The Radio Luminosity Function and Galaxy Evolution in the Coma Cluster

Abstract

We investigate the radio luminosity function (RLF) and radio source population for two fields within the Coma cluster of galaxies. Our VLA data reach down to log(L) = 20.23 W/Hz for Coma, and we associate 249 sources with optical counterparts from the SDSS. Comprehensive optical spectroscopy identifies 38 of these as members of the Coma cluster, evenly split between AGN and star-forming galaxies (SFG). The radio-detected SFG are the dominant population only for ~21 < log(L) < ~22 W/Hz, an interesting result given that star formation dominates field RLFs for log(L) < ~23. The majority of the radio-detected SFGs have characteristics of starbursts, including high specific star formation rates and optical spectra with strong emission lines. In conjunction with prior studies on post-starburst galaxies within the Coma cluster, this is consistent with a picture in which late-type galaxies entering Coma undergo a starburst prior to a rapid cessation of star formation. Optically bright elliptical galaxies (Mr <= -20.5) make the largest contribution to the radio luminosity function at both the high (log(L) >~ 22.48 W/Hz) and low (log(L) <~ 21 W/Hz) ends. Through a stacking analysis of these optically-bright ellipticals we find that they continue to harbor radio sources down to log(L) = 19.48. However, contrary to published results for the Virgo cluster we find no evidence for the existence of a population of optically faint (Mr ~ -14) dwarf ellipticals hosting strong radio AGN.