Quasars: The characteristic spectrum and the induced radiative heating

Abstract

Using information on the cosmic X-ray background and the cumulative light of active galactic nuclei (AGN) at infrared wavelengths, the estimated local mass density of galactic massive black holes (MBHs) and published AGN composite spectra in the optical, UV and X-ray, we compute the characteristic angular-integrated, broad-band spectral energy distribution of the average quasar in the universe. We demonstrate that the radiation from such sources can photoionize and Compton heat the plasma surrounding them up to an equilibrium Compton temperature (TC) of 2 × 107 K. It is shown that circumnuclear obscuration cannot significantly affect the net gas Compton heating and cooling rates, so that the above TC value is approximately characteristic of both obscured and unobscured quasars. This temperature is above typical gas temperatures in elliptical galaxies and just above the virial temperatures of giant ellipticals. The general results of this work can be used for accurate calculations of the feedback effect of MBHs on both their immediate environs and the more distant interstellar medium of their host galaxies.