Black hole demographics from the M•-σ relation

We analyse a sample of 32 galaxies for which a dynamical estimate of the mass of the hot stellar component, M-bulge, is available. For each of these galaxies, we calculate the mass of the central black hole, M-., using the tight empirical correlation between M-. and bulge stellar velocity dispersion. The frequency function N[log(M.Mbulge)] is reasonably well described as a Gaussian with < log(M.Mbulge)> approximate to -2.90 and standard deviation similar to0.45; the implied mean ratio of black hole mass to bulge mass is a factor of similar to5 smaller than generally quoted in the literature. We present marginal evidence for a lower, average black hole mass fraction in more massive galaxies. The total mass density in black holes in the local Universe is estimated to be similar to 5x10(5) M-. Mpc(3), consistent with that inferred from high-redshift (z similar to2) active galactic nuclei.