Unification of Radio Galaxies and their Accretion Jet Properties

Abstract

We investigate the relation between black hole mass, M bh, and jet power, Q jet, for a sample of BL Lacs and radio quasars. We find that BL Lacs are separated from radio quasars by the FR I/II dividing line in M bh–Q jet plane, which strongly supports the unification scheme of FR I/BL Lac and FR II/radio quasar. The Eddington ratio distribution of BL Lacs and radio quasars exhibits a bimodal nature with a rough division at L bol/L Edd~0.01, which imply that they may have different accretion modes. We calculate the jet power extracted from advection-dominated accretion flow (ADAF), and find that it requires dimensionless angular momentum of black hole j ≃ 0.9 − 0.99 to reproduce the dividing line between FR I/II or BL Lac/radio quasar if dimensionless accretion rate \(\dot{m}=0.01\) is adopted, which is required by the above bimodal distribution of Eddington ratios. Our results suggest that black holes in radio galaxies are rapidly spinning.