Evidence for Steep Luminosity Functions in Clusters of Galaxies

Abstract

Luminosity functions have been obtained for very faint dwarf galaxies in the cores of four rich clusters of galaxies (Abell 2052, Abell 2107, Abell 2199, and Abell 2666). It is found that the luminosity function of dwarf galaxies rises very steeply in these clusters with a power-law slope of α ˜ -2.2 (down to limiting absolute magnitudesM1 ˜ -13 and MB ˜ -11 forH0 = 75 km s-1 Mpc-1 ). A steepening of the luminosity function toward low luminosities may in fact be a common feature of both cluster and field populations. Such a result may explain the observed excess counts of faint, intermediate-redshift galaxies in the universe without having to resort to more exotic phenomena. An alternate explanation is that star formation in dwarf galaxies is less affected by gas loss in the richest clusters because of the dense, hot intracluster medium found in such environments.