INVESTIGATION OF THE OPTICAL-FIELDS OF FLAT-SPECTRUM RADIO-SOURCES TO FAINT LIMITING MAGNITUDES

A deep optical survey of the fields of 16 flat-spectrum radio sources has been carried out using the Hale 5-m telescope, with a prototype charge-coupled device as a detector. These sources are members of a complete sample, selected as having 5(2.7GHz) > 1.5 Jy, and were either unidentified, or were identified with very faint objects on the prints of the Palomar Sky Survey. Identifications are found for 12 of these objects; six are galaxies and six are stellar objects. Identifications for the 2.7-GHz sample are therefore now 96 per cent complete, allowing much improved redshift distributions to be derived. Values of V/Vmax- for the sample members have also been calculated, with the result that (V/Vmax) for the flat-spectrum quasars is 0.68, rather than the values nearer 0.5 derived from studies of deeper samples. This result indicates that both the steep-spectrum and flat-spectrum quasars undergo similar degrees of cosmological evolution. © 1981 Royal Astronomical Society.