Kinematics of Arp 270: gas flows, nuclear activity and two regimes of star formation

TL;DR

This study investigates gas flows, nuclear activity, and star formation regimes in the Arp 270 galaxy system using H-alpha emission data, revealing inflows, outflows, and two distinct star formation modes.

Contribution

It provides new insights into the kinematics, nuclear activity, and star formation regimes in Arp 270, including measurements of HII regions and evidence for different formation mechanisms.

Findings

Detection of gas inflow and superwind outflows in NGC 3396.

Identification of two distinct star formation regimes based on luminosity.

High velocity dispersions in luminous HII regions suggest formation from massive gravitationally bound clouds.

Abstract

We have observed the Arp 270 system (NGC 3395 & NGC 3396) in H{\alpha} emission using the GH{\alpha}FaS Fabry-Perot spectrometer on the 4.2m William Herschel Telescope (La Palma). In NGC 3396, which is edge-on to us, we detect gas inflow towards the centre, and also axially confined opposed outflows, characteristic of galactic superwinds, and we go on to examine the possibility that there is a shrouded AGN in the nucleus. The combination of surface brightness, velocity and velocity dispersion information enabled us to measure the radii, FWHM, and the masses of 108 HII regions in both galaxies. We find two distinct modes of physical behaviour, for high and lower luminosity regions. We note that the most luminous regions show especially high values for their velocity dispersions and hypothesize that these occur because the higher luminosity regions form from higher mass, gravitationally bound clouds while those at lower luminosity HII regions form within molecular clouds of lower mass, which are pressure confined.