The Rise of Dwarfs and the Fall of Giants: Galaxy Formation Feedback Signatures in the Halo Satellite Luminosity Function

Abstract

The observed luminosity function (LF) of satellite galaxies shows several interesting features that require a better understanding of gas-thermodynamic processes and feedback effects related to reionization and galaxy formation. In galaxy clusters, the abundance of dwarf galaxies is consistent with the expectation based on the subhalo mass function, whereas in galaxy groups, a relatively small abundance of dwarfs is expected based on models of photoionization. In all halo systems, however, there is a dip in the abundance of galaxies with luminosities in the range ~2 × 108 L☉ to 1010 L☉, corresponding to subhalo mass scales between ~5 × 1010 M☉ and a few times 1011 M☉. Photoionization from reionization has been used to explain statistics of the dwarf population, with larger systems forming prior to, and smaller systems forming subsequent to, reionization. The observed dip in the LF is an imprint of small dwarf galaxies (<~2 × 108 L☉) that formed prior to reionization. The galactic winds powered by supernovae in these dwarf galaxies propagate energy and metals to large distances such that the intergalactic medium is uniformly enriched to a level of 10-3 Z☉. The associated energy raises the intergalactic medium temperature and the Jeans mass to a range 1010-1011 M☉ at z ~ 3.4-6.0. Because the epoch of nonlinearity for halos in this mass range is at z ≥ 3.4-4.4, their gas content, hence star formation, is greatly suppressed on average and leads to the observed dip in the observed LF at z = 0.