The dwarf galaxy population of the Coma cluster to M_R=-11

Abstract

We present the luminosity function (LF) and measurements of the scalelengths, colours, and radial distribution of dwarf galaxies in the Coma cluster down to R=24. Our survey area is 674 arcmin^2; this is the deepest and most detailed survey covering such a large area. Our measurements agree with those of most previous authors at bright and intermediate magnitudes. The new results are: 1) Galaxies in the Coma cluster have a luminosity function that is steep (α\sim -1.7) for -15 < M_R < -11, and is shallower brighter than this. The curvature in the LF at M_R \sim -15 is statistically significant. 2) The galaxies that contribute most strongly to the luminosity function at -14 < M_R < -12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma. 3) These galaxies with -14 < M_R < -12 have a colour distribution that is very strongly peaked at B-R = 1.3. This is suggestive of a substantial degree of homogeneity in their star formation histories and metallicities. 4) These galaxies with -14 < M_R < -12 also appear to be more confined to the cluster core (r \sim 200 kpc) than the brighter galaxies.