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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 Dwarfs
We 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.
| The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei, and Stellar Halos
We present the results of a Hubble Space Telescope WFPC2 F555W and F814Wsurvey of 69 dwarf elliptical galaxies (dEs) in the Virgo and FornaxClusters and Leo Group. The V-I colors of the dE globular clusters,nuclei, and underlying field-star populations are used to trace the dEstar formation histories. We find that the dE globular clustercandidates are as blue as the metal-poor globular clusters of the MilkyWay. The observed correlation of the dE globular cluster systems' V-Icolor with the luminosity of the host dE is strong evidence that theglobular clusters were formed within the halos of dEs and do not have apregalactic origin. Assuming that the majority of dE clusters are old,the mean globular cluster color-host galaxy luminosity correlationimplies a cluster metallicity-galaxy luminosity relation of~L0.22+/-0.05B, which issignificantly shallower than the field-star metallicity-host galaxyluminosity relationship observed in Local Group dwarfs(~L0.4). The dE stellar envelopes are0.1-0.2 mag redder in V-I than their globular clusters and nuclei. Thiscolor offset implies separate star formation episodes within the dEs forthe clusters and field stars, while the very blue colors of two dEnuclei trace a third star formation event in those dEs less than 1 Gyrago.
| Spectrophotometry of galaxies in the Virgo cluster. II. The data
Drift-scan mode (3600-6800 Å) spectra with 500
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Extragalactic Globular Clusters. IV. The Data
We have explored the use of absorption line strength indices, measuredfrom integrated globular cluster spectra, to predict mean metallicity inlate-type stellar systems. In previous papers we identified the bestindices for such metallicity calibrations out of ~13 measured in a largesample of galactic and M31 cluster spectra. In this paper we present theindividual measurements of 13 indices and averages of multiplemeasurements, where appropriate. Data are given for 151 M31 globularclusters, 88 galaxies, 22 M33 cluster candidates, 10 M87 clusters, eightM81 globular clusters, three Fornax dwarf galaxy clusters, "standard"stars from the lists of Faber et al., stars in the open cluster NGC 188and, for completeness, other stars observed as candidate globularclusters.
| 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.
| An investigation of dwarf galaxies in the Virgo cluster
It is noted in the present 21-cm H I observations of a sample of 32dwarf irregular (dI) and 12 dwarf elliptical (dE) galaxies located inthe Virgo cluster that, while 18 of the 32 dIs were detected in H I,none of the dEs were detected at the 2-3 million solar mass level. Thisdisparity in H I content between dIs and dEs effectively dispels thepossibility that the dEs are currently in a state of quiescence betweenbursts of star formation. Optical spectroscopy, CCD images, and IRphotometry for a limited subsample of the dwarfs indicate that the dEs,although very H I-poor, have observed (J-K) colors which indicate highmetallicity; this suggests a degree of enrichment due to multiplegenerations of star formation.
| A catalog of dwarf galaxies in Virgo
A 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.
| Structure and stellar content of dwarf elliptical galaxies
A small number of low-luminosity elliptical galaxies are studied usingphotoelectric and photographic techniques. The color-magnitude relationfor ellipticals now extends from M(v) = -23 to -15, and is linear overthat range with a slope of 0.10 in U-V per visual magnitude. Galaxieswhich are known to contain a large number of young stars are from 0.10to 0.20 mag bluer than the lower envelope of the ellipticalcolor-magnitude relation. This difference can be accounted for by a lackof the most massive stars in a young population. Thus, the Balmerabsorption line spectra of the dwarf ellipticals which have beenobserved by others can be best understood as the signature of a youngpopulation which no longer has an upper main sequence of stars.
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