The galaxy luminosity function and its evolution withChandra

Abstract

AIMS: We have compiled one of the largest normal-galaxy samples ever to probe X-ray luminosity function evolution separately for early and late-type systems. METHODS: We selected 207 normal galaxies up to redshift z~1.4, with data from four major Chandra X-ray surveys, namely the Chandra deep fields (north, south and extended) and XBootes, and a combination of X-ray and optical criteria. We used template spectral energy-distribution fitting to obtain separate early- and late-type sub-samples, made up of 101 and 106 systems, respectively. For the full sample, as well as the two sub-samples, we obtained luminosity functions using both a non-parametric and a parametric, maximum-likelihood method. RESULTS: For the full sample, the non-parametric method strongly suggests luminosity evolution with redshift. The maximum-likelihood estimate shows that this evolution follows ~(1+z)^k_total, k_total=2.2+-0.3. For the late-type sub-sample, we obtained k_late=2.4^+1.0_-2.0. We detected no significant evolution in the early-type sub-sample. The distributions of early and late-type systems with redshift show that late types dominate at z>~0.5 and hence drive the observed evolution for the total sample. CONCLUSIONS: Our results support previous results in X-ray and other wavebands, which suggests luminosity evolution with k=2-3.