Kinematics of the ionized and molecular gas in nearby luminous infrared interacting galaxies

TL;DR

This study investigates the internal kinematics and physical properties of star-forming regions and molecular clouds in interacting luminous infrared galaxies, revealing higher surface densities and gravitationally dominated clouds compared to non-interacting galaxies.

Contribution

It combines optical and millimeter observations to analyze the kinematics and physical conditions of star-forming regions in interacting galaxies, highlighting their similarity to high-redshift starburst environments.

Findings

Higher star formation rate and molecular gas surface densities than in non-interacting galaxies.

Star-forming regions are in virial equilibrium and gravitationally dominated.

Enhanced velocity dispersion correlates with higher gas surface density.

Abstract

We have observed three luminous infrared galaxy systems (LIRGS) which are pairs of interacting galaxies, with the Galaxy H$\alpha$ Fabry-Perot system (GH$\alpha$FaS) mounted on the 4.2m William Herschel Telescope at the Roque de los Muchachos Observatory, and combined the observations with the Atacama Large Millimeter Array (ALMA) observations of these systems in CO emission to compare the physical properties of the star formation regions and the molecular gas clouds, and specifically the internal kinematics of the star forming regions. We identified 88 star forming regions in the H$\alpha$ emission data-cubes, and 27 molecular cloud complexes in the CO emission data-cubes. The surface densities of the star formation rate and the molecular gas are significantly higher in these systems than in non-interacting galaxies and the Galaxy, and are closer to the surface densities of the star formation rate and the molecular gas of extreme star forming galaxies at higher redshifts. The large values of the velocity dispersion also show the enhanced gas surface density. The HII regions are situated on the ${\rm{SFR}}-\sigma_v$ envelope, and so are also in virial equilibrium. Since the virial parameter decreases with the surface densities of both the star formation rate and the molecular gas, we claim that the clouds presented here are gravitationally dominated rather than being in equilibrium with the external pressure.