The radio-luminosity - black hole mass correlation for quasars from the FIRST Bright Quasar Survey, and a ``unification scheme'' for radio-loud and radio-quiet quasars

Abstract

Several independent lines of evidence now point to a correlation between black hole mass, M_bh, and radio-luminosity. In this paper we discuss the correlation for quasars from the FIRST Bright Quasar Survey (FBQS), using black hole mass estimates from Hbeta linewidths. The FBQS objects fill in the gap between the radio-loud and radio-quiet quasars in the radio-luminosity - optical-luminosity plane, and we find that they fill the corresponding gap in the M_bh - radio luminosity correlation. There is thus a continuous variation of radio luminosity with M_bh, and no evidence for a ``switch'' at some set of critical parameter values which turns on powerful radio jets. By combining the FBQS data with that for quasars from the Palomar-Green survey we find evidence for a dependence of radio-luminosity on accretion rate relative to the Eddington limit, L/L_Edd, as well as on M_bh, consistent with the well-known radio-optical correlation for radio-loud quasars. We therefore suggest a new scheme to ``unify'' radio-loud and radio-quiet objects in which radio luminosity scales proportional to M_bh^{1.9+/-0.2}(L/L_Edd)^{1.0} for L/L_Edd~0.1, with an apparently weaker accretion rate dependence at low L/L_Edd. The scatter about this relation is +/-1.1 dex, and may well hide significant contributions from other physical effects, such as black hole spin and radio source environment.