Mechanical feedback in the molecular ISM of luminous IR galaxies

TL;DR

This study analyzes molecular emission lines in luminous IR galaxies to understand the physical state of their nuclear interstellar medium, revealing distinct regimes influenced by UV, X-ray, and mechanical feedback.

Contribution

It introduces a comprehensive comparison of molecular line observations with models including various heating mechanisms, identifying three distinct ISM regimes in luminous IR galaxies.

Findings

Identification of three ISM regimes: XDRs, UV-dominated high-density PDRs, and mechanically heated lower-density PDRs.

Correlation between star formation evolution and the dominant heating mechanism in the nuclear ISM.

Mechanical feedback becomes dominant as star formation progresses and gas density decreases.

Abstract

Aims: Molecular emission lines originating in the nuclei of luminous infra-red galaxies are used to determine the physical properties of the nuclear ISM in these systems. Methods: A large observational database of molecular emission lines is compared with model predictions that include heating by UV and X-ray radiation, mechanical heating, and the effects of cosmic rays. Results: The observed line ratios and model predictions imply a separation of the observedsystems into three groups: XDRs, UV-dominated high-density (n>=10^5 cm-3) PDRs, and lower-density (n=10^4.5 cm-3) PDRs that are dominated by mechanical feedback. Conclusions: The division of the two types of PDRs follows naturally from the evolution of the star formation cycle of these sources, which evolves from deeply embedded young stars, resulting in high-density (n>=10^5 cm-3) PDRs, to a stage where the gas density has decreased (n=10^4.5 cm-3) and mechanical feedback from supernova shocks dominates the heating budget.