The Black Hole to Bulge Mass Relation in Active Galactic Nuclei

The masses of the central black holes in Active Galactic Nuclei (AGNs) can be estimated using the broad emission-lines as a probe of the virial mass inside the BLR. Using reverberation mapping to determine the size of the Broad Line Region (BLR) and the width of the variable component of the line profile Hβ line it is possible to find quite accurate virial mass estimates for AGN with adequate data. Compiling a sample of AGN with reliable central masses and bulge magnitudes we find an average black hole to bulge mass ratio of 0.0003, a factor of 20 less than the value found for normal galaxies and for bright quasars. This lower ratio is more consistent with the black hole mass density predicted from quasar light, and agrees with the value found for our Galaxy. We argue that the black hole to bulge mass ratio actually has a significantly larger range than indicated by MBHs detected in normal galaxies (using stellar dynamics) and in bright quasars, which may be biased towards larger black holes , and derive a scenario of black hole growth that explains the observed distribution. Subject headings: Galaxy: center — galaxies: active — galaxies: nuclei — galaxies: Seyfert — black holes — quasars: emission-lines — dark matter