PRIMUS: An observationally motivated model to connect the evolution of
  the AGN and galaxy populations out to z~1
  We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion
rate. Our model is based on measurements indicating that the specific accretion
rate distribution is a universal function across a wide range of host stellar
mass with slope gamma_1 = -0.65 and an overall normalization that evolves with
redshift. We test several simple assumptions to extend this model to high
specific accretion rates (beyond the measurements) and compare the predictions
for the XLF with the observed data. We find good agreement with a model that
allows for a break in the specific accretion rate distribution at a point
corresponding to the Eddington limit, a steep power-law tail to super-Eddington
ratios with slope gamma_2 = -2.1 +0.3 -0.5, and a scatter of 0.38 dex in the
scaling between black hole and host stellar mass. Our results show that samples
of low luminosity AGNs are dominated by moderately massive galaxies (M* ~
10^{10-11} M_sun) growing with a wide range of accretion rates due to the shape
of the galaxy stellar mass function rather than a preference for AGN activity
at a particular stellar mass. Luminous AGNs may be a severely skewed population
with elevated black hole masses relative to their host galaxies and in rare
phases of rapid accretion.
