CENSORS: A Combined EIS-NVSS Survey Of Radio Sources - I. Sample definition, radio data and optical identifications

Abstract

A new sample of radio sources, with the designated name CENSORS (A Combined EIS-NVSS Survey Of Radio Sources), has been defined by combining the National Radio Astronomy Observatory Very Large Array Sky Survey (NVSS) at 1.4 GHz with the ESO Imaging Survey (EIS) Patch D, a 3° by 2° region of sky centred at RA 09 h 51 m 36 s .0, Dec. -21°00'00 (J2000). New radio observations of 199 NVSS radio sources with NVSS flux densities S 1 . 4 G H z > 7.8 mJy are presented, and are compared with the EIS I-band imaging observations which reach a depth of I ∼ 23; optical identifications are obtained for over two-thirds of the ∼150 confirmed radio sources within the EIS field. The radio sources have a median linear size of 6 arcsec, consistent with the trend for lower flux density radio sources to be less extended. Other radio source properties, such as the lobe flux density ratios, are consistent with those of brighter radio source samples. From the optical information, 30-40 per cent of the sources are expected to lie at redshifts z ≥ 1.5. One of the key goals of this survey is to accurately determine the high-redshift evolution of the radio luminosity function. These radio sources are at the ideal flux density level to achieve this goal; at redshifts z ∼ 2 they have luminosities which are around the break of the luminosity function and so provide a much more accurate census of the radio source population at those redshifts than the existing studies of extreme, high radio power sources. Other survey goals include investigating the dual-population unification schemes for radio sources, studying the radio luminosity dependence of the evolution of radio source environments, and understanding the radio power dependence of the K-z relation for radio galaxies.