The Dust-to-gas Ratio and the Role of Radiation Pressure in Luminous, Obscured Quasars

Abstract

Abstract The absence of high-Eddington-ratio, obscured active galactic nuclei (AGNs) in local (z ≲ 0.1) samples of moderate-luminosity AGNs has generally been explained to result from radiation pressure on the dusty gas governing the level of nuclear (≲10 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 submillimeter selected AGNs at quasar luminosities. Whereas moderate-luminosity, obscured AGNs in the local universe have a range of lower Eddington ratios (f Edd ∼ 0.001–0.1), the most luminous (L bol ≳ 1046 erg s−1) IR/submillimeter-bright, obscured quasars out to z ∼ 3 commonly have very high Eddington ratios (f Edd ∼ 0.11). 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 because of the short timescale for which quasars are most luminous. When adopting quasar evolutionary scenarios, extended (∼102–3 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.