Molecular gas inflows and outflows in ultraluminous infrared galaxies at z ∼ 0.2 and one QSO at z = 6.1⋆

Abstract

Aims. Our aim is to search for and characterize inflows and outflows of molecular gas in four ultraluminous infrared galaxies (ULIRGs; L IR > 10 12 L ⊙ ) at z ∼ 0.2−0.3 and one distant quasi-stellar object (QSO) at z = 6.13. Methods. We used Herschel /PACS and ALMA Band 7 observations of the hydroxyl molecule (OH) line at rest-frame wavelength 119 μ m, which in absorption can provide unambiguous evidence of inflows or outflows of molecular gas in nuclear regions of galaxies. Our study contributes to doubling the number of OH 119 μ m observations of luminous systems at z ∼ 0.2−0.3, and pushes the search for molecular outflows based on the OH 119 μ m transition to z ∼ 6.

Results. We detect OH 119 μ m high-velocity absorption wings in three of the four ULIRGs. In two cases, IRAS F20036−1547 and IRAS F13352+6402, the blueshifted absorption profiles indicate the presence of powerful and fast (∼200−500 km s −1 ) molecular gas outflows. Consistent with an inside-out quenching scenario, these outflows are depleting the central reservoir of star-forming molecular gas at a rate similar to that of intense star formation activity. For the starburst-dominated system IRAS 10091+4704, we detect an inverted P Cygni profile that is unique among ULIRGs and indicates the presence of a fast (∼400 km s −1 ) inflow of molecular gas at a rate of ∼100 M ⊙ yr −1 towards the central region. Finally, we tentatively detect (∼3 σ ) the OH 119 μ m doublet in absorption in the z = 6.13 QSO ULAS J131911+095051. The OH 119 μ m feature is blueshifted with a median velocity that suggests the presence of a molecular outflow, although characterized by a modest molecular mass loss rate of ∼200 M ⊙ yr −1 . This value is comparable to the small mass outflow rates found in the stacking of the [C II ] spectra of other z ∼ 6 QSOs and suggests that ejective feedback in this phase of the evolution of ULAS J131911+095051 has subsided.