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Hubble Space Telescope WFPC2 Imaging of Three Low Surface Brightness Dwarf Elliptical Galaxies in the Virgo Cluster
Utilizing the F814W and F300W filters, Hubble Space Telescope Wide FieldPlanetary Camera 2 (WFPC2) images were taken of three low surfacebrightness dwarf elliptical galaxies in the Virgo Cluster. The intent ofthe observations was to determine the small-scale structure in theseenigmatic galaxies and to attempt to learn something about the nature oftheir giant branches through the detection of luminosity fluctuations.In two of the three studied galaxies, V7L3 and V1L4, the luminosityfluctuations in the inner, constant surface brightness regions wereunambiguously detected. At the nominal distance of the Virgo Cluster,the measured luminosity fluctuations in the F814W band yields a densityof 2-10 red giants per pixel. In the most extreme of these two cases,V7L3, we derive a surface density of giant stars of ~3 per 10 pc^2.Using the observed B-V and V-I colors as a constraint, we could find nomodel that would reproduce the observed fluctuation signal and bluecolors if there were a significant population of M giants in thesesystems. Overall, our results are consistent with a mean spectral typeof K0-K2, which implies a relatively metal-poor population. The thirdsystem, V2L8, did not have a detectable fluctuation signal, whichpossibly implies that it is not in the Virgo Cluster. Interestingly,this system is highly nucleated. Our observations have resolved thisnucleus, and if V2L8 is in Virgo, then we have discovered what is likelythe smallest bulge measured to date, having an effective radius of only50 pc. This bulge is quite red (as red as giant ellipticals), and it isentirely possible that this nucleated dwarf elliptical galaxy, in fact,is a very large galaxy located in the background. As such, it is highlyreminiscent of the manner in which Malin 1 was discovered. Opticalspectroscopy of this nucleus is required to confirm this. Finally, wefind no evidence for small-scale clumping of stars in any of the studiedsystems at this much-improved spatial resolution. This implies thatthese systems are dynamically well relaxed and that the physical causeof their observed low surface brightnesses is their low density. Whenimaged at the high spatial resolution of the WFPC2 (~6 pc pixel^-1), thegalaxies are easy to look right through without even knowing that theyare present in the very middle of the WFPC2 frame. They appear only aselevated ``sky noise.''
| Virgo dwarfs - New light on faint galaxies
Photographically amplified UK Schmidt plates have been used to define anew sample of low surface brightness (LSB) galaxies in the VirgoCluster. One of these galaxies is the largest, most gas-rich spiralgalaxy known, located well beyond the Virgo Cluster. The rest of the 137galaxies appear to be dwarf ellipticals. CCD photometry shows that thefaint galaxies are well modeled by an exponential radial profile. Thecolors of very LSB galaxies in Virgo are unusually blue in B-V, bluerthan the metal-poor Galactic globular clusters. If these galaxies do notviolate the mass-metallicity relation, then they must have smaller meanages than Galactic globulars. It is confirmed that any faint galaxysurvey tends to choose objects of a luminosity and surface brightnessthat give them the maximum angular size on the discovery material.
| H I detection survey of a complete magnitude-limited sample of dwarf irregular galaxies in the Virgo Cluster area
New single-beam Arecibo H I observations of 298 late-type galaxies inthe Virgo Cluster drawn mostly from the new catalog of Binggeli,Sandage, and Tammann (1985) are presented. Two hundred seventeen ofthese constitute a magnitude-limited 'complete sample' of such galaxies,types Sdm through Im and BCD. Sixty-one percent of this 'completesample' was detected, greatly enhancing the store of redshifts and H Imasses for such galaxies in the Virgo Cluster. For detected galaxies,heliocentric velocities, 50 percent profile widths, and single-beamfluxes are presented. For those that escaped detection, upper limits arecomputed to the flux appropriate to the redshift range (-600 to +3000km/s).
| UBV colors of Virgo cluster irregular galaxies
Photoelectric UBV aperture photometry is presented for 65 dwarfirregular and morphologically related types of galaxies that areprobable Virgo cluster members. Virgo cluster Irr galaxies cover a widerrange in color than typical samples of field Irr systems, primarily dueto the presence of unusually red Im galaxies in Virgo. The extremelyblue 'blue compact dwarf' and the red amorphous galaxies in Virgo alsostand out on a UBV color-color plot, but the majority of Virgo Irrs areundistinguished in terms of UBV colors. Statistical correlations arefound between colors and location within the cluster. Red Irrs often arein elliptical galaxy rich, dense areas of the cluster, while the blueIrrs roughly follow the spiral distribution pattern. Thus a connectionexists between environment and the properties of Irrs. Simplestatistical tests for ongoing stripping as the source of red Irrs,however, yields null results.
| 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 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.
| The distribution of Sculptor-type dwarf galaxies.
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