Spectroscopic determination of the luminosity function in the galaxy clusters A2199 and Virgo

We report a new determination of the faint end of the galaxy luminosity function (LF) in the nearby clusters Abell 2199 and Virgo using data from the Sloan Digital Sky Survey (SDSS) and the Hectospec multifiber spectrograph on the MMT. The luminosity function of A2199 is consistent with a single Schechter function to Mr = -15.6 + 5 log h(70) with a faint-end slope of alpha = -1.13 +/- 0.07 (statistical). The LF in Virgo extends to M-r approximate to -13.5 approximate to M* + 8 and has a slope of a = -1.28 +/- 0.06 (statistical). The red sequence of cluster members is prominent in both clusters, and almost no cluster galaxies are redder than this sequence. A large fraction of photometric red-sequence galaxies lies behind the cluster. We compare our results to previous estimates and find poor agreement with estimates based on statistical background subtraction but good agreement with estimates based on photometric membership classifications (e. g., colors, morphology, surface brightness). We conclude that spectroscopic data are critical for estimating the faint end of the LF in clusters. The faint-end slope we find is consistent with values found for field galaxies, weakening any argument for environmental evolution in the relative abundance of dwarf galaxies. However, dwarf galaxies in clusters are significantly redder than field galaxies of similar luminosity or mass, indicating that star-formation processes in dwarfs do depend on environment.