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

We present rest-frame optical spectroscopic observations of 18 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 16 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 13 targets with a clear detection of the [O III]λ5007 ̊A emission line, 12 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 with respect to the narrow emission component. These line properties provide strong evidence for the presence of massive ionized outflows of up to 8000 M⊙ yr−1, with a median of 230 M⊙ yr−1. Three sources, and possibly as many as seven, show optical emission line ratios consistent with vigorous ongoing star formation. The resulting Balmer line star-formation rates, uncorrected for reddening, range from 30–1300 M⊙ yr−1, with a median of 80 M⊙ yr−1. Estimates of the SFR from SED fitting of the mid and far-infrared emission suggest significantly higher values. We estimate the central black hole masses to be of order 108−10 M⊙, assuming the present-day MBH −σ∗ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the AGN-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.