Environmental dependences of the molecular cloud lifecycle in 54 main sequence galaxies
Jaeyeon Kim
Tuesday, Dec. 6th, 12:30CET
The processes of star formation and feedback take place on the scales of giant molecular clouds (GMCs; ~100 pc) within galaxies and play a major role in governing galaxy evolution. However, the detailed characteristics of these processes are unknown due to a lack of systematic observational constraints, and it is still a key open question which physical mechanisms regulate the evolutionary cycle between gas and stars in galaxies. By capitalizing on cloud-scale resolution, galaxy-wide CO and Halpha observations from the PHANGS survey, I have systematically established the evolutionary timeline from molecular clouds to exposed young stellar regions, across 54 star-forming main-sequence galaxies, which is the largest and most statistically complete sample to-date. I find that clouds live for about 1-3 GMC crossing times (5-30 Myr). CO and Halpha emission are found coincident for 1-5Myr, during which stellar feedback efficiently disperses the surrounding molecular gas. These timescales show galaxy-to-galaxy variations, correlating with galactic-scale environmental properties (e.g. molecular gas surface density, stellar mass). These correlations can be physically understood, revealing the role of galactic-scale dynamical processes on the small-scale evolutionary cycle of molecular clouds, star-formation, and feedback. Beyond the exposed phase of star formation traced by Halpha, I have recently shown that the earliest phases of star formation, still deeply embedded, can be characterized using infra-red observations. However, such measurements were only possible in the five nearest galaxies in my sample (D < 3.5Mpc), due to the limited resolution of Spitzer. Using novel JWST observations of NGC628, I now demonstrate that the heavily obscured star formation can be characterized at a distance of 9.8Mpc, pioneering the way for the systematic characterization of the early phases of star formation across the 19 nearby galaxy population (up to 20Mpc) with the PHANGS-JWST survey.