The mass function of active black holes in the local universe

We present the first measurement of the BH mass function for broad-line active galaxies in the local universe. Using the similar to 8500 broad-line active galaxies from SDSS DR4, we construct a broad-line luminosity function that agrees very well with the local soft X-ray luminosity function. Using standard virial relations, we then convert observed broadline luminosities andwidths into BH masses. Amass function constructed in this way has the unique capability to probe the mass region < 10(6) M-circle dot, which, while insignificant in terms of total BH mass density, nevertheless may place important constraints on the mass distribution of seed BHs in the early universe. The characteristic local active BH has a mass of similar to 10(7) M-circle dot radiating at 10% of the Eddington rate. The active fraction is a strong function of BH mass; at both higher and lower masses the active mass function falls more steeply than one would infer from the distribution of bulge luminosity. The deficit of local massive radiating BHs is a well-known phenomenon, while we present the first robust measurement of a decline in the space density of active BHs at low mass.