BH mass determination of low redshift quasars

We present the analysis of the photometric and spectroscopic properties of a sample of 29 low redshift (z < 0.6) QSOs for which both HST WFPC2 optical 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) line width and the 1350 angstrom continuum luminosity. From these quantifies we can estimate the black bole (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.