Black hole demographics from the 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     is reasonably well described as a Gaussian with     and standard deviation ～0.45; the implied mean ratio of black hole mass to bulge mass is a factor of ～5 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 ～     consistent with that inferred from high-redshift     active galactic nuclei.