Remnants of the quasars

Assuming a standard black hole accretion model for quasars, we estimate the present total mass density, |BH|⁠, of quasar remnants using recent observations of quasar populations and of typical quasar spectra over a wide wavelength range. We find |BH (1. 4-2. 2) 10⁵ 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 Sołtan (1982). A typical bright galaxy is thus expected to contain a central black hole of | 10⁷ h^-3 M_|⁠. Furthermore, we expect that ≳ 50 per cent of |BH| is contributed by objects of mass | 10⁸ h^-2 M_| and ≳ 10 per cent by those more massive than about |6 10⁸ h^-2 M_|⁠.