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|Dwarf elliptical galaxies in the M81 Group - The structure and stellar populations of BK5N and F8D1|
We have carried out a CCD survey of the M81 Group to search for analogsto Local Group dwarf elliptical (dE) galaxies. All the M81 dwarfspreviously identified in photographic surveys were recovered, and wealso discovered several new systems whose surface brightnesses fallwithin the range found for Local Group dE's. We have obtained HubbleSpace Telescope Wide Field Planetary Camera 2 images through the F555Wand F814W filters of two M81 Group dE's, BK5N and a new system,designated F8D1. The resulting color-magnitude diagrams show the upper 2mag of the red giant branch. The I magnitudes of the red giant branchtip in both galaxies yield distances that are consistent with membershipin the M81 Group. Surface brightness and total magnitude measurementsindicate that BK5N and F8D1 have similar central surface brightnesses,but F8D1's larger length scale results in its being 3 mag more luminousthan BK5N. BK5N lies on the relation between central surface brightnessand absolute magnitude defined by Local Group dwarf elliptical galaxies,but F8D1 does not. F8D1 is more luminous for its central surfacebrightness than the relation predicts, similar to the large low surfacebrightness dwarf galaxies found in, for example, Virgo. The mean colorof the giant branch is used to establish the mean abundance of eachgalaxy. F8D1, the more luminous galaxy, is significantly more metal-richthan BK5N.
|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.
|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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