Identifications of FIRST radio sources in the NOAO Deep Wide‐Field Survey

Abstract

AbstractIn this paper we present the results of an optical and near infrared identification of 514 radio sources from the FIRST survey (Faint Images of the Radio Sky Survey at Twenty centimetres) with a flux‐density limit of 1 mJy in the NOAO Deep Wide‐Field Survey (NDWFS) Boötes field. Using optical (Bw, R, I) and K band data with approximate limits of Bw ∼ 25.5 mag, R ∼ 25.8 mag, I ∼ 25.5 mag and K ∼ 19.4 mag, optical counterparts have been identified for 378 of 514 FIRST radio sources. This corresponds to an identification rate of 34% in four bands (BwRIK), 60% in optical bands (BwRI) and 74% in the I band. Photometric redshifts for these sources have been computed using the hyperz code. The inclusion of quasar template spectra in hyperz is investigated. We note that the photometric data are, in many cases, best matched to templates with very short star‐formation timescales and the inferred ages of identified galaxies depend strongly on the assumptions about the star‐formation timescale. The redshifts obtained are fairly consistent with those expected from the K ‐z relation for brighter radio sources but there is more scatter in the K ‐z diagram at z < 1. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)