A multi-frequency study of the deep Pavo field

Abstract

We test the prediction of Hamilton and Helfand (1993) that faint radio selected galaxies are a new class contributing to the diffuse X-ray background (XRB) radiation. The test is based on the correlation of X-ray optical and radio positions for sources detected in ROSAT (S0.08?2.4 keV> 6 x 10?15 erg cm?2 s?1, 69 sources) and ATCA (S1.42GHz >250 ?Jy, 93 sources) observations of the Einstein Pavo field. A total of six ATCA radio sources inside the inner ring of the ROSAT image are located within 10" of the ROSAT X-ray positions, with one associated by random chance. Hence, five of the X-ray population are radio-emitters. Four of these sources in common to radio and X-ray surveys are identified in optical frequencies from which one is a well known (ATCAJ211544-675404) quasi stellar object (QSO). Another source (ATCAJ211139-674902) can be seen at optical frequencies and therefore is very likely to be a QSO. Two more of these sources are clear Active Galactic Nuclei (AGN) candidates (ATCAJ211217-674914 and ATCAJ211451-680038). Radio and X-ray source ATCAJ211420-680109= RXJ211420-680108 is a galaxy cluster candidate. The remaining source ATCAJ211414-675052, is a star-forming galaxy candidate assuming it is not associated by random chance. Even though the statistical sample is small this does not support the postulate that star-forming galaxies are significant contributors to the soft X-ray source population. This implies the contribution of radio emitting X-ray sources to the diffuse XRB at S0.08?2.4 keV > 6 x 10?15 erg cm?2 s?1 is at most a few per cent.