Black hole demographics from the M bullet -   relation

We analyse a sample of 32 galaxies for which a dynamical estimate of the mass of the hot stellar component, Mbulge, 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 Nlog(M● / Mbulge) is reasonably well described as a Gaussian with 〈log(M● / Mbulge)〉 ≈ − 2.90 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 ∼5 × 105 M⊙ Mpc −3, consistent with that inferred from high-redshift (z ∼ 2) active galactic nuclei.