A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) -: III.: Spectroscopic observations

The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4-GHz radio survey selected from the NRAO VLA Sky Survey (NVSS) and complete to a flux density of 7.2 mJy. It targets the ESO Imaging Survey (EIS) Patch D, which is a 3 x 2-deg(2) field centred on 09(h)51(m)36(s).0-21 degrees 00'00 '' (J2000). This paper presents the results of spectroscopic observations of 143 of the 150 CENSORS sources. The primary motivation for these observations is to achieve sufficient spectroscopic completeness so that the sample may be used to investigate the evolution of radio sources. The observations result in secure spectroscopic redshifts for 63 per cent of the sample and likely redshifts (based on a single emission line, for example) for a further 8 per cent. Following the identification of the quasars and star-forming galaxies in the CENSORS sample, estimated redshifts are calculated for the remainder of the sample via the K - z relation for radio galaxies. Comparison of the redshift distribution of the CENSORS radio sources to distributions predicted by the various radio luminosity function evolution models of Dunlop & Peacock, results in no good match. This demonstrates that this sample can be used to expand upon previous work in that field.