Shocked Gas in IRAS F17207-0014: ISM Collisions and Outflows

TL;DR

This study uses optical and near-infrared observations to analyze shock phenomena and galactic winds in the merging ULIRG IRAS F17207-0014, revealing widespread shocks and collimated outflows associated with galaxy interaction.

Contribution

It provides high-resolution evidence of two types of shocks near the nuclei, linking them to ISM collisions and outflow activity in a merging galaxy.

Findings

Widespread shocks are present throughout the galaxy, especially at large radii.

Two types of shocks near the nuclei: diffuse shocks from ISM collision and collimated shocks from outflows.

Strong shocks extend about 400 pc from the nuclear disks, indicating active outflow processes.

Abstract

We combine optical and near-infrared AO-assisted integral field observations of the merging ULIRG IRAS F17207-0014 from the Wide-Field Spectrograph (WiFeS) and Keck/OSIRIS. The optical emission line ratios [N II]/H$\alpha$, [S II]/H$\alpha$, and [O I]/H$\alpha$ reveal a mixing sequence of shocks present throughout the galaxy, with the strongest contributions coming from large radii (up to 100% at $\sim$5 kpc in some directions), suggesting galactic-scale winds. The near-infrared observations, which have approximately 30 times higher spatial resolution, show that two sorts of shocks are present in the vicinity of the merging nuclei: low-level shocks distributed throughout our field-of-view evidenced by an H$_{2}$/Br$\gamma$ line ratio of $\sim$0.6-4, and strong collimated shocks with a high H$_{2}$/Br$\gamma$ line ratio of $\sim$4-8, extending south from the two nuclear disks approximately 400 pc ($\sim$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 disks.