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

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 radio-quiet quasars (RQQs) with very high significance (≫ 99.99%), with mean black-hole masses of < log(Mbh/M⊙) >= 8.89 ± 0.02 and < log(Mbh/M⊙) >= 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. ∆Mhost = 0.4 − 0.5 magnitudes). Within the SDSS samples, black-hole mass is strongly correlated with both radio luminosity and the radio-loudness R parameter (> 7σ significance), although the range in radio luminosity at a given blackhole 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.