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 M-bh/M-sph congruent to 0.002, in good agreement with that observed locally for quiescent galaxies of similar stellar mass (M-sph congruent to 5 x 10(11) M-circle dot). However, the 3CRR black-hole:spheroid ratio is found to evolve as M-bh/M-sph (1 + z)(2.07 +/- 0.76), reaching M-bh/M-sph congruent to 0.008 by redshift z congruent to 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. (c) 2006 Elsevier B.V. All rights reserved.