Shocked gas in IRAS F17207-0014: ISM collisions and outflows

Abstract

We combine optical and near-infrared adaptive optics-assisted integral field observations of the merging ultraluminous infrared galaxies IRAS F17207-0014 from the Wide-Field Spectrograph and Keck/OH-Suppressing Infra-Red Imaging Spectrograph (OSIRIS). The optical emission line ratios [NII]/Hα, [SII]/Hα, and [O I]/Hα reveal a mixing sequence of shocks present throughout the galaxy, with the strongest contributions coming from large radii (up to 100 per cent at ~5 kpc in some directions), suggesting galactic-scale winds. The near-infrared observations, which have approximately 30 times higher spatial resolution, show that two sorts of shocks are present in the vicinity of the merging nuclei: low-level shocks distributed throughout our field-of-view evidenced by an H2/Brγ line ratio of ~0.6-4, and strong collimated shocks with a high H2/Brγ line ratio of ~4-8, extending south from the two nuclear discs approximately 400 pc (~0.5 arcsec). Our data suggest that the diffuse shocks are caused by the collision of the interstellar media associated with the two progenitor galaxies and the strong shocks trace the base of a collimated outflow coming from the nucleus of one of the two discs.