Letter to the Editor

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

¹ Departamento de Astronomía, Universidad de Concepción, Barrio Universitario, Concepción, Chile
e-mail: rhc@astro-udec.cl
² Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstr., 85748 Garching, Germany
³ Department of Astronomy and Joint Space-Science Institute, Univ. of Maryland, College Park, MD 20742, USA
⁴ Space Telescope Science Institute, Baltimore, MD 21218, USA
⁵ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁶ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁷ Departamento de Física y Matemáticas, Univ. de Alcalá, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
⁸ George Mason University, Department of Physics & Astronomy, MS 3F3, 4400 University Drive, Fairfax, VA 22030, USA
⁹ Raymond and Beverly Sackler School of Physics & Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel
¹⁰ Sub-department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH, UK

Received: 14 November 2019
Accepted: 11 December 2019

Abstract

Aims. Our aim is to search for and characterize inflows and outflows of molecular gas in four ultraluminous infrared galaxies (ULIRGs; L_IR >  10¹²L_⊙) 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 μm, 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 μm observations of luminous systems at z ∼ 0.2−0.3, and pushes the search for molecular outflows based on the OH 119 μm transition to z ∼ 6.

Results. We detect OH 119 μm 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 (∼3σ) the OH 119 μm doublet in absorption in the z = 6.13 QSO ULAS J131911+095051. The OH 119 μm 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.