The radio-loud fraction of QSOs and its dependence on magnitude and redshift

Abstract

The first determination of the optical evolution and luminosity function of radio-loud quasars is obtained from the PG sample, the only sizeable complete sample of optically selected quasars with full radio information. The optical evolution of radio-loud quasars is found to be similar to (if the R definition of radio-loudness is applied), or possibly stronger than (if the luminosity definition is applied), the evolution of radio-quiet quasars. The shapes of the luminosity functions for the radio-loud and radio-quiet classes appear to be different in both cases. The relative number of radio-loud quasars is in fact a function of optical luminosity, ranging (locally) from ∼ 20-50 per cent at M B ≤ −24.5 to ∼ 7-8 per cent at fainter absolute magnitudes; in total, about 16-20 per cent of quasars brighter than ∼ − 21.5 are radio-loud