2004MNRAS.352.1005G

In this paper, we cross-correlate the FIRST (Faint Images of the Radio Sky at Twenty centimeters) 1.4-GHz radio survey with a wide-field (1.6 deg²) shallow [f_X(0.5-8keV) ~ 10^–14erg/s]XMM-Newton survey. We find 12 X-ray/radio matches representing 4 per cent of the X-ray-selected sample. Most of them are found to be associated with active galactic nuclei (a total of nine) on the basis of the observed optical spectra (three), radio morphology (two) or X-ray/optical properties (four), whereas one radio source is identified with an X-ray-selected cluster. We also find two sources associated with low-redshift galaxies with narrow emission line optical spectra, X-ray luminosity L_X(0.5-8keV) ~ 10⁴¹erg/s, radio luminosity density L_1.4GHz~ 5x10²²W/Hz and logf_X/f_opt~-2, suggesting `normal' star-forming galaxies. We argue that radio surveys combined with X-ray samples could provide a powerful tool for identifying X-ray-selected `normal' galaxies powered by stellar processes. Finally, radio-loud and radio-quiet systems in the present sample have mean X-ray spectral properties consistent with Γ~ 1.9.