On Quasar Masses and Quasar Host Galaxies

The mass of massive black holes in quasar cores can be deduced using thetypical velocities of Hb-emitting clouds in the Broad Line Region (BLR) and thesize of this region. However, this estimate depends on various assumptions andis susceptible to large systematic errors. The Hb-deduced black hole mass in asample of 14 bright quasars is found here to correlate with the quasar hostgalaxy luminosity, as determined with the Hubble Space Telescope (HST). Thiscorrelation is similar to the black hole mass vs. bulge luminosity correlationfound by Magorrian et al. in a sample of 32 nearby normal galaxies. Thesimilarity of the two correlations is remarkable since the two samples involveapparently different types of objects and since the black hole mass estimatesin quasars and in nearby galaxies are based on very different methods. This similarity provides a ``calibration'' of the Hb-deduced black hole massestimate, suggesting it is accurate to +-0.5 on log scale. The similarity ofthe two correlations also suggests that quasars reside in otherwise normalgalaxies, and that the luminosity of quasar hosts can be estimated to +-0.5 magbased on the quasar continuum luminosity and the Hb line width. Future imagingobservations of additional broad-line active galaxies with the HST are requiredin order to explore the extent, slope, and scatter of the black hole mass vs.host bulge luminosity correlation in active galaxies.Comment: Accepted for publication in ApJ Letters, 7 pages, aas2pp4.st