Evolution of faint radio sources in the VIDEO-XMM3 field

TL;DR

This study investigates the cosmic evolution of faint radio sources up to redshift 2.5, revealing mild positive evolution driven by star-forming galaxies at low redshifts and a slowdown at higher redshifts, informing AGN feedback understanding.

Contribution

It combines deep radio survey data with multi-band photometric redshifts to analyze the evolution of faint radio sources, highlighting differential evolution of star-forming galaxies and AGN.

Findings

Radio sources increase in density by a factor of ~3 up to z~1.2

Star-forming galaxies evolve as (1+z)^{2.47}

AGN evolve as (1+z)^{1.18}

Abstract

It has been speculated that low luminosity radio-loud AGN have the potential to serve as an important source of AGN feedback, and may be responsible for suppressing star-formation activity in massive elliptical galaxies at late times. As such the cosmic evolution of these sources is vitally important to understanding the significance of such AGN feedback processes and their influence on the global star-formation history of the universe. In this paper we present a new investigation of the evolution of faint radio sources out to $z{\sim}2.5$. We combine a 1 square degree VLA radio survey, complete to a depth of 100 $\mu$Jy, with accurate 10 band photometric redshifts from the VIDEO and CFHTLS surveys. The results indicate that the radio population experiences mild positive evolution out to $z{\sim}1.2$ increasing their space density by a factor of $\sim$3, consistent with results of several previous studies. Beyond $z$=1.2 there is evidence of a slowing down of this evolution. Star-forming galaxies drive the more rapid evolution at low redshifts, $z{<}$1.2, while more slowly evolving AGN populations dominate at higher redshifts resulting in a decline in the evolution of the radio luminosity function at $z{>}$1.2. The evolution is best fit by pure luminosity evolution with star-forming galaxies evolving as $(1+z)^{2.47\pm0.12}$ and AGN as $(1+z)^{1.18\pm0.21}$.