Spectral Classification and Ionized Gas Outflows in $z\sim2$ WISE-Selected Hot Dust-Obscured Galaxies

TL;DR

This study uses VLT/XSHOOTER spectra to analyze ionized gas outflows and AGN characteristics in $z ilde{2}$ Hot Dust-Obscured Galaxies, revealing significant outflows and feedback effects impacting galaxy evolution.

Contribution

It provides the first detailed spectral analysis of Hot DOGs at $z ilde{2}$, highlighting prevalent ionized outflows and their implications for AGN unification and galaxy feedback models.

Findings

Most Hot DOGs show ionized gas outflows with broad, blueshifted emission lines.

Outflow rates exceed black hole accretion and star formation rates, indicating strong feedback.

Broad emission lines are often due to outflows, affecting black hole mass estimates.

Abstract

We present VLT/XSHOOTER rest-frame UV-optical spectra of 10 Hot Dust-Obscured Galaxies (Hot DOGs) at $z\sim2$ to investigate AGN diagnostics and to assess the presence and effect of ionized gas outflows. Most Hot DOGs in this sample are narrow-line dominated AGN (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 H$\alpha$ (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 ($\rm \gtrsim10^{3}\,M_{\odot}\,yr^{-1}$) are greater than the black hole accretion and star formation rates, with feedback efficiencies ($\sim0.1-1\%$) consistent with negative feedback to the host galaxy's star formation in merger-driven quasar activity scenarios. We find 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.