The Young, the Old, and the Dusty: Stellar Populations of AGN Hosts
  Studying the average properties of active galactic nuclei (AGN) host stellar
populations is an important step in understanding the role of AGN in galaxy
evolution and the processes which trigger and fuel AGN activity. Here we
calculate model spectral energy distributions (SEDs) that include emission from
the AGN, the host galaxy stellar population, and dust enshrouded star
formation. Using the framework of cosmic X-ray background population synthesis
modeling, the model AGN hosts are constrained using optical (B band) and near
infrared (J band, 3.6 um, 5.7 um, 8.0 um, and 24 um) luminosity functions and
number counts. It is found that at z < 1, type 1 and type 2 AGN hosts have
similar stellar populations, in agreement with the orientation based unified
model and indicative of secular evolution. At z > 1, type 2 AGN hosts are
intrinsically different from type 1 AGN hosts, suggesting that the simple
orientation based unified model does not hold at z > 1. Also, it is found that
if Compton thick (CT) AGN evolve like less obscured type 2 AGN, then, on
average, CT AGN hosts are similar to type 2 AGN hosts; however, if CT
obscuration is connected to an evolutionary stage of black hole growth, then CT
AGN hosts will also be in specific evolutionary stages. Multi-wavelength
selection criteria of CT AGN are discussed.
