The X-ray luminosity function of galaxies and its evolution

TL;DR

This study analyzes the X-ray luminosity function of galaxies across cosmic time, revealing that late-type galaxies exhibit significant luminosity evolution consistent with optical blue galaxies, while early-types show weaker evolution.

Contribution

It provides one of the largest samples to date for studying galaxy X-ray luminosity functions and their evolution, using both parametric and non-parametric methods.

Findings

Total galaxy luminosity evolves as (1+z)^2.2

Late-type galaxies drive the evolution trend

Early-type galaxies show weaker or no evolution

Abstract

We compile one of the largest ever samples to probe the X-ray normal galaxy luminosity function and its evolution with cosmic time. In particular, we select 207 galaxies (106 late and 101 early-type systems) from the Chandra Deep Field North and South surveys, the Extended Chandra Deep Field South and the XBOOTES survey. We derive the luminosity function separately for the total (early+late), the early and the late-type samples using both a parametric maximum likelihood method, and a variant of the non-parametric 1/V_m method. Although the statistics is limited, we find that the total (early+late) galaxy sample is consistent with a Pure Luminosity evolution model where the luminosity evolves according to L(z) ~ (1+z)^2.2. The late-type systems appear to drive this trend while the early-type systems show much weaker evidence for evolution. We argue that the X-ray evolution of late-type systems is consistent with that of blue galaxies in the optical. In contrast there is a mismatch between the X-ray evolution of early-type systems and that of red galaxies at optical wavelengths.