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|Detailed Surface Photometry of Dwarf Elliptical and Dwarf S0 Galaxies in the Virgo Cluster|
We analyze new V-band images of 14 dwarf S0 galaxies and 10 dwarfelliptical galaxies in the Virgo Cluster, in combination with R-bandimages of 70 dwarf elliptical galaxies from an earlier paper. We computethe intensity-weighted mean ellipticity, the mean deviations fromelliptical isophotes, and a newly defined parameter to measure isophotaltwists. We also fit each major-axis profile to a power lawSigma(a)~exp[-(a/a_s)^n], where n is allowed to vary. Consistent withother studies of the Virgo dwarf ellipticals, we find that the profileshapes for the entire sample is strongly peaked near n=1 (exponentialprofiles) and that no galaxies have n=1/4 (de Vaucouleurs profile). Thefaintest galaxies all have nearly exponential profiles, while thebrighter ones on average have n<1. The correlation betweenellipticity and the boxy/disky parameter is similar to that of largeelliptical galaxies, suggesting that dwarfs may also be divided into twogroups with differing internal dynamics. The Virgo dEs also show agreater degree of isophotal twisting than more luminous ellipticalgalaxies. There does not seem to be any combination of parameters fromthe surface photometry that statistically correlates with the dE/dS0designation: in particular, the dS0 galaxies do not, on average, havemore pointed (disky) isophotes than the dEs.
|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.
|The flattening distribution of dwarf elliptical galaxies in the Virgo Cluster|
We have obtained R-band surface photometry of 70 dwarf ellipticalgalaxies in the Virgo Cluster. We find, in contrast to the results ofearlier studies, that the dwarfs have a markedly flatter distribution ofellipticities than either 'normal' elliptical galaxies or brightestcluster ellipticals. The ensemble of nucleated dwarfs is rounder thanthe non-nucleated galaxies. Neither the nucleated nor the nonnucleateddwarfs, however, have distributions as round as giant ellipticals.
|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.
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