Probing the coevolution of supermassive black holes and galaxies using gravitationally lensed quasar hosts

In the present-day universe, supermassive black hole masses (M-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-BH, derived using the virial method, and the stellar R- band bulge luminosity (L-R) or stellar bulge mass (M-*) at epochs of 1 less than or similar to z less than or similar to 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-BH-L-R relation is nearly the same (to within similar to 0.3 mag) as it is today. When the observed L-R are corrected for luminosity evolution, this means that the black holes grew in mass faster than their hosts, with the M-BH/M-* mass ratio being a factor of greater than or similar to 4(-1)(+2) times larger at z > 1.7 than it is today. By the redshift range 1 less than or similar to z less than or similar to 1.7 (8-10 Gyr ago), the M-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-BH/M-* rises with look-back time, although it may saturate at approximate to 6 times the local value. Scenarios in which moderately luminous quasar hosts at z greater than or similar to 1.7 were fully formed bulges that passively faded to the present epoch are ruled out.