2020ApJ...905...16F

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 8000 M_☉yr^–1, with a median of 150 M_☉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_☉yr^–1, with a median of 50 M_☉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 10^8–10M_☉, assuming the present-day M_BH–σ_* 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.