2025/07/17 by Lee, Amanda M, Koda, Jin, Egusa, Fumi +4
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2507.13498
We present early results from a high-resolution analysis (∼100-200pc) of the CO(2-1)/CO(1-0) line ratio in twelve nearby galaxies. We use new ALMA CO(1-0) observations from the Fundamental CO(1-0) Transition Survey (FACTS), and re-imaged CO(2-1) data from PHANGS. We make empirical classifications based on the optical and molecular gas morphologies, which show clear systematic trends in the variation of R21 as a function of galactic structure. The sample includes barred and unbarred, and flocculent galaxies. The barred spiral galaxies follow a general trend: R21 is high in the center, low along the bar, increases at the bar ends, and then declines in the outer parts of the disk. The structure dependence suggests the importance of galactic dynamics on molecular gas evolution, and consequently on star formation, in galaxies. R21 fluctuates in the spiral arms for both barred and unbarred galaxies. HII regions increase R21 locally in their surrounding gas and are often associated with galactic structures. Together, R21 varies systematically as a function of galactic structure, dynamics, and star formation activity.