High-velocity extended molecular outflow in the star-formation dominated luminous infrared galaxy ESO 320-G030

We analyze new high spatial resolution (∼60 pc) ALMA CO(2-1) observations of the isolated luminous infrared galaxy ESO 320-G030 (d = 48 Mpc) in combination with ancillary Hubble Space Telescope optical and near infrared (IR) imaging, as well as VLT/SINFONI near-IR integral field spectroscopy. We detect a high-velocity (∼450 km s) spatially resolved (size∼2.5 kpc; dynamical time ∼3 Myr) massive (∼10 M; Ṁ ∼ 2-8 M yr) molecular outflow that has originated in the central ∼250 pc. We observe a clumpy structure in the outflowing cold molecular gas with clump sizes between 60 and 150 pc and masses between 10 and 10 M. The mass of the clumps decreases with increasing distance, while the velocity is approximately constant. Therefore, both the momentum and kinetic energy of the clumps decrease outwards. In the innermost (∼100 pc) part of the outflow, we measure a hot-to-cold molecular gas ratio of 7 × 10, which is similar to that measured in other resolved molecular outflows. We do not find evidence of an ionized phase in this outflow. The nuclear IR and radio properties are compatible with strong and highly obscured star-formation (A ∼ 4.6 mag; star formation rate ∼ 15 M yr). We do not find any evidence for the presence of an active galactic nucleus. We estimate that supernova explosions in the nuclear starburst (ν ∼ 0.2 yr) can power the observed molecular outflow. The kinetic energy and radial momentum of the cold molecular phase of the outflow correspond to about 2% and 20%, respectively, of the supernovae output. The cold molecular outflow velocity is lower than the escape velocity, so the gas will likely return to the galaxy disk. The mass loading factor is ∼0.1-0.5, so the negative feedback owing to this star-formation-powered molecular outflow is probably limited.
We acknowledge support from the Spanish Plan Nacional de Astronomía y Astrofísica through grants AYA2010-21161-C02-01 and AYA2012-32295. A.A.-H. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness through grant AYA2015-64346-C2-1-P. B.E. acknowledges funding through the European Union FP7-PEOPLE2013-IEF grant 624351