Spectral Classification and Ionized Gas Outflows in z ∼ 2 WISE-selected Hot Dust-obscured Galaxies

Abstract

Abstract We present Very Large Telescope/XSHOOTER rest-frame UV–optical spectra of 10 hot dust-obscured galaxies (Hot DOGs) at z ∼ 2 to investigate active galactic nucleus (AGN) diagnostics and assess the presence and effect of ionized gas outflows. Most Hot DOGs in this sample are narrow-line-dominated AGNs (type 1.8 or higher) and have higher Balmer decrements than typical type 2 quasars. Almost all (8/9) sources show evidence for ionized gas outflows in the form of broad and blueshifted [O iii] profiles, and some sources have such profiles in Hα (5/7) or [O ii] (3/6). Combined with the literature, these results support additional sources of obscuration beyond the simple torus invoked by AGN unification models. Outflow rates derived from the broad [O iii] line (≳103 M ⊙ yr−1) are greater than the black hole accretion and star formation rates, with feedback efficiencies (∼0.1%–1%) consistent with negative feedback to the host galaxy’s star formation in merger-driven quasar activity scenarios. We find that the broad emission lines in luminous, obscured quasars are often better explained by outflows within the narrow-line region and caution that black hole mass estimates for such sources in the literature may have substantial uncertainty. Regardless, we find lower bounds on the Eddington ratio for Hot DOGs near unity.