Radio-quiet objects in the 2QZ survey

Co-addition of blank-field Faint Images of the Radio Sky at Twenty-centimeters (FIRST) data at the location of over 8000 quasi-stellar objects (QSOs) in the 2QZ survey has yielded statistical detections of radio quiet QSOs with median flux levels of 20–40 μJy. We show that the total radio flux of radio-quiet QSOs in the 2QZ is consistent with a smooth extrapolation of the 2QZ radio-loud QSO number flux distribution based on the slope of the relation flattening near the FIRST flux limit. However, we are unable to distinguish a smooth extrapolation of the luminosity function to faint levels from a bimodal luminosity function with a break close to or below the FIRST radio detection limit. We also demonstrate that the redshift dependence of the median radio-to-optical spectral index αRO for these radio-quiet QSOs is consistent with that obtained for individual radio-loud 2QZ QSOs detected by FIRST.