalactic astrophysics. They are expected to originate as the first units in Cold Dark-Matter cosmology. They are the galaxy type most sensitive to environmental influences and their division into multiple types with various properties have invoked the picture of their variant morphological transformations. Detailed observations reveal characteristics which allow to deduce the evolutionary paths and to witness how the environment has affected the evolution. Here we review peculiarities of general morphological DG types and refer to processes which can deplete gas-rich irregular DGs leading to dwarf ellipticals, while gas replenishment implies an evolutionary cycling. Finally, as the less understood DG types the Milky Way satellite dwarf spheroidal galaxies are discussed in the context of transformation.

  1. Dwarf-Galaxy Cosmology

    CERN Document Server

    Schulte-Ladbeck, Regina; Brinks, Elias; Kravtsov, Andrey

    2010-01-01

    Dwarf galaxies provide opportunities for drawing inferences about the processes in the early universe by observing our "cosmological backyard"-the Local Group and its vicinity. This special issue of the open-access journal Advances in Astronomy is a snapshot of the current state of the art of dwarf-galaxy cosmology.

  2. A common colour-magnitude relation from giant elliptical galaxies to globular clusters?

    CERN Document Server

    Castelli, A V Smith; Richtler, T; Faifer, F; Forte, J C; Cellone, S A

    2009-01-01

    We discuss the existence of a common colour-magnitude relation (CMR) of metal-poor globular clusters and early-type galaxies, i.e. giant ellipticals, normal ellipticals and lenticulars, dwarf ellipticals and lenticulars, and dwarf spheroidals. Such CMR would cover a range of ~ 14 mag, extending from the brightest galaxies, down to the globular clusters on the fainter side.

  3. Morphological transformations of Dwarf Galaxies in the Local Group

    CERN Document Server

    Carraro, Giovanni

    2014-01-01

    In the Local Group there are three main types of dwarf galaxies: Dwarf Irregulars, Dwarf Spheroidals, and Dwarf Ellipticals. Intermediate/transitional types are present as well. This contribution reviews the idea that the present day variety of dwarf galaxy morphologies in the Local Group might reveal the existence of a transformation chain of events, of which any particular dwarf galaxy represents a manifestation of a particular stage. In other words, all dwarf galaxies that now are part of the Local Group would have formed identically in the early universe, but then evolved differently because of morphological transformations induced by dynamical processes like galaxy harassment, ram pressure stripping, photo-evaporation, and so forth. We start describing the population of dwarf galaxies and their spatial distribution in the LG. Then, we describe those phenomena that can alter the morphology of a dwarf galaxies, essentially by removing, partially or completely, their gas content. Lastly, we discuss morpholo...

  4. Understanding dwarf galaxies as galactic building blocks

    CERN Document Server

    Tosi, M P

    2003-01-01

    This is a summary of a general discussion held during the third EuroConference on galaxy evolution. Various observational features of the stellar populations in present--day dwarf galaxies were presented to introduce the discussion on the possibility that these systems be the main building blocks of spiral and elliptical galaxies. Many people in the audience turned out to think that the inconsistencies among the observed properties of large and dwarf galaxies are too many to believe that the former are built up only by means of successive accretions of the latter. However, theorists of hierarchical galaxy formation suggested that present--day dwarfs are not representative of the galactic building blocks, which may be completely invisible nowadays. Some of them suggested that, contrary to what is usually assumed in hierarchical modelling, the actual building blocks were still fully gaseous systems when their major mergers occurred. If this is the case, then most of the inconsistencies can be overcome, and the ...

  5. Dynamical Masses of Elliptical Galaxies

    CERN Document Server

    Gerhard, O E

    2002-01-01

    Recent progress in the dynamical analysis of elliptical galaxy kinematics is reviewed. Results reported briefly include (i) the surprisingly uniform anisotropy structure of luminous ellipticals, (ii) their nearly flat (to $\\sim 2R_e$) circular velocity curves, (iii) the Tully-Fisher and $M/L - L$ relations and the connection to the Fundamental Plane, and (iv) the large halo mass densities implied by the dynamical models.

  6. Dwarf spheroidal galaxies keystones of galaxy evolution

    CERN Document Server

    Gallagher, S C; Gallagher, S; Wyse, F G

    1994-01-01

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

  7. Optical observation of supernova remnant in elliptical galaxy NGC 185

    Science.gov (United States)

    Vučetić, M.; Arbutina, B.; Pavlovic, M. Z.; Ciprijanovic, A.; Urosevic, D.; Petrov, N.; Onić, D.; Trcka, A.

    2016-06-01

    In this paper we discuss the previously known optical supernova remnant (SNR) in NGC 185 galaxy, a dwarf elliptical companion of the Andromeda galaxy, in order to gain more information about its properties and evolutionary status. To this end, we observed a central portion of NGC 185, through the narrowband Hα and [SII]} filters, on a 2m RCC-telescope at National astronomical observatory Rozhen, Bulgaria. Also, we performed MHD simulations using the Pluto code, for the case of low environmental density and high pressure, in order to discuss evolution of a SNR in a gas poor dwarf galaxy.

  8. Isolated compact elliptical galaxies: Stellar systems that ran away

    CERN Document Server

    Chilingarian, Igor

    2015-01-01

    Compact elliptical galaxies form a rare class of stellar system (~30 presently known) characterized by high stellar densities and small sizes and often harboring metal-rich stars. They were thought to form through tidal stripping of massive progenitors, until two isolated objects were discovered where massive galaxies performing the stripping could not be identified. By mining astronomical survey data, we have now found 195 compact elliptical galaxies in all types of environment. They all share similar dynamical and stellar population properties. Dynamical analysis for nonisolated galaxies demonstrates the feasibility of their ejection from host clusters and groups by three-body encounters, which is in agreement with numerical simulations. Hence, isolated compact elliptical and isolated quiescent dwarf galaxies are tidally stripped systems that ran away from their hosts.

  9. Quantitative analysis of spirality in elliptical galaxies

    CERN Document Server

    Dojcsak, Levente

    2013-01-01

    We use an automated galaxy morphology analysis method to quantitatively measure the spirality of galaxies classified manually as elliptical. The data set used for the analysis consists of 60,518 galaxy images with redshift obtained by the Sloan Digital Sky Survey (SDSS) and classified manually by Galaxy Zoo, as well as the RC3 and NA10 catalogues. We measure the spirality of the galaxies by using the Ganalyzer method, which transforms the galaxy image to its radial intensity plot to detect galaxy spirality that is in many cases difficult to notice by manual observation of the raw galaxy image. Experimental results using manually classified elliptical and S0 galaxies with redshift <0.3 suggest that galaxies classified manually as elliptical and S0 exhibit a nonzero signal for the spirality. These results suggest that the human eye observing the raw galaxy image might not always be the most effective way of detecting spirality and curves in the arms of galaxies.

  10. Weak homology of elliptical galaxies

    CERN Document Server

    Bertin, G; Principe, M D

    2002-01-01

    We start by studying a small set of objects characterized by photometric profiles that have been pointed out to deviate significantly from the standard R^{1/4} law. For these objects we confirm that a generic R^{1/n} law, with n a free parameter, can provide superior fits (the best-fit value of n can be lower than 2.5 or higher than 10), better than those that can be obtained by a pure R^{1/4} law, by an R^{1/4}+exponential model, and by other dynamically justified self--consistent models. Therefore, strictly speaking, elliptical galaxies should not be considered homologous dynamical systems. Still, a case for "weak homology", useful for the interpretation of the Fundamental Plane of elliptical galaxies, could be made if the best-fit parameter n, as often reported, correlates with galaxy luminosity L, provided the underlying dynamical structure also follows a systematic trend with luminosity. We demonstrate that this statement may be true even in the presence of significant scatter in the correlation n(L). Pr...

  11. Galaxy evolution. Isolated compact elliptical galaxies: stellar systems that ran away.

    Science.gov (United States)

    Chilingarian, Igor; Zolotukhin, Ivan

    2015-04-24

    Compact elliptical galaxies form a rare class of stellar system (~30 presently known) characterized by high stellar densities and small sizes and often harboring metal-rich stars. They were thought to form through tidal stripping of massive progenitors, until two isolated objects were discovered where massive galaxies performing the stripping could not be identified. By mining astronomical survey data, we have now found 195 compact elliptical galaxies in all types of environment. They all share similar dynamical and stellar population properties. Dynamical analysis for nonisolated galaxies demonstrates the feasibility of their ejection from host clusters and groups by three-body encounters, which is in agreement with numerical simulations. Hence, isolated compact elliptical and isolated quiescent dwarf galaxies are tidally stripped systems that ran away from their hosts.

  12. Manganese in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    North, P.; Cescutti, G.; Jablonka, P.; Hill, V.; Shetrone, M.; Letarte, B.; Lemasle, B.; Venn, K. A.; Battaglia, G.; Tolstoy, E.; Irwin, M. J.; Primas, F.; Francois, P.

    We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other

  13. Lopsidedness in dwarf irregular galaxies

    CERN Document Server

    Heller, A B; Almoznino, E; Van Zee, L; Salzer, J J; Heller, Ana B.; Brosch, Noah; Almoznino, Elchanan; Zee, Liese van; Salzer, John J.

    2000-01-01

    We quantify the amplitude of the lopsidedness, the azimuthal angular asymmetry index, and the concentration of star forming regions, as represented by the distribution of the H$\\alpha$ emission, in a sample of 78 late-type irregular galaxies. We bin the observed galaxies in two groups representing blue compact galaxies (BCDs) and low surface brightness dwarf galaxies (LSBs). The light distribution is analysed with a novel algorithm, which allows detection of details in the light distribution pattern. We find that while the asymmetry of the underlying continuum light, representing the older stellar generations, is relatively small, the H$\\alpha$ emission is very asymmetric and is correlated in position angle with the continuum light. We test a model of random star formation over the extent of a galaxy by simulating HII regions in artificial dwarf galaxies. The implication is that random star formation over the full extent of a galaxy may be generated in LSB dwarf-irregular galaxies but not in BCD galaxies.

  14. Formation, Evolution and Properties of Isolated Field Elliptical Galaxies

    CERN Document Server

    Niemi, Sami-Matias; Nurmi, Pasi; Saar, Enn

    2010-01-01

    [Abridged] We study the properties, evolution and formation mechanisms of isolated field elliptical galaxies. We create a mock catalogue of isolated field elliptical galaxies from the Millennium Simulation Galaxy Catalogue, and trace their merging histories. The formation, identity and assembly redshifts of simulated isolated and non-isolated elliptical galaxies are studied and compared. Observational and numerical data are used to compare age, mass, and the colour-magnitude relation. Our results, based on simulation data, show that almost seven per cent of all elliptical galaxies brighter than -19mag in B-band can be classified as isolated field elliptical galaxies. Isolated field elliptical galaxies show bluer colours than non-isolated elliptical galaxies and they appear younger, in a statistical sense, according to their mass weighted age. Isolated field elliptical galaxies also form and assemble at lower redshifts compared to non-isolated elliptical galaxies. About 46 per cent of isolated field elliptical...

  15. Collisionless evaporation from cluster elliptical galaxies

    CERN Document Server

    Muccione, V

    2003-01-01

    We describe a particular aspect of the effects of the parent cluster tidal field (CTF) on stellar orbits inside cluster Elliptical galaxies. In particular we discuss, with the aid of a simple numerical model, the possibility that collisionless stellar evaporation from elliptical galaxies is an effective mechanism for the production of the recently discovered intracluster stellar populations. A preliminary investigation, based on very idealized galaxy density profiles (Ferrers density distributions), showed that over an Hubble time, the amount of stars lost by a representative galaxy may sum up to the 10% of the initial galaxy mass, a fraction in interesting agreement with observational data. The effectiveness of this mechanism is due to the fact that the galaxy oscillation periods near equilibrium configurations in the CTF are comparable to stellar orbital times in the external galaxy regions. Here we extend our previous study to more realistic galaxy density profiles, in particular by adopting a triaxial Her...

  16. Isolated elliptical galaxies in the local Universe

    CERN Document Server

    Lacerna, I; Avila-Reese, V; Abonza-Sane, J; del Olmo, A

    2015-01-01

    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. 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 about the nature of a particular set of blue and star-forming isolated ellipticals identified here. We study 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 analyze in more detail the blue star-forming isolated ellipticals through photometric characterization using GALFIT and infer their star formation history using STARLIGHT. 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 qu...

  17. Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics

    NARCIS (Netherlands)

    Toloba, E.; Boselli, A.; Cenarro, A. J.; Peletier, R. F.; Gorgas, J.; Gil de Paz, A.; Munoz-Mateos, J. C.

    We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy

  18. Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics

    NARCIS (Netherlands)

    Toloba, E.; Boselli, A.; Cenarro, A. J.; Peletier, R. F.; Gorgas, J.; Gil de Paz, A.; Munoz-Mateos, J. C.

    2011-01-01

    We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy

  19. Dust processing in elliptical galaxies

    CERN Document Server

    Hirashita, Hiroyuki; Villaume, Alexa; Srinivasan, Sundar

    2015-01-01

    We reconsider the origin and processing of dust in elliptical galaxies. We theoretically formulate the evolution of grain size distribution, taking into account dust supply from asymptotic giant branch (AGB) stars and dust destruction by sputtering in the hot interstellar medium (ISM), whose temperature evolution is treated by including two cooling paths: gas emission and dust emission (i.e. gas cooling and dust cooling). With our new full treatment of grain size distribution, we confirm that dust destruction by sputtering is too efficient to explain the observed dust abundance even if AGB stars continue to supply dust grains, and that, except for the case where the initial dust-to-gas ratio in the hot gas is as high as $\\sim 0.01$, dust cooling is negligible compared with gas cooling. However, we show that, contrary to previous expectations, cooling does not help to protect the dust; rather, the sputtering efficiency is raised by the gas compression as a result of cooling. We additionally consider grain grow...

  20. Dwarf galaxies : Important clues to galaxy formation

    NARCIS (Netherlands)

    Tolstoy, E

    2003-01-01

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

  1. HST detection of spiral structure in two Coma Cluster dwarf galaxies

    CERN Document Server

    Graham, A W; Guzmán, R; Graham, Alister W.; Jerjen, Helmut; Guzman, Rafael

    2003-01-01

    We report the discovery of (stellar) spiral-like structure in Hubble Space Telescope images of two dwarf galaxies (GMP 3292 and GMP 3629) belonging to the Coma cluster. GMP 3629 is the faintest such galaxy detected in a cluster environment, and it is the first such galaxy observed in the dense Coma cluster. The large bulge and the faintness of the broad spiral-like pattern in GMP 3629 suggests that its disk may have been largely depleted. >We may therefore have found an example of the ``missing link'' in theories of galaxy evolution which have predicted that dwarf spiral galaxies, particularly in clusters, evolve into dwarf elliptical galaxies.

  2. The formation history of elliptical galaxies

    CERN Document Server

    De Lucia, G; White, S D M; Croton, D; Kauffmann, G; Lucia, Gabriella De; Springel, Volker; White, Simon D. M.; Croton, Darren; Kauffmann, Guinevere

    2006-01-01

    We take advantage of the largest high-resolution simulation of cosmic structure growth ever carried out -- the Millennium Simulation of the concordance LambdaCDM cosmogony -- to study how the star formation histories, ages and metallicities of elliptical galaxies depend on environment and on stellar mass. We concentrate on a galaxy formation model which is tuned to fit the joint luminosity/colour/morphology/clustering distribution of low redshift galaxies. Massive ellipticals in this model have higher metal abundances, older luminosity-weighted ages, shorter star formation timescales, but lower assembly redshifts than less massive systems. Within clusters the typical masses, ages and metal abundances of ellipticals are predicted to decrease, on average, with increasing distance from the cluster centre. We also quantify the effective number of progenitors of ellipticals as a function of present stellar mass, finding typical numbers below 2 for M* < 10^{11} Msun, rising to about 5 for the most massive system...

  3. A Study of Dwarf Galaxies in Five Rich Clusters I: Abell 1689 and Abell 1703

    Science.gov (United States)

    Bruursema, Justice; Riley, S.; Ford, H. C.; Zekser, K. C.; Infante, L.; Postman, M.

    2008-05-01

    Dwarf galaxies play an important role in understanding galactic formation, cluster dynamics, and large scale structure. Although local dwarf populations have been well studied, dwarf galaxies outside the local supercluster remain relatively unexamined. Using ACS Investigation Definition Team data, we examine the dwarf galaxy populations of A1689 (z=0.1832), A1703 (z=0.2580), A2218 (z=0.1756), CL0024+16 (z=0.395), and MS1358+62 (z=0.328). We have modeled and subtracted the light from the brighter elliptical galaxies using the XVISTA subroutine SNUC. An assumption of concentric elliptical isophotes is made and the position angle, ellipticity, and brightness are fit using a nonlinear least-squares algorithm. The subtraction of the models reveals a population of dwarf galaxies usually hidden by the light of bright ellipticals. SExtractor and Bayesian Photometric Redshifts (BPZ) are used in order to identify cluster members. With the 0.05" per pixel resolution of ACS and a completeness of mF625 = 28 we are able to identify approximately 1000 dwarf galaxies candidates, defined as MF625 > -18, in all five clusters combined. We will discuss the results of this research including, but not limited to, dwarf galaxy luminosity functions, radial distribution, and the characteristics of dwarfs compared to those in other well studied clusters. ACS was developed under NASA contract NAS5-32865, and this research was supported by NASA grant NAG5-7697.

  4. Unveiling the Secret of a Virgo Dwarf Galaxy

    Science.gov (United States)

    2000-05-01

    Dwarf galaxies may not be as impressive in appearance as their larger brethren, but they are at least as interesting from a scientific point of view. And sometimes they may have hidden properties that will only be found by means of careful observations, probing the signals of their stars at the faintest level. Such as the entirely unexpected, well developed spiral structure within an otherwise seemingly normal dwarf elliptical galaxy! This is the surprise result of a new study by a team of astronomers [1], headed by Helmut Jerjen from the Australian National University (Canberra) who obtained detailed observations with the ESO Very Large Telescope (VLT) of the dwarf galaxy IC 3328 in the Virgo Cluster of Galaxies, some 50 million light-years away. Dwarf galaxies Dwarf galaxies are present in all major clusters of galaxies and dominate by numbers in the universe. They may contain a few (tens of) millions of stars, as compared to galaxies of normal size with hundreds of billions of stars. About two dozen dwarf galaxies are known in the "Local Group" of galaxies of which the Milky Way galaxy in which we live is also a member. The Large and Small Magellanic Clouds are some of the best known dwarf galaxies - they are of the irregular type - while NGC 147 and NGC 205, two companions to the great Andromeda Galaxy, are of the elliptical type. Dwarf elliptical galaxies are characterized by their smooth appearance. From various studies, it is known that they are tri-axial ellipsoids of different degrees of elongation. Some are almost spherical while others are more pancake- or cigar-shaped. Like the elliptical galaxies of normal size, dwarf ellipticals are almost pure aggregates of stars. In contrast, spiral galaxies also contain clouds of gas and dust. The visible mass of spiral galaxies is in a rotating disk. Dwarf ellipticals generally keep their form because of the random motions of their stars. VLT observations of dwarf elliptical galaxies Using the FORS1 multi

  5. AGN feedback in elliptical galaxies: numerical simulations

    CERN Document Server

    Ciotti, L

    2011-01-01

    The importance of feedback (radiative and mechanical) from massive black holes at the centers of elliptical galaxies is not in doubt, given the well established relation among black hole mass and galaxy optical luminosity. Here, with the aid of high-resolution hydrodynamical simulations, we discuss how this feedback affects the hot ISM of isolated elliptical galaxies of different mass. The cooling and heating functions include photoionization plus Compton heating, the radiative transport equations are solved, and the mechanical feedback due to the nuclear wind is also described on a physical basis; star formation is considered. In the medium-high mass galaxies the resulting evolution is highly unsteady. At early times major accretion episodes caused by cooling flows in the recycled gas produced by stellar evolution trigger AGN flaring: relaxation instabilities occur so that duty cycles are small enough to account for the very small fraction of massive ellipticals observed to be in the QSO-phase, when the accr...

  6. A Population of Compact Elliptical Galaxies Detected with the Virtual Observatory

    CERN Document Server

    Chilingarian, Igor; Revaz, Yves; Dodonov, Serguei; Durand, Daniel; Durret, Florence; Micol, Alberto; Slezak, Eric

    2009-01-01

    Compact elliptical galaxies are characterized by small sizes and high stellar densities. They are thought to form through tidal stripping of massive progenitors. However, only a handful of them were known, preventing us from understanding the role played by this mechanism in galaxy evolution. We present a population of 21 compact elliptical galaxies gathered with the Virtual Observatory. Follow-up spectroscopy and data mining, using high-resolution images and large databases, show that all the galaxies exhibit old metal-rich stellar populations different from those of dwarf elliptical galaxies of similar masses but similar to those of more massive early-type galaxies, supporting the tidal stripping scenario. Their internal properties are reproduced by numerical simulations, which result in compact dynamically hot remnants resembling the galaxies in our sample.

  7. The Shapes and Ages of Elliptical Galaxies

    CERN Document Server

    De Jong, R S; Jong, Roelof S. de; Davies, Roger L.

    1996-01-01

    In this paper we investigate the relation between the detailed isophotal shape of elliptical galaxies and the strength of the H beta absorption in their spectra. We find that disky galaxies have higher H beta indices. Stellar population synthesis models show that the H beta line is a good age indicator, hence disky galaxies tend to have younger mean ages than boxy galaxies. We show that the observed trend can be brought about by a contaminating young population, which we associate with the disky component. This population need only account for a small fraction of the total mass, for example if a contaminating population of age of 2 Gyrs is superimposed on an old (12 Gyr) elliptical galaxy, then the observed trend can be explained if it contributes only 10% to the total mass. The size of this effect is consistent with the estimates of disk-to-total light ratios from surface photometry.

  8. Stars at Low Metallicity in Dwarf Galaxies

    NARCIS (Netherlands)

    Tolstoy, Eline; Battaglia, Giuseppina; Cole, Andrew; Hunt, LK; Madden, S; Schneider, R

    2008-01-01

    Dwarf galaxies offer an opportunity to understand the properties of low metallicity star formation both today and at the earliest times at the, epoch of the formation of the first stars. Here we concentrate on two galaxies in the Local Group: the dwarf irregular galaxy Leo A, which has been the rece

  9. Dark matter in dwarf galaxies

    OpenAIRE

    Roos, Matts

    2017-01-01

    Although the cusp-core controversy for dwarf galaxies is seen as a problem, I argue that the cored central profiles can be explained by flattened cusps because they suffer from conflicting measurements and poor statistics and because there is a large number of conventional processes that could have flattened them since their creation, none of which requires new physics. Other problems, such as "too big to fail", are not discussed.

  10. Radio Mode Outbursts in Giant Elliptical Galaxies

    CERN Document Server

    Nulsen, Paul; Forman, William; Churazov, Eugene; McNamara, Brian; David, Laurence; Murray, Stephen

    2009-01-01

    Outbursts from active galactic nuclei (AGN) affect the hot atmospheres of isolated giant elliptical galaxies (gE's), as well as those in groups and clusters of galaxies. Chandra observations of a sample of nearby gE's show that the average power of AGN outbursts is sufficient to stop their hot atmospheres from cooling and forming stars, consistent with radio mode feedback models. The outbursts are intermittent, with duty cycles that increases with size.

  11. The Blue Straggler Population in Dwarf Galaxies

    CERN Document Server

    Momany, Yazan

    2014-01-01

    In this chapter I review the recent developments regarding the study of Blue Stragglers (BSS) in dwarf galaxies. The loose density environment of dwarf galaxies resembles that of the Galactic Halo, hence it is natural to compare their common BSS properties. At the same time, it is unescapable to compare with the BSS properties in Galactic Globular clusters, which constitute the reference point for BSS studies. Admittedly, the literature on BSS in dwarf galaxies is not plentiful. The limitation is mostly due to the large distance to even the closest dwarf galaxies. Nevertheless, recent studies have allowed a deeper insight on the BSS photometric properties that are worth examining.

  12. Mining the Suzaku Archive for Elliptical Galaxies

    Science.gov (United States)

    Loewenstein, Michael

    Despite significant progress, our understanding of the formation and evolution of giant elliptical galaxies is incomplete. Many unresolved details about the star formation and assembly history, dissipation and feedback processes, and how these are connected in space and time relate to complex gasdynamical processes that are not directly observable, but that leave clues in the form of the level and pattern of heavy element enrichment in the hot ISM. The low background and relatively sharp spectral resolution of the Suzaku X-ray Observatory XIS CCD detectors enable one to derive a particularly extensive abundance pattern in the hot ISM out to large galactic radii for bright elliptical galaxies. These encode important clues to the chemical and dynamical history of elliptical galaxies. The Suzaku archive now includes data on many of the most suitable galaxies for these purposes. To date, these have been analyzed in a very heterogeneous manner -- some at an early stage in the mission using instrument calibration and analysis tools that have greatly evolved in the interim. Given the level of maturity of the data archive, analysis software, and calibration, the time is right to undertake a uniform analysis of this sample and interpret the results in the context of a coherent theoretical framework for the first time. We propose to (1) carefully and thoroughly analyze the available X-ray luminous elliptical galaxies in the Suzaku database, employing the techniques we have established in our previous work to measure hot ISM abundance patterns. Their interpretation requires careful deconstruction within the context of physical gasdynamical and chemical evolutionary models. Since we have developed models for elliptical galaxy chemical evolution specifically constructed to place constraints on the history and development of these systems based on hot ISM abundances, we are uniquely positioned to interpret -- as well as to analyze -- X-ray spectra of these objects. (2) We will

  13. Manganese in dwarf spheroidal galaxies

    CERN Document Server

    North, P; Jablonka, P; Hill, V; Shetrone, M; Letarte, B; Lemasle, B; Venn, K A; Battaglia, G; Tolstoy, E; Irwin, M J; Primas, F; Francois, P

    2012-01-01

    We provide manganese abundances (corrected for the effect of the hyperfine structure) for a large number of stars in the dwarf spheroidal galaxies Sculptor and Fornax, and for a smaller number in the Carina and Sextans dSph galaxies. Abundances had already been determined for a number of other elements in these galaxies, including alpha and iron-peak ones, which allowed us to build [Mn/Fe] and [Mn/alpha] versus [Fe/H] diagrams. The Mn abundances imply sub-solar [Mn/Fe] ratios for the stars in all four galaxies examined. In Sculptor, [Mn/Fe] stays roughly constant between [Fe/H]\\sim -1.8 and -1.4 and decreases at higher iron abundance. In Fornax, [Mn/Fe] does not vary in any significant way with [Fe/H]. The relation between [Mn/alpha] and [Fe/H] for the dSph galaxies is clearly systematically offset from that for the Milky Way, which reflects the different star formation histories of the respective galaxies. The [Mn/alpha] behavior can be interpreted as a result of the metal-dependent Mn yields of type II and ...

  14. The Stellar Halos of Massive Elliptical Galaxies

    CERN Document Server

    Greene, Jenny E; Comerford, Julia M; Gebhardt, Karl; Adams, Joshua J

    2012-01-01

    We use the Mitchell Spectrograph (formerly VIRUS-P) on the McDonald Observatory 2.7m Harlan J. Smith Telescope to search for the chemical signatures of massive elliptical galaxy assembly. The Mitchell Spectrograph is an integral-field spectrograph with a uniquely wide field of view (107x107 sq arcsec), allowing us to achieve remarkably high signal-to-noise ratios of ~20-70 per pixel in radial bins of 2-2.5 times the effective radii of the eight galaxies in our sample. Focusing on a sample of massive elliptical galaxies with stellar velocity dispersions sigma* > 150 km/s, we study the radial dependence in the equivalent widths (EWs) of key metal absorption lines. By twice the effective radius, the Mgb EWs have dropped by ~50%, and only a weak correlation between sigma* and Mgb EW remains. The Mgb EWs at large radii are comparable to those seen in the centers of elliptical galaxies that are approximately an order of magnitude less massive. We find that the well-known metallicity gradients often observed within ...

  15. Dusty Feedback from Massive Black Holes in Two Elliptical Galaxies

    Science.gov (United States)

    Temi, P.; Brighenti, F.; Mathews, W. G.; Amblard, A.; Riguccini, L.

    2013-01-01

    Far-infrared dust emission from elliptical galaxies informs us about galaxy mergers, feedback energy outbursts from supermassive black holes and the age of galactic stars. We report on the role of AGN feedback observationally by looking for its signatures in elliptical galaxies at recent epochs in the nearby universe. We present Herschel observations of two elliptical galaxies with strong and spatially extended FIR emission from colder grains 5-10 kpc distant from the galaxy cores. Extended excess cold dust emission is interpreted as evidence of recent feedback-generated AGN energy outbursts in these galaxies, visible only in the FIR, from buoyant gaseous outflows from the galaxy cores.

  16. Young circumnuclear disks in elliptical galaxies

    Science.gov (United States)

    Sil'Chenko, Olga K.

    2009-04-01

    By means of integral-field spectroscopy with the Multi-Pupil Field/Fiber Spectrograph of the Russian 6-m telescope we have studied the central parts of NGC 759 and NGC 83— regular (non-interacting, without strong nuclear activity) round red luminous ( M B =-20.8--21.6) elliptical galaxies which are however known to possess molecular gas. In both galaxies we have found central stellar disks with the extension of 1-2 kpc along the radius which are evidently being formed just now.

  17. Globular Cluster System erosion in elliptical galaxies

    CERN Document Server

    Capuzzo-Dolcetta, Roberto

    2009-01-01

    In this paper we analyze data of 8 elliptical galaxies in order to study the difference between their globular cluster systems (GCSs) radial distributions and those of the galactic stellar component. In all the galaxies studied here the globular cluster system density profile is significantly flatter toward the galactic centre than that of stars. If this difference is interpreted as a depauperation of the initial GC population, the estimated number of missing globular clusters is significant, ranging from 21% to 71% of their initial population abundance in the eight galaxies examined. The corresponding mass lost to the central galactic region is 7x10^7-1.85x10^9 solar masses. All this mass carried toward central galactic regions have likely had an important feedback on the innermost galactic region, including its violent transient activity (AGN) and local massive black hole formation and growth.

  18. Indirect dark matter detection for flattened dwarf galaxies

    Science.gov (United States)

    Sanders, Jason L.; Evans, N. Wyn; Geringer-Sameth, Alex; Dehnen, Walter

    2016-09-01

    Gamma-ray experiments seeking to detect evidence of dark matter annihilation in dwarf spheroidal galaxies require knowledge of the distribution of dark matter within these systems. We analyze the effects of flattening on the annihilation (J) and decay (D) factors of dwarf spheroidal galaxies with both analytic and numerical methods. Flattening has two consequences: first, there is a geometric effect as the squeezing (or stretching) of the dark matter distribution enhances (or diminishes) the J-factor; second, the line of sight velocity dispersion of stars must hold up the flattened baryonic component in the flattened dark matter halo. We provide analytic formulas and a simple numerical approach to estimate the correction to the J- and D-factors required over simple spherical modeling. The formulas are validated with a series of equilibrium models of flattened stellar distributions embedded in flattened dark-matter distributions. We compute corrections to the J- and D-factors for the Milky Way dwarf spheroidal galaxies under the assumption that they are all prolate or all oblate and find that the hierarchy of J-factors for the dwarf spheroidals is slightly altered (typical correction factors for an ellipticity of 0.4 are 0.75 for the oblate case and 1.6 for the prolate case). We demonstrate that spherical estimates of the D-factors are very insensitive to the flattening and introduce uncertainties significantly less than the uncertainties in the D-factors from the other observables for all the dwarf spheroidals (for example, +10 per cent/-3 per cent for a typical ellipticity of 0.4). We conclude by investigating the spread in correction factors produced by triaxial figures and provide uncertainties in the J-factors for the dwarf spheroidals using different physically motivated assumptions for their intrinsic shape and axis alignments. We find that the uncertainty in the J-factors due to triaxiality increases with the observed ellipticity and, in general, introduces

  19. Shell Galaxies, Dynamical Friction, and Dwarf Disruption

    CERN Document Server

    Ebrova, Ivana; Canalizo, Gabriela; Bennert, Nicola; Jilkova, Lucie

    2009-01-01

    Using N-body simulations of shell galaxies created in nearly radial minor mergers, we investigate the error of collision dating, resulting from the neglect of dynamical friction and of gradual disruption of the cannibalized dwarf.

  20. Kinematic Constraints on Evolutionary Scenarios for Blue Compact Dwarf Galaxies I. Neutral Gas Dynamics

    CERN Document Server

    Van Zee, L; Skillman, E D; Zee, Liese van; Salzer, John J.; Skillman, Evan D.

    2001-01-01

    We present the results of high spatial resolution HI synthesis observations of six blue compact dwarf (BCD) galaxies. Optically, the selected galaxies have smooth, symmetric isophotes, and thus are the most likely of the BCD class to fade into an object morphologically similar to a dwarf elliptical when the current starburst ends. The neutral gas in all six galaxies appears to be rotationally supported, however, indicating that true morphological transformation from a BCD to a dE will require significant loss of angular momentum. Based on the observed neutral gas dynamics of these and other BCDs, it is unlikely that present-day BCDs will evolve directly into dwarf ellipticals after a starburst phase. We discuss alternative evolutionary scenarios for BCDs and place them within the larger context of galaxy formation and evolution models.

  1. Metals and ionizing photons from dwarf galaxies

    NARCIS (Netherlands)

    Salvadori, S.; Tolstoy, E.; Ferrara, A.; Zaroubi, S.

    2014-01-01

    We estimate the potential contribution of M <10(9)M(circle dot) dwarf galaxies to the reionization and early metal enrichment of the Milky Way environment, or circum-Galactic medium. Our approach is to use the observed properties of ancient stars ()under tilde>12 Gyr old) measured in nearby dwarf ga

  2. Metallic Winds in Dwarf Galaxies

    Science.gov (United States)

    Robles-Valdez, F.; Rodríguez-González, A.; Hernández-Martínez, L.; Esquivel, A.

    2017-02-01

    We present results from models of galactic winds driven by energy injected from nuclear (at the galactic center) and non-nuclear starbursts. The total energy of the starburst is provided by very massive young stellar clusters, which can push the galactic interstellar medium and produce an important outflow. Such outflow can be a well or partially mixed wind, or a highly metallic wind. We have performed adiabatic 3D N-Body/Smooth Particle Hydrodynamics simulations of galactic winds using the gadget-2 code. The numerical models cover a wide range of parameters, varying the galaxy concentration index, gas fraction of the galactic disk, and radial distance of the starburst. We show that an off-center starburst in dwarf galaxies is the most effective mechanism to produce a significant loss of metals (material from the starburst itself). At the same time, a non-nuclear starburst produces a high efficiency of metal loss, in spite of having a moderate to low mass loss rate.

  3. Evolution of dwarf galaxies : A dynamical perspective

    NARCIS (Netherlands)

    Lelli, Federico; Fraternali, Filippo; Verheijen, Marc

    2014-01-01

    For a rotating galaxy, the inner circular-velocity gradient dRV(0) provides a direct estimate of the central dynamical mass density, including gas, stars, and dark matter. We consider 60 low-mass galaxies with high-quality H I and/or stellar rotation curves (including starbursting dwarfs, irregulars

  4. Evolution of dwarf galaxies: a dynamical perspective

    NARCIS (Netherlands)

    Lelli, Federico; Fraternali, Filippo; Verheijen, Marc

    2014-01-01

    For a rotating galaxy, the inner circular-velocity gradient dRV(0) provides a direct estimate of the central dynamical mass density, including gas, stars, and dark matter. We consider 60 low-mass galaxies with high-quality H I and/or stellar rotation curves (including starbursting dwarfs, irregulars

  5. On the origin of bursts in blue compact dwarf galaxies: clues from kinematics and stellar populations

    CERN Document Server

    Koleva, M; Zeilinger, W W; Verbeke, R; Schroyen, J; Vermeylen, L

    2014-01-01

    Blue compact dwarf galaxies (BCDs) form stars at, for their sizes, extraordinarily high rates. In this paper, we study what triggers this starburst and what is the fate of the galaxy once its gas fuel is exhausted. We select four BCDs with smooth outer regions, indicating them as possible progenitors of dwarf elliptical galaxies. We have obtained photometric and spectroscopic data with the FORS and ISAAC instruments on the VLT. We analyse their infra-red spectra using a full spectrum fitting technique which yields the kinematics of their stars and ionized gas together with their stellar population characteristics. We find that the_stellar_ velocity to velocity dispersion ratio (v/sigma) of our BCDs is of the order of 1.5, similar to that of dwarf elliptical galaxies. Thus, those objects do not require significant (if any) loss of angular momentum to fade into early type dwarfs. This finding is in discordance with previous studies, which however compared the stellar kinematics of dwarf elliptical galaxies with...

  6. Missing dark matter in dwarf galaxies?

    CERN Document Server

    Oman, Kyle A; Sales, Laura V; Fattahi, Azadeh; Frenk, Carlos S; Sawala, Till; Schaller, Matthieu; White, Simon D M

    2016-01-01

    We use cosmological hydrodynamical simulations of the APOSTLE project to examine the fraction of baryons in $\\Lambda$CDM haloes that collect into galaxies. This `galaxy formation efficiency' correlates strongly and with little scatter with halo mass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy may thus be used to place a lower limit on total halo mass and, consequently, on its asymptotic maximum circular velocity. A number of dwarfs seem to violate this constraint, having baryonic masses up to ten times higher than expected from their rotation speeds, or, alternatively, rotating at only half the speed expected for their mass. Taking the data at face value, either these systems have formed galaxies with extraordinary efficiency - highly unlikely given their shallow potential wells - or they inhabit haloes with extreme deficits in their dark matter content. This `missing dark matter' is reminiscent of the inner mass deficits of galaxies with slowly-rising rotation curves, but extends...

  7. Solo Dwarfs I: Survey introduction and first results for the Sagittarius Dwarf Irregular Galaxy

    CERN Document Server

    Higgs, C R; Irwin, M; Bate, N F; Lewis, G F; Walker, M G; Cote, P; Venn, K; Battaglia, G

    2016-01-01

    We introduce the Solitary Local Dwarfs Survey (Solo), a wide field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multi-band imaging from CFHT/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than Mv = -18 situated beyond the nominal virial radius of the Milky Way and M31 (>300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius Dwarf Irregular Galaxy (Sag DIG), one of the most isolated, low mass galaxies, located at the edge of the Local Group. We analyze its resolved stellar populations and their spatial distributions. We provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag./sq.arcsec. Sag DIG is well described by a highly elliptical (disk-like) system following a single component...

  8. Elliptical Galaxies: Rotationally Distorted, After All

    Directory of Open Access Journals (Sweden)

    Caimmi, R.

    2009-12-01

    Full Text Available On the basis of earlier investigations onhomeoidally striated Mac Laurin spheroids and Jacobi ellipsoids (Caimmi and Marmo2005, Caimmi 2006a, 2007, different sequences of configurations are defined and represented in the ellipticity-rotation plane, $({sf O}hat{e}chi_v^2$. The rotation parameter, $chi_v^2$, is defined as the ratio, $E_mathrm{rot}/E_mathrm{res}$, of kinetic energy related to the mean tangential equatorial velocity component, $M(overline{v_phi}^2/2$, to kineticenergy related to tangential equatorial component velocity dispersion, $Msigma_{phiphi}^2/2$, andresidual motions, $M(sigma_{ww}^2+sigma_{33}^2/2$.Without loss of generality (above a thresholdin ellipticity values, the analysis is restricted to systems with isotropic stress tensor, whichmay be considered as adjoint configurationsto any assigned homeoidally striated density profile with anisotropic stress tensor, different angular momentum, and equal remaining parameters.The description of configurations in the$({sf O}hat{e}chi_v^2$ plane is extendedin two respects, namely (a from equilibriumto nonequilibrium figures, where the virialequations hold with additional kinetic energy,and (b from real to imaginary rotation, wherethe effect is elongating instead of flattening,with respect to the rotation axis.An application is made toa subsample $(N=16$ of elliptical galaxies extracted from richer samples $(N=25,~N=48$of early type galaxies investigated within theSAURON project (Cappellari et al. 2006, 2007.Sample objects are idealized as homeoidallystriated MacLaurinspheroids and Jacobi ellipsoids, and theirposition in the $({sf O}hat{e}chi_v^2$plane is inferred from observations followinga procedure outlined in an earlier paper(Caimmi 2009b. The position of related adjoint configurations with isotropic stresstensor is also determined. With a singleexception (NGC 3379, slow rotators arecharacterized by low ellipticities $(0lehat{e}<0.2$, low anisotropy parameters$(0ledelta<0

  9. Dwarf galaxies in the dynamically evolved NGC 1407 Group

    Science.gov (United States)

    Trentham, Neil; Tully, R. Brent; Mahdavi, Andisheh

    2006-07-01

    The NGC 1407 Group stands out among nearby structures by its properties that suggest it is massive and evolved. It shares properties with entities that have been called fossil groups: the 1.4m differential between the dominant elliptical galaxy and the second brightest galaxy comes close to satisfying the definition that has been used to define the fossil class. There are few intermediate-luminosity galaxies, but a large number of dwarfs in the group. We estimate there are 250 group members to the depth of our survey. The slope of the faint end of the luminosity function (reaching MR = -12) is α = -1.35. Velocities for 35 galaxies demonstrate that this group with one dominant galaxy has a mass of 7 × 1013Msolar and M/LR = 340Msolar/Lsolar. Two galaxies in close proximity to NGC 1407 have very large blueshifts. The most notable is the second brightest galaxy, NGC 1400, with a velocity of -1072 km s-1 with respect to the group mean. We report the detection of X-ray emission from this galaxy and from the group.

  10. Dwarf galaxies in the Dynamically Evolved NGC 1407 Group

    CERN Document Server

    Trentham, N; Tully, R B; Mahdavi, Andisheh; Trentham, Neil

    2006-01-01

    The NGC 1407 Group stands out among nearby structures by its properties that suggest it is massive and evolved. It shares properties with entities that have been called fossil groups: the 1.4 magnitude differential between the dominant elliptical galaxy and the second brightest galaxy comes close to satisfying the definition that has been used to define the fossil class. There are few intermediate luminosity galaxies, but a large number of dwarfs in the group. We estimate there are 250 group members to the depth of our survey. The slope of the faint end of the luminosity function (reaching M_R = -12) is alpha = -1.35. Velocities for 35 galaxies demonstrate that this group with one dominant galaxy has a mass of 7 X 10^13 M_sun and M/L_R = 340. Two galaxies in close proximity to NGC 1407 have very large blueshifts. The most notable is the second brightest galaxy, NGC 1400, with a velocity of -1072 km/s with respect to the group mean. We report the detection of X-ray emission from this galaxy and from the group.

  11. Tidal Dwarf Galaxies and Missing Baryons

    Directory of Open Access Journals (Sweden)

    Frederic Bournaud

    2010-01-01

    Full Text Available Tidal dwarf galaxies form during the interaction, collision, or merger of massive spiral galaxies. They can resemble “normal” dwarf galaxies in terms of mass, size, and become dwarf satellites orbiting around their massive progenitor. They nevertheless keep some signatures from their origin, making them interesting targets for cosmological studies. In particular, they should be free from dark matter from a spheroidal halo. Flat rotation curves and high dynamical masses may then indicate the presence of an unseen component, and constrain the properties of the “missing baryons,” known to exist but not directly observed. The number of dwarf galaxies in the Universe is another cosmological problem for which it is important to ascertain if tidal dwarf galaxies formed frequently at high redshift, when the merger rate was high, and many of them survived until today. In this paper, “dark matter” is used to refer to the nonbaryonic matter, mostly located in large dark halos, that is, CDM in the standard paradigm, and “missing baryons” or “dark baryons” is used to refer to the baryons known to exist but hardly observed at redshift zero, and are a baryonic dark component that is additional to “dark matter”.

  12. The Intrinsic Shapes of Low-Surface-Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf Galaxies

    CERN Document Server

    Sung, E C; Ryden, S; Patterson, J; Chun, M S; Kim, H I; Lee, W B; Sung, Eon-Chang; Han, Cheongho; Chun, Moon-Suk; Kim, Ho-Il; Lee, Woo-Baik

    1998-01-01

    In this paper, we measure the ellipticities of 30 LSB dI galaxies and compare the ellipticity distribution with that of 80 dEs (Ryden & Terndrup 1994; Ryden et al. 1998) and 62 BCDs (Sung et al. 1998). We find that the ellipticity distribution of LSB dIs is very similar to that of BCDs, and marginally different from that of dEs. We then determine the distribution of intrinsic shapes of dI galaxies and compare to those of other type dwarf galaxies under various assumptions. First, we assume that LSB dIs are either all oblate or all prolate, and use non-parametric analysis to find the best-fitting distribution of intrinsic shapes. With this assumption, we find that the scarcity of nearly circular LSB dIs implies, at the 99% confidence level, that they cannot be a population of randomly oriented oblate or prolate objects. Next, we assume that dIs are triaxial, and use parametric analysis to find permissible distributions of intrinsic shapes. We find that if the intrinsic axis ratios, $\\beta$ and parameters f...

  13. New Ultra-Compact Dwarf Galaxies in Clusters

    Science.gov (United States)

    Kohler, Susanna

    2017-02-01

    How do ultra-compact dwarf galaxies (UCDs) galaxies that are especially small and dense form and evolve? Scientists have recently examined distant galaxy clusters, searching for more UCDs to help us answer this question.Origins of DwarfsIn recent years we have discovered a growing sample of small, very dense galaxies. Galaxies that are tens to hundreds of light-years across, with masses between a million and a billion solar masses, fall into category of ultra-compact dwarfs (UCDs).An example of an unresolved compact object from the authors survey that is likely an ultra-compact dwarf galaxy. [Adapted from Zhang Bell 2017]How do these dense and compact galaxies form? Two possibilities are commonly suggested:An initially larger galaxy was tidally stripped during interactions with other galaxies in a cluster, leaving behind only its small, dense core as a UCD.UCDs formed as compact galaxies at very early cosmic times. The ones living in a massive dark matter halo may have been able to remain compact over time, evolving into the objectswe see today.To better understand which of these formation scenarios applies to which galaxies, we need a larger sample size! Our census of UCDs is fairly limited and because theyare small and dim, most of the ones weve discovered are in the nearby universe. To build a good sample, we need to find UCDs at higher redshifts as well.A New SampleIn a recent study, two scientists from University of Michigan have demonstrated how we might find more UCDs. Yuanyuan Zhang (also affiliated with Fermilab) and Eric Bell used the Cluster Lensing and Supernova Survey with Hubble (CLASH) to search 17 galaxy clusters at intermediate redshifts of 0.2 z 0.6, looking for unresolved objects that might be UCDs.The mass and size distributions of the UCD candidates reported in this study, in the context of previously known nuclear star clusters, globular clusters (GCs), UCDs, compact elliptical galaxies (cEs), and dwarf galaxies. [Zhang Bell 2017]Zhang and

  14. Stellar Populations in Dwarf Galaxies A Review of the Contribution of HST to our Understanding of the Nearby Universe

    CERN Document Server

    Tolstoy, E

    2000-01-01

    This review aims to give an overview of the contribution of the Hubble Space Telescope to our understanding of the detailed properties of Local Group dwarf galaxies and their older stellar populations. The exquisite stable high spatial resolution combined with photometric accuracy of images from the Hubble Space Telescope have allowed us to probe further back into the history of star formation of a large variety of different galaxy types with widely differing star formation properties. We have learnt several important things about dwarf galaxy evolution from these studies. Firstly we have found that no two galaxies have identical star formation histories; some galaxies may superficially look the same today, but they have invariably followed different paths to this point. Now that we have managed to probe deep into the star formation history of dwarf irregular galaxies in the Local Group it is obvious that there are a number of similarities with the global properties of dwarf elliptical/spheroidal type galaxie...

  15. Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

    Science.gov (United States)

    Wheeler, Coral Rose

    2016-06-01

    The high dark matter content and the shallow potential wells of low mass galaxies (10^3 Msun 10 Gyr), having had their star formation shut down by reionization. Additionally, we show that the kinematics and ellipticities of isolated simulated dwarf centrals are consistent with observed dSphs satellites without the need for harassment from a massive host. We further show that most (but not all) observed *isolated* dIrrs in the Local Volume also have dispersion-supported stellar populations, contradicting the previous view that these objects are rotating. Finally, we investigate the stellar age gradients in dwarfs — showing that early mergers and strong feedback can create an inverted gradient, with the older stars occupying larger galactocentric radii.These results offer an interesting direction in testing models that attempt to solve dark matter problems via explosive feedback episodes. Can the same models that create large cores in simulated dwarfs preserve the mild stellar rotation that is seen in a minority of isolated dIrrs? Can the bursty star formation that created a dark matter core also match observed stellar gradients in low mass galaxies? Comparisons between our simulations and observed dwarfs should provide an important benchmark for this question going forward.

  16. The dynamical fingerprint of core scouring in massive elliptical galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Thomas, J.; Saglia, R. P.; Bender, R.; Erwin, P.; Fabricius, M., E-mail: jthomas@mpe.mpg.de [Max Planck-Institute for extraterrestrial Physics, P.O. Box 1312, Giessenbachstr. 1, D-85741 Garching (Germany)

    2014-02-10

    The most massive elliptical galaxies have low-density centers or cores that differ dramatically from the high-density centers of less massive ellipticals and bulges of disk galaxies. These cores have been interpreted as the result of mergers of supermassive black hole binaries, which depopulate galaxy centers by gravitationally slingshotting central stars toward large radii. Such binaries naturally form in mergers of luminous galaxies. Here, we analyze the population of central stellar orbits in 11 massive elliptical galaxies that we observed with the integral field spectrograph SINFONI at the European Southern Observatory Very Large Telescope. Our dynamical analysis is orbit-based and includes the effects of a central black hole, the mass distribution of the stars, and a dark matter halo. We show that the use of integral field kinematics and the inclusion of dark matter is important to conclude on the distribution of stellar orbits in galaxy centers. Six of our galaxies are core galaxies. In these six galaxies, but not in the galaxies without cores, we detect a coherent lack of stars on radial orbits in the core region and a uniform excess of radial orbits outside of it: when scaled by the core radius r{sub b} , the radial profiles of the classical anisotropy parameter β(r) are nearly identical in core galaxies. Moreover, they quantitatively match the predictions of black hole binary simulations, providing the first convincing dynamical evidence for core scouring in the most massive elliptical galaxies.

  17. Photometric properties of Local Volume dwarf galaxies

    CERN Document Server

    Sharina, M E; Dolphin, A E; Karachentseva, V E; Tully, R Brent; Karataeva, G M; Makarov, D I; Makarova, L N; Sakai, S; Shaya, E J; Nikolaev, E Yu; Kuznetsov, A N

    2007-01-01

    We present surface photometry and metallicity measurements for 104 nearby dwarf galaxies imaged with the Advanced Camera for Surveys and Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. In addition, we carried out photometry for 26 galaxies of the sample and for Sextans~B on images of the Sloan Digital Sky Survey. Our sample comprises dwarf spheroidal, irregular and transition type galaxies located within ~10 Mpc in the field and in nearby groups: M81, Centaurus A, Sculptor, and Canes Venatici I cloud. It is found that the early-type galaxies have on average higher metallicity at a given luminosity in comparison to the late-type objects. Dwarf galaxies with M_B > -12 -- -13 mag deviate toward larger scale lengths from the scale length -- luminosity relation common for spiral galaxies, h \\propto L^{0.5}_B. The following correlations between fundamental parameters of the galaxies are consistent with expectations if there is pronounced gas-loss through galactic winds: 1) between the luminosit...

  18. Massive Star Clusters in Dwarf Galaxies

    CERN Document Server

    Larsen, Soeren S

    2015-01-01

    Dwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%-25%, an order of magnitude higher than the 1%-2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their initial masses. More generally, the number of metal-poor field stars in these galaxies is today less than what would originally have been present in the form of low-mass clusters if the initial cluster mass function was a power-law extending down to low masses. This may imply that the initial GC mass function in these dwarf galaxies was significantly more top-heavy than typically observed in present-day star forming environments.

  19. Blue diffuse dwarf galaxies: a clearer picture

    Science.gov (United States)

    James, Bethan L.; Koposov, Sergey E.; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.; McQuinn, Kristen B. W.

    2017-03-01

    The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e. galaxies with population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ∼150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43 population synthesis models and estimated to be in the range log (M*/M⊙) ≃ 5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.

  20. A Study of Dwarf Galaxies in Five Rich Clusters II: A2218, CL0024+16, and MS1358+62

    Science.gov (United States)

    Riley, Seamus; Bruursema, J.; Ford, H. C.; Zekser, K. C.; Infante, L.; Postman, M.

    2008-05-01

    Dwarf galaxies play an important role in understanding galactic formation, cluster dynamics, and large scale structure. Although local dwarf populations have been well studied, dwarf galaxies outside the local supercluster remain relatively unexamined. Using ACS Investigation Definition Team data, we examine the dwarf galaxy populations of A1689 (z=0.1832), A1703 (z=0.2580), A2218 (z=0.1756), CL0024+16 (z=0.395), and MS1358+62 (z=0.328). We have modeled and subtracted the light from the brighter elliptical galaxies using the XVISTA subroutine SNUC. An assumption of concentric elliptical isophotes is made and the position angle, ellipticity, and brightness are fit using a nonlinear least-squares algorithm. The subtraction of the models reveals a population of dwarf galaxies usually hidden by the light of bright ellipticals. SExtractor and Bayesian Photometric Redshifts (BPZ) are used in order to identify cluster members. With the 0.05” per pixel resolution of ACS and a completeness of mF625 = 28 we are able to identify approximately 1000 dwarf galaxies candidates, defined as MF625 > -18, in all five clusters combined. We will discuss the results of this research including, but not limited to, dwarf galaxy luminosity functions, radial distribution, and the characteristics of dwarfs compared to those in other well studied clusters. ACS was developed under NASA contract NAS5-32865, and this research was supported by NASA grant NAG5-7697.

  1. Mergers of elliptical galaxies and the fundamental plane

    NARCIS (Netherlands)

    Gonzalez-Garcia, AC; van Albada, TS; AvilaReese,; Firmani, C; Frenk, CS; Allen, YC

    2003-01-01

    N-body simulations have been carried out in order to explore the final state of elliptical galaxies after encounters and more expecifically whether the Fundamental Plane (FP hereafter) relation is affected by merging.

  2. The influence of binary stars on dwarf spheroidal galaxy kinematics

    CERN Document Server

    Hargreaves, J C; Annan, J D

    1995-01-01

    We have completed a Monte-Carlo simulation to estimate the effect of binary star orbits on the measured velocity dispersion in dwarf spheroidal galaxies. This paper analyses previous attempts at this calculation, and explains the simulations which were performed with mass, period and ellipticity distributions similar to that measured for the solar neighbourhood. The conclusion is that with functions such as these, the contribution of binary stars to the velocity dispersion is small. The distributions are consistent with the percentage of binaries detected by observations, although this is quite dependent on the measuring errors and on the number of years over which measurements have been taken. For binaries to be making a significant contribution to the dispersion measured in dSph galaxies, the distributions of the orbital parameters would need to be very different from those of stars in the solar neighbourhood. In particular more smaller period orbits with higher mass secondaries would be required. The shape...

  3. AGB Connection and Ultraviolet Luminosity Excess in Elliptical Galaxies

    CERN Document Server

    Buzzoni, Alberto

    2008-01-01

    Relying on infrared surface brightness fluctuactions to trace AGB properties in a sample of elliptical galaxies in the Virgo and Fornax clusters, we assess the puzzling origin of the "UV-upturn" phenomenon, recently traced down to the presence of a hot horizontal branch stellar component. We find that the UV-upturn actually signals a profound change in the c-m diagram of stellar populations in elliptical galaxies, involving both the hot stellar component and red-giant evolution.

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

    Energy Technology Data Exchange (ETDEWEB)

    Sweet, Sarah M.; Drinkwater, Michael J. [School of Mathematics and Physics, University of Queensland, Qld 4072 (Australia); Meurer, Gerhardt; Bekki, Kenji [School of Physics, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Dopita, Michael A.; Nicholls, David C. [Research School of Astronomy and Astrophysics, Australian National University, Cotter Road, Weston ACT 2611 (Australia); Kilborn, Virginia, E-mail: sarah@sarahsweet.com.au [Swinburne University of Technology, Mail number H30, PO Box 218, Hawthorn, Victoria 3122 (Australia)

    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.

  5. Star formation history in forming dwarf galaxies

    Science.gov (United States)

    Berczik, P.; Kravchuk, S. G.

    The processes of formation and evolution of isolated dwarf galaxies over the Hubble timescale is followed by means of SPH techniques. As an initial protogalaxy perturbation we consider an isolated, uniform, solid -- body rotated sphere involved into the Hubble flow and made of dark and baryonic matter in a 10:1 ratio. The simulations are carried out for the set of models having spin parameters lambda in the range from 0.01 to 0.08 and the total mass of dark matter 1011 M_odot . Our model includes gasdynamics, radiative processes, star formation, supernova feedback and simplified chemistry. The application of modified star formation criterion which accounts for chaotic motions and the time lag between initial development of suitable conditions for star formation and star formation itself (Berczik P.P, Kravchuk S.G. 1997, Ap.Sp.Sci.) provides the realistic description of the process of galaxy formation and evolution. Two parameters: total mass and initial angular momentum of the dwarf protogalaxy play the crucial role in its star formation activity. After the 15 Gyr of the evolution the rapidly rotated dwarf galaxies manifest themselves as an extremly gasrich, heavy element deficient objects showing the initial burst of star formation activity in several spatially separated regions. Slowly rotating objects manifest themselves finally as typical evolved dwarf galaxies.

  6. Blue straggler stars in dwarf spheroidal galaxies

    NARCIS (Netherlands)

    Mapelli, M.; Ripamonti, E.; Tolstoy, E.; Sigurdsson, S.; Irwin, M. J.; Battaglia, G.

    2007-01-01

    Blue straggler star (BSS) candidates have been observed in all old dwarf spheroidal galaxies (dSphs), however whether or not they are authentic BSSs or young stars has been a point of debate. To both address this issue and obtain a better understanding of the formation of BSSs in different environme

  7. Investigating the Density of Isolated Field Elliptical Galaxies

    Science.gov (United States)

    Ulgen, E. Kaan

    2016-02-01

    In this thesis, 215.590 elliptical galaxies with M(r) ≤ -21 in the CFHTLS-W1 field which is covering 72 sq. deg on the sky are examined . Criterion given by Smith et al. (2004) has been used to determine isolated elliptical galaxies. 118 isolated elliptical galaxies have been determined in total. By using g, r and i photometric bands, the true-colour images of candidates are produced and visually inspected. In order to have a clean list of IfEs some candidates are excluded from the final sample after visual inspection. The final sample consists of 60 IfEs which corresponds to the 0.027 per cent of the whole sample. In other words, IfE density in the W1 is 0.8 IfE / sq.deg. Since the formation of the ellipticals in the isolated regions is not known clearly, it is crucial to determine IfEs and compare their photometric and morphological properties to the normal or cluster ellipticals. When the (g-i) distributions of three different elliptical galaxy class are compared, it is found that they have almost the same colours. When the redshift distributions of the galaxies are considered, it can be seen that IfEs formed later than the cluster and normal ellipticals. The average redshift of IfEs is determined as zphot=0.284, while for normal and cluster ellipticals, it is, respectively, 0.410 and 0.732. In addition, when the effective radii of the three elliptical systems are considered, it is found that the IfEs are bigger than the other two elliptical classes.

  8. Stellar ages and metallicities of nearby elliptical galaxies

    Institute of Scientific and Technical Information of China (English)

    Bai-Tian Tang; Qiu-Sheng Gu; Song Huang

    2009-01-01

    Stellar ages and metallicities are crucial for understanding the formation and evolution of elliptical galaxies.However,due to the age-metallicity degeneracy,it is hard to measure these two parameters accurately with broad-hand photometry.In this paper,we observed high-resolution spectra for a sample of 20 nearby elliptical galaxies (EGs) with the NAOC 2.16 m telescope,and determined stellar ages and metallicities by using the empirical population synthesis and Lick/IDS index system methods.We found that stellar ages from these two methods are consistent with each other for purely old EGs; however,stellar metallicities show a zeropoint offset of 0.5 Z_⊙.Our results confirm that stellar populations in low-density environment galaxies are more diverse compared to their high-density counterparts.We also investigated the element abundance-galaxy mass relation for nearby elliptical galaxies.

  9. A Study of Binary Stellar Population Synthesis of Elliptical Galaxies

    Institute of Scientific and Technical Information of China (English)

    Zhong-Mu Li; Feng-Hui Zhang; Zhan-Wen Han

    2006-01-01

    We determined the relative stellar ages and metallicities of about 80 elliptical galaxies in both low and high density environments using the latest binary stellar population (BSP) synthesis model and tested the predictions of a recent hierarchical formation model that adopted the new ACDM cosmology.The stellar ages and metallicities were estimated from two high-quality published spectra line indices, the Hβ and [MgFe] indices. The results show that the stellar populations of elliptical galaxies are older than 3.9 Gyr and more metal rich than 0.02. Most of our results are in agreement with the model predictions: (1) elliptical galaxies in denser environment are redder and have older populations than field galaxies; (2)elliptical galaxies with more massive stellar components are redder and have older and more metal rich populations than less massive ones; (3) the most massive galaxies have the oldest and most metal rich stars. However, some of our results differ from the model predictions on the metallicity distributions of low- and high-density elliptical galaxies and the dependence on the distance to the cluster center.

  10. HI Recycling Formation of Tidal Dwarf Galaxies

    CERN Document Server

    Duc, P A; Duc, Pierre-Alain; Brinks, Elias

    2000-01-01

    Galactic collisions trigger a number of phenomena, such as transportation inward of gas from distances of up to kiloparsecs from the center of a galaxy to the nuclear region, fuelling a central starburst or nuclear activity. The inverse process, the ejection of material into the intergalactic medium by tidal forces, is another important aspect and can be studied especially well through detailed HI observations of interacting systems which have shown that a large fraction of the gaseous component of colliding galaxies can be expelled. Part of this tidal debris might fall back, be dispersed throughout the intergalactic medium or recondense to form a new generation of galaxies: the so-called tidal dwarf galaxies. The latter are nearby examples of galaxies in formation. The properties of these recycled objects are reviewed here and different ways to identify them are reviewed.

  11. Satellite Dwarf Galaxies in a Hierarchical Universe: The Prevalence of Dwarf-Dwarf Major Mergers

    CERN Document Server

    Deason, Alis; Garrison-Kimmel, Shea

    2014-01-01

    Mergers are a common phenomenon in hierarchical structure formation, especially for massive galaxies and clusters, but their importance for dwarf galaxies in the Local Group remains poorly understood. We investigate the frequency of major mergers between dwarf galaxies in the Local Group using the ELVIS suite of cosmological zoom-in dissipationless simulations of Milky Way- and M31-like host halos. We find that ~10% of satellite dwarf galaxies with M_star > 10^6 M_sun that are within the host virial radius experienced a major merger of stellar mass ratio closer than 0.1 since z = 1, with a lower fraction for lower mass dwarf galaxies. Recent merger remnants are biased towards larger radial distance and more recent virial infall times, because most recent mergers occurred shortly before crossing within the virial radius of the host halo. Satellite-satellite mergers also occur within the host halo after virial infall, catalyzed by the large fraction of dwarf galaxies that fell in as part of a group. The merger ...

  12. The dynamical fingerprint of core scouring in massive elliptical galaxies

    CERN Document Server

    Thomas, J; Bender, R; Erwin, P; Fabricius, M

    2013-01-01

    The most massive elliptical galaxies have low density centers or cores that differ dramatically from the high-density centres of less massive ellipticals and bulges of disk galaxies. These cores have been interpreted as the result of mergers of supermassive black hole binaries, which depopulate galaxy centres by gravitationally slingshotting central stars towards large radii. Such binaries naturally form in mergers of luminous galaxies. Here we analyse the population of central stellar orbits in 11 massive elliptical galaxies that we observed with the integral-field spectrograph SINFONI at the ESO-VLT. Our dynamical analysis is orbit-based and includes the effects of a central black hole, the mass distribution of the stars and a dark-matter halo. We show that the use of integral-field kinematics and the inclusion of dark matter is important to conclude upon the distribution of stellar orbits in galaxy centers. Six of our galaxies are core galaxies. In these six galaxies, but not in the galaxies without cores,...

  13. Satellites and Haloes of Dwarf Galaxies

    CERN Document Server

    Sales, Laura V; White, Simon D M; Navarro, Julio F

    2012-01-01

    We study the abundance of satellite galaxies as a function of primary stellar mass using the SDSS/DR7 spectroscopic catalogue. In contrast with previous studies, which focussed mainly on bright primaries, our central galaxies span a wide range of stellar mass, 10^7.5 < M_*^pri/M_sun < 10^11, from dwarfs to central cluster galaxies. Our analysis confirms that the average number of satellites around bright primaries, when expressed in terms of satellite-to-primary stellar mass ratio (m_*^sat/M_*^pri), is a strong function of M_*^pri. On the other hand, satellite abundance is largely independent of primary mass for dwarf primaries (M_*^pri<10^10 M_sun). These results are consistent with galaxy formation models in the LCDM scenario. We find excellent agreement between SDSS data and semi-analytic mock galaxy catalogues constructed from the Millennium-II Simulation. Satellite galaxies trace dark matter substructure in LCDM, so satellite abundance reflects the dependence on halo mass, M_200, of both substru...

  14. An Overview of the Dwarf Galaxy Survey

    CERN Document Server

    Madden, S C; Galametz, M; Cormier, D; Lebouteiller, V; Galliano, F; Hony, S; Bendo, G J; Smith, M W L; Pohlen, M; Roussel, H; Sauvage, M; Wu, R; Sturm, E; Poglitsch, A; Contursi, A; Doublier, V; Baes, M; Barlow, M J; Boselli, A; Boquien, M; Carlson, L R; Ciesla, L; Cooray, A; Cortese, L; De Looze, I; Irwin, J A; Isaak, K; Kamenetzky, J; Karczewski, O L; Lu, N; MacHattie, J A; Halloran, B O; Parkin, T J; Rangwala, N; Schirm, M R P; Schulz, B; Spinoglio, L; Vaccari, M; Wilson, C D; Wozniak, H

    2013-01-01

    The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Zsun, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mic with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mic, [OI] 63 mic, [OI] 145 mic, [OIII] 88 mic, [NIII] 57 mic and [NII...

  15. White dwarf-red dwarf binaries in the Galaxy

    NARCIS (Netherlands)

    Besselaar, E.J.M. van den

    2007-01-01

    This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are

  16. Missing dark matter in dwarf galaxies?

    Science.gov (United States)

    Oman, Kyle A.; Navarro, Julio F.; Sales, Laura V.; Fattahi, Azadeh; Frenk, Carlos S.; Sawala, Till; Schaller, Matthieu; White, Simon D. M.

    2016-08-01

    We use cosmological hydrodynamical simulations of the APOSTLE project along with high-quality rotation curve observations to examine the fraction of baryons in ΛCDM haloes that collect into galaxies. This `galaxy formation efficiency' correlates strongly and with little scatter with halo mass, dropping steadily towards dwarf galaxies. The baryonic mass of a galaxy may thus be used to place a lower limit on total halo mass and, consequently, on its asymptotic maximum circular velocity. A number of observed dwarfs seem to violate this constraint, having baryonic masses up to 10 times higher than expected from their rotation speeds, or, alternatively, rotating at only half the speed expected for their mass. Taking the data at face value, either these systems have formed galaxies with extraordinary efficiency - highly unlikely given their shallow potential wells - or their dark matter content is much lower than expected from ΛCDM haloes. This `missing dark matter' is reminiscent of the inner mass deficit of galaxies with slowly rising rotation curves, but cannot be explained away by star formation-induced `cores' in the dark mass profile, since the anomalous deficit applies to regions larger than the luminous galaxies themselves. We argue that explaining the structure of these galaxies would require either substantial modification of the standard ΛCDM paradigm or else significant revision to the uncertainties in their inferred mass profiles, which should be much larger than reported. Systematic errors in inclination may provide a simple resolution to what would otherwise be a rather intractable problem for the current paradigm.

  17. Dissecting the morphological and spectroscopic properties of galaxies in the local Universe: I. Elliptical galaxies

    CERN Document Server

    Aguerri, J A L; Almeida, J Sánchez; Munoz-Tunon, C

    2012-01-01

    We revisit the scaling relations and star-forming histories of local elliptical galaxies using a novel selection method applied to the Sloan Digital Sky Survey DR7. We combine two probability-based automated spectroscopic and morphological classifications of about 600000 galaxies with z<0.25 to isolate true elliptical galaxies. Our sample selection method does not introduce artificial cuts in the parameters describing the galaxy but instead it associates to every object a weight measuring the probability of being in a given spectro-morphological class. Thus the sample minimizes the selection biases. We show that morphologically defined ellipticals are basically distributed in 3 spectral classes, which dominate at different stellar masses. The bulk of the population (about 50%) is formed by a well defined class of galaxies with old stellar populations that formed their stars at very early epochs in a short episode of star formation. They dominate the scaling relations of elliptical galaxies known from previ...

  18. Pulsar searches in nearby dwarf spheroidal galaxies

    Science.gov (United States)

    Rubio-Herrera, Eduardo; Maccarone, Thomas

    2013-03-01

    We have been undertaking a comprehensive survey for pulsars and fast radio transients in the dwarf spheroidal satellite galaxies of the Milky Way using the Green Bank Radio Telescope operating at a central frequency of 350 MHz. Our search pipeline allows the detection of periodical signals and single dispersed pulses and it is optimized to search for millisecond radio pulsars. Here we present preliminary results of the searches we have conducted in the Ursa Minoris, Draco and Leo I dwarf spheroidal satellite galaxies. Our searches have revealed no periodic signals but a few unconfirmed millisecond single pulses at various dispersion measures, possibly related to neutron stars. Detecting neutron stars in these systems can potentially help to test the existence of haloes of dark matter surrounding these systems as predicted by Dehnen & King (2006).

  19. Tests of Modified Gravity with Dwarf Galaxies

    CERN Document Server

    Jain, Bhuvnesh

    2011-01-01

    In modified gravity theories that seek to explain cosmic acceleration, dwarf galaxies in low density environments can be subject to enhanced forces. The class of scalar-tensor theories, which includes f(R) gravity, predict such a force enhancement (massive galaxies like the Milky Way can evade it through a screening mechanism that protects the interior of the galaxy from this "fifth" force). We study observable deviations from GR in the disks of late-type dwarf galaxies moving under gravity. The fifth-force acts on the dark matter and HI gas disk, but not on the stellar disk owing to the self-screening of main sequence stars. We find four distinct observable effects in such disk galaxies: 1. A displacement of the stellar disk from the HI disk. 2. Warping of the stellar disk along the direction of the external force. 3. Enhancement of the rotation curve measured from the HI gas compared to that of the stellar disk. 4. Asymmetry in the rotation curve of the stellar disk. We estimate that the spatial effects can...

  20. Dwarf Galaxies in the Coma Cluster: II. Spectroscopic and Photometric Fundamental Planes

    CERN Document Server

    Kourkchi, E; Carter, D; Mobasher, B

    2011-01-01

    We present a study of the fundamental plane, FP, for a sample of 71 dwarf galaxies in the core of Coma cluster in magnitude range $-21 < M_I <-15$. Taking advantage of high resolution DEIMOS spectrograph on Keck II for measuring the internal velocity dispersion of galaxies and high resolution imaging of HST/ACS, which allows an accurate surface brightness modeling, we extend the fundamental plane (FP) of galaxies to $\\sim$1 magnitude fainter luminosities than all the previous studies of the FP in Coma cluster. We find that, the scatter about the FP depends on the faint-end luminosity cutoff, such that the scatter increases for fainter galaxies. The residual from the FP correlates with the galaxy colour, with bluer galaxies showing larger residuals from FP. We find $M/L \\propto M^{-0.15\\pm0.22}$ in F814W-band indicating that in faint dwarf ellipticals, the $M/L$ ratio is insensitive to the mass. We find that less massive dwarf ellipticals are bluer than their brighter counterparts, possibly indicating on...

  1. The Unexpected Past of a Dwarf Galaxy

    Science.gov (United States)

    1996-08-01

    New Light on Cannibalism in the Local Group of Galaxies The Local Group of Galaxies consists of a few large spiral galaxies - for instance the Milky Way galaxy in which we live, and the Andromeda galaxy that is visible to the unaided eye in the northern constellation of the same name - as well as two dozen much smaller galaxies of mostly irregular shape. Whereas the larger galaxies have extended halos of very old stars, no such halos have ever been seen around the smaller ones. Now, however, Dante Minniti and Albert Zijlstra [1], working at the ESO 3.5-metre New Technology Telescope (NTT), have found a large halo of old and metal-poor stars around one of the dwarf galaxies in the Local Group. This finding is quite unexpected. It revises our understanding of star formation in these galaxies and provides important information about the past evolution of galaxies [2]. Galaxy halos The Milky Way galaxy is surrounded by a large, roughly spherical halo of old stars. The diameter is about 100,000 light years and the stars therein, known as Population II stars, are among the oldest known, with ages of 10 billion years or even more. They also differ from the younger stars nearer to the main plane of the Milky Way (in which our 4.7 billion year old Sun is located) by being very metal-poor. Many of the halo stars consist almost solely of hydrogen and helium, reflecting the composition of matter in the young Universe. This halo is important for our understanding of the processes that led to the formation of the Milky Way galaxy. It is believed that many of the halo stars and those of the same type found in globular clusters existed already before the Milky Way had fully formed. Galaxy cannibalism Many astronomers suspect that galaxies evolve and gradually grow larger and heavier by practising cannibalism on their own kind. In this picture, when two galaxies collide in space, the stars and nebulae in the smaller one will disperse and soon be taken over by the larger one, which

  2. PERSEUS I: A DISTANT SATELLITE DWARF GALAXY OF ANDROMEDA

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Nicolas F.; Laevens, Benjamin P. M. [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l' Université, F-67000 Strasbourg (France); Schlafly, Edward F.; Rix, Hans-Walter [Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany); Slater, Colin T.; Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States); Bernard, Edouard J.; Ferguson, Annette M. N. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Finkbeiner, Douglas P. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Burgett, William S.; Chambers, Kenneth C.; Hodapp, Klaus W.; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Morgan, Jeffrey S.; Tonry, John L. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Draper, Peter W.; Metcalfe, Nigel [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Price, Paul A., E-mail: nicolas.martin@astro.unistra.fr [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); and others

    2013-12-10

    We present the discovery of a new dwarf galaxy, Perseus I/Andromeda XXXIII, found in the vicinity of Andromeda (M31) in stacked imaging data from the Pan-STARRS1 3π survey. Located 27.°9 away from M31, Perseus I has a heliocentric distance of 785 ± 65 kpc, compatible with it being a satellite of M31 at 374{sub −10}{sup +14} kpc from its host. The properties of Perseus I are typical for a reasonably bright dwarf galaxy (M{sub V} = –10.3 ± 0.7), with an exponential half-light radius of r{sub h} = 1.7 ± 0.4 arcmin or r{sub h}=400{sub −85}{sup +105} pc at this distance, and a moderate ellipticity (ϵ=0.43{sub −0.17}{sup +0.15}). The late discovery of Perseus I is due to its fairly low surface brightness (μ{sub 0}=25.7{sub −0.9}{sup +1.0} mag arcsec{sup –2}), and to the previous lack of deep, high quality photometric data in this region. If confirmed to be a companion of M31, the location of Perseus I, far east from its host, could place interesting constraints on the bulk motion of the satellite system of M31.

  3. Dwarf Galaxies in the Coma Cluster: I. Velocity Dispersion Measurements

    CERN Document Server

    Kourkchi, E; Carter, D; Karick, A M; Mármol-Queraltó, E; Chiboucas, K; Tully, R B; Mobasher, B; Guzmán, R; Matković, A; Gruel, N

    2011-01-01

    We present the study of a large sample of early-type dwarf galaxies in the Coma cluster observed with DEIMOS on the Keck II to determine their internal velocity dispersion. We focus on a subsample of 41 member dwarf elliptical galaxies for which the velocity dispersion can be reliably measured, 26 of which were studied for the first time. The magnitude range of our sample is $-21

  4. Perseus I: A distant satellite dwarf galaxy of Andromeda

    CERN Document Server

    Martin, Nicolas F; Slater, Colin T; Bernard, Edouard J; Rix, Hans-Walter; Bell, Eric F; Ferguson, Annette M N; Finkbeiner, Douglas P; Laevens, Benjamin P M; Burgett, William S; Chambers, Kenneth C; Draper, Peter W; Hodapp, Klaus W; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A; Metcalfe, Nigel; Morgan, Jeffrey S; Price, Paul A; Tonry, John L; Wainscoat, Richard J; Waters, Christopher

    2013-01-01

    We present the discovery of a new dwarf galaxy, Perseus I/Andromeda XXXIII, found in the vicinity of Andromeda (M31) in stacked imaging data from the Pan-STARRS1 3{\\pi} survey. Located 27.9{\\deg} away from M31, Perseus I has a heliocentric distance of 785 +/- 65 kpc, compatible with it being a satellite of M31 at 374 +14/-10 kpc from its host. The properties of Perseus I are typical for a reasonably bright dwarf galaxy (M_V = -10.3 +/- 0.7), with an exponential half-light radius of r_h = 1.7 +/- 0.4 arcminutes or r_h = 400 +105/-85 pc at this distance, and a moderate ellipticity (\\epsilon = 0.43 +0.15/-0.17). The late discovery of Perseus I is due to its fairly low surface brightness (\\mu_0=25.7 +1.0/-0.9 mag/arcsec^2), and to the previous lack of deep, high quality photometric data in this region. If confirmed to be a companion of M31, the location of Perseus I, far east from its host, could place interesting constraints on the bulk motion of the satellite system of M31.

  5. Interpreting Central Surface Brightness and Color Profiles in Elliptical Galaxies

    Science.gov (United States)

    Silva, David R.; Wise, Michael W.

    1996-01-01

    Hubble Space Telescope imagery has revealed dust features in the central regions of many (50%--80%) nearby bright elliptical galaxies. If these features are an indication of an underlying smooth diffuse dust distribution, then the interpretation of central surface brightness and color profiles in elliptical galaxies becomes significantly more difficult. In this Letter, diagnostics for constraining the presence of such an underlying central dust distribution are presented. We show that easily detectable central color gradients and flattened central surface brightness profiles can be induced by even small amounts of smoothly distributed dust (~100 M⊙). Conversely, combinations of flat surface brightness profiles and flat color gradients or steep surface brightness profiles and steep color gradients are unlikely to be caused by dust. Taken as a whole, these results provide a simple observational tautology for constraining the existence of smooth diffuse dust distributions in the central regions of elliptical galaxies.

  6. Origin of the colour-magnitude relation of elliptical galaxies

    CERN Document Server

    Kodama, T; Kodama, Tadayuki; Arimoto, Nobuo

    1996-01-01

    Evolutionary models of elliptical galaxies are constructed by using a new population synthesis code. Model parameters are calibrated to reproduce the observed colour-magnitude (CM) relation of Coma ellipticals in $V-K$ vs. $M_{V}$ diagram. The SEDs are degenerated in stellar age and metallicity. An attempt is performed to break this degeneracy, by simulating evolution of the CM relation of elliptical galaxies, based on the two alternative interpretations; i.e., the CM relation reflects different mean stellar age or various stellar metallicity. A confrontation with the CM diagrams of E/S0 galaxies in the two distant clusters Abell 2390 ($z=0.228$) and Abell 851 ($z=0.407$) reinsures previous contentions that the CM relation is primarily a metallicity effect. This conclusion does not depend either on the model parameters, or on the cosmological parameters adopted.

  7. On the Assembly of Dwarf Galaxies in Clusters and their Efficient Formation of Globular Clusters

    CERN Document Server

    Mistani, Pouria A; Pillepich, Annalisa; Sanchez-Janssen, Ruben; Vogelsberger, Mark; Nelson, Dylan; Rodriguez-Gomez, Vicente; Torrey, Paul; Hernquist, Lars

    2015-01-01

    Galaxy clusters contain a large population of low mass dwarf elliptical galaxies whose exact origin is unclear: their colors, structural properties and kinematics differ substantially from those of dwarf irregulars in the field. We use the Illustris cosmological simulation to study differences in the assembly paths of dwarf galaxies (3e8 < M_*/M_sun < 1e10) according to their environment. We find that cluster dwarfs achieve their maximum total and stellar mass on average ~ 8 and ~ 4.5 Gyr ago, respectively, around the time of infall into the clusters. In contrast, field dwarfs not subjected to environmental stripping, reach their maximum mass at redshift z = 0. This different assembly history naturally produces a color bimodality, with blue isolated dwarfs and redder cluster dwarfs exhibiting negligible star-formation today. The cessation of star formation happens over median times 3.5-5 Gyr depending on stellar mass, and shows a large scatter (~ 1-8 Gyr), with the lower values associated with starburst...

  8. Global HI Kinematics in Dwarf Galaxies

    CERN Document Server

    Stilp, Adrienne M; Warren, Steven R; Skillman, Evan; Ott, Juergen; Koribalski, Baerbel

    2013-01-01

    HI line widths are typically interpreted as a measure of ISM turbulence, which is potentially driven by star formation. In an effort to better understand the possible connections between line widths and star formation, we have characterized \\hi{} kinematics in a sample of nearby dwarf galaxies by co-adding line-of-sight spectra after removing the rotational velocity to produce an average, global \\hi{} line profile. These "superprofiles" are composed of a central narrow peak (~6-10 km/s) with higher-velocity wings to either side that contain ~10-15% of the total flux. The superprofiles are all very similar, indicating a universal global HI profile for dwarf galaxies. We compare characteristics of the superprofiles to various galaxy properties, such as mass and measures of star formation (SF), with the assumption that the superprofile represents a turbulent peak with energetic wings to either side. We use these quantities to derive average scale heights for the sample galaxies. When comparing to physical proper...

  9. Dwarf Galaxies in Voids: Dark Matter Halos and Gas Cooling

    CERN Document Server

    Hoeft, Matthias

    2010-01-01

    Galaxy surveys have shown that luminous galaxies are mainly distributed in large filaments and galaxy clusters. The remaining large volumes are virtually devoid of luminous galaxies. This is in concordance with the formation of the large-scale structure in Universe as derived from cosmological simulations. However, the numerical results indicate that cosmological voids are abundantly populated with dark matter haloes which may in principle host dwarf galaxies. Observational efforts have in contrast revealed, that voids are apparently devoid of dwarf galaxies. We investigate the formation of dwarf galaxies in voids by hydrodynamical cosmological simulations. Due to the cosmic ultra-violet background radiation low-mass haloes show generally are reduced baryon fraction. We determine the characteristic mass below which dwarf galaxies are baryon deficient. We show that the circular velocity below which the accretion of baryons is suppressed is approximately 40 km/s. The suppressed baryon accretion is caused by the...

  10. Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and Outstanding Issues

    CERN Document Server

    Kormendy, John

    2015-01-01

    This is the summary chapter of a review book on galaxy bulges. Bulge properties and formation histories are more varied than those of ellipticals. I emphasize two advances: 1 - "Classical bulges" are observationally indistinguishable from ellipticals, and like them, are thought to form by major galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming (except in S0s) than are ellipticals. Theys are products of the slow ("secular") evolution of galaxy disks: bars and other nonaxisymmetries move disk gas toward the center, where it starbursts and builds relatively flat, rapidly rotating components. This secular evolution is a new area of galaxy evolution work that complements hierarchical clustering. 2 - Disks of high-redshift galaxies are unstable to the formation of mass clumps that sink to the center and merge - an alternative channel for the formation of classical bulges. I review successes and unsolved problems in the formation of bulges+ellipticals and their coevolution (or not) with...

  11. POSSIBLE SOURCES OF UV RADIATION IN ELLIPTICAL GALAXIES

    Directory of Open Access Journals (Sweden)

    F. C. Hernández

    2009-01-01

    Full Text Available We have compiled a sample of 519 nearby (z < 0:13 elliptical galaxies, selected by matching the Galaxy Evolution Explorer (GALEX Medium Imaging Survey (MIS with the Sloan Digital Sky Survey (SDSS Fourth Data Release (DR4. Our galaxies are bright, with r < 16:8 and have FUV (far ultraviolet an NUV (near ultraviolet emission. We build a UV Color Magnitude Relation (CMR using GALEX and SDSS photometric bands, and analyze the evolution of this CMR for these galaxies using stellar population synthesis models. We nd that these galaxies may have su ered a small amount of recent residual star formation (1{2% of the galaxy mass. Extreme Horizontal Branch (EHB stars can explain galaxies with 4 < NUV- r < 5:4.

  12. Dwarf Galaxies in Voids: Dark Matter Halos and Gas Cooling

    Directory of Open Access Journals (Sweden)

    Matthias Hoeft

    2010-01-01

    Full Text Available Galaxy surveys have shown that luminous galaxies are mainly distributed in large filaments and galaxy clusters. The remaining large volumes are virtually devoid of luminous galaxies. This is in concordance with the formation of the large-scale structure in the universe as derived from cosmological simulations. However, the numerical results indicate that cosmological voids are abundantly populated with dark matter haloes which may in principle host dwarf galaxies. Observational efforts have in contrast revealed that voids are apparently devoid of dwarf galaxies. We investigate the formation of dwarf galaxies in voids by hydrodynamical cosmological simulations. Due to the cosmic ultraviolet background radiation low-mass haloes show generally a reduced baryon fraction. We determine the characteristic mass below which dwarf galaxies are baryon deficient. We show that the circular velocity below which the accretion of baryons is suppressed is approximately 40 kms−1. The suppressed baryon accretion is caused by the photo-heating due to the UV background. We set up a spherical halo model and show that the effective equation of the state of the gas in the periphery of dwarf galaxies determines the characteristic mass. This implies that any process which heats the gas around dwarf galaxies increases the characteristic mass and thus reduces the number of observable dwarf galaxies.

  13. The Faint Globular Cluster in the Dwarf Galaxy Andromeda I

    Science.gov (United States)

    Caldwell, Nelson; Strader, Jay; Sand, David J.; Willman, Beth; Seth, Anil C.

    2017-09-01

    Observations of globular clusters in dwarf galaxies can be used to study a variety of topics, including the structure of dark matter halos and the history of vigorous star formation in low-mass galaxies. We report on the properties of the faint globular cluster (M V -3.4) in the M31 dwarf galaxy Andromeda I. This object adds to the growing population of low-luminosity Local Group galaxies that host single globular clusters.

  14. The Isolated Elliptical NGC 1132 Evidence For a Merged Group of Galaxies?

    CERN Document Server

    Mulchaey, J S; Mulchaey, John S.; Zabludoff, Ann I.

    1999-01-01

    Numerical simulations predict that some poor groups of galaxies have merged by the present epoch into giant ellipticals (cf. Barnes 1989). To identify the possible remnants of such mergers, we have compiled a sample of nearby, isolated ellipticals (Colbert, Mulchaey, & Zabludoff 1998). ASCA observations of the first galaxy studied, NGC 1132 reveal an X-ray halo that extends out to at least 250 kpc. The temperature, metallicity and luminosity of NGC 1132's X-ray halo are comparable to those of poor group halos. The total mass inferred from the X-ray emission is also like that of an X-ray detected group. Optical imaging uncovers a dwarf galaxy population clustered about NGC 1132 that is consistent in number density and in projected radial distribution with that of an X-ray group. The similarities of NGC 1132 to poor groups in both the X-ray band and at the faint end of the galaxy luminosity function, combined with the deficit of luminous galaxies in the NGC 1132 field, are compatible with the merged group p...

  15. The Alignment of Red-Sequence Dwarf Galaxies

    Science.gov (United States)

    Archer, Haylee; Barkhouse, Wayne; Burgad, Jaford; Foote, Gregory; Rude, Cody; Lopez-Cruz, Omar

    2015-01-01

    The alignment of cluster galaxies has been used to determine the impact of the high-density environment on the evolution of galaxies. We have undertaken a study to measure the alignment of cluster dwarf galaxies based on a sample of 57 low-redshift Abell clusters imaged at KPNO using the 0.9-meter telescope. To supplement our KPNO sample, we have included an additional 64 low-redshift clusters from the WINGS dataset. From the combined cluster sample (121 clusters), we have selected cluster dwarf galaxies based on their position relative to the cluster red-sequence. We present our preliminary results based on the alignment of the dwarf galaxies with: 1) the major axis of the brightest cluster galaxy, 2) the major axis of the cluster defined by position of the cluster members, and 3) a radius vector pointing from the cluster center to the dwarf galaxy.

  16. The redshift evolution of the stellar populations in elliptical galaxies

    CERN Document Server

    Bender, R; Bruzual, A G; Bender, Ralf; Ziegler, Bodo; Bruzual, Gustavo

    1996-01-01

    Velocity dispersions \\sigma and Mg absorption line-strengths Mg_b have been measured for a sample of 16 ellipticals in 3 clusters at a redshift of 0.37. Like local cluster ellipticals, these objects show a correlation between Mg_b and \\sigma. However, at any given \\sigma, the mean Mg_b of the ellipticals at z=0.37 is weaker than the mean Mg_b of their local relatives in the Coma and Virgo clusters. The Mg_b weakening is smallest for the most luminous ellipticals and larger for the fainter objects. This is unambiguous evidence for {\\it small but significant passive evolution} of the stellar populations of elliptical galaxies with redshift. It requires that the bulk of the stars in cluster ellipticals has formed at z>2. The most luminous objects may even have formed at z>4. The Mg_b-\\sigma test is a very reliable estimator for the evolution of old stellar populations because it is virtually independent from the stellar initial mass function (IMF) and from the metallicities of the galaxies. Furthermore, the infl...

  17. Formation of Isolated Dwarf Galaxies with Feedback

    CERN Document Server

    Sawala, Till; White, Simon D M

    2009-01-01

    We present results of high resolution hydrodynamical simulations of the formation and evolution of dwarf spheroidal galaxies. Our simulations start from cosmological initial conditions at high redshift. They include metal-dependent cooling, star formation, feedback from type II and type Ia supernovae and UV background radiation, with sub-grid recipes identical to those applied in a previous study of Milky Way type galaxies. We find that a combination of feedback and the cosmic UV background is necessary to explain the properties of dwarf spheroidal galaxies in isolation, and that their effect is strongly moderated by the depth of the gravitational potential. Taking this into account, our models naturally reproduce the observed luminosities and metallicities. The final objects have halo masses between 2.3*10^8 and 1.1*10^9 solar masses, mean velocity dispersions between 6.5 and 9.7 kms^-1, stellar masses ranging from 5*10^5 to 1.2*10^7 solar masses, median metallicities between [Fe/H] = -1.8 and -1.1, and half...

  18. GLOBAL H I KINEMATICS IN DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Stilp, Adrienne M.; Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Warren, Steven R.; Skillman, Evan [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455 (United States); Ott, Juergen [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Koribalski, Baerbel [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)

    2013-03-10

    H I line widths are typically interpreted as a measure of interstellar medium turbulence, which is potentially driven by star formation (SF). In an effort to better understand the possible connections between line widths and SF, we have characterized H I kinematics in a sample of nearby dwarf galaxies by co-adding line-of-sight spectra after removing the rotational velocity to produce average global H I line profiles. These ''superprofiles'' are composed of a central narrow peak ({approx}6-10 km s{sup -1}) with higher-velocity wings to either side that contain {approx}10%-15% of the total flux. The superprofiles are all very similar, indicating a universal global H I profile for dwarf galaxies. We compare characteristics of the superprofiles to various galaxy properties, such as mass and measures of SF, with the assumption that the superprofile represents a turbulent peak with energetic wings to either side. We use these quantities to derive average scale heights for the sample galaxies. When comparing to physical properties, we find that the velocity dispersion of the central peak is correlated with ({Sigma}{sub HI}). The fraction of mass and characteristic velocity of the high-velocity wings are correlated with measures of SF, consistent with the picture that SF drives surrounding H I to higher velocities. While gravitational instabilities provide too little energy, the SF in the sample galaxies does provide enough energy through supernovae, with realistic estimates of the coupling efficiency, to produce the observed superprofiles.

  19. Dwarf satellite galaxies in the modified dynamics

    CERN Document Server

    Milgrom, M

    2000-01-01

    In the modified dynamics (MOND) the inner workings of dwarf satellites can be greatly affected by their mother galaxy-over and beyond its tidal effects. Because of MOND's nonlinearity a system's internal dynamics can be altered by an external field in which it is immersed (even when this field, by itself, is constant in space). As a result, the size and velocity dispersion of the satellite vary as the external field varies along its orbit. A notable outcome of this is a substantial increase in the dwarf's vulnerability to eventual tidal disruption-rather higher than Newtonian dynamics (with a dark-matter halo) would lead us to expect for a satellite with given observed parameters.

  20. Accretion phenomena in nearby star-forming dwarf galaxies

    Science.gov (United States)

    Annibali, F.; Tosi, M.; Aloisi, A.; Bellazzini, M.; Buzzoni, A.; Cignoni, M.; Ciotti, L.; Cusano, F.; Nipoti, C.; Sacchi, E.; Paris, D.; Romano, D.

    2017-03-01

    We present two pilot studies for the search and characterization of accretion events in star-forming dwarf galaxies. Our strategy consists of two complementary approaches: i) the direct search for stellar substructures around dwarf galaxies through deep wide-field imaging, and ii) the characterization of the chemical properties in these systems up to large galacto-centric distances. We show our results for two star-forming dwarf galaxies, the starburst irregular NGC 4449, and the extremely metal-poor dwarf DDO 68.

  1. FINDING DWARF GALAXIES FROM THEIR TIDAL IMPRINTS

    Energy Technology Data Exchange (ETDEWEB)

    Chakrabarti, Sukanya [Physics Department, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431 (United States); Bigiel, Frank [Institut fuer Theoretische Astrophysik, Universitaet Heidelberg Albert-Ueberle Str. 2 69120 Heidelberg (Germany); Chang, Philip [Physics Department, University of Wisconsin-Milwaukee, P.O. Box 413, 2200 E. Kenwood Blvd., Milwaukee, WI 53201-0413 (United States); Blitz, Leo, E-mail: schakra1@fau.edu, E-mail: chang65@uwm.edu [Astronomy Department, UC Berkeley, 601 Campbell Hall, Berkeley, CA 94720 (United States)

    2011-12-10

    We describe ongoing work on a new method that allows one to approximately determine the mass and relative position (in galactocentric radius and azimuth) of galactic companions purely from analysis of observed disturbances in gas disks. We demonstrate the validity of this method, which we call Tidal Analysis, by applying it to local spirals with known optical companions, namely M51 and NGC 1512. These galaxies span the range from having a very low mass companion ({approx}one-hundredth the mass of the primary galaxy) to a fairly massive companion ({approx}one-third the mass of the primary galaxy). This approach has broad implications for many areas of astrophysics-for the indirect detection of dark matter (or dark-matter-dominated dwarf galaxies), and for galaxy evolution in its use to decipher the dynamical impact of satellites on galactic disks. Here, we provide a proof of principle of the method by applying it to infer and quantitatively characterize optically visible galactic companions of local spirals, from the analysis of observed disturbances in outer gas disks.

  2. Blue diffuse dwarf galaxies: a clearer picture

    CERN Document Server

    James, Bethan L; Stark, Daniel P; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W; McQuinn, Kristen B W

    2016-01-01

    The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e., galaxies with <1/10 solar metallicity. However, due to the bright emission line based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014 we reoriented this search using only morphological properties and uncovered a population of ~150 `blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their SDSS photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43<12+log(O/H)<8.01), with ~20% of our sample classified as being XMP galaxies, and find they are actively forming stars at rates ...

  3. Star formation in proto dwarf galaxies

    Science.gov (United States)

    Noriega-Crespo, A.; Bodenheimer, P.; Lin, D. N. C.; Tenorio-Tagle, G.

    1990-01-01

    The effects of the onset of star formation on the residual gas in primordial low-mass Local-Group dwarf spheroidal galaxies is studied by a series of hydrodynamical simulations. The models have concentrated on the effect of photoionization. The results indicate that photoionization in the presence of a moderate gas density gradient can eject most of the residual gas on a time scale of a few 10 to the 7th power years. High central gas density combined with inefficient star formation, however, may prevent mass ejection. The effect of supernova explosions is discussed briefly.

  4. Spitzer Observations of Tidal Dwarf Galaxies

    CERN Document Server

    Higdon, Sarah J U

    2007-01-01

    We present Spitzer observations of Tidal Dwarf Galaxies (TDGs) in three interacting systems: NGC 5291, Arp105 and Stephan's Quintet. The spectra show bright emission from polyaromatic hydrocarbons (PAHs), nebular lines and warm molecular hydrogen, characteristic of recent episodes of star formation. The PAH emission that falls in the IRAC 8.0 micron band leads to the TDGs having an extremely red IRAC color, with [4.5] - [8.0] > 3. The emission from PAHs is characterized by a model with mainly neutral 100-C PAH atoms.

  5. The Cores of Elliptical Galaxies in Coma

    Science.gov (United States)

    Lucey, John

    1995-07-01

    The cores of galaxies are astrophysically unique. They canhost high energy nuclei, star formation and perhaps even blackholes. HST observations have established that the cores ofellipticals are related to their global properties, and so canbe used as diagnostics of the physical processes occurring atthe time of formation. HST images of galaxy cores havedistinguished two different types of core luminosity profiles:`soft' and `hard' types. It is suggested that luminous, slowlyrotating galaxies have `soft' cores and the less luminousdisky galaxies have `hard' cores. This can be interpreted interms of a formation scenario based on a merger hierarchy inwhich the low luminosity systems experience highly dissipativemergers, but as the luminous systems are assembled the mergersbecome increasingly stellar. In this picture, the type of corea galaxy generates is intimately related to its evolutionaryhistory, i.e. the degree of interaction/merging experiencedand the availability of cold gas. In turn, this should notonly depend on luminosity but also on the galaxy's localenvironment. Here we propose to test the gaseous/stellarmerger picture by imaging a set of Coma cluster ellipticalsfrom a wide range of cluster radii. In the gas poorenvironment of the cluster core there may be insufficent coldgas for the low luminosity galaxies to form `hard' cores.Similarly, at the cluster turnround radius even luminousgalaxies may have experienced a dissipative core formation andpossess

  6. Morphology of Dwarf Galaxies in Isolated Satellite Systems

    Science.gov (United States)

    Ann, Hong Bae

    2017-08-01

    The environmental dependence of the morphology of dwarf galaxies in isolated satellite systems is analyzed to understand the origin of the dwarf galaxy morphology using the visually classified morphological types of 5836 local galaxies with z ≲ 0.01. We consider six sub-types of dwarf galaxies, dS0, dE, dE_{bc}, dSph, dE_{blue}, and dI, of which the first four sub-types are considered as early-type and the last two as late-type. The environmental parameters we consider are the projected distance from the host galaxy (r_{p}), local and global background densities, and the host morphology. The spatial distributions of dwarf satellites of early-type galaxies are much different from those of dwarf satellites of late-type galaxies, suggesting the host morphology combined with r_{p} plays a decisive role on the morphology of the dwarf satellite galaxies. The local and global background densities play no significant role on the morphology of dwarfs in the satellite systems hosted by early-type galaxies. However, in the satellite system hosted by late-type galaxies, the global background densities of dE and dSph satellites are significantly different from those of dE_{bc}, dE_{blue}, and dI satellites. The blue-cored dwarf satellites (dE_{bc}) of early-type galaxies are likely to be located at r_{p} > 0.3 Mpc to keep their cold gas from the ram pressure stripping by the hot corona of early-type galaxies. The spatial distribution of dE_{bc} satellites of early-type galaxies and their global background densities suggest that their cold gas is intergalactic material accreted before they fall into the satellite systems.

  7. Lost and found dark matter in elliptical galaxies.

    Science.gov (United States)

    Dekel, A; Stoehr, F; Mamon, G A; Cox, T J; Novak, G S; Primack, J R

    2005-09-29

    There is strong evidence that the mass of the Universe is dominated by dark matter, which exerts gravitational attraction but whose exact nature is unknown. In particular, all galaxies are believed to be embedded in massive haloes of dark matter. This view has recently been challenged by the observation of surprisingly low random stellar velocities in the outskirts of ordinary elliptical galaxies, which has been interpreted as indicating a lack of dark matter. Here we show that the low velocities are in fact compatible with galaxy formation in dark-matter haloes. Using numerical simulations of disk-galaxy mergers, we find that the stellar orbits in the outer regions of the resulting ellipticals are very elongated. These stars were torn by tidal forces from their original galaxies during the first close passage and put on outgoing trajectories. The elongated orbits, combined with the steeply falling density profile of the observed tracers, explain the observed low velocities even in the presence of large amounts of dark matter. Projection effects when viewing a triaxial elliptical can lead to even lower observed velocities along certain lines of sight.

  8. The Dragonfly Nearby Galaxies Survey. II. Ultra-Diffuse Galaxies near the Elliptical Galaxy NGC 5485

    Science.gov (United States)

    Merritt, Allison; van Dokkum, Pieter; Danieli, Shany; Abraham, Roberto; Zhang, Jielai; Karachentsev, I. D.; Makarova, L. N.

    2016-12-01

    We present the unexpected discovery of four ultra-diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of 10″-38″ and central surface brightnesses of 25.6-27.7 mag arcsec-2 in the g-band. We subsequently obtained follow-up observations with HST to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of HST/ACS, which implies distances of D\\gt 17.5 Mpc. We show that the galaxies are most likely associated with a background group at ˜27 Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of 2.6-4.9 kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo, and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonstrates that the UDG phenomenon is not exclusive to cluster environments. Furthermore, their morphologies seem less regular than those of the cluster populations, which may suggest a different formation mechanism or be indicative of a threshold in surface density below which UDGs are unable to maintain stability.

  9. The Dragonfly Nearby Galaxies Survey. II. Ultra diffuse galaxies near the elliptical galaxy NGC 5485

    CERN Document Server

    Merritt, Allison; Danieli, Shany; Abraham, Roberto; Zhang, Jielai; Karachentsev, I D; Makarova, L N

    2016-01-01

    We present the unexpected discovery of four ultra diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of $10"-38"$ and central surface brightnesses of $25.6-27.7$ mag arcsec$^{-2}$ in g-band. We subsequently obtained follow-up observations with $HST$ to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of $HST$/ACS, which implies distances of $D > 17.5$ Mpc. We show that the galaxies are most likely associated with a background group at $\\sim 27$ Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of $2.6-4.9$ kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonst...

  10. Dark Matter Deprivation in Field Elliptical Galaxy NGC 7507

    CERN Document Server

    Lane, Richard R; Richtler, Tom

    2014-01-01

    Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of LCDM cosmologies, all galaxies should have a large dark matter component. We use penalised pixel fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling we produce best fit models to the velocity dispersion. We find that NGC 7507 has a two component stellar halo, with the outer halo and inner haloes counter rotating. The velocity dispersion profile exhibits an increase at ~70" (~7.9 kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy which include ~100 times less dark matter than predicted by LCDM, although mildly anisotropic models that are completely dark matter free fit almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at a...

  11. Cold gas in group-dominant elliptical galaxies

    CERN Document Server

    O'Sullivan, E; Hamer, S; Salomé, P; Babul, A; Raychaudhury, S

    2014-01-01

    We present IRAM 30m telescope observations of the CO(1-0) and (2-1) lines in a sample of 11 group-dominant elliptical galaxies selected from the CLoGS nearby groups sample. Our observations confirm the presence of molecular gas in 4 of the 11 galaxies at >4sigma significance, and combining these with data from the literature we find a detection rate of 43+-14%, significantly higher than for the wider population of elliptical galaxies, and comparable to the detection rate for nearby radio galaxies. Those group-dominant galaxies which are detected typically contain ~2x10^8 Msol of molecular gas, and although most have low star formation rates (<1 Msol/yr) they have short depletion times, indicating that the gas must be replenished on timescales ~10^8 yr. Almost all of the galaxies contain active nuclei, and we note that while CO detections are more common in the most radio-loud galaxies, the mass of molecular gas required to power the active nuclei through accretion is small compared to the masses observed. ...

  12. The Carnegie-Irvine Galaxy Survey. III. The Three-Component Structure of Nearby Elliptical Galaxies

    CERN Document Server

    Huang, Song; Peng, Chien Y; Li, Zhao-Yu; Barth, Aaron J

    2012-01-01

    Motivated by recent developments in our understanding of the formation and evolution of massive galaxies, we explore the detailed photometric structure of a representative sample of 94 bright, nearby elliptical galaxies, using high-quality optical images from the Carnegie-Irvine Galaxy Survey. The sample spans a range of environments and stellar masses, from M* = 10^{10.2} to 10^{12.0} solar mass. We exploit the unique capabilities of two-dimensional image decomposition to explore the possibility that local elliptical galaxies may contain photometrically distinct substructure that can shed light on their evolutionary history. Compared with the traditional one-dimensional approach, these two-dimensional models are capable of consistently recovering the surface brightness distribution and the systematic radial variation of geometric information at the same time. Contrary to conventional perception, we find that the global light distribution of the majority (>75%) of elliptical galaxies is not well described by ...

  13. The Size Evolution of Elliptical Galaxies

    CERN Document Server

    Xie, Lizhi; Cooper, Andrew P; Frenk, Carlos S; Li, Ran; Gao, Liang

    2014-01-01

    Recent work has suggested that the amplitude of the size mass relation of massive early type galaxies evolves with redshift. Here we use a semi-analytical galaxy formation model to study the size evolution of massive early type galaxies. We find this model is able to reproduce the amplitude of present day amplitude and slope of the relation between size and stellar mass for these galaxies, as well as its evolution. The amplitude of this relation reflects the typical compactness of dark halos at the time when most of the stars are formed. This link between size and star formation epoch is propagated in galaxy mergers. Mergers of high or moderate mass ratio (less than 1:3) become increasingly important with increasing present day stellar mass for galaxies more massive than $10^{11.4}M_{\\odot}$. At lower masses, low mass ratio mergers play a more important role. In situ star formation contribute more to the size growth than it does to stellar mass growth. We also find that, for ETGs identified at $z=2$, minor me...

  14. Testing modified gravity with dwarf spheroidal galaxies

    Science.gov (United States)

    Haghi, Hosein; Amiri, Vahid

    2016-12-01

    The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light (M*/L) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion (σlos) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant M*/L ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters α and μ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The H I Nearby Galaxy Survey catalogue of galaxies. We find that the derived M*/L ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of the dSph with reasonable M*/L values, we must vary α and μ on a case by case basis. A common pair of values cannot be found for all dSphs. Comparing with the values found from rotation curve fitting, it appears that μ correlates strongly with galaxy luminosity, shedding doubt on it as a universal constant.

  15. Simulating Compact Elliptical Galaxy Formation by Tidal Stripping for Comparison to the RESOLVE Survey

    Science.gov (United States)

    Ray, Christine; Snyder, Elaine M.; Kannappan, Sheila; Sinha, Manodeep; RESOLVE Team

    2016-01-01

    Observations of compact elliptical galaxies (cEs) have uncovered abnormally high velocity dispersions and surface brightnesses for objects of their mass. These properties indicate that they may be the tidally stripped remnants of larger disk galaxies. We test this tidal stripping scenario using N-body simulations of cE formation with the Gadget-2 code. We track the velocity dispersions of stellar particles within the half-light radius throughout our simulations, which allows us to compare our simulated galaxies with velocity dispersion data for cEs in the RESOLVE survey. We first consider initial conditions similar to published work, which report stripping of a large spiral galaxy (stellar mass ~ 10^11 solar masses) to cE size in a cluster potential. We find that the density of the disk galaxy is too high to allow it to lose particles to the less dense cluster. We argue that the initial position of the galaxy with respect to the cluster as well as the large size of the cluster particles in comparison to the size of the galaxy particles artificially heightened the stripping percentages reported in previous work. We hypothesize that only a dwarf galaxy with a shallower density profile can be stripped to cE size, and we present initial efforts to test this idea. We simulate a dwarf galaxy based on a real system in the RESOLVE survey, with stellar mass 10^9 solar masses and half-light radius 1.15 kpc. Within ~700 pc our dwarf is denser than our cluster, suggesting the stripped remnant should be close to the size of RESOLVE cEs. This radius contains approximately 13% of the total stellar mass of the galaxy, or ~2 x 10^8 solar masses. We therefore expect our stripped remnant to be at least this massive, although the impact parameter of the orbit will determine how much mass is actually removed. We discuss the position of our simulated galaxies compared to RESOLVE cEs in the velocity dispersion vs. mass plane. This research has been supported by National Science

  16. Cores in Dwarf Galaxies from Fermi Repulsion

    CERN Document Server

    Randall, Lisa; Unwin, James

    2016-01-01

    We show that Fermi repulsion can lead to cored density profiles in dwarf galaxies for sub-keV fermionic dark matter. We treat the dark matter as a quasi-degenerate self-gravitating Fermi gas and calculate its density profile assuming hydrostatic equilibrium. We find that suitable dwarf galaxy cores of larger than 130 pc can be achieved for fermion dark matter with mass in the range 70 eV - 400 eV. While in conventional dark matter scenarios, such sub-keV thermal dark matter would be excluded by free streaming bounds, the constraints are ameliorated in models with dark matter at lower temperature than conventional thermal scenarios, such as the Flooded Dark Matter model that we have previously considered. Modifying the arguments of Tremaine and Gunn we derive a conservative lower bound on the mass of fermionic dark matter of 70 eV and a stronger lower bound from Lyman-$\\alpha$ clouds of about 470 eV, leading to slightly smaller cores than have been observed. We comment on this result and how the tension is rel...

  17. Outliers from the Mass--Metallicity Relation I: A Sample of Metal-Rich Dwarf Galaxies from SDSS

    CERN Document Server

    Peeples, Molly S; Stanek, K Z

    2008-01-01

    We have identified a sample of 41 low-mass high--oxygen abundance outliers from the mass--metallicity relation of star-forming galaxies measured by Tremonti et al (2004). These galaxies, which have 8.6 M_B > -19.1 and 7.4 < log M_*/M_solar < 10, are surprisingly non-pathological. They have typical specific star formation rates, they are fairly isolated and, with few exceptions, have no obvious companions. Morphologically, they are similar to dwarf spheroidal or dwarf elliptical galaxies. We predict that their observed high oxygen abundances are due to relatively low gas masses, concluding that these are transitional dwarf galaxies nearing the end of their star formation activity.

  18. Elliptical Galaxies and Bulges of Disc Galaxies: Summary of Progress and Outstanding Issues

    Science.gov (United States)

    Kormendy, John

    Bulge components of disc galaxies are the high-density centers interior to their outer discs. Once thought to be equivalent to elliptical galaxies, their observed properties and formation histories turn out to be richer and more varied than those of ellipticals. This book reviews progress in many areas of bulge studies. Two advances deserve emphasis: (1) Observations divide bulges into "classical bulges" that look indistinguishable from ellipticals and "pseudobulges" that are discier and (except in S0s) more actively star-forming than are ellipticals. Classical bulges and ellipticals are thought to form by major galaxy mergers. Discy pseudobulges are a product of the slow ("secular") evolution of galaxy discs. Nonaxisymmetries such as bars and oval distortions transport some disc gas toward the center, where it starbursts and builds a dense central component that is discier in structure than are classical bulges. Secular evolution explains many regular structures (e.g., rings) seen in galaxy discs. It is a new area of galaxy evolution work that complements hierarchical clustering. (2) Studies of high-redshift galaxies reveal that their discs are so gas-rich that they are violently unstable to the formation of mass clumps that sink to the center and merge. This is an alternative channel for the formation of classical bulges. This chapter summarizes big-picture successes and unsolved problems in the formation of bulges and ellipticals and their coevolution (or not) with supermassive black holes. I present an observer's perspective on simulations of cold dark matter galaxy formation including baryonic physics. Our picture of the quenching of star formation is becoming general and secure at redshifts z 1000 in mass but that differ from each other as we observe over that whole range. A related difficulty is how hierarchical clustering makes so many giant, bulgeless galaxies in field but not cluster environments. I present arguments that we rely too much on star

  19. Stellar populations in dwarf galaxies: A review of the contribution of HST to our understanding of the nearby universe

    Science.gov (United States)

    Tolstoy, Eline

    This review aims to give an overview of the contribution of the Hubble Space Telescope to our understanding of the detailed properties of Local Group dwarf galaxies and their older stellar populations. The exquisite stable high spatial resolution combined with photometric accuracy of images from the Hubble Space Telescope have allowed us to probe further back into the history of star formation of a large variety of different galaxy types with widely differing star formation properties. It has allowed us to extend our studies out to the edges of the Local Group and beyond with greater accuracy than ever before. We have learned several important things about dwarf galaxy evolution from these studies. Firstly we have found that no two galaxies have identical star formation histories; some galaxies may superficially look the same today, but they have invariably followed different paths to this point. Now that we have managed to probe deep into the star formation history of dwarf irregular galaxies in the Local Group it is obvious that there are a number of similarities with the global properties of dwarf elliptical/spheroidal type galaxies, which were previously thought to be quite distinct. The elliptical/spheroidals tend to have one or more discrete episodes of star formation through-out their history and dwarf irregulars are characterized by quasi-continuous star-formation. The previous strong dichotomy between these two classes has been weakened by these new results and may stem from the differences in the environment in which these similar mass galaxies were born into or have inhabited for most of their lives. The more detailed is our understanding of star formation processes and their effect on galaxy evolution in the nearby Universe the better we will understand the results from studies of the integrated light of galaxies in the high-redshift Universe.

  20. Polytropic dark haloes of elliptical galaxies

    Science.gov (United States)

    Saxton, Curtis J.; Ferreras, Ignacio

    2010-06-01

    The kinematics of stars and planetary nebulae in early-type galaxies provide vital clues to the enigmatic physics of their dark matter haloes. We fit published data for 14 such galaxies using a spherical, self-gravitating model with two components: (i) a Sérsic stellar profile fixed according to photometric parameters, and (ii) a polytropic dark matter halo that conforms consistently to the shared gravitational potential. The polytropic equation of state can describe extended theories of dark matter involving self-interaction, non-extensive thermostatistics or boson condensation (in a classical limit). In such models, the flat-cored mass profiles widely observed in disc galaxies are due to innate dark physics, regardless of any baryonic agitation. One of the natural parameters of this scenario is the number of effective thermal degrees of freedom of dark matter (Fd) which is proportional to the dark heat capacity. By default, we assume a cosmic ratio of baryonic and dark mass. Non-Sérsic kinematic ideosyncrasies and possible non-sphericity thwart fitting in some cases. In all 14 galaxies, the fit with a polytropic dark halo improves or at least gives similar fits to the velocity dispersion profile, compared to a stars-only model. The good halo fits usually prefer Fd values from six to eight. This range complements the recently inferred limit of 7 < Fd < 10, derived from constraints on galaxy cluster core radii and black hole masses. However, a degeneracy remains: radial orbital anisotropy or a depleted dark mass fraction could shift our models' preference towards lower Fd; whereas a loss of baryons would favour higher Fd.

  1. Life and times of dwarf spheroidal galaxies

    CERN Document Server

    Salvadori, S; Schneider, R

    2008-01-01

    We propose a cosmological scenario for the formation and evolution of dwarf spheroidal galaxies (dSphs), satellites of the Milky Way (MW). An improved version of the semi-analytical code GAMETE (GAlaxy Merger Tree & Evolution) is used to follow the dSphs evolution simultaneously with the MW formation, matching the observed properties of both. In this scenario dSph galaxies represent fossil objects virializing at z = 7.2 +/- 0.7 (i.e. in the pre-reionization era z > z_rei = 6) in the MW environment, which at that epoch has already been pre-enriched up to [Fe/H] ~ -3; their dynamical masses are in the narrow range M = (1.6 +/- 0.7) x 10^8 M_sun, although a larger spread might be introduced by a more refined treatment of reionization. Mechanical feedback effects are dramatic in such low-mass objects, causing the complete blow-away of the gas ~100 Myr after the formation epoch: 99% of the present-day stellar mass, M_* = (3 +/- 0.7) x 10^6 M_sun, forms during this evolutionary phase, i.e. their age is >13 Gyr....

  2. Testing modified gravity with dwarf spheroidal galaxies

    CERN Document Server

    Haghi, Hosein

    2016-01-01

    The observed velocity dispersion of the classical dwarf spheroidal (dSph) galaxies of the Milky Way (MW) requires the Newtonian stellar mass-to-light ($M_*/L$) ratios in the range of about 10 to more than 100 solar units that are well outside the acceptable limit predicted by stellar population synthesis models. Using Jeans analysis, we calculate the line-of-sight velocity dispersion ($\\sigma_{\\emph{los}}$) of stars in eight MW dSphs in the context of the modified gravity (MOG) theory of Moffat, assuming a constant $M_*/L$ ratio without invoking the exotic cold dark matter. First, we use the weak field approximation of MOG and assume the two parameters $ \\alpha $ and $ \\mu $ of the theory to be constant as has already been inferred from fitting to the observed rotational data of The HI Nearby Galaxy Survey catalogue of galaxies. We find that the derived $M_*/L$ ratios for almost all dSphs are too large to be explained by the stellar population values. In order to fit the line-of-sight velocity dispersions of ...

  3. Star Formation History of Dwarf Galaxies in Cosmological Hydrodynamic Simulations

    Directory of Open Access Journals (Sweden)

    Kentaro Nagamine

    2010-01-01

    Full Text Available We examine the past and current work on the star formation (SF histories of dwarf galaxies in cosmological hydrodynamic simulations. The results obtained from different numerical methods are still somewhat mixed, but the differences are understandable if we consider the numerical and resolution effects. It remains a challenge to simulate the episodic nature of SF history in dwarf galaxies at late times within the cosmological context of a cold dark matter model. More work is needed to solve the mysteries of SF history of dwarf galaxies employing large-scale hydrodynamic simulations on the next generation of supercomputers.

  4. Abundance ratios in the hot ISM of elliptical galaxies

    CERN Document Server

    Pipino, A

    2011-01-01

    To constrain the recipes put forth to solve the theoretical Fe discrepancy in the hot interstellar medium of elliptical galaxies and at the same time explain the [alpha/Fe] ratios. In order to do so we use the latest theoretical nucleosynthetic yields, we incorporate the dust, we explore differing SNIa progenitor scenarios by means of a self-consistent chemical evolution model which reproduces the properties of the stellar populations in elliptical galaxies. Models with Fe-only dust and/or a lower effective SNIa rate achieve a better agreement with the observed Fe abundance. However, a suitable modification to the SNIa yield with respect to the standard W7 model is needed to fully match the abundance ratio pattern. The 2D explosion model C-DDT by Maeda et al. (2010) is a promising candidate for reproducing the [Fe/H] and the [alpha/Fe] ratios. (A&A format)

  5. Polytropic dark halos of elliptical galaxies

    CERN Document Server

    Saxton, Curtis J

    2010-01-01

    The kinematics of stars and planetary nebulae in early type galaxies provide vital clues to the enigmatic physics of their dark matter halos. We fit published data for fourteen such galaxies using a spherical, self-gravitating model with two components: (1) a Sersic stellar profile fixed according to photometric parameters, and (2) a polytropic dark matter halo that conforms consistently to the shared gravitational potential. The polytropic equation of state can describe extended theories of dark matter involving self-interaction, non-extensive thermostatistics, or boson condensation (in a classical limit). In such models, the flat-cored mass profiles widely observed in disc galaxies are due to innate dark physics, regardless of any baryonic agitation. One of the natural parameters of this scenario is the number of effective thermal degrees of freedom of dark matter (F_d) which is proportional to the dark heat capacity. By default we assume a cosmic ratio of baryonic and dark mass. Non-Sersic kinematic ideosy...

  6. Characterizing the population of active galactic nuclei in dwarf galaxies

    Science.gov (United States)

    Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena; Greene, Jenny E.

    2017-01-01

    Clues to super-massive black hole (BH) formation and growth reside in the population and properties of BHs in local dwarf galaxies. The masses of BHs in these systems are our best observational constraint on the masses of the first BH "seeds" at high redshift. Moreover, present-day dwarf galaxies are unlikely to have undergone major mergers, making them a relatively pristine testbed for studying triggers of BH accretion. However, in order to find BHs in dwarf galaxies outside the Local Group, it is necessary to search for signatures of accretion, i.e., active galactic nuclei (AGN). Until recently, only a handful of dwarf galaxies were known to contain AGN. However, large surveys such as the SDSS have led to the production of samples of over a hundred dwarf galaxies with AGN signatures (see e.g., Reines et al. 2013). My dissertation work has involved in-depth, multi-wavelength follow-up of nearby (z<0.055) dwarf galaxies with optical spectroscopic AGN signatures in SDSS.I analyzed high resolution spectra of dwarf galaxies with narrow-line AGN, which led to the discovery of a 50,000 MSun BH in the nucleus of RGG 118 - the smallest BH yet reported in a galaxy nucleus (Baldassare et al. 2015). I also used multi-epoch optical spectroscopy to study the nature of broad H-alpha emission in dwarf galaxies. A characteristic signature of dense gas orbiting around a BH, broad emission can also be produced by transient stellar processes. I showed that broad H-alpha in star-forming dwarf galaxies fades over a baseline of 5-10 years, and is likely produced by e.g., a Type II SN as opposed to an AGN. However, broad emission in dwarf galaxies with AGN/composite narrow lines is persistent and consistent across observations, suggesting an AGN origin (Baldassare et al. 2016). Finally, I analyzed X-ray and UV observations of dwarf galaxies with broad and narrow-line AGN signatures. All targets had nuclear X-ray detections at levels significantly higher than expected from X-ray binaries

  7. Drivers of HI Turbulence in Dwarf Galaxies

    CERN Document Server

    Stilp, Adrienne M; Skillman, Evan D; Warren, Steven R; Ott, Juergen; Koribalski, Baerbel

    2013-01-01

    Neutral hydrogen (HI) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation (SF), recent studies have shown that this driving mechanism may not be dominant in regions of low SF rate surface density (SFRSD), such as found in dwarf galaxies or the outer regions of spirals. We have generated average HI line profiles in a number of nearby dwarfs and low-mass spirals by co-adding HI spectra in regions with either a common radius or SFRSD. We find that the spatially-resolved superprofiles are composed of a central narrow peak (5-15 km/s) with higher velocity wings to either side. With the assumption that the central peak reflects the turbulent velocity dispersion, we compare HI kinematics to local ISM properties, including surface mass densities and measures of SF. The HI velocity dispersion is correlated most strongly with surface mass density, which points at a gravitational origin for turbulence, but it is...

  8. Dwarf galaxies in the Antlia Cluster: First results

    CERN Document Server

    Castelli, A V S; Cellone, S A; Richtler, T; Dirsch, B; Infante, L; Aruta, C; Gómez, M

    2006-01-01

    We present the first results of a project aimed to study the galaxy population of the Antlia cluster, the third nearest galaxy cluster after Virgo and Fornax. The observations for the Antlia project consist of Washington wide-field images taken with the MOSAIC camera mounted at the prime focus of the CTIO 4-m Blanco telescope. Our preliminary results correspond to the identification and classification of dwarf galaxies in the central cluster region, extending the list of Ferguson & Sandage (1990). The final aim of our project is to study the luminosity function, morphology and structural parameters of dwarf galaxies in the Antlia cluster with a more complete sample.

  9. The formation of ultra-compact dwarf galaxies and nucleated dwarf galaxies

    CERN Document Server

    Goerdt, Tobias; Kazantzidis, Stelios; Kaufmann, Tobias; Macciò, Andrea V; Stadel, Joachim

    2007-01-01

    Ultra compact dwarf galaxies (UCDs) have similar properties as massive globular clusters or the nuclei of nucleated galaxies. Recent observations suggesting a high dark matter content and a steep spatial distribution within groups and clusters provide new clues as to their origins. We perform high-resolution N-body / Smoothed Particle Hydrodynamics simulations designed to elucidate two possible formation mechanisms for these systems: the merging of globular clusters in the centre of a dark matter halo, or the massively stripped remnant of a nucleated galaxy. Both models produce density profiles as well as the half light radii that can fit the observational constraints. However, we show that the first scenario results to UCDs that are underluminous and contain no dark matter. This is because the sinking process ejects most of the dark matter particles from the halo centre. Stripped nuclei give a more promising explanation, especially if the nuclei form via the sinking of gas, funneled down inner galactic bars,...

  10. The structural and dynamical properties of compact elliptical galaxies

    Science.gov (United States)

    Yıldırım, Akın; van den Bosch, Remco C. E.; van de Ven, Glenn; Martín-Navarro, Ignacio; Walsh, Jonelle L.; Husemann, Bernd; Gültekin, Kayhan; Gebhardt, Karl

    2017-07-01

    Dedicated photometric and spectroscopic surveys have provided unambiguous evidence for a strong stellar mass-size evolution of galaxies within the last 10 Gyr. The likely progenitors of today's most massive galaxies are remarkably small, discy, passive and have already assembled much of their stellar mass at redshift z = 2. An in-depth analysis of these objects, however, is currently not feasible due to the lack of high-quality, spatially resolved photometric and spectroscopic data. In this paper, we present a sample of nearby compact elliptical galaxies (CEGs), which bear resemblance to the massive and quiescent galaxy population at earlier times. Hubble Space Telescope (HST) and wide-field integral field unit (IFU) data have been obtained, and are used to constrain orbit-based dynamical models and stellar population synthesis (SPS) fits, to unravel their structural and dynamical properties. We first show that our galaxies are outliers in the present-day stellar mass-size relation. They are, however, consistent with the mass-size relation of compact, massive and quiescent galaxies at redshift z = 2. The compact sizes of our nearby galaxies imply high central stellar mass surface densities, which are also in agreement with the massive galaxy population at higher redshift, hinting at strong dissipational processes during their formation. Corroborating evidence for a largely passive evolution within the last 10 Gyr is provided by their orbital distribution as well as their stellar populations, which are difficult to reconcile with a very active (major) merging history. This all supports that we can use nearby CEGs as local analogues of the high-redshift, massive and quiescent galaxy population, thus providing additional constraints for models of galaxy formation and evolution.

  11. Satellite galaxies around present-day massive ellipticals

    CERN Document Server

    Ruiz, Pablo; Mármol-Queraltó, Esther

    2013-01-01

    Using the spectroscopic and photometric catalogues of the Sloan Digital Sky Survey (SDSS DR7), we have explored the satellite distribution around $\\sim$1000 massive (M$_\\star$$\\gtrsim$2$\\times$10$^{11}$M$_\\odot$) visually classified elliptical galaxies down to a satellite mass ratio of 1:400 (i.e. 5$\\times$$10^{8}$$\\lesssim$M$_{sat}$$\\lesssim$2$\\times$10$^{11}$M$_\\odot$). Our host galaxies were selected to be representative of a mass complete sample. The satellites of these galaxies were searched within a projected radial distance of 100 kpc to their hosts. We have found that only 17-23% of the massive ellipticals has at least a satellite down to a mass ratio 1:10. This number increases to 40-52% if we explore satellites down to 1:100 and is $>$55-70% if we go further down to 1:400. The average projected radial distance of the satellites to their hosts is $\\sim$59 kpc (which can be decreased down to 49-51 kpc if we account for incompleteness effects). The number of satellites per galaxy host only increases ve...

  12. The distribution of Infrared point sources in nearby elliptical galaxies

    Science.gov (United States)

    Gogoi, Rupjyoti; Misra, Ranjeev; Puthiyaveettil, Shalima

    Infra-red point sources in nearby early-type galaxies are often counterparts of sources in other wavebands such as optical and X-rays. In particular, the IR counterpart of X-ray sources may be due to a globular cluster hosting the X-ray source or could be associated directly with the binary, providing crucial information regarding their environment. In general, the IR sources would be from globular clusters and their IR colors would provide insight into their stellar composition. However, many of the IR sources maybe background objects and it is important to identify them or at least quantify the level of background contamination. Archival Spitzer IRAC images provide a unique opportunity to study these sources in nearby Ellipticals and in particular to estimate the distributions of their IR luminosity, color and distance from the center. We will present the results of such an analysis for three nearby galaxies. We have also estimated the background contamination using several blank fields. Our preliminary results suggest that IR colors can be effectively used to differentiate between the background and sources in the galaxy, and that the distribution of sources are markedly different for different Elliptical galaxies.

  13. Mergers in Galaxy Groups. II. The Fundamental Plane of Elliptical Galaxies

    CERN Document Server

    Taranu, Dan S; Yee, H K C

    2014-01-01

    Observations consistently show that elliptical galaxies follow a tight "fundamental plane" scaling relation between size, mean surface brightness and velocity dispersion, with the form R $\\propto {\\sigma}^a {\\mu}^b$. This relation not only has very small (<0.05 dex) intrinsic scatter, but also has significantly different coefficients from the expect virial scaling (a "tilt"). We analyze hundreds of simulations of elliptical galaxies formed from mergers of spiral galaxies in groups to determine if the fundamental plane can emerge from multiple, mostly minor and hierarchical collisionless mergers. We find that these simulated ellipticals lie on a similar fundamental plane with a~1.7 and b~0.3. The scatter about this plane is even smaller than observed, while the tilt is in the correct sense, although a is larger than for typical observations. This demonstrates that collisionless mergers can contribute significantly to the tilt of the fundamental plane, contrary to previous claims that only gas dissipation co...

  14. Dwarf galaxies beyond our doorstep: the Centaurus A group

    CERN Document Server

    Crnojević, D; Cole, A A; Koch, A; Rejkuba, M; Da Costa, G; Jerjen, H

    2010-01-01

    The study of dwarf galaxies in groups is a powerful tool for investigating galaxy evolution, chemical enrichment and environmental effects on these objects. Here we present results obtained for dwarf galaxies in the Centaurus A complex, a dense nearby (~4 Mpc) group that contains two giant galaxies and about 30 dwarf companions of different morphologies and stellar contents. We use archival optical (HST/ACS) and near-infrared (VLT/ISAAC) data to derive physical properties and evolutionary histories from the resolved stellar populations of these dwarf galaxies. In particular, for early-type dwarfs we are able to construct metallicity distribution functions, find population gradients and quantify the intermediate-age star formation episodes. For late-type dwarfs, we compute recent (~1 Gyr) star formation histories and study their stellar distribution. We then compare these results with properties of the dwarfs in our Milky Way and in other groups. Our work will ultimately lead to a better understanding of the e...

  15. A PAndAS view of M31 dwarf elliptical satellites: NGC147 and NGC185

    CERN Document Server

    Crnojević, D; Irwin, M J; McConnachie, A W; Bernard, E J; Fardal, M A; Ibata, R A; Lewis, G F; Martin, N F; Navarro, J F; Noël, N E D; Pasetto, S

    2014-01-01

    We exploit data from the Pan-Andromeda Archaeological Survey (PAndAS) to study the extended structures of M31's dwarf elliptical companions, NGC147 and NGC185. Our wide-field, homogeneous photometry allows to construct deep colour-magnitude diagrams (CMDs) which reach down to $\\sim3$ mag below the red giant branch (RGB) tip. We trace the stellar components of the galaxies to surface brightness of $\\mu_g \\sim 32$ mag arcsec$^{-2}$ and show they have much larger extents ($\\sim5$ kpc radii) than previously recognised. While NGC185 retains a regular shape in its peripheral regions, NGC147 exhibits pronounced isophotal twisting due to the emergence of symmetric tidal tails. We fit single Sersic models to composite surface brightness profiles constructed from diffuse light and star counts and find that NGC147 has an effective radius almost 3 times that of NGC185. In both cases, the effective radii that we calculate are larger by a factor of $\\sim2$ compared to most literature values. We also calculate revised total...

  16. Mechanical AGN Feedback: Controlling the Thermodynamical Evolution of Elliptical Galaxies

    CERN Document Server

    Gaspari, M; Temi, P

    2012-01-01

    A fundamental gap in the current understanding of galaxies concerns the thermodynamical evolution of the ordinary, baryonic matter. On one side, radiative emission drastically decreases the thermal energy content of the interstellar plasma (ISM), inducing a slow cooling flow toward the centre. On the other side, the active galactic nucleus (AGN) struggles to prevent the runaway cooling catastrophe, injecting huge amount of energy in the ISM. The present study intends to deeply investigate the role of mechanical AGN feedback in (isolated or massive) elliptical galaxies, extending and completing the mass range of tested cosmic environments. Our previously successful feedback models, in galaxy clusters and groups, demonstrated that AGN outflows, self-regulated by cold gas accretion, are able to properly quench the cooling flow, without destroying the cool core. Via 3D hydrodynamic simulations (FLASH 3.3), including also stellar evolution, we show that massive mechanical AGN outflows can indeed solve the cooling ...

  17. Chemodynamic evolution of dwarf galaxies in tidal fields

    CERN Document Server

    Williamson, David; Romeo, Alessandro B

    2016-01-01

    The mass-metallicity relation shows that the galaxies with the lowest mass have the lowest metallicities. As most dwarf galaxies are in group environments, interaction effects such as tides could contribute to this trend. We perform a series of smoothed particle hydrodynamics (SPH) simulations of dwarf galaxies in external tidal fields to examine the effects of tides on their metallicities and metallicity gradients. In our simulated galaxies, gravitational instabilities drive gas inwards and produce centralized star formation and a significant metallicity gradient. Strong tides can contribute to these instabilities, but their primary effect is to strip the outer low-metallicity gas, producing a truncated gas disk with a large metallicity. This suggests that the role of tides on the mass-metallicity relation is to move dwarf galaxies to higher metallicities.

  18. The prevalence of dwarf galaxy compact groups over cosmic time

    Science.gov (United States)

    Wiens, Christopher

    2017-01-01

    Galaxy interactions are critical to the evolution of the universe, influencing everything from star formation to the structure of the known universe. By studying galaxy interactions through computer simulations, we are instantaneously able to observe processes that normally take billions of years. “Compact groups” are extremely dense assemblies of at least 3 but typically no more than 10 galaxies that are interacting gravitationally. These groups yield much information about galaxy interactions and mergers in dense environments but are difficult to observe at high redshifts. Compact groups of only dwarf galaxies probe a regime of galaxy evolution that has been hypothesized to be common in the early universe. Here we investigate the populations of such dwarf galaxy compact groups in the Millennium II simulation. Millennium II is a massive n-body simulation of cold dark matter particles on a time scale equivalent to the known universe; allowing us to access to high redshift galaxies and the ability to track their descendants. Our preliminary findings indicate that these dwarf galaxy compact groups do exist in the Millennium II simulation. In the simulation, there is a non-inconsequential number of dwarf compact groups with an evolutionary track that mirrors the more massive compact groups with a peak in groups around a redshift of 2.

  19. AGB Connection and Ultraviolet Luminosity Excess in Elliptical Galaxies

    Science.gov (United States)

    Buzzoni, Alberto; González-Lópezlira, Rosa A.

    2008-10-01

    Relying on infrared surface brightness fluctuactions to trace AGB properties in a sample of elliptical galaxies in the Virgo and Fornax Clusters, we assess the puzzling origin of the ``UV upturn'' phenomenon, recently traced to the presence of a hot horizontal branch (HB) stellar component. The UV upturn actually signals a profound change in the galaxy stellar populations, involving both the hot stellar component and red giant evolution. In particular, the strengthening of the UV rising branch is always seen to correspond to a shortening in AGB deployment; this trend can be readily interpreted as an age effect, perhaps mildly modulated by metal abundance. Brightest stars in ellipticals are all found to be genuine AGB members, all the way, and with the AGB tip exceeding the RGB tip by some 0.5-1.5 mag. The inferred core mass of these stars is found to be lesssim0.57 M⊙ among giant ellipticals. This value accounts for the recognized deficiency of planetary nebulae in these galaxies, as a result of a lengthy transition time for the post-AGB stellar core to become a hard UV emitter and eventually ``fire up'' the nebula. The combined study of galaxy (1550 - V)0 color and integrated Hβ index points to a a bimodal temperature distribution for the HB with both a red clump and an extremely blue component, in a relative proportion [N(RHB) : N(BHB)] ~ [80 : 20]. For the BHB stellar population, [Fe/H] values of either simeq-0.7 or gtrsim+0.5 dex may provide the optimum ranges to feed the needed low-mass stars (M*ll 0.58 M⊙) that at some stage begin to join the standard red clump stars.

  20. The effect of gravitational tides on dwarf spheroidal galaxies

    CERN Document Server

    Nichols, Matthew; Jablonka, Pascale

    2014-01-01

    The effect of the local environment on the evolution of dwarf spheroidal galaxies is poorly understood. We have undertaken a suite of simulations to investigate the tidal impact of the Milky Way on the chemodynamical evolution of dwarf spheroidals that resemble present day classical dwarfs using the SPH code GEAR. After simulating the models through a large parameter space of potential orbits the resulting properties are compared with observations from both a dynamical point of view, but also from the, often neglected, chemical point of view. In general, we find that tidal effects quench the star formation even inside gas-endowed dwarfs. Such quenching, may produce the radial distribution of dwarf spheroidals from the orbits seen within large cosmological simulations. We also find that the metallicity gradient within a dwarf is gradually erased through tidal interactions as stellar orbits move to higher radii. The model dwarfs also shift to higher $\\langle$[Fe/H]$\\rangle$/L ratios, but only when losing $>$$20...

  1. Ellipticity of dark matter halos with galaxy-galaxy weak lensing

    CERN Document Server

    Mandelbaum, R; Broderick, T; Seljak, U; Brinkmann, J; Mandelbaum, Rachel; Hirata, Christopher M.; Broderick, Tamara; Seljak, Uros; Brinkmann, Jonathan

    2005-01-01

    We present the results of attempts to detect the ellipticity of dark matter halos using galaxy-galaxy weak lensing with SDSS data. We use 2,020,256 galaxies brighter than r=19 with photometric redshifts (divided into colour and luminosity subsamples) as lenses and 31,697,869 source galaxies. We search for and identify several signal contaminants, which if not removed lead to a spurious detection. These include systematic shear that leads to a slight spurious alignment of lens and source ellipticities, intrinsic alignments (due to contamination of the source sample by physically-associated lens source pairs), and anisotropic magnification bias. We develop methods that allow us to remove these contaminants to the signal. We split the analysis into blue (spiral) and red (elliptical) galaxies. Assuming Gaussian errors as in previous work and a power-law profile, we find f_h=e_h/e_g=0.1+/-0.06 for red galaxies and -0.8+/-0.4 for blue galaxies using 20-300 kpc/h, averaged over luminosity. Inclusion of the more real...

  2. Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics

    CERN Document Server

    Toloba, E; Cenarro, A J; Peletier, R F; Gorgas, J; de Paz, A Gil; Munoz-Mateos, J C

    2010-01-01

    We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy population inhabiting clusters. We confirm that dEs are not dark matter dominated galaxies, at least up to the half-light radius. We also find that the observed galaxies in the outer parts of the cluster are mostly rotationally supported systems with disky morphological shapes. Rotationally supported dEs have rotation curves similar to those of star forming galaxies of similar luminosity and follow the Tully-Fisher relation. This is expected if dE galaxies are the descendant of low luminosity star forming systems which recently entered the cluster environment and lost their gas due to a ram pressure stripping event, quenching their star formation activity and transforming into quiescent systems, but conserving the...

  3. Wave Dark Matter and Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Parry, Alan R.

    We explore a model of dark matter called wave dark matter (also known as scalar field dark matter and boson stars) which has recently been motivated by a new geometric perspective by Bray. Wave dark matter describes dark matter as a scalar field which satisfies the Einstein-Klein-Gordon equations. These equations rely on a fundamental constant Upsilon (also known as the "mass term'' of the Klein-Gordon equation). Specifically, in this dissertation, we study spherically symmetric wave dark matter and compare these results with observations of dwarf spheroidal galaxies as a first attempt to compare the implications of the theory of wave dark matter with actual observations of dark matter. This includes finding a first estimate of the fundamental constant Upsilon. In the introductory Chapter 1, we present some preliminary background material to define and motivate the study of wave dark matter and describe some of the properties of dwarf spheroidal galaxies. In Chapter 2, we present several different ways of describing a spherically symmetric spacetime and the resulting metrics. We then focus our discussion on an especially useful form of the metric of a spherically symmetric spacetime in polar-areal coordinates and its properties. In particular, we show how the metric component functions chosen are extremely compatible with notions in Newtonian mechanics. We also show the monotonicity of the Hawking mass in these coordinates. Finally, we discuss how these coordinates and the metric can be used to solve the spherically symmetric Einstein-Klein-Gordon equations. In Chapter 3, we explore spherically symmetric solutions to the Einstein-Klein-Gordon equations, the defining equations of wave dark matter, where the scalar field is of the form f(t, r) = eiotF(r) for some constant o ∈ R and complex-valued function F(r). We show that the corresponding metric is static if and only if F( r) = h(r)eia for some constant alpha ∈ R and real-valued function h(r). We describe the

  4. Stellar populations of massive elliptical galaxies in very rich clusters

    CERN Document Server

    Carretero, C; Beckman, J E

    2006-01-01

    We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z~0.2: A115, A655, A963 and A2111. Using the new, high-resolution stellar populations models developed in our group, we obtained accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe. We have found that [CN/H] and [Mg/H] are correlated with sigma while [Fe/H] and Log(age) are not. In addition, both abundance ratios [CN/Fe] and [Mg/Fe] increase with sigma. Furthermore, the [CN/H]-sigma and [CN/Fe]-sigma slopes are steeper for galaxies in very rich clusters than those in the less dense Virgo and Coma clusters. On the other hand, [Mg/H]-sigma and [Mg/Fe]-sigma slopes keep constant as functions of the environment. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ~1 Gyr. This result implies that massive ellipti...

  5. Probing the Central Regions of Nearby Compact Elliptical Galaxies

    CERN Document Server

    Davidge, T J; McGregor, P J

    2008-01-01

    K-band spectroscopic observations recorded with NIFS+ALTAIR on Gemini North are used to probe the central arcsec of the compact elliptical galaxies NGC 4486B, NGC 5846A, and M32. The angular resolution of these data is ~0.1 arcsec FWHM. The central stellar contents of NGC 4486B and NGC 5846A are similar, in the sense that they occupy the same regions of the (Ca I, 12CO), (Na I, 12CO) and (13CO, 12CO) diagrams. The NGC 4486B and NGC 5846A observations depart from the sequence defined by solar neighborhood giants in the (Na I, 12CO) diagram, in a sense that is consistent with both galaxies having non-solar chemical mixtures. For comparison, the M32 data is consistent with a chemical enrichment history like that in the Galactic disk; M32 could not have formed from the stripping of a larger elliptical galaxy. The behaviour of the near-infrared line indices as a function of radius is also investigated. The radial gradients that are present in NGC 4486B and NGC 5846A at large radii break down or reverse within the ...

  6. Mid-UV Determination of Elliptical Galaxy Abundances and Ages

    CERN Document Server

    Lotz, J M; Bohlin, R C; Lotz, Jennifer M.; Ferguson, Henry C.; Bohlin, Ralph C.

    1999-01-01

    We investigate the effects of abundance and age on the mid-UV spectra and Mg_{2} strengths of stellar populations using simple population synthesis models. These models are used to constrain the star formation history of four nearby elliptical galaxies and spiral bulges. The mid-UV (1800 - 3200 Å) light of evolved stellar populations (> 1 Gyr) is dominated by the main sequence turn-off, unlike the optical light which is dominated by the red giant branch. A detailed investigation of the mid-UV features of elliptical galaxies may help break the age-metallicity degeneracy that plagues optical techniques. Also, a better understanding of this wavelength region is useful for the studies of 0.5 $\\leq$ z $\\leq$ 1.5 galaxies for which the rest frame mid-UV is redshifted into the visible. We create simple, single age (3-20 Gyr), single metallicity (Z = 0.0004 - 0.05) spectral energy distributions (SEDs) extending into the UV using the Kurucz model stellar fluxes. Comparison to standard stars' mid-UV spectra reveals th...

  7. AGN-stimulated Cooling of Hot Gas in Elliptical Galaxies

    CERN Document Server

    Valentini, Milena

    2015-01-01

    We study the impact of relatively weak AGN feedback on the interstellar medium of intermediate and massive elliptical galaxies. We find that the AGN activity, while globally heating the ISM, naturally stimulates some degree of hot gas cooling on scales of several kpc. This process generates the persistent presence of a cold ISM phase, with mass ranging between 10$^4$ and $\\gtrsim$ 5 $\\times$ 10$^7$ M$_\\odot$, where the latter value is appropriate for group centered, massive galaxies. Widespread cooling occurs where the ratio of cooling to free-fall time before the activation of the AGN feedback satisfies $t_{cool}/t_{ff} \\lesssim 70$, that is we find a less restrictive threshold than commonly quoted in the literature. This process helps explaining the body of observations of cold gas (both ionized and neutral/molecular) in Ellipticals and, perhaps, the residual star formation detected in many early-type galaxies. The amount and distribution of the off-center cold gas vary irregularly with time. The cold ISM v...

  8. Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

    Science.gov (United States)

    Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

    2012-01-01

    We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

  9. Dark influences: imprints of dark satellites on dwarf galaxies

    NARCIS (Netherlands)

    Starkenburg, T. K.; Helmi, A.

    2015-01-01

    Context. In the context of the current Λ cold dark matter cosmological model small dark matter halos are abundant and satellites of dwarf galaxies are expected to be predominantly dark. Since low mass galaxies have smaller baryon fractions, interactions with these satellites may leave particularly d

  10. The mass content of the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Battaglia, G.; Helmi, A.; Tolstoy, E.; Irwin, M.; Andersen, J; BlandHawthorn, J; Nordstrom, B

    2009-01-01

    We present a new determination of the mass content of the Sculptor dwarf spheroidal galaxy, based on a novel approach which takes into account the two distinct stellar populations present in this galaxy. This method helps to partially break the well-known mass-anisotropy degeneracy present in the mo

  11. Formation Histories of Dwarf Galaxies in the Local Group

    CERN Document Server

    Ricotti, M; Ricotti, Massimo; Gnedin, Nickolay Y.

    2004-01-01

    We compare the properties of dwarf galaxies in the Local Group with the simulated galaxies formed before reionization in a cosmological simulation of unprecedented spatial and mass resolution. We find that a subset of the Local Group dwarfs are remarkably similar to the simulated dwarf galaxies in all their properties. Based on this similarity, we propose the hypothesis that Local Group dwarfs form in a variety of ways: some of them are ``true fossils'' of the pre-reionization era, some of them form most of their stars later, after reionization (we call them ``survivors'' of the reionization era), and the rest of them form an intermediate group of ``polluted fossils''. We also identify a simple observational test that is able to falsify our hypothesis.

  12. The Cold Gas Content of Bulgeless Dwarf Galaxies

    CERN Document Server

    Pilkington, K; Calura, F; Brooks, A M; Mayer, L; Brook, C B; Stinson, G S; Thacker, R J; Few, C G; Cunnama, D; Wadsley, J

    2011-01-01

    We present an analysis of the neutral hydrogen (HI) properties of a fully cosmological hydrodynamical dwarf galaxy, run with varying simulation parameters. As reported by Governato et al. (2010), the high resolution, high star formation density threshold version of this galaxy is the first simulation to result in the successful reproduction of a (dwarf) spiral galaxy without any associated stellar bulge. We have set out to compare in detail the HI distribution and kinematics of this simulated bulgeless disk with what is observed in a sample of nearby dwarfs. To do so, we extracted the radial gas density profiles, velocity dispersion (e.g., velocity ellipsoid, turbulence), and the power spectrum of structure within the cold interstellar medium from the simulations. The highest resolution dwarf, when using a high density star formation threshold comparable to densities of giant molecular clouds, possesses bulk characteristics consistent with those observed in nature, though the cold gas is not as radially exten...

  13. The Mass Dependence of Dwarf Satellite Galaxy Quenching

    Science.gov (United States)

    Slater, Colin T.; Bell, Eric F.

    2014-09-01

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low-mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic Clouds. While almost all of the low-mass (M sstarf 5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to account for the change in quenched fractions. Though neither model predicts the quenching effectiveness a priori, this modeling illustrates the physical requirements that the observed quenched fractions place on possible quenching mechanisms.

  14. Dark matter deprivation in the field elliptical galaxy NGC 7507

    Science.gov (United States)

    Lane, Richard R.; Salinas, Ricardo; Richtler, Tom

    2015-02-01

    Context. Previous studies have shown that the kinematics of the field elliptical galaxy NGC 7507 do not necessarily require dark matter. This is troubling because, in the context of ΛCDM cosmologies, all galaxies should have a large dark matter component. Aims: Our aims are to determine the rotation and velocity dispersion profile out to larger radii than do previous studies, and, therefore, more accurately estimate of the dark matter content of the galaxy. Methods: We use penalised pixel-fitting software to extract velocities and velocity dispersions from GMOS slit mask spectra. Using Jeans and MONDian modelling, we then produce models with the goal of fitting the velocity dispersion data. Results: NGC 7507 has a two-component stellar halo, with the outer halo counter rotating with respect to the inner halo, with a kinematic boundary at a radius of ~110'' (~12.4 kpc). The velocity dispersion profile exhibits an increase at ~70'' (~7.9 kpc), reminiscent of several other elliptical galaxies. Our best fit models are those under mild anisotropy, which include ~100 times less dark matter than predicted by ΛCDM, although mildly anisotropic models that are completely dark matter free fit the measured dynamics almost equally well. Our MONDian models, both isotropic and anisotropic, systematically fail to reproduce the measured velocity dispersions at almost all radii. Conclusions: The counter-rotating outer halo implies a merger remnant, as does the increase in velocity dispersion at ~70''. From simulations it seems plausible that the merger that caused the increase in velocity dispersion was a spiral-spiral merger. Our Jeans models are completely consistent with a no dark matter scenario, however, some dark matter can be accommodated, although at much lower concentrations than predicted by ΛCDM simulations. This indicates that NGC 7507 may be a dark matter free elliptical galaxy. Regardless of whether NGC 7507 is completely dark matter free or very dark matter poor

  15. Star Formation and the ISM in Dwarf Galaxies

    CERN Document Server

    Young, L M; Dohm-Palmer, R C; Lo, K Y

    2000-01-01

    High spatial and spectral resolution observations of the atomic interstellar medium in nearby dwarf galaxies reveal evidence for warm and cold neutral gas, just like the phases in our own Galaxy. The cold or quiescent phase (about 20% of the HI in the galaxies studied, except for LGS 3) seems to be associated with star formation activity--- it may mark the regions where the conditions are right for star formation. These results help to explain the patterns of star formation activity which are seen in color-magnitude data for the dwarf irregulars.

  16. Optical and Near Infrared studies of the photometric structure and starburst activity of Blue Compact Dwarf Galaxies

    Science.gov (United States)

    Noeske, K. G.

    2003-03-01

    This thesis describes three studies of Blue Compact Dwarf Galaxies (BCDs), focussed on the structure of the stellar components, the star-forming activity, and the environment of such galaxies, as well as the physical background of their morphological variety. The analysis of deep Near Infrared (NIR) image data of a significant sample of BCDs allows to study the evolved stellar low surface brightness (LSB) components of BCDs more precisely than previous studies at visible wavelengths. Azimuthally averaged radial surface brightness profiles (SBPs) show an exponential intensity distribution of the stellar LSB components at large galactocentric radii. This result, along with the derived exponential scale lengths which are systematically smaller than those of dwarf Irregular and dwarf Elliptical galaxies, agrees with previous optical studies. Towards smaller radii, however, the NIR data reveal an inwards-flattening of the SBPs of the stellar LSB components with respect to their outer exponential slopes in more than half of the BCDs under study. Such inwards-flattening exponential SBPs are frequent in dwarf Irregulars and dwarf Ellipticals, but were hitherto largely undiscovered in the stellar hosts of BCDs. The physical origin of such SBPs in dwarf galaxies is to date not understood. Empirical approaches to their systematization and quantitative investigation are discussed, along with the various implications of the discovery of such SBPs in many BCDs for the understanding of such galaxies. Based on the derived structural information on the stellar LSB components and the starburst components, the hypothesis is raised that below a certain threshold density of the stellar LSB component, of the order of 0.4 solar masses per cubic parsec, burst-like star formation does not occur in gas-rich dwarf galaxies. On this hypothesis, the observed relations between the structure of the stellar LSB components of BCDs and their luminosity can be reproduced, as well as the systematic

  17. Globular cluster system erosion and nucleus formation in elliptical galaxies

    CERN Document Server

    Capuzzo-Dolcetta, R

    1998-01-01

    The radial distribution of globular clusters in galaxies is always less peaked to the centre than the halo stars'. Extending previous work to a sample of HST globular cluster systems in ellipticals, we evaluate the number of clusters lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. It results that the initial populations of globular clusters were from 25% to 50% richer than now. This significant number of missing globular clusters supports the hypothesis that a large quantity of globular cluster mass in form of globular clusters decayed and destroyed has been lost to the galactic centres, where plausibly contributed to formation and feeding of a mas sive object therein. It is relevant noting that the observed correlation between the core radius of the globular cluster system and the parent galaxy luminosity can be interpreted as a result of evolution.

  18. Violent Relaxation, Dynamical Instabilities and the Formation of Elliptical Galaxies

    Science.gov (United States)

    Aguilar, L. A.

    1990-11-01

    RESUMEN: El problema de la formaci6n de galaxias elfpticas por medjo de colapso gravitacional sin disipaci6n de energfa es estudiado usando un gran numero de simulaciones numericas. Se muestra que este tipo de colapsos, partiendo de condiciones iniciales frfas donde la energfa cinetica inicial representa s6lo un 5%, 0 , de a potencial inicial, produce sistemas relajados de forma triaxial muy similares a las galaxias elfpticas reales en sus formas y perfiles de densidad en proyecci6i . La forina triaxial resulta de la acci6n de una inestabilidad dinamica que aparece en sistemas 'inicos dominados por movimientos radiales, mientras que el perfil de densidad final Cs debido al llamado relajamiento violento que tiende a producir una distribuci6n en espacio fase unica. Estos dos fen6menos tienden a borrar los detalles particulares sobre las condiciones iniciales y dan lugar a una evoluci6n convergente hacia sistemas realistas, esto innecesario el uso de condiciones iniciales especiales (excepto por Ia condici6i de que estas deben ser frfas). Las condiciones iniciales frfas producen los movimientos radiales y fluctuaciones de la energfa potencial requeridos por ambos fen6menos. ABSTRACT: The problem of formation of elliptical galaxies via dissipationless collapse is studied using a large set of numerical simulations. It is shown that dissipationless collapses from cold initial conditions, where the total initial kinetic energy is less than 5% ofthe initial potential energy, lead to relaxed triaxial systems ery similar to real elliptical galaxies ii projected shape and density profiles. The triaxial shape is due to the of a dynamical instability that appears on systems dominated by radial orbits, while final density profile is due to violent relaxation that tends to produce a unique distribution iii space. These two phenomena erase memory of the initial prodtice a convergent evolution toward realistic systems, thus making unnecessary use o[special initial conditions (other

  19. The Axis of Opportunity: The Large-Scale Correlation of Elliptical Galaxies

    OpenAIRE

    Longo, Michael J.

    2007-01-01

    This paper has been withdrawn by the author due to the discovery of a serious bias resulting from the systematic dimming of galaxies with larger ellipticities away from the North Galactic Pole. Thus the conclusion that there is a special axis along which the elliptical galaxies tend to be aligned is incorrect.

  20. ANDROMEDA XXIX: A NEW DWARF SPHEROIDAL GALAXY 200 kpc FROM ANDROMEDA

    Energy Technology Data Exchange (ETDEWEB)

    Bell, Eric F.; Slater, Colin T. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2011-11-20

    We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15 Degree-Sign from M31, with a distance inferred from the tip of the red giant branch of 730 {+-} 75 kpc, corresponding to a three-dimensional separation from M31 of 207{sup +20}{sub -2} kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is M{sub V} = -8.3 {+-} 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] {approx}-1.8. The half-light radius of And XXIX is 360 {+-} 60 pc and its ellipticity is 0.35 {+-} 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.

  1. Keck spectroscopy and NGVS photometry in the direction of the Virgo cluster: Globular cluster satellites of dwarf ellipticals, Milky Way halo substructure, and large-scale structure in the background

    Science.gov (United States)

    Muller, Meredith; Toloba, E.; Guhathakurta, P.; Yagati, S.; Chen, J.; Cote, P.; Dorman, C.; Ferrarese, L.; Peng, E. W.; Next Generation Virgo Cluster Survey Collaboration

    2014-01-01

    The Virgo cluster, the nearest large galaxy cluster, is a rich repository of dwarf elliptical (dE) galaxies. The formation mechanism of dE galaxies remains the subject of much debate. Dwarf galaxies in general are believed to be building blocks in the hierarchical growth of galaxies as per the “cold dark matter” model of structure formation. Globular cluster (GC) satellites serve as important tracers of dark matter in the outer regions of dEs (beyond 1 half-light radius). This project presents new spectroscopic data from Keck's DEIMOS, which specifically targeted low-luminosity (-17 cannibalism events, and identify two new superclusters of galaxies in the background using redshift distribution. This research was carried out under the auspices of UCSC's Science Internship Program. We thank the National Science Foundation for funding support. ET was supported by a Fulbright fellowship.

  2. Nuclear Outbursts in the Elliptical Galaxy NGC 4472

    Science.gov (United States)

    Biller, B.; Jones, C.; Forman, W.

    2001-12-01

    We present the analysis of the Chandra ACIS observations of the giant elliptical galaxy NGC 4472. The Chandra Observatory's arcsec resolution reveals a number of new features, specifically: 1) an ~8 arcmin streamer or arm (this corresponds to a linear size of 36 kpc) extending southwest of the galaxy and an assymetrical, somewhat truncated streamer to the northeast. Smaller, morphologically similar structures are observed in NGC 4636 (Jones et al. 2001) and are explained as shocks from a nuclear outburst in the recent past. The larger size of the NGC 4472 streamers requires a correspondingly higher energy input compared to the NGC 4636 case. The asymmetry of the streamers may be due to the interaction of NGC 4472 with the ambient Virgo cluster gas. 2) A string of small, extended sources south of the nucleus. These sources may stem from an interaction of NGC 4472 with the galaxy UGC 7637. 3) X-ray cavities corresponding to radio lobes, where expanding radio plasma has evacuated the X-ray emitting gas. We also present a luminosity function for the X-ray point sources detected within NGC 4472 which we compare to that for other early type galaxies. This work was supported by CXC contract number NAS8-39073 and the Smithsonian Institution.

  3. Models of steady state cooling flows in elliptical galaxies

    Science.gov (United States)

    Vedder, Peter W.; Trester, Jeffrey J.; Canizares, Claude R.

    1988-01-01

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

  4. Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

    CERN Document Server

    Wheeler, Coral; Bullock, James S; Boylan-Kolchin, Michael; Elbert, Oliver; Garrison-Kimmel, Shea; Hopkins, Philip F; Keres, Dusan

    2015-01-01

    We present FIRE/Gizmo hydrodynamic zoom-in simulations of isolated dark matter halos, two each at the mass of classical dwarf galaxies ($M_{\\rm vir} \\simeq 10^{10} M_{\\odot}$) and ultra-faint galaxies ($M_{\\rm vir} \\simeq 10^9 M_{\\odot}$), and with two feedback implementations. The resultant central galaxies lie on an extrapolated abundance matching relation from $M_{\\star} \\simeq 10^6$ to $10^4 M_{\\odot}$ without a break. Every host is filled with subhalos, many of which form stars. Our dwarfs with $M_{\\star} \\simeq 10^6 M_{\\odot}$ each have 1-2 well-resolved satellites with $M_{\\star} = 3-200 \\times 10^3 M_{\\odot}$. Even our isolated ultra-faint galaxies have star-forming subhalos. If this is representative, dwarf galaxies throughout the universe should commonly host tiny satellite galaxies of their own. We combine our results with the ELVIS simulations to show that targeting $\\sim 50~ \\rm kpc$ regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by $\\sim 35\\%...

  5. 3D Simulations of Galactic Winds in Dwarf Galaxies

    CERN Document Server

    Marcolini, A; D'Ercole, A; Marcolini, Andrea; Brighenti, Fabrizio; Ercole, Annibale D'

    2002-01-01

    We present 3D hydrodynamical simulations of galactic winds in dwarf, gas-rich galaxies. The galaxy is moving through the ICM of a small galaxy group at v=200 km/s. The ram pressure removes the galactic gas at large radii, but does not strongly influence the ISM near the center. A starburst generates a galactic wind. The newly produced metals are expelled in the ICM and carried to large distance from the galaxy by the ram pressure. 500 Myr after the starburst only a few percent of the heavy elements produced are present in the central region of the dwarf galaxy. A large collection of ram pressure + wind models will be presented in a forthcoming paper.

  6. On the Metallicity of Star-forming Dwarf Galaxies

    CERN Document Server

    Legrand, F; Silich, S A; Kunth, D; Cerviño, M; Legrand, Francois; Tenorio-Tagle, Guillermo; Silich, Sergiy; Kunth, Daniel; Cervino, Miguel

    2001-01-01

    We construct three extreme different scenarios of the star formation histories applicable to a sample of dwarf galaxies, based either on their present metallicity or their luminosity. The three possible scenarios imply different mechanical energy input rates and these we compare with the theoretical lower limits established for the ejection of processed matter out of dwarf galaxies. The comparison strongly points at the existence of extended gaseous haloes in these galaxies, acting as the barrier that allows galaxies to retain their metals and enhance their abundance. At the same time our findings strongly point at a continuous star-forming process, rather than to coeval bursts, as the main contributors to the overall metallicity in our galaxy sample.

  7. New Low Surface Brightness Dwarf Galaxies Detected Around Nearby Spirals

    CERN Document Server

    Karachentsev, I D; Zilch, T; Blauensteiner, M; Elvov, M; Hochleitner, P; Hubl, B; Kerschhuber, G; Küppers, S; Neyer, F; Pölzl, R; Remmel, P; Schneider, O; Sparenberg, R; Trulson, U; Willems, G; Ziegler, H

    2015-01-01

    We conduct a survey of low surface brightness (LSB) satellite galaxies around the Local Volume massive spirals using long exposures with small amateur telescopes. We identified 27 low and very low surface brightness objects around the galaxies NGC,672, 891, 1156, 2683, 3344, 4258, 4618, 4631, and 5457 situated within 10 Mpc from us, and found nothing new around NGC,2903, 3239, 4214, and 5585. Assuming that the dwarf candidates are the satellites of the neighboring luminous galaxies, their absolute magnitudes are in the range of -8.6 > M_B > -13.3, their effective diameters are 0.4-4.7 kpc, and the average surface brightness is 26.1 mag/sq arcsec. The mean linear projected separation of the satellite candidates from the host galaxies is 73 kpc. Our spectroscopic observations of two LSB dwarfs with the Russian 6-meter telescope confirm their physical connection to the host galaxies NGC,891 and NGC,2683.

  8. A Census of Baryons and Dark Matter in an Isolated, Milky Way-sized Elliptical Galaxy

    CERN Document Server

    Humphrey, Philip J; Canizares, Claude R; Fabian, Andrew C; Miller, Jon M

    2010-01-01

    We present a study of the dark and luminous matter in the isolated elliptical galaxy NGC720, based on deep X-ray data taken with Chandra and Suzaku. The gas is reliably measured to ~R2500, allowing us to place good constraints on the enclosed mass and baryon fraction (fb) within this radius (M2500=1.6e12+/-0.2e12 Msun, fb(2500)=0.10+/-0.01; systematic errors are <~20%). The data indicate that the hot gas is close to hydrostatic, which is supported by good agreement with a kinematical analysis of the dwarf satellite galaxies. We confirm a dark matter (DM) halo at ~20-sigma. Assuming an NFW DM profile, our physical model for the gas distribution enables us to obtain meaningful constraints at scales larger than R2500, revealing that most of the baryons are in the hot gas. We find that fb within Rvir is consistent with the Cosmological value, confirming theoretical predictions that a ~Milky Way-mass (Mvir=3.1e12+/-0.4e12 Msun) galaxy can sustain a massive, quasi-hydrostatic gas halo. While fb is higher than th...

  9. Ultraluminous X-ray bursts in two ultracompact companions to nearby elliptical galaxies

    CERN Document Server

    Irwin, Jimmy A; Sivakoff, Gregory R; Romanowsky, Aaron J; Lin, Dacheng; Speegle, Tyler; Prado, Ian; Mildebrath, David; Strader, Jay; Liu, Jifeng; Miller, Jon M

    2016-01-01

    An X-ray flaring source was found near the galaxy NGC 4697. Two flares were seen, separated by four years. The flux increased by a factor of 90 on a timescale of about one minute. Both flares were very brief. There is no optical counterpart at the position of the flares, but if the source was at the distance of NGC 4697, the luminosities were 10^39 erg/s. Here we report the results of a search of archival X-ray data for 70 nearby galaxies looking for similar such flares. We found two flaring sources in globular clusters or ultra-compact dwarf companions of parent elliptical galaxies. One source flared once to a peak luminosity of 9 x 10^40 erg/s, while the other flared five times to 10^40 erg/s. All of the flare rise times were <1 minute, and they then decayed over about an hour. When not flaring, the sources appear to be normal accreting neutron star or black hole X-ray binaries, but they are located in old stellar populations, unlike the magnetars, anomalous X-ray pulsars or soft gamma repeaters that hav...

  10. On the formation of dwarf galaxies and stellar haloes

    Science.gov (United States)

    Read, J. I.; Pontzen, A. P.; Viel, M.

    2006-09-01

    Using analytic arguments and a suite of very high resolution (~103Msolar per particle) cosmological hydrodynamical simulations, we argue that high-redshift, z ~ 10, M ~ 108Msolar haloes, form the smallest `baryonic building block' (BBB) for galaxy formation. These haloes are just massive enough to efficiently form stars through atomic line cooling and to hold on to their gas in the presence of supernova (SN) winds and reionization. These combined effects, in particular that of the SN feedback, create a sharp transition: over the mass range 3-10 × 107Msolar, the BBBs drop two orders of magnitude in stellar mass. Below ~2 × 107Msolar, galaxies will be dark with almost no stars and no gas. Above this scale is the smallest unit of galaxy formation: the BBB. We show that the BBBs have stellar distributions which are spheroidal, of low rotational velocity, old and metal poor: they resemble the dwarf spheroidal galaxies (dSphs) of the Local Group (LG). Unlike the LG dSphs, however, they contain significant gas fractions. We connect these high-redshift BBBs to the smallest dwarf galaxies observed at z = 0 using linear theory. A small fraction (~100) of these gas-rich BBBs at high redshift fall in to a galaxy the size of the Milky Way (MW). We suggest that 10 per cent of these survive to become the observed LG dwarf galaxies at the present epoch. This is consistent with recent numerical estimates. Those infalling haloes on benign orbits which keep them far away from the MW or Andromeda manage to retain their gas and slowly form stars - these become the smallest dwarf irregular galaxies; those on more severe orbits lose their gas faster than they can form stars and become the dwarf spheroidals. The remaining 90 per cent of the BBBs will be accreted. We show that this gives a metallicity and total stellar mass consistent with the MW old stellar halo.

  11. The link between mass distribution and starbursts in dwarf galaxies

    CERN Document Server

    McQuinn, Kristen B W; Skillman, Evan D; Dolphin, Andrew E; McGaugh, Stacy S; Williams, Benjamin F

    2015-01-01

    Recent studies have shown that starburst dwarf galaxies have steeply rising rotation curves in their inner parts, pointing to a close link between the intense star formation and a centrally concentrated mass distribution (baryons and dark matter). More quiescent dwarf irregulars typically have slowly rising rotation curves, although some "compact" irregulars with steep, inner rotation curves exist. We analyze archival Hubble Space Telescope images of two nearby "compact" irregular galaxies (NGC 4190 and NGC 5204), which were selected solely on the basis of their dynamical properties and their proximity. We derive their recent star-formation histories by fitting color-magnitude diagrams of resolved stellar populations, and find that the star-formation properties of both galaxies are consistent with those of known starburst dwarfs. Despite the small sample, this strongly reinforces the notion that the starburst activity is closely related to the inner shape of the potential well.

  12. Charting Unexplored Dwarf Galaxy Territory With RR Lyrae

    CERN Document Server

    Baker, Mariah

    2015-01-01

    Observational bias against finding Milky Way (MW) dwarf galaxies at low Galactic latitudes (b 50 kpc in these unmined regions of parameter space, with only modest contamination from interloper groups when large halo structures are excluded. For example, a friends-of-friends (FOF) search with a linking length of 500 pc could reveal dwarf galaxies more luminous than M_V = -3.2 mag and with surface brightnesses as faint as 31 mag arcsec^-2 (or even fainter, depending on RR Lyrae specific frequency). Although existing public RR Lyrae catalogs are highly incomplete at d > 50 kpc and/or include 600 kpc, LSST is the only planned survey that will be both wide-field and deep enough to use RR Lyrae to definitively measure the Milky Way's dwarf galaxy census to extremely low surface brightnesses, and through the Galactic plane.

  13. Dwarf spheroidal galaxies and Bose-Einstein condensate dark matter

    CERN Document Server

    Diez-Tejedor, Alberto; Profumo, Stefano

    2014-01-01

    We constrain the parameters of a self-interacting massive dark matter scalar particle in a condensate using the kinematics of the eight brightest dwarf spheroidal satellites of the Milky Way. For the case of an attractive self-interaction the condensate develops a mass density profile with a characteristic scale radius that is closely related to the fundamental parameters of the theory. We find that the velocity dispersion of dwarf spheroidal galaxies suggests a scale radius of the order of 1 kpc, in tension with previous results found using the rotational curve of low-surface-brightness and dwarf galaxies. We discuss the implications of our findings for the particle dark matter model and argue that a single classical coherent state cannot play, in general, a relevant role for the description of dark matter in galaxies.

  14. Formation of ultra-compact blue dwarf galaxies and their evolution into nucleated dwarfs

    CERN Document Server

    Bekki, Kenji

    2015-01-01

    We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf-dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf-dwarf mergers. We find that the remnants of dwarf-dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z~[0.2-1]Z_sun). We also find that the remnants of these mergers can have rather high mass-densities (10^4 M_sun pc^-3) within the central 10 pc and small half-light radii (40-100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R<100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multi...

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

    CERN Document Server

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

    2015-01-01

    We present DEIMOS multi-object spectroscopy (MOS) of 22 star-forming dwarf galaxies located in four gas-rich groups, including six newly-discovered dwarfs. Two of the galaxies are strong tidal dwarf galaxy (TDG) candidates based on our luminosity-metallicity relation definition. We model the rotation curves of these galaxies. Our sample shows low mass-to-light ratios (M/L=0.73$\\pm0.39M_\\odot/L_\\odot$) as expected for young, star-forming dwarfs. One of the galaxies in our sample has an apparently strongly-falling rotation curve, reaching zero rotational velocity outside the turnover radius of $r_{turn}=1.2r_e$. This may be 1) a polar ring galaxy, with a tilted bar within a face-on disk; 2) a kinematic warp. These scenarios are indistinguishable with our current data due to limitations of slit alignment inherent to MOS-mode observations. We consider whether TDGs can be detected based on their tidal radius, beyond which tidal stripping removes kinematic tracers such as H$\\alpha$ emission. When the tidal radius i...

  16. Infrared Observations of Star-Forming Dwarf Galaxies with Spitzer

    Science.gov (United States)

    Rosenberg, J. L.; Ashby, M. L. N.; Salzer, J. J.

    2004-12-01

    We present a study of the infrared properties of a sample of actively star-forming dwarf galaxies (MB >-18) drawn from the KPNO International Spectroscopic Survey. Nearby actively star-forming dwarf galaxies are possible analogs to the high redshift star-forming systems that serve as galactic building blocks in hierarchical galaxy formation scenarios. These galaxies are gas-rich, metal-poor systems undergoing bursts of star formation in the local universe. A subset of such objects from the line-flux limited objective-prism survey of Salzer et al. (2001) lie in the NOAO Bootes field, and have therefore been observed by Spitzer as part of the IRAC Shallow Survey. We use the IRAC data to measure the stellar mass in these galaxies. In addition, we examine whether these metal-poor dwarf galaxies show warm dust emission, and examine whether it traces the star formation as it does in normal disk galaxies. J. L. Rosenberg would like to acknowledge the NSF Astronomy and Astrophysics Fellowship for support of this work. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. Support for this work was provided by NASA.

  17. Velocity structure of the dwarf galaxy population in the Centaurus cluster

    CERN Document Server

    Stein, P; Federspiel, M

    1997-01-01

    Based on the photometric survey of the inner region of the Centaurus cluster (Jerjen & Dressler 1997a) we measured redshifts for a deep, surface brightness limited sample of galaxies using the MEFOS multifibre spectrograph at the ESO 3.6m telescope. With the new data set radial velocities for 120 centrally located cluster members become available which is equivalent to 78% of all known cluster galaxies in the region brighter than B_T=18.5. The relevant aspect of this investigation is that new redshifts for 32 dwarf galaxies have been measured, rising the total number to 48. We investigate the prominent bimodal velocity distribution of Centaurus in more detail, discussing the very different characteristics of the velocity distributions for the main Hubble types E&S0, spirals, Im&BCD, and dE&dS0. The nucleated, bright dwarf ellipticals are the only galaxies with a Gaussian-like distribution centred at 3148+/-98 km/s. The remarkable coincidence of this velocity with the mean velocity of Cen30 and...

  18. Identification of old tidal dwarfs near early-type galaxies from deep imaging and HI observations

    CERN Document Server

    Duc, Pierre-Alain; McDermid, Richard M; Cuillandre, Jean-Charles; Serra, Paolo; Bournaud, Frédéric; Cappellari, Michele; Emsellem, Eric

    2014-01-01

    It has recently been proposed that the dwarf spheroidal galaxies located in the Local Group disks of satellites (DoSs) may be tidal dwarf galaxies (TDGs) born in a major merger at least 5 Gyr ago. Whether TDGs can live that long is still poorly constrained by observations. As part of deep optical and HI surveys with the CFHT MegaCam camera and Westerbork Synthesis Radio Telescope made within the ATLAS3D project, and follow-up spectroscopic observations with the Gemini-North telescope, we have discovered old TDG candidates around several early-type galaxies. At least one of them has an oxygen abundance close to solar, as expected for a tidal origin. This confirmed pre-enriched object is located within the gigantic, but very low surface brightness, tidal tail that emanates from the elliptical galaxy, NGC 5557. An age of 4 Gyr estimated from its SED fitting makes it the oldest securely identified TDG ever found so far. We investigated the structural and gaseous properties of the TDG and of a companion located in...

  19. METALLICITY DISTRIBUTION FUNCTIONS OF FOUR LOCAL GROUP DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Ross, Teresa L.; Holtzman, Jon [Department of Astronomy, New Mexico State University, P.O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001 (United States); Saha, Abhijit [NOAO, 950 Cherry Avenue, Tucson, AZ 85726-6732 (United States); Anthony-Twarog, Barbara J., E-mail: rosst@nmsu.edu, E-mail: holtz@nmsu.edu, E-mail: bjat@ku.edu [Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045-7582 (United States)

    2015-06-15

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

  20. Low radiative efficiency accretion in the nuclei of elliptical galaxies

    CERN Document Server

    Matteo, T D; Allen, S W; Narayan, R; Fabian, A C

    1999-01-01

    The discovery of hard, power-law X-ray emission from a sample of six nearby elliptical galaxies, including the dominant galaxies of the Virgo,Fornax and Centaurus clusters (M87, NGC 1399 and NGC 4696, respectively), and NGC 4472, 4636 and 4649 in the Virgo cluster, has important implications for the study of quiescent supermassive black holes. We describe how the broad band spectral energy distributions of these galaxies, which accrete from their hot gaseous halos at rates comparable to their Bondi rates, can be explained by low-radiative efficiency accretion flows in which a significant fraction of the mass, angular momentum and energy is removed from the flows by winds. The observed suppression of the synchrotron component in the radio band and the systematically hard X-ray spectra, which are interpreted as thermal bremsstrahlung emission, support the conjecture that significant mass outflow is a natural consequence of systems accreting at low-radiative efficiencies. We briefly discuss an alternative model ...

  1. Radial orbital anisotropy and the Fundamental Plane of elliptical galaxies

    CERN Document Server

    Nipoti, C; Ciotti, L; Nipoti, Carlo; Londrillo, Pasquale; Ciotti, Luca

    2002-01-01

    The existence of the Fundamental Plane (FP) imposes strong constraints on the structure and dynamics of elliptical galaxies, and thus contains important information on the processes of their formation and evolution. Here we focus on the relations between the FP thinness and tilt and the amount of radial orbital anisotropy. By using N-body simulations of galaxy models characterized by observationally motivated density profiles, and also allowing for the presence of live, massive dark matter halos, we explore the impact of radial orbital anisotropy and instability on the FP properties. The numerical results confirm a previous semi--analytical finding: the requirement of stability matches almost exactly the thinness of the FP. In other words, galaxy models that are radially anisotropic enough to be found outside the observed FP (with their isotropic parent models lying on the FP) are unstable, and their end--products fall back on the FP itself. We also find that a systematic increase of radial orbit anisotropy w...

  2. Is AGN feedback necessary to form red elliptical galaxies?

    CERN Document Server

    Khalatyan, A; Schramm, M; Gottlöber, S; Steinmetz, M; Wisotzki, L

    2007-01-01

    We have used GADGET2 to simulate the formation of an elliptical galaxy in a cosmological dark matter halo with mass 3x10^12M_Sun/h. Using a stellar population synthesis model has allowed us to compute magnitudes, colours and surface brightness profiles. We have included a model to follow the growth of a central black hole and we have compared the results of simulations with and without feedback from AGNs. We have studied the interplay between cold gas accretion and merging in the development of galactic morphologies, the link between colour and morphology evolution, the effect of AGN feedback on the photometry of early type galaxies, the redshift evolution in the properties of quasar hosts, and the impact of AGN winds on the chemical enrichment of the intergalactic medium (IGM). We have found that the early phases of galaxy formation are driven by the accretion of cold filamentary flows, which form a disc at the centre of the dark matter halo. When the dark matter halo is sufficiently massive to support the p...

  3. Exploring the Interstellar Media of Optically Compact Dwarf Galaxies

    CERN Document Server

    Most, Hans P; Salzer, John J; Rosenberg, Jessica J; Engstrom, Eric; Fliss, Palmer

    2013-01-01

    We present new Very Large Array HI spectral line, archival Sloan Digital Sky Survey, and archival Spitzer Space Telescope imaging of eight star-forming blue compact dwarf galaxies that were selected to be optically compact (optical radii less than 1 kpc). These systems have faint blue absolute magnitudes (M_B >= -17), ongoing star formation (based on emission-line selection by the H alpha or [OIII] lines), and are nearby (mean velocity = 3315 km/s = 45 Mpc). One galaxy in the sample, ADBS 113845+2008, is found to have an HI halo that extends 58 r-band scale lengths from its stellar body. In contrast, the rest of the sample galaxies have HI radii to optical-scale-length ratios ranging from 9.3 to 26. The size of the HI disk in the "giant disk" dwarf galaxy ADBS 113845+2008 appears to be unusual as compared to similarly compact stellar populations.

  4. FORMATION OF ULTRA-COMPACT BLUE DWARF GALAXIES AND THEIR EVOLUTION INTO NUCLEATED DWARFS

    Energy Technology Data Exchange (ETDEWEB)

    Bekki, Kenji [ICRAR, M468, The University of Western Australia 35 Stirling Highway, Crawley Western Australia, 6009 (Australia)

    2015-10-10

    We propose that there is an evolutionary link between ultra-compact blue dwarf galaxies (UCBDs) with active star formation and nucleated dwarfs based on the results of numerical simulations of dwarf–dwarf merging. We consider the observational fact that low-mass dwarfs can be very gas-rich, and thereby investigate the dynamical and chemical evolution of very gas-rich, dissipative dwarf–dwarf mergers. We find that the remnants of dwarf–dwarf mergers can be dominated by new stellar populations formed from the triggered starbursts and consequently can have blue colors and higher metallicities (Z ∼ [0.2–1]Z{sub ⊙}). We also find that the remnants of these mergers can have rather high mass densities (10{sup 4} M{sub ⊙} pc{sup −3}) within the central 10 pc and small half-light radii (40−100 pc). The radial stellar structures of some merger remnants are similar to those of nucleated dwarfs. Star formation can continue in nuclear gas disks (R < 100 pc) surrounding stellar galactic nuclei (SGNs) so that the SGNs can finally have multiple stellar populations with different ages and metallicities. These very compact blue remnants can be identified as UCBDs soon after merging and as nucleated dwarfs after the young stars fade. We discuss these results in the context of the origins of metal-rich ultra-compact dwarfs and SGNs.

  5. An observer's guide to the (Local Group) dwarf galaxies: predictions for their own dwarf satellite populations

    CERN Document Server

    Dooley, Gregory A; Yang, Tianyi; Willman, Beth; Griffen, Brendan F; Frebel, Anna

    2016-01-01

    A recent surge in the discovery of new ultrafaint dwarf satellites of the Milky Way has inspired the idea of searching for faint satellites, $10^3\\, \\mathrm{M_{\\odot}}99\\%$ chance that at least one satellite with stellar mass $M_*> 10^5 \\, \\mathrm{M_{\\odot}}$ exists around the combined five Local Group field dwarf galaxies with the largest stellar mass. When considering satellites with $M_*> 10^4 \\, \\mathrm{M_{\\odot}}$, we predict a combined $5-25$ satellites for the five largest field dwarfs, and $10-50$ for the whole Local Group field dwarf population. Because of the relatively small number of predicted dwarfs, and their extended spatial distribution, a large fraction each Local Group dwarf's virial volume will need to be surveyed to guarantee discoveries. We compute the predicted number of satellites in a given field of view of specific Local Group galaxies, as a function of minimum satellite luminosity, and explicitly obtain such values for the Solitary Local dwarfs survey. Uncertainties in abundance matc...

  6. The Metallicity of Void Dwarf Galaxies

    NARCIS (Netherlands)

    Kreckel, K.; Croxall, K.; Groves, B.; van de Weygaert, R.; Pogge, R. W.

    2015-01-01

    The current ΛCDM cosmological model predicts that galaxy evolution proceeds more slowly in lower density environments, suggesting that voids are a prime location to search for relatively pristine galaxies that are representative of the building blocks of early massive galaxies. To test the assumptio

  7. Prediction of galaxy ellipticities and reduction of shape noise in cosmic shear measurements

    CERN Document Server

    Croft, Rupert A C; Schuster, Thomas S; Schafer, Chad M

    2015-01-01

    The intrinsic scatter in the ellipticities of galaxies about the mean shape, known as "shape noise," is the most important source of noise in weak lensing shear measurements. Several approaches to reducing shape noise have recently been put forward, using information beyond photometry, such as radio polarization and optical spectroscopy. Here we investigate how well the intrinsic ellipticities of galaxies can be predicted using other, exclusively photometric parameters. These parameters (such as galaxy colours) are already available in the data and do not necessitate additional, often expensive observations. We apply two regression techniques, generalized additive models (GAM) and projection pursuit regression (PPR) to the publicly released data catalog of galaxy properties from CFHTLenS. In our simple analysis we find that the individual galaxy ellipticities can indeed be predicted from other photometric parameters to better precision than the scatter about the mean ellipticity. This means that without addit...

  8. The Dwarf Galaxy Population in Nearby Groups. The data

    CERN Document Server

    Carrasco, E R; Infante, L; Carrasco, Eleazar R.; Oliveira, Claudia M. de; Infante, Leopoldo

    2006-01-01

    We used V and I CCD photometry to search for low-surface brightness dwarf galaxies (LSBD) in the central ( 22.5 V mag/arcsec^2, h > 1.5 arcsec, and diameters larger than 1.2 h^-1 kpc. Twenty of the eighty galaxies are extended LSB galaxies that were detected only on smoothed images, after masking all high surface brightness objects. The completeness in the detection is ~80% for galaxies with V<=20 and 22.5galaxies in smoothed images instead. The detected LSBD galaxies are highly concentrated towards the center of the four groups in the inner 250 h^-1 kpc. The best fit power-law slope of the surface density distribution is, on average, beta ~ -1.5 (R < 250 h^-1 kpc), in agreement with the values found for satellites dwarfs around isolated E/S0 galaxies and in X-ray groups. The LSBD galaxies in the Mv-mu0 plane does not show a clear c...

  9. The Horizontal Branch of the Sculptor Dwarf galaxy

    NARCIS (Netherlands)

    Salaris, Maurizio; Boer, Thomas de; Tolstoy, Eline; Fiorentino, Giuliana; Cassisi, Santi

    2013-01-01

    We have performed the first detailed simulation of the horizontal branch of the Sculptor dwarf spheroidal galaxy by means of synthetic modelling techniques, taking consistently into account the star formation history and metallicity evolution as determined from the main sequence and red giant branch

  10. Sulphur, zinc and carbon in the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Skúladóttir, Ása

    2016-01-01

    The Sculptor dwarf spheroidal galaxy is a Milky Way satellite with predominantly old stellar population, and therefore the ideal target to study early chemical evolution. The chemical abundances of photospheres of stars reveal the composition of their birth environment; studying stars of different a

  11. Fast radio burst tied to distant dwarf galaxy (Image 2)

    National Science Foundation

    2017-06-07

    Full Text Available Radio telescope at Arecibo only localized the fast radio burst to the area inside the two circles in this image, but the Very Large Array was able to pinpoint it as a dwarf galaxy within the square (shown at intersection of cross hairs in enlarged box)

  12. The environment of nearby Blue Compact Dwarf Galaxies

    CERN Document Server

    Lopez-Sanchez, Angel R; van Eymeren, Janine; Esteban, Cesar; Popping, Attila; Hibbard, John

    2009-01-01

    We are obtaining deep multiwavelength data of a sample of nearby blue compact dwarf galaxies (BCDGs) combining broad-band optical/NIR and H$\\alpha$ photometry, optical spectroscopy and 21-cm radio observations. Here we present HI results obtained with the Australia Telescope Compact Array for some BCDGs, all showing evident interaction features in their neutral gas component despite the environment in which they reside. Our analysis strongly suggests that interactions with or between low-luminosity dwarf galaxies or HI clouds are the main trigger mechanism of the star-forming bursts in BCDGs; however these dwarf objects are only detected when deep optical images and complementary HI observations are performed. Are therefore BCDGs real isolated systems?

  13. Actively Star Forming Elliptical Galaxies at Low Redshifts in the Sloan Digital Sky Survey

    CERN Document Server

    Fukugita, M; Turner, E L; Helmboldt, J; Nichol, R C; Fukugita, Masataka; Nakamura, Osamu; Turner, Edwin L.; Helmboldt, Joe

    2004-01-01

    We report discovery of actively star forming elliptical galaxies in a morphologically classified sample of bright galaxies at a low redshift obtained from the Sloan Digital Sky Survey. The emission lines of these galaxies do not show the characteristics of active galactic nuclei, and thus their strong H$\\alpha$ emission is ascribed to star formation with a rate nearly as high as that is seen in typical late spiral galaxies. This is taken as evidence against the traditional view that all elliptical galaxies formed early and now evolve only passively. The frequency of such star forming elliptical galaxies is a few tenths of a percent in the sample, but increases to 3% if we include active S0 galaxies. We may identify these galaxies as probable progenitors of so-called E+A galaxies that show the strong Balmer absorption feature of A stars superimposed on an old star population. The approximate match of the abundance of active elliptical plus S0 galaxies with that of E+A galaxies indicates that the duration of su...

  14. The Local Tully–Fisher Relation for Dwarf Galaxies

    Science.gov (United States)

    Karachentsev, Igor D.; Kaisina, Elena I.; Kashibadze (Nasonova, Olga G.

    2017-01-01

    We study different incarnations of the Tully–Fisher (TF) relation for the Local Volume (LV) galaxies taken from Updated Nearby Galaxy Catalog. The UNGC sample contains 656 galaxies with W50 H i-line-width estimates, mostly belonging to low-mass dwarfs. Of them, 296 objects have distances measured with accuracies better than 10%. For the sample of 331 LV galaxies having baryonic masses {log}{M}{bar}> 5.8{log} {M}ȯ , we obtain a relation {log}{M}{bar}=2.49{log}{W}50+3.97 with an observed scatter of 0.38 dex. The largest factors affecting the scatter are observational errors in K-band magnitudes and W50 line widths for the tiny dwarfs, as well as uncertainty of their inclinations. We find that accounting for the surface brightness of the LV galaxies or their gas fraction, specific star-formation rate, or isolation index does not essentially reduce the observed scatter on the baryonic TF diagram. We also notice that a sample of 71 dSph satellites of the Milky Way and M31 with a known stellar velocity dispersion σ* tends to follow nearly the same bTF relation, having slightly lower masses than that of late-type dwarfs.

  15. Dwarf Galaxy Starburst Statistics in the Local Volume

    CERN Document Server

    Lee, Janice C; Funes, José G S J; Shoko Sakai; Akiyama, Sanae

    2008-01-01

    An unresolved question in galaxy evolution is whether the star formation histories of low mass systems are preferentially dominated by starbursts or modes that are more quiescent and continuous. Here, we quantify the prevalence of global starbursts in dwarf galaxies at the present epoch, and infer their characteristic durations and amplitudes. The analysis is based on the H-alpha component of the 11 Mpc H-alpha UV Galaxy Survey (11HUGS), which is providing H-alpha and GALEX UV imaging for an approximately volume-limited sample of ~300 star-forming galaxies within 11 Mpc. We first examine the completeness properties of the sample, and then directly tally the number of bursting dwarfs and compute the fraction of star formation that is concentrated in such systems. Our results are consistent with a picture where dwarfs that are currently experiencing massive global bursts are just the ~6% tip of a low-mass galaxy iceberg. Moreover, bursts are only responsible for about a quarter of the total star formation in th...

  16. THE PRIMEVAL POPULATIONS OF THE ULTRA-FAINT DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.; Avila, Roberto J.; Ferguson, Henry C., E-mail: tbrown@stsci.edu, E-mail: tumlinson@stsci.edu, E-mail: jkalirai@stsci.edu, E-mail: avila@stsci.edu, E-mail: ferguson@stsci.edu [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); and others

    2012-07-01

    We present new constraints on the star formation histories of the ultra-faint dwarf (UFD) galaxies, using deep photometry obtained with the Hubble Space Telescope (HST). A galaxy class recently discovered in the Sloan Digital Sky Survey, the UFDs appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in efforts to understand the missing satellite problem. They are the least luminous, most dark-matter-dominated, and least chemically evolved galaxies known. Our HST survey of six UFDs seeks to determine if these galaxies are true fossils from the early universe. We present here the preliminary analysis of three UFD galaxies: Hercules, Leo IV, and Ursa Major I. Classical dwarf spheroidals of the Local Group exhibit extended star formation histories, but these three Milky Way satellites are at least as old as the ancient globular cluster M92, with no evidence for intermediate-age populations. Their ages also appear to be synchronized to within {approx}1 Gyr of each other, as might be expected if their star formation was truncated by a global event, such as reionization.

  17. Suppression of dwarf galaxy formation by cosmic reionization.

    Science.gov (United States)

    Wyithe, J Stuart B; Loeb, Abraham

    2006-05-18

    A large number of faint galaxies, born less than a billion years after the Big Bang, have recently been discovered. Fluctuations in the distribution of these galaxies contributed to a scatter in the ionization fraction of cosmic hydrogen on scales of tens of megaparsecs, as observed along the lines of sight to the earliest known quasars. Theoretical simulations predict that the formation of dwarf galaxies should have been suppressed after cosmic hydrogen was reionized, leading to a drop in the cosmic star-formation rate. Here we report evidence for this suppression. We show that the post-reionization galaxies that produced most of the ionizing radiation at a redshift z approximately 5.5 must have had a mass in excess of approximately 10(10.9 +/- 0.5) solar masses (M(o)) or else the aforementioned scatter would have been smaller than observed. This limiting mass is two orders of magnitude larger than the galaxy mass that is thought to have dominated the reionization of cosmic hydrogen (approximately 10(8) M(o)). We predict that future surveys with space-based infrared telescopes will detect a population of smaller galaxies that reionized the Universe at an earlier time, before the epoch of dwarf galaxy suppression.

  18. Estimating interstellar extinction toward to elliptical galaxies and star clusters

    Science.gov (United States)

    Amores, E. B.; Lépine, J. R. D.

    2006-08-01

    The ability to estimate interstellar extinction is essential for color corrections and distance calculations of all sorts of astronomical objects being fundamental for galactic structure studies. We performed comparisons of interstellar extinction models by Amores & Lépine ( 2005). These models are based on the hypothesis that gas and dust are homogeneously mixed, and make use of the dust-to gas ratio. The gas density distribution used in the models is obtained from the gas large scale surveys: Berkeley and Parkes HI surveys and from the Columbia University CO survey. In the present work, we compared these models with extinction predictions of elliptical galaxies (gE) and star clusters. We used the similar sample of gE galaxies proposed by Burstein for the comparison between the extinction calculation methods of Burstein & Heiles (1978, 1982) and of Schlegel et al. (1998) extending the comparison to our models. We found rms differences equal to 0.0179 and 0.0189 mag respectively, in the comparison of the predictions of our "model A" with the two methods mentioned. The comparison takes into account the "zero points" introduced by Burstein. The correlation coefficient obtained in the comparison is around 0.85. These results bring to light that our models can be safely used for the estimation of extinction in our Galaxy for extragalactic work, as an alternative method to the BH and SFD predictions. In the comparison with the globular clusters we found rms differences equal to 0.32 and 0.30 for our models A and S, respectively. For the open clusters we made comparisons using different samples and the rms differences were around 0.25.

  19. Estimating interstellar extinction towards elliptical galaxies and star clusters.

    Science.gov (United States)

    de Amôres, E. B.; Lépine, J. R. D.

    The ability to estimate interstellar extinction is essential for color corrections and distance calculations of all sorts of astronomical objects being fundamental for galactic structure studies. We performed comparisons of interstellar extinction models by Amores & Lépine (2005) that are available at: http://www.astro.iag.usp.br/\\symbol{126}amores. These models are based on the hypothesis that gas and dust are homogeneously mixed, and make use of the dust-to gas ratio. The gas density distribution used in the models is obtained from the gas large scale surveys: Berkeley and Parkes HI surveys and from the Columbia University CO survey. In the present work, we compared these models with extinction predictions of elliptical galaxies (gE) and star clusters. We used the similar sample of gE galaxies proposed by Burstein for the comparison between the extinction calculation methods of Burstein & Heiles (1978, 1982) and of Schlegel et al. (1998) extending the comparison to our models. We found rms differences equal to 0.0179 and 0.0189 mag respectively, in the comparison of the predictions of our "model A" with the two methods mentioned. The comparison takes into account the "zero points" introduced by Burstein. The correlation coefficient obtained in the comparison is around 0.85. These results bring to light that our models can be safely used for the estimation of extinction in our Galaxy for extragalactic work, as an alternative method to the BH and SFD predictions. In the comparison with the globular clusters we found rms differences equal to 0.32 and 0.30 for our models A and S, respectively. For the open clusters we made comparisons using different samples and the rms differences were around 0.25.

  20. Dynamics of elliptical galaxies with planetary nebulae in modified Newtonian dynamics

    Science.gov (United States)

    Tian, Yong; Ko, Chung-Ming

    2016-10-01

    The dynamics of an elliptical galaxy within a couple of effective radii can be probed effectively by stars. However, at larger distances planetary nebulae (PNe) replace stars as the tracer of the dynamics. Making use of the motion of PNe, Romanowsky et al. measured the dynamics of three luminous elliptical galaxies (NGC821, NGC3379 and NGC4494) at large distances from the galactic centre. They found that little dark matter is needed up to six effective radii. Milgrom & Sanders showed that this result can be understood in the framework of MOdified Newtonian Dynamics (MOND). As more data are available in the past decade, we revisit this problem. We combine PNe data (up to six to eight effective radii) and stellar data from SAURON of seven elliptical galaxies, including those three galaxies in Romanowsky et al. with updated data and four other galaxies which have not been analysed before. We conclude that the dynamics of these galaxies can be well explained by MOND.

  1. Cosmological simulations of dwarf galaxies with cosmic ray feedback

    Science.gov (United States)

    Chen, Jingjing; Bryan, Greg L.; Salem, Munier

    2016-08-01

    We perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic rays (CRs) generated by supernovae, including the effect of diffusion. We first look at the effect of varying the uncertain CR parameters by repeatedly simulating a single galaxy. Then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8 to 30 × 1010 M⊙. We find that including CR feedback (with diffusion) consistently leads to disc-dominated systems with relatively flat rotation curves and constant star formation rates. In contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. The CR simulations very well match the observed baryonic Tully-Fisher relation, but have a lower gas fraction than in real systems. We also find that the dark matter cores of the CR feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core.

  2. Cosmological Simulations of Dwarf Galaxies with Cosmic Ray Feedback

    CERN Document Server

    Chen, Jingjing; Salem, Munier

    2016-01-01

    We perform zoom-in cosmological simulations of a suite of dwarf galaxies, examining the impact of cosmic-rays generated by supernovae, including the effect of diffusion. We first look at the effect of varying the uncertain cosmic ray parameters by repeatedly simulating a single galaxy. Then we fix the comic ray model and simulate five dwarf systems with virial masses range from 8-30 $\\times 10^{10}$ Msun. We find that including cosmic ray feedback (with diffusion) consistently leads to disk dominated systems with relatively flat rotation curves and constant star formation rates. In contrast, our purely thermal feedback case results in a hot stellar system and bursty star formation. The CR simulations very well match the observed baryonic Tully-Fisher relation, but have a lower gas fraction than in real systems. We also find that the dark matter cores of the CR feedback galaxies are cuspy, while the purely thermal feedback case results in a substantial core.

  3. Stellar Kinematics and Metallicities in the Ultra-faint Dwarf Galaxy Reticulum II

    Science.gov (United States)

    Simon, J. D.; Drlica-Wagner, A.; Li, T. S.; Nord, B.; Geha, M.; Bechtol, K.; Balbinot, E.; Buckley-Geer, E.; Lin, H.; Marshall, J.; Santiago, B.; Strigari, L.; Wang, M.; Wechsler, R. H.; Yanny, B.; Abbott, T.; Bauer, A. H.; Bernstein, G. M.; Bertin, E.; Brooks, D.; Burke, D. L.; Capozzi, D.; Carnero Rosell, A.; Carrasco Kind, M.; D'Andrea, C. B.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Dodelson, S.; Cunha, C. E.; Estrada, J.; Evrard, A. E.; Fausti Neto, A.; Fernandez, E.; Finley, D. A.; Flaugher, B.; Frieman, J.; Gaztanaga, E.; Gerdes, D.; Gruen, D.; Gruendl, R. A.; Honscheid, K.; James, D.; Kent, S.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Maia, M. A. G.; March, M.; Martini, P.; Miller, C. J.; Miquel, R.; Ogando, R.; Romer, A. K.; Roodman, A.; Rykoff, E. S.; Sako, M.; Sanchez, E.; Schubnell, M.; Sevilla, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Tucker, D.; Vikram, V.; Walker, A. R.; Wester, W.; DES Collaboration

    2015-07-01

    We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8+/- 0.5 {km} {{{s}}}-1 and a velocity dispersion of 3.3+/- 0.7 {km} {{{s}}}-1. The mass-to-light ratio of Ret II within its half-light radius is 470+/- 210 {M}⊙ /{L}⊙ , demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 {km} {{{s}}}-1, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 ± 0.09 dex, and we identify several extremely metal-poor stars with {{[Fe/H]}}\\lt -3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of {{[Fe/H]}}=-2.65+/- 0.07, Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is {{log}}10(J)=18.8+/- 0.6 {GeV}{ }2 {{cm}}-5 within 0.°2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies. Based on data obtained from the ESO Science Archive Facility under request number 157689.

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

    CERN Document Server

    Sanchez-Conde, Miguel A; Zandanel, F; Gomez, Mario E; Prada, F

    2011-01-01

    In the last few years, most of the attention in gamma-ray dark matter (DM) searches has been devoted to neutralino annihilations in nearby dwarf galaxies. However, massive galaxy clusters in the local Universe may constitute very good targets as well. The main aim of this work is to compare both dwarf galaxies and local 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 and galaxy clusters, 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 and, given the morphology of its annihilation signal, it is also one of the objects more readily observable by IACTs. As for galaxy clusters, Virgo represents the one with the hi...

  5. UVES Abundances of Stars in Nearby Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Tolstoy, Eline; Venn, Kim; Shetrone, Matt; Primas, Francesca; Hill, Vanessa; Kaufer, Andreas; Szeifert, Thomas

    2002-07-01

    It is a truth universally acknowledged, that a galaxy in possession of a good quantity of gas must want to form stars. It is the details of how and why that baffle us all. The simplest theories either would have this process a carefully self-regulated affair, or one that goes completely out of control and is capable of wrecking the galaxy which hosts it. Of course the majority of galaxies seem to amble along somewhere between these two extremes, and the mean properties tend to favour a quiescent self-regulated evolutionary scenario. But there area variety of observations which require us to invoke transitory ‘bursts’ of star-formation at one time or another in most galaxy types. Several nearby dwarf spheroidal galaxies have clearly determined star-formation histories with apparent periods of zero star formation followed by periods of fairly active star formation. If we are able to understand what separated these bursts we would understand several important phenomena in galaxy evolution. Were these galaxies able to clear out their gas reservoir in a burst of star formation? How did this gas return? or did it? Have these galaxies receieved gas from the IGM instead? Could stars from these types of galaxy contribute significantly to the halo population in our Galaxy? To answer these questions we need to combine accurate stellar photometry and Colour-Magnitude Diagram interpretation with detailed metal abundances to combine a star-formation rate versus time with a range of element abundances with time. Different elements trace different evolutionary process (e.g., relative contributions of type I and II supernovae). We often aren't even sure of the abundance spread in these galaxies. We have collected detailed high resolution UVES spectra of four nearby dwarf spheroidal galaxies (Sculptor, Fornax, Leo I & Carina) to begin to answer these questions. This is a precursor study to a more complete study with FLAMES. We presented at this meeting the initial results for

  6. The Evolution of Nearby Dwarf Galaxies

    NARCIS (Netherlands)

    Tolstoy, E.; Koleva, M; Prugniel, P; Vauglin,

    2011-01-01

    Within the Local Universe galaxies can be studied in great detail star by star. The Colour-Magnitude Diagram synthesis analysis method is well established as the most accurate way to determine the detailed star formation history of galaxies going back to the earliest times. This approach has benefit

  7. Dwarf Galaxies in the Local Group

    NARCIS (Netherlands)

    Tolstoy, Eline; Bruzual, GA; Charlot, S

    2010-01-01

    Within the Local Universe galaxies can be studied in great detail star by star. The Color-Magnitude Diagram synthesis analysis method is well established as the most accurate way to determine the detailed star formation history of galaxies going back to the earliest times. This approach received a s

  8. The Structure of Galaxies: III. Two Structural Families of Ellipticals

    CERN Document Server

    Schombert, James M

    2015-01-01

    Using isophotal radius correlations for a sample of 2MASS ellipticals, we have constructed a series of template surface brightness profiles to describe the profile shapes of ellipticals as a function of luminosity. The templates are a smooth function of luminosity, yet are not adequately matched to any fitting function supporting the view that ellipticals are weakly non-homologous with respect to structure. Through comparison to the templates, it is discovered that ellipticals are divided into two families; those well matched to the templates and a second class of ellipticals with distinctly shallower profile slopes. We refer to these second type of ellipticals as D class, an old morphological designation acknowledging diffuse appearance on photographic material. D ellipticals cover the same range of luminosity, size and kinematics as normal ellipticals, but maintain a signature of recent equal mass dry mergers. We propose that normal ellipticals grow after an initial dissipation formation era by accretion of...

  9. Compact Stellar Systems in the Fornax Cluster Super-massive Star Clusters or Extremely Compact Dwarf Galaxies?

    CERN Document Server

    Drinkwater, M J; Gregg, M D; Phillipps, S

    2000-01-01

    We describe a population of compact objects in the centre of the Fornax Cluster which were discovered as part of our 2dF Fornax Spectroscopic Survey. These objects have spectra typical of old stellar systems, but are unresolved on photographic sky survey plates. They have absolute magnitudes -13dwarf galaxies. These objects are all within 30 arcminutes of the central galaxy of the cluster, NGC 1399, but are distributed over larger radii than the globular cluster system of that galaxy. We suggest that these objects are either super-massive star clusters (intra-cluster globular clusters or tidally stripped nuclei of dwarf galaxies) or a new type of low-luminosity compact elliptical dwarf (M32-type) galaxy. The best way to test these hypotheses will be to obtain high resolution imaging and high-dispersion spectroscopy to determine their structures and mass-to-light ratios. This will allow us ...

  10. Gas, Stars and Star Formation in ALFALFA Dwarf Galaxies

    CERN Document Server

    Huang, S; Giovanelli, R; Brinchmann, J; Stierwalt, S; Neff, S G

    2012-01-01

    We examine the global properties of the stellar and HI components of 229 low HI mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with HI masses < 10^{7.7} M_sun and HI line widths < 80 km s^{-1}. SDSS data are combined with photometric properties derived from GALEX to derive stellar masses (M_*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs) and estimates of their SFRs and M_* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M_* < 10^8 M_sun is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of t...

  11. Stripped elliptical galaxies as probes of ICM physics: I. Tails, wakes, and flow patterns in and around stripped ellipticals

    CERN Document Server

    Roediger, E; Nulsen, P E J; Forman, W R; Machacek, M; Randall, S; Jones, C; Churazov, E; Kokotanekova, R

    2014-01-01

    (abridged) Elliptical cluster galaxies are successively stripped of their gaseous atmospheres due to their motion through the ICM. The stripped galactic gas forms a 'tail' in the galaxy's wake. Deep X-ray observations reveal the fine-structure of the gas tail and of the interface between galactic gas and ICM. This fine-structure depends on dynamic conditions (galaxy potential, initial gas contents, orbit in the host cluster), stripping stage (early infall, pre-/post-pericenter passage), and on the still ill-constrained ICM plasma properties (thermal conductivity, viscosity, magnetic field structure). In a series of papers, we aim at disentangling dynamic and plasma effects in order to use observed stripped ellipticals as probes of the ICM plasma properties. This first paper determines flow phases and flow patterns of successive gas stripping by means of hydrodynamical simulations. During quasi-steady stripping, the flow of ICM around the remnant atmosphere is similar to the flow around solid bodies, including...

  12. Mid-infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei

    Science.gov (United States)

    Hainline, Kevin N.; Reines, Amy E.; Greene, Jenny E.; Stern, Daniel

    2016-12-01

    Searching for active galactic nuclei (AGNs) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ˜18,000 nearby dwarf galaxies (M * great care must be taken when selecting AGNs in dwarf galaxies using infrared colors, as star-forming dwarf galaxies are capable of heating dust in such a way that mimics the infrared colors of more luminous AGNs. In particular, a simple W1-W2 color cut alone should not be used to select AGNs in dwarf galaxies. With these complications in mind, we present a sample of 41 dwarf galaxies that fall in the WISE infrared color space typically occupied by more luminous AGNs and that are worthy of follow-up observations.

  13. First confirmed ultra-compact dwarf galaxy in the NGC 5044 group

    Science.gov (United States)

    Faifer, Favio R.; Escudero, Carlos G.; Scalia, María C.; Smith Castelli, Analía V.; Norris, Mark; De Rossi, María E.; Forte, Juan C.; Cellone, Sergio A.

    2017-03-01

    Context. Ultra-compact dwarfs (UCDs) are stellar systems displaying colours and metallicities between those of globular clusters (GCs) and early-type dwarf galaxies, as well as sizes of Reff ≲ 100 pc and luminosities in the range -13.5 GMOS deep images of several fields around NGC 5044 and in spectroscopic multi-object data of one of these fields, we detected an unresolved source with g' 20.6 mag, compatible with being an UCD. Its radial velocity was obtained with FXCOR and the penalized pixel-fitting (pPXF) code. To study its stellar population content, we measured the Lick/IDS indices and compared them with predictions of single stellar population models, and we used the full spectral fitting technique. Results: The spectroscopic analysis of the UCD revealed a radial velocity that agrees with the velocity of the elliptical galaxy NGC 5044. From the Lick/IDS indices, we have obtained a luminosity-weighted age and metallicity of 11.7+ 1.4-1.2 Gyr and [Z/H] = -0.79 ± 0.04 dex, respectively, as well as [α/ Fe] = 0.30 ± 0.06. From the full spectral fitting technique, we measured a lower age (8.52 Gyr) and a similar total metallicity ([Z/H] = -0.86 dex). Conclusions: Our results indicate that NGC 5044-UCD1 is most likely an extreme GC (MV -12.5 mag) belonging to the GC system of the elliptical galaxy NGC 5044.

  14. The unexpected diversity of dwarf galaxy rotation curves

    CERN Document Server

    Oman, Kyle A; Fattahi, Azadeh; Frenk, Carlos S; Sawala, Till; White, Simon D M; Bower, Richard; Crain, Robert A; Furlong, Michelle; Schaller, Matthieu; Schaye, Joop; Theuns, Tom

    2015-01-01

    We examine the circular velocity profiles of galaxies in {\\Lambda}CDM cosmological hydrodynamical simulations from the EAGLE and LOCAL GROUPS projects and compare them with a compilation of observed rotation curves of galaxies spanning a wide range in mass. The shape of the circular velocity profiles of simulated galaxies varies systematically as a function of galaxy mass, but shows remarkably little variation at fixed maximum circular velocity. This is especially true for low-mass dark matter-dominated systems, reflecting the expected similarity of the underlying cold dark matter haloes. This is at odds with observed dwarf galaxies, which show a large diversity of rotation curve shapes, even at fixed maximum rotation speed. Some dwarfs have rotation curves that agree well with simulations, others do not. The latter are systems where the inferred mass enclosed in the inner regions is much lower than expected for cold dark matter haloes and include many galaxies where previous work claims the presence of a con...

  15. The distribution of alpha elements in Andromeda dwarf galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Vargas, Luis C.; Geha, Marla C.; Tollerud, Erik J., E-mail: luis.vargas@yale.edu [Department of Astronomy, Yale University, 260 Whitney Avenue, New Haven, CT 06511 (United States)

    2014-07-20

    We present alpha to iron abundance ratios for 226 individual red giant branch stars in nine dwarf galaxies of the Andromeda (M31) satellite system. The abundances are measured from the combined signal of Mg, Si, Ca, and Ti lines in Keck/DEIMOS medium-resolution spectra. This constitutes the first large sample of alpha abundance ratios measured in the M31 satellite system. The dwarf galaxies in our sample exhibit a variety of alpha abundance ratios, with the average values in each galaxy ranging from approximately solar ([α/Fe] ∼ + 0.0) to alpha-enhanced ([α/Fe] ∼ + 0.5). These variations do not show a correlation with internal kinematics, environment, or stellar density. We confirm radial gradients in the iron abundance of two galaxies out of the five with sufficient data (NGC 185 and And II). There is only tentative evidence for an alpha abundance radial gradient in NGC 185. We homogeneously compare our results to the Milky Way classical dwarf spheroidals, finding evidence for wider variation in average alpha abundance. In the absence of chemical abundances for the M31 stellar halo, we compare to the Milky Way stellar halo. A stellar halo comprised of disrupted M31 satellites is too metal-rich and inconsistent with the Milky Way halo alpha abundance distribution even if considering only satellites with predominantly old stellar populations. The M31 satellite population provides a second system in which to study chemical abundances of dwarf galaxies and reveals a wider variety of abundance patterns than the Milky Way.

  16. Virgo Cluster and field dwarf ellipticals in 3D: I. On the variety of stellar kinematic and line-strength properties

    CERN Document Server

    Ryś, Agnieszka; van de Ven, Glenn

    2012-01-01

    We present the first large-scale stellar kinematic and line-strength maps for dwarf elliptical galaxies (9 in the Virgo Cluster and 3 in the field environment) obtained with the SAURON integral-field unit. No two galaxies in our sample are alike: we see that the level of rotation is not tied to flattening (we have, e.g. round rotators and flattened nonrotators); we observe kinematic twists in 1 Virgo and 1 field object; we discover large-scale kinematically-decoupled components in 2 field galaxies; we see varying gradients in line-strength maps, from nearly flat to strongly peaked in the center. The great variety of morphological, kinematic, and stellar population parameters seen in our data points to a formation scenario in which properties are shaped stochastically. A combined effect of ram-pressure stripping and galaxy harassment is the most probable explanation. We show the need for a comprehensive analysis of kinematic, dynamical, and stellar population properties which will enable us to place dwarf elli...

  17. The Mass Dependence of Dwarf Satellite Galaxy Quenching

    CERN Document Server

    Slater, Colin T

    2014-01-01

    We combine observations of the Local Group with data from the NASA-Sloan Atlas to show the variation in the quenched fraction of satellite galaxies from low mass dwarf spheroidals and dwarf irregulars to more massive dwarfs similar to the Magellanic clouds. While almost all of the low mass ($M_\\star \\lesssim 10^7$ $M_\\odot$) dwarfs are quenched, at higher masses the quenched fraction decreases to approximately 40-50%. This change in the quenched fraction is large, and suggests a sudden change in the effectiveness of quenching that correlates with satellite mass. We combine this observation with models of satellite infall and ram pressure stripping to show that the low mass satellites must quench within 1-2 Gyr of pericenter passage to maintain a high quenched fraction, but that many more massive dwarfs must continue to form stars today even though they likely fell in to their host >5 Gyr ago. We also characterize how the susceptibility of dwarfs to ram pressure must vary as a function of mass if it is to acco...

  18. The star cluster system of the luminous elliptical galaxy NGC 1600

    CERN Document Server

    Santiago, B X

    2008-01-01

    Luminous elliptical galaxies generally display a rich star cluster system, whose properties provide strong constraints on the physics of galaxy formation and evolution. Star cluster system studies, however, concentrate on galaxies located in nearby or rich galaxy clusters. We acquired deep B and I images of NGC 1600, a luminous elliptical in a galaxy group to study its star cluster system. The images were obtained with the Optical Imager at the SOAR telescope. The sample selection incompleteness was assessed as a function of magnitude and image background level. Source counts were measured for different elliptical annuli from the centre of NGC 1600, background subtracted, and fitted with a Gaussian function. Colour distributions were derived as a function of galactocentric distance for sources measured successfully in both filters. Typical ages and metallicities were estimated based on single stellar population models. A clear excess of point sources around NGC 1600 was found in relation to the nearby field. ...

  19. The specific entropy of elliptical galaxies an explanation for profile-shape distance indicators?

    CERN Document Server

    Lima-Neto, G B; Márquez, I; Neto, Gastao B. Lima; Gerbal, Daniel; Marquez, Isabel

    1999-01-01

    Dynamical systems in equilibrium have a stationary entropy; we suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a unique specific entropy. This uniqueness, a priori unknown, should be reflected in correlations between the parameters describing the mass (light) distribution in galaxies. Following recent photometrical work (Caon et al. 1993; Graham & Colless 1997; Prugniel & Simien 1997), we use the Sersic law to describe the light profile of elliptical galaxies and an analytical approximation to its three dimensional deprojection. The specific entropy is calculated supposing that the galaxy behaves as a spherical, isotropic, one-component system in hydrostatic equilibrium, obeying the ideal gas state equations. We predict a relation between the 3 parameters of the Sersic, defining a surface in the parameter space, an `Entropic Plane', by analogy with the well-known Fundamental Plane. We have analysed elliptical galaxies in Coma and ABCG 85 clusters and a gr...

  20. The Mbh-sigma relation as a constraint on the formation of elliptical galaxies

    CERN Document Server

    Ciotti, L

    2001-01-01

    Most elliptical galaxies contain central black holes, whose masses scale proportionally to the observed central velocity dispersions of the host galaxies according to the so-called Mbh-sigma relation. Here we discuss some consequences that can be derived by combining the Mbh-sigma relation with the scaling relation describing the Fundamental Plane of elliptical galaxies. In particular, the possibility of substantial dissipationless merging in the formation and evolution of elliptical galaxies is discussed. Enforcing the merger end-products to satisfy the two scaling relations mentioned above, a major role of dissipation in galaxy formation is strongly suggested by our analysis. Moreover, we show that existing observational data may shed some light on the complex process of black hole merging.

  1. Elliptical Galaxies with Emission Lines from the Sloan Digital Sky Survey

    Institute of Scientific and Technical Information of China (English)

    Ying-He Zhao; Qiu-Sheng Gu; Zhi-Xin Peng; Lei Shi; Xin-Lian Luo; Qiu-He Peng

    2006-01-01

    As part of a study of star formation history along the Hubble sequence,we present here the results for 11 elliptical galaxies with strong nebular emission lines. After removing the dilution from the underlying old stellar populations by use of stellar population synthesis model, we derive the accurate fluxes of all the emission lines in these objects, which are then classified, using emission line ratios,into one Seyfert 2, six LINERs and four HⅡ galaxies. We also identify one HⅡ galaxy (A1216+04) as a hitherto unknown Wolf-Rayet galaxy from the presence of the WolfRayet broad bump at 4650 A. We propose that the star-forming activities in elliptical galaxies are triggered by either galaxy-galaxy interaction or the merging of a small satellite/a massive star cluster, as has been suggested by recent numerical simulations.

  2. Prediction of galaxy ellipticities and reduction of shape noise in cosmic shear measurements

    Science.gov (United States)

    Croft, Rupert A. C.; Freeman, Peter E.; Schuster, Thomas S.; Schafer, Chad M.

    2017-08-01

    The intrinsic scatter in the ellipticities of galaxies about the mean shape, known as `shape noise', is the most important source of noise in weak lensing shear measurements. Several approaches for reducing shape noise have recently been put forward, using information beyond photometry, such as radio polarization and optical spectroscopy. Here we investigate how well the intrinsic ellipticities of galaxies can be predicted using other exclusively photometric parameters. These (such as galaxy colours) are already available in the data and do not necessitate additional, often expensive observations. We apply a regression technique, generalized additive models to the publicly released galaxy property data from CFHTLenS. We find that the individual galaxy ellipticities can be predicted from other photometric parameters to better precision than the scatter about the mean ellipticity. The ellipticity contribution to the shear can apparently therefore be measured to higher precision, comparable to using a larger sample of galaxies. Using only parameters unaffected by lensing (e.g. surface brightness, colour), our best-fitting model leads to a gain (for the ellipticity contribution only) equivalent to having 12 per cent more galaxies in the sample. Allowing parameters correlated with lensing increases the apparent gains (we find 52.5 per cent), but these would likely be negated by correlations between the predictor and measured shear. We caution that the ultimate usefulness of this method will depend on careful treatment of the effect of the point spread function and input parameter measurement. This is to avoid information on the ellipticity contaminating the estimated ellipticity through observational effects rather than true physical correlations.

  3. NICMOS observations of high redshift radio galaxies witnessing the formation of bright elliptical galaxies?

    CERN Document Server

    Pentericci, L; Röttgering, H J A; Miley, G K; Van Breugel, W; Fosbury, R A E

    2001-01-01

    We present the results of a near infrared imaging program of a sample of 19 radio galaxies with redshift between 1.7 and 3.2, using the NICMOS Camera 2 on the Hubble Space Telescope. The galaxies were observed in H-band which, for 18 of the 19 targets, samples the rest-frame optical emission longwards of the 4000 A break. The images show a wide range of morphologies, from unresolved to compact systems, to systems with substructures such as multiple emission peaks, to systems comprised of several components spread over large areas. The morphologies of 5 of the lowest redshift targets are well represented by a de Vaucouleurs profile, consistent with them being elliptical galaxies. Their average effective radius is a factor of 2 smaller than that of z=1 3CR radio galaxies at similar restframe wavelengths. The near infrared continuum light is generally well aligned with the radio axis and the aligned light has typical V-H colors of around 3.5-4. For several galaxies where WFPC2 images were available, we computed ...

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

    Energy Technology Data Exchange (ETDEWEB)

    Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Holtzman, Jon [Department of Astronomy, New Mexico State University, Box 30001, 1320 Frenger Street, Las Cruces, NM 88003 (United States); Gilbert, Karoline M.; Dalcanton, Julianne J.; Williams, Benjamin F., E-mail: drw@ucsc.edu [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)

    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.

  5. The PAndAS View of the Andromeda Satellite System. II. Detailed Properties of 23 M31 Dwarf Spheroidal Galaxies

    Science.gov (United States)

    Martin, Nicolas F.; Ibata, Rodrigo A.; Lewis, Geraint F.; McConnachie, Alan; Babul, Arif; Bate, Nicholas F.; Bernard, Edouard; Chapman, Scott C.; Collins, Michelle M. L.; Conn, Anthony R.; Crnojević, Denija; Fardal, Mark A.; Ferguson, Annette M. N.; Irwin, Michael; Mackey, A. Dougal; McMonigal, Brendan; Navarro, Julio F.; Rich, R. Michael

    2016-12-01

    We present a comprehensive analysis of the structural properties and luminosities of the 23 dwarf spheroidal galaxies that fall within the footprint of the Pan-Andromeda Archaeological Survey (PAndAS). These dwarf galaxies represent the large majority of Andromeda’s known satellite dwarf galaxies and cover a wide range in luminosity (-11.6≲ {M}V≲ -5.8 or {10}4.2≲ L≲ {10}6.5 {L}⊙ ) and surface brightness (25.1≲ {μ }0≲ 29.3 mag arcsec-2). We confirm most previous measurements, but we find And XIX to be significantly larger than before ({r}h={3065}-935+1065 {pc}, {M}V=-{10.1}-0.4+0.8) and cannot derive parameters for And XXVII as it is likely not a bound stellar system. We also significantly revise downward the luminosities of And XV and And XVI, which are now {M}V˜ -7.5 or L˜ {10}5 {L}⊙ . Finally, we provide the first detailed analysis of Cas II/And XXX, a fairly faint system ({M}V=-{8.0}-0.3+0.4) of typical size ({r}h=270+/- 50 {pc}), located in close proximity to the two bright elliptical dwarf galaxies NGC 147 and NGC 185. Combined with the set of homogeneous distances published in an earlier contribution, our analysis dutifully tracks all relevant sources of uncertainty in the determination of the properties of the dwarf galaxies from the PAndAS photometric catalog. We further publish the posterior probability distribution functions of all the parameters we fit for in the form of MCMC chains available online; these inputs should be used in any analysis that aims to remain truthful to the data and properly account for covariance between parameters.

  6. Dynamical mass modeling of dispersion-supported dwarf galaxies

    Science.gov (United States)

    Wolf, Joseph

    The currently favored cold dark matter cosmology (LCDM) has had much success in reproducing the large scale structure of the universe. However, on smaller scales there are some possible discrepancies when attempting to match galactic observations with properties of halos in dissipationless LCDM simulations. One advantageous method to test small scale simulations with observations is through dynamical mass modeling of nearby dwarf spheroidal galaxies (dSphs). The stellar tracers of dSphs are dispersion-supported, which poses a significant challenge in accurately deriving mass profiles. Unlike rotationally-supported galaxies, the dynamics of which can be well-approximated by one-dimensional physics, modeling dispersion-supported systems given only line-of-sight data results in a well-known degeneracy between the mass profile and the velocity dispersion anisotropy. The core of this dissertation is rooted in a new advancement which we have discovered: the range of solutions allowed by the mass-anisotropy degeneracy varies as a function of radius, with a considerable minimal near the deprojected half-light radius of almost all observed dispersion-supported galaxies. This finding allows for a wide range of applications in galaxy formation scenarios to be explored in an attempt to address, amongst other hypotheses, whether the LCDM framework needs to be modified in order to reproduce observations on the small scale. This thesis is comprised of both the derivation of this finding, and its applicability to all dispersion-supported systems, ranging from dwarfs galaxies consisting of a few hundred stars to systems of 'intracluster light', containing over a trillion stars. Rarely does one have the privilege of working with systems that span such a large range in luminosity (or any intrinsic property) in a short graduate career. Although the large applicability of this scale-free finding allows for discussion in many subfields, this thesis will mainly focus on one topic: dwarf

  7. Dark Matter Identification with Gamma Rays from Dwarf Galaxies

    CERN Document Server

    Perelstein, Maxim

    2010-01-01

    If the positron fraction and combined electron-positron flux excesses recently observed by PAMELA, FERMI and HESS are due to dark matter annihilation into lepton-rich final states, the accompanying final state radiation (FSR) photons may be detected by ground-based atmospheric Cherenkov telescopes (ACTs). Satellite dwarf galaxies in the vicinity of the Milky Way are particularly promising targets for this search. We find that current and near-future ACTs have an excellent potential for discovering the FSR photons from dwarfs, although a discovery cannot be guaranteed due to large uncertainties in the fluxes resulting from lack of precise knowledge of dark matter distribution within the dwarfs. We also investigate the possibility of discriminating between different dark matter models based on the measured FSR photon spectrum. For typical parameters, we find that the ACTs can reliably distinguish models predicting dark matter annihilation into two-lepton final states from those favoring four-lepton final states...

  8. Calibrating UV Star Formation Rates for Dwarf Galaxies from STARBIRDS

    CERN Document Server

    McQuinn, Kristen B W; Dolphin, Andrew E; Mitchell, Noah P

    2015-01-01

    Integrating our knowledge of star formation traced by observations at different wavelengths is essential for correctly interpreting and comparing star formation activity in a variety of systems and environments. This study compares extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with color-magnitude diagram (CMD) based star formation rates (SFRs) derived from resolved stellar populations and CMD fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The datasets are from the panchromatic STARBurst IRregular Dwarf Survey (STARBIRDS) and include deep legacy GALEX UV imaging, HST optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated near UV fluxes predicted from the CMD-based SFRs - using four different models - agree with the measured, extinction corrected, integrated near UV fluxes from GALEX images, but the far UV predicted fluxes do not. Further, we find a systematic deviation between the SFRs based on integrated far U...

  9. Constraints on mass loss of globular clusters in dwarf galaxies

    CERN Document Server

    Larsen, S S; Brodie, J P

    2013-01-01

    The Fornax dwarf spheroidal galaxy is well known for its very high globular cluster specific frequency, SN=26. Furthermore, while the field star metallicity distribution peaks at [Fe/H]=-1, four of the five GCs have [Fe/H]<-2. Only about 5 percent of the field stars have such low metallicities. Hence, a very large fraction of about 1/5-1/4 of the most metal-poor stars belong to the four most metal-poor GCs. This implies that these clusters could, at most, have been a factor of 4-5 more massive initially. A second, even more extreme case may be the IKN dwarf galaxy where SN=124. Although metallicities are not accurately known, the GCs account for about 13 percent of the total V-band luminosity of IKN.

  10. The local Tully-Fisher relation for dwarf galaxies

    CERN Document Server

    Karachentsev, Igor D; Kashibadze, Olga G

    2016-01-01

    We study different incarnations of the Tully-Fisher (TF) relation for the Local Volume (LV) galaxies taken from Updated Nearby Galaxy Catalog. The UNGC sample contains 656 galaxies with $W_{50}$ HI-line-width estimates, mostly belonging to low mass dwarfs. Of them, 296 objects have distances measured with accuracy better than 10%. For the sample of 331 LV galaxies having baryonic masses $\\log M_{bar} > 5.8 \\log M_\\odot$ we obtain a relation $\\log M_{bar}= 2.49 \\log W_{50} + 3.97$ with observed scatter of 0.38 dex. The largest factors affecting the scatter are observational errors in $K$-band magnitudes and $W_{50}$ line widths for the tiny dwarfs, as well as uncertainty of their inclinations. We find that accounting for the surface brightness of the LV galaxies, or their gas fraction, or specific star formation rate, or the isolation index do not reduce essentially the observed scatter on the baryonic TF-diagram. We also notice that a sample of 71 dSph satellites of the Milky Way and M31 with known stellar ve...

  11. New dwarf galaxy candidates in the Centaurus group

    CERN Document Server

    Müller, Oliver; Binggeli, Bruno

    2015-01-01

    Recent studies of the distribution and kinematics of the Milky Way and Andromeda satellite galaxy systems have confirmed the existence of coplanar, corotating structures of galaxies. In addition to the 'missing satellite problem', these structures pose a major challenge to the standard $\\Lambda$CDM scenario of structure formation. We complement the efforts made by the dwarf galaxy community to extend these studies to other nearby galaxy groups by systematically searching for faint, unresolved dwarf members with a low surface brightness in the Southern Centaurus group of galaxies. The aim is to determine whether these coplanar, corotating structures are a universal phenomenon. We imaged an area of 60 square degrees (0.3 Mpc$^2$) around the M83 subgroup with the wide-field Dark Energy Camera (DECam) at the CTIO 4 m Blanco telescope in $g$ and $r$ down to a limiting surface brightness of $\\mu_r\\approx 30$ mag arcsec$^{-2}$. Various image-filtering techniques were applied to the DECam data to enhance the visibili...

  12. Intrinsic alignments of disc and elliptical galaxies in the MassiveBlack-II and Illustris simulations

    Science.gov (United States)

    Tenneti, Ananth; Mandelbaum, Rachel; Di Matteo, Tiziana

    2016-11-01

    We study the shapes and intrinsic alignments of discs and elliptical galaxies in the MassiveBlack-II (MBII) and Illustris cosmological hydrodynamic simulations, with volumes of (100 h-1 Mpc)3 and (75 h-1 Mpc)3, respectively. We find that simulated disc galaxies are more oblate in shape and more misaligned with the shape of their host dark matter subhalo when compared with ellipticals. The disc major axis is found to be oriented towards the location of nearby elliptical galaxies. We also find that the discs are thinner in MBII and misalignments with dark matter halo orientations are smaller in both discs and ellipticals when compared with Illustris. As a result, the intrinsic alignment correlation functions at fixed mass have a higher amplitude in MBII than in Illustris. Finally, at scales above ˜0.1 h-1 Mpc, the intrinsic alignment two-point correlation functions for disc galaxies in both simulations are consistent with a null detection, unlike those for ellipticals. Despite significant differences in the treatments of hydrodynamics and baryonic physics in the simulations, we find that the wδ + correlation function scales similarly with transverse separation. However, the less massive galaxies show different scale dependence in the ellipticity-direction correlation. This result indicates that, while hydrodynamic simulations are a promising tool to study intrinsic alignments, further study is needed to understand the impact of differences in the implementations of hydrodynamics and baryonic feedback.

  13. The star-formation histories of elliptical galaxies across the fundamental plane

    CERN Document Server

    Nolan, L A; Panter, B; Jiménez, R; Heavens, A F; Smith, G; Nolan, Louisa A.; Jimenez, Raul

    2006-01-01

    We present the first results from a study designed to test whether, given high-quality spectrophotometry spanning the mid-UV--optical wavelength regime, it is possible to distinguish the metal content (Z) and star-formation history (sfh) of individual elliptical galaxies with sufficient accuracy to establish whether their formation history is linked to their detailed morphology and position on the Fundamental Plane. From a detailed analysis of UV-optical spectrophotometry of the `cuspy' elliptical galaxy NGC 3605 and the giant elliptical NGC 5018 we find that: 1) optical spectra with l > 3500 A may not contain sufficient data to robustly uncover all the stellar populations present in individual galaxies, even in such relatively passive objects as ellipticals, 2) the addition of the UV data approaching l = 2500 A holds the key to establishing well-constrained sfhs, from which we can infer a formation and evolution history which is consistent with their photometric properties, 3) despite the superficial similar...

  14. Ultra-diffuse galaxies: the high-spin tail of the abundant dwarf galaxy population

    CERN Document Server

    Amorisco, N C

    2016-01-01

    Recent observations have revealed the existence of an abundant population of faint, low surface brightness (SB) galaxies, which appear to be numerous and ubiquitous in nearby galaxy clusters, including the Virgo, Coma and Fornax clusters. With median stellar masses of dwarf galaxies, these ultra-diffuse galaxies (UDGs) have unexpectedly large sizes, corresponding to a mean SB of $24\\lesssim\\langle\\mu_e\\rangle_r\\ {\\rm mag}^{-1} {\\rm arcsec}^2\\lesssim27$ within the effective radius. We show that the UDG population represents the tail of galaxies formed in dwarf-sized haloes with higher-than-average angular momentum at collapse. By adopting the standard model of disk formation -- in which the size of galaxies is set by the spin of the halo -- we recover both the abundance of UDGs as a function of the host cluster mass and the distribution of sizes within the UDG population. According to this model, UDGs are not failed $L_*$ galaxies, but genuine dwarfs, and their low SB is not uniquely connected to the harsh clu...

  15. Dwarf galaxies: quantity and varietyÂ

    Science.gov (United States)

    Cellone, S. A.; Buzzoni, A.

    The structural properties and stellar populations of 79 low- and intermediate-luminosity galaxies in the NGC5044 Group are analized. The galaxies in the sample are re-classified into different morphological subgroups, with emphasis on the identification of objects showing a bulge+disk structure. The behaviour of their properties against their (projected) position within the group is addressed, looking for evidences for possible environmental effects. The observations were obtained at ESO (1999-2000) and CASLEO (1996-1999). Nearly 50% of the data presented here are new. FULL TEXT IN SPANISH

  16. Proceedings of the Bonn/Bochum-Graduiertenkolleg Workshop 'The Magellanic Clouds and Other Dwarf Galaxies'

    OpenAIRE

    Richtler, Tom; Braun, Jochen M.

    1998-01-01

    The Workshop 'The Magellanic Clouds and Other Dwarf Galaxies' was held at the Physikzentrum Bad Honnef in January 1998. The proceedings comprise 79 contributions. About 1/3 of the 352 pages contain the following Reviews: The Violent Interstellar Medium in Dwarf Galaxies: Atomic Gas (Elias Brinks and Fabian Walter), Hot Gas in the Large Magellanic Cloud (You-Hua Chu), Astrophysics of Dwarf Galaxies: Structures and Stellar Populations (John S. Gallagher), Star-forming regions and ionized gas in...

  17. The entropy of elliptical galaxies in Coma a clue for a distance indicator

    CERN Document Server

    Gerbal, D; Márquez, I; Verhagen, H; Gerbal, Daniel; Neto, Gastao B. Lima; Marquez, Isabel; Verhagen, Huub

    1997-01-01

    We have fitted the surface brightness of a sample of 79 elliptical galaxies pertaining to the Coma cluster of galaxies using the Sersic profile. This model is defined through three primary parameters: scale length (a), intensity ($\\Sigma_0$), and a shape parameter (\

  18. The SAURON project - VI. Line strength maps of 48 elliptical and lenticular galaxies

    NARCIS (Netherlands)

    Kuntschner, Harald; Emsellem, Eric; Bacon, R.; Bureau, M.; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. T.; Falcon-Barroso, Jesus; Krajnovic, Davor; McDermid, Richard M.; Peletier, Reynier F.; Sarzi, Marc

    2006-01-01

    We present absorption line strength maps of 48 representative elliptical and lenticular galaxies obtained as part of a survey of nearby galaxies using our custom-built integral-field spectrograph, SAURON, operating on the William Herschel Telescope. Using high-quality spectra, spatially binned to a

  19. The PN.S Elliptical Galaxy Survey: a standard ΛCDM halo around NGC 4374?

    NARCIS (Netherlands)

    Napolitano, N. R.; Romanowsky, A. J.; Capaccioli, M.; Douglas, N. G.; Arnaboldi, M.; Coccato, L.; Gerhard, O.; Kuijken, K.; Merrifield, M. R.; Bamford, S. P.; Cortesi, A.; Das, P.; Freeman, K. C.

    2011-01-01

    As part of our current programme to test ΛCDM predictions for dark matter (DM) haloes using extended kinematical observations of early-type galaxies, we present a dynamical analysis of the bright elliptical galaxy NGC 4374 (M84) based on ˜450 planetary nebulae (PNe) velocities from the PN.Spectrogra

  20. VERITAS Deep Observations of the Dwarf Spheroidal Galaxy Segue 1

    CERN Document Server

    Aliu, E; Arlen, T; Aune, T; Beilicke, M; Benbow, W; Bouvier, A; Bradbury, S M; Buckley, J H; Bugaev, V; Byrum, K; Cannon, A; Cesarini, A; Christiansen, J L; Ciupik, L; Collins-Hughes, E; Connolly, M P; Cui, W; Decerprit, G; Dickherber, R; Dumm, J; Errando, M; Falcone, A; Feng, Q; Ferrer, F; Finley, J P; Finnegan, G; Fortson, L; Furniss, A; Galante, N; Gall, D; Godambe, S; Griffin, S; Grube, J; Gyuk, G; Hanna, D; Holder, J; Huan, H; Hughes, G; Humensky, T B; Kaaret, P; Karlsson, N; Kertzman, M; Khassen, Y; Kieda, D; Krawczynski, H; Krennrich, F; Lee, K; Madhavan, A S; Maier, G; Majumdar, P; McArthur, S; McCann, A; Moriarty, P; Mukherjee, R; Ong, R A; Orr, M; Otte, A N; Park, N; Perkins, J S; Pohl, M; Prokoph, H; Quinn, J; Ragan, K; Reyes, L C; Reynolds, P T; Roache, E; Rose, H J; Ruppel, J; Saxon, D B; Schroedter, M; Sembroski, G H; Senturk, G D; Skole, C; Smith, A W; Staszak, D; Telezhinsky, I; Tesic, G; Theiling, M; Thibadeau, S; Tsurusaki, K; Varlotta, A; Vassiliev, V V; Vincent, S; Vivier, M; Wagner, R G; Wakely, S P; Ward, J E; Weekes, T C; Weinstein, A; Weisgarber, T; Williams, D A; Zitzer, B

    2012-01-01

    The VERITAS array of Cherenkov telescopes has carried out a deep observational program on the nearby dwarf spheroidal galaxy Segue 1. We report on the results of nearly 48 hours of good quality selected data, taken between January 2010 and May 2011. No significant $\\gamma$-ray emission is detected at the nominal position of Segue 1, and upper limits on the integrated flux are derived. According to recent studies, Segue 1 is the most dark matter-dominated dwarf spheroidal galaxy currently known. We derive stringent bounds on various annihilating and decaying dark matter particle models. The upper limits on the velocity-weighted annihilation cross-section are $\\mathrm{^{95% CL} \\lesssim 10^{-23} cm^{3} s^{-1}}$, improving our limits from previous observations of dwarf spheroidal galaxies by at least a factor of two for dark matter particle masses $\\mathrm{m_{\\chi}\\gtrsim 300 GeV}$. The lower limits on the decay lifetime are at the level of $\\mathrm{\\tau^{95% CL} \\gtrsim 10^{24} s}$. Finally, we address the inte...

  1. Faint Dwarf Galaxies in Hickson Compact Group 90

    CERN Document Server

    Ordenes-Briceño, Yasna; 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

    2016-01-01

    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 $0.7\\!\\lesssim\\! r_{\\rm eff}/{\\rm kpc}\\! \\lesssim\\! 1.5$ with luminosities of $-11.65\\!\\lesssim\\! M_U\\! \\lesssim\\! -9.42$ and $-12.79\\!\\lesssim\\! M_I\\! \\lesssim\\! -10.58$ mag, corresponding to a color range of $(U\\!-\\!I)_0\\!\\simeq\\!1.1\\!-\\!2.2$ mag and surface brightness levels of $\\mu_U\\!\\simeq\\!28.1\\,{\\rm mag/arcsec^2}$ and $\\mu_I\\!\\simeq\\!27.4\\,{\\rm mag/arcsec^2}$. Their colours and luminosities are consistent with a diverse set of stellar population properties. Assuming solar and 0.02 Z$_\\odot$ metallicities we obtain stellar masses in the range $M_*|_{Z_\\odot} \\simeq 10^{5.7-6.3} M_{\\odot}$ and $M_*|_{0.02\\,Z_\\odot}\\!\\simeq\\!10^{6.3-8}\\,M_{\\odot}$. Three dwarfs are ol...

  2. Dwarf Galaxies, MOND, and Relativistic Gravitation

    Directory of Open Access Journals (Sweden)

    Arthur Kosowsky

    2010-01-01

    Certain limits of these theories can also give the accelerating expansion of the Universe. The standard dark matter cosmology boasts numerous manifest triumphs; however, alternatives should also be pursued as long as outstanding observational issues remain unresolved, including the empirical successes of MOND on galaxy scales and the phenomenology of dark energy.

  3. Optical-Near Infrared Color Gradients of Elliptical Galaxies and Their Environmental Dependence

    CERN Document Server

    Ko, J; Ko, Jongwan; Im, Myungshin

    2005-01-01

    We have studied the environmental effect on optical-NIR color gradients of 273 nearby elliptical galaxies. Color gradient is a good tool to study the evolutionary history of elliptical galaxies, since the steepness of the color gradient reflects merging history of early types. When an elliptical galaxy goes through many merging events, the color gradient can be get less steep or reversed due to mixing of stars. One simple way to measure color gradient is to compare half-light radii in different bands. We have compared the optical and near infrared half-light radii of 273 early-type galaxies from Pahre(1999). Not surprisingly, we find that r$_{e}$(V)s (half-light radii measured in V-band) are in general larger than r$_{e}$(K)s (half-light radii measured in K-band). However, when divided into different environments, we find that elliptical galaxies in the denser environment have gentler color gradients than those in the less dense environment. Our finding suggests that elliptical galaxies in the dense environme...

  4. A Study of the Star-forming Dwarf Galaxy NGC 855 with Spitzer

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    We present a study of the dwarf elliptical galaxy NGC 855 using the narrow-band Ha and Spitzer data. Both the Ha and Spitzer IRAC images confirm star-forming activity in the center of NGC 855. We obtained a star formation rate (SFR) of 0.022 and 0.025 M☉yr-1, respectively, from the Spitzer IRAC 8.0 μm and MIPS 24 μm emission data. The HI observa tion suggests that the star-forming activity might be triggered by a minor merger. We also find that there is a distinct IR emission region in 5.8 and 8.0μm bands, located at about 10 "away from the nucleus of NGC 855. Given the strong 8.0μm but faint Hα emission, we expect that it is a heavily obscured star-forming region, which needs to be confirmed by further optical spectroscopic observations.

  5. HERSCHEL SPECTROSCOPIC OBSERVATIONS OF LITTLE THINGS DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Cigan, Phil; Young, Lisa [Physics Department, New Mexico Institute of Mining and Technology, Socorro, NM 87801 (United States); Cormier, Diane [Institut für Theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany); Lebouteiller, Vianney; Madden, Suzanne [Laboratoire AIM, CEA/DSM—CNRS—Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette (France); Hunter, Deidre [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Brinks, Elias [Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB (United Kingdom); Elmegreen, Bruce [IBM T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Hts., NY 10598 (United States); Schruba, Andreas [Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching (Germany); Heesen, Volker, E-mail: pcigan@alumni.nmt.edu [School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ (United Kingdom); Collaboration: LITTLE THINGS Team

    2016-01-15

    We present far-infrared (FIR) spectral line observations of five galaxies from the Little Things sample: DDO 69, DDO 70, DDO 75, DDO 155, and WLM. While most studies of dwarfs focus on bright systems or starbursts due to observational constraints, our data extend the observed parameter space into the regime of low surface brightness dwarf galaxies with low metallicities and moderate star formation rates. Our targets were observed with Herschel at the [C ii] 158 μm, [O i] 63 μm, [O iii] 88 μm, and [N ii] 122 μm emission lines using the PACS Spectrometer. These high-resolution maps allow us for the first time to study the FIR properties of these systems on the scales of larger star-forming complexes. The spatial resolution in our maps, in combination with star formation tracers, allows us to identify separate photodissociation regions (PDRs) in some of the regions we observed. Our systems have widespread [C ii] emission that is bright relative to continuum, averaging near 0.5% of the total infrared (TIR) budget—higher than in solar-metallicity galaxies of other types. [N ii] is weak, suggesting that the [C ii] emission in our galaxies comes mostly from PDRs instead of the diffuse ionized interstellar medium (ISM). These systems exhibit efficient cooling at low dust temperatures, as shown by ([O i]+[C ii])/TIR in relation to 60 μm/100 μm, and low [O i]/[C ii] ratios which indicate that [C ii] is the dominant coolant of the ISM. We observe [O iii]/[C ii] ratios in our galaxies that are lower than those published for other dwarfs, but similar to levels noted in spirals.

  6. Unequal-mass galaxy merger remnants: spiral-like morphology but elliptical-like kinematics

    CERN Document Server

    Bournaud, F; Jog, C J

    2004-01-01

    It is generally believed that major galaxy mergers with mass ratios in the range 1:1-3:1 result in remnants that have properties similar to elliptical galaxies, and minor mergers below 10:1 result in disturbed spiral galaxies. The intermediate range of mass ratios 4:1-10:1 has not been studied so far. Using N-body simulations, we show that such mergers can result in very peculiar systems, that have the morphology of a disk galaxy with an exponential profile, but whose kinematics is closer to that of elliptical systems. These objects are similar to those recently observed by Jog & Chitre (2002). We present two cases with mass ratios 4.5:1 and 7:1, and show that the merging causes major heating and results in the appearance of elliptical-type kinematics, while surprisingly the initial spiral-like mass profile is conserved.

  7. HI Gas in Disk and Dwarf Galaxies in the Semi-analytic Models of Galaxy Formation†

    Science.gov (United States)

    Fu, Jian; Wang, Jing; Luo, Yu

    We construct the radially-resolved semi-analytic models of galaxy formation based on the L-Galaxies model framework, which include both atomic and molecular gas phase in ISM. The models run on the halo outputs of ΛCDM cosmology N-body simulation. Our models can reproduce varies observations of HI gas in nearby galaxies, e.g. the HI mass function, the HI-to-star ratio vs stellar mass and stellar surface density, universal HI radial surface density profile in outer disks etc. We also give the physical origin of HI size-mass relation. Based on our model results for local dwarf galaxies, we show that the ``missing satellite problem'' also exists in the HI component, i.e., the models over-predict dwarf galaxies with low HI mass around the Milky Way. That is a shortcoming of current ΛCDM cosmology framework. Future survey for HI gas in local dwarf galaxies (e.g. MeerKAT, SKA & FAST) can help to verify the nature of dark matter (cold or warm).

  8. A vast, thin plane of corotating dwarf galaxies orbiting the Andromeda galaxy.

    Science.gov (United States)

    Ibata, Rodrigo A; Lewis, Geraint F; Conn, Anthony R; Irwin, Michael J; McConnachie, Alan W; Chapman, Scott C; Collins, Michelle L; Fardal, Mark; Ferguson, Annette M N; Ibata, Neil G; Mackey, A Dougal; Martin, Nicolas F; Navarro, Julio; Rich, R Michael; Valls-Gabaud, David; Widrow, Lawrence M

    2013-01-03

    Dwarf satellite galaxies are thought to be the remnants of the population of primordial structures that coalesced to form giant galaxies like the Milky Way. It has previously been suspected that dwarf galaxies may not be isotropically distributed around our Galaxy, because several are correlated with streams of H I emission, and may form coplanar groups. These suspicions are supported by recent analyses. It has been claimed that the apparently planar distribution of satellites is not predicted within standard cosmology, and cannot simply represent a memory of past coherent accretion. However, other studies dispute this conclusion. Here we report the existence of a planar subgroup of satellites in the Andromeda galaxy (M 31), comprising about half of the population. The structure is at least 400 kiloparsecs in diameter, but also extremely thin, with a perpendicular scatter of less than 14.1 kiloparsecs. Radial velocity measurements reveal that the satellites in this structure have the same sense of rotation about their host. This shows conclusively that substantial numbers of dwarf satellite galaxies share the same dynamical orbital properties and direction of angular momentum. Intriguingly, the plane we identify is approximately aligned with the pole of the Milky Way's disk and with the vector between the Milky Way and Andromeda.

  9. Andromeda IV, a solitary gas-rich dwarf galaxy

    CERN Document Server

    Karachentsev, I D; Tully, R B; Makarova, L N; Sharina, M E; Begum, A; Rizzi, L

    2015-01-01

    Observations are presented of the isolated dwarf irregular galaxy And IV made with the Hubble Space Telescope Advanced Camera for Surveys and the Giant Metrewave Radio Telescope in the 21 cm HI line. We determine the galaxy distance of $7.17\\pm0.31$ Mpc using the Tip of Red Giant Branch method. The galaxy has a total blue absolute magnitude of -12.81 mag, linear Holmberg diameter of 1.88 kpc and an HI-disk extending to 8.4 times the optical Holmberg radius. The HI mass-to-blue luminosity ratio for And IV amounts $12.9~M_{\\odot}/L_{\\odot}$. From the GMRT data we derive the rotation curve for the HI and fit it with different mass models. We find that the data are significantly better fit with an iso-thermal dark matter halo, than by an NFW halo. We also find that MOND rotation curve provides a very poor fit to the data. The fact that the iso-thermal dark matter halo provides the best fit to the data supports models in which star formation feedback results in the formation of a dark matter core in dwarf galaxies...

  10. The universal rotation curve of dwarf disk galaxies

    CERN Document Server

    Karukes, Ekaterina V

    2016-01-01

    We use the concept of the spiral rotation curves universality (see Parsic et al. 1996) to investigate the luminous and dark matter properties of the dwarf disk galaxies in the local volume (size $\\sim11$ Mpc). Our sample includes 36 objects with rotation curves carefully selected from the literature. We find that, despite the large variations of our sample in luminosities ($\\sim$ 2 of dex), the rotation curves in specifically normalized units, look all alike and lead to the lower-mass version of the universal rotation curve of spiral galaxies found in Parsic et al. 1996. We mass model $V(R/R_{opt})/V_{opt}$, the double normalized universal rotation curve of dwarf disk galaxies: the results show that these systems are totally dominated by dark matter whose density shows a core size between 2 and 3 stellar disk scale lengths. Similar to galaxies of different Hubble types and luminosities, the core radius $r_0$ and the central density $\\rho_0$ of the dark matter halo of these objects are related by $ \\rho_0 r_0 ...

  11. Structure and Kinematics of the Nearby Dwarf Galaxy UGCA 105

    CERN Document Server

    Schmidt, Philip; Gentile, Gianfranco; Oh, Se-Heon; Schuberth, Ylva; Bekhti, Nadya Ben; Winkel, Benjamin; Klein, Uli

    2013-01-01

    Owing to their shallow stellar potential, dwarf galaxies possess thick gas disks, which makes them good candidates for studies of the galactic vertical kinematical structure. We present 21 cm line observations of the isolated nearby dwarf irregular galaxy UGCA 105, taken with the Westerbork Synthesis Radio Telescope (WSRT), and analyse the geometry of its neutral hydrogen (HI) disk and its kinematics. The galaxy shows a fragmented HI distribution. It is more extended than the optical disk, and hence allows one to determine its kinematics out to very large galacto-centric distances. The HI kinematics and morphology are well-ordered and symmetric for an irregular galaxy. The HI is sufficiently extended to observe a substantial amount of differential rotation. Moreover, UGCA 105 shows strong signatures for the presence of a kinematically anomalous gas component. Performing tilted-ring modelling by use of the least-squares fitting routine TiRiFiC, we found that the HI disk of UGCA 105 has a moderately warped and ...

  12. Structural analysis of the Sextans dwarf spheroidal galaxy

    Science.gov (United States)

    Roderick, T. A.; Jerjen, H.; Da Costa, G. S.; Mackey, A. D.

    2016-07-01

    We present wide-field g- and i-band stellar photometry of the Sextans dwarf spheroidal galaxy and its surrounding area out to four times its half-light radius (rh = 695 pc), based on images obtained with the Dark Energy Camera at the 4-m Blanco telescope at CTIO. We find clear evidence of stellar substructure associated with the galaxy, extending to a distance of 82 arcmin (2 kpc) from its centre. We perform a statistical analysis of the overdensities and find three distinct features, as well as an extended halo-like structure, to be significant at the 99.7 per cent confidence level or higher. Unlike the extremely elongated and extended substructures surrounding the Hercules dwarf spheroidal galaxy, the overdensities seen around Sextans are distributed evenly about its centre, and do not appear to form noticeable tidal tails. Fitting a King model to the radial distribution of Sextans stars yields a tidal radius rt = 83.2 arcmin ± 7.1 arcmin (2.08 ± 0.18 kpc), which implies the majority of detected substructure is gravitationally bound to the galaxy. This finding suggests that Sextans is not undergoing significant tidal disruption from the Milky Way, supporting the scenario in which the orbit of Sextans has a low eccentricity.

  13. How Typical Are The Local Group Dwarf Galaxies?

    CERN Document Server

    Weisz, Daniel R; Dalcanton, Julianne J; Skillman, Evan D; Holtzman, Jon; Williams, Benjamin F; Gilbert, Karoline M; Seth, Anil C; Cole, Andrew; Gogarten, Stephanie M; Rosema, Keith; Karachentsev, Igor D; McQuinn, Kristen B W; Zaritsky, Dennis

    2011-01-01

    We compare the star formation histories (SFHs) of Local Group (LG) dwarf galaxies with those in the volume-limited ACS Nearby Galaxy Survey Treasury (ANGST) sample (D~4Mpc). The SFHs were derived in a uniform manner from high quality optical color-magnitude diagrams constructed from HST imaging. The mean cumulative SFHs of the LG and ANGST dwarf galaxies are all very similar for the three different morphological types (dSph/dE, dI, dI/dSph). The star formation rates (SFRs) at earliest times are measurably higher than the average lifetime SFRs, while SFRs are lower at later times. We find that the systematic uncertainties, due to varying photometric depths and uncertainties in the stellar models, are similar to any differences between the mean cumulative SFHs of the LG and ANGST samples, indicating consistency between the samples. As for the ANGST galaxies alone, we find the combined LG and ANGST samples, are generally consistent with the cosmic SFH and that the mean cumulative SFHs are not well described by s...

  14. Comparison of Alternative Gravity Models in Dwarf Galaxy Rotation Curves

    Science.gov (United States)

    Harrington, Justin; Saintable, Taylor; O'Brien, James

    2017-01-01

    Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf Galaxies serve as an increasingly interesting testing ground of rotation curve dynamics due to their increased stellar formation and typically rising rotation curve. These galaxies usually are not dominated by typical stellar structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories such as NFW (∧ CDM) struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Here, we present a thorough application of alternative gravitational models (conformal gravity and MOND) to a 2010 dwarf galaxy sample from Swaters et al. An analysis and discussion of the results of the fitting procedure of the two alternative gravitational models are explored. We posit here that both the Conformal Gravity and MOND can provide an accurate description of the galactic dynamics without the need for copious dark matter.

  15. EXPLORING THE INTERSTELLAR MEDIA OF OPTICALLY COMPACT DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Most, Hans P.; Cannon, John M.; Engstrom, Eric; Fliss, Palmer [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Salzer, John J. [Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States); Rosenberg, Jessica L., E-mail: hmost@macalester.edu, E-mail: jcannon@macalester.edu, E-mail: slaz@astro.indiana.edu, E-mail: jrosenb4@gmu.edu [School of Physics, Astronomy, and Computational Science, George Mason University, Fairfax, VA 22030 (United States)

    2013-06-15

    We present new Very Large Array H I spectral line, archival Sloan Digital Sky Survey, and archival Spitzer Space Telescope imaging of eight star-forming blue compact dwarf galaxies that were selected to be optically compact (optical radii <1 kpc). These systems have faint blue absolute magnitudes (M{sub B} {approx}> -17), ongoing star formation (based on emission-line selection by the H{alpha} or [O III] lines), and are nearby (mean velocity = 3315 km s{sup -1} {approx_equal} 45 Mpc). One galaxy in the sample, ADBS 113845+2008, is found to have an H I halo that extends 58 r-band scale lengths from its stellar body. In contrast, the rest of the sample galaxies have H I radii to optical-scale-length ratios ranging from 9.3 to 26. The size of the H I disk in the 'giant disk' dwarf galaxy ADBS 113845+2008 appears to be unusual as compared with similarly compact stellar populations.

  16. Tidal Streams in Newly Discovered compact elliptical (cE) galaxies

    CERN Document Server

    Huxor, Avon; Price, James; Harniman, Rob

    2010-01-01

    We present two newly-discovered, compact elliptical (cE) galaxies, which exhibit clear evidence of tidal steams, found in a search of SDSS DR7. The structural parameters of the cEs are derived using GALFIT and give effective radii < 400 pc. They also possess young to intermediate-age stellar populations. These two cEs provide direct evidence, a "smoking gun", for the process of tidal stripping that is believed to be the origin of M32-type galaxies. Both are found in small group environments with many late-type galaxies, suggesting that we may be seeing the formation of such galaxies in dynamically young galaxy groups.

  17. Chemical Abundance Patterns and the Early Environment of Dwarf Galaxies

    CERN Document Server

    Corlies, Lauren; Tumlinson, Jason; Bryan, Greg

    2013-01-01

    Recent observations suggest that abundance pattern differences exist between low metallicity stars in the Milky Way stellar halo and those in the dwarf satellite galaxies. This paper takes a first look at what role the early environment for pre-galactic star formation might have played in shaping these stellar populations. In particular, we consider whether differences in cross-pollution between the progenitors of the stellar halo and the satellites could help to explain the differences in abundance patterns. Using an N-body simulation, we find that the progenitor halos of the main halo are primarily clustered together at z=10 while the progenitors of the satellite galaxies remain on the outskirts of this cluster. Next, analytically modeled supernova-driven winds show that main halo progenitors cross-pollute each other more effectively while satellite galaxy progenitors remain more isolated. Thus, inhomogeneous cross-pollution as a result of different high-z spatial locations of each system's progenitors can ...

  18. VLT/UVES abundances in four nearby dwarf spheroidal galaxies. II. Implications for understanding galaxy evolution

    NARCIS (Netherlands)

    Tolstoy, E; Venn, KA; Shetrone, M; Primas, F; Hill, [No Value; Kaufer, A; Szeifert, T

    2003-01-01

    We have used the Ultraviolet Visual-Echelle Spectrograph (UVES) on Kueyen (UT2) of the Very Large Telescope to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies (dSph's) : Sculptor, Fornax, Carina, and Leo I. We measure the abundance variations of

  19. Search for Blue Compact Dwarf Galaxies During Quiescence

    CERN Document Server

    Almeida, J Sanchez; Amorin, R; Aguerri, J A; Sanchez-Janssen, R; Tenorio-Tagle, G

    2008-01-01

    Blue Compact Dwarf (BCD) galaxies are metal poor systems going through a major starburst that cannot last for long. We have identified galaxies which may be BCDs during quiescence (QBCD), i.e., before the characteristic starburst sets in or when it has faded away. These QBCD galaxies are assumed to be like the BCD host galaxies. The SDSS/DR6 database provides ~21500 QBCD candidates. We also select from SDSS/DR6 a complete sample of BCD galaxies to serve as reference. The properties of these two galaxy sets have been computed and compared. The QBCD candidates are thirty times more abundant than the BCDs, with their luminosity functions being very similar except for the scaling factor, and the expected luminosity dimming associated with the end of the starburst. QBCDs are redder than BCDs, and they have larger HII region based oxygen abundance. QBCDs also have lower surface brightness. The BCD candidates turn out to be the QBCD candidates with the largest specific star formation rate (actually, with the largest...

  20. Indirect Dark Matter Detection for Flattened Dwarf Galaxies

    CERN Document Server

    Sanders, Jason L; Geringer-Sameth, Alex; Dehnen, Walter

    2016-01-01

    We analyze the effects of flattening on the annihilation (J) and decay (D) factors of dwarf spheroidal galaxies with both analytic and numerical methods. Flattening has two consequences: first, there is a geometric effect as the squeezing (or stretching) of the dark matter distribution enhances (or diminishes) the J-factor; second, the line of sight velocity dispersion of stars must hold up the flattened baryonic component in the flattened dark matter halo. We provide analytic formulae and a simple numerical approach to estimate the correction to the J- and D-factors required over simple spherical modeling. The formulae are validated with a series of equilibrium models of flattened stellar distributions embedded in flattened dark-matter distributions. We compute corrections to the J- and D-factors for the Milky Way dwarf spheroidal galaxies under the assumption that they are prolate or oblate and find that the hierarchy of J-factors for the dwarf spheroidals is slightly altered. We demonstrate that spherical ...

  1. Discovery of a close pair of faint dwarf galaxies in the halo of Centaurus A

    CERN Document Server

    Crnojević, D; Caldwell, N; Guhathakurta, P; McLeod, B; Seth, A; Simon, J; Strader, J; Toloba, E

    2014-01-01

    As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS) we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of $\\sim$90 kpc from the nearby elliptical galaxy NGC5128 (CenA). We measure a tip of the red giant branch distance to each dwarf, finding $D=3.63 \\pm 0.41$ Mpc for CenA-MM-Dw1 and $D=3.60 \\pm 0.41$ Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC5128. A qualitative analysis of the color magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch ($\\gtrsim 12$ Gyr, [Fe/H]$\\sim-1.7$ to -1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities ($M_V=-10.9\\pm0.3$ for CenA-MM-Dw1 and $-8.4\\pm0.6$ for CenA-MM-Dw2) and half-light radii ($r_{h}=1.4\\pm0.04$ kpc for CenA-MM-Dw1 and $0.36\\pm0.08$ kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. Cen...

  2. Collisionless evaporation from cluster elliptical galaxies: a contributor to the intracluster stellar population

    CERN Document Server

    Muccione, V

    2004-01-01

    By means of simple numerical models we discuss whether "collisionless stellar evaporation" from cluster elliptical galaxies could be an effective mechanism for the production of intracluster stellar populations. The effectiveness of this mechanism is due to the fact that, for realistic galaxy and cluster models, the galaxy oscillation periods near equilibrium configurations in the cluster tidal field are of the same order of stellar orbital times in the external parts of the galaxies themselves. With the aid of Monte-Carlo simulations we explore the evolution of stellar orbits in oscillating galaxies placed near different equilibrium positions. We found that, over an Hubble time, the main effect is a substantial expansion of the galactic outskirts, particularly affecting the galaxy at the cluster center and those orbiting near the cluster core radius: overall, approximately the 10% of the galaxy mass is affected. Thus, the proposed mechanism could be of some importance in the shaping of the halo of cD galaxie...

  3. Hubble space telescope counts of elliptical galaxies constraints on cosmological models?

    CERN Document Server

    Driver, S P; Phillipps, S; Bristow, P D; Driver, Simon P; Windhorst, Rogier A; Phillipps, Steven; Bristow, Paul D

    1995-01-01

    The interpretation of galaxy number counts in terms of cosmological models is fraught with difficulty due to uncertainties in the overall galaxy population (mix of morphological types, luminosity functions etc.) and in the observations (loss of low surface brightness images, image blending etc.). Many of these can be overcome if we use deep high resolution imaging of a single class of high surface brightness galaxies, whose evolution is thought to be fairly well understood. This is now possible by selecting elliptical and S0 galaxies using Hubble Space Telescope images from the Medium Deep Survey and other ultradeep WFPC2 images. In the present paper, we examine whether such data can be used to discriminate between open and closed universes, or between conventional cosmological models and those dominated by a cosmological constant. We find, based on the currently available data, that unless elliptical galaxies undergo very strong merging since z \\sim 1 (and/or very large errors exist in the morphological clas...

  4. Galaxy merging, the Fundamental Plane of elliptical galaxies, and the Mbh-sigma relation

    CERN Document Server

    Nipoti, C; Ciotti, L

    2003-01-01

    We explore the effects of dissipationless merging on the Fundamental Plane of elliptical galaxies by using a N-body code based on a new, high performance numerical scheme (Dehnen 2002). We investigate the extreme cases of galaxy growth by equal mass merging and accretion of small stellar systems; in a subset of simulations we also consider the presence of dark matter halos around the merging galaxies. Curiously, we found that the Fundamental Plane is preserved by major merging, while in the accretion scenario its edge--on thickness is only marginally reproduced, with substantial thickening in the case of merging with low angular momentum. We also found that both the Faber-Jackson and Kormendy relations are not reproduced by the simulations. Finally, we discuss the implications of our results for the origin of the Mbh-sigma and Magorrian relations. We found that dissipationless merging is unable to reproduce the Mbh-sigma relation, if Mbhs add linearly (while the Magorrian relation is nicely reproduced); on th...

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

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez-Conde, Miguel A.; /KIPAC, Menlo Park /SLAC /IAC, La Laguna /Laguna U., Tenerife; Cannoni, Mirco; /Huelva U.; Zandanel, Fabio; /IAA, Granada; Gomez, Mario E.; /Huelva U.; 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

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

    Energy Technology Data Exchange (ETDEWEB)

    Sánchez-Conde, Miguel A. [SLAC National Laboratory and Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park, CA 94025 (United States); Cannoni, Mirco; Gómez, Mario E. [Dpto. Física Aplicada, Facultad de Ciencias Experimentales, Universidad de Huelva, 21071 Huelva (Spain); Zandanel, Fabio; Prada, Francisco, E-mail: masc@stanford.edu, E-mail: mirco.cannoni@dfa.uhu.es, E-mail: fabio@iaa.es, E-mail: mario.gomez@dfa.uhu.es, E-mail: fprada@iaa.es [Instituto de Astrofísica de Andalucía (CSIC), E-18008, Granada (Spain)

    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

  7. Herschel Spectroscopic Observations of LITTLE THINGS Dwarf Galaxies

    CERN Document Server

    Cigan, Phil; Cormier, Diane; Lebouteiller, Vianney; Madden, Suzanne; Hunter, Deidre; Brinks, Elias; Elmegreen, Bruce; Schruba, Andreas; Heesen, Volker

    2015-01-01

    We present far-infrared spectral line observations of five galaxies from the LITTLE THINGS sample: DDO 69, DDO 70, DDO 75, DDO 155, and WLM. While most studies of dwarfs focus on bright systems or starbursts due to observational constraints, our data extend the observed parameter space into the regime of low surface brightness dwarf galaxies with low metallicities and moderate star formation rates. Our targets were observed with Herschel at the [CII] 158um, [OI] 63um, [OIII] 88um, and NII 122um emission lines using the PACS Spectrometer. These high-resolution maps allow us for the first time to study the far-infrared properties of these systems on the scales of larger star-forming complexes. The spatial resolution in our maps, in combination with star formation tracers, allows us to identify separate PDRs in some of the regions we observed. Our systems have widespread [CII] emission that is bright relative to continuum, averaging near 0.5% of the total infrared budget - higher than in solar-metallicity galaxi...

  8. Candidate tidal dwarf galaxies associated with the Stephan's Quintet

    CERN Document Server

    De Oliveira, C M; Amram, P; Balkowski, C; Bolte, M

    2001-01-01

    We present kinematic and photometric evidence for the presence of seven candidate tidal dwarf galaxies in Stephan's quintet. The central regions of the two most probable parent galaxies, N7319 and N7318B, contain little or no gas whereas the intragroup medium, and particularly the optical tails that seem to be associated with N7318B are rich in cold and ionized gas. Two tidal-dwarf candidates may be located at the edge of a tidal tail, one within a tail and for four others there is no obvious stellar/gaseous bridge between them and the parent galaxy. Two of the candidates are associated with HI clouds, one of which is, in addition, associated with a CO cloud. All seven regions have low continuum fluxes and high H$\\alpha$ luminosity densities (F(H$\\alpha$) = 1 -- 60 $\\times$ 10$^{-14}$ erg s$^{-1}$ cm$^{-2}$). Their magnitudes (M$_B =$ --16.1 to --12.6), sizes ($\\sim$ 3.5 h$_{75}^{-1}$ kpc), colors (typically $B-R = 0.7$) and gas velocity gradients ($\\sim$ 8 -- 26 h$_{75}$ km s$^{-1}$ kpc$^{-1}$) are typical f...

  9. Metallicity Distribution Functions of Four Local Group dwarf galaxies

    CERN Document Server

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

    2015-01-01

    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 (WFC3) instrument aboard 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 (CEM) 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 spher...

  10. Dark Matter Identification using Gamma Rays from Dwarf Galaxies

    CERN Document Server

    Shakya, Bibhushan

    2010-01-01

    If the positron fraction and combined electron-positron flux excesses recently observed by PAMELA, Fermi and HESS have a dark matter origin, final state radiation (FSR) photons from dark matter annihilation into lepton-rich final states may be detected with observations of satellite dwarf galaxies of the Milky Way by ground-based atmospheric Cherenkov telescopes (ACTs). We find that current and near-future ACTs have excellent potential for such detection, although a discovery cannot be guaranteed due to large uncertainties in the distribution of dark matter within the dwarfs. We find that models predicting dark matter annihilation into two-lepton final states and those favoring four-lepton final states (as in, for example, "axion portal" models) can be reliably distinguished using the FSR photon spectrum once measured, and the dark matter particle mass can also be accurately determined.

  11. A VIRIAL CORE IN THE SCULPTOR DWARF SPHEROIDAL GALAXY

    Energy Technology Data Exchange (ETDEWEB)

    Agnello, A.; Evans, N. W., E-mail: aagnello@ast.cam.ac.uk, E-mail: nwe@ast.cam.ac.uk [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)

    2012-08-01

    The projected virial theorem is applied to the case of multiple stellar populations in the nearby dwarf spheroidal galaxies. As each population must reside in the same gravitational potential, this provides strong constraints on the nature of the dark matter halo. We derive necessary conditions for two populations with Plummer or exponential surface brightnesses to reside in a cusped Navarro-Frenk-White (NFW) halo. We apply our methods to the Sculptor dwarf spheroidal, and show that there is no NFW halo compatible with the energetics of the two populations. The dark halo must possess a core radius of {approx}120 pc for the virial solutions for the two populations to be consistent. This conclusion remains true, even if the effects of flattening or self-gravity of the stellar populations are included.

  12. Effects of Tides on Milky Way Dwarf Satellite Galaxies

    Science.gov (United States)

    Wang, Mei-Yu; Strigari, Louis; Fattahi, Azadeh; Frenk, Carlos S.; Cooper, Andrew; Lovell, Mark; Navarro, Julio F.; Sawala, Till; Zentner, Andrew

    2017-01-01

    Using detailed observations of the Local Group to study wide-ranging questions in galaxy formation and dark matter physics - has become a rich field over the past decade. In this talk, I will present frameworks that address some of these questions by combining high-precision stellar kinematic measurements with state-of-art cosmological hydrodynamical N-body simulations. I will demonstrate that the properties of dark matter subhalo of individual satellite galaxies implied by stellar kinematic data can be linked to the galaxy evolution mechanisms such as infall time and the gravitational tidal interaction with Milky Way potential. In the cold dark matter (CDM) scenario, some dwarf galaxies explicitly require to be shaped under significant gravitational tidal forces, which will leave imprints on their stellar distribution and kinematics. I will discuss how these features could serve as a test to the nature of dark matter or stellar feedback strength. I will also discuss how we can study the tidally “disturbed” or even “destroyed” satellite galaxies as building blocks to our Milky Way stellar halo by understanding the properties of their progenitors and observation limit imposed by current and future surveys.

  13. Globular clusters indicate ultra diffuse galaxies are dwarfs

    CERN Document Server

    Beasley, Michael A

    2016-01-01

    We present an analysis of archival {\\it HST/ACS} imaging in the F475W ($g_{475}$), F606W ($V_{606}$) and F814W ($I_{814}$) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5$\\sigma$ completeness limit of the imaging ($I_{814}=$27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of $32\\pm6$ and a $V$-band specific frequency, $S_N=33\\pm6$. Based on comparisons to the GC systems of Local galaxies, we show that both the absolute number and the colors of the GC system of DF17 are consistent with the GC system of a dark-matter dominated dwarf galaxy with virial mass $\\sim1.0\\times10^{11}$~\\msun and a dark-to-stellar mass ratio, $M_{vir} / M_{ star}\\sim 1300$. Based on the stellar mass-growth of the Milky Way, we show that DF17 cannot be understood as a failed Milky Way-like system, but is more similar to quenched Large Magel...

  14. Black Holes at the Centers of Nearby Dwarf Galaxies

    CERN Document Server

    Moran, Edward C; Sugarman, Hannah R; Velez, Darik O; Eracleous, Michael

    2014-01-01

    Using a distance-limited portion of the Sloan Digital Sky Survey (SDSS) Data Release 7, we have identified 28 active galactic nuclei (AGNs) in nearby (d < 80 Mpc) low-mass, low-luminosity dwarf galaxies. The accreting objects at the galaxy centers are expected to be intermediate-mass black holes (IMBHs) with M_BH < 1e6 M_sun. The AGNs were selected using several optical emission-line diagnostics after careful modeling of the continuum present in the spectra. We have limited our survey to objects with spectral characteristics similar to those of Seyfert nuclei, excluding emission-line galaxies with ambiguous spectra that could be powered by stellar processes. The host galaxies in our sample are thus the least massive objects in the very local universe certain to contain central black holes. Given our focus on the nearest objects included in the SDSS, our survey is more sensitive to low-luminosity emission than previous optical searches for AGNs in low-mass galaxies. The [O III] lambda5007 luminosities of...

  15. Dissipative dark matter and the rotation curves of dwarf galaxies

    Science.gov (United States)

    Foot, R.

    2016-07-01

    There is ample evidence from rotation curves that dark matter halos around disk galaxies have nontrivial dynamics. Of particular significance are: a) the cored dark matter profile of disk galaxies, b) correlations of the shape of rotation curves with baryonic properties, and c) Tully-Fisher relations. Dark matter halos around disk galaxies may have nontrivial dynamics if dark matter is strongly self interacting and dissipative. Multicomponent hidden sector dark matter featuring a massless `dark photon' (from an unbroken dark U(1) gauge interaction) which kinetically mixes with the ordinary photon provides a concrete example of such dark matter. The kinetic mixing interaction facilitates halo heating by enabling ordinary supernovae to be a source of these `dark photons'. Dark matter halos can expand and contract in response to the heating and cooling processes, but for a sufficiently isolated halo could have evolved to a steady state or `equilibrium' configuration where heating and cooling rates locally balance. This dynamics allows the dark matter density profile to be related to the distribution of ordinary supernovae in the disk of a given galaxy. In a previous paper a simple and predictive formula was derived encoding this relation. Here we improve on previous work by modelling the supernovae distribution via the measured UV and Hα fluxes, and compare the resulting dark matter halo profiles with the rotation curve data for each dwarf galaxy in the LITTLE THINGS sample. The dissipative dark matter concept is further developed and some conclusions drawn.

  16. The evolutionary history of low-luminosity local group dwarf galaxies

    Science.gov (United States)

    van den Bergh, Sidney

    1994-06-01

    The stellar content of Local Group dwarfs fainter than MV = -14.0 is found to correlate with distance from the Galaxy (or M31). Dwarf spheroidals located close to the Galaxy, such as Ursa Minor and Draco, only experienced star formation early in their lifetimes. Dwarf spheroidals at intermediate distances, like Leo I, Fornax, and Carina, underwent significant star formation more recently. Finally, star formation is presently still going on in distant dwarfs such as DDO 210 and Phoenix. Leo II and Tucana are, however, dwarfs that do not conform to this pattern. It is tentatively suggested that ram pressure stripping, strong supernova-driven winds, or a high UV flux form the protoGalaxy (or proto-M31) might have removed gas from dwarf galaxies at small galactocentric distances.

  17. Dynamical family properties and dark halo scaling relations of giant elliptical galaxies

    CERN Document Server

    Gerhard, O E; Saglia, R P; Bender, R; Gerhard, Ortwin; Kronawitter, Andi; Bender, Ralf

    2001-01-01

    Based on a uniform dynamical analysis of line-profile shapes for 21 luminous round elliptical galaxies, we have investigated the dynamical family relations of ellipticals: (i) The circular velocity curves (CVCs) of elliptical galaxies are flat to within ~10% for R>~0.2R_e. (ii) Most ellipticals are moderately radially anisotropic; their dynamical structure is surprisingly uniform. (iii) Elliptical galaxies follow a Tully-Fisher (TF) relation, with v_c^max=300 km/s for an L_B^* galaxy. At given v_c^max, they are ~1 mag fainter in B and appear to have slightly lower baryonic mass than spirals even for maximum M/L_B. (iv) The luminosity dependence of M/L_B is confirmed. The tilt of the Fundamental Plane is not caused by dynamical non-homology, nor only by an increasing dark matter fraction with L. It is, however, consistent with stellar population models based on published metallicities and ages. The main driver is therefore probably metallicity, and a secondary population effect is needed to explain the K-band ...

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

    CERN Document Server

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

    2014-01-01

    We present uniformly measured star formation histories (SFHs) of 40 Local Group 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 $\\tau$ $\\sim$ 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 (dTrans), and dwarf ellipticals (dEs) can be approximated by the combination of an exponentially declining SFH ($\\tau$ $\\sim$ 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\\%...

  19. Explaining the Color Distributions of Globular Cluster Systems in Elliptical Galaxies

    CERN Document Server

    Yoon, S J; Lee, Y W; Yoon, Suk-Jin; Yi, Sukyoung Ken

    2006-01-01

    The colors of globular clusters in most of large elliptical galaxies are bimodal. This is generally taken as evidence for the presence of two cluster subpopulations that have different geneses. Here we find however that, due to the non-linear nature of the metallicity-to-color transformation, a coeval group of old clusters with a unimodal metallicity spread can exhibit color bimodality. The models of cluster colors indicate that the horizontal-branch stars are the main drivers behind the empirical non-linearity. We show that the scenario gives remarkably simple and cohesive explanations for all the key observations, and could simplify theories of elliptical galaxy formation.

  20. Chemical enrichment in Ultra-Faint Dwarf galaxies

    Science.gov (United States)

    Romano, Donatella

    2016-08-01

    Our view of the Milky Way's satellite population has radically changed after the discovery, ten years ago, of the first Ultra-Faint Dwarf galaxies (UFDs). These extremely faint, dark-matter dominated, scarcely evolved stellar systems are found in ever-increasing number in our cosmic neighbourhood and constitute a gold-mine for studies of early star formation conditions and early chemical enrichment pathways. Here we show what can be learned from the measurements of chemical abundances in UFD stars read through the lens of chemical evolution studies, point out the limitations of the classic approach, and discuss the way to go to improve the models.

  1. Chemical Evolution of Mn in Three Dwarf Spheroidal Galaxies

    Indian Academy of Sciences (India)

    Men-Quan Liu; Jie Zhang

    2014-09-01

    Based on an improved model, more reasonable nucleosyn-thesis and explosion rate of SNeIa and CCSNe, we studied Mn evolution for three local dwarf spheroidal galaxies (dSphs), considering the detailed SNe yield and explosion rates for different types of progenitors. The results can explain the main observation ofMn abundance for tens stars in those dSphs, and give some constraints to the nucleosynthesis and explosion ratio of different types of supernovae and Star Formation Rates (SFR) in those dSphs.

  2. Globular Clusters Indicate That Ultra-diffuse Galaxies Are Dwarfs

    Science.gov (United States)

    Beasley, Michael A.; Trujillo, Ignacio

    2016-10-01

    We present an analysis of archival HST/ACS imaging in the F475W (g 475), F606W (V 606), and F814W (I 814) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed to be located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5σ completeness limit of the imaging (I 814 = 27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of 27 ± 5 and a V-band specific frequency S N = 28 ± 5. Based on comparisons to the GC systems of local galaxies, we show that both the absolute number and the colors of the GC system of DF17 are consistent with the GC system of a dark-matter-dominated dwarf galaxy with virial mass ˜9.0 × 1010 M ⊙ and a dark-to-stellar mass ratio M vir/M star ˜ 1000. Based on the stellar mass growth of the Milky Way, we show that DF17 cannot be understood as a failed Milky-Way-like system, but is more similar to quenched Large-Magellanic-Cloud-like systems. We find that the mean color of the GC population, g 475-I 814 = 0.91 ± 0.05 mag, coincides with the peak of the color distribution of intracluster GCs and is also similar to those of the blue GCs in the outer regions of massive galaxies. We suggest that both the intracluster GC population in Coma and the blue peak in the GC populations of massive galaxies may be fed—at least in part—by the disrupted equivalents of systems such as DF17.

  3. Abundances as Tracers of the Formation and Evolution of (Dwarf) Galaxies

    CERN Document Server

    Tolstoy, E

    2004-01-01

    This aims to be an overview of what detailed observations of individual stars in nearby dwarf galaxies may teach us about galaxy evolution. This includes some early results from the DART (Dwarf Abundances and Radial velocity Team) Large Programme at ESO. This project has used 2.2m/WFI and VLT/FLAMES to obtain spectra of large samples of individual stars in nearby dwarf spheroidal galaxies and determine accurate abundances and kinematics. These results can be used to trace the formation and evolution of nearby galaxies from the earliest times to the present.

  4. The Horizontal Branch of the Sculptor Dwarf galaxy

    CERN Document Server

    Salaris, Maurizio; Tolstoy, Eline; Fiorentino, Giuliana; Cassisi, Santi

    2013-01-01

    We have performed the first detailed simulation of the horizontal branch of the Sculptor dwarf spheroidal galaxy by means of synthetic modelling techniques,taking consistently into account the star formation history and metallicity evolution as determined from the main sequence and red giant branch spectroscopic observations. The only free parameter in the whole analysis is the integrated mass loss of red giant branch stars. This is the first time that synthetic horizontal branch models, consistent with the complex star formation history of a galaxy, are calculated and matched to the observations. We find that the metallicity range covered by the star formation history, as constrained by observations, plus a simple mass loss law, enable us to cover both the full magnitude and colour range of HB stars. In addition the number count distribution along the observed horizontal branch, can be also reproduced, provided that the red giant branch mass loss is mildly metallicity dependent, with a very small dispersion ...

  5. Star formation rate in Holmberg IX dwarf galaxy

    Directory of Open Access Journals (Sweden)

    Anđelić M.M.

    2011-01-01

    Full Text Available In this paper we use previously determined Hα fluxes for dwarf galaxy Holmberg IX (Arbutina et al. 2009 to calculate star formation rate (SFR in this galaxy. We discuss possible contaminations of Hα flux and, for the first time, we take into account optical emission from supernova remnants (SNRs as a possible source of contamination of Hα flux. Derived SFR for Holmberg IX is 3:4 x 10-4M.yr-1. Our value is lower then in previous studies, due to luminous shock-heated source M&H 9-10, possible hypernova remnant, which we excluded from the total Hα flux in our calculation of SFR.

  6. The dynamics of Andromeda's dwarf galaxies and stellar streams

    CERN Document Server

    Collins, Michelle L M; Ibata, Rodrigo A; Martin, Nicolas F; Preston, Janet

    2016-01-01

    As part of the Z-PAndAS Keck II DEIMOS survey of resolved stars in our neighboring galaxy, Andromeda (M31), we have built up a unique data set of measured velocities and chemistries for thousands of stars in the Andromeda stellar halo, particularly probing its rich and complex substructure. In this contribution, we will discuss the structural, dynamical and chemical properties of Andromeda's dwarf spheroidal galaxies, and how there is no observational evidence for a difference in the evolutionary histories of those found on and off M31's vast plane of satellites. We will also discuss a possible extension to the most significant merger event in M31 - the Giant Southern Stream - and how we can use this feature to refine our understanding of M31's mass profile, and its complex evolution.

  7. Cusp-core transformations in dwarf galaxies: observational predictions

    CERN Document Server

    Teyssier, Romain; Dubois, Yohan; Read, Justin

    2012-01-01

    The presence of a dark matter core in the central kiloparsec of many dwarf galaxies has been a long standing problem in galaxy formation theories based on the standard cold dark matter paradigm. Recent cosmological simulations, based on Smooth Particle Hydrodynamics and rather strong feedback recipes have shown that it was indeed possible to form extended dark matter cores using baryonic processes related to a more realistic treatment of the interstellar medium. Using adaptive mesh refinement, together with a new, stronger supernovae feedback scheme that we have recently implemented in the RAMSES code, we show that it is also possible to form a prominent dark matter core within the well-controlled framework of an isolated, initially cuspy, 10 billion solar masses dark matter halo. Although our numerical experiment is idealized, it allows a clean and unambiguous identification of the dark matter core formation process. Our dark matter inner profile is well fitted by a pseudo-isothermal profile with a core radi...

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

    Science.gov (United States)

    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.

  9. The Mid-Infrared Properties of Blue Compact Dwarf Galaxies

    CERN Document Server

    Yanling Wu; Houck, J R; Bernasrd-Salas, J; Lebouteiller, V

    2008-01-01

    The unprecedented sensitivity of the Spitzer Space Telescope has enabled us for the first time to detect a large sample of Blue Compact Dwarf galaxies (BCDs), which are intrinsically faint in the infrared. In the present paper we present a summary of our findings which providing essential information on the presence/absence of the Polycyclic Aromatic Hydrocarbon features in metal-poor environments. In addition, using Spitzer/IRS high-resolution spectroscopy, we study the elemental abundances of neon and sulfur in BCDs and compare with the results from optical studies. Finally, we present an analysis of the mid- and far-infrared to radio correlation in low luminosity low metallicity galaxies.

  10. Globular cluster clustering and tidal features around ultra compact dwarf galaxies in the halo of NGC1399

    CERN Document Server

    Voggel, Karina; Richtler, Tom

    2015-01-01

    We present a novel approach to constrain the formation channels of Ultra-Compact Dwarf Galaxies (UCDs). This inhomogeneous class of objects of remnants of tidally stripped dwarf elliptical galaxies and high mass globular clusters. We use three methods to unravel their nature: 1) we analysed their surface brightness profiles, 2) we carried out a direct search for tidal features around UCDs and 3) we compared the spatial distribution of GCs and UCDs in the halo of their host galaxy. Based on FORS2 observations, we have studied the detailed structural composition of a large sample of 97 UCDs in the halo of NGC1399, the central galaxy of the Fornax cluster, by analysing theirsurface brightness profiles. We derived the structural parameters of 13 extended UCDs modelling them with a single Sersic function and decomposing them into composite King and Sersic profiles. We find evidence for faint stellar envelopes at mu=~26 mag\\arcsec^-2 surrounding the UCDs up to an extension of 90pc in radius. We also show new eviden...

  11. Virgo cluster early-type dwarf galaxies with the Sloan Digital Sky Survey. III. Subpopulations: distributions, shapes, origins

    CERN Document Server

    Lisker, T; Binggeli, B; Glatt, K; Lisker, Thorsten; Grebel, Eva K.; Binggeli, Bruno; Glatt, Katharina

    2007-01-01

    From a quantitative analysis of 413 Virgo cluster early-type dwarf galaxies (dEs) with Sloan Digital Sky Survey imaging data, we find that the dE class can be divided into multiple subpopulations that differ significantly in their morphology and clustering properties. Three dE subclasses are shaped like thick disks and show no central clustering: (1) dEs with disk features like spiral arms or bars, (2) dEs with central star formation, and (3) ordinary, bright dEs that have no or only a weak nucleus. These populations probably formed from infalling progenitor galaxies. In contrast, ordinary nucleated dEs follow the picture of classical dwarf elliptical galaxies in that they are spheroidal objects and are centrally clustered like E and S0 galaxies, indicating that they have resided in the cluster since a long time, or were formed along with it. These results define a morphology-density relation within the dE class. We find that the difference in the clustering properties of nucleated dEs and dEs with no or only...

  12. Hunting for Infrared Signatures of Supermassive Black Hole Activity in Dwarf Galaxies

    Science.gov (United States)

    Hainline, Kevin; Reines, Amy; Greene, Jenny; Stern, Daniel

    2016-08-01

    In order to explore the origin of the relationship between the growth of a galaxy and its central supermassive black hole, evidence must be found for black holes in galaxies at a wide range in masses. Searching for supermassive black holes in dwarf galaxies is especially important as these objects have less complicated merger histories, and they may host black holes that are similar to early proposed ``seed'' black holes. However, this selection is complicated by the fact that star formation in these dwarf galaxies can often mask the optical signatures of supermassive black hole growth and active galactic nucleus (AGN) activity in these objects. The all-sky infrared coverage offered by the Wide-field Infrared Survey Explorer (WISE) has been used to great success to select AGNs in more massive galaxies, but great care must be used when using infrared selection techniques on samples of dwarf galaxies. In particular, compact, highly star-forming dwarf galaxies can have infrared colors that may lead them to be erroneously selected as AGNs. In this talk, I will discuss recent work exploring infrared selection of AGN candidates in dwarf galaxies, and present a set of potential IR dwarf-galaxy AGN candidates. I will also outline the importance in these results with respect to future selection of AGNs in low-metallicity galaxies at high-redshift.

  13. Delayed Star Formation in Isolated Dwarf Galaxies: HST Star Formation History of the Aquarius Dwarf Irregular

    CERN Document Server

    Cole, Andrew A; Dolphin, Andrew E; Skillman, Evan D; McConnachie, Alan W; Brooks, Alyson M; Leaman, Ryan

    2014-01-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ~10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ~10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ~2). The star formation rate increased dramatically ~6-8 Gyr ago (z ~ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M(HI)/M(stellar), dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CD...

  14. TESTING YUKAWA-LIKE POTENTIALS FROM f(R)-GRAVITY IN ELLIPTICAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Napolitano, N. R. [INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16, 80131-Napoli (Italy); Capozziello, S.; Capaccioli, M. [Dipartimento di Scienze Fisiche, Universita di Napoli ' Federico II' , Napoli (Italy); Romanowsky, A. J. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Tortora, C., E-mail: napolita@na.astro.it [Institut fuer Theoretische Physik, Universitaet Zuerich, Winterthurerstrasse 190, CH-8057, Zuerich (Switzerland)

    2012-04-01

    We present the first analysis of extended stellar kinematics of elliptical galaxies where a Yukawa-like correction to the Newtonian gravitational potential derived from f(R)-gravity is considered as an alternative to dark matter. In this framework, we model long-slit data and planetary nebula data out to 7 R{sub eff} of three galaxies with either decreasing or flat dispersion profiles. We use the corrected Newtonian potential in a dispersion-kurtosis Jeans analysis to account for the mass-anisotropy degeneracy. We find that these modified potentials are able to fit nicely all three elliptical galaxies and the anisotropy distribution is consistent with that estimated if a dark halo is considered. The parameter which measures the 'strength' of the Yukawa-like correction is, on average, smaller than the one found previously in spiral galaxies and correlates both with the scale length of the Yukawa-like term and the orbital anisotropy.

  15. Testing Yukawa-like potentials from f(R)-gravity in elliptical galaxies

    CERN Document Server

    Napolitano, N R; Romanowsky, A J; Capaccioli, M; Tortora, C

    2012-01-01

    We present the first analysis of extended stellar kinematics of elliptical galaxies where a Yukawa--like correction to the Newtonian gravitational potential derived from f(R)-gravity is considered as an alternative to dark matter. In this framework, we model long-slit data and planetary nebulae data out to 7 Re of three galaxies with either decreasing or flat dispersion profiles. We use the corrected Newtonian potential in a dispersion-kurtosis Jeans analysis to account for the mass-anisotropy degeneracy. We find that these modified potentials are able to fit nicely all three elliptical galaxies and the anisotropy distribution is consistent with that estimated if a dark halo is considered. The parameter which measures the "strength" of the Yukawa-like correction is, on average, smaller than the one found previously in spiral galaxies and correlates both with the scale length of the Yukawa-like term and the orbital anisotropy.

  16. Testing Yukawa-like Potentials from f(R)-gravity in Elliptical Galaxies

    Science.gov (United States)

    Napolitano, N. R.; Capozziello, S.; Romanowsky, A. J.; Capaccioli, M.; Tortora, C.

    2012-04-01

    We present the first analysis of extended stellar kinematics of elliptical galaxies where a Yukawa-like correction to the Newtonian gravitational potential derived from f(R)-gravity is considered as an alternative to dark matter. In this framework, we model long-slit data and planetary nebula data out to 7 R eff of three galaxies with either decreasing or flat dispersion profiles. We use the corrected Newtonian potential in a dispersion-kurtosis Jeans analysis to account for the mass-anisotropy degeneracy. We find that these modified potentials are able to fit nicely all three elliptical galaxies and the anisotropy distribution is consistent with that estimated if a dark halo is considered. The parameter which measures the "strength" of the Yukawa-like correction is, on average, smaller than the one found previously in spiral galaxies and correlates both with the scale length of the Yukawa-like term and the orbital anisotropy.

  17. At the heart of the matter: the origin of bulgeless dwarf galaxies and Dark Matter cores

    CERN Document Server

    Governato, Fabio; Mayer, Lucio; Brooks, Alyson; Rhee, George; Wadsley, James; Jonsson, Patrik; Willman, Beth; Stinson, Greg; Quinn, Thomas; Madau, Piero

    2009-01-01

    For almost two decades the properties of "dwarf" galaxies have challenged the Cold Dark Matter (CDM) paradigm of galaxy formation. Most observed dwarf galaxies consists of a rotating stellar disc embedded in a massive DM halo with a near constant-density core. Yet, models based on the CDM scenario invariably form galaxies with dense spheroidal stellar "bulges" and steep central DM profiles, as low angular momentum baryons and DM sink to the center of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different DM particle candidate. This Letter presents new hydrodynamical simulations in a Lambda$CDM framework where analogues of dwarf galaxies, bulgeless and with a shallow central DM profile, are formed. This is achieved by resolving the inhomogeneous interstellar medium, resultin...

  18. Stripped Elliptical Galaxies as Probes of ICM Physics: I. Tails, Wakes, and Flow Patterns in and Around Stripped Ellipticals

    Science.gov (United States)

    Roediger, E.; Kraft, R. P.; Nulsen, P. E. J.; Forman, W. R.; Machacek, M.; Randall, S.; Jones, C.; Churazov, E.; Kokotanekova, R.

    2015-06-01

    Elliptical cluster galaxies are progressively stripped of their atmospheres due to their motion through the intracluster medium (ICM). Deep X-ray observations reveal the fine-structure of the galaxy’s remnant atmosphere and its gas tail and wake. This fine-structure depends on dynamic conditions (galaxy potential, initial gas contents, orbit through the host cluster), orbital stage (early infall, pre-/post-pericenter passage), and ICM plasma properties (thermal conductivity, viscosity, magnetic field structure). We aim to disentangle dynamic and plasma effects in order to use stripped ellipticals as probes of ICM plasma properties. This first paper of a series investigates the hydrodynamics of progressive gas stripping by means of inviscid hydrodynamical simulations. We distinguish a long-lasting initial relaxation phase and a quasi-steady stripping phase. During quasi-steady stripping, the ICM flow around the remnant atmosphere resembles the flow around solid bodies, including a “deadwater” region in the near wake. Gas is stripped from the remnant atmosphere predominantly at its sides via Kelvin-Helmholtz instabilities. The downstream atmosphere is largely shielded from the ICM wind and thus shaped into a tail. Observationally, both this “remnant tail” and the stripped gas in the wake can appear as a “tail”, but only in the wake can galactic gas mix with the ambient ICM. While the qualitative results are generic, the simulations presented here are tailored to the Virgo elliptical galaxy M89 (NGC 4552) for the most direct comparison to observations. Papers II and III of this series describe the effect of viscosity and compare to Chandra and XMM-Newton observations, respectively.

  19. STRIPPED ELLIPTICAL GALAXIES AS PROBES OF ICM PHYSICS. I. TAILS, WAKES, AND FLOW PATTERNS IN AND AROUND STRIPPED ELLIPTICALS

    Energy Technology Data Exchange (ETDEWEB)

    Roediger, E. [Hamburger Sternwarte, Universität Hamburg, Gojensbergsweg 112, D-21029 Hamburg (Germany); Kraft, R. P.; Nulsen, P. E. J.; Forman, W. R.; Machacek, M.; Randall, S.; Jones, C. [Harvard/Smithsonian Center for Astrophysics, 60 Garden Street MS-4, Cambridge, MA 02138 (United States); Churazov, E. [MPI für Astrophysik, Karl-Schwarzschild-Str. 1, Garching, D-85741 (Germany); Kokotanekova, R., E-mail: eroediger@hs.uni-hamburg.de [AstroMundus Master Programme, University of Innsbruck, Technikerstr. 25/8, 6020 Innsbruck (Austria)

    2015-06-10

    Elliptical cluster galaxies are progressively stripped of their atmospheres due to their motion through the intracluster medium (ICM). Deep X-ray observations reveal the fine-structure of the galaxy’s remnant atmosphere and its gas tail and wake. This fine-structure depends on dynamic conditions (galaxy potential, initial gas contents, orbit through the host cluster), orbital stage (early infall, pre-/post-pericenter passage), and ICM plasma properties (thermal conductivity, viscosity, magnetic field structure). We aim to disentangle dynamic and plasma effects in order to use stripped ellipticals as probes of ICM plasma properties. This first paper of a series investigates the hydrodynamics of progressive gas stripping by means of inviscid hydrodynamical simulations. We distinguish a long-lasting initial relaxation phase and a quasi-steady stripping phase. During quasi-steady stripping, the ICM flow around the remnant atmosphere resembles the flow around solid bodies, including a “deadwater” region in the near wake. Gas is stripped from the remnant atmosphere predominantly at its sides via Kelvin–Helmholtz instabilities. The downstream atmosphere is largely shielded from the ICM wind and thus shaped into a tail. Observationally, both this “remnant tail” and the stripped gas in the wake can appear as a “tail”, but only in the wake can galactic gas mix with the ambient ICM. While the qualitative results are generic, the simulations presented here are tailored to the Virgo elliptical galaxy M89 (NGC 4552) for the most direct comparison to observations. Papers II and III of this series describe the effect of viscosity and compare to Chandra and XMM-Newton observations, respectively.

  20. TiNy Titans: The Role of Dwarf-Dwarf Interactions in the Evolution of Low Mass Galaxies

    CERN Document Server

    Stierwalt, S; Patton, D; Johnson, K; Kallivayalil, N; Putman, M; Privon, G; Ross, G

    2014-01-01

    We introduce TiNy Titans (TNT), the first systematic study of star formation and the subsequent processing of the interstellar medium in interacting dwarf galaxies. Here we present the first results from a multiwavelength observational program based on a sample of 104 dwarf galaxy pairs selected from a range of environments within the SDSS and caught in various stages of interaction. The TNT dwarf pairs span mass ratios of M1/M2 100 A, occur in 20% of TNT dwarf pairs, regardless of environment, compared to only 6-8% of matched unpaired dwarfs. Starbursts can be triggered throughout the merger (out to large pair separations) and not just approaching coalescence. Despite their enhanced star formation, most TNT dwarf pairs have similar gas fractions relative to unpaired dwarfs. Thus, there may be significant reservoirs of diffuse, non-starforming gas surrounding the dwarf pairs or the gas consumption timescales may be long in the starburst phase. The only TNT dwarf pairs with low gas fractions (fgas <0.4) and...

  1. A Forming Pair of Dwarf Galaxies and Its DM Halo

    Science.gov (United States)

    Pustilnik, S. A.; Brinks, E.; Thuan, T. X.; Izotov, Yu.; Lipovetsky, V.

    SBS 0335-052 and its companion 0335-052W are shown to be a unique pair of currently forming dwarf galaxies associated with a huge HI cloud (Izotov et al. 1997, Lipovetsky et al. 1997, Thuan et al. 1997, Pustilnik et al. 1997). We present the analysis of the velocity field of this HI cloud, obtained with the VLA, and the model of its rotation curve to derive the total mass distribution in this system. We argue that this gas cloud is rotationally supported in the gravitational potential of a massive DM halo, and discuss the implications of this fact for galaxy formation and evolution scenarios. This unique system apparently preserves the original unperturbed structure of its DM halo and is thus very valuable to confront halo properties with model predictions. The parameters of the DM halo and neutral gas set limits, based on observational evidence, to the range of physical conditions under which a pristine hydrogen cloud can survive as a stable object over cosmlogical time scales. We discuss the possible effect of the massive spiral galaxy at the projected distance of about 100/h kpc to these forming galaxies.

  2. The Correlation Dimension of Young Stars in Dwarf Galaxies

    CERN Document Server

    Odekon, M C

    2006-01-01

    We present the correlation dimension of resolved young stars in four actively star-forming dwarf galaxies that are sufficiently resolved and transparent to be modeled as projections of three-dimensional point distributions. We use data in the Hubble Space Telescope archive; photometry for one of them, UGCA 292, is presented here for the first time. We find that there are statistically distinguishable differences in the nature of stellar clustering among the sample galaxies. The young stars of VII Zw 403, the brightest galaxy in the sample, have the highest value for the correlation dimension and also the most dramatic decrease with logarithmic scale, falling from $1.68\\pm0.14$ to $0.10\\pm0.05$ over less than a factor of ten in $r$. This decrease is consistent with the edge effect produced by a projected Poisson distribution within a 2:2:1 ellipsoid. The young stars in UGC 4483, the faintest galaxy in the sample, exhibit very different behavior, with a constant value of about 0.5 over this same range in $r$, e...

  3. Integral Field Spectroscopy of Blue Compact Dwarf Galaxies

    CERN Document Server

    Garcia-Lorenzo, Begona; Caon, Nicola; Monreal-Ibero, Ana; Kehrig, Carolina

    2008-01-01

    We present results on integral-field optical spectroscopy of five luminous Blue Compact Dwarf galaxies. The data were obtained using the fiber system INTEGRAL attached at the William Herschel telescope. The galaxies Mrk 370, Mrk 35, Mrk 297, Mrk 314 and III Zw 102 were observed. The central 33"x29" regions of the galaxies were mapped with a spatial resolution of 2"/spaxel, except for Mrk 314, in which we observed the central 16"x12" region with a resolution of 0.9"/spaxel$. We use high-resolution optical images to isolate the star-forming knots in the objects; line ratios, electron densities and oxygen abundances in each of these regions are computed. We build continuum and emission-line intensity maps as well as maps of the most relevant line ratios: [OIII]5007\\Hb, [NII]6584\\Ha, and Ha\\Hb, which allow us to obtain spatial information on the ionization structure and mechanisms. We also derive the gas velocity field from the Ha and [OIII]5007 emission lines. We find that all the five galaxies are in the high e...

  4. Galactic winds and circulation of the ISM in dwarf galaxies

    CERN Document Server

    D'Ercole, A

    1999-01-01

    We study, through 2D hydrodynamical simulations, the feedback of a starburst on the ISM of typical gas rich dwarf galaxies. The main goal is to address the circulation of the ISM and metals following the starburst. We assume a single-phase rotating ISM in equilibrium in the galactic potential generated by a stellar disk and a spherical dark halo. The starburst is assumed to occur in a small volume in the center of the galaxy, and it generates a mechanical power of 3.8e39 erg/s or 3.8e40 erg/s for 30 Myr. We found, consistently with previous investigations, that the galactic wind is not very effective in removing the ISM. The metal rich stellar ejecta, instead, may be efficiently expelled from the galaxy and dispersed in the intergalactic medium. Moreover, we found that the central region of the galaxy is always replenished with cold and dense gas after a few 100 Myr from the starbust, achieving the requisite for a new star formation event in 0.5-1 Gyr. The hydrodynamical evolution of galactic winds is thus co...

  5. Stellar Substructures Around the Hercules Dwarf Spheroidal Galaxy

    Science.gov (United States)

    Roderick, T. A.; Jerjen, H.; Mackey, A. D.; Da Costa, G. S.

    2015-05-01

    We present deep g and i band Dark Energy Camera stellar photometry of the Hercules Milky Way satellite galaxy, and its surrounding field, out to a radial distance of 5.4 times the tidal radius. We have identified nine extended stellar substructures associated with the dwarf; preferentially distributed along the major axis of the galaxy. Two significant over-densities lie outside the 95% confidence band for the likely orbital path of the galaxy and appear to be free-floating tidal debris. We estimate the luminosity of the new stellar substructures, and find that approximately the same amount of stellar flux is lying in these extended structures as inside the main body of Hercules. We also analyze the distribution of candidate blue-horizontal-branch stars and find agreement with the alignment of the substructures at a confidence level greater than 98%. Our analysis provides a quantitative demonstration that Hercules is a strongly tidally disrupted system, with noticeable stellar features at least 1.9 kpc away from the galaxy.

  6. Evolution of dwarf galaxies simulated in the cosmological LCDM scenario

    Science.gov (United States)

    Gonzalez-Samaniego, Alejandro; Colin, Pedro; Avila-Reese, Vladimir; Rodriguez-Puebla, Aldo; Valenzuela, Octavio

    2014-03-01

    We present results from numerical simulations of low-mass galaxies with the aim to explore the way their stellar masses are assembled. We analyze how the mass assembly histories of the parent halo determine the growth of their host galaxy and its implications on the current paradigm of formation and evolution of low-mass structures in the LCDM scenario. We have found that low-mass galaxies simulated in this scenario assemble their stellar masses following roughly the dark matter halo assembly, which seems to be in tension with the downsizing trend suggested by current observational inferences. We show that there is no more room to increase the strength of feedback from astrophysical processes in order to deviate strongly the stellar mass assembly from the dark halo one, as has been recently invoked to solve some of the potential issues faced by CDM-based simulations of dwarf galaxies. Alejandro González acknowledges finacial support from UNAM, Fundacion UNAM, and the APS to attend this meeting.

  7. The Origin of Dwarf Early-Type Galaxies

    CERN Document Server

    Toloba, Elisa

    2012-01-01

    Abridge. We have conducted a spectrophotometric study of dwarf early-type galaxies (dEs) in the Virgo cluster and in regions of lower density. We have found that these galaxies show many properties in common with late-type galaxies but not with more massive early-types (E/S0). The properties of the dEs in Virgo show gradients within the cluster. dEs in the outer parts of the Virgo cluster are kinematically supported by rotation, while those in the center are supported by the random motions of their stars (i.e. pressure supported). The rotationally supported dEs have disky isophotes and faint underlying spiral/irregular substructures, they also show younger ages than those pressure supported, which have boxy isophotes and are smooth and regular, without any substructure. We compare the position of these dEs with massive early-type galaxies in the Faber-Jackson and Fundamental Plane relations, and we find that, although there is no difference between the position of rotationally and pressure supported dEs, both...

  8. The Dearth of Neutral Hydrogen in Galactic Dwarf Spheroidal Galaxies

    CERN Document Server

    Spekkens, K; Mason, B S; Willman, B; Aguirre, J E

    2014-01-01

    We present new upper limits on the neutral hydrogen (HI) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA (ALFALFA) survey and Galactic All-Sky Survey (GASS) data. All of the limits Mlim are more stringent than previously reported values, and those from the GBT improve upon contraints in the literature by a median factor of 23. Normalizing by V-band luminosity Lv and dynamical mass Mdyn, we find Mlim/Lv ~ 10^{-3} Mo/Lo and Mlim/Mdyn ~ 5 x 10^{-5}, irrespective of location in the Galactic halo. Comparing these relative HI contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our HI upper limits therefore provide the clearest picture yet of the environmental dependence of the HI content in Local Volume dwarfs. If ram pressure stripping explains the dearth of HI in these ...

  9. Spectral Energy Distribution Mapping of Two Elliptical Galaxies on Sub-kpc Scales

    Science.gov (United States)

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

    2017-01-01

    We use high-resolution Herschel-PACS data of two nearby elliptical galaxies, IC 1459 and NGC 2768, to characterize their dust and stellar content. IC 1459 and NGC 2768 have an unusually large amount of dust for elliptical galaxies ((1–3) × 105 {M}ȯ ); this dust is also not distributed along the stellar content. Using data from GALEX (ultra-violet) to PACS (far-infrared, FIR), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.″2 pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young stars, and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (∼0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial distance with a fairly steep gradient for elliptical galaxies.

  10. Dynamics of Elliptical Galaxies with Planetary Nebulae in Modified Newtonian Dynamics

    CERN Document Server

    Tian, Yong

    2016-01-01

    The dynamics of an elliptical galaxy within a couple of effective radii can be probed effectively by stars. However, at larger distances planetary nebulae (PNe) replace stars as the tracer of the dynamics. Making use of the motion of PNe, Romanowsky et al. (2003) measured the dynamics of three luminous elliptical galaxies (NGC821, NGC3379, and NGC4494) at large distances from the galactic center. They found that little dark matter is needed up to 6 effective radii. Milgrom & Sanders (2003) showed that this result can be understood in the framework of MOdified Newtonian Dynamics (MOND). As more data are available in the past decade, we revisit this problem. We combine PNe data (up to 6{8 effective radii) and stellar data from SAURON of 7 elliptical galaxies, including those 3 galaxies in Romanowsky et al. (2003) with updated data and 4 other galaxies which have not been analyzed before. We conclude that the dynamics of these galaxies can be well explained by MOND.

  11. Multiple minor mergers: formation of elliptical galaxies and constraints for the growth of spiral disks

    CERN Document Server

    Bournaud, Frederic; Combes, Francoise

    2007-01-01

    Multiple, sequential mergers are unavoidable in the hierarchical build-up picture of galaxies, in particular for the minor mergers that are frequent and highly likely to have occured several times for most present-day galaxies. However the effect of repeated minor mergers on galactic structure and evolution has not been studied systematically so far. In this paper, we present a numerical study of multiple, subsequent, minor galaxy mergers, with various mass ratios ranging from 4:1 to 50:1. The N-body simulations include gas dynamics and star formation. We study the morphological and kinematical properties of the remnants, and show that several so-called "minor" mergers can lead to the formation of elliptical-like galaxies, that have global morphological and kinematical properties similar to that observed in real elliptical galaxies. The properties of these systems are compared with that of elliptical galaxies produced by the standard scenario of one single major merger. We thus show that repeated minor merger...

  12. Metal Diffusion in Smoothed Particle Hydrodynamics Simulations of Dwarf Galaxies

    Science.gov (United States)

    Williamson, David; Martel, Hugo; Kawata, Daisuke

    2016-05-01

    We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]-[Fe/H] distribution in the gas and cuts off the gas metallicity distribution function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between “metal mass-loading” (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even when the diffusion coefficient is calculated in different ways. The effectiveness of outflows at removing metals from dwarf galaxies and the metal distribution of the gas is thus dependent on the strength of diffusion. By contrast, we show that the metallicities of stars are not strongly dependent on the strength of diffusion, provided that some diffusion is present.

  13. Using M Dwarfs to Map Extinction in the Local Galaxy

    Science.gov (United States)

    Jones, David; West, A. A.; Foster, J.

    2011-01-01

    We use spectra of more than 56,000 M dwarfs from the Sloan Digital Sky Survey (SDSS) to create a high-latitude extinction map of the local Galaxy. Our technique compares spectra from low-extinction lines of sight as determined by Schlegel, Finkbeiner, & Davis to other SDSS spectra in order to derive improved distances and accurate extinctions for the stars in the SDSS data release 7 M dwarf sample. Unlike most previous studies, which have used a two-color method to determine extinction, we fit extinction curves to fluxes across the entire spectral range from 5700 to 9200 angstroms for every star in our sample. Our result is an extinction map that extends from a few tens of pc to approximately 2 kpc from the Sun. We also use a similar technique to create a map of Rv values within approximately 1 kpc of the Sun and find that they are roughly consistent with the widely accepted diffuse interstellar medium value of 3.1. Using our extinction data, we derive a dust scale height for the local galaxy of 176 ± 15 parsecs.

  14. New low surface brightness dwarf galaxies in the Centaurus group

    CERN Document Server

    Müller, Oliver; Binggeli, Bruno

    2016-01-01

    We conducted an extensive CCD search for faint, unresolved dwarf galaxies of very low surface brightness in the whole Centaurus group region encompassing the Cen A and M 83 subgroups lying at a distance of roughly 4 and 5 Mpc, respectively. The aim is to significantly increase the sample of known Centaurus group members down to a fainter level of completeness, serving as a basis for future studies of the 3D structure of the group. Following our previous survey of 60 square degrees covering the M 83 subgroup, we extended and completed our survey of the Centaurus group region by imaging another 500 square degrees area in the g and r bands with the wide-field Dark Energy Survey Camera at the 4m Blanco telescope at CTIO. The limiting central surface brightness reached for suspected Centaurus members is $\\mu_r \\approx 29$ mag arcsec$^{-2}$, corresponding to an absolute magnitude $M_r \\approx -9.5$. The images were enhanced using different filtering techniques. We found 41 new dwarf galaxy candidates, which togethe...

  15. EXTREME EMISSION-LINE GALAXIES IN CANDELS: BROADBAND-SELECTED, STARBURSTING DWARF GALAXIES AT z > 1

    Energy Technology Data Exchange (ETDEWEB)

    Van der Wel, A.; Rix, H.-W.; Jahnke, K. [Max-Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Straughn, A. N. [Astrophysics Science Division, Goddard Space Flight Center, Code 665, Greenbelt, MD 20771 (United States); Finkelstein, S. L.; Salmon, B. W. [George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States); Koekemoer, A. M.; Ferguson, H. C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Weiner, B. J. [Steward Observatory, 933 N. Cherry St., University of Arizona, Tucson, AZ 85721 (United States); Wuyts, S. [Max-Planck-Institut fuer Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Bell, E. F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Faber, S. M.; Trump, J. R.; Koo, D. C. [UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Scarlata, C. [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. S.E. Minneapolis, MN 55455 (United States); Hathi, N. P. [Observatories of the Carnegie Institution of Washington, Pasadena, CA 91101 (United States); Dunlop, J. S. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ (United Kingdom); Newman, J. A. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O' Hara Street, Pittsburgh, PA 15260 (United States); Dickinson, M. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); De Mello, D. F., E-mail: vdwel@mpia.de [Department of Physics, The Catholic University of America, Washington, DC 20064 (United States); and others

    2011-12-01

    We identify an abundant population of extreme emission-line galaxies (EELGs) at redshift z {approx} 1.7 in the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey imaging from Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3). Sixty-nine EELG candidates are selected by the large contribution of exceptionally bright emission lines to their near-infrared broadband magnitudes. Supported by spectroscopic confirmation of strong [O III] emission lines-with rest-frame equivalent widths {approx}1000 A-in the four candidates that have HST/WFC3 grism observations, we conclude that these objects are galaxies with {approx}10{sup 8} M{sub Sun} in stellar mass, undergoing an enormous starburst phase with M{sub *}/ M-dot{sub *} of only {approx}15 Myr. These bursts may cause outflows that are strong enough to produce cored dark matter profiles in low-mass galaxies. The individual star formation rates and the comoving number density (3.7 Multiplication-Sign 10{sup -4} Mpc{sup -3}) can produce in {approx}4 Gyr much of the stellar mass density that is presently contained in 10{sup 8}-10{sup 9} M{sub Sun} dwarf galaxies. Therefore, our observations provide a strong indication that many or even most of the stars in present-day dwarf galaxies formed in strong, short-lived bursts, mostly at z > 1.

  16. Elliptical galaxies interacting with the cluster tidal field origin of the intracluster stellar population

    CERN Document Server

    Muccione, V

    2002-01-01

    With the aid of simple numerical models, we discuss a particular aspect of the interaction between stellar orbital periods inside elliptical galaxies (Es) and the parent cluster tidal field (CTF), i.e., the possibility that collisionless stellar evaporation from Es is an effective mechanism for the production of the recently discovered intracluster stellar populations (ISP). These very preliminary investigations, based on idealized galaxy density profiles (such as Ferrers density distributions) show that, over an Hubble time, the amount of stars lost by a representative galaxy may sum up to the 10% of the initial galaxy mass, a fraction in interesting agreement with observational data. The effectiveness of this mechanism is due to the fact that the galaxy oscillation periods near its equilibrium configurations in the CTF are of the same order of stellar orbital times in the external galaxy regions.

  17. Composite Stellar Populations and Element by Element Abundances in the Milky Way Bulge and Elliptical Galaxies

    CERN Document Server

    Tang, Baitian; Davis, A Bianca

    2014-01-01

    This paper explores the integrated-light characteristics of the Milky Way (MW) bulge and to what extent they match those of elliptical galaxies in the local universe. We model composite stellar populations with realistic abundance distribution functions (ADFs), tracking the trends of individual elements as a function of overall heavy element abundance as actually observed in MW bulge stars. The resultant predictions for absorption feature strengths from the MW bulge mimic elliptical galaxies better than solar neighborhood stars do, but the MW bulge does not match elliptical galaxies, either. Comparing bulge versus elliptical galaxies, Fe, Ti, and Mg trend about the same for both but C, Na, and Ca seem irreconcilably different. Exploring the behavior of abundance compositeness leads to the concepts of "red lean" where a narrower ADF appears more metal rich than a wide one, and "red spread" where the spectral difference between wide and narrow ADFs increases as the ADF peak is moved to more metal-rich values. T...

  18. Stellar halos and elliptical galaxy formation: Origin of dynamical properties of the planetary nebular systems

    CERN Document Server

    Bekki, K; Bekki, Kenji; Peng, Eric

    2006-01-01

    Recent spectroscopic observations of planetary nebulae (PNe) in several elliptical galaxies have revealed structural and kinematical properties of the outer stellar halo regions. In order to elucidate the origin of the properties of these planetary nebula systems (PNSs), we consider the merger scenario in which an elliptical galaxy is formed by merging of spiral galaxies. Using numerical simulations, we particularly investigate radial profiles of projected PNe number densities, rotational velocities, and velocity dispersions of PNSs extending to the outer halo regions of elliptical galaxies formed from major and unequal-mass merging. We find that the radial profiles of the project number densities can be fitted to the power-law and the mean number density in the outer halos of the ellipticals can be more than an order of magnitude higher than that of the original spiral's halo. The PNSs are found to show a significant amount of rotation (V/sigma >0.5) in the outer halo regions ($R$ $>$ $5R_{\\rm e}$) of the el...

  19. ESTIMATING DISTANCES TO ELLIPTIC GALAXIES WITH A MASS-LUMINOSITY-RELATION

    NARCIS (Netherlands)

    VANALBADA, TS; BERTIN, G; STIAVELLI, M

    1995-01-01

    We argue that the physical reason for the success of the Fundamental Plane and the D-n-sigma relation as distance estimators for elliptical galaxies is the existence of a relation between luminosity and mass with small intrinsic scatter. Therefore a better understanding of the luminosity and mass va

  20. X-ray overluminous elliptical galaxies: A new class of mass concentrations in the universe?

    DEFF Research Database (Denmark)

    Vikhlinin, A.; McNamara, B.R.; Hornstrup, Allan;

    1999-01-01

    We detect four isolated, X-ray overluminous [L-x > 2 x 10(43) (h/0.5)(-2) ergs s(-1)] elliptical galaxies (OLEGs) in our 160 deg(2) ROSAT PSPC survey. The extent of their X-ray emission, total X-ray luminosity, total mass, and mass of the hot gas in these systems corresponds to poor clusters, and...

  1. Steady state cooling flow models with gas loss for normal elliptical galaxies

    Science.gov (United States)

    Sarazin, Craig L.; Ashe, Gregory A.

    1989-01-01

    A grid of cooling flow models for the hot gas in normal elliptical galaxies is calculated, including the loss of gas due to inhomogeneous cooling. The loss process is modeled as a distributed sink for the gas with the rate of loss being proportional to the local cooling rate. The cooling flow models with gas loss have smaller sonic radii, smaller inflow rates in their central regions, lower densities, and higher temperatures than homogeneous models. The reduction in the amount of hot gas flowing into the center of the models brings the models into much better agreement with the observed X-ray surface brightness profiles of elliptical galaxies. However, there is a large dispersion in the observed X-ray luminosities of ellipticals, and this cannot be explained by variations in the efficiency of gas loss. The gas-loss models have X-ray surface brightness profiles which are much less centrally peaked than the no-gas-loss models.

  2. Early-type dwarf galaxies with multicomponent stellar structure: Are they remnants of disc galaxies strongly transformed by their environment?

    CERN Document Server

    Aguerri, J Alfonso L

    2016-01-01

    The surface brightness distribution of $\\sim$30-40$\\%$ of the early-type dwarf galaxies with $-18 \\leq M_{B} \\leq -15$ in the Virgo and the Coma clusters is fitted by models that include two structural components (S\\`ersic + exponential) as for bright disc galaxies.The goal of the present study is to determine whether early-type dwarf galaxies with a two-component stellar structure in the Virgo and the Coma clusters are low-luminosity copies of bright disc galaxies or are the remnants of bright galaxies strongly transformed by cluster environmental effects.I analysed the location of bright disc galaxies and early-type dwarfs in the $r_{b,e}/h$- $n$ plane. The location in this plane of the two-component dwarf galaxies was compared with the remnants of tidally disrupted disc galaxies reported by numerical simulations. Bright unbarred disc galaxies show a strong correlation in the $r_{b,e}/h$-$n$ plane. Galaxies with larger S\\`ersic shape parameters show a higher $r_{b,e}/h$ ratio. In contrast, two-component ear...

  3. Dynamical Evolution of Elliptical Galaxies with Central Singularities

    CERN Document Server

    Merritt, D; Merritt, David; Quinlan, Gerald

    1997-01-01

    We study the effect of a massive central singularity on the structure of a triaxial galaxy using N-body simulations. Starting from a single initial model, we grow black holes with various final masses Mh and at various rates, ranging from impulsive to adiabatic. In all cases, the galaxy achieves a final shape that is nearly spherical at the center and close to axisymmetric throughout. However, the rate of change of the galaxy's shape depends strongly on the ratio Mh/Mg of black hole mass to galaxy mass. When Mh/Mg 2%, the galaxy becomes axisymmetric in little more than a crossing time. We propose that the rapid evolution toward axisymmetric shapes that occurs when Mh/Mg > 2% provides a negative feedback mechanism which limits the mass of central black holes by cutting off their supply of fuel.

  4. The specific entropy of elliptical galaxies: an explanation for profile-shape distance indicators?

    Science.gov (United States)

    Lima Neto, G. B.; Gerbal, D.; Márquez, I.

    1999-10-01

    Dynamical systems in equilibrium have a stationary entropy; we suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have in principle a unique specific entropy. This uniqueness, a priori unknown, should be reflected in correlations between the fundamental parameters describing the mass (light) distribution in galaxies. Following recent photometrical work on elliptical galaxies by Caon et al., Graham & Colless and Prugniel & Simien, we use the Sérsic law to describe the light profile and an analytical approximation to its three-dimensional deprojection. The specific entropy is then calculated, supposing that the galaxy behaves as a spherical, isotropic, one-component system in hydrostatic equilibrium, obeying the ideal-gas equations of state. We predict a relation between the three parameters of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an `Entropic Plane', by analogy with the well-known Fundamental Plane. We have analysed elliptical galaxies in two rich clusters of galaxies (Coma and ABCG 85) and a group of galaxies (associated with NGC 4839, near Coma). We show that, for a given cluster, the galaxies follow closely a relation predicted by the constant specific entropy hypothesis with a typical dispersion (one standard deviation) of 9.5per cent around the mean value of the specific entropy. Moreover, assuming that the specific entropy is also the same for galaxies of different clusters, we are able to derive relative distances between Coma, ABGC 85, and the group of NGC 4839. If the errors are due only to the determination of the specific entropy (about 10per cent), then the error in the relative distance determination should be less than 20per cent for rich clusters. We suggest that the unique specific entropy may provide a physical explanation for the distance indicators based on the Sérsic profile put forward by Young & Currie and recently discussed by Binggeli & Jerjen.

  5. The faint outer regions of the Pegasus Dwarf Irregular galaxy: a much larger and undisturbed galaxy

    CERN Document Server

    Kniazev, Alexei; Hoffman, G Lyle; Grebel, Eva K; Zucker, Daniel B; Pustilnik, Simon A

    2009-01-01

    We investigate the spatial extent and structure of the Pegasus dwarf irregular galaxy using deep, wide-field, multicolour CCD photometry from the Sloan Digital Sky Survey (SDSS) and new deep HI observations. We study an area of ~0.6 square degrees centred on the Pegasus dwarf that was imaged by SDSS. Using effective filtering in colour-magnitude space we reduce the contamination by foreground Galactic field stars and increase significantly the contrast in the outer regions of the Pegasus dwarf. Our extended surface photometry, reaches down to a surface brightness magnitude mu_r~32 mag/sq.arcsec. It reveals a stellar body with a diameter of ~8 kpc that follows a Sersic surface brightness distribution law, which is composed of a significantly older stellar population than that observed in the ~2 kpc main body. The galaxy is at least five times more extended than listed in NED. The faint extensions of the galaxy are not equally distributed around its circumference; the north-west end is more jagged than the sout...

  6. Cusp-core transformations in dwarf galaxies: observational predictions

    Science.gov (United States)

    Teyssier, Romain; Pontzen, Andrew; Dubois, Yohan; Read, Justin I.

    2013-03-01

    The presence of a dark matter core in the central kiloparsec of many dwarf galaxies has been a long-standing problem in galaxy formation theories based on the standard cold dark matter paradigm. Recent simulations, based on smooth particle hydrodynamics and rather strong feedback recipes, have shown that it was indeed possible to form extended dark matter cores using baryonic processes related to a more realistic treatment of the interstellar medium. Using adaptive mesh refinement, together with a new, stronger supernova feedback scheme that we have recently implemented in the RAMSES code, we show that it is also possible to form a prominent dark matter core within the well-controlled framework of an isolated, initially cuspy, 1010 M⊙ dark matter halo. Although our numerical experiment is idealized, it allows a clean and unambiguous identification of the dark matter core formation process. Our dark matter inner profile is well fitted by a pseudo-isothermal profile with a core radius of 800 pc. The core formation mechanism is consistent with the one proposed by Pontzen & Governato. We highlight two key observational predictions of all simulations that find cusp-core transformations: (i) a bursty star formation history with a peak-to-trough ratio of 5 to 10 and a duty cycle comparable to the local dynamical time and (ii) a stellar distribution that is hot with v/σ ˜ 1. We compare the observational properties of our model galaxy with recent measurements of the isolated dwarf Wolf-Lundmark-Mellote (WLM). We show that the spatial and kinematical distribution of stars and H I gas are in striking agreement with observations, supporting the fundamental role played by stellar feedback in shaping both the stellar and dark matter distribution.

  7. The origin of prolate rotation in dwarf spheroidal galaxies formed by mergers of disky dwarfs

    CERN Document Server

    Ebrova, Ivana

    2015-01-01

    Motivated by the discovery of prolate rotation of stars in Andromeda II, a dwarf spheroidal companion of M31, we study the origin of this type of streaming motion via mergers of disky dwarf galaxies. We simulate merger events between two identical dwarfs changing the initial inclination of their disks with respect to the orbit and the amount of orbital angular momentum. On radial orbits the amount of prolate rotation in the merger remnants correlates strongly with the inclination of the disks and is well understood as due to the conservation of the angular momentum component of the disks along the merger axis. For non-radial orbits prolate rotation may still be produced if the orbital angular momentum is initially not much larger than the intrinsic angular momentum of the disks. The orbital structure of the remnants with significant rotation is dominated by box orbits in the center and long-axis tubes in the outer parts. We also detect significant figure rotation resulting from the tidal distortion of the dis...

  8. Anomalous evolution of the dwarf galaxy HIPASS J1321-31

    NARCIS (Netherlands)

    Pritzl, BJ; Knezek, PM; Gallagher, JS; Grossi, M; Disney, MJ; Minchin, RF; Freeman, KC; Tolstoy, E; Saha, A

    2003-01-01

    We present Hubble Space Telescope/WFPC2 observations of the dwarf galaxy HIPASS J1321-31. This unusual galaxy lies in the direction of the Centaurus A group of galaxies and has a color-magnitude diagram with a distinctive red plume of luminous stars. This feature could arise from (1) a red giant bra

  9. Alignment of Red-Sequence Cluster Dwarf Galaxies: From the Frontier Fields to the Local Universe

    Science.gov (United States)

    Barkhouse, Wayne Alan; Archer, Haylee; Burgad, Jaford; Foote, Gregory; Rude, Cody; Lopez-Cruz, Omar

    2015-08-01

    Galaxy clusters are the largest virialized structures in the universe. Due to their high density and mass, they are an excellent laboratory for studying the environmental effects on galaxy evolution. Numerical simulations have predicted that tidal torques acting on dwarf galaxies as they fall into the cluster environment will cause the major axis of the galaxies to align with their radial position vector (a line that extends from the cluster center to the galaxy's center). We have undertaken a study to measure the redshift evolution of the alignment of red-sequence cluster dwarf galaxies based on a sample of 57 low-redshift Abell clusters imaged at KPNO using the 0.9-meter telescope, and 64 clusters from the WINGS dataset. To supplement our low-redshift sample, we have included galaxies selected from the Hubble Space Telescope Frontier fields. Leveraging the HST data allows us to look for evolutionary changes in the alignment of red-sequence cluster dwarf galaxies over a redshift range of 0 < z < 0.35. The alignment of the major axis of the dwarf galaxies is measured by fitting a Sersic function to each red-sequence galaxy using GALFIT. The quality of each model is checked visually after subtracting the model from the galaxy. The cluster sample is then combined by scaling each cluster by r200. We present our preliminary results based on the alignment of the red-sequence dwarf galaxies with: 1) the major axis of the brightest cluster galaxy, 2) the major axis of the cluster defined by the position of cluster members, and 3) a radius vector pointing from the cluster center to individual dwarf galaxies. Our combined cluster sample is sub-divided into different radial regions and redshift bins.

  10. The observed properties of dwarf galaxies in and around the Local Group

    CERN Document Server

    McConnachie, Alan W

    2012-01-01

    Positional, structural and dynamical parameters for all dwarf galaxies in and around the Local Group are presented, and various aspects of our observational understanding of this volume-limited sample are discussed. Over 100 nearby galaxies that have distance estimates placing them within 3Mpc of the Sun are identified. This distance threshold samples dwarfs in a large range of environments, from the satellite systems of the MW and M31, to the dwarfs in the outer regions of the Local Group, to the numerous isolated galaxies found in its surroundings. It extends to, but does not include, the galaxies associated with the next nearest groups. Our basic knowledge of this important galactic subset and their resolved stellar populations will continue to improve dramatically over the coming years with existing and future observational capabilities, and they will continue to provide the most detailed information available on numerous aspects of dwarf galaxy formation and evolution. Basic observational parameters, suc...

  11. Line-of-sight velocity distributions of low-luminosity elliptical galaxies

    CERN Document Server

    Halliday, C E; Kuntschner, H; Birkinshaw, M; Bender, R; Saglia, R P; Baggley, G; Davies, Roger L.; Kuntschner, Harald; Bender, Ralf; Baggley, Glenn

    2001-01-01

    The shape of the line-of-sight velocity distribution (LOSVD) is measured for a sample of 14 elliptical galaxies, predominantly low-luminosity ellipticals. The sample is dominated by galaxies in the Virgo cluster but also contains ellipticals in nearby groups and low density environments. The parameterization of the LOSVD due to Gerhard and van der Marel and Franx is adopted, which measures the asymmetrical and symmetrical deviations of the LOSVD from a Gaussian by the amplitudes h3 and h4 of the Gauss-Hermite series. Rotation, velocity dispersion, h3 and h4 are determined as a function of radius for both major and minor axes. Non-Gaussian LOSVDs are found for all galaxies along the major axes. Deviations from a Gaussian LOSVD along the minor axis are of much lower amplitude if present at all. Central decreases in velocity dispersion are found for three galaxies. Two galaxies have kinematically-decoupled cores: NGC 4458 and the well-known case of NGC 3608.

  12. Episodic model for star formation history and chemical abundances in giant and dwarf galaxies

    Science.gov (United States)

    Debsarma, Suma; Chattopadhyay, Tanuka; Das, Sukanta; Pfenniger, Daniel

    2016-11-01

    In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic haloes, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The derived periods of oscillation vary in the range (0.1-3.0) × 107 yr depending on various parameters existing from giant to dwarf galaxies. The evolution of metallicity varies in giant and dwarf galaxies and depends on the outflow process. Observed abundances in dwarf galaxies can be reproduced under fast outflow together with slow evaporation of cold gases into hot gas whereas slow outflow and fast evaporation is preferred for giant galaxies. The variation of metallicities in dwarf galaxies supports the fact that low rate of SNII production in dwarf galaxies is responsible for variation in metallicity in dwarf galaxies of similar masses as suggested by various authors.

  13. Direct evidence of hierarchical assembly at low masses from isolated dwarf galaxy groups

    Science.gov (United States)

    Stierwalt, S.; Liss, S. E.; Johnson, K. E.; Patton, D. R.; Privon, G. C.; Besla, G.; Kallivayalil, N.; Putman, M.

    2017-01-01

    The demographics of dwarf galaxy populations have long been in tension with predictions from the Λ cold dark matter (ΛCDM) paradigm 1-4 . If primordial density fluctuations were scale-free as predicted, dwarf galaxies should themselves host dark-matter subhaloes 5 , the most massive of which may have undergone star formation resulting in dwarf galaxy groups. Ensembles of dwarf galaxies are observed as sate­llites of more massive galaxies 6-9 , and there is observational 10 and theoretical 11 evidence to suggest that these satellites at redshift z = 0 were captured by the massive host halo as a group. However, the evolution of dwarf galaxies is highly susceptible to environment 12-14 , making these satellite groups imperfect probes of ΛCDM in the low-mass regime. Here we report one of the clearest examples yet of hierarchical structure formation at low masses: using deep multi-wavelength data, we identify seven isolated, spectroscopically confirmed groups of only dwarf galaxies. Each group hosts three to five known members, has a baryonic mass of ~4.4 × 109 to 2 × 1010 solar masses (M ⊙), and requires a mass-to-light ratio of <100 to be gravitationally bound. Such groups are predicted to be rare theoretically and found to be rare observationally at the current epoch, and thus provide a unique window into the possible formation mechanism of more massive, isolated galaxies.

  14. Radio continuum JVLA observations of the dwarf galaxy Sextans A

    Science.gov (United States)

    Monkiewicz, Jacqueline A.; Powell, Devon; Dettmar, Ralf-Juergen; Bomans, Dominik; Bowman, Judd D.; Scannapieco, Evan

    2017-06-01

    We present 20-cm Jansky Very Large Array (JVLA) observations of the star-forming dwarf galaxy Sextans A. Located at the outer edge of the Local Group, with an oxygen abundance of less than one-tenth of the Solar abundance (12+log O/H = 7.49), Sextans A provides a nearby laboratory for the study of low-metallicity star formation processes. This galaxy is a weak source in the infrared, but exhibits evidence for vigorous star formation-powered outflows in ionized gas, including large-scale H-alpha shells and filaments up to a kpc in length. Sextans A has not previously been detected in radio continuum. The upgraded JVLA and WIDAR correlator provide enhanced sensitivity over previous studies. We resolve a 3.0 mJy (+/- 0.3 mJy) continuum source centered on the brightest star formation region in Sextans A. Using two relatively interference-free windows at 1.4 GHz and 1.85 GHz, we are able to measure the spectral slope of the detected emission. We estimate the non-thermal contribution and the strength of the galaxy's magnetic field. We discuss the impact of low metallicity on the reliability of the IR/radio relation.

  15. The structure of Andromeda II dwarf spheroidal galaxy

    CERN Document Server

    del Pino, Andrés; Hidalgo, Sebastian L; Fouquet, Sylvain

    2016-01-01

    We analyze in detail the spatial distribution and kinematic properties of two different stellar populations in Andromeda II (And II) dwarf spheroidal galaxy. We obtained their detailed surface density maps, together with their radial density profiles. The two populations differ not only in age and metallicity, but also in their spatial distribution and kinematics. Old stars ($\\gtrsim 11$ Gyr) follow a round distribution well fitted by truncated density profiles. These stars rotate around the projected optical major axis of the galaxy with line-of-sight velocities $v_{los}(r_h) = 16 \\pm 3$ km s$^{-1}$ and a velocity gradient of $2.06 \\pm 0.21$ km s$^{-1}$ arcmin$^{-1}$. Intermediate-age stars ($\\lesssim 9$ Gyr) concentrate in the centre of the galaxy and form an elongated structure extending along the projected optical major axis. This structure appears to rotate with a steeper velocity gradient, $2.24 \\pm 0.22$ km s$^{-1}$ arcmin$^{-1}$, and around the optical minor axis. The centres of rotation and kinetic p...

  16. Unbiased constraints on ultralight axion mass from dwarf spheroidal galaxies

    CERN Document Server

    Gonzáles-Morales, Alma X; Peñarrubia, Jorge; Ureña-López, Luis

    2016-01-01

    It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_a\\sim 10^{-22}\\text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSph's to show that the "mass-anisotropy degeneracy" in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with ...

  17. In-spiraling Clumps in Blue Compact Dwarf Galaxies

    CERN Document Server

    Elmegreen, Bruce G; Hunter, Deidre

    2012-01-01

    Giant star-formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the BCD phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived....

  18. On the Fate of Processed Matter in Dwarf Galaxies

    CERN Document Server

    Silich, S A; Silich, Sergey A.; Tenorio-Tagle, Guillermo

    1998-01-01

    Two dimensional calculations of the evolution of remnants generated by the strong mechanical energy deposited by stellar clusters in dwarf galaxies (M \\si $10^9 - 10^{10}$ \\msun) are presented. The evolution is followed for times longer than both the blowout time and the presumed span of energy injection generated by a coeval massive stellar cluster. The remnants are shown to end up wrapping around the central region of the host galaxy, while growing to kpc-scale dimensions. Properties of the remnants such as luminosity, size, swept up mass, and expansion speed are given as a function of time for all calculated cases. The final fate of the swept-up galactic gas and of the matter processed by the central starburst is shown to be highly-dependent on the properties of the low density galactic halo. Superbubbles powered by star clusters, with properties similar to those inferred from the observations, slow down in the presence of an extended halo to expansion speeds smaller than the host galaxy escape velocity. V...

  19. The Dynamical and Chemical Evolution of Dwarf Spheroidal Galaxies

    CERN Document Server

    Revaz, Y; Sawala, T; Hill, V; Letarte, B; Irwin, M; Battaglia, G; Helmi, A; Shetrone, M D; Tolstoy, E; Venn, K A

    2009-01-01

    We present a large sample of fully self-consistent hydrodynamical Nbody/Tree-SPH simulations of isolated dwarf spheroidal galaxies (dSphs). It has enabled us to identify the key physical parameters and mechanisms at the origin of the observed variety in the Local Group dSph properties. The initial total mass (gas + dark matter) of these galaxies is the main driver of their evolution. Star formation (SF) occurs in series of short bursts. In massive systems, the very short intervals between the SF peaks mimic a continuous star formation rate, while less massive systems exhibit well separated SF bursts, as identified observationally. The delay between the SF events is controlled by the gas cooling time dependence on galaxy mass. The observed global scaling relations, luminosity-mass and luminosity-metallicity, are reproduced with low scatter. We take advantage of the unprecedentedly large sample size and data homogeneity of the ESO Large Programme DART, and add to it a few independent studies, to constrain the s...

  20. Dwarf galaxy formation with H2-regulated star formation

    CERN Document Server

    Kuhlen, M; Madau, P; Smith, B; Wise, J

    2011-01-01

    We describe cosmological galaxy formation simulations with the adaptive mesh refinement code Enzo that incorporate a star formation prescription regulated by the local abundance of molecular hydrogen. We show that this H2-regulated prescription leads to a suppression of star formation in low mass halos (M_h 4, alleviating some of the dwarf galaxy problems faced by theoretical galaxy formation models. H2 regulation modifies the efficiency of star formation of cold gas directly, rather than indirectly reducing the cold gas content with "supernova feedback". We determine the local H2 abundance in our most refined grid cells (76 proper parsec in size at z=4) by applying the model of Krumholz, McKee, & Tumlinson, which is based on idealized 1D radiative transfer calculations of H2 formation-dissociation balance in ~100 pc atomic--molecular complexes. Our H2-regulated simulations are able to reproduce the empirical (albeit lower z) Kennicutt-Schmidt relation, including the low Sigma_gas cutoff due to the transi...

  1. Measuring the extent of x-ray emitting hot gas haloes around elliptical galaxies

    Science.gov (United States)

    Alpaslan, Mehmet; Marcum, Pamela M.

    2017-01-01

    The hot, x-ray emitting gas halos around galaxies can serve as tracers of previous merger history, and provide insight into the formation processes of elliptical galaxies. In order to better understand the relationship between a galaxy's local environment and its x-ray emitting hot gas corona, we examine the x-ray emission from 117 early type galaxies selected from SDSS DR12 that have been observed with Chandra's ACIS detector. We have developed a new methodology for determining the effective and Petrosian radii of the x-ray emission from the hot coronae of these galaxies, and with it find a positive correlation between fifth nearest neighbour density and corona size. Notably, we do not see a corresponding correlation between size and other galaxy properties such as mass, r-band Petrosian radius, and metallicity. These results suggest that the physical processes that drive the extension of the hot gas halo do not significantly influence the stellar content of the elliptical galaxy.

  2. Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies.

    Science.gov (United States)

    McConnell, Nicholas J; Ma, Chung-Pei; Gebhardt, Karl; Wright, Shelley A; Murphy, Jeremy D; Lauer, Tod R; Graham, James R; Richstone, Douglas O

    2011-12-08

    Observational work conducted over the past few decades indicates that all massive galaxies have supermassive black holes at their centres. Although the luminosities and brightness fluctuations of quasars in the early Universe suggest that some were powered by black holes with masses greater than 10 billion solar masses, the remnants of these objects have not been found in the nearby Universe. The giant elliptical galaxy Messier 87 hosts the hitherto most massive known black hole, which has a mass of 6.3 billion solar masses. Here we report that NGC 3842, the brightest galaxy in a cluster at a distance from Earth of 98 megaparsecs, has a central black hole with a mass of 9.7 billion solar masses, and that a black hole of comparable or greater mass is present in NGC 4889, the brightest galaxy in the Coma cluster (at a distance of 103 megaparsecs). These two black holes are significantly more massive than predicted by linearly extrapolating the widely used correlations between black-hole mass and the stellar velocity dispersion or bulge luminosity of the host galaxy. Although these correlations remain useful for predicting black-hole masses in less massive elliptical galaxies, our measurements suggest that different evolutionary processes influence the growth of the largest galaxies and their black holes.

  3. Dilution in elliptical galaxies: Implications for the relation between metallicity, stellar mass and star formation rate

    CERN Document Server

    Yates, Robert M

    2013-01-01

    We investigate whether gradual dilution of the gas in some elliptical galaxies is the cause of a positive correlation between star formation rate (SFR) and gas-phase metallicity (Zg) at high stellar mass (M*) in the local Universe. To do this, two classes of massive (M* >= 10^10.5 Msun) galaxy are selected from the Sloan Digital Sky Survey (SDSS) and the Munich semi-analytic model of galaxy formation, L-Galaxies. The first class is selected by high specific star formation rates (sSFR) and high Zg, and the second class by low sSFR and low Zg. These criteria roughly distinguish disc-dominant galaxies from metal-poor, elliptical galaxies. In the semi-analytic model, the second class of galaxies obtain low sSFR and low Zg due to gradual dilution of the interstellar medium by accretion of metal-poor gas via infalling clumps and low-mass satellites. This occurs after a merger-induced starburst and the associated supernova feedback have quenched most of the original gas reservoir. A number of signatures of this evol...

  4. The rapid assembly of an elliptical galaxy of 400 billion solar masses at a redshift of 2.3.

    Science.gov (United States)

    Fu, Hai; Cooray, Asantha; Feruglio, C; Ivison, R J; Riechers, D A; Gurwell, M; Bussmann, R S; Harris, A I; Altieri, B; Aussel, H; Baker, A J; Bock, J; Boylan-Kolchin, M; Bridge, C; Calanog, J A; Casey, C M; Cava, A; Chapman, S C; Clements, D L; Conley, A; Cox, P; Farrah, D; Frayer, D; Hopwood, R; Jia, J; Magdis, G; Marsden, G; Martínez-Navajas, P; Negrello, M; Neri, R; Oliver, S J; Omont, A; Page, M J; Pérez-Fournon, I; Schulz, B; Scott, D; Smith, A; Vaccari, M; Valtchanov, I; Vieira, J D; Viero, M; Wang, L; Wardlow, J L; Zemcov, M

    2013-06-20

    Stellar archaeology shows that massive elliptical galaxies formed rapidly about ten billion years ago with star-formation rates of above several hundred solar masses per year. Their progenitors are probably the submillimetre bright galaxies at redshifts z greater than 2. Although the mean molecular gas mass (5 × 10(10) solar masses) of the submillimetre bright galaxies can explain the formation of typical elliptical galaxies, it is inadequate to form elliptical galaxies that already have stellar masses above 2 × 10(11) solar masses at z ≈ 2. Here we report multi-wavelength high-resolution observations of a rare merger of two massive submillimetre bright galaxies at z = 2.3. The system is seen to be forming stars at a rate of 2,000 solar masses per year. The star-formation efficiency is an order of magnitude greater than that of normal galaxies, so the gas reservoir will be exhausted and star formation will be quenched in only around 200 million years. At a projected separation of 19 kiloparsecs, the two massive starbursts are about to merge and form a passive elliptical galaxy with a stellar mass of about 4 × 10(11) solar masses. We conclude that gas-rich major galaxy mergers with intense star formation can form the most massive elliptical galaxies by z ≈ 1.5.

  5. The Molecular ISM of Dwarf Galaxies on Kiloparsec Scales: A New Survey for CO in Northern, IRAS-detected Dwarf Galaxies

    CERN Document Server

    Leroy, A; Simon, J D; Blitz, L; Leroy, Adam; Bolatto, Alberto D.; Simon, Joshua D.; Blitz, Leo

    2005-01-01

    We present a new survey for CO in dwarf galaxies using the Kitt Peak 12m telescope. We observed the central regions of 121 northern dwarfs with IRAS detections and no known CO emission. We detect CO in 28 of these galaxies and marginally detect another 16, increasing by about 50% the number of such galaxies known to have significant CO emission. The galaxies we detect are comparable in mass to the LMC, although somewhat brighter in CO and fainter in the FIR. Within dwarfs, we find that the CO luminosity, L_CO, is most strongly correlated with the K-band and the far infrared luminosities. There are also strong correlations with the radio continuum and B-band luminosities, and linear diameter. We suggest that L_CO and L_K correlate well because the stellar component of a galaxy dominates the midplane gravitational field and thus sets the pressure of the atomic gas, which controls the formation of H_2 from HI. We compare our sample with more massive galaxies and find that dwarfs and large galaxies obey the same ...

  6. The Origin of Dwarf Galaxies in Clusters: The Faint-End Slope of Abell 85 Galaxy Luminosity Function

    Science.gov (United States)

    Agulli, I.; Aguerri, J. A. L.; Barrena, R.; Diaferio, A.; Sánchez-Janssen, R.

    2016-10-01

    Dwarf galaxies (Mb>-18) are important because of their cosmological interest as tests of hierarchical theories. The formation of these galaxies is still an open question but red dwarf galaxies are preferentially located in high density environments, indicating that they are end-products of galaxy transformations in clusters. Deep spectroscopic studies of galaxy clusters are needed to put some constraints on dwarf galaxy formation and evolution. We have observed and analyzed Abell 85, a nearby (z = 0.055) and massive cluster down to M*+6, using the MOS instruments VIMOS@VLT and AF2@WHT. The first and powerful tool to study the characteristics of galaxies and compare with different density environments is the galaxy luminosity function. The comparison of the results for Abell 85 with literature outcomes for clusters and field, allows us to conclude that, at least for this cluster, the environment plays a major role in the nature of the faint-end galaxies, transforming blue dwarfs in the field into red ones in the cluster, but not in the formation of the luminosity function slope.

  7. Chandra & XMM-Newton Observations of NGC5253. Analysis of the X-ray Emission from a Dwarf Starburst Galaxy

    CERN Document Server

    Summers, L K; Strickland, D K; Heckman, T M; Summers, Lesley K.; Stevens, Ian R.; Strickland, David K.; Heckman, Timothy M.

    2004-01-01

    We present Chandra and XMM-Newton X-ray data of NGC5253, a local starbursting dwarf elliptical galaxy, in the early stages of a starburst episode. Contributions to the X-ray emission come from discrete point sources and extended diffuse emission, in the form of what appear to be multiple superbubbles, and smaller bubbles probably associated with individual star clusters. Chandra detects 17 sources within the optical extent of NGC5253 down to a completeness level corresponding to a luminosity of 1.5E37 erg/s.The slope of the point source X-ray luminosity function is -0.54, similar to that of other nearby dwarf starburst galaxies. Several different types of source are detected within the galaxy, including X-ray binaries and the emission associated with star-clusters. Comparison of the diffuse X-ray emission with the observed Halpha emission shows similarities in their extent. The best spectral fit to the diffuse emission is obtained with an absorbed, two temperature model giving temperatures for the two gas com...

  8. Transformation of a Virgo Cluster Dwarf Irregular Galaxy by Ram Pressure Stripping: IC3418 and its Fireballs

    CERN Document Server

    Kenney, Jeffrey D P; Jachym, Pavel; Crowl, Hugh H; Dague, William; Chung, Aeree; van Gorkom, Jacqueline; Vollmer, Bernd

    2013-01-01

    We present optical imaging and spectroscopy and HI imaging of the Virgo Cluster galaxy IC 3418, which is likely a "smoking gun" example of the transformation of a dwarf irregular into a dwarf elliptical galaxy by ram pressure stripping. IC 3418 has a spectacular 17 kpc length UV-bright tail comprised of knots, head-tail, and linear stellar features. The only H-alpha emission arises from a few HII regions in the tail, the brightest of which are at the heads of head-tail UV sources whose tails point toward the galaxy ("fireballs"). Several of the elongated tail sources have H-alpha peaks outwardly offset by 80-150 pc from the UV peaks, suggesting that gas clumps continue to accelerate through ram pressure, leaving behind streams of newly formed stars which have decoupled from the gas. Absorption line strengths, measured from Keck DEIMOS spectra, together with UV colors, show star formation stopped 300+/-100 Myr ago in the main body, and a strong starburst occurred prior to quenching. While neither H-alpha nor H...

  9. Analysis of luminosity distributions and shape parameters of strong gravitational lensing elliptical galaxies

    CERN Document Server

    Biernaux, J; Sluse, D; Chantry, V

    2016-01-01

    Luminosity profiles of galaxies acting as strong gravitational lenses can be tricky to study. Indeed, strong gravitational lensing images display several lensed components, both point-like and diffuse, around the lensing galaxy. Those objects limit the study of the galaxy luminosity to its inner parts. Therefore, the usual fitting methods perform rather badly on such images. Previous studies of strong lenses luminosity profiles using software such as GALFIT or IMFITFITS and various PSF-determining methods have resulted in discrepant results. The present work aims at investigating the causes of those discrepancies, as well as at designing more robust techniques for studying the morphology of early-type lensing galaxies with the ability to subtract a lensed signal from their luminosity profiles. We design a new method to independently measure each shape parameter, namely, the position angle, ellipticity, and half-light radius of the galaxy. Our half-light radius measurement method is based on an innovative sche...

  10. UV Excess and AGB Evolution in Elliptical-Galaxy Stellar Populations

    Science.gov (United States)

    González-Lópezlira, R. A.; Buzzoni, A.

    2009-03-01

    The puzzling origin of the ``UV-upturn'' phenomenon, observed in some elliptical galaxies, has recently been settled by identifying hot HB stars as main contributors to galaxy ultraviolet luminosity excess. While a blue HB morphology seems a natural characteristic of metal-poor stellar populations, its appearance in metal-rich systems, often coupled with a poorer rate of planetary nebulae per unit galaxy luminosity, might be calling for an intimate connection between UV excess and AGB properties in early-type galaxies. In this work, we want to briefly assess this issue relying on infrared surface brightness fluctuations as a powerful tool to trace AGB properties in external galaxies with unresolved stellar populations.

  11. UV excess and AGB evolution in elliptical-galaxy stellar populations

    CERN Document Server

    Gonzalez-Lopezlira, Rosa A

    2007-01-01

    The puzzling origin of the ``UV-upturn'' phenomenon, observed in some elliptical galaxies, has recently been settled by identifying hot HB stars as main contributors to galaxy ultraviolet luminosity excess. While a blue HB morphology seems a natural characteristic of metal-poor stellar populations, its appearence in metal-rich systems, often coupled with a poorer rate of planetary nebulae per unit galaxy luminosity, might be calling for an intimate connection between UV excess and AGB properties in early-type galaxies. In this work, we want to briefly assess this issue, relying on infrared surface brightness fluctuations as a powerful tool to trace AGB properties in external galaxies with unresolved stellar populations.

  12. The Arecibo Galaxy Environment Survey VIII : Discovery of an Isolated Dwarf Galaxy in the Local Volume

    CERN Document Server

    Taylor, R; Herbst, H; Smith, R

    2014-01-01

    The Arecibo Galaxy Environment Survey (AGES) has detected a nearby HI source at a heliocentric velocity of +363 km/s . The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey (SDSS) data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object : 1) It is within the Local Group, in which case its HI properties are comparable with recently discovered ultra-compact high velocity clouds; 2) It is just behind the Local Group, in which case its optical characteristics are similar to the newly discovered Leo P galaxy; 3) It is a blue compact dwarf galaxy within the local volume but not associated with the Local Group. We find the third possibility to be the most likely, based on distance estimates from the Tully-Fisher relation and its velocity relative to the Local Group.

  13. The Mgb-$\\sigma$ Relation of Elliptical Galaxies at z=0.37

    CERN Document Server

    Ziegler, B L; Ziegler, Bodo L.; Bender, Ralf

    1997-01-01

    We derive absorption indices of ellipticals in clusters at z=0.37 from medium-resolution spectroscopy together with kinematical parameters. These galaxies exhibit a relationship between the Mgb linestrength and their internal velocity dispersion similar to local dynamically hot galaxies. But for any given sigma, Mgb of the distant ellipticals is significantly lower than the mean value of the nearby sample. The difference of Mgb between the two samples is small and can be fully attributed to the younger age of the distant stellar populations in accordance with the passive evolution model. The low reduction of Mgb at a look-back time of about 5 Gyrs requires that the bulk of the stars in cluster ellipticals have formed at very high redshifts of z_f>2. For the most massive galaxies, where the reduction is even lower, z_f probably exceeds 4. Unlike most methods to measure the evolution of ellipticals using luminosities, surface brightnesses or colours, the Mgb linestrength does not depend on corrections for extin...

  14. Measurements of Far-UV Emission from Elliptical Galaxies at z = 0.375

    CERN Document Server

    Brown, T M; Deharveng, J M; Jedrzejewski, R I; Brown, Thomas M.; Ferguson, Henry C.; Deharveng, Jean-Michel; Jedrzejewski, Robert I.

    1998-01-01

    The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant ellipticals, and is thought to arise primarily from low-mass evolved stars on the extreme horizontal branch and beyond. Models suggest that the UV upturn is a very strong function of age for these old stellar populations, increasing as the galaxy gets older. In some models the change in UV/optical flux ratio is a factor of 25 over timescales of less than 3 Gyr. To test the predictions for rapid evolution of the UV upturn, we have observed a sample of normal elliptical galaxies in the z=0.375 cluster Abell 370 with the Faint Object Camera aboard the Hubble Space Telescope. A combination of two long-pass filters was used to isolate wavelengths shortward of rest-frame 2700 A, providing a measurement of the UV upturn at a lookback time of approximately 4 Gyr. Surprisingly, the four ellipticals observed show a range of UV upturn strength that is similar to that seen in n...

  15. Gravitational wave radiation from a double white dwarf system inside our galaxy: a potential method for seeking strange dwarfs

    Institute of Scientific and Technical Information of China (English)

    Zhan-Kui Lü; Shi-Wei Wu; Zhi-Cheng Zeng

    2009-01-01

    Like the investigation of double white dwarf (DWD) systems, strange dwarf (SD) - white dwarf (WD) system evolution in Laser Interferometer Space Antenna (LISA)'s absolute amplitude-frequency diagram is investigated. Since there is a strange quark core inside an SD, SDs' radii are significantly smaller than the value predicted by the standard WD model, which may strongly affect the gravitational wave (GW) signal in the mass-transferring phases of binary systems. We study how an SD-WD binary evolves across LISA's absolute amplitude-frequency diagram. In principle, we provide an executable way to detect SDs in the Galaxy's DWD systems by radically new windows offered by GW detectors.

  16. Abundant Molecular Gas in Tidal Dwarf Galaxies On-going Galaxy Formation

    CERN Document Server

    Braine, J; Lisenfeld, U; Charmandaris, V; Vallejo, O; Leon, S; Brinks, E

    2001-01-01

    [Abridged...] We investigate the process of galaxy formation as can be observed in the only currently forming galaxies -- the so-called Tidal Dwarf Galaxies, hereafter TDGs -- through observations of the molecular gas detected via its CO emission. These objects are formed of material torn off of the outer parts of a spiral disk due to tidal forces in a collision between two massive galaxies. Molecular gas is a key element in the galaxy formation process, providing the link between a cloud of gas and a bona fide galaxy. We have detected CO in 8 TDGs (two of them have already been published in Braine et al. 2000), with an overall detection rate of 80%, showing that molecular gas is abundant in TDGs, up to a few 10^8 M_sun. The CO emission coincides both spatially and kinematically with the HI emission, indicating that the molecular gas forms from the atomic hydrogen where the HI column density is high. A possible trend of more evolved TDGs having greater molecular gas masses is observed, in accord with the tran...

  17. Metal diffusion in smoothed particle hydrodynamics simulations of dwarf galaxies

    CERN Document Server

    Williamson, David John; Kawata, Daisuke

    2016-01-01

    We perform a series of smoothed particle hydrodynamics simulations of isolated dwarf galaxies to compare different metal mixing models. In particular, we examine the role of diffusion in the production of enriched outflows, and in determining the metallicity distributions of gas and stars. We investigate different diffusion strengths, by changing the pre-factor of the diffusion coefficient, by varying how the diffusion coefficient is calculated from the local velocity distribution, and by varying whether the speed of sound is included as a velocity term. Stronger diffusion produces a tighter [O/Fe]-[Fe/H] distribution in the gas, and cuts off the gas metallicity distribution function at lower metallicities. Diffusion suppresses the formation of low-metallicity stars, even with weak diffusion, and also strips metals from enriched outflows. This produces a remarkably tight correlation between "metal mass-loading" (mean metal outflow rate divided by mean metal production rate) and the strength of diffusion, even...

  18. Dark Matter in $\\gamma$ lines: Galactic Center vs dwarf galaxies

    CERN Document Server

    Lefranc, Valentin; Panci, Paolo; Sala, Filippo; Silk, Joseph

    2016-01-01

    We provide CTA sensitivities to Dark Matter (DM) annihilation in $\\gamma$-ray lines, from the observation of the Galactic Center (GC) as well as, for the first time, of dwarf Spheroidal galaxies (dSphs). We compare the GC reach with that of dSphs as a function of a putative core radius of the DM distribution, which is itself poorly known. We find that the currently best dSph candidates constitute a more promising target than the GC, for core radii of one to a few kpc. We use the most recent instrument response functions and background estimations by CTA, on top of which we add the diffuse photon component. Our analysis is of particular interest for TeV-scale electroweak multiplets as DM candidates, such as the supersymmetric Wino and the Minimal Dark Matter fiveplet, whose predictions we compare with our projected sensitivities.

  19. THE DEARTH OF NEUTRAL HYDROGEN IN GALACTIC DWARF SPHEROIDAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Spekkens, Kristine; Urbancic, Natasha [Department of Physics, Royal Military College of Canada, P.O. Box 17000, Station Forces, Kingston, Ontario K7K 7B4 (Canada); Mason, Brian S. [National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States); Willman, Beth [Haverford College, 370 Lancaster Avenue, Haverford, PA 19041 (United States); Aguirre, James E., E-mail: kristine.spekkens@rmc.ca [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States)

    2014-11-01

    We present new upper limits on the neutral hydrogen (H I) content within the stellar half-light ellipses of 15 Galactic dwarf spheroidal galaxies (dSphs), derived from pointed observations with the Green Bank Telescope (GBT) as well as Arecibo L-band Fast ALFA survey and Galactic All-Sky Survey data. All of the limits M{sub H} {sub I}{sup lim} are more stringent than previously reported values, and those from the GBT improve upon constraints in the literature by a median factor of 23. Normalizing by V-band luminosity L{sub V} and dynamical mass M {sub dyn}, we find M{sub H} {sub I}{sup lim}/L{sub V}∼10{sup −3} M{sub ⊙}/L{sub ⊙} and M{sub H} {sub I}{sup lim}/M{sub dyn}∼5×10{sup −5}, irrespective of location in the Galactic halo. Comparing these relative H I contents to those of the Local Group and nearby neighbor dwarfs compiled by McConnachie, we find that the Galactic dSphs are extremely gas-poor. Our H I upper limits therefore provide the clearest picture yet of the environmental dependence of the H I content in Local Volume dwarfs. If ram pressure stripping explains the dearth of H I in these systems, then orbits in a relatively massive Milky Way are favored for the outer halo dSph Leo I, while Leo II and Canes Venatici I have had a pericentric passage in the past. For Draco and Ursa Minor, the interstellar medium mass that should accumulate through stellar mass loss in between pericentric passages exceeds M{sub H} {sub I}{sup lim} by a factor of ∼30. In Ursa Minor, this implies that either this material is not in the atomic phase, or that another mechanism clears the recycled gas on shorter timescales.

  20. The same with less: The cosmic web of warm versus cold dark matter dwarf galaxies

    CERN Document Server

    Reed, Darren S; Smith, Robert E; Potter, Doug; Stadel, Joachim; Moore, Ben

    2014-01-01

    We explore fundamental properties of the distribution of low mass dark matter halos within the cosmic web using warm dark matter (WDM) and cold dark matter (CDM) cosmological simulations. Using self abundance-matched mock galaxy catalogs, we show that the distribution of dwarf galaxies in a WDM universe, wherein low mass halo formation is heavily suppressed, is nearly indistinguishable to that of a CDM universe whose low mass halos are not seen because galaxy formation is suppressed below some threshold halo mass. However, if the scatter between dwarf galaxy luminosity and halo properties is large enough, low mass CDM halos would sometimes host relatively bright galaxies thereby populating CDM voids with the occasional isolated galaxy and reducing the numbers of completely empty voids. Otherwise, without high mass to light scatter, all mock galaxy clustering statistics that we consider--the auto-correlation function, the numbers and radial profiles of satellites, the numbers of isolated galaxies, and the PDF ...

  1. First Stellar Abundances in the Dwarf Irregular Galaxy IC 1613

    Science.gov (United States)

    Tautvaišienė, Gražina; Geisler, Doug; Wallerstein, George; Borissova, Jura; Bizyaev, Dmitry; Pagel, Bernard E. J.; Charbonnel, Corinne; Smith, Verne

    2007-12-01

    Chemical abundances in three M supergiants in the Local Group dwarf irregular galaxy IC 1613 have been determined using high-resolution spectra obtained with the UVES spectrograph on the ESO 8.2 m Kueyen telescope. A detailed synthetic-spectrum analysis has been used to determine the atmospheric parameters and abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Fe, Co, Ni, La, and Eu. We find the overall metallicity of the stars to be [Fe/H] = -0.67 ± 0.09 and the age 9-13 Myr, which is in excellent agreement with the present-day values in the age-metallicity relationship model of IC 1613 by Skillman et al. We have found that the three supergiants investigated have a mean [α/Fe] equal to about -0.1, which is lower than seen in Galactic stars at the same metallicity and is in agreement with the results obtained in other dwarf irregular galaxies. The oxygen abundances are in agreement with the upper values of the nebular oxygen determinations in IC 1613. The abundance ratios of s- and r-process elements to iron are enhanced relative to solar by about 0.3 dex. The abundance pattern of the elements studied is similar to that of the Small Magellanic Cloud, except for Co and Ni, which are underabundant in the SMC. The observed elemental abundances are generally in very good agreement with the recent chemical evolution model of Yuk and Lee. Based on observations collected with the Very Large Telescope and the 2.2 m Telescope of the European Southern Observatory within the Observing Programs 70.B-0361(A) and 072.D-0113(D).

  2. Ejection of Supernova-Enriched Gas From Dwarf Disk Galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Fragile, P C; Murray, S D; Lin, D C

    2004-06-15

    We examine the efficiency with which supernova-enriched gas may be ejected from dwarf disk galaxies, using a methodology previously employed to study the self-enrichment efficiency of dwarf spheroidal systems. Unlike previous studies that focused on highly concentrated starbursts, in the current work we consider discrete supernova events spread throughout various fractions of the disk. We model disk systems having gas masses of 10{sup 8} and 10{sup 9} M{sub {circle_dot}} with supernova rates of 30, 300, and 3000 Myr{sup -1}. The supernova events are confined to the midplane of the disk, but distributed over radii of 0, 30, and 80% of the disk radius, consistent with expectations for Type II supernovae. In agreement with earlier studies, we find that the enriched material from supernovae is largely lost when the supernovae are concentrated near the nucleus, as expected for a starburst event. In contrast, we find the loss of enriched material to be much less efficient (as low as 21%) when the supernovae occur over even a relatively small fraction of the disk. The difference is due to the ability of the system to relax following supernova events that occur over more extended regions. Larger physical separations also reduce the likelihood of supernovae going off within low-density ''chimneys'' swept out by previous supernovae. We also find that, for the most distributed systems, significant metal loss is more likely to be accompanied by significant mass loss. A comparison with theoretical predications indicates that, when undergoing self-regulated star formation, galaxies in the mass range considered shall efficiently retain the products of Type II supernovae.

  3. The early days of the Sculptor dwarf spheroidal galaxy

    CERN Document Server

    Jablonka, P; Mashonkina, L; Hill, V; Revaz, Y; Shetrone, M; Starkenburg, E; Irwin, M; Tolstoy, E; Battaglia, G; Venn, K; Helmi, A; Primas, F; Francois, P

    2015-01-01

    We present the high resolution spectroscopic study of five -3.9<=[Fe/H]<=-2.5 stars in the Local Group dwarf spheroidal, Sculptor, thereby doubling the number of stars with comparable observations in this metallicity range. We carry out a detailed analysis of the chemical abundances of alpha, iron peak, light and heavy elements, and draw comparisons with the Milky Way halo and the ultra faint dwarf stellar populations. We show that the bulk of the Sculptor metal-poor stars follows the same trends in abundance ratios versus metallicity as the Milky Way stars. This suggests similar early conditions of star formation and a high degree of homogeneity of the interstellar medium. We find an outlier to this main regime, which seems to miss the products of the most massive of the TypeII supernovae. In addition to its value to help refining galaxy formation models, this star provides clues to the production of cobalt and zinc. Two of our sample stars have low odd-to-even barium isotope abundance ratios, suggesti...

  4. Primordial alignment of elliptical galaxies in intermediate redshift clusters

    CERN Document Server

    Rong, Yu; Liao, Jin-Yuan

    2015-01-01

    We measure primordial alignments for the red galaxies in the sample of eight massive galaxy clusters in the southern sky from the CLASH-VLT Large Programme, at a median redshift of 0.375. We find primordial alignment with about $3\\sigma$ significance in the four dynamically young clusters, but null detection of primordial alignment in the four highly relaxed clusters. The observed primordial alignment is not dominated by any single one of the four dynamically young clusters, and is primarily due to a population of bright galaxies ($M_r<-20.5\\ \\rm{m}$) residing in the region 300 to 810 kpc from the cluster centers. For the first time, we point out that the combination of radial alignment and halo alignment can cause fake primordial alignment. Finally, we find that the detected alignment for the dynamically young clusters is real rather than fake primordial alignment.

  5. Star Cluster Luminosity Functions and Cluster Formation Efficiencies in LEGUS Dwarf Galaxies

    Science.gov (United States)

    Cook, David O.; Lee, Janice C.; Adamo, Angela; Kim, Hwiyun; Ryon, Jenna E.; LEGUS Team

    2017-01-01

    We present preliminary results of star cluster luminosity functions (LFs) and cluster formation efficiencies (Γ) in the LEGUS dwarf galaxy sub-sample. We have used a combination of automated and visual identification techniques to allow us to construct a more complete sample of clusters in these low-mass, low-SFR environments compared to previous studies of dwarf galaxies. Cluster properties are derived from fitting UV and optical (NUV-I) HST photometry to both deterministic and stochastic single-aged stellar populations models. We compare the cluster formation efficiencies and LF slopes to those of previous studies in both dwarf and massive spiral galaxy environments. Recent studies have found that both the LF slope and Γ form trends with galaxy environment. Our LF slope and Γ measurements in the LEGUS dwarfs will allow us to test these trends in the extreme, low-SFR regime and provide a better understanding of the star formation process.

  6. Triangulum II: A Very Dense Ultra-Faint Dwarf Galaxy

    CERN Document Server

    Kirby, Evan N; Simon, Joshua D; Guhathakurta, Puragra

    2015-01-01

    Laevens et al. recently discovered Triangulum II, a satellite of the Milky Way. Its Galactocentric distance is 36 kpc, and its luminosity is only 450 L_sun. We measured the radial velocities of six members stars with Keck/DEIMOS, and we found a velocity dispersion of sigma_v = 5.1 -1.4 +4.0 km/s. We also measured the metallicities of three stars and found a range of 0.8 dex in [Fe/H]. The velocity and metallicity dispersions identify Triangulum II as a dark matter-dominated galaxy. The galaxy is moving very quickly toward the Galactic center (v_GSR = -262 km/s). Although it might be in the process of being tidally disrupted as it approaches pericenter, there is no strong evidence for disruption. The ellipticity is low, and the mean velocity, = -382.1 +/- 2.9 km/s, rules out an association with the Triangulum-Andromeda substructure or the Pan-Andromeda Archaeological Survey (PAndAS) stellar stream. If Triangulum II is in dynamical equilibrium, then it would have a mass-to-light ratio of 3600 -2100 +3500 M_sun...

  7. Detection of Prominent Stellar Disks in the Progenitors of Present-day Massive Elliptical Galaxies

    Science.gov (United States)

    Davari, Roozbeh H.; Ho, Luis C.; Mobasher, Bahram; Canalizo, Gabriela

    2017-02-01

    Massive galaxies at high redshifts (z > 2) show different characteristics from their local counterparts: they are compact and most likely have a disk. In this study, we trace the evolution of local massive galaxies by performing a detailed morphological analysis, namely, fitting single Sérsic profiles and performing bulge+disk decompositions. We analyze ∼250 massive galaxies selected from all CANDELS fields (COSMOS, UDS, EGS, GOODS-South, and GOODS-North). We confirm that both star-forming and quiescent galaxies increase their sizes significantly from z ≈ 2.5 to the present day. The global Sérsic index of quiescent galaxies increases over time (from n ≈ 2.5 to n > 4), while that of star-forming galaxies remains roughly constant (n ≈ 2.5). By decomposing galaxy profiles into bulge+disk components, we find that massive galaxies at high redshift have prominent stellar disks, which are also evident from visual inspection of the images. By z ≈ 0.5, the majority of the disks disappear and massive quiescent galaxies begin to resemble the local elliptical galaxies. Star-forming galaxies have lower bulge-to-total ratios (B/T) than their quiescent counterparts in each redshift bin. The bulges of star-forming and quiescent galaxies follow different evolutionary histories, while their disks evolve similarly. Based on our morphological analysis and previous cosmological simulations, we argue that major mergers, along with minor mergers, have played a crucial role in the significant increase in size of high-z galaxies and the destruction of their massive and large-scale disks.

  8. Should Elliptical Galaxies Be Idealised as Collisionless Equilibria?

    OpenAIRE

    Kandrup, Henry E.

    2000-01-01

    This talk summarises several different lines of argument suggesting that one should not expect cuspy nonaxisymmetric galaxies to exist as robust, long-lived collisionless equilibria, i.e., that such objects should not be idealised as time-independent solutions to the collisionless Boltzmann equation.

  9. The extremely low-metallicity tail of the Sculptor dwarf spheroidal galaxy

    NARCIS (Netherlands)

    Starkenburg, E.; Hill, V.; Tolstoy, E.; François, P.; Irwin, M. J.; Boschman, L.; Venn, K. A.; de Boer, T. J. L.; Lemasle, B.; Jablonka, P.; Battaglia, G.; Groot, P.; Kaper, L.

    2013-01-01

    We present abundances for seven stars in the (extremely) low-metallicity tail of the Sculptor dwarf spheroidal galaxy, from spectra taken with X-shooter on the ESO VLT. Targets were selected from the Ca II triplet (CaT) survey of the dwarf abundances and radial velocities team (DART) using the lates

  10. Dwarf spheroidal galaxies as degenerate gas of free fermions

    Energy Technology Data Exchange (ETDEWEB)

    Domcke, Valerie; Urbano, Alfredo, E-mail: valerie.domcke@sissa.it, E-mail: alfredo.urbano@sissa.it [SISSA - International School for Advanced Studies, via Bonomea 256, Trieste, 34136 Italy (Italy)

    2015-01-01

    In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass m{sub f}. We assume that on galactic scales these fermions are capable of forming a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting con figuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to m{sub f}. After reviewing the basic formalism, we test this scenario against experimental data describing the velocity dispersion of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit to the data and realistic predictions for the size of DM halos providing that m{sub f}≅ 200 eV. Furthermore, we show that in this setup larger galaxies correspond to the non-degenerate limit of the gas. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance and the bound on the free-streaming length constrains the inflation model in terms of inflaton mass, its branching ratio into DM and the reheating temperature.

  11. The effect of tides on the Fornax dwarf spheroidal galaxy

    CERN Document Server

    Battaglia, Giuseppina; Nipoti, Carlo

    2015-01-01

    Estimates of the mass distribution and dark-matter (DM) content of dwarf spheroidal galaxies (dSphs) are usually derived under the assumption that the effect of the tidal field of the host galaxy is negligible over the radial extent probed by kinematic data-sets. We assess the implications of this assumption in the specific case of the Fornax dSph by means of N-body simulations of a satellite orbiting around the Milky Way. We consider observationally-motivated orbits and we tailor the initial distributions of the satellite's stars and DM to match, at the end of the simulations, the observed structure and kinematics of Fornax. In all our simulations the present-day observable properties of Fornax are not significantly influenced by tidal effects. The DM component is altered by the interaction with the Galactic field (up to 20% of the DM mass within 1.6 kpc is lost), but the structure and kinematics of the stellar component are only mildly affected even in the more eccentric orbit (more than 99% of the stellar ...

  12. Tidal Dwarf Galaxies: Disc Formation at z=0

    CERN Document Server

    Lelli, Federico; Brinks, Elias; McGaugh, Stacy S

    2015-01-01

    Collisional debris around interacting and post-interacting galaxies often display condensations of gas and young stars that can potentially form gravitationally bound objects: Tidal Dwarf Galaxies (TDGs). We summarise recent results on TDGs, which are originally published in Lelli et al. (2015, A&A). We study a sample of six TDGs around three different interacting systems, using high-resolution HI observations from the Very Large Array. We find that the HI emission associated to TDGs can be described by rotating disc models. These discs, however, would have undergone less than one orbit since the time of the TDG formation, raising the question of whether they are in dynamical equilibrium. Assuming that TDGs are in dynamical equilibrium, we find that the ratio of dynamical mass to baryonic mass is consistent with one, implying that TDGs are devoid of dark matter. This is in line with the results of numerical simulations where tidal forces effectively segregate dark matter in the halo from baryonic matter i...

  13. The far-infrared - radio correlation in dwarf galaxies

    CERN Document Server

    Schleicher, Dominik R G

    2016-01-01

    The far-infrared - radio correlation connects star formation and magnetic fields in galaxies, and has been confirmed over a large range of far-infrared luminosities. Recent investigations indicate that it may even hold in the regime of local dwarf galaxies, and we explore here the expected behavior in the regime of star formation surface densities below 0.1 M_sun kpc^{-2} yr^{-1}. We derive two conditions that can be particularly relevant for inducing a change in the expected correlation: a critical star formation surface density to maintain the correlation between star formation rate and the magnetic field, and a critical star formation surface density below which cosmic ray diffusion losses dominate over their injection via supernova explosions. For rotation periods shorter than 1.5x10^7 (H/kpc)^2 yrs, with H the scale height of the disk, the first correlation will break down before diffusion losses are relevant, as higher star formation rates are required to maintain the correlation between star formation ...

  14. Metals Removed by Outflows from Milky Way Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan N; Finlator, Kristian

    2011-01-01

    The stars in the dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are significantly more metal-poor than would be expected from a closed box model of chemical evolution. Gas outflows likely carried away most of the metals produced by the dSphs. Based on previous Keck/DEIMOS observations and models, we calculate the mass in Mg, Si, Ca, and Fe expelled from each of eight dSphs. Essentially, these masses are the differences between the observed amount of metals present in the dSphs' stars today and the inferred amount of metals produced by supernovae. We conclude that the dSphs lost 96% to >99% of the metals their stars manufactured. We apply the observed mass function of Milky Way dSphs to the ejected mass function to determine that a single large dSph, like Fornax, lost more metals over 10 Gyr than all smaller dSphs combined. Therefore, small galaxies like dSphs are not significant contributors to the metal content of the intergalactic medium. Finally, we compare our ejected mass function to previo...

  15. Carbon and Oxygen Abundances in Low Metallicity Dwarf Galaxies

    CERN Document Server

    Berg, Danielle A; Henry, Richard B C; Erb, Dawn K; Carigi, Leticia

    2016-01-01

    The study of carbon and oxygen abundances yields information on the time evolution and nucleosynthetic origins of these elements, yet remains relatively unexplored. At low metallicities (12+log(O/H) < 8.0), nebular carbon measurements are limited to rest-frame UV collisionally excited emission lines. Therefore, we present UV spectrophotometry of 12 nearby, low-metallicity, high-ionization HII regions in dwarf galaxies obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope. We present the first analysis of the C/O ratio in local galaxies based solely on simultaneous significant detections of the UV O^+2 and C^+2 collisionally excited lines in seven of our targets and five objects from the literature, to create a final sample of 12 significant detections. Our sample is complemented by optical SDSS spectra, from which we measured the nebular physical conditions and oxygen abundances using the direct method. At low metallicity (12+log(O/H) < 8.0), no clear trend is evident in C/O vs. O/...

  16. APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy

    Science.gov (United States)

    Hasselquist, Sten; Shetrone, Matthew; Smith, Verne; Holtzman, Jon; McWilliam, Andrew; Fernández-Trincado, J. G.; Beers, Timothy C.; Majewski, Steven R.; Nidever, David L.; Tang, Baitian; Tissera, Patricia B.; Fernández Alvar, Emma; Allende Prieto, Carlos; Almeida, Andres; Anguiano, Borja; Battaglia, Giuseppina; Carigi, Leticia; Delgado Inglada, Gloria; Frinchaboy, Peter; García-Hernández, D. A.; Geisler, Doug; Minniti, Dante; Placco, Vinicius M.; Schultheis, Mathias; Sobeck, Jennifer; Villanova, Sandro

    2017-08-01

    The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is the largest sample of Sgr stars with detailed chemical abundances, and it is the first time that C, N, P, K, V, Cr, Co, and Ni have been studied at high resolution in this galaxy. We find that the Sgr stars with [Fe/H] ≳ -0.8 are deficient in all elemental abundance ratios (expressed as [X/Fe]) relative to the Milky Way, suggesting that the Sgr stars observed today were formed from gas that was less enriched by Type II SNe than stars formed in the Milky Way. By examining the relative deficiencies of the hydrostatic (O, Na, Mg, and Al) and explosive (Si, P, K, and Mn) elements, our analysis supports the argument that previous generations of Sgr stars were formed with a top-light initial mass function, one lacking the most massive stars that would normally pollute the interstellar medium with the hydrostatic elements. We use a simple chemical-evolution model, flexCE, to further support our claim and conclude that recent stellar generations of Fornax and the Large Magellanic Cloud could also have formed according to a top-light initial mass function.

  17. Jeans Analysis for Dwarf Spheroidal Galaxies in Wave Dark Matter

    CERN Document Server

    Chen, Shu-Rong; Chiueh, Tzihong

    2016-01-01

    Observations suggest that dwarf spheroidal (dSph) galaxies exhibit large constant-density cores in the centers, which can hardly be explained by dissipationless cold dark matter simulations. Wave dark matter (${\\psi {\\rm DM}}$), characterized by a single parameter, the dark matter particle mass $m_{\\psi}$, predicts a central soliton core in every galaxy arising from quantum pressure against gravity. Here we apply Jeans analysis to the kinematic data of eight classical dSphs so as to constrain $m_{\\psi}$, and obtain $m_{\\psi}=1.18_{-0.24}^{+0.28}\\times10^{-22}{\\,\\rm eV}$ and $m_{\\psi}=1.79_{-0.33}^{+0.35}\\times10^{-22}{\\,\\rm eV}~(2\\sigma)$ using the observational data sets of Walker et al. (2007) and Walker et al. (2009b), respectively. We show that the estimate of $m_{\\psi}$ is sensitive to the dSphs kinematic data sets and is robust to various models of stellar density profile. We also consider multiple stellar subpopulations in dSphs and find consistent results. This mass range of $m_{\\psi}$ is in good agre...

  18. A Star Formation Law for Dwarf Irregular Galaxies

    CERN Document Server

    Elmegreen, Bruce G

    2015-01-01

    The radial profiles of gas, stars, and far ultraviolet radiation in 20 dwarf Irregular galaxies are converted to stability parameters and scale heights for a test of the importance of two-dimensional (2D) instabilities in promoting star formation. A detailed model of this instability involving gaseous and stellar fluids with self-consistent thicknesses and energy dissipation on a perturbation crossing time give the unstable growth rates. We find that all locations are effectively stable to 2D perturbations, mostly because the disks are thick. We then consider the average volume densities in the midplanes, evaluated from the observed HI surface densities and calculated scale heights. The radial profiles of the star formation rates are equal to about 1% of the HI surface densities divided by the free fall times at the average midplane densities. This 1% resembles the efficiency per unit free fall time commonly found in other cases. There is a further variation of this efficiency with radius in all of our galaxi...

  19. Multiple stellar population in the Sextans dwarf spheroidal galaxy?

    CERN Document Server

    Bellazzini, M; Pancino, E

    2001-01-01

    We present wide field (33 X 34 arcmin^2) multiband (BVI) CCD photometry (down to I <= 20.5) of the very low surface brightness dwarf Spheroidal (dSph) galaxy Sextans. In the derived Color Magnitude Diagrams we have found evidences suggesting the presence of multiple stellar populations in this dSph. In particular we discovered: {\\it (i)} a Blue Horizontal Branch (HB) tail that appears to lie on a brighter sequence with respect to the prominent Red HB and the RR Lyrae stars, very similar to what found by Majewski et al. (1999) for the Sculptor dSph; {\\it (ii)} hints of a bimodal distribution in color of the RGB stars; {\\it (iii)} a double RGB-bump. All these features suggest that (at least) two components are present in the old stellar population of this galaxy: a main one with [Fe/H]~ -1.8 and a minor component around [Fe/H]<~ -2.3. The similarity with the Sculptor case may indicate that multiple star formation episodes are common also in the most nearby dSphs that ceased their star formation activity a...

  20. The Low-luminosity Galaxy Population in the NGC 5044 Group

    Science.gov (United States)

    Cellone, S. A.; Buzzoni, A.

    Detailed surface photometry for 79 (mostly dwarf) galaxies in the NGC5044 Group area is analysed, revealing the existence of different morphologies among objects originally classified as early-type dwarfs. Particularly, a significant fraction of bright dwarf "ellipticals" show a distinct bulge+disc structure; we thus re-classify these objects as dwarf lenticulars (dS0).

  1. Study of the nature of dark matter in halos of dwarf galaxies

    Science.gov (United States)

    Karmakar, Pradip; Chattopadhyay, Tanuka; Chattopadhyay, Asis Kumar

    2015-08-01

    The kinematics of dwarf galaxies are strongly influenced by dark matter down to small galactocentric radii. So they are good candidates to investigate the nature of Dark Matter. In the present work we have carried out mass modeling of a number of recently observed dwarf galaxies Swaters et al. in Astron. Astrophys. 493:871, 2009. We have used a Navarro-Frenk-White (NFW) halo, Freeman disc along with a gaseous disc for modeling the observed rotation curves of those dwarf galaxies. For comparison we also used a Burkert halo, Freeman disc and gaseous disc. For both the scenario we have performed Kolmogorov-Smirnov (KS) test between the observed and predicted rotational velocity profiles. The tests are rejected for NFW halo almost in 50 per cent cases but they are accepted almost for all cases for Burkert halo, preferring a Burkert halo model generally for dwarf galaxies. The above results reveal a constant density core of dark matter (DM) in the halos of dwarf galaxies compared to a cuspy nature of NFW halo and a possible challenge to -CDM scenario for the nature of dark matter in most of the dwarf galaxies.

  2. Galaxy And Mass Assembly (GAMA): The unimodal nature of the dwarf galaxy population

    CERN Document Server

    Mahajan, Smriti; Driver, S; Kelvin, Lee S; Hopkins, A M; Baldry, I; Phillipps, S; Bland-Hawthorn, J; Brough, S; Loveday, J; Penny, Samantha J; Robotham, A S G

    2014-01-01

    In this paper we aim to (i) test the number of statistically distinct classes required to classify the local galaxy population, and, (ii) identify the differences in the physical and star formation properties of visually-distinct galaxies. To accomplish this, we analyse the structural parameters (effective radius r_e, effective surface brightness within r_e (mu_e), central surface brightness (mu_0), and S'ersic index (n)), obtained by fitting the light profile of 432 galaxies (0.002dwarf galaxies (irregulars, blue spheroids and low surface brightness galaxies) form a unimodal population in a parameter space mapped by mu_e, mu_0, n, r_e, SFR, sSFR, M*, M_{dust} and (g-i). The SFR and sSFR distribution of passively evolving ...

  3. Cold dust but warm gas in the unusual elliptical galaxy NGC 4125

    CERN Document Server

    Wilson, C D; Foyle, K; Parkin, T J; Cooper, E Mentuch; Roussel, H; Sauvage, M; Smith, M W L; Baes, M; Bendo, G; Boquien, M; Boselli, A; Ciesla, L; Clements, D L; Cooray, A; De Looze, I; Galametz, M; Gear, W; Lebouteiller, V; Madden, S; Pereira-Santaella, M; Remy-Ruyer, A

    2013-01-01

    Data from the Herschel Space Observatory have revealed an unusual elliptical galaxy, NGC 4125, which has strong and extended submillimeter emission from cold dust but only very strict upper limits to its CO and HI emission. Depending on the dust emissivity, the total dust mass is 2-5x10^6 Msun. While the neutral gas-to-dust mass ratio is extremely low (= 10^4 K faster than the dust is evaporated. If galaxies like NGC 4125, where the far-infrared emission does not trace neutral gas in the usual manner, are common at higher redshift, this could have significant implications for our understanding of high redshift galaxies and galaxy evolution.

  4. Identifying old Tidal Dwarf Galaxies in Simulations and in the Nearby Universe

    CERN Document Server

    Duc, P A; Masset, F; Bournaud, Frederic; Duc, Pierre-Alain; Masset, Frederic

    2004-01-01

    Most Tidal Dwarf Galaxies (TDGs) so-far discussed in the literature may be considered as young ones or even newborns, as they are still physically linked to their parent galaxies by an umbilical cord: the tidal tail at the tip of which they are usually observed. Old Tidal Dwarf Galaxies, completely detached from their progenitors, are still to be found. Using N--body numerical simulations, we have shown that tidal objects as massive as 10^9 solar masses may be formed in interacting systems and survive for more than one Gyr. Old TDGs should hence exist in the Universe. They may be identified looking at a peculiarity of their "genetic identity card": a relatively high abundance in heavy elements, inherited from their parent galaxies. Finally, using this technique, we revisit the dwarf galaxies in the local Universe trying to find arguments pro and con a tidal origin.

  5. VizieR Online Data Catalog: Tucana dwarf galaxy VI photometry (Castellani+, 1996)

    Science.gov (United States)

    Castellani, M.; Marconi, G.; Buonanno, R.

    2000-11-01

    We present deep CCD photometry for the dwarf galaxy in Tucana (l=323, b=-47.4). The data indicate that the galaxy is dominated by an intermediate/old stellar population with metallicity similar to that of the galactic globular clusters NGC 6752 and NGC 7089 (M2) (we find [Fe/H]=~-1.56). The distance modulus we derived, (m-M)V=~24.72+/-0.2, makes clear that this galaxy belongs to the Local Gro up. Tucana is clearly different from other dwarf galaxies, such as Leo I (Lee et al., 1993AJ....106.1420L), or Phoenix (Ortolani and Gratton, 1988PASP..100.1405O), because there is no evidence of a young stellar population (t<=5Gyrs) We suggest that the Tucana Galaxy is a genuine dwarf spheroidal in which no recent burst of star formation occurred. (1 data file).

  6. Star Formation in NGC4532/DDO 137'S Tidal Dwarf Galaxies and 500 KPC HI Stream

    Science.gov (United States)

    Higdon, Sarah

    Mergers and close-passages between gas rich galaxies can result in the formation of long HI/stellar streams. The tidally induced star formation and gas concentrations can result in the creation of tidal dwarf galaxies (TDGs). TDGs may contribute significantly to the dwarf galaxy population, by far the most common galaxy type in the current epoch. We have discovered one of the longest known tidal streams (500 kpc) in the NGC 4535/DDO 137 system. We propose 3 ksec FUV/NUV images centered on the stream and its five TDGs. We will readily detect faint/low mass star forming regions (~2E-17 erg s-1 cm-2 A-1) to 5-sigma. The GALEX observations are a unique opportunity to undertake a sensitive and comprehensive study of tidally induced star formation, dwarf galaxy formation and inter-galactic enrichment in this system.

  7. Dynamical masses and non-homology of massive elliptical galaxies grown by dry mergers

    CERN Document Server

    Frigo, Matteo

    2016-01-01

    We study whether dry merger-driven size growth of massive elliptical galaxies depends on their initial structural concentration, and analyse the validity of the homology hypothesis for virial mass determination in massive ellipticals grown by dry mergers. High-resolution simulations of a few realistic merger trees, starting with compact progenitors of different structural concentrations (S\\'ersic indices n), show that galaxy growth has little dependence on the initial S\\'ersic index (larger n leads to slightly larger size growth), and depends more on other particulars of the merger history. We show that the deposition of accreted matter in the outer parts leads to a systematic and predictable breaking of the homology between remnants and progenitors, which we characterize through the evolution, during the course of the merger history, of virial coefficients K = GM/Re \\sigma^2 associated to the most commonly-used dynamical and stellar mass parameters. The virial coefficient for the luminous mass, K , is about ...

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

    Energy Technology Data Exchange (ETDEWEB)

    Tollerud, Erik J.; Geha, Marla C. [Astronomy Department, Yale University, P.O. Box 208101, New Haven, CT 06510 (United States); Grcevich, Jana [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States); Putman, Mary E. [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Stern, Daniel, E-mail: erik.tollerud@yale.edu, E-mail: marla.geha@yale.edu, E-mail: jgrcevich@amnh.org, E-mail: mputman@astro.columbia.edu, E-mail: daniel.k.stern@jpl.nasa.gov [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Mail Stop 169-221, Pasadena, CA 91109 (United States)

    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.

  9. Phase-space constraints on visible and dark matter distributions in elliptical galaxies

    CERN Document Server

    Ciotti, L

    1999-01-01

    There are observational and theoretical indications that both the visible (stars) and the dark matter density distributions in elliptical galaxies increase significantly up to the galactic center. I present here some analytical results obtained with the aid of self-consistent, spherically symmetric two component galaxy models. These results suggest the possibility that this similar behavior could be a direct consequence of the structural and dynamical constraints imposed by the request of positivity of the phase-space distribution function of each density component.

  10. Structure and Evolution of Interstellar Gas in Flattened, Rotating Elliptical Galaxies

    Science.gov (United States)

    Brighenti, Fabrizio; Mathews, William G.

    1996-10-01

    We study the time-dependent evolution of interstellar gas in a family of elliptical galaxies having identical masses and central densities but various ellipticities and total angular momenta. Dark halos are assumed to be flattened in the same manner as the stars. Normal mass loss from evolving galactic stars is sufficient to account for the amount of hot interstellar gas observed. Gas ejected from stars shares the random motions of the stars and the bulk stellar velocity relative to the local interstellar medium; the ejected gas thermalizes to a temperature similar to the virial temperature of the stellar system. The random stellar motions and galactic rotation are found by solving Jeans's equations in cylindrical geometry. For a sequence of galaxies differing only in degree of flattening-E0, E2, and E4-we find that the X-ray images and luminosities are not very different. As the hot interstellar gas loses energy by radiation, it cools to the very center of these nonrotating galaxies regardless of flattening. The X-ray surface brightness is generally slightly steeper than the optical surface brightness of starlight. However, when a small but typical galactic rotation is introduced, the evolution of the interstellar medium is radically altered. The average X- ray surface brightness {SIGMA}_X_ is lower in the galactic center compared to nonrotating galaxies. This lower {SIGMA}_X_ can be achieved without invoking an ad hoc mass dropout from the hot gas. As the gas cools in rotating galaxies, it is deposited in a large disk comparable in size to the effective radius. Alter evolving for several gigayears, most of the new gas in the cooling flow is constrained by angular momentum conservation to arrive at the outer edge of the disk, Causing a local enhancement in the X-ray surface brightness. This results in flattened inner X-ray surface brightness contours that have peanut shapes when viewed nearly perpendicular to the axis of galactic rotation. As gas approaches the

  11. Ultraviolet radiation from evolved stellar populations II. the ultraviolet upturn phenomenon in elliptical galaxies

    CERN Document Server

    Dorman, B; Rood, R T; Ben Dorman; Robert W O'Connell; Robert T Rood

    1994-01-01

    We present an analysis of the far-ultraviolet upturn phenomenon (UVX) observed in elliptical galaxies and spiral galaxy bulges. Our premise is that the UV radiation from these systems emanates primarily from extreme horizontal branch (EHB) stars and their progeny. We re-derive the broad-band UV colors 1500-V and 2500-V for globular clusters and elliptical galaxies from the available satellite data and investigate color-color and color-line strength correlations. We also provide the ingredients necessary for constructing models with arbitrary HB morphologies. Our models accurately predict the range of UV colors observed for the globular clusters, given known constraints on their age, abundances, and HB morphologies. Models with \\feh \\gta 0 which do not contain EHB stars cannot reproduce the colors of most of the galaxies. However, only small EHB fractions are required: \\lta 5\\% for the bulk of the E galaxies and \\sim 20\\% for those with the strongest UVX. Our models accurately predict the range of UV colors ob...

  12. Discovery of Strong Lensing by an Elliptical Galaxy at z=0.0345

    CERN Document Server

    Smith, R J; Lucey, J R; Tonry, J; Rousseaux, Germain; Smith, Russell J.; Blakeslee, John P.; Lucey, John R.; Tonry, John

    2005-01-01

    We have discovered strong gravitational lensing by the galaxy ESO325-G004, in images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The lens galaxy is a boxy group-dominant elliptical at z=0.0345, making this the closest known galaxy-scale lensing system. The lensed object is very blue (B-I = 1.1), and forms two prominent arcs and a less extended third image. The Einstein radius is R_Ein=1.9 kpc (~3 arcsec on the sky, cf. 12 arcsec effective radius of the lens galaxy). Assuming a high redshift for the source, the mass within R_Ein is 1.4x10^11 M_sun, and the I-band mass-to-light ratio is 1.8 (M/L)_sun. The equivalent velocity dispersion is sigma_lens=310 km/s, in excellent agreement with the measured stellar dispersion sigma_v=320 km/s. Modeling the lensing potential with a singular isothermal ellipse (SIE), we find close agreement with the light distribution. The best fit SIE model reproduces the ellipticity of the lens galaxy to ~10%, and its position angle within 1 degree. The...

  13. Spiral-like Light Profiles but Elliptical-like Kinematics in Mergers of Galaxies

    CERN Document Server

    Jog, C J; Jog, Chanda J.; Chitre, Aparna

    2002-01-01

    It is commonly accepted that a merger of two spiral galaxies results in a remnant with an elliptical-like surface-brightness profile. Surprisingly, our recent study (Chitre & Jog 2002) of the 2MASS data for twenty-seven advanced mergers of galaxies has shown that half of these have a light distribution that decreases exponentially with radius. Such a distribution normally characterizes a rotationally supported disk in a spiral galaxy. Here we show from kinematic data for two of these mergers, Arp 224 and Arp 214, that the main support against gravitational collapse comes from pressure due to random motion of stars as seen in an elliptical galaxy rather than from rotation. The origin of the unusual combination of properties seen here is a puzzle. The standard theoretical N-body models in the literature cannot account for these systems. Further observational and dynamical studies of this new class of merger remnants are needed, and would be important for understanding merger dynamics and galaxy evolution.

  14. Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales

    CERN Document Server

    Amblard, Alexandre; Gaspari, Massimo; Brighenti, Fabrizio

    2016-01-01

    We use high-resolution Herschel-PACS data of 2 nearby elliptical galaxies, IC1459 & NGC2768 to characterize their dust and stellar content. IC1459 & NGC2768 have an unusually large amount of dust for elliptical galaxies (1-3 x 10^5 Msun), this dust is also not distributed along the stellar content. Using data from GALEX (ultraviolet) to PACS (far-infrared), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.2" pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young star and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (~ 0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial d...

  15. Dissecting the size evolution of elliptical galaxies since z~1: puffing up vs minor merging scenarios

    CERN Document Server

    Trujillo, Ignacio; de la Rosa, Ignacio G

    2011-01-01

    We have explored the buildup of the local mass-size relation of elliptical galaxies using two visually classified samples. At low redshift we compiled a subsample of 2,656 elliptical galaxies from SDSS, whereas at higher redshift (up to z~1) we extracted a sample of 228 object from the HST/ACS images of the GOODS. All the galaxies in our study have spectroscopic data, allowing us to determine the age and mass of the stellar component. Using the fossil record information contained in the stellar populations of our local sample, we do not find any evidence for an age segregation at a given stellar mass depending on the size of the galaxies. At a fixed dynamical mass there is only a <9% size difference in the two extreme age quartiles of our sample. Consequently, the local evidence does not support a scenario whereby the present-day mass-size relation has been progressively established via a bottom-up sequence, where older galaxies occupy the lower part this relation, remaining in place since their formation....

  16. The Mg-$\\sigma$ Relation of Elliptical Galaxies at Various Redshifts

    CERN Document Server

    Ziegler, B L; Bender, Ralf; Ziegler, Bodo L

    1997-01-01

    The correlation between the Mg absorption index and the velocity dispersion (sigma) of local elliptical galaxies is very tight. Because the Mg absorption depends on both metallicity and age of the underlying stellar population the observed Mg-sigma relation constrains the possible variation in metallicity and age for a given velocity dispersion. For a time interval with no change in metallicity any variation of the Mg index is caused only by the aging of the stars. We have measured the Mg absorption and velocity dispersion of ellipticals in three clusters at a redshift of z=0.37 and established their Mg-sigma relation. For any given sigma, the measured Mg absorption is weaker than the mean value for local ellipticals. Since the evolution of bright cluster ellipticals between z=0.4 and today is most probably only `passive' this reduction in Mg can be attributed solely to the younger age of the stellar population. The small weakening of the Mg absorption of the distant galaxies compared to the local values impl...

  17. Halo ellipticity of GAMA galaxy groups from KiDS weak lensing

    CERN Document Server

    van Uitert, Edo; Joachimi, Benjamin; Schneider, Peter; Bland-Hawthorn, Joss; Choi, Ami; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Hopkins, Andrew M; Klaes, Dominik; Kuijken, Konrad; Nakajima, Reiko; Napolitano, Nicola R; Schrabback, Tim; Valentijn, Edwin; Viola, Massimo

    2016-01-01

    We constrain the average halo ellipticity of ~2 600 galaxy groups from the Galaxy And Mass Assembly (GAMA) survey, using the weak gravitational lensing signal measured from the overlapping Kilo Degree Survey (KiDS). To do so, we quantify the azimuthal dependence of the stacked lensing signal around seven different proxies for the orientation of the dark matter distribution, as it is a priori unknown which one traces the orientation best. On small scales, the major axis of the brightest group/cluster member (BCG) provides the best proxy, leading to a clear detection of an anisotropic signal. In order to relate that to a halo ellipticity, we have to adopt a model density profile. We derive new expressions for the quadrupole moments of the shear field given an elliptical model surface mass density profile. Modeling the signal with an elliptical Navarro-Frenk-White (NFW) profile on scales < 250 kpc, which roughly corresponds to half the virial radius, and assuming that the BCG is perfectly aligned with the dar...

  18. Elliptical Galaxy Kinematics and Dark Matter Halos with VIRUS-P

    Science.gov (United States)

    Murphy, Jeremy; Gebhardt, K.; Greene, J. E.; Graves, G.

    2012-01-01

    Dark matter is now ubiquitous in galactic astronomy, yet our understanding of both its extent, shape, and influence on the evolution of galaxies remains poorly understood. In the case of giant elliptical galaxies, which typically reside in dense environments and accumulate their mass via a range of processes, yet maintain tight scaling relations between a wide variety of their parameters, our understanding of the dizzying variety of mechanisms involved is a work in progress. To this end I will discuss an ongoing project being carried out at McDonald Observatory using the VIRUS-P integral field spectrograph to characterize the dark matter halos, stellar anisotropy and stellar abundance patterns of the most massive galaxies in the local universe from measurements of integrated stellar light. We have observed 23 giant elliptical galaxies over a range of environments. Seven of the 23 galaxies in our data set our Brightest Cluster Galaxies (BCG). I will present spectra and kinematics for a subsample of the survey. Three-integral axisymmetric dynamical modeling, based on Schwarzschild's method of orbit-superposition, will be presented for 3 BCGs in our sample (NGC 4472, M87 and NGC 2832). For the case of M87 we have data extending to 5 effective radii which allows for a direct comparison between stellar kinematics and other mass tracers typically used at large radial distances where the stellar light has historically been too faint to extract reliable kinematics. The mass distribution of all 3 of these galaxies is dominated by their dark matter halo at large radii. The degree of stellar radial and tangential anisotropy of the stars is returned from the modeling process. I will discuss how the stellar anisotropy, combined with stellar abundance patterns from measurements of the Lick indices, can be used to infer how the most massive galaxies accumulated their mass over time.

  19. VizieR Online Data Catalog: The CGS. IV. Elliptical galaxies colors (Huang+, 2016)

    Science.gov (United States)

    Huang, S.; Ho, L. C.; Peng, C. Y.; Li, Z.-Y.; Barth, A. J.

    2016-07-01

    This work uses the multi-band optical images of nearby ellipticals from the Carnegie-Irvine Galaxy Survey (CGS; Ho et al. 2011, J/ApJS/197/21, Paper I). The observations were made using the 100 inch du Pont telescope at Las Campanas Observatory to provide high-quality Johnson/Kron-Cousins BVRI images during the period 2003 February to 2006 June. (1 data file).

  20. Large-scale environmental dependence of gas-phase metallicity in dwarf galaxies

    CERN Document Server

    Douglass, Kelly A

    2016-01-01

    We study how the cosmic environment affects galaxy evolution in the Universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII] 3727, [OIII] 4363, and [OIII] 4959,5007, we estimate the abundance of oxygen with the Direct Te method. We estimate the metallicity of 37 void dwarf galaxies and 75 dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as re-processed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are equally abundant in both voids...

  1. Episodic Model For Star Formation History and Chemical Abundances in Giant and Dwarf Galaxies

    CERN Document Server

    Debsarma, Suma; Das, Sukanta; Pfenniger, Daniel

    2016-01-01

    In search for a synthetic understanding, a scenario for the evolution of the star formation rate and the chemical abundances in galaxies is proposed, combining gas infall from galactic halos, outflow of gas by supernova explosions, and an oscillatory star formation process. The oscillatory star formation model is a consequence of the modelling of the fractional masses changes of the hot, warm and cold components of the interstellar medium. The observed periods of oscillation vary in the range $(0.1-3.0)\\times10^{7}$\\,yr depending on various parameters existing from giant to dwarf galaxies. The evolution of metallicity varies in giant and dwarf galaxies and depends on the outflow process. Observed abundances in dwarf galaxies can be reproduced under fast outflow together with slow evaporation of cold gases into hot gas whereas slow outflow and fast evaporation is preferred for giant galaxies. The variation of metallicities in dwarf galaxies supports the fact that low rate of SNII production in dwarf galaxies i...

  2. Stellar populations of Virgo cluster early-type dwarf galaxies with and without discs: a dichotomy in age?

    CERN Document Server

    Paudel, S; Kuntschner, H; Grebel, E; Glatt, K

    2010-01-01

    [Abridged] Using VLT/FORS2 spectroscopy, we have studied the properties of the central stellar populations of a sample of 38 nucleated early-type dwarf (dE) galaxies in the Virgo Cluster. We find that these galaxies do not exhibit the same average stellar population characteristics for different morphological subclasses. The nucleated galaxies without discs are older and more metal poor than the dEs with discs . The alpha-element abundance ratio appears consistent with the solar value for both morphological types. Besides a well-defined relation of metallicity and luminosity, we also find a clear anti-correlation between age and luminosity. More specifically, there appears to be a bimodality: brighter galaxies, including the discy ones, exhibit significantly younger ages than fainter dEs. Therefore, it appears less likely that fainter and brighter dEs have experienced the same evolutionary history, as the well-established trend of decreasing average stellar age when going from the most luminous ellipticals to...

  3. Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II

    CERN Document Server

    Simon, J D; Li, T S; Nord, B; Geha, M; Bechtol, K; Balbinot, E; Buckley-Geer, E; Lin, H; Marshall, J; Santiago, B; Strigari, L; Wang, M; Wechsler, R H; Yanny, B; Abbott, T; Bauer, A H; Bernstein, G M; Bertin, E; Brooks, D; Burke, D L; Capozzi, D; Rosell, A Carnero; Kind, M Carrasco; D'Andrea, C B; da Costa, L N; DePoy, D L; Desai, S; Diehl, H T; Dodelson, S; Cunha, C E; Estrada, J; Evrard, A E; Neto, A Fausti; Fernandez, E; Finley, D A; Flaugher, B; Frieman, J; Gaztanaga, E; Gerdes, D; Gruen, D; Gruendl, R A; Honscheid, K; James, D; Kuehn, K; Kuropatkin, N; Lahav, O; Maia, M A G; March, M; Martini, P; Miller, C J; Miquel, R; Ogando, R; Romer, A K; Roodman, A; Rykoff, E S; Sako, M; Sanchez, E; Schubnell, M; Sevilla, I; Smith, R C; Soares-Santos, M; Sobreira, F; Suchyta, E; Swanson, M E C; Tarle, G; Thaler, J; Tucker, D; Vikram, V; Walker, A R; Wester, W

    2015-01-01

    We present Magellan/M2FS, VLT/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of 62.8 +/- 0.5 km/s and a velocity dispersion of 3.3 +/- 0.7 km/s. The mass-to-light ratio of Ret II within its half-light radius is 470 +/- 210 Msun/Lsun, demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 km/s, respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 +/- 0.09 dex, and we identify several extremely metal-poor stars with [Fe/H] < -3. In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a me...

  4. Phenomenological approach to the modelling of elliptical galaxies: The problem of the mass-to-light ratio

    Directory of Open Access Journals (Sweden)

    Samurović S.

    2007-01-01

    Full Text Available In this paper the problem of the phenomenological modelling of elliptical galaxies using various available observational data is presented. Recently, Tortora, Cardona and Piedipalumbo (2007 suggested a double power law expression for the global cumulative mass-to-light ratio of elliptical galaxies. We tested their expression on a sample of ellipticals for which we have the estimates of the mass-to-light ratio beyond ~ 3 effective radii, a region where dark matter is expected to play an important dynamical role. We found that, for all the galaxies in our sample, we have α + β > 0, but that this does not necessarily mean a high dark matter content. The galaxies with higher mass (and higher dark matter content also have higher value of α+β. It was also shown that there is an indication that the galaxies with higher value of the effective radius also have higher dark matter content. .

  5. Phenomenological Approach to the Modelling of Elliptical Galaxies: The Problem of the Mass-to-Light Ratio

    Science.gov (United States)

    Samurovic, S.

    2007-06-01

    In this paper the problem of the phenomenological modelling of elliptical galaxies using various available observational data is presented. Recently, Tortora, Cardona and Piedipalumbo (2007) suggested a double power law expression for the global cumulative mass-to-light ratio of elliptical galaxies. We tested their expression on a sample of ellipticals for which we have the estimates of the mass-to-light ratio beyond ˜ 3 effective radii, a region where dark matter is expected to play an important dynamical role. We found that, for all the galaxies in our sample, we have α+β>0, but that this does not necessarily mean a high dark matter content. The galaxies with higher mass (and higher dark matter content) also have higher value of α +β. It was also shown that there is an indication that the galaxies with higher value of the effective radius also have higher dark matter content.

  6. GALEX observations of the UV surface brightness and color profiles of the Local Group elliptical galaxy M32 (NGC221)

    CERN Document Server

    De Paz, A G; Sohn, Y J; Lee, Y W; Seibert, M; Rich, R M; Bianchi, L; Barlow, T A; Byun, Y I; Donas, J; Forster, K; Friedman, P G; Heckman, T M; Jelinsky, P N; Malina, R F; Martin, D C; Milliard, B; Morrissey, P F; Neff, S G; Schiminovich, D; Siegmund, O H W; Small, T; Szalay, A S; Welsh, B Y; Wyder, T K

    2004-01-01

    M32, the compact elliptical-galaxy companion to the Andromeda spiral galaxy has been imaged by the Galaxy Evolution Explorer (GALEX) in two ultraviolet bands, centered at ~1500 (FUV) and 2300 Angstroms (NUV). The imaging data have been carefully decomposed so as to properly account for the complicated background contamination from the disk of M31. We have derived the surface brightness and color profiles finding a slightly positive color gradient of Delta(FUV-B)/Delta log(r)=+0.15+/-0.03 within one effective radius. Earlier data from the Ultraviolet Imaging Telescope suggested that M32 had an extremely large (negative) FUV-optical color gradient (Delta(FUV-B)/Delta log(r)<-2), inverted with respect to the majority of gradients seen in giant elliptical galaxies. Our new results show that, despite of its very low UV-upturn, M32 has similar UV properties to those observed in luminous elliptical galaxies.

  7. Young tidal dwarf galaxies cannot be used to probe dark matter in galaxies

    CERN Document Server

    Flores, H; Fouquet, S; Puech, M; Kroupa, P; Yang, Y; Pawlowski, M

    2015-01-01

    The location of dark-matter free, tidal dwarf galaxies (TDGs) in the baryonic Tully Fisher (bTF) diagram has been used to test cosmological scenarios, leading to various and controversial results. Using new high-resolution 3D spectroscopic data, we re-investigate the morpho-kinematics of these galaxies to verify whether or not they can be used for such a purpose. We find that the three observed TDGs are kinematically not virialized and show complex morphologies and kinematics, leading to considerable uncertainties about their intrinsic rotation velocities and their locations on the bTF. Only one TDG can be identify as a (perturbed) rotation disk that it is indeed a sub-component of NGC5291N and that lies at $<$1$\\sigma$ from the local bTF relation. It results that the presently studied TDGs are young, dynamically forming objects, which are not enough virialized to robustly challenge cosmological scenarios.

  8. FOSSIL EVIDENCE FOR THE TWO-PHASE FORMATION OF ELLIPTICAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Huang Song [School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China); Ho, Luis C. [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Peng, Chien Y. [Giant Magellan Telescope Organization, 251 South Lake Avenue, Suite 300, Pasadena, CA 91101 (United States); Li Zhaoyu [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030 (China); Barth, Aaron J. [Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575 (United States)

    2013-05-10

    Massive early-type galaxies (ETGs) have undergone dramatic structural evolution over the last 10 Gyr. A companion paper shows that nearby elliptical galaxies with M{sub *} {>=} 1.3 Multiplication-Sign 10{sup 11} M{sub Sun} generically contain three photometric subcomponents: a compact inner component with effective radius R{sub e} {approx}< 1 kpc, an intermediate-scale middle component with R{sub e} Almost-Equal-To 2.5 kpc, and an extended outer envelope with R{sub e} Almost-Equal-To 10 kpc. Here we attempt to relate these substructures with the properties of ETGs observed at higher redshifts. We find that a hypothetical structure formed from combining the inner and middle components of local ellipticals follows a strikingly tight stellar mass-size relation, one that resembles the distribution of ETGs at z Almost-Equal-To 1. Outside of the central kpc, the median stellar mass surface density profiles of this composite structure agree closest with those of massive galaxies that have similar cumulative number density at 1.5 < z < 2.0 within the uncertainty. We propose that the central substructures in nearby ellipticals are the evolutionary descendants of the ''red nuggets'' formed under highly dissipative (''wet'') conditions at high redshifts, as envisioned in the initial stages of the two-phase formation scenario recently advocated for massive galaxies. Subsequent accretion, plausibly through dissipationless (''dry'') minor mergers, builds the outer regions of the galaxy identified as the outer envelope in our decomposition. The large scatter exhibited by this component on the stellar mass-size plane testifies to the stochastic nature of the accretion events.

  9. Disruption of a Dwarf Galaxy Under Strong Shocking: The Origin of omega Centauri

    CERN Document Server

    Tsuchiya, T; Dinescu, D I

    2004-01-01

    We perform N-body simulations of the dynamical evolution of a dwarf galaxy falling into the Milky Way galaxy in order to understand the formation scenario of the peculiar globular cluster $\\omega$ Centauri. We use self-consistent models of the bulge and the disc of the Milky Way, as well as of the dwarf galaxy, and explore a range of dwarf models with different density distributions. Namely, we use King (1966) and Hernquist (1990) density profiles to model the density distribution in the dwarf. The central region of our King model has a density profile approximately $\\propto r^{-2}$, while that of the Hernquist model is $\\propto r^{-1}$. The difference in the dwarf's density distributions leads to distinct evolutionary scenarios. The King model dwarf loses its mass exponentially as a function of apocentric distance, with the mass-loss rate depending on the initial mass and size of the dwarf. Regardless of the initial mass and size, the King model dwarf remains more massive than $10^8$ \\msun after a few Gyr of...

  10. Dark influences II. Gas and star formation in minor mergers of dwarf galaxies with dark satellites

    NARCIS (Netherlands)

    Starkenburg, T. K.; Helmi, A.; Sales, L. V.

    2016-01-01

    Context. It has been proposed that mergers induce starbursts and lead to important morphological changes in galaxies. Most studies so far have focused on large galaxies, but dwarfs might also experience such events, since the halo mass function is scale-free in the concordance cosmological model.

  11. Mass-to-Light versus Color Relations for Dwarf Irregular Galaxies

    Science.gov (United States)

    Herrmann, Kimberly A.; Hunter, Deidre Ann; Zhang, Hong-Xin; Elmegreen, Bruce; LITTLE THINGS

    2017-01-01

    We have determined new relations between UBV colors and mass-to-light (M/L) ratios for dwarf irregular galaxies, as well as for transformed g‧ - r‧. These M/L to color relations (MLCRs) are based on stellar mass density profiles determined for 34 LITTLE THINGS dwarfs from spectral energy distribution fitting to multi-wavelength surface photometry in passbands from the FUV to the NIR. These relations can be used to determine stellar masses in dwarf irregular galaxies for situations where other determinations of stellar mass are not possible. Our MLCRs are shallower than comparable MLCRs in the literature determined for spiral galaxies. We divided our dwarf data into four metallicity bins and found indications of a steepening of the MLCR with increased oxygen abundance, perhaps due to more line blanketing occurring at higher metallicity.

  12. Unveiling a Rich System of Faint Dwarf Galaxies in the Next Generation Fornax Survey

    CERN Document Server

    Munoz, Roberto P; Puzia, Thomas H; Taylor, Matthew A; Ordenes-Briceno, Yasna; Alamo-Martinez, Karla; Ribbeck, Karen X; Angel, Simon; Capaccioli, Massimo; Cote, Patrick; Ferrarese, Laura; Galaz, Gaspar; Hempel, Maren; Hilker, Michael; Jordan, Andres; Lancon, Ariane; Mieske, Steffen; Paolillo, Maurizio; Richtler, Tom; Sanchez-Janssen, Ruben; Zhang, Hongxin

    2015-01-01

    We report the discovery of 158 previously undetected dwarf galaxies in the Fornax cluster central regions using a deep coadded $u, g$ and $i$-band image obtained with the DECam wide-field camera mounted on the 4-meter Blanco telescope at the Cerro Tololo Interamerican Observatory as part of the {\\it Next Generation Fornax Survey} (NGFS). The new dwarf galaxies have quasi-exponential light profiles, effective radii $0.1\\!\\!75\\%$ at luminosities brighter than $M_i\\!\\simeq\\!-15.0$ mag to $0\\%$ at luminosities fainter than $M_i\\!\\simeq\\!-10.0$ mag. The two-point correlation function analysis of the NGFS dwarf sample shows an excess on length scales below $\\sim\\!100$ kpc, pointing to the clustering of dwarf galaxies in the Fornax cluster core.

  13. Surveying for Dwarf Galaxies Within Voids FN2 and FN8

    Science.gov (United States)

    McNeil, Stephen; Draper, Chris; Moody, J. Ward

    2016-10-01

    The presence or absence of dwarf galaxies with Mr' > -14 in low-density volumes correlates with dark matter halos and how they affect galaxy formation. We are conducting a redshifted Hα imaging survey for dwarf galaxies with Mr' > -13 in the heart of the well-defined voids FN2 and FN8 using the KPNO 4m Mayall telescope and Mosaic Imager. These data have furnished over 600 strong candidates in a four square degree area. Follow-up spectra finding none of these candidates to be within the void volumes will constrain the dwarf population there to be 2 to 8% of the cosmic mean. Conversely, finding even one Hα dwarf in the void heart will challenge several otherwise successful theories of large-scale structure formation.

  14. Deep imaging of the shell elliptical galaxy NGC 3923 with MegaCam

    Science.gov (United States)

    Bílek, M.; Cuillandre, J.-C.; Gwyn, S.; Ebrová, I.; Bartošková, K.; Jungwiert, B.; Jílková, L.

    2016-04-01

    Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number of stellar shells, probable remnants of an accreted galaxy. Despite its uniqueness, the deepest images of its outskirts come from the 1980s. On the basis of the modified Newtonian dynamics (MOND), it has recently been predicted that a new shell lies in this region. Aims: We obtain the deepest image ever of the galaxy, map the tidal features in it, and search for the predicted shell. Methods: The image of the galaxy was taken by the MegaCam camera at the Canada-France-Hawaii Telescope in the g'-band. It reached the surface-brightness limit of 29 mag arcsec-2. In addition, we reanalyzed an archival HST image of the galaxy. Results: We detected up to 42 shells in NGC 3923. This is by far the highest number among all shell galaxies. We present the description of the shells and other tidal features in the galaxy. A probable progenitor of some of these features was discovered. The shell system likely originates from two or more progenitors. The predicted shell was not detected, but the new image revealed that the prediction was based on incorrect assumptions and poor data. The reduced images (FITS files) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A77

  15. VLT\\/UVES Abundances in Four Nearby Dwarf Spheroidal Galaxies II. Implications for Understanding Galaxy Evolution

    CERN Document Server

    Tolstoy, E; Shetrone, M; Primas, F; Hill, V; Szeifert, A K T; Tolstoy, Eline

    2003-01-01

    We have used UVES on VLT-UT2 to take spectra of 15 individual red giant stars in the centers of four nearby dwarf spheroidal galaxies: Sculptor, Fornax, Carina and Leo I. We measure the abundance variations of numerous elements in these low mass stars with a range of ages (1-15Gyr old). This means that we can effectively measure the chemical evolution of these galaxies WITH TIME. Our results show a significant spread in metallicity with age, but an overall trend consistent with what might be expected from a closed (or perhaps leaky) box chemical evolution scenario over the last 10-15Gyr. We notice that each of these galaxies show broadly similar abundance patterns for all elements measured. This suggests a fairly uniform progression of chemical evolution with time, despite quite a large range of star formation histories. It seems likely that these galaxies had similar initial conditions, and evolve in a similar manner with star formation occurring at a uniformly low rate, even if at different times. With our ...

  16. Disky elliptical galaxies and the allegedly over-massive black hole in the compact massive `ES' galaxy NGC 1271

    CERN Document Server

    Graham, Alister W; Savorgnan, Giulia A D

    2016-01-01

    While spiral and lenticular galaxies have large-scale disks extending beyond their bulges, and most local early-type galaxies with 10^{10} < M_*/M_Sun < 2x10^{11} contain a disk (e.g., ATLAS^3D), the early-type galaxies do possess a range of disk sizes. The edge-on, `intermediate-scale' disk in the `disky elliptical' galaxy NGC 1271 has led to some uncertainty as to what is its spheroidal component. Walsh et al. reported a directly measured black hole mass of 3x10^9 M_Sun for this galaxy; which they remarked was an order of magnitude greater than what they expected based on their derivation of the host spheroid's luminosity. Our near-infrared image analysis supports a small embedded disk within a massive spheroidal component with M_{sph,*} = (0.9+/-0.2)x10^{11} M_Sun (using M_*/L_H = 1.4 from Walsh et al.). This places NGC 1271 just 1.6-sigma above the near-linear M_bh-M_{sph,*} relation for early-type galaxies. Therefore, past speculation that there may be a systematic difference in the black hole scal...

  17. VIMOS Integral Field Spectroscopy of Gaseous Nebulae in Local Group Dwarf Galaxies

    Science.gov (United States)

    Held, E. V.; Gullieuszik, M.; Saviane, I.; Sabbadin, F.; Momany, Y.; Rizzi, L.; Bresolin, F.

    The study of very metal-poor dwarf irregular (dIrr) galaxies is fundamental to test the cosmological scenarios of galaxy formation. Among Local Group galaxies, Leo A and SagDIG are probably the most metal-poor dwarfs, as suggested by estimates of their nebular abundances based on the empirical method [I. Saviane, L. Rizzi, E.V. Held, F. Bresolin, Y. Momany in Astron. Astrophys. 390, 59 (2002); E.D. Skillman, R. Terlevich, J. Melnick in Mon. Not. R. Astron. Soc. 240, 563 (1989); L. van Zee, E.D. Skillman, M.P. Haynes in Astrophys. J. 637, 269 (2006)].

  18. Suppression of star formation in dwarf galaxies by grain photoelectric feedback

    CERN Document Server

    Forbes, John C; Goldbaum, Nathan J; Dekel, Avishai

    2016-01-01

    Photoelectric heating has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies found some indication that photoelectric heating could suppress star formation. However, simulations that include photoelectric heating have typically found that it has little effect on the rate of star formation in either spiral galaxies or dwarfs suggesting that supernovae and not photoelectric heating are responsible for setting the star formation law in galaxies. This result is in tension with recent work indicating that a star formation law that depends on galaxy metallicity, as expected for photoelectric heating but not for supernovae, reproduces the present-day galaxy population better than a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, where the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space- and time-dependent photoelectric heating, and we resolve...

  19. Observations of the impact of starbursts on the interstellar medium in dwarf galaxies

    Science.gov (United States)

    Marlowe, Amanda T.; Heckman, Timothy M.; Wyse, Rosemary F. G.; Schommer, Robert

    1995-01-01

    Dwarf galaxies play a crucial role in our understanding of the formation and evolution of galaxies, and the concept of supernova-driven mass outflows is a vital ingredient in theories of the structure and evolution of dwarf galaxies. Despite the theoretical importance of these outflows, there is a very limited amount of direct observational evidence for their existence. We have therefore begun a detailed multi-wave-band search for outflows in dwarf (M(sub B) greater than or = -18) galaxies with extensive recent or ongoing centrally concentrated star formation. We report the first results of this search in the present paper. Observations of the ionized gas in dwarf amorphous galaxies with centrally concentrated populations of massive stars provide evidence for the large-scale expansion of their expansion of their ionized interstellar media. Fabry-Perot H alpha images reveal the presence of kiloparsec-scale 'superbubbles' and filaments which tend to be oriented along the galaxy minor axis. These structures are comparable in size to the chracteristic optical sizes of the galaxies, and dominate the morphology of the galaxies at low surface brightness in H alpha. Since expanding structure of this size and velocity are not observed in all low-mass galaxies with recent or ongoing star formation, we suggest that we are witnessing transient events that likely have a relatively low 'duty cycle' in such galaxies. That is, we argue that the particular galaxies in the present paper have had significantly elevated star formation rates over the past 10(exp 7)-10(exp 8) yr (i.e., these are starburst or young poststarburst systems). This interpretation is consistent with the optical colors and emission-line properties of these galaxies.

  20. Stellar Populations and Chemical Evolution of Late--Type Dwarf Galaxies

    CERN Document Server

    Tosi, M P

    2001-01-01

    Some aspects of the chemical evolution of late-type dwarf galaxies are reviewed, together with their implications on three issues of cosmological relevance: similarity to primeval galaxies, derivation of the primordial helium abundance, contribution to the excess of faint blue galaxies. A more detailed approach to model their evolution is suggested. The importance of deriving the star formation history in these systems by studying their resolved stellar populations is emphasized.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-01

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

  2. On Wave Dark Matter, Shells in Elliptical Galaxies, and the Axioms of General Relativity

    CERN Document Server

    Bray, Hubert L

    2012-01-01

    This paper is a sequel to the author's paper entitled "On Dark Matter, Spiral Galaxies, and the Axioms of General Relativity" [arXiv:1004.4016] which explored a geometrically natural axiomatic definition for dark matter modeled by a scalar field satisfying the Einstein-Klein-Gordon wave equations which, after much calculation, was shown to be consistent with the observed spiral and barred spiral patterns in disk galaxies. We give an update on where things stand on this "wave dark matter" model of dark matter (aka scalar field dark matter and boson stars), an interesting alternative to the WIMP model of dark matter, and discuss how it has the potential to help explain the long-observed interleaved shell patterns, also known as ripples, in the images of elliptical galaxies.

  3. Comptonization of cosmic microwave background photons in dwarf spheroidal galaxies

    Science.gov (United States)

    Culverhouse, Thomas L.; Evans, N. Wyn; Colafrancesco, S.

    2006-05-01

    We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich (SZ) effect. For an assumed neutralino mass of 10 GeV and beam size of 1 arcsec, the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as the Atacama Large Millimetre Array. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable now. None the less, we conclude that searching for the dark matter induced SZ effect is a promising way of constraining the dark distribution in dSphs, especially if the particles are light.

  4. Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies

    CERN Document Server

    Culverhouse, T L; Colafrancesco, S; Culverhouse, Thomas L.

    2006-01-01

    We present theoretical modelling of the electron distribution produced by annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In particular, we follow up the idea of Colafrancesco (2004) and find that such electrons distort the cosmic microwave background (CMB) by the Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for dSph models with a soft core. By contrast, it is of the order of micro-Kelvin for the strongly cusped dSph models favoured by some cosmological simulations. Although this is out of reach of current instruments, it may well be detectable by future mm telescopes, such as ALMA. We also show that the upscattered CMB photons have energies within reach of upcoming X-ray observatories, but that the flux of such photons is too small to be detectable soon. Nonetheless, we conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is a promising way of constraining ...

  5. Dwarf spheroidal galaxies as degenerate gas of free fermions

    CERN Document Server

    Domcke, Valerie

    2014-01-01

    In this paper we analyze a simple scenario in which Dark Matter (DM) consists of free fermions with mass $m_f$. We assume that on galactic scales these fermions are capable to form a degenerate Fermi gas, in which stability against gravitational collapse is ensured by the Pauli exclusion principle. The mass density of the resulting configuration is governed by a non-relativistic Lane-Emden equation, thus leading to a universal cored profile that depends only on one free parameter in addition to $m_f$. After reviewing the basic formalism, we test this scenario against experimental data describing the dispersion velocity of the eight classical dwarf spheroidal galaxies of the Milky Way. We find that, despite its extreme simplicity, the model exhibits a good fit of the data and realistic predictions for the size of DM halos providing that $m_f \\simeq 200$ eV. We propose a concrete realization of this model in which DM is produced non-thermally via inflaton decay. We show that imposing the correct relic abundance...

  6. Ultrafaint Dwarf Galaxies - the lowest mass relics from before reionization

    CERN Document Server

    Bland-Hawthorn, Joss; Webster, David

    2015-01-01

    New observations indicate that ultrafaint dwarf galaxies (UFD) -- the least luminous systems bound by dark matter halos (<10^5 Lsun) -- may have formed before reionization. The extrapolated virial masses today are uncertain with estimates ranging from 10^8 Msun to 10^9 Msun. We show that the progenitor halo masses of UFDs can be as low as Mvir = 10^7 Msun. Under the right conditions, such a halo can survive the energy input of a supernova and its radiative progenitor. A clumpy medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping because the coupling efficiency of the explosive energy is much lower than for a diffuse ISM. With the aid of the 3D hydro/ionization code Fyris, we show that sufficient baryons are retained to form stars following a single supernova event in dark matter halos down to Mvir ~ 10^7 Msun with radiative cooling. The gas survives the SN explosion, is enriched with the abundance yields of the discrete events, and reaches surf...

  7. Kinematic sub-populations in dwarf spheroidal galaxies

    CERN Document Server

    Ural, Ugur; Koch, Andreas; Gilmore, Gerard; Beers, Timothy C; Belokurov, Vasily; Evans, N Wyn; Grebel, Eva K; Vidrih, Simon; Zucker, Daniel B

    2008-01-01

    We present new spectroscopic data for twenty six stars in the recently-discovered Canes Venatici I (CVnI) dwarf spheroidal galaxy. We use these data to investigate the recent claim of the presence of two dynamically inconsistent stellar populations in this system (Ibata et al., 2006). We do not find evidence for kinematically distinct populations in our sample and we are able to obtain a mass estimate for CVnI that is consistent with all available data, including previously published data. We discuss possible differences between our sample and the earlier data set and study the general detectability of sub-populations in small kinematic samples. We conclude that in the absence of supporting observational evidence (for example, metallicity gradients), sub-populations in small kinematic samples (typically fewer than 100 stars) should be treated with extreme caution, as their detection depends on multiple parameters and rarely produces a signal at the 3sigma confidence level. It is therefore essential to determi...

  8. The star formation history of the Sculptor Dwarf Irregular Galaxy

    CERN Document Server

    Lianou, Sophia

    2012-01-01

    [abridged] We study the resolved stellar populations and derive the SFH of the SDIG, a gas-rich dwarf galaxy member of the NGC7793 subgroup in the Sculptor group. We construct a CMD using archival HST observations and examine its stellar content. We derive its SFH using a maximum-likelihood fit to the CMD. The CMD shows that SDIG contains stars from 10Myr to several Gyr old, as revealed from the MS, BL, luminous AGB, and RGB stars. The young stars with ages less than ~250Myr show a spatial distribution confined to its central regions, and additionally the young MS stars exhibit an off-center density peak. The intermediate-age and older stars are more spatially extended. SDIG is dominated by intermediate-age stars with an average age of 6.4Gyr. The average metallicity inferred is [M/H]\\approx -1.5dex. Its SFH is consistent with a constant SFR, except for ages younger than ~200Myr. The lifetime average SFR is 1.3x10^{-3} Mo/yr. More recently than 100Myr, there has been a burst of SF at a rate ~2-3 times higher ...

  9. Bubble-Induced Star Formation in Dwarf Irregular Galaxies

    CERN Document Server

    Kawata, Daisuke; Barnes, David J; Grand, Robert J J; Rahimi, Awat

    2013-01-01

    To study the star formation and feedback mechanism, we simulate the evolution of an isolated dwarf irregular galaxy (dIrr) in a fixed dark matter halo, similar in size to WLM. We use the new version of our original N-body/smoothed particle chemodynamics code, GCD+, which adopts improved hydrodynamics, metal diffusion between the gas particles and new modelling of star formation and stellar wind and supernovae (SNe) feedback. Comparing the simulations with and without stellar feedback effects, we demonstrate that the collisions of bubbles produced by strong feedback can induce star formation in a more widely spread area. We also demonstrate that the metallicity in star forming regions is kept low due to the mixing of the metal-rich bubbles and the metal-poor inter-stellar medium. Our simulations also suggest that the bubble-induced star formation leads to many counter-rotating stars. The bubble-induced star formation could be a dominant mechanism to maintain star formation in dIrrs, which is different from lar...

  10. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    CERN Document Server

    Yuan, Zhen; Jing, Y P

    2015-01-01

    Fornax is the brightest Milky Way (MW) dwarf spheroidal galaxy and its star formation history (SFH) has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH using a simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe) as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass M_x of the gas to mix with the ejecta from each SN. The choice of M_x depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = t_sat . Our results indicate that due to the global gas outflow at t > t_sat , part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  11. On the R-Process Enrichment of Dwarf Spheroidal Galaxies

    CERN Document Server

    Bramante, Joseph

    2016-01-01

    Recent observations of Reticulum II have uncovered an overabundance of r-process elements, compared to similar ultra-faint dwarf spheroidal galaxies (UFDs). Because the metallicity and star formation history of Reticulum II appear consistent with all known UFDs, the high r-process abundance of Reticulum II suggests enrichment through a single, rare event, such as a double neutron star (NS) merger. However, we note that this scenario is extremely unlikely, as binary stellar evolution models require significant supernova natal kicks to produce NS-NS or NS-black hole mergers, and these kicks would efficiently remove compact binary systems from the weak gravitational potentials of UFDs. We examine alternative mechanisms for the production of r-process elements in UFDs, including a novel mechanism wherein NSs in regions of high dark matter density implode after accumulating a black-hole-forming mass of dark matter. We find that r-process proto-material ejection by tidal forces, when a single neutron star implodes ...

  12. X-RAY SOURCES IN THE DWARF SPHEROIDAL GALAXY DRACO

    Energy Technology Data Exchange (ETDEWEB)

    Sonbas, E. [University of Adiyaman, Department of Physics, 02040 Adiyaman (Turkey); Rangelov, B.; Kargaltsev, O.; Dhuga, K. S.; Hare, J.; Volkov, I., E-mail: edasonbas@yahoo.com [Department of Physics, The George Washington University, Washington, DC 20052 (United States)

    2016-04-10

    We present the spectral analysis of an 87 ks XMM-Newton observation of Draco, a nearby dwarf spheroidal galaxy. Of the approximately 35 robust X-ray source detections, we focus our attention on the brightest of these sources, for which we report X-ray and multiwavelength parameters. While most of the sources exhibit properties consistent with active galactic nuclei, few of them possess the characteristics of low-mass X-ray binaries (LMXBs) and cataclysmic variable (CVs). Our analysis places constraints on the population of X-ray sources with L{sub X} > 3 × 10{sup 33} erg s{sup −1} in Draco, suggesting that there are no actively accreting black hole and neutron star binaries. However, we find four sources that could be quiescent state LMXBs/CVs associated with Draco. We also place constraints on the central black hole luminosity and on a dark matter decay signal around 3.5 keV.

  13. FUSE observations of the Blue Compact Dwarf Galaxy Mrk 59

    CERN Document Server

    Thuan, T X; Izotov, Yu I

    2001-01-01

    New FUSE far-UV spectroscopy of the nearby metal-deficient (Zsun/8) cometary Blue Compact Dwarf (BCD) galaxy Markarian (Mrk) 59 is discussed. The data are used to investigate element abundances in its interstellar medium. The H I absorption lines are characterized by narrow cores which are interstellar in origin and by broad wings which are stellar in origin. The mean interstellar H I column density is ~ 7x10E20 cm-2 in Mrk 59. No H2 lines are seen and N(H2) is < 10E15 cm-2 at the 10 sigma level. The lack of diffuse H2 is due to the combined effect of a strong UV radiation field which destroys the H2 molecules and a low metallicity which leads to a scarcity of dust grains necessary for H2 formation. P-Cygni profiles of the S VI 933.4, 944.5 A and O VI 1031.9, 1037.6 A lines are seen, indicating the presence of very hot O stars and a stellar wind terminal velocity of ~ 1000 km/s. By fitting the line profiles with multiple components having each a velocity dispersion b = 7 km/s and spanning a radial velocity...

  14. A Chemical Evolution Model for the Fornax Dwarf Spheroidal Galaxy

    Directory of Open Access Journals (Sweden)

    Yuan Zhen

    2016-01-01

    Full Text Available Fornax is the brightest Milky Way (MW dwarf spheroidal galaxy and its star formation history (SFH has been derived from observations. We estimate the time evolution of its gas mass and net inflow and outflow rates from the SFH usinga simple star formation law that relates the star formation rate to the gas mass. We present a chemical evolution model on a 2D mass grid with supernovae (SNe as sources of metal enrichment. We find that a key parameter controlling the enrichment is the mass Mx of the gas to mix with the ejecta from each SN. The choice of Mx depends on the evolution of SN remnants and on the global gas dynamics. It differs between the two types of SNe involved and between the periods before and after Fornax became an MW satellite at time t = tsat. Our results indicate that due to the global gas outflow at t > tsat, part of the ejecta from each SN may directly escape from Fornax. Sample results from our model are presented and compared with data.

  15. Chemical Enrichment and the Origin of the Colour-Magnitude Relation of Elliptical Galaxies in a Hierarchical Merger Model

    CERN Document Server

    Kauffmann, G; Kauffmann, Guinevere; Charlot, Stephane

    1997-01-01

    In this paper, we present a model of the formation and chemical enrichment of elliptical galaxies that differs from the conventional picture in two ways: 1)Ellipticals do not form in a single monolithic collapse and burst of star formation at high redshift. Instead, most of their stars form at modest rates in disk galaxies, which then merge to form the ellipticals. 2)Galaxies do not undergo closed-box chemical evolution. Instead, metals can be transferred between the stars, cold gas and the hot gas halos of the galaxies. It is assumed that metals are ejected out of disk galaxies during supernova explosions and these metals enter the hot gas component. The fact that metals are more easily ejected from small galaxies leads to the establishment of a mass-metallicity relation for the disk systems. Big ellipticals are more metal rich because they are formed from the mergers of bigger disks. We use semi-analytic techniques to follow the formation, evolution, and chemical enrichment of cluster ellipticals in a mergi...

  16. Delayed star formation in isolated dwarf galaxies: Hubble space telescope star formation history of the Aquarius dwarf irregular

    Energy Technology Data Exchange (ETDEWEB)

    Cole, Andrew A. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania, 7001 Australia (Australia); Weisz, Daniel R. [Department of Astronomy, University of California at Santa Cruz, 1156 High Street, Santa Cruz, CA 95064 (United States); Dolphin, Andrew E. [Raytheon, 1151 East Hermans Road, Tucson, AZ 85706 (United States); Skillman, Evan D. [Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55441 (United States); McConnachie, Alan W. [NRC Herzberg Institute of Astrophysics, Dominion Astrophysical Observatory, Victoria, BC, V9E 2E7 Canada (Canada); Brooks, Alyson M. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, 136 Frelinghuysen Road, Piscataway, NJ 08854 (United States); Leaman, Ryan, E-mail: andrew.cole@utas.edu.au, E-mail: drw@ucsc.edu, E-mail: adolphin@raytheon.com, E-mail: skillman@astro.umn.edu, E-mail: alan.mcconnachie@nrc-cnrc.gc.ca, E-mail: abrooks@physics.rutgers.edu, E-mail: rleaman@iac.es [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)

    2014-11-01

    We have obtained deep images of the highly isolated (d = 1 Mpc) Aquarius dwarf irregular galaxy (DDO 210) with the Hubble Space Telescope Advanced Camera for Surveys. The resulting color-magnitude diagram (CMD) reaches more than a magnitude below the oldest main-sequence turnoff, allowing us to derive the star formation history (SFH) over the entire lifetime of the galaxy with a timing precision of ≈10% of the lookback time. Using a maximum likelihood fit to the CMD we find that only ≈10% of all star formation in Aquarius took place more than 10 Gyr ago (lookback time equivalent to redshift z ≈ 2). The star formation rate increased dramatically ≈6-8 Gyr ago (z ≈ 0.7-1.1) and then declined until the present time. The only known galaxy with a more extreme confirmed delay in star formation is Leo A, a galaxy of similar M {sub H} {sub I}/M {sub *}, dynamical mass, mean metallicity, and degree of isolation. The delayed stellar mass growth in these galaxies does not track the mean dark matter accretion rate from CDM simulations. The similarities between Leo A and Aquarius suggest that if gas is not removed from dwarf galaxies by interactions or feedback, it can linger for several gigayears without cooling in sufficient quantity to form stars efficiently. We discuss possible causes for the delay in star formation including suppression by reionization and late-time mergers. We find reasonable agreement between our measured SFHs and select cosmological simulations of isolated dwarfs. Because star formation and merger processes are both stochastic in nature, delayed star formation in various degrees is predicted to be a characteristic (but not a universal) feature of isolated small galaxies.

  17. Fall of associations of dwarf galaxies into the Milky Way halo

    Science.gov (United States)

    Benavides, J.; Casas Miranda, R. A.

    2017-07-01

    Inside the Local Group, the satellite galaxies of the Milky Way don't have an isotropic distribution, instead most of them lie on structure almost perpendicular to the plane of the disk of the galaxy, called VPOS. At present there is not a theoretical model that correctly explain both the abundance and spatial distribution of these objects within the Local Group. This work presents a study, using Newtonian N-body numerical simulations, on the formation of disk satellites of the Milky Way (DoS) from accretion of dwarf galaxies that fall into the dark matter halo of the Milky Way following parabolic orbits with initial distances of 4, 2 and 1 Mpc. We analysed the morphological properties of dwarfs after 10 Gy of fall proposed for interaction with the Milky Way, the obtained spatial distributions about the plane of the host galaxy and the radial distances at which they are located. We found that, after 10 Gy of fall, the structures remain compact while keeping its spherical profile. Only associations of dwarf galaxies at distances of 1 Mpc manage to enter the halo of the Galaxy and could be considered as progenitors of DoS. This is supported by the fact that these closest associations are those that had precipitated into the halo of the Galaxy, and there are not observed associations of dwarfs at these distances, being the association 14+12 the closest to the Milky Way at 1.37 Mpc.

  18. Testing MOG, non-local gravity and MOND with rotation curves of dwarf galaxies

    Science.gov (United States)

    Zhoolideh Haghighi, M. H.; Rahvar, S.

    2017-07-01

    Modified gravity (MOG) and non-local gravity (NLG) are two alternative theories to general relativity. They are able to explain the rotation curves of spiral galaxies and clusters of galaxies without including dark matter. In the weak-field approximation, these two theories have similar forms, with an effective gravitational potential that has two components: (i) Newtonian gravity with the gravitational constant enhanced by a factor (1 + α) and (ii) a Yukawa-type potential that produces a repulsive force with length-scale 1/μ. In this work, we compare the rotation curves of dwarf galaxies in the LITTLE THINGS catalogue with predictions of MOG, NLG and modified Newtonian dynamics (MOND). We find that the universal parameters of the MOG and NLG theories can fit the rotation curves of dwarf galaxies only at the expense of systematically high stellar mass-to-light ratios at 3.6 μm. For instance, in MOG, half of the galaxies have best-fitting stellar M/L ratios larger than 10. It seems that such a big stellar mass-to-light ratio is in contradiction with observations of nearby stars in the Milky Way and with stellar population synthesis models; however, the stellar mass-to-light ratio of dwarf galaxies is not observed directly by the astrophysical methods. Future observations of binary stars in the dwarf galaxies will identify M/L and consequently examine different modified gravity models.

  19. Mid-Infrared Colors of Dwarf Galaxies: Young Starbursts Mimicking Active Galactic Nuclei

    CERN Document Server

    Hainline, Kevin N; Greene, Jenny E; Stern, Daniel

    2016-01-01

    Searching for active galactic nuclei (AGN) in dwarf galaxies is important for our understanding of the seed black holes that formed in the early Universe. Here, we test infrared selection methods for AGN activity at low galaxy masses. Our parent sample consists of ~18,000 nearby dwarf galaxies (M*< 3 x 10^9 Msun, $z<0.055$) in the Sloan Digital Sky Survey with significant detections in the first three bands of the AllWISE data release from the Wide-field Infrared Survey Explorer (WISE). First, we demonstrate that the majority of optically-selected AGNs in dwarf galaxies are not selected as AGNs using WISE infrared color diagnostics and that the infrared emission is dominated by the host galaxies. We then investigate the infrared properties of optically-selected star-forming dwarf galaxies, finding that the galaxies with the reddest infrared colors are the most compact, with blue optical colors, young stellar ages and large specific star formation rates. These results indicate that great care must be tak...

  20. High-resolution mass models of dwarf galaxies from LITTLE THINGS

    CERN Document Server

    Oh, Se-Heon; Brinks, Elias; Elmegreen, Bruce G; Schruba, Andreas; Walter, Fabian; Rupen, Michael P; Young, Lisa M; Simpson, Caroline E; Johnson, Megan; Herrmann, Kimberly A; Ficut-Vicas, Dana; Cigan, Phil; Heesen, Volker; Ashley, Trisha; Zhang, Hong-Xin

    2015-01-01

    We present high-resolution rotation curves and mass models of 26 dwarf galaxies from LITTLE THINGS. LITTLE THINGS is a high-resolution Very Large Array HI survey for nearby dwarf galaxies in the local volume within 11 Mpc. The rotation curves of the sample galaxies derived in a homogeneous and consistent manner are combined with Spitzer archival 3.6 micron and ancillary optical U, B, and V images to construct mass models of the galaxies. We decompose the rotation curves in terms of the dynamical contributions by baryons and dark matter halos, and compare the latter with those of dwarf galaxies from THINGS as well as Lambda CDM SPH simulations in which the effect of baryonic feedback processes is included. Being generally consistent with THINGS and simulated dwarf galaxies, most of the LITTLE THINGS sample galaxies show a linear increase of the rotation curve in their inner regions, which gives shallower logarithmic inner slopes alpha of their dark matter density profiles. The mean value of the slopes of the 2...

  1. THE NUMBER OF TIDAL DWARF SATELLITE GALAXIES IN DEPENDENCE OF BULGE INDEX

    Energy Technology Data Exchange (ETDEWEB)

    López-Corredoira, Martín [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain); Kroupa, Pavel, E-mail: martinlc@iac.es, E-mail: pavel@astro.uni-bonn.de [Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, Nussallee 14-16, D-53115 Bonn (Germany)

    2016-01-20

    We show that a significant correlation (up to 5σ) emerges between the bulge index, defined to be larger for a larger bulge/disk ratio, in spiral galaxies with similar luminosities in the Galaxy Zoo 2 of the Sloan Digital Sky Survey and the number of tidal-dwarf galaxies in the catalog by Kaviraj et al. In the standard cold or warm dark matter cosmological models, the number of satellite galaxies correlates with the circular velocity of the dark matter host halo. In generalized gravity models without cold or warm dark matter, such a correlation does not exist, because host galaxies cannot capture infalling dwarf galaxies due to the absence of dark-matter-induced dynamical friction. However, in such models, a correlation is expected to exist between the bulge mass and the number of satellite galaxies because bulges and tidal-dwarf satellite galaxies form in encounters between host galaxies. This is not predicted by dark matter models in which bulge mass and the number of satellites are a priori uncorrelated because higher bulge/disk ratios do not imply higher dark/luminous ratios. Hence, our correlation reproduces the prediction of scenarios without dark matter, whereas an explanation is not found readily from the a priori predictions of the standard scenario with dark matter. Further research is needed to explore whether some application of the standard theory may explain this correlation.

  2. Tidal Interaction as the origin of early-type dwarf galaxies in group environment

    CERN Document Server

    Paudel, Sanjaya

    2014-01-01

    We present a sample of dwarf galaxies that suffer ongoing disruption by the tidal force of nearby massive galaxies. Analysing structural and stellar population properties using the archival imaging and spectroscopic data from the Sloan Digital Sky Survey (SDSS), we find that they are likely a `smoking gun' example of the formation of early-type dwarf galaxies (dEs) in the galaxy group environment through the tidal stirring. Inner cores of these galaxies are fairly intact and the observed light profiles are well fitted with the Sersic functions, while the tidally stretched stellar halos are prominent in the outer parts. They are all located within the 50 kpc sky-projected distance from the center of host galaxies and no dwarf galaxies have relative line-of-sight velocity larger than 205 km/s to their hosts. We derive the Composite Stellar Population (CSP) properties these galaxies by fitting the SDSS optical spectra to a multiple-burst composite stellar population model. We find that these galaxies accumulate ...

  3. The number of tidal dwarf satellite galaxies in dependence of bulge index

    CERN Document Server

    Lopez-Corredoira, Martin

    2015-01-01

    We show that a significant correlation (up to 5sigma) emerges between the bulge index, defined to be larger for larger bulge/disk ratio, in spiral galaxies with similar luminosities in the Galaxy Zoo 2 of SDSS and the number of tidal-dwarf galaxies in the catalogue by Kaviraj et al. (2012). In the standard cold or warm dark-matter cosmological models the number of satellite galaxies correlates with the circular velocity of the dark matter host halo. In generalized-gravity models without cold or warm dark matter such a correlation does not exist, because host galaxies cannot capture in-falling dwarf galaxies due to the absence of dark-matter-induced dynamical friction. However, in such models a correlation is expected to exist between the bulge mass and the number of satellite galaxies, because bulges and tidal-dwarf satellite galaxies form in encounters between host galaxies. This is not predicted by dark matter models in which bulge mass and the number of satellites are a priori uncorrelated because higher b...

  4. The ACS Nearby Galaxy Survey Treasury VIII. The Global Star Formation Histories of 60 Dwarf Galaxies in the Local Volume

    CERN Document Server

    Weisz, Daniel R; Williams, Benjamin F; Gilbert, Karoline M; Skillman, Evan D; Seth, Anil C; Dolphin, Andrew E; McQuinn, Kristen B W; Gogarten, Stephanie M; Holtzman, Jon; Rosema, Keith; Cole, Andrew; Karachentsev, Igor D; Zaritsky, Dennis

    2011-01-01

    We present uniformly measured star formation histories (SFHs) of 60 nearby (D~4Mpc) dwarf galaxies based on CMDs of resolved stellar populations from images taken with HST as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dSph/dE, 5 dwarf spiral, 28 dI, 12 transition, and 3 tidal dwarf galaxies. From the best fit SFHs we find three significant results: (1) the average dwarf galaxy formed >50% of its stars by z~2 and 60% of its stars by z~1, regardless of current morphological type; (2) the mean SFHs of dIs, dTrans, and dSphs are similar over most of cosmic time, with the clearest differences appearing during the most recent 1 Gyr; and (3) the mean values are inconsistent with simple SFH models, e.g., exponentially declining SFRs. The mean SFHs are in general agreement with the cosmic SFH, although we observe offsets near z~1 that could be evidence that low mass systems experienced delayed star formation relative to more massive galaxies. The sample shows ...

  5. The no-spin zone: rotation versus dispersion support in observed and simulated dwarf galaxies

    Science.gov (United States)

    Wheeler, Coral; Pace, Andrew B.; Bullock, James S.; Boylan-Kolchin, Michael; Oñorbe, Jose; Elbert, Oliver D.; Fitts, Alex; Hopkins, Philip F.; Kereš, Dušan

    2017-02-01

    We perform a systematic Bayesian analysis of rotation versus dispersion support (vrot/σ) in 40 dwarf galaxies throughout the local volume (LV) over a stellar mass range of 10^{3.5} M_{⊙}sample have vrot/σ ≲ 1.0, while all have vrot/σ ≲ 2.0. These results challenge the traditional view that the stars in gas-rich dwarf irregulars (dIrrs) are distributed in cold, rotationally supported stellar discs, while gas-poor dwarf spheroidals (dSphs) are kinematically distinct in having dispersion-supported stars. We see no clear trend between vrot/σ and distance to the closest L⋆ galaxy, nor between vrot/σ and M⋆ within our mass range. We apply the same Bayesian analysis to four FIRE hydrodynamic zoom-in simulations of isolated dwarf galaxies (10^9 M_{⊙}population of dIrrs and dSphs without the need to subject these dwarfs to any external perturbations or tidal forces. We posit that most dwarf galaxies form as puffy, dispersion-dominated systems, rather than cold, angular-momentum-supported discs. If this is the case, then transforming a dIrr into a dSph may require little more than removing its gas.

  6. VizieR Online Data Catalog: Dwarf galaxies surface brightness profiles. II. (Herrmann+, 2016)

    Science.gov (United States)

    Herrmann, K. A.; Hunter, D. A.; Elmegreen, B. G.

    2016-07-01

    Our galaxy sample (see Table1) is derived from the survey of nearby (>30Mpc) late-type galaxies conducted by Hunter & Elmegreen 2006 (cat. J/ApJS/162/49). The full survey includes 94 dwarf Irregulars (dIms), 26 Blue Compact Dwarfs (BCDs), and 20 Magellanic-type spirals (Sms). The 141 dwarf sample presented in the first paper of the present series (Paper I; Herrmann et al. 2013, Cat. J/AJ/146/104) contains one fewer Sm galaxy and two additional dIm systems than the original survey. A multi-wavelength data set has been assembled for these galaxies. The data include Hα images (129 galaxies with detections) to trace star formation over the past 10Myr (Hunter & Elmegreen 2004, Cat. J/AJ/128/2170) and satellite UV images (61 galaxies observed) obtained with the Galaxy Evolution Explorer (GALEX) to trace star formation over the past ~200Myr. The GALEX data include images from two passbands with effective wavelengths of 1516Å (FUV) and 2267Å (NUV) and resolutions of 4'' and 5.6'', respectively. Three of the galaxies in our sample with NUV data do not have FUV data. To trace older stars we have UBV images, which are sensitive to stars formed over the past 1Gyr for on-going star formation, and images in at least one band of JHK for 40 galaxies in the sample, which integrates the star formation over the galaxy's lifetime. Note that nine dwarfs are missing UB data and three more are missing U-band data. In addition we made use of 3.6μm images (39 galaxies) obtained with the Infrared Array Camera (IRAC) in the Spitzer archives also to probe old stars. (3 data files).

  7. Dust origin in late-type dwarf galaxies: ISM growth vs. type II supernovae

    CERN Document Server

    Zhukovska, Svitlana

    2014-01-01

    We re-evaluate the roles of different dust sources in dust production as a function of metallicity in late-type dwarf galaxies, with the goal of understanding the relation between dust content and metallicity. The dust content ol late-type dwarf galaxies with episodic star formation is studied with a multicomponent model of dust evolution, which includes dust input from AGB stars, type II SNe and dust growth by accretion of atoms in the ISM. Dust growth in the ISM becomes an important dust source in dwarf galaxies, on the timescale of 0.1 - a few Gyrs. It increases the dust-to-gas ratio (DGR) during post-burst evolution, unlike type II SNe, which eject grains to the ISM only during starbursts. Before the dust growth in the ISM overtakes the dust production, AGB stars can be major sources of dust in metal-poor dwarf galaxies. Our models reproduce the relation between the DGR and oxygen abundance, derived from observations of a large sample of dwarf galaxies. The steep decrease in the DGR at low O values is exp...

  8. The Carnegie-Irvine Galaxy Survey. IV. A Method to Determine the Average Mass Ratio of Mergers That Built Massive Elliptical Galaxies

    CERN Document Server

    Huang, Song; Peng, Chien Y; Li, Zhao-Yu; Barth, Aaron J

    2016-01-01

    Many recent observations and numerical simulations suggest that nearby massive, early-type galaxies were formed through a "two-phase" process. In the proposed second phase, the extended stellar envelope was accumulated through many dry mergers. However, details of the past merger history of present-day ellipticals, such as the typical merger mass ratio, are difficult to constrain observationally. Within the context and assumptions of the two-phase formation scenario, we propose a straightforward method, using photometric data alone, to estimate the average mass ratio of mergers that contributed to the build-up of massive elliptical galaxies. We study a sample of nearby massive elliptical galaxies selected from the Carnegie-Irvine Galaxy Survey, using two-dimensional analysis to decompose their light distribution into an inner, denser component plus an extended, outer envelope, each having a different optical color. The combination of these two substructures accurately recovers the negative color gradient exhi...

  9. A close look at the Centaurus A group of galaxies IV. Recent star formation histories of late-type dwarfs around CenA

    CERN Document Server

    Crnojević, D; Cole, A A

    2012-01-01

    We study a sample of 5 dwarf irregular galaxies in the CenA/M83 group, which are companions to the giant elliptical CenA. We aim at deriving their physical properties over their lifetime and compare them to those of dwarfs located in different environments. We use archival HST/ACS data and apply synthetic color-magnitude diagram fitting in order to reconstruct the past star formation activity of the target galaxies. The average star formation rate for the studied galaxies ranges from 10^{-3} up to \\sim 7x10^{-2} M_odot/yr, and their mean metallicities correlate with their luminosities (from [Fe/H]\\sim -1.4 up to \\sim -1.0). The form of the star formation histories varies across the sample, with quiescent periods alternating with intermittent enhancements in the star formation (from a few up to several times the average lifetime value). The dwarfs in this sample formed ~35% to ~60% of their stellar content prior to ~5 Gyr ago. The resulting star formation histories for the CenA companions are similar to those ...

  10. Correlations Between Supermassive Black Holes, Velocity Dispersions, and Mass Deficits in Elliptical Galaxies with Cores

    CERN Document Server

    Kormendy, John; 10.1088/0004-637X/691/2/L142

    2009-01-01

    High-dynamic-range surface photometry in a companion paper makes possible accurate measurement of the stellar light deficits L_def and mass deficits M_def associated with the cores of elliptical galaxies. We show that L_def correlates with the velocity dispersion sigma of the host galaxy bulge averaged outside the central region that may be affected by a supermassive black hole (BH). We confirm that L_def correlates with BH mass MBH. Also, the fractional light deficit L_def/L correlates with MBH/M, the ratio of BH mass to the galaxy stellar mass. All three correlations have scatter similar to or smaller than the scatter in the well known correlation between MBH and sigma. The new correlations are remarkable in view of the dichotomy between ellipticals with cores and those with central extra light. Core light deficit correlates closely with MBH and sigma, but extra light does not. This supports the suggestion that extra light Es are made in wet mergers with starbursts whereas core Es are made in dry mergers. A...

  11. Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies

    Science.gov (United States)

    Lowenstein, Michael

    2013-01-01

    The amount of metals in the Intracluster Medium (ICM) in rich galaxy clusters exceeds that expected based on the observed stellar population by a large factor. We quantify this discrepancy--which we term the "cluster elemental abundance paradox"--and investigate the required properties of the ICM-enriching population. The necessary enhancement in metal enrichment may, in principle, originate in the observed stellar population if a larger fraction of stars in the supernova-progenitor mass range form from an initial mass function (IMF) that is either bottom-light or top-heavy, with the latter in some conflict with observed ICM abundance ratios. Other alternatives that imply more modest revisions to the IMF, mass return and remnant fractions, and primordial fraction, posit an increase in the fraction of 3-8 solar mass stars that explode as SNIa or assume that there are more stars than conventionally thought--although the latter implies a high star formation efficiency. We discuss the feasibility of these various solutions and the implications for the diversity of star formation, the process of elliptical galaxy formation, and the nature of this hidden source of ICM metal enrichment in light of recent evidence of an elliptical galaxy IMF that, because it is skewed to low masses, deepens the paradox.

  12. Nuclear stellar discs in low-luminosity elliptical galaxies: NGC 4458 and NGC 4478

    CERN Document Server

    Morelli, L; Corsini, E M; Pizzella, A; Thomas, D; Saglia, R P; Davies, R L; Bender, R; Birkinshaw, M; Bertola, F

    2004-01-01

    We present the detection of nuclear stellar discs in the low-luminosity elliptical galaxies NGC 4458 and NGC 4478, which are known to host a kinematically-decoupled core. Using archival HST imaging, and available absorption line-strength index data based on ground-based spectroscopy, we investigate the photometric parameters and the properties of the stellar populations of these central structures. Their scale length, h, and face-on central surface brightness, mu_0^c, fit on mu_0^c-h relation for galaxy discs. For NGC 4458 these parameters are typical for nuclear discs, while the same quantities for NGC 4478 lie between those of nuclear discs and the discs of discy ellipticals. We present Lick/IDS absorption line-strength measurements of Hbeta, Mgb, along the major and minor axes of the galaxies. We model these data with simple stellar populations that account for the alpha/Fe overabundance. The counter-rotating central disc of NGC 4458 is found to have similar properties to the decoupled cores of bright ell...

  13. An actively accreting massive black hole in the dwarf starburst galaxy Henize 2-10.

    Science.gov (United States)

    Reines, Amy E; Sivakoff, Gregory R; Johnson, Kelsey E; Brogan, Crystal L

    2011-02-03

    Supermassive black holes are now thought to lie at the heart of every giant galaxy with a spheroidal component, including our own Milky Way. The birth and growth of the first 'seed' black holes in the earlier Universe, however, is observationally unconstrained and we are only beginning to piece together a scenario for their subsequent evolution. Here we report that the nearby dwarf starburst galaxy Henize 2-10 (refs 5 and 6) contains a compact radio source at the dynamical centre of the galaxy that is spatially coincident with a hard X-ray source. From these observations, we conclude that Henize 2-10 harbours an actively accreting central black hole with a mass of approximately one million solar masses. This nearby dwarf galaxy, simultaneously hosting a massive black hole and an extreme burst of star formation, is analogous in many ways to galaxies in the infant Universe during the early stages of black-hole growth and galaxy mass assembly. Our results confirm that nearby star-forming dwarf galaxies can indeed form massive black holes, and that by implication so can their primordial counterparts. Moreover, the lack of a substantial spheroidal component in Henize 2-10 indicates that supermassive black-hole growth may precede the build-up of galaxy spheroids.

  14. THE DARK HALO-SPHEROID CONSPIRACY AND THE ORIGIN OF ELLIPTICAL GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Remus, Rhea-Silvia; Burkert, Andreas; Dolag, Klaus [Universitaets-Sternwarte Muenchen, Scheinerstr. 1, D-81679 Muenchen (Germany); Johansson, Peter H. [Department of Physics, University of Helsinki, Gustaf Haellstroemin katu 2a, FI-00014 Helsinki (Finland); Naab, Thorsten; Oser, Ludwig [Max-Planck-Institute for Astrophysics, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany); Thomas, Jens, E-mail: rhea@usm.lmu.de [Max-Planck-Institute for Extraterrestrial Physics, P.O. Box 1312, D-85748 Garching (Germany)

    2013-04-01

    Dynamical modeling and strong-lensing data indicate that the total density profiles of early-type galaxies are close to isothermal, i.e., {rho}{sub tot}{proportional_to}r {sup {gamma}} with {gamma} Almost-Equal-To -2. To understand the origin of this universal slope we study a set of simulated spheroids formed in isolated binary mergers as well as the formation within the cosmological framework. The total stellar plus dark matter density profiles can always be described by a power law with an index of {gamma} Almost-Equal-To -2.1 with a tendency toward steeper slopes for more compact, lower-mass ellipticals. In the binary mergers the amount of gas involved in the merger determines the precise steepness of the slope. This agrees with results from the cosmological simulations where ellipticals with steeper slopes have a higher fraction of stars formed in situ. Each gas-poor merger event evolves the slope toward {gamma} {approx} -2, once this slope is reached further merger events do not change it anymore. All our ellipticals have flat intrinsic combined stellar and dark matter velocity dispersion profiles. We conclude that flat velocity dispersion profiles and total density distributions with a slope of {gamma} {approx} -2 for the combined system of stars and dark matter act as a natural attractor. The variety of complex formation histories as present in cosmological simulations, including major as well as minor merger events, is essential to generate the full range of observed density slopes seen for present-day elliptical galaxies.

  15. Observational Constraints on the Molecular Gas Content in Nearby Starburst Dwarf Galaxies

    CERN Document Server

    McQuinn, Kristen B W; Dalcanton, Julianne J; Dolphin, Andrew E; Cannon, John M; Holtzman, Jon; Weisz, Daniel R; Williams, Benjamin F

    2012-01-01

    Using star formation histories derived from optically resolved stellar populations in nineteen nearby starburst dwarf galaxies observed with the Hubble Space Telescope, we measure the stellar mass surface densities of stars newly formed in the bursts. By assuming a star formation efficiency (SFE), we then calculate the inferred gas surface densities present at the onset of the starbursts. Assuming a SFE of 1%, as is often assumed in normal star-forming galaxies, and assuming that the gas was purely atomic, translates to very high HI surface densities (~10^2-10^3 Msun pc^-2), which are much higher than have been observed in dwarf galaxies. This implies either higher values of SFE in these dwarf starburst galaxies or the presence of significant amounts of H_2 in dwarfs (or both). Raising the assumed SFEs to 10% or greater (in line with observations of more massive starbursts associated with merging galaxies), still results in HI surface densities higher than observed in 10 galaxies. Thus, these observations app...

  16. Interstellar Medium Oxygen Abundances of Dwarf Irregular Galaxies in Centaurus A and Nearby Groups

    CERN Document Server

    Lee, Henry; Grebel, E K; 10.1111/j.1365-2966.2007.11481.x

    2008-01-01

    We present results of optical spectroscopy of 35 H II regions from eight dwarf galaxies in the Centaurus A group. [O III]4363 A is detected in ESO272-G025 and ESO324-G024, and direct oxygen abundances of 12+log(O/H) = 7.76 +/- 0.09 and 7.94 +/- 0.11 are derived, respectively. For the remaining galaxies, abundances are derived using common bright-line methods. To compare the influence of group environments on dwarf galaxies, we have also gathered data for additional dwarf irregular galaxies from the Cen A and the Sculptor groups from the literature. We have examined possible relationships between oxygen abundance, gas fraction, effective chemical yield, and tidal indices. Despite large positive tidal indices for a number of Cen A dwarfs in the present sample, there is no clear separation between galaxies with positive tidal indices and galaxies with negative tidal indices in the luminosity-metallicity, metallicity-gas fraction, and metallicity-tidal index diagrams. The H I surface mass density decreases with i...

  17. Bulgeless dwarf galaxies and dark matter cores from supernova-driven outflows.

    Science.gov (United States)

    Governato, F; Brook, C; Mayer, L; Brooks, A; Rhee, G; Wadsley, J; Jonsson, P; Willman, B; Stinson, G; Quinn, T; Madau, P

    2010-01-14

    For almost two decades the properties of 'dwarf' galaxies have challenged the cold dark matter (CDM) model of galaxy formation. Most observed dwarf galaxies consist of a rotating stellar disk embedded in a massive dark-matter halo with a near-constant-density core. Models based on the dominance of CDM, however, invariably form galaxies with dense spheroidal stellar bulges and steep central dark-matter profiles, because low-angular-momentum baryons and dark matter sink to the centres of galaxies through accretion and repeated mergers. Processes that decrease the central density of CDM halos have been identified, but have not yet reconciled theory with observations of present-day dwarfs. This failure is potentially catastrophic for the CDM model, possibly requiring a different dark-matter particle candidate. Here we report hydrodynamical simulations (in a framework assuming the presence of CDM and a cosmological constant) in which the inhomogeneous interstellar medium is resolved. Strong outflows from supernovae remove low-angular-momentum gas, which inhibits the formation of bulges and decreases the dark-matter density to less than half of what it would otherwise be within the central kiloparsec. The analogues of dwarf galaxies-bulgeless and with shallow central dark-matter profiles-arise naturally in these simulations.

  18. Suppression of star formation in dwarf galaxies by photoelectric grain heating feedback

    Science.gov (United States)

    Forbes, John C.; Krumholz, Mark R.; Goldbaum, Nathan J.; Dekel, Avishai

    2016-07-01

    Photoelectric heating—heating of dust grains by far-ultraviolet photons—has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation; however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity—as is expected with photoelectric heating, but not with supernovae—reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space- and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time, suppressing the rate by more than an order of magnitude relative to simulations with only supernovae.

  19. Suppression of star formation in dwarf galaxies by photoelectric grain heating feedback.

    Science.gov (United States)

    Forbes, John C; Krumholz, Mark R; Goldbaum, Nathan J; Dekel, Avishai

    2016-07-28

    Photoelectric heating--heating of dust grains by far-ultraviolet photons--has long been recognized as the primary source of heating for the neutral interstellar medium. Simulations of spiral galaxies have shown some indication that photoelectric heating could suppress star formation; however, simulations that include photoelectric heating have typically shown that it has little effect on the rate of star formation in either spiral galaxies or dwarf galaxies, which suggests that supernovae are responsible for setting the gas depletion time in galaxies. This result is in contrast with recent work indicating that a star formation law that depends on galaxy metallicity--as is expected with photoelectric heating,but not with supernovae--reproduces the present-day galaxy population better than does a metallicity-independent one. Here we report a series of simulations of dwarf galaxies, the class of galaxy in which the effects of both photoelectric heating and supernovae are expected to be strongest. We simultaneously include space and time-dependent photoelectric heating in our simulations, and we resolve the energy-conserving phase of every supernova blast wave, which allows us to directly measure the relative importance of feedback by supernovae and photoelectric heating in suppressing star formation. We find that supernovae are unable to account for the observed large gas depletion times in dwarf galaxies. Instead, photoelectric heating is the dominant means by which dwarf galaxies regulate their star formation rate at any given time,suppressing the rate by more than an order of magnitude relative to simulations with only supernovae.

  20. Extended stellar substructure surrounding the Boötes I dwarf spheroidal galaxy

    Science.gov (United States)

    Roderick, T. A.; Mackey, A. D.; Jerjen, H.; Da Costa, G. S.

    2016-10-01

    We present deep stellar photometry of the Boötes I dwarf spheroidal galaxy in g- and i-band filters, taken with the Dark Energy Camera at Cerro Tololo in Chile. Our analysis reveals a large, extended region of stellar substructure surrounding the dwarf, as well as a distinct overdensity encroaching on its tidal radius. A radial profile of the Boötes I stellar distribution shows a break radius indicating the presence of extra-tidal stars. These observations strongly suggest that Boötes I is experiencing tidal disruption, although not as extreme as that exhibited by the Hercules dwarf spheroidal. Combined with revised velocity dispersion measurements from the literature, we see evidence suggesting the need to review previous theoretical models of the Boötes I dwarf spheroidal galaxy.

  1. Extended stellar substructure surrounding the Bo\\"otes I dwarf spheroidal galaxy

    CERN Document Server

    Roderick, T A; Jerjen, H; Da Costa, G S

    2016-01-01

    We present deep stellar photometry of the Bo\\"otes I dwarf spheroidal galaxy in g and i band filters, taken with the Dark Energy Camera at Cerro Tololo in Chile. Our analysis reveals a large, extended region of stellar substructure surrounding the dwarf, as well as a distinct over-density encroaching on its tidal radius. A radial profile of the Bo\\"otes I stellar distribution shows a break radius indicating the presence of extra-tidal stars. These observations strongly suggest that Bo\\"otes I is experiencing tidal disruption, although not as extreme as that exhibited by the Hercules dwarf spheroidal. Combined with revised velocity dispersion measurements from the literature, we see evidence suggesting the need to review previous theoretical models of the Bo\\"otes I dwarf spheroidal galaxy.

  2. Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches

    CERN Document Server

    Klop, Niki; Hayashi, Kohei; Ando, Shin'ichiro

    2016-01-01

    Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way highly dominated by dark matter. Therefore, they are prime targets to search for signals from dark matter annihilation using gamma-ray observations. We analyse about 7 years of PASS8 Fermi data for seven classical dwarf galaxies, including Draco, adopting both the widely used Navarro-Frenk-White (NFW) profile and observationally motivated axisymmetric density profiles. For four of the selected dwarfs (Sextans, Carina, Sculptor and Fornax) axisymmetric mass models suggest a cored density profile rather than the commonly adopted cusped profile. We found that upper limits on the annihilation cross section for some of these dwarfs are significantly higher than the ones achieved using an NFW profile. Therefore, upper limits in the literature obtained using cusped profiles like the NFW might have been overestimated. Our results eventually show that it is extremely important to use observationally motivated density profiles going beyond the usu...

  3. Andromeda XXVIII: A Dwarf Galaxy More Than 350 kpc from Andromeda

    CERN Document Server

    Slater, Colin T; Martin, Nicolas F

    2011-01-01

    We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently-released SDSS DR8. The galaxy is a likely satellite of Andromeda, and, at a separation of $365^{+17}_{-1}$ kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is $650^{+150}_{-80}$ kpc, and analysis of its structure and luminosity show that it has an absolute magnitude of $M_V = -8.5^{+0.4}_{-1.0}$ and half-light radius of $r_h = 210^{+60}_{-50}$ pc, similar to many other faint Local Group dwarfs. With presently-available imaging we are unable to determine if there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or dwarf irregular.

  4. ANDROMEDA XXVIII: A DWARF GALAXY MORE THAN 350 kpc FROM ANDROMEDA

    Energy Technology Data Exchange (ETDEWEB)

    Slater, Colin T.; Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Martin, Nicolas F. [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

    2011-11-20

    We report the discovery of a new dwarf galaxy, Andromeda XXVIII, using data from the recently released Sloan Digital Sky Survey Data Release 8. The galaxy is a likely satellite of Andromeda, and, at a separation of 365{sup +17}{sub -1} kpc, would be one of the most distant of Andromeda's satellites. Its heliocentric distance is 650{sup +150}{sub -80} kpc, and analysis of its structure and luminosity shows that it has an absolute magnitude of M{sub V} = -8.5{sup +0.4}{sub -1.0} and half-light radius of r{sub h} = 210{sup +60}{sub -50} pc, similar to many other faint Local Group dwarfs. With presently available imaging we are unable to determine whether there is ongoing or recent star formation, which prevents us from classifying it as a dwarf spheroidal or a dwarf irregular.

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

    NARCIS (Netherlands)

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

    2015-01-01

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

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

    NARCIS (Netherlands)

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

    2015-01-01

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

  7. OBSERVATIONAL CONSTRAINTS ON THE MOLECULAR GAS CONTENT IN NEARBY STARBURST DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    McQuinn, Kristen B. W.; Skillman, Evan D. [Department of Astronomy, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States); Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F. [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Cannon, John M. [Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States); Holtzman, Jon, E-mail: kmcquinn@astro.umn.edu [Department of Astronomy, New Mexico State University, Box 30001, Department 4500, 1320 Frenger Street, Las Cruces, NM 88003 (United States)

    2012-06-01

    Using star formation histories derived from optically resolved stellar populations in 19 nearby starburst dwarf galaxies observed with the Hubble Space Telescope, we measure the stellar mass surface densities of stars newly formed in the bursts. By assuming a star formation efficiency (SFE), we then calculate the inferred gas surface densities present at the onset of the starbursts. Assuming an SFE of 1%, as is often assumed in normal star-forming galaxies, and assuming that the gas was purely atomic, translates to very high H I surface densities ({approx}10{sup 2}-10{sup 3} M{sub Sun} pc{sup -2}), which are much higher than have been observed in dwarf galaxies. This implies either higher values of SFE in these dwarf starburst galaxies or the presence of significant amounts of H{sub 2} in dwarfs (or both). Raising the assumed SFEs to 10% or greater (in line with observations of more massive starbursts associated with merging galaxies), still results in H I surface densities higher than observed in 10 galaxies. Thus, these observations appear to require that a significant fraction of the gas in these dwarf starbursts galaxies was in the molecular form at the onset of the bursts. Our results imply molecular gas column densities in the range 10{sup 19}-10{sup 21} cm{sup -2} for the sample. In the galaxies where CO observations have been made, these densities correspond to values of the CO-H{sub 2} conversion factor (X{sub CO}) in the range >(3-80) Multiplication-Sign 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -1}, or up to 40 Multiplication-Sign greater than Galactic X{sub CO} values.

  8. Dynamical masses and non-homology of massive elliptical galaxies grown by dry mergers

    Science.gov (United States)

    Frigo, M.; Balcells, M.

    2017-08-01

    We study whether dry merger-driven size growth of massive elliptical galaxies depends on their initial structural concentration, and analyse the validity of the homology hypothesis for virial mass determination in massive ellipticals grown by dry mergers. High-resolution simulations of a few realistic merger trees, starting with compact progenitors of different structural concentrations (Sérsic indices n), show that galaxy growth has little dependence on the initial Sérsic index (larger n leads to slightly larger size growth), and depends more on other particulars of the merger history. We show that the deposition of accreted matter in the outer parts leads to a systematic and predictable breaking of the homology between remnants and progenitors, which we characterize through the evolution, during the course of the merger history, of virial coefficients K≡ G M / R_e σ _e^2 associated with the most commonly used dynamical and stellar mass parameters. The virial coefficient for the luminous mass, K⋆, is ∼50 per cent larger at the start of the merger evolution at z ≈ 2 than in z = 0 remnants. Ignoring virial evolution leads to biased virial mass estimates. We provide K corresponding to a variety of dynamical and stellar mass parameters, and provide recipes for the dynamical determination of galaxy masses. For massive, non-compact ellipticals, the popular expression M = 5 R_e σ _e^2 / G underestimates the dynamical mass within the luminous body by factors of up to 4; it instead provides an approximation to the total stellar mass with smaller uncertainty than current stellar-population models.

  9. DRIVERS OF H I TURBULENCE IN DWARF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Stilp, Adrienne M.; Dalcanton, Julianne J. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Skillman, Evan [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Warren, Steven R. [Department of Astronomy, University of Maryland, CSS Building, Room 1024, Stadium Drive, College Park, MD 20742-2421 (United States); Ott, Juergen [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Koribalski, Baerbel [Australia Telescope National Facility, CSIRO Astronomy and Space Science, P.O. Box 76, Epping, NSW 1710 (Australia)

    2013-08-20

    Neutral hydrogen (H I) velocity dispersions are believed to be set by turbulence in the interstellar medium (ISM). Although turbulence is widely believed to be driven by star formation, recent studies have shown that this driving mechanism may not be dominant in regions of low star formation surface density ({Sigma}{sub SFR}), such those as found in dwarf galaxies or the outer regions of spirals. We have generated average H I line profiles in a number of nearby dwarfs and low-mass spirals by co-adding H I spectra in subregions with either a common radius or {Sigma}{sub SFR}. We find that the individual spatially resolved ''superprofiles'' are composed of a central narrow peak ({approx}5-15 km s{sup -1}) with higher velocity wings to either side, similar to their global counterparts as calculated for the galaxy as a whole. Under the assumption that the central peak reflects the H I turbulent velocity dispersion, we compare measures of H I kinematics determined from the superprofiles to local ISM properties, including surface mass densities and measures of star formation. The shape of the wings of the superprofiles do not show any correlation with local ISM properties, which indicates that they may be an intrinsic feature of H I line-of-sight spectra. On the other hand, the H I velocity dispersion is correlated most strongly with baryonic and H I surface mass density, which points toward a gravitational origin for turbulence, but it is unclear which, if any, gravitational instabilities are able to operate efficiently in these systems. Star formation energy is typically produced at a level sufficient to drive H I turbulent motions at realistic coupling efficiencies in regimes where {Sigma}{sub SFR} {approx}> 10{sup -4} M{sub Sun} yr{sup -1} kpc{sup -2}, as is typically found in inner spiral disks. At low star formation intensities, on the other hand, star formation cannot supply enough energy to drive the observed turbulence, nor does it uniquely

  10. The Nature of the Low-Metallicity ISM in the Dwarf Galaxy NGC 1569

    CERN Document Server

    Galliano, F; Jones, A P; Wilson, C D; Bernard, J P; Le Peintre, F

    2002-01-01

    We are modeling the spectra of dwarf galaxies from infrared to submillimeter wavelengths to understand the nature of the various dust components in low-metallicity environments, which may be comparable to the ISM of galaxies in their early evolutionary state. The overall nature of the dust in these environments appears to differ from those of higher metallicity starbursting systems. Here, we present a study of one of our sample of dwarf galaxies, NGC 1569, which is a nearby, well-studied starbursting dwarf. Using ISOCAM, IRAS, ISOPHOT and SCUBA data with the Desert et al. (1990) model, we find consistency with little contribution from PAHs and Very Small Grains and a relative abundance of bigger colder grains, which dominate the FIR and submillimeter wavelengths. We are compelled to use 4 dust components, adding a very cold dust component, to reproduce the submillimetre excess of our observations.

  11. Prolate rotation and metallicity gradient in the transforming dwarf galaxy Phoenix

    Science.gov (United States)

    Kacharov, Nikolay; Battaglia, Giuseppina; Rejkuba, Marina; Cole, Andrew A.; Carrera, Ricardo; Fraternali, Filippo; Wilkinson, Mark I.; Gallart, Carme G.; Irwin, Mike; Tolstoy, Eline

    2017-04-01

    Transition type dwarf galaxies are thought to be systems undergoing the process of transformation from a star-forming into a passively evolving dwarf, which makes them particularly suitable to study evolutionary processes driving the existence of different dwarf morphological types. Here we present results from a spectroscopic survey of ∼200 individual red giant branch stars in the Phoenix dwarf, the closest transition type with a comparable luminosity to 'classical' dwarf galaxies. We measure a systemic heliocentric velocity Vhelio = -21.2 ± 1.0 km s-1. Our survey reveals the clear presence of prolate rotation that is aligned with the peculiar spatial distribution of the youngest stars in Phoenix. We speculate that both features might have arisen from the same event, possibly an accretion of a smaller system. The evolved stellar population of Phoenix is relatively metal-poor ( = -1.49 ± 0.04 dex) and shows a large metallicity spread (σ[Fe/H] = 0.51 ± 0.04 dex), with a pronounced metallicity gradient of -0.13 ± 0.01 dex arcmin-1 similar to luminous, passive dwarf galaxies. We also report a discovery of an extremely metal-poor star candidate in Phoenix and discuss the importance of correcting for spatial sampling when interpreting the chemical properties of galaxies with metallicity gradients. This study presents a major leap forward in our knowledge of the internal kinematics of the Phoenix transition type dwarf galaxy and the first wide area spectroscopic survey of its metallicity properties. A table containing the measured velocities, metallicities, and CaT equivalent widths of all spectroscopic targets is available online at the CDS.

  12. Globular Clusters, Ultracompact Dwarfs, and Dwarf Galaxies in Abell 2744 at the Redshift of 0.308

    CERN Document Server

    Lee, Myung Gyoon

    2016-01-01

    We report a photometric study of globular clusters (GCs), ultracompact dwarfs (UCDs), and dwarf galaxies in the giant merging galaxy cluster Abell 2744 at z = 0.308. Color-magnitude diagrams of the point sources derived from deep F814W (restframe r') and F105W (restframe I) images of Abell 2744 in the Hubble Space Telescope Frontier Field show a rich population of point sources whose colors are similar to those of typical GCs. These sources are as bright as -14.9 < M_r' < -11.4 (26.0 < F814W < 29.5) mag, being mostly UCDs and bright GCs in Abell 2744. The luminosity function (LF) of these sources shows a break at M_r' ~ -12.9 (F814W ~ 28.0) mag, indicating a boundary between UCDs and bright GCs. The numbers of GCs and UCDs are estimated to be N_GC = 385,000+-24,000, and 147 +- 26, respectively. The clustercentric radial number density profiles of the UCDs and bright GCs show similar slopes, but these profiles are much steeper than that of the dwarf galaxies and the mass density profile based on gr...

  13. Implications for the origin of early-type dwarf galaxies - the discovery of rotation in isolated, low-mass early-type galaxies

    Science.gov (United States)

    Janz, Joachim; Penny, Samantha J.; Graham, Alister W.; Forbes, Duncan A.; Davies, Roger L.

    2017-07-01

    We present the discovery of rotation in quenched, low-mass early-type galaxies that are isolated. This finding challenges the claim that (all) rotating dwarf early-type galaxies in clusters were once spiral galaxies that have since been harassed and transformed into early-type galaxies. Our search of the Sloan Digital Sky Survey data within the Local Volume (z half-light radius Re in the best cases, and beyond Re/2 for all. They reveal a variety of behaviours similar to those of a comparison sample of early-type dwarf galaxies in the Virgo cluster observed by Toloba et al. Both samples have similar frequencies of slow and fast rotators, as well as kinematically decoupled cores. This, and especially the finding of rotating quenched low-mass galaxies in isolation, reveals that the early-type dwarfs in galaxy clusters need not be harassed or tidally stirred spiral galaxies.

  14. Massive blue early-type galaxies in the SDSS. I. A new population of recently quenched elliptical galaxies

    CERN Document Server

    McIntosh, Daniel H; Cooper, Andrew; Bell, Eric F; Keres, Dusan; Bosch, Frank C van den; Gallazzi, Anna; Haines, Tim; Mann, Justin; Pasquali, Anna; Christian, Allison M

    2013-01-01

    We use the SDSS to explore early-type galaxies (ETGs) that are plausibly in transition between the red sequence and the blue cloud. Through careful morphological inspection, we identify 1500 unusually blue elliptical galaxies among a larger sample of blue ETGs with 0.011e10 h^{-2} M_sun. Blue ellipticals comprise 3.7% of all ETGs with 1e1050% of the expected quiescent growth at z~0 assuming this phase lasts 0.5Gyr. Based on color, stellar M/L ratios and metallicity estimates, we argue that RQEs have recent SFHs that differ from rejuvenated ETGs. Yet, a significant but small incidence (5%) of RQEs with E+A spectra implies that the quenching of most RQEs did not involve a large starburst. Most (90%) RQEs reside at the centers of 3x10^{12}h^{-1} M_sun groups, which agrees well with the `small group scale' in which spiral merging onto the halo center is maximally efficient. The preferred RQE environment rules out satellite-specific quenching processes for most. Under the assumption that most RQEs were quenched by...

  15. Cores in dwarf galaxies from dark matter with a Yukawa potential.

    Science.gov (United States)

    Loeb, Abraham; Weiner, Neal

    2011-04-29

    We show that cold dark matter particles interacting through a Yukawa potential could naturally explain the recently observed cores in dwarf galaxies without affecting the dynamics of objects with a much larger velocity dispersion, such as clusters of galaxies. The velocity dependence of the associated cross section as well as the possible exothermic nature of the interaction alleviates earlier concerns about strongly interacting dark matter. Dark matter evaporation in low-mass objects might explain the observed deficit of satellite galaxies in the Milky Way halo and have important implications for the first galaxies and reionization.

  16. Understanding the internal dynamics of elliptical galaxies without non-baryonic dark matter

    CERN Document Server

    Dabringhausen, J; Famaey, B; Fellhauer, M

    2016-01-01

    Assuming virial equilibrium and Newtonian dynamics, low-mass early-type galaxies have larger velocity dispersions than expected from the amount of baryons they contain. The conventional interpretation of this finding is that their dynamics is dominated by non-baryonic matter. However, there is also strong evidence that many low-mass early-type galaxies formed as tidal dwarf galaxies, which would contain almost no dark matter. Using an extensive catalogue of early-type galaxies, we therefore discuss how the internal dynamics of early-type galaxies in general can be understood by replacing the assumption of non-baryonic dark matter with two alternative assumptions. The first assumption is that Milgromian dynamics (i.e., MOND) is valid, which changes the effective gravitational force in the weak-field limit. The second assumption is that binary stars affect the observed line-of-sight velocity dispersions. Some moderate discrepancies between observed and predicted velocity dispersions remain also when these effec...

  17. Gas-Bearing Early-Type Dwarf Galaxies in Virgo: Evidence for Recent Accretion

    CERN Document Server

    Hallenbeck, Gregory; Huang, Shan; Haynes, Martha P; Giovanelli, Riccardo; Boselli, Alessandro; Boissier, Samuel; Heinis, Sebastien; Cortese, Luca; Fabello, Silvia

    2012-01-01

    We investigate the dwarf (M_B> -16) galaxies in the Virgo cluster in the radio, optical, and ultraviolet regimes. Of the 365 galaxies in this sample, 80 have been detected in HI by the Arecibo Legacy Fast ALFA survey. These detections include 12 early-type dwarfs which have HI and stellar masses similar to the cluster dwarf irregulars and BCDs. In this sample of 12, half have star-formation properties similar to late type dwarfs, while the other half are quiescent like typical early-type dwarfs. We also discuss three possible mechanisms for their evolution: that they are infalling field galaxies that have been or are currently being evolved by the cluster, that they are stripped objects whose gas is recycled, and that the observed HI has been recently reaccreted. Evolution by the cluster adequately explains the star-forming half of the sample, but the quiescent class of early-type dwarfs is most consistent with having recently reaccreted their gas.

  18. A VLT/FORS2 spectroscopic survey of individual stars in a transforming dwarf galaxy

    CERN Document Server

    Battaglia, G; Rejkuba, M

    2016-01-01

    Understanding the properties of dwarf galaxies is important not only to put them in their proper cosmological context, but also to understand the formation and evolution of the most common type of galaxies. Dwarf galaxies are divided into two main classes, dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs), which differ from each other mainly because the former are gas-rich objects currently forming stars, while the latter are gas-deficient with no on-going star formation. Transition types (dT) are thought to represent dIs in the process of losing their gas, and can therefore shed light into the possible process of dwarf irregulars (dIrrs) becoming gas-deficient, passively evolving galaxies. Here we present preliminary results from our wide-area VLT/FORS2 MXU spectroscopic survey of the Phoenix dT, from which we obtained line-of-sight velocities and metallicities from the nIR Ca II triplet lines for a large sample of individual Red Giant Branch stars.

  19. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor

    CERN Document Server

    Frebel, Anna; Simon, Joshua D

    2009-01-01

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. Based on the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. However, verification of the iron-deficiency and measurements of additional elements, such as the alpha-element Mg, are mandatory for demonstrating that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming the iron abundance of less than 1/4000th that of the Sun, and showing that the overall abundance pattern mirrors th...

  20. Chemical Abundances of Seven Irregular and Three Tidal Dwarf Galaxies in the M81 Group

    CERN Document Server

    Croxall, Kevin V; Lee, Henry; Skillman, Evan D; Lee, Janice C; Côté, Stéphanie; Kennicutt, Robert C; Miller, Bryan W; 10.1088/0004-637X/705/1/723

    2009-01-01

    We have derived nebular abundances for 10 dwarf galaxies belonging to the M81 Group, including several galaxies which do not have abundances previously reported in the literature. For each galaxy, multiple H \\ii regions were observed with GMOS-N at the Gemini Observatory in order to determine abundances of several elements (oxygen, nitrogen, sulfur, neon, and argon). For seven galaxies, at least one H \\ii region had a detection of the temperature sensitive [OIII] $\\lambda$4363 line, allowing a "direct" determination of the oxygen abundance. No abundance gradients were detected in the targeted galaxies and the observed oxygen abundances are typically in agreement with the well known metallicity-luminosity relation. However, three candidate "tidal dwarf" galaxies lie well off this relation, UGC 5336, Garland, and KDG 61. The nature of these systems suggests that UGC 5336 and Garland are indeed recently formed systems, whereas KDG 61 is most likely a dwarf spheroidal galaxy which lies along the same line of sigh...