Fundamental galaxy parameters for radio-loud active galactic nuclei and the black hole-radio power connection

Abstract

We have determined the central velocity dispersions and surface brightness profiles for a sample of powerful radio galaxies in the redshift range 0.06 < z < 0.31, which were selected on the basis of their young radio source. The optical hosts follow the fundamental plane of elliptical galaxies, showing that young radio sources reside in normal ellipticals, as do other types of radio galaxies into which these objects are believed to evolve. As young radio sources are relatively straightforward to select and the contributions of the active galactic nuclei (AGN) light to the optical spectra are minimal, these objects can readily be used to study the evolution of the fundamental plane of elliptical galaxies out to z = 1, independent of optical selection effects. The black hole masses, M b h , of the objects in our sample have been determined using the tight empirical relation of M b h with central velocity dispersion, σ e , and for literature samples of classical radio galaxies and optically selected ellipticals. Only the optically selected inactive galaxies are found to exhibit a correlation between M b h and radio luminosity. In contrast, the radio powers of the AGN in the samples do not correlate with M b h at all, with objects at a given black hole mass ranging over seven orders of magnitude in radio power. It is unlikely that beaming of the radio emission is responsible for the range in radio powers. We have been able to tie in the local population of powerful radio sources with its parent population of inactive elliptical galaxies: the local black hole mass function has been determined using the elliptical galaxy luminosity function and the Faber-Jackson and M b h -σ relations. This was combined with the fraction of radio-loud black holes as a function of M b h , as determined from the optically selected galaxy sample, to derive the local volume-density of radio galaxies and the distribution of their black hole masses. These are shown to be consistent with the local radio luminosity function and the distribution of black hole masses as found in the radio-selected samples, and confirms that elliptical galaxies comprise the large majority of the radio-loud population of active galaxies.