**AAS 199th meeting, Washington, DC, January 2002**

*Session 25. Black Holes, Dark Matter and X-ray Sources in Extragalactic Systems*

Oral, Monday, January 7, 2002, 10:00-11:30am, International Ballroom East
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## [25.04] The Black Hole Mass Density from Velocity Dispersions

*M.C. Aller, D.O. Richstone (University of Michigan)*

Using a basic assumption that the bulge velocity dispersion
of a galaxy can be used to predict the mass of its
supermassive black hole, it is possible to estimate the mass
density of black holes in the universe. Constructing the
number density as a function of galaxy velocity dispersion
from published data, an expression for the number density of
black holes as a function of mass can be constructed. By
taking a Schechter-type luminosity function for a given
galaxy type, and applying an appropriate bulge-to-total
galaxy magnitude correction, the number density as a
function of bulge luminosity can be obtained. This function
may then be combined with a Faber-Jackson power law relating
velocity dispersion and luminosity to obtain a velocity
dispersion function for each galaxy type. By coupling this
dispersion function with a relationship between the mass of
the black hole and the velocity dispersion of its host
galaxy, it is possible to produce an expression for the
number density of black holes as a function of black hole
mass for each galaxy type, which is of a similar form to a
Schechter function. By integrating this function over all
black hole mass, an estimate of the mass density of black
holes for a given galaxy type may be obtained. Summing over
all galaxy types, the cumulative mass density of black holes
is found to be 6 \cdot 10^{5} solar masses per cubic
megaparsec for an h=1 universe.

The authors acknowledge support from NASA/Space Telescope
Science Institute.

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