On the evolution of the black-hole : spheroid mass ratio

We present the results of a study which uses the 3CRR sample of radio-loud active galactic nuclei (AGN) to investigate the evolution of the black-hole:spheroid relation in the most massive early-type galaxies from 0 < z < 2. Radio-loud unification is exploited to obtain virial (line-width) black-hole mass estimates from the 3CRR quasars, and stellar mass estimates from the 3CRR radio galaxies, thereby providing black-hole and stellar mass estimates for a single population of early-type galaxies. At low redshift (z < 1) the 3CRR sample is consistent with a black-hole:spheroid ratio of Mbh/Msph ≃ 0.002, in good agreement with that observed locally for quiescent galaxies of similar stellar mass (Msph ≃ 5 × 1011Mȯ). However, the 3CRR black-hole:spheroid ratio is found to evolve as Mbh/Msph ∝ (1 + z)2.07±0.76, reaching Mbh/Msph ≃ 0.008 by redshift z ≃ 2, providing further evidence that, at least for massive early-type galaxies, the growth of the central supermassive black-hole may be completed before that of the host spheroid. © 2006 Elsevier B.V. All rights reserved