Dwarf Galaxies in the Coma Cluster

Previous abstract Next abstract

Session 107 -- Galaxies: Morphology and Interactions
Display presentation, Thursday, 12, 1995, 9:20am - 6:30pm

[107.01] Dwarf Galaxies in the Coma Cluster

Jeff Secker and William E. Harris (McMaster University)

The Coma galaxy cluster (A1656) is the nearest very-rich Abell cluster (richness-class 2); for a mean recession velocity of $v = 7000$ km/s, it is at a distance of 93.3 Mpc ($H_0 = 75$ km/s/Mpc). The central core is dominated by two supergiants, NGC 4889 and the cD NGC 4874. Our present purpose is to characterize the dwarf elliptical (dE) galaxy population in this extremely high-density galaxy environment, and thus to help constrain current ideas about the formation and evolution of dEs.

Using a 2048$^2$ CCD on the KPNO 4-m telescope, we have obtained 6x900-second exposure series in $R$ and $B$. The overlapping galaxy fields cover an area of 0.252 deg$^2$, with two fields on the core and two extending radially outwards 1 Mpc from the cluster core. We also obtained two remote background fields to use for statistical number correction. We have developed a code (DYNAMO) to automate object detection, photometry and classification, and have tested it on artificially generated images. Briefly, we define our total magnitude interior to a circular aperture of radius $2r_1$, based upon the intensity-weighted radial moment $r_1$ as a measure of the half-flux radius. Fixed-aperture techniques are used to obtain accurate, integrated colors, independent of object morphology. The process of discrimination between galaxy and starlike objects is performed interactively, through parameter-space culling, color-magnitude diagram discrimination, and statistical number correction with the remote background fields.

Preliminary results pertinent to some of the following questions will be presented: the spatial distribution of the faint dwarfs (are they smoothly distributed in the potential well of the cluster as a whole, or are they clustered about the larger galaxies?); the faint-end of the galaxy luminosity function (can we constrain the slope?); the dwarf-to-giant ratio (does n(dE)/n(E) for the Coma cluster increase over that observed for the Virgo cluster?).

Thursday program listing