REMNANTS OF THE QUASARS

Assuming a standard black hole accretion model for quasars, we estimate the present total mass density, rho(BH), of quasar remnants using recent observations of quasar populations and of typical quasar spectra over a wide wavelength range. We find rho(BH) greater than or similar to (1.4-2.2) x 10(5) M . 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 greater-than-or-similar-to 10(7) h-3 M . . Furthermore, we expect that greater than or similar to 50 per cent of rho(BH) is contributed by objects of mass greater than or similar to 10(8) h-2 M . and greater than or similar to 10 per cent by those more massive than about 6 x 10(8) h-2 M . .