Evolution of faint radio sources in the VIDEO-XMM3 field

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 $(1+z)^{1.18\pm0.21}$.