The bimodal radio luminosity function of quasars

Sensitive radio observations have been made of a sample of optically selected quasars. The sample was chosen to cover a wide range of optical luminosity but only a narrow range of redshift (1.8 < z < 2.5), so that the redshift-dependence of the radio properties of quasars could be eliminated and the relationship between optical and radio luminosities studied directly. Strong evidence is found for the existence of two populations of quasar. The quasars which are radio-loud in this sample are predominantly compact or flat-spectrum sources and have radio luminosities L5GHz > 1025 W Hz-1 sr-1. The radio-quiet quasars have L5GHz < 1024 W Hz-1 sr-1. There are no quasars with intermediate radio luminosities in the sample. (author)