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 Virgo Cluster Early-Type Dwarf Galaxies with the Sloan Digital Sky Survey. I. On the Possible Disk Nature of Bright Early-Type DwarfsWe present a systematic search for disk features in 476 Virgo Clusterearly-type dwarf (dE) galaxies. This is the first such study of analmost-complete, statistically significant dE sample, which includes allcertain or possible cluster members with mB<=18 that arecovered by the optical imaging data of the Sloan Digital Sky Survey DataRelease 4. Disk features (spiral arms, edge-on disks, or bars) wereidentified by applying unsharp masks to a combined image from threebands (g, r, and i), as well as by subtracting the axisymmetric lightdistribution of each galaxy from that image. Fourteen objects areunambiguous identifications of disks, 10 objects show probable disk''features, and 17 objects show possible disk'' features. The numberfraction of these galaxies, for which we introduce the term dEdi,''reaches more than 50% at the bright end of the dE population anddecreases to less than 5% for magnitudes mB>16. Althoughpart of this observed decline might be due to the lower signal-to-noiseratio at fainter magnitudes, we show that it cannot be caused solely bythe limitations of our detection method. The luminosity function of ourfull dE sample can be explained by a superposition of dEdis and ordinarydEs, strongly suggesting that dEdis are a distinct type of galaxy. Thisis supported by the projected spatial distribution: dEdis show basicallyno clustering and roughly follow the spatial distribution of spirals andirregulars, whereas ordinary dEs are distributed similarly to thestrongly clustered E/S0 galaxies. While the flattening distribution ofordinary dEs is typical for spheroidal objects, the distribution ofdEdis is significantly different and agrees with their being flat oblateobjects. We therefore conclude that the dEdis are not spheroidalgalaxies that just have an embedded disk component but are instead apopulation of genuine disk galaxies. Several dEdis display well-definedspiral arms with grand-design features that clearly differ from theflocculent, open arms typical for late-type spirals that have frequentlybeen proposed as progenitors of dEs. This raises the question of whatprocess is able to create such spiral arms-with pitch angles like thoseof Sab/Sb galaxies-in bulgeless dwarf galaxies. Distances, Metallicities, and Ages of Dwarf Elliptical Galaxies in the Virgo Cluster from Surface Brightness FluctuationsWe have employed FORS1 and 2 at the Very Large Telescope at the EuropeanSouthern Observatory (ESO) to acquire deep B and R-band CCD images of 16dwarf elliptical (dE) galaxies in the direction of the Virgo cluster.For each dwarf, we measure the apparent R-band surface brightnessfluctuation (SBF) magnitude mR and the (B-R)0color in a number of fields at different galactocentric distances. Fromthe field-to-field variation of the two quantities, we determine the SBFdistance by means of the (B-R)0-MR relation. Thederived distances of the dwarfs range from 14.9 to 21.3 Mpc, with a mean1 σ uncertainty of 1.4 Mpc or 8% of the distance, which confirmsthat there is considerable depth in the distance distribution ofearly-type cluster members. For VCC 1104 (IC 3388), our SBF distancemodulus of (m-M)SBF=31.15+/-0.19 (17.0+/-1.5 Mpc) is in goodagreement with the Harris et al result of(m-M)TRGB=30.98+/-0.19 mag (15.7+/-1.5 Mpc) based on HubbleSpace Telescope (HST) observations and the tip magnitude of the redgiant branch. Combining our results with existing distances for giantVirgo ellipticals, we identify two major galaxy concentrations in thedistance distribution: a broad primary clump around (M-m)=31.0 mag (15.8Mpc) and a narrow secondary clump around 31.33 mag (18.5 Mpc). Anadaptive kernel analysis finds the two concentrations to be significantat the 99% (2.5 σ) and 89% (1.6 σ) levels, respectively.While the near-side clump of Virgo early-type galaxies can be associatedwith the subcluster centered on M87, the second clump is believed to bemainly due to the far side infalling group of galaxies around M86. Theages and metallicities of the dE stellar populations are estimated bycombining the observed (B-R)0 colors with Worthey's stellarpopulation synthesis models. It appears that the Virgo dE galaxies covera wider range in metallicity, from [Fe/H]~-1.4 (VCC 0815) to -0.5 (NGC4415), than Fornax cluster dEs. The derived metallicities place theVirgo dEs on the extension of the metallicity-luminosity relationdefined by the low-luminosity Local Group dEs. The data further suggestan age range from genuinely old (~17 Gyr) stellar systems such as IC3019 and IC 0783 to intermediate-age (8-12 Gyr) dwarfs such as NGC 4431and IC 3468. VLT surface photometry and isophotal analysis of early-type dwarf galaxies in the Virgo clusterWe have carried out surface photometry and an isophotal analysis for asample of 25 early-type dwarf (dE and dS0) galaxies in the Virgo clusterbased on CCD images taken at the VLT with FORS1 and FORS2. For eachgalaxy we present B and R-band surface brightness profiles, as well asthe radial colour (B-R) profile. We give total apparent BR magnitudes,effective radii, effective surface brightnesses and total colourindices. The light profiles have been fitted with Sérsic modelsand the corresponding parameters are compared to the ones for otherclasses of objects. In general, dEs and dS0s bridge the gap in parameterspace between the giant ellipticals and the low-luminosity dwarfspheroidals in the Local Group, in accordance with previous findings.However, the observed profiles of the brightest cluster dwarfs showsignificant deviations from a simple Sérsic model, indicatingthat there is more inner structure than just a nucleus. This picture isreinforced by our isophotal analysis where complex radial dependenciesof ellipticity, position angle, and isophotal shape parameter a_4 areexhibited not only by objects like IC 3328, for which the presence of adisk component has been confirmed, but by many apparently normal dEs aswell. In addition, we find a relation between the effective surfacebrightness, at a given luminosity, and the strength of the offset of thegalaxy's nucleus with respect to the center of the isophotes. Dwarfswith large nuclear offsets also tend to have stronger isophotal twists.However, such twists are preferentially found in apparently round(epsilon < 0.3) galaxies and are always accompanied by significantradial changes of the ellipticity, which clearly points to a projectioneffect. In sum, our findings suggest the presence of substructure inmost, and preferentially in the less compact, bright early-type dwarfs.The physical (dynamical) meaning of this has yet to be explored.Based on observations collected at the European Southern Observatory(ESO 63.O-0055 and 65.N-0062).Figure \ref{fig1} is only available in electronic form athttp://www.edpsciences.org Galaxy Populations and Evolution in Clusters. I. Dynamics and the Origin of Low-Mass Galaxies in the Virgo ClusterEarly-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. Total magnitude, radius, colour indices, colour gradients and photometric type of galaxiesWe present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory. 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. Distances to 64 Virgo dwarf-elliptical galaxies and the depth in their spatial distributionWe derive distances for 64 dwarf ellipticals (dEs) in the direction ofthe Virgo cluster's (VC) core, by means of the luminosity-profilecurvature (L-n) relationship and by means of their global scalelengths,which we find to be correlated with the shapes of theirsurface-brightness profiles. The great depth we find in the spatialdistribution of Virgo dEs is not consistent with a unimodal distributiondue to a single spherically symmetric concentration of galaxies. Thisdepth is also sufficient to explain much of the disagreement over theVC's distance, and thereby much of the Hubble-constant (H_0)controversy. The surface brightness test for the expansion of the universe. II - Radii, surface brightness, and absolute magnitude correlations for nearby E galaxiesData for elliptical galaxies in the Virgo, Fornax, and Coma clusters andin the general field are analyzed in order to determine the dispersionin average surface brightness. The data are discussed using measures ofboth the effective radius and the Petrosian r(eta) radii. The dispersionis found to be about 0.5 mag after reducing the data to absolutemagnitude M(B) = -22. This value is smaller than the 1.8 mag Tolman (1 +z) exp 4 factor, even at the modest redshift of z = 0.5, showing thatthe Tolman test is feasible in practice as well as in principle. Surface photometry of dwarf elliptical galaxies in the Virgo clusterPhotographic surface photometry is carried out for 69 dwarf ellipticalsin the central region of the Virgo Cluster, using two plates in the Bband taken with the 2.5 m du Pont telescope at Las Campanas Observatory.Luminosity profiles and various photometric parameters are obtained, andthe following three results are derived: (1) All the dwarf ellipticalsin the sample have luminosity profiles consistent with exponential lawsexcept for six galaxies which are probably giant ellipticals in thebackground. If they are physcial members of the Virgo Cluster, they maybe identified with 'classical' dwarf ellipticals recognized by Wirth andGallagher. (2) The distribution of apparent flattenings of dwarfellipticals suggests that the population of dwarf ellipticals is notdominated by flat disk systems like spiral galaxies, in spite of theirexponential profiles. (3) Two important diagrams, a diagram ofconcentration index versus absolute magnitude and a diameter versussurface brightness diagram (DSBD), show a hint of structuraldiscontinuity in the sequence of spheroidal stellar systems consistingof giant ellilpticals, dwarf ellipticals, and globular clusters. 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. A catalog of dwarf galaxies in VirgoA catalog listing the location, apparent angular diameter, type,estimated central light concentration, and estimated brightness of 846dwarf galaxies in a 200-deg-sq region in Virgo is presented. Thegalaxies comprise 634 ellipticals, 137 IC-3475-type galaxies, 73 dwarfspirals and irregulars, and two objects which are jets of normalgalaxies, and were found on nine long-exposure IIIa-J-emulsion platesmade with the 1.2-m-Schmidt telescope at Palomar Observatory from 1971to 1976. Concordances to other catalogs, tables of additionalparameters, maps, graphs, and photographs are provided. The projecteddistributions of normal and dwarf galaxies and the dependence ofapparent luminosity on central light concentration are discussed. It isfound that dwarf ellipticals and IC-3475-type galaxies are probablemembers of the Virgo cluster, while dwarf spirals and possibly dwarfirregulars are not.
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