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The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster
The ACS Virgo Cluster Survey consists of HST ACS imaging for 100early-type galaxies in the Virgo Cluster, observed in the F475W (~SDSSg) and F850LP (~SDSS z) filters. We derive distances for 84 of thesegalaxies using the method of surface brightness fluctuations (SBFs),present the SBF distance catalog, and use this database to examine thethree-dimensional distribution of early-type galaxies in the VirgoCluster. The SBF distance moduli have a mean (random) measurement errorof 0.07 mag (0.5 Mpc), or roughly 3 times better than previous SBFmeasurements for Virgo Cluster galaxies. Five galaxies lie at a distanceof d~23 Mpc and are members of the W' cloud. The remaining 79 galaxieshave a narrow distribution around our adopted distance of=16.5+/-0.1 (random mean error) +/-1.1 Mpc (systematic). Therms distance scatter of this sample is σ(d)=0.6+/-0.1 Mpc, withlittle or no dependence on morphological type or luminosity class (i.e.,0.7+/-0.1 and 0.5+/-0.1 Mpc for the giants and dwarfs, respectively).The back-to-front depth of the cluster measured from our sample ofearly-type galaxies is 2.4+/-0.4 Mpc (i.e., +/-2 σ of theintrinsic distance distribution). The M87 (cluster A) and M49 (clusterB) subclusters are found to lie at distances of 16.7+/-0.2 and16.4+/-0.2 Mpc, respectively. There may be a third subcluster associatedwith M86. A weak correlation between velocity and line-of-sight distancemay be a faint echo of the cluster velocity distribution not having yetcompletely virialized. In three dimensions, Virgo's early-type galaxiesappear to define a slightly triaxial distribution, with axis ratios of(1:0.7:0.5). The principal axis of the best-fit ellipsoid is inclined~20°-40° from the line of sight, while the galaxies belonging tothe W' cloud lie on an axis inclined by ~10°-15°.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theassociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Optical/near-infrared colours of early-type galaxies and constraints on their star formation histories
We introduce and discuss the properties of a theoretical (B-K)(J-K)integrated colour diagram for single-age, single-metallicity stellarpopulations. We show how this combination of integrated colours is ableto largely disentangle the well-known age-metallicity degeneracy whenthe age of the population is greater than ~300Myr, and thus providesvaluable estimates of both age and metallicity of unresolved stellarsystems. We discuss in detail the effect on this colour-colour diagramof α-enhanced metal abundance ratios (typical of the oldestpopulations in the Galaxy), the presence of blue horizontal branch starsunaccounted for in the theoretical calibration and of statistical colourfluctuations in low-mass stellar systems. In the case of populationswith multiple stellar generations, the luminosity-weighted mean ageobtained from this diagram is shown to be heavily biased towards theyoungest stellar components. We then apply this method to several datasets for which optical and near-infrared photometry are available in theliterature. We find that Large Magellanic Cloud and M31 clusters havecolours which are consistent with the predictions of the models, butthese do not provide a sensitive test due to the fluctuations which arepredicted by our modelling of the Poisson statistics in such low-masssystems. For the two Local Group dwarf galaxies NGC 185 and 6822, themean ages derived from the integrated colours are consistent with thestar formation histories inferred independently from photometricobservations of their resolved stellar populations.The methods developed here are applied to samples of nearby early-typegalaxies with high-quality aperture photometry in the literature. Asample of bright field and Virgo cluster elliptical galaxies is found toexhibit a range of luminosity-weighted mean ages from 3 to 14Gyr, with amean of ~8Gyr, independent of environment, and mean metallicities at orjust above the solar value. Colour gradients are found in all of thegalaxies studied, in the sense that central regions are redder. Apartfrom two radio galaxies, where the extreme central colours are clearlydriven by the active galactic nucleus, and one galaxy which also shows aradial age gradient, these colour changes appear consistent withmetallicity changes at a constant mean age. Finally, aperture data forfive Virgo early-type dwarf galaxies show that these galaxies appear tobe shifted to lower mean metallicities and lower mean ages (range1-6Gyr) than their higher luminosity counterparts.
| The ACS Virgo Cluster Survey. VIII. The Nuclei of Early-Type Galaxies
The ACS Virgo Cluster Survey is a Hubble Space Telescope program toobtain high-resolution imaging in widely separated bandpasses (F475W~gand F850LP~z) for 100 early-type members of the Virgo Cluster, spanninga range of ~460 in blue luminosity. We use this large, homogenous dataset to examine the innermost structure of these galaxies and tocharacterize the properties of their compact central nuclei. We presenta sharp upward revision in the frequency of nucleation in early-typegalaxies brighter than MB~-15 (66%<~fn<~82%)and show that ground-based surveys underestimated the number of nucleidue to surface brightness selection effects, limited sensitivity andpoor spatial resolution. We speculate that previously reported claimsthat nucleated dwarfs are more concentrated toward the center of Virgothan their nonnucleated counterparts may be an artifact of theseselection effects. There is no clear evidence from the properties of thenuclei, or from the overall incidence of nucleation, for a change atMB~-17.6, the traditional dividing point between dwarf andgiant galaxies. There does, however, appear to be a fundamentaltransition at MB~-20.5, in the sense that the brighter,``core-Sérsic'' galaxies lack resolved (stellar) nuclei. A searchfor nuclei that may be offset from the photocenters of their hostgalaxies reveals only five candidates with displacements of more than0.5", all of which are in dwarf galaxies. In each case, however, theevidence suggests that these ``nuclei'' are, in fact, globular clustersprojected close to the galaxy photocenter. Working from a sample of 51galaxies with prominent nuclei, we find a median half-light radius of=4.2 pc, with the sizes of individual nucleiranging from 62 pc down to <=2 pc (i.e., unresolved in our images) inabout a half-dozen cases. Excluding these unresolved objects, the nucleisizes are found to depend on nuclear luminosity according to therelation rh L0.50+/-0.03. Because the largemajority of nuclei are resolved, we can rule out low-level AGNs as anexplanation for the central luminosity excess in almost all cases. Onaverage, the nuclei are ~3.5 mag brighter than a typical globularcluster. Based on their broadband colors, the nuclei appear to have oldto intermediate age stellar populations. The colors of the nuclei ingalaxies fainter than MB~-17.6 are tightly correlated withtheir luminosities, and less so with the luminosities of their hostgalaxies, suggesting that their chemical enrichment histories weregoverned by local or internal factors. Comparing the nuclei to the``nuclear clusters'' found in late-type spiral galaxies reveals a closematch in terms of size, luminosity, and overall frequency. A formationmechanism that is rather insensitive to the detailed properties of thehost galaxy properties is required to explain this ubiquity andhomogeneity. The mean of the frequency function for thenucleus-to-galaxy luminosity ratio in our nucleated galaxies,=-2.49+/-0.09 dex (σ=0.59+/-0.10), isindistinguishable from that of the SBH-to-bulge mass ratio,=-2.61+/-0.07dex (σ=0.45+/-0.09), calculated in 23 early-type galaxies withdetected supermassive black holes (SBHs). We argue that the compactstellar nuclei found in many of our program galaxies are the low-masscounterparts of the SBHs detected in the bright galaxies. If thisinterpretation is correct, then one should think in terms of ``centralmassive objects''-either SBHs or compact stellar nuclei-that accompanythe formation of almost all early-type galaxies and contain a meanfraction ~0.3% of the total bulge mass. In this view, SBHs would be thedominant formation mode above MB~-20.5.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
| Globular Clusters in Virgo Ellipticals: Unexpected Results for Giants and Dwarfs from Advanced Camera for Surveys Imaging
We have analyzed archival Hubble Space Telescope Advanced Camera forSurveys images in g and z of the globular cluster (GC) systems of 53ellipticals in the Virgo Cluster, spanning massive galaxies to dwarfellipticals (dEs). Several new results emerged. (1) In the giantellipticals (gEs) M87 and NGC 4649, there is a correlation betweenluminosity and color for individual blue (metal-poor) GCs, such thatmore massive GCs are more red (metal-rich). A plausible interpretationof this result is self-enrichment, and a speculative suggestion is thatthese GCs once possessed dark matter halos. (2) The dispersion in coloris nearly twice as large for the metal-rich GCs as for the metal-poorGCs. However, there is evidence for a nonlinear relation between g-z andmetallicity, and the dispersion in metallicity may be the same for bothsubpopulations. (3) Very luminous, intermediate-color GCs are common ingEs. These objects may be remnants of many stripped dwarfs, analogs ofω Cen in the Galaxy. (4) There is a continuity of GC system colorsfrom gEs to some dEs; in particular, many dEs have metal-rich GCsubpopulations. We also confirm the GC color-galaxy luminosity relationsfound previously for both metal-poor and metal-rich GC subpopulations.(5) There are large differences in GC specific frequency among dEs,independent of the presence of a nucleus and the fraction of metal-richGCs. Over -15
| A Search for Low Surface Brightness Structure around Compact Narrow Emission Line Galaxies
As the most extreme members of the rapidly evolving faint blue galaxypopulation at intermediate redshift, the compact narrow emission linegalaxies (CNELGs) are intrinsically luminous(-22<~MB<~-18) with narrow emission line widths (30 kms-1<~σ<~125 km s-1). Their nature isheavily debated: they may be low-mass starbursting galaxies that willfade to present-day dwarf galaxies or bursts of star formationtemporarily dominating the flux of more massive galaxies, possiblyrelated to in situ bulge formation or the formation of cores ofgalaxies. We present deep, high-quality (~0.6"-0.8") images with CFHT of27 CNELGs. One galaxy shows clear evidence for a tidal tail; the othersare not unambiguously embedded in galactic disks. Approximately 55% ofthe CNELGs have sizes consistent with local dwarfs of small tointermediate sizes, while 45% have sizes consistent with large dwarfs ordisk galaxies. At least four CNELGs cannot harbor substantial underlyingdisk material; they are low-luminosity galaxies at the present epoch(MB>-18). Conversely, 15 are not blue enough to fade tolow-luminosity dwarfs (MB>-15.2). The majority of theCNELGs are consistent with progenitors of intermediate-luminosity dwarfsand low-luminosity spiral galaxies with small disks. CNELGs are aheterogeneous progenitor population with significant fractions (up to44%) capable of fading into today's faint dwarfs(MB>-15.2), while 15%-85% may only experience anapparently extremely compact CNELG phase at intermediate redshift butremain more luminous galaxies at the present epoch.Based on observations obtained at the Canada-France-Hawaii Telescope,which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France, and the University of Hawaii.
| The ACS Virgo Cluster Survey. IX. The Color Distributions of Globular Cluster Systems in Early-Type Galaxies
We present the color distributions of globular cluster (GC) systems for100 early-type galaxies observed in the ACS Virgo Cluster Survey, thedeepest and most homogeneous survey of this kind to date. On average,galaxies at all luminosities in our study (-22
| The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation
We have measured half-light radii, rh, for thousands ofglobular clusters (GCs) belonging to the 100 early-type galaxiesobserved in the ACS Virgo Cluster Survey and the elliptical galaxy NGC4697. An analysis of the dependencies of the measured half-light radiion both the properties of the GCs themselves and their host galaxiesreveals that, in analogy with GCs in the Galaxy but in a milder fashion,the average half-light radius increases with increasing galactocentricdistance or, alternatively, with decreasing galaxy surface brightness.For the first time, we find that the average half-light radius decreaseswith the host galaxy color. We also show that there is no evidence for avariation of rh with the luminosity of the GCs. Finally, wefind in agreement with previous observations that the averagerh depends on the color of GCs, with red GCs being ~17%smaller than their blue counterparts. We show that this difference isprobably a consequence of an intrinsic mechanism, rather than projectioneffects, and that it is in good agreement with the mechanism proposed byJordán. We discuss these findings in light of two simple picturesfor the origin of the rh of GCs and show that both lead to abehavior in rough agreement with the observations. After accounting forthe dependencies on galaxy color, galactocentric radius, and underlyingsurface brightness, we show that the average GC half-light radii can be successfully used as a standard ruler fordistance estimation. We outline the methodology, provide a calibrationfor its use, and discuss the prospects for this distance estimator withfuture observing facilities. We find =2.7+/-0.35 pcfor GCs with (g-z)=1.2 mag in a galaxy with color(g-z)gal=1.5 mag and at an underlying surface z-bandbrightness of μz=21 mag arcsec-2. Using thistechnique, we place an upper limit of 3.4 Mpc on the 1 σline-of-sight depth of the Virgo Cluster. Finally, we examine the formof the rh distribution for our sample galaxies and provide ananalytic expression that successfully describes this distribution.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| A Comparison of Surface Brightness Profiles for Ultracompact Dwarfs and Dwarf Elliptical Nuclei: Implications for the ``Threshing'' Scenario
Using imaging from the Hubble Space Telescope, we derive surfacebrightness profiles for ultracompact dwarfs in the Fornax Cluster andfor the nuclei of dwarf elliptical galaxies in the Virgo Cluster.Ultracompact dwarfs are more extended and have higher surfacebrightnesses than typical dwarf nuclei, while the luminosities, colors,and sizes of the nuclei are closer to those of Galactic globularclusters. This calls into question the production of ultracompact dwarfsvia ``threshing,'' whereby the lower surface brightness envelope of adwarf elliptical galaxy is removed by tidal processes, leaving behind abare nucleus. Threshing may still be a viable model if the relativelybright Fornax ultracompact dwarfs considered here are descended fromdwarf elliptical galaxies whose nuclei are at the upper end of theirluminosity and size distributions.
| The structure of elliptical galaxies in the Virgo cluster. Results from the INT Wide Field Survey
We report on a complete CCD imaging survey of 226 elliptical galaxies inthe North-East quadrant of the Virgo cluster, representative of theproperties of giant and dwarf elliptical galaxies in this cluster. Wefit their radial light profiles with the Sersic r1/n model oflight distribution. We confirm the result of Graham & Guzman(\cite{Graham03}, AJ, 125, 2936) that the apparent dichotomy between Eand dE galaxies in the luminosity-< μ>e plane nolonger appears when other structural parameters are considered and canbe entirely attributed to the onset of ``core'' galaxies atBT -20.5 mag. When ``core'' galaxies are notconsidered, E and dE form a unique family with n linearly increasingwith the luminosity. For 90 galaxies we analyze the B-I color indices,both in the nuclear and in the outer regions. Both indices are bluertoward fainter luminosities. We find also that the outer color gradientsdo not show any significant correlation with the luminosity. The scatterin all color indicators increases significantly toward lowerluminosities, e.g. galaxies fainter than BT -15 have aB-I spread > 0.5 mag.Table 2, Figs. 13 and 14 are only available in electronic form athttp://www.edpsciences.org
| The ACS Virgo Cluster Survey. II. Data Reduction Procedures
The ACS Virgo Cluster Survey is a large program to carry out multicolorimaging of 100 early-type members of the Virgo Cluster using theAdvanced Camera for Surveys (ACS) on the Hubble Space Telescope. DeepF475W and F850LP images (~SDSS g and z) are being used to study thecentral regions of the program galaxies, their globular cluster systems,and the three-dimensional structure of Virgo itself. In this paper, wedescribe in detail the data reduction procedures used for the survey,including image registration, drizzling strategies, the computation ofweight images, object detection, the identification of globular clustercandidates, and the measurement of their photometric and structuralparameters.Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The ACS Virgo Cluster Survey. I. Introduction to the Survey
The Virgo Cluster is the dominant mass concentration in the LocalSupercluster and the largest collection of elliptical and lenticulargalaxies in the nearby universe. In this paper, we present anintroduction to the ACS Virgo Cluster Survey: a program to image, in theF475W and F850LP bandpasses (~Sloan g and z), 100 early-type galaxies inthe Virgo Cluster using the Advanced Camera for Surveys on the HubbleSpace Telescope. We describe the selection of the program galaxies andtheir ensemble properties, the choice of filters, the field placementand orientation, the limiting magnitudes of the survey, coordinatedparallel observations of 100 ``intergalactic'' fields with WFPC2, andsupporting ground-based spectroscopic observations of the programgalaxies. In terms of depth, spatial resolution, sample size, andhomogeneity, this represents the most comprehensive imaging survey todate of early-type galaxies in a cluster environment. We brieflydescribe the main scientific goals of the survey, which include themeasurement of luminosities, metallicities, ages, and structuralparameters for the many thousands of globular clusters associated withthese galaxies, a high-resolution isophotal analysis of galaxiesspanning a factor of ~450 in luminosity and sharing a commonenvironment, the measurement of accurate distances for the full sampleof galaxies using the method of surface brightness fluctuations, and adetermination of the three-dimensional structure of Virgo itself.ID="FN1"> 1Based on observations with the NASA/ESA Hubble SpaceTelescope obtained at the Space Telescope Science Institute, which isoperated by the association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
| Stellar Populations of Dwarf Elliptical Galaxies: UBVRI Photometry of Dwarf Elliptical Galaxies in the Virgo Cluster
We present UBVRI surface photometry for 16 dwarf elliptical galaxies inthe Virgo Cluster with previously measured kinematic properties. Theglobal optical colors are red, with median values for the sample of0.24+/-0.03 in U-B, 0.77+/-0.02 in B-V, and 1.02+/-0.03 in V-I. Werecover the well-known color-magnitude relation for cluster galaxies butfind no significant difference in dominant stellar population betweenrotating and nonrotating dwarf elliptical galaxies; the average age ofthe dominant stellar population is 5-7 Gyr in all 16 galaxies in thissample. Analysis of optical spectra confirm these age estimates andindicate Fe and Mg abundances in the range of 1/20 to one-third ofsolar, as expected for low-luminosity galaxies. Based on Lick indicesand simple stellar population models, the derived [α/Fe] ratiosare subsolar to solar, indicating a more gradual chemical enrichmenthistory for dE's as compared with giant elliptical galaxies in the VirgoCluster. These observations confirm the marked difference in stellarpopulation and stellar distribution between dwarf and giant ellipticalgalaxies and further substantiate the need for alternative evolutionaryscenarios for the lowest mass cluster galaxies. We argue that it islikely that several different physical mechanisms played a significantrole in the production of the Virgo Cluster dE galaxies including insitu formation, infall of dE's that were once part of Local Groupanalogs, and transformation of dwarf irregular galaxies by the clusterenvironment. The observations support the hypothesis that a largefraction of the Virgo Cluster dE's are formed by ram pressure strippingof gas from infalling dI's.Based on observations with the VATT: the Alice P. Lennon Telescope andthe Thomas J. Bannan Astrophysics Facility.
| Rotationally Supported Virgo Cluster Dwarf Elliptical Galaxies: Stripped Dwarf Irregular Galaxies?
New observations of 16 dwarf elliptical galaxies (dEs) in the VirgoCluster indicate that at least seven dEs have significant velocitygradients along their optical major axis, with typical rotationamplitudes of 20-30 km s-1. Of the remaining nine galaxies inthis sample, six have velocity gradients of less than 20 kms-1 kpc-1, while the other three observations hadtoo low a signal-to-noise ratio to determine an accurate velocitygradient. Typical velocity dispersions for these galaxies are ~44+/-5 kms-1, indicating that rotation can be a significant componentof the stellar dynamics of Virgo dEs. When corrected for the limitedspatial extent of the spectral data, the rotation amplitudes of therotating dEs are comparable to those of similar-brightness dwarfirregular galaxies (dIs). Evidence of a relationship between therotation amplitude and galaxy luminosity is found and, in fact, agreeswell with the Tully-Fisher relation. The similarity in the scalingrelations of dIs and dEs implies that it is unlikely that dEs evolvefrom significantly more luminous galaxies. These observations reaffirmthe possibility that some cluster dEs may be formed when the neutralgaseous medium is stripped from dIs in the cluster environment. Wehypothesize that several different mechanisms are involved in thecreation of the overall population of dEs and that stripping ofinfalling dIs may be the dominant process in the creation of dEs inclusters like Virgo.
| Radio continuum spectra of galaxies in the Virgo cluster region
New radio continuum observations of galaxies in the Virgo cluster regionat 4.85, 8.6, and 10.55 GHz are presented. These observations arecombined with existing measurements at 1.4 and 0.325 GHz. The sampleincludes 81 galaxies where spectra with more than two frequencies couldbe derived. Galaxies that show a radio-FIR excess exhibit centralactivity (HII, LINER, AGN). The four Virgo galaxies with the highestabsolute radio excess are found within 2° of the centerof the cluster. Galaxies showing flat radio spectra also host activecenters. There is no clear trend between the spectral index and thegalaxy's distance to the cluster center.Figure 3 is only available in electronic form athttp://www.edpsciences.orgTable 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1
| Galaxy Populations and Evolution in Clusters. IV. Deep H I Observations of Dwarf Elliptical Galaxies in the Virgo Cluster
In this paper we present deep Arecibo H I and WIYN optical observationsof Virgo Cluster dwarf elliptical galaxies. Based on this data we arguethat a significant fraction of low-mass galaxies in the Virgo Clusterrecently underwent evolution. Our new observations consist of H I 21 cmline observations for 22 classified dE galaxies with optical radialvelocities consistent with membership in the Virgo Cluster. Clustermembers VCC 390 and VCC 1713 are detected with H I massesMHI=6×107 and 8×107Msolar, respectively, while MHI values in theremaining 20 dE galaxies have upper limits as low as~5×105 Msolar. We combine our results withthose for 26 other Virgo Cluster dE galaxies with H I observations inthe literature, seven of which have H I detection claims. New opticalimages from the WIYN telescope of five of these H I-detected dEgalaxies, along with archival data, suggest that seven of the claimeddetections are true H I detections, yielding a ~15% detection rate.These H I-detected, classified dE galaxies are preferentially locatednear the periphery of the Virgo Cluster. Three Virgo dE galaxies haveobserved H I velocity widths greater than 200 km s-1,possibly indicating the presence of a large dark matter content ortransient extended H I. We discuss the possible origins of these objectsand argue that they originate from field galaxies accreted onto highangular momentum orbits by Virgo in the last few Gyr. As a result ofthis, we argue, these galaxies are slowly transformed within the clusterby gradual gas-stripping processes, associated truncation of starformation, and passive fading of stellar populations. Low-mass,early-type cluster galaxies are therefore currently being produced asthe product of cluster environmental effects. We utilize our results ina simple model to estimate the recent (past 1-3 Gyr) average massaccretion rate into the Virgo Cluster, deriving a value of M~50Msolar yr-1.
| A search for Low Surface Brightness galaxies in the near-infrared. I. Selection of the sample
A sample of about 3800 Low Surface Brightness (LSB) galaxies wasselected using the all-sky near-infrared (J, H and Ks-band)2MASS survey. The selected objects have a mean central surfacebrightness within a 5'' radius around their centre fainter than 18 magarcsec-2 in the Ks band, making them the lowestsurface brightness galaxies detected by 2MASS. A description is given ofthe relevant properties of the 2MASS survey and the LSB galaxy selectionprocedure, as well as of basic photometric properties of the selectedobjects. The latter properties are compared to those of other samples ofgalaxies, of both LSBs and ``classical'' high surface brightness (HSB)objects, which were selected in the optical. The 2MASS LSBs have aBT_c-KT colour which is on average 0.9 mag bluerthan that of HSBs from the NGC. The 2MASS sample does not appear tocontain a significant population of red objects.All tables and Figs. 2a-c are only available in electronic form athttp://www.edpsciences.org
| The luminosity function of the Virgo Cluster from MB=-22 to -11
We measure the galaxy luminosity function (LF) for the Virgo Clusterbetween blue magnitudes MB=-22 and -11 from wide-fieldcharge-coupled device (CCD) imaging data. The LF is only graduallyrising for -22
| Galaxy Populations and Evolution in Clusters. I. Dynamics and the Origin of Low-Mass Galaxies in the Virgo Cluster
Early-type dwarfs are the most common galaxy in the local universe, yettheir origin and evolution remain a mystery. Various cosmologicalscenarios predict that dwarf-like galaxies in dense areas are the firstto form and hence should be the oldest stellar systems in clusters. Byusing radial velocities of early-type dwarfs in the Virgo cluster wedemonstrate that these galaxies are not an old cluster population buthave signatures of production from the infall of field galaxies.Evidence of this includes the combined large dispersions andsubstructure in spatial and kinematic distributions for Virgo early-typedwarfs and a velocity dispersion ratio with giant ellipticals expectedfor virialized and accreted populations. We also argue that thesegalaxies cannot originate from accreted field dwarfs, but must havephysically evolved from a precursor population, of different morphology,that fell into Virgo some time in the past.
| 1.65 μm (H-band) surface photometry of galaxies. VII. Dwarf galaxies in the Virgo Cluster
We present near-infrared H-band (1.65 μm) observations and surfacebrightness profile decompositions for 75 faint (13.5 <~ mp<~ 18.5) galaxies, primarily taken among dwarf Ellipticals members ofthe Virgo cluster, with some Centaurus Cluster members, a BCD and twopeculiar galaxies taken as fillers. We model their surface brightnessprofiles with a de Vaucouleurs (D), exponential (E), mixed (bulge+diskor M) or truncated (T) law, and we derive for each galaxy the H bandeffective surface brightness (μe) and effective radius(re), the asymptotic total magnitude HT and thelight concentration index C31, defined as the ratio betweenthe radii that enclose 75% and 25% of the total light HT. Fora subsample we compare the NIR surface photometry with similar datataken in the B and V bands, and we give the B-H and B-V color profiles.Combining the present data with those previously obtained by our group(1157 objects) we analyze the NIR properties of a nearly completesample, representative of galaxies of all morphological types, spanning4 decades in luminosity. We confirm our earlier claim that the presenceof cusps and extended haloes in the light profiles (C31>5)is a strong, non-linear function of the total luminosity. We also findthat: i) among dE and dS0 galaxies D profiles are absent; 50% of thedecompositions are of type M, the remaining being of type E or T. ii)Less than 50% of the giant elliptical galaxies have pure D profiles, themajority being represented by M profiles. iii) Most giant galaxies (fromelliptical to Sb) have M profiles. iv) Most of late type spirals (Scd toBCD) have either E or T profiles. v) The type of decomposition is astrong function of the total H band luminosity, independent of theHubble classification: the fraction of type E decompositions decreaseswith increasing luminosity, while those of type M increase withluminosity. Pure D profiles are absent in the low luminosity rangeLH<1010 Lsolar and become dominantabove 1011 Lsolar, while T profiles are presentonly among low luminosity galaxies. vi) We find that dE-peculiargalaxies have structural parameters indistinguishable from those oflate-type dwarfs, thus they might represent the missing link between dEsand dIs. Based on observations taken with the ESO/NTT (ESO program64.N-0288), with the Telescopio Nazionale Galileo (TNG) operated on theisland of La Palma by the Centro Galileo Galilei of the CNAA at theSpanish Observatorio del Roque de los Muchachos of the IAC, with the SanPedro Martir 2.1~m telescope of the Observatorio Astronomico Nacional(OAN, Mexico), and with the OHP 1.2~m telescope, operated by the FrenchCNRS.
| On the local radio luminosity function of galaxies. I. The Virgo cluster
We cross-correlate the galaxies brighter than m_B=18 in the Virgocluster with the radio sources in the NVSS survey (1.4 GHz), resultingin 180 radio-optical identifications. We determine the radio luminosityfunction of the Virgo galaxies, separately for the early- andlate-types. Late-type galaxies develop radio sources with a probabilityproportional to their optical luminosity. In fact their radio/optical(R_B) distribution is gaussian, centered at log R_B ~ -0.5, i.e. theradio luminosity is ~ 0.3 of the optical one. The probability oflate-type galaxies to develop radio sources is almost independent oftheir detailed Hubble type, except for Sa (and S0+S0a) which are afactor of ~ 5 less frequent than later types at any R_B. Giantelliptical galaxies feed ``monster" radio sources with a probabilitystrongly increasing with mass. However the frequency of fainter radiosources is progressively less sensitive on the system mass. The faintestgiant E galaxies (M_B=-17) have a probability of feeding low power radiosources similar to that of dwarf E galaxies as faint as M_B=-13. Table~1is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Studies of the Virgo Cluster. II - A catalog of 2096 galaxies in the Virgo Cluster area.
The present catalog of 2096 galaxies within an area of about 140 sq degapproximately centered on the Virgo cluster should be an essentiallycomplete listing of all certain and possible cluster members,independent of morphological type. Cluster membership is essentiallydecided by galaxy morphology; for giants and the rare class of highsurface brightness dwarfs, membership rests on velocity data. While 1277of the catalog entries are considered members of the Virgo cluster, 574are possible members and 245 appear to be background Zwicky galaxies.Major-to-minor axis ratios are given for all galaxies brighter than B(T)= 18, as well as for many fainter ones.
| Uppsala General Catalogue of Galaxies. Data for 12,921 galaxies north of delta =-2 30.
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