The bimodal radio luminosity function of quasars.
Abstract
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 L_5 GHz_ > 10^25^ W Hz^-1^ sr^-1^. The radio-quiet quasars have L_5 GHz_ < 10^24^ W Hz^-1^ sr^-1^. There are no quasars with intermediate radio luminosities in the sample. The fraction of quasars which are radio- loud is a function of redshift and probably of optical luminosity also, and these effects may be understood as the mixing of two quasar populations with differing luminosity functions and differing amounts of cosmological evolution. There is no evidence for a correlation between radio and optical luminosities of the radio-loud quasars.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 1990
- Bibcode:
- 1990MNRAS.244..207M
- Keywords:
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- Quasars;
- Radio Astronomy;
- Radio Emission;
- Astronomical Spectroscopy;
- Luminosity;
- Red Shift;
- Astrophysics