The cosmic evolution of low-luminosity radio sources from the Sloan Digital Sky Survey Data Release 1

In this paper we constrain the evolution in the comoving space density for low-luminosity [typically Fanaroff-Riley type I (FRI)] radio sources as a function of cosmic epoch by matching deep radio surveys [Westerbork Northern Sky Survey (WENSS), Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and NRAO VLA Sky Survey (NVSS)] with the Sloan Digital Sky Survey (SDSS). This results in 1014 matched radio sources covering an effective area of 0.217 sr, 686 with L-325 (MHz) < 10(25) W Hz(-1) sr(-1), which is an order of magnitude larger than any previous study at these luminosities. Using the non-parametric V/V (max) test we show that low-luminosity radio sources evolve differently from their more powerful, predominantly Fanaroff-Riley type II (FRII), counterparts. Indeed, we find that the lower luminosity population is consistent with a constant comoving space density with redshift, as opposed to the strong positive evolution for the more powerful sources.