The Radio Loudness Dichotomy: Environment or Black-Hole Mass?

Abstract

The results of a comprehensive study of the cluster environments and black-hole masses of an optically matched sample of radio-loud and radio-quiet quasars are presented. No evidence is found for a difference in large-scale environments, with both quasar classes found to be located in clusters of Abell class similar to 0. Conversely, virial black-hole mass estimates based on H,3 line-widths show a clear difference in the quasar black-hole mass distributions. Our results suggest that a black-hole mass of similar to 10(9) M-circle dot is required to produce a powerful radio-loud quasar, and that it is black-hole mass and accretion rate which hold the key to the radio-loudness dichotomy.