Eddington ratio and accretion efficiency in AGN evolution
  The cosmological evolution of Active Galactic Nuclei (AGN) is important for
understanding the mechanism of accretion onto supermassive black holes, and the
related evolution of the host galaxy. In this work, we include objects with
very low Eddington ratio (10^{-3} - 10^{-2}) in an evolution scenario, and
compare the results with the observed local distribution of black holes. We
test several possibilities for the AGN population, considering obscuration and
dependence with luminosity, and investigate the role of the Eddington ratio and
radiative accretion efficiency on the shape of the evolved mass function. We
find that three distinct populations of AGN can evolve with a wider parameter
range than is usually considered, and still be consistent with the local mass
function. In general, the black holes in our solutions are spinning rapidly.
Taking fixed values for accretion efficiency and Eddington ratio neither
provides a full knowledge of the evolution mechanism nor is consistent with the
existence of low Eddington ratio objects.
