The BH mass of nearby QSOs: a comparison of the bulge luminosity and virial methods

We report on the analysis of the photometric and spectroscopic properties of a sample of 29 low-redshift (z < 0.6) QSOs for which both Hubble Space Telescope (HST) WFPC2 images and ultraviolet HST FOS spectra are available. For each object we measure the R-band absolute magnitude of the host galaxy, the C (IV) (1550 angstrom) linewidth and the 1350 angstrom continuum luminosity. From these quantities we can estimate the black hole (BH) mass through the M-BH-L-bulge relation for inactive galaxies, and from the virial method based on the kinematics of the regions emitting the broad-lines. The comparison of the masses derived from the two methods yields information on the geometry of the gas emitting regions bound to the massive BH. The cumulative distribution of the linewidths is consistent with that produced by matter laying in planes with inclinations uniformly distributed between similar to 10 degrees and similar to 50 degrees, which corresponds to a geometrical factor f similar to 1.3. Our results are compared with those of the literature and discussed within the unified model of active galactic nuclei.