The relationship between radio luminosity and black hole mass in optically selected quasars

Abstract

Using a sample of more than 6000 quasars from the Sloan Digital Sky Survey (SDSS), we compare the black hole mass distributions of radio‐loud and radio‐quiet quasars. Based on the virial black hole mass estimator, the radio‐loud quasars (RLQs) are found to harbour systematically more massive black holes than are the radio‐quiet quasars (RQQs) with very high significance (≫99.99 per cent), with mean black hole masses of 〈log(Mbh/M⊙)〉= 8.89 ± 0.02 and 8.69 ± 0.01 for the RLQs and RQQs respectively. Crucially, the new RLQ and RQQ samples have indistinguishable distributions on the redshift–optical luminosity plane, excluding the possibility that either parameter is responsible for the observed black hole mass difference. Moreover, this black hole mass difference is shown to be in good agreement with the optical luminosity difference observed between RLQ and RQQ host galaxies at low redshift (i.e. ΔMhost= 0.4–0.5 mag). Within the SDSS samples, black hole mass is strongly correlated with both radio luminosity and the radio‐loudness parameter (>7σ significance), although the range in radio luminosity at a given black hole mass is several orders of magnitude. It is therefore clear that the influence of additional physical parameters or evolution must also be invoked to explain the quasar radio‐loudness dichotomy.