The Assembly of Supermassive Black Holes at z < 1 in Early-type Galaxies from Scaling Relations

The assembly of supermassive black hole (SMBH) mass (M-center dot) and stellar mass (M-*) in galaxies can be studied via the redshift evolution of the M-center dot-M-* relation, but the ways in which selection bias and physical assembly channels affect this evolution are uncertain. To address this, we compare the M-center dot-M-* relation for local massive (M-* > 10(10.5 )M(circle dot)) quiescent early-type galaxies (ETGs) to that for massive ETGs hosting active galactic nuclei (AGN) at z similar to 0.8. The restrictions on stellar mass and galaxy type limit the assembly channels that may connect the two relations. For the local sample we find log(M-center dot)=8.80+1.10(logM(& lowast;)-11), in line with prior work. For the z similar to 0.8 sample we find a bias-corrected relation: log(M-center dot)=7.80+1.25(logM(& lowast;)-11). We show, however, that this relation depends on the stellar and SMBH mass functions used to compute the selection bias, the virial relation, the virial factor, and the active fraction, which together introduce uncertainty of up to similar to 0.6 dex in the z similar to 0.8 relation. Adopting reasonable choices of these parameters then our z similar to 0.8 relation lies above that for z similar to 0 AGN by similar to 0.5 dex, but below our z similar to 0 ETG relation by 0.4-1 dex in SMBH mass. We discuss possible sources of this offset, including further bias corrections, "downsizing" in SMBH mass assembly, and preferential SMBH growth. Our results highlight the need to reduce uncertainties from selection and measurement bias in SMBH and stellar masses at all redshifts.