Remnants of the quasars.

Assuming a standard black hole accretion model for quasars, we estimate the present total mass density, ρ_BH_ of quasar remnants using recent observations of quasar populations and of typical quasar spectra over a wide wavelength range. We find ρ_BH_>~(1.4-2.2)x 10^5^ M_sun_ Mpc^-3^ for a quasar radiative efficiency of 0.1. This is an upward revision by a factor of 3.0-4.6 from a decade-old estimate by Soltan. A typical bright galaxy is thus expected to contain a central black hole of >~ 10^7^ h^-3^ M_sun_. Furthermore, we expect that >~ 50 per cent of ρ_BH_ is contributed by objects of mass >~10^8^h^-2^M_sun_ and >~ 10 per cent by those more massive than about 6x10^8^ h^-2^ M_sun_.