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

We investigate the cosmic evolution of low-luminosity (L-1.4 GHz < 1025 W Hz-1 sr-1) radio sources in the XMM Large Scale Structure Survey (XMM-LSS) field. 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-max statistic and the radio luminosity function of these matched sources to quantify the evolution of the comoving space density of the low-luminosity radio sources in our sample. Our results indicate that the low-luminosity sources evolve differently from their high-luminosity counterparts out to a redshift of z similar to 0.8. The derived luminosity function is consistent with an increase in the comoving space density of low-luminosity sources by a factor of similar to 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 approximately > 10 band photometry. This offers a promising method for conducting similar analyses over the whole sky with future near- and mid-infrared surveys.