Quantitative analysis of the molecular gas morphology in nearby disk galaxies.

This article presents a quantitative and statistical analysis of molecular gas morphology in 73 nearby galaxies using high-resolution CO (J = 2–1) data from the PHANGS-ALMA survey conducted with the Atacama Large Millimeter/submillimeter Array (ALMA). The study applies the model-independent CAS classification scheme—comprising concentration (C), asymmetry (A), and clumpiness (S) parameters—to characterize molecular gas distributions. Key findings include a significant correlation between asymmetry and clumpiness, suggesting that galaxies with distorted molecular gas distributions tend to have more local clumps, and a higher central concentration of molecular gas in barred spiral galaxies, with concentration positively correlated to bar length. The results also indicate that CAS parameters can effectively distinguish galaxy types based on molecular gas morphology, offering a framework for understanding molecular gas evolution and providing a basis for future morphological classification of gas and dust in more distant galaxies observed with ALMA.