Increased molecular gas velocity dispersion and star formation efficiency in barred galaxy centres

TL;DR

This study analyzes high-resolution CO data to compare molecular gas properties and star formation efficiency in barred versus unbarred galaxy centers, revealing higher velocity dispersions and shorter depletion times in barred galaxies.

Contribution

It introduces a velocity dispersion-dependent CO-to-H2 conversion factor and demonstrates differences in gas dynamics and star formation efficiency between barred and unbarred galaxy centers.

Findings

Barred galaxy centers have higher molecular gas velocity dispersions.

Star formation depletion times are shorter in barred galaxy centers.

Velocity dispersion correlates with star formation rate, indicating non-circular motions.

Abstract

Work by the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) collaboration found higher molecular gas surface densities and velocity dispersions in the centres of barred galaxies compared to unbarred galaxies. We explore central molecular gas using published high resolution (150 pc) measurements of CO$(2-1)$ from the PHANGS-ALMA survey and a new velocity dispersion-dependent prescription for the CO-to-H$_{2}$ conversion factor $\alpha_{\rm{CO}}$. Comparisons of the molecular gas surface density, velocity dispersion, star formation rate, and depletion time reveal that these quantities are different in the centres of barred and unbarred galaxies. Gas depletion times are found to be shorter in barred galaxy centres. Even when we control for the presence of an AGN, the velocity dispersion and depletion time are found to be statistically different between barred and unbarred galaxy centres. The higher velocity dispersion suggests extra non-circular motions, possibly due to the inflow of gas along the bar, that are not constant but must increase as the star formation rate increases.