The evolution of radio sources in the UKIDSS-DXS XMM-LSS field

TL;DR

This study examines how low luminosity radio sources in the XMM-LSS field evolve over cosmic time, revealing a moderate increase in their space density up to redshift 0.8, and demonstrating a practical method for future large-scale surveys.

Contribution

It provides the first detailed analysis of low luminosity radio source evolution using combined radio and near-infrared data, introducing a simplified $K-z$ diagram approach.

Findings

Low luminosity sources evolve differently than high luminosity ones.

The co-moving space density increases by a factor of ~1.5 at z=0.8.

The $K-z$ diagram method yields results consistent with more complex photometric redshift analyses.

Abstract

We investigate the cosmic evolution of low luminosity ($L_{\rm{1.4GHz}}<10^{25}\rm{W~Hz^{-1}sr^{-1}}$) radio sources in the XMM Large Scale Structure survey field (XMM-LSS). We match low frequency selected (610~MHz) radio sources in the XMM-LSS field with near infrared $K$-band observations over the same field from the UKIRT Infrared Deep Sky Survey. We use both the mean $V/V_{\rm{max}}$ statistic and the radio luminosity function of these matched sources to quantify the evolution of the co-moving space density of the low luminosity radio sources in our sample. Our results indicate that the low luminosity sources evolve differently to their high luminosity counterparts out to a redshift of z$\sim$0.8. The derived luminosity function is consistent with an increase in the co-moving space density of low luminosity sources by a factor of $\sim$1.5 at z=0.8. We show that the use of the $K-z$ diagram for the radio source population, although coarser than a full photometric redshift analysis, produces consistent results with previous studies using $\sim >10$ band photometry. This offers a promising method for conducting similar analyses over the whole sky with future near- and mid-infrared surveys.