On the evolution of the black hole:spheroid mass ratio
Abstract
We present the results of a study which uses the 3CRR sample of radio-loud active galactic nuclei to investigate the evolution of the black-hole:spheroid mass ratio 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 mass ratio of Mbh/Msph ~0.002, in good agreement with that observed locally for quiescent galaxies of similar stellar mass (Msph ~5x1011 Msun). However, over the redshift interval 0<z<2 the 3CRR black-hole:spheroid mass ratio is found to evolve as Mbh/Msph (1+z)2.070.76, reaching Mbh/Msph ~0.008 by redshift z~2. This evolution is found to be inconsistent with the local black hole:spheroid mass ratio remaining constant at a moderately significant level (98%). If confirmed, the detection of evolution in the 3CRR black-hole:spheroid mass ratio further strengthens the 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.
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