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Star Clusters in Virgo and Fornax Dwarf Irregular Galaxies
We present the results of a search for clusters in dwarf irregulargalaxies in the Virgo and Fornax Clusters using Hubble Space Telescope(HST) WFPC2 snapshot data. The galaxy sample includes 28 galaxies, 11 ofwhich are confirmed members of the Virgo and Fornax Clusters. In the 11confirmed members, we detect 237 cluster candidates and determine theirV magnitudes, V-I colors, and core radii. After statistical subtractionof background galaxies and foreground stars, most of the clustercandidates have V-I colors of -0.2 and 1.4, V magnitudes lying between20 and 25 mag, and core radii between 0 and 6 pc. Using Hαobservations, we find that 26% of the blue cluster candidates are mostlikely H II regions. The rest of the cluster candidates are most likelymassive (>104 Msolar) young and old clusters. Acomparison between the red cluster candidates in our sample and theMilky Way globular clusters shows that they have similar luminositydistributions but that the red cluster candidates typically have largercore radii. Assuming that the red cluster candidates are in factglobular clusters, we derive specific frequencies (SN)ranging from ~0 to 9 for the galaxies. Although the values areuncertain, seven of the galaxies appear to have specific frequenciesgreater than 2. These values are more typical of elliptical andnucleated dwarf elliptical galaxies than they are of spiral or LocalGroup dwarf irregular galaxies.
| The kinematics of the Virgo cluster revisited
The paper updates the velocity data of Virgo cluster galaxies andreconsiders the kinematic structure of the Virgo cluster. New velocitiesare given for 144 galaxies listed in the Virgo Cluster Catalog (VCC).Improved velocities are given for another 131 VCC galaxies. The Virgocluster is disentangled from its surrounding clouds of galaxies, and thelikely members of each of these clouds are listed. The velocitydistribution of dwarf elliptical cluster members is found to be highlyasymmetric. This phenomenon is interpreted as evidence for the imminentmerging of two subclusters in the core region, which points to thedynamical youth of the Virgo cluster. The mean heliocentric velocity ofthe Virgo cluster is estimated at 1050 +/- 35 km/s.
| 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.
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