The Dust-to-Gas Ratio and the Role of Radiation Pressure in Luminous,
  Obscured Quasars
  The absence of high Eddington ratio, obscured Active Galactic Nuclei (AGN) in
local ($z\lesssim0.1$) samples of moderate luminosity AGN has generally been
explained to result from radiation pressure on the dusty gas governing the
level of nuclear ($\lesssim10$pc) obscuration. However, very high accretion
rates are routinely reported among obscured quasars at higher luminosities, and
may require a different feedback mechanism. We compile constraints on
obscuration and Eddington ratio for samples of X-ray, optical, infrared, and
submm selected AGN at quasar luminosities. Whereas moderate luminosity,
obscured AGN in the local universe have a range of lower Eddington ratios
($f_{\rm Edd} \sim 0.001-0.1$), the most luminous ($L_{\rm bol} \gtrsim 10^{46}
$erg s$^{-1}$) IR/submm-bright, obscured quasars out to $z\sim3$ commonly have
very high Eddington ratios ($f_{\rm Edd} \sim 0.1-1$). This apparent lack of
radiation pressure feedback in luminous obscured quasars is likely coupled with
AGN timescales, such that a higher fraction of luminous obscured quasars are
seen due to the short timescale for which quasars are most luminous. Adopting
quasar evolutionary scenarios, extended ($\sim10^{2-3}$pc) obscuration may work
together with the shorter timescales to explain the observed fraction of
obscured, luminous quasars, while outflows driven by radiation pressure will
slowly clear this material over the AGN lifetime.
