Remnants of the quasars

Assuming a standard black hole accretion model for quasars, we estimate the present total mass density, |ρBH|⁠, of quasar remnants using recent observations of quasar populations and of typical quasar spectra over a wide wavelength range. We find |ρBH (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 |ρBH| 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_|⁠.