The fraction of galaxies that contain active nuclei and their accretion rates

We investigate the relationship between the present day optical luminosity function of galaxies and the X–ray luminosity function of Seyfert 1s to determine the fraction of galaxies which host Seyfert 1 nuclei and their Eddington ratios. The local type 1 AGN X–ray luminosity function is well reproduced if ∼ 1% of all galaxies are type 1 Seyferts which have Eddington ratios of ∼ 10−3. However, in such a model the X–ray luminosity function is completely dominated by AGN in E and S0 galaxies, contrary to the observed mix of Seyfert host galaxies. To obtain a plausible mix of AGN host galaxy morphologies requires that the most massive black holes in E and S0 galaxies accrete with lower Eddington ratios, or have a lower incidence of Seyfert activity, than the central black holes of later type galaxies.