Black Hole Demographics from the M(BH)-sigma Relation
Abstract
We analyze 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, MBH, using the tight empirical correlation between MBH and the bulge stellar velocity dispersion. The frequency function N(log MBH/Mbulge) is reasonably well described as a Gaussian with <log MBH/Mbulge> ~ -2.90 and standard deviation 0.45; the implied mean ratio of black hole to bulge mass is a factor 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 x 105 solar masses per cubic megaparsec, consistent with that inferred from high redshift (z ~ 2) AGNs.
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