Molecular Gas Heating, Star Formation Rate Relations, and AGN Feedback in Infrared-luminous Galaxy Mergers

TL;DR

This study investigates the heating mechanisms of molecular gas in infrared-luminous galaxy mergers, revealing different excitation sources for various CO lines and the impact of AGN activity on starburst heating efficiency.

Contribution

It combines archival CO line data with radiative transfer modeling to distinguish heating sources and explores AGN feedback effects on molecular gas heating in galaxy mergers.

Findings

CO 1-0 and 5-4 to 9-8 lines mainly heated by starburst and host galaxy.

Higher CO lines (10-9 to 13-12) influenced by starburst, AGN, shocks, and mechanical heating.

AGN luminosity does not affect molecular gas heating overall, but can reduce starburst heating efficiency in some cases.

Abstract

We examine the origin of molecular gas heating in a sample of 42 infrared-luminous galaxies at $z<0.3$ by combining two sets of archival data. First, integrated CO line luminosities in the 1-0 and 5-4 through 13-12 transitions. Second, results from radiative transfer modelling that decompose their bolometric emission into starburst, AGN, and host galaxy components. We find that the CO 1-0 and 5-4 through 9-8 lines primarily arise via radiative heating in the starburst and the host galaxy. In contrast, the CO 10-9 through 13-12 lines may arise primarily in the starburst and AGN, with an increasing contribution from mechanical heating and shocks. For the sample as a whole, we find no evidence that AGN luminosity affects the heating of molecular gas by star formation. However, for starbursts with low initial optical depths, a more luminous AGN may reduce the efficiency of starburst heating of the CO 5-4 and above lines, consistent with negative AGN feedback.