On the geometry of broad emission region in quasars

We study the geometry of the H beta broad emission region by comparing the M-BH values derived from H beta through the virial relation with those obtained from the host galaxy luminosity in a sample of 36 low-redshift (z similar to 0.3) quasars. This comparison lets us infer the geometrical factor f needed to deproject the line-of-sight velocity component of the emitting gas. The wide range of f values we found, together with the strong dependence of f on the observed linewidth, suggests that a disc-like model for the broad-line region is preferable to an isotropic model, both for radio-loud and radio-quiet quasars. We examined similar observations of the C-IV line and found no correlation in the width of the two lines. Our results indicate that an inflated disc broad-line region, in which the Carbon line is emitted in a flat disc while H beta is produced in a geometrically thick region, can account for the observed differences in the width and shape of the two emission lines.