Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts

In the present-day universe, supermassive black hole masses (M sub(BH)) appear to be strongly correlated with their galaxy's bulge luminosity, among other properties. In this study we explore the analogous relationship between M sub(BH), derived using the virial method, and the stellar R-band bulge luminosity (L sub(R)) or stellar bulge mass (M*) at epochs of 1 z 4.5, using a sample of 31 gravitationally lensed AGNs and 20 nonlensed AGNs. At redshifts z > 1.7 (10-12 Gyr ago), we find that the observed M sub(BH)-L sub(R) relation is nearly the same (to within 60.3 mag) as it is today. When the observed L sub(R) are corrected for luminosity evolution, this means that the black holes grew in mass faster than their hosts, with the M sub(BH)/M* mass ratio being a factor of 4 super(-1 +2) times larger at z > 1.7 than it is today. By the redshift range 1 z 1.7 (8-10 Gyr ago), the M sub(BH)/M* ratio is at most 2 times higher than today, but it may be consistent with no evolution. Combining the results, we conclude that the ratio M sub(BH)/M* rises with look-back time, although it may saturate at -6 times the local value. Scenarios in which moderately luminous quasar hosts at z 1.7 were fully formed bulges that passively faded to the present epoch are ruled out.