Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES

We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to $8000M_{\odot }{yr}^{-1}$, with a median of $150M_{\odot }{yr}^{-1}$. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 $M_{\odot }{yr}^{-1}$, with a median of $50M_{\odot }{yr}^{-1}$. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order ${10}^{8-10}{M}_{\odot }$, assuming the present-day $M_{BH}\text{--}{\sigma }_{\ast }$ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution.