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

December 2020 • 2020ApJ...905...16F

Authors • Finnerty, Luke • Larson, Kirsten • Soifer, B. T. • Armus, Lee • Matthews, Keith • Jun, Hyunsung D. • Moon, Dae-Sik • Melbourne, Jason • Gomez, Percy • Tsai, Chao-Wei • Díaz-Santos, Tanio • Eisenhardt, Peter • Cushing, Michael

Abstract • 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 $8000\ {M}_{\odot }\,{\mathrm{yr}}^{-1}$ , with a median of $150\ {M}_{\odot }\,{\mathrm{yr}}^{-1}$ . 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 ${M}_{\odot }\,{\mathrm{yr}}^{-1}$ , with a median of $50\ {M}_{\odot }\,{\mathrm{yr}}^{-1}$ . 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 ${M}_{\mathrm{BH}}\mbox{--}{\sigma }_{* }$ 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.


IPAC Authors


Lee Armus

Senior Scientist