Molecular Outflows in Local ULIRGs: Energetics from Multitransition OH Analysis

Abstract

We report on the energetics of molecular outflows in 14 local Ultraluminous Infrared Galaxies (ULIRGs) that show unambiguous outflow signatures (P-Cygni profiles or high-velocity absorption wings) in the far-infrared lines of OH measured with the Herschel/PACS spectrometer. All sample galaxies are gas-rich mergers at various stages of the merging process. Detection of both ground-state (at 119 and 79 µm) and one or more radiatively-excited (at 65 and 84 µm) lines allows us to model the nuclear gas ( 300 pc) as well as the more extended components using spherically symmetric radiative transfer models. Reliable models and the corresponding energetics are found in 12 of the 14 sources. The highest molecular outflow velocities are found in buried sources, in which slower but massive expansion of the nuclear gas is also observed. With the exception of a few outliers, the outflows have momentum fluxes of (2 − 5) × L IR /c and mechanical luminosities of (0.1 − 0.3)% of L IR . The moderate momentum boosts in these sources ( 3) suggest that the outflows are mostly momentum-driven by the combined effects of AGN and nuclear starbursts, as a result of radiation pressure, winds, and supernovae remnants. In some sources (∼ 20%), however, powerful (10 10.5−11 L ⊙ ) AGN feedback and (partially) energy-conserving phases are required, with momentum boosts in the range 3 − 20. These outflows appear to be stochastic, strong-AGN feedback events that occur throughout the merging process. In a few sources, the outflow activity in the innermost regions has subsided in the last ∼ 1 Myr. While OH traces the molecular outflows at sub-kpc scales, comparison of the masses traced by OH with those previously inferred from tracers of more extended outflowing gas suggests that most mass is loaded (with loading factors ofṀ /SFR = 1 − 10) from the central galactic cores (a few × 100 pc), qualitatively consistent with an ongoing inside-out quenching of star formation. Outflow depletion timescales are < 10 8 yr, shorter than the gas consumption timescales by factors of 1.1 − 15, and are anti-correlated with the AGN luminosity.

Outflows of hot molecular gas in ultra-luminous infrared galaxies mapped with VLT-SINFONI

“…The outflow velocities that we observe in the H 2 line with SINFONI are within the range of the OH outflows detected with Herschel. However, the mass outflow rates derived from OH measurements by Sturm et al (2011) and González-Alfonso et al (2017) are nearly ubiquitouslyṀ H 2 > ∼ 100 M yr −1 . Our SINFONI data suggest also here that either molecular outflow rates in nearby ULIRGs are much more moderate than predicted based on OH studies, or that our assumed hot-to-cold gas mass ratio for H 2 outflows in ULIRGs is too large.…”

“…Some of the most spectacular molecular gas outflows in ULIRGs have been detected with the Herschel Space Observatory in the OH line (e.g., Sturm et al 2011;Spoon et al 2013;Veilleux et al 2013;González-Alfonso et al 2017). The outflow velocities that we observe in the H 2 line with SINFONI are within the range of the OH outflows detected with Herschel.…”

“…According to González-Alfonso et al (2017), this could suggest that OH and CO trace outflows in different regions of the galaxy. After all, they argue that as the outflowing gas expands and breaks up into clumps, it will "cover a decreasing fraction of the far-IR continuum".…”

“…These studies focused on the coldest phase of molecular outflows, by using strong tracers like CO andOH 119µm (e.g., Feruglio et al 2010, 2015;Fischer et al 2010;Chung et al 2011;Sturm et al 2011;Spoon et al 2013;Veilleux et al 2013;Dasyra & Combes 2012;Dasyra et al 2014;Cicone et al 2014;Sakamoto et al 2014;García-Burillo et al 2015;Aalto et al 2015;Pereira-Santaella et al 2016;González-Alfonso et al 2017). Direct measurements of molecular hydrogen in outflows rely on detecting warm and hot H 2 emission in the mid-to near-IR (e.g., Valentijn & van der Article number, page 1 of 11 arXiv:1708.09503v1 [astro-ph.GA] 30 Aug 2017 A&A proofs: manuscript no.…”

Quasar-mode Feedback in Nearby Type 1 Quasars: Ubiquitous Kiloparsec-scale Outflows and Correlations with Black Hole Properties

“…An increasingly large body of evidence points to the presence of wide-angle, galaxy-scale outflows of gas and dust in the host galaxies of many nearby Type 2 quasars (Westmoquette et al 2012;Rupke & Veilleux 2013a,b;Veilleux et al 2013a;Cicone et al 2014;Harrison et al 2014;McElroy et al 2015;Bae et al 2017;González-Alfonso et al 2017;Wylezalek et al 2017). These galactic winds, driven by the radiative and mechanical luminosity of the central engine, expel gas from the nucleus, and thereby from the sites of ongoing star formation and black hole accretion.…”