The dwarf galaxy population of the Coma cluster to MR = -11: a detailed description

We present the luminosity function 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 arcmin2; 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 as follows. Galaxies in the Coma cluster have a luminosity function φ(L)∝Lα that is steep (α ∼ −1.7) for − 15 <MR<−11, and is shallower brighter than this. The curvature in the luminosity function at MR∼−15 is statistically significant. The galaxies that contribute most strongly to the luminosity function at −14<MR<−12 have colours and scalelengths that are consistent with those of local dwarf spheroidal galaxies placed at the distance of Coma. These galaxies with −14<MR<−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. These galaxies with −14<MR<−12 also appear to be more confined to the cluster core (r∼200 kpc) than the brighter galaxies. Alternatively, this observation may be explained in part or whole by the presence of an anomalously high number of background galaxies behind the cluster core. Velocity measurements of these galaxies would distinguish between these two possibilities.