AGN and their host galaxies in the local Universe: two mass independent
  Eddington ratio distribution functions characterize black hole growth
  We use a phenomenological model to show that black hole growth in the local
Universe (z < 0.1) can be described by two separate, mass independent Eddington
ratio distribution functions (ERDFs). We assume that black holes can be divided
into two independent groups: those with radiatively efficient accretion,
primarily hosted by optically blue and green galaxies, and those with
radiatively inefficient accretion, which are mainly found in red galaxies. With
observed galaxy stellar mass functions as input, we show that the observed AGN
luminosity functions can be reproduced by using mass independent, broken power
law shaped ERDFs. We use the observed hard X-ray and 1.4 GHz radio luminosity
functions to constrain the ERDF for radiatively efficient and inefficient AGN,
respectively. We also test alternative ERDF shapes and mass dependent models.
Our results are consistent with a mass independent AGN fraction and AGN hosts
being randomly drawn from the galaxy population. We argue that the ERDF is not
shaped by galaxy-scale effects, but by how efficiently material can be
transported from the inner few parsecs to the accretion disc. Our results are
incompatible with the simplest form of mass quenching where massive galaxies
host higher accretion rate AGN. Furthermore, if reaching a certain Eddington
ratio is a sufficient condition for maintenance mode, it can occur in all red
galaxies, not just the most massive ones.
