PHANGS-ALMA: Demographics and Environment-dependence of Molecular Cloud Properties

I will show what PHANGS-ALMA tells us about the demographics and environment-dependence of the cloud-scale properties of molecular gas. PHANGS-ALMA is an ALMA large program obtaining arcsecond resolution CO imaging of ∼80 nearby, star-forming galaxies. With its linear resolution (40-120 pc) matching the typical size of individual giant molecular clouds (GMCs), PHANGS-ALMA is providing the most detailed and complete view of GMC properties across the local galaxy population. The first set of CO imaging data reveals a wide range of molecular cloud surface density and mass, velocity dispersion, and turbulent pressure. Combing these CO maps with multi-wavelength data, we conduct one of the first quantitative and complete study on the correlation between cloud-scale molecular gas properties with their local environment (characterized at kilo parsec resolution). Both molecular cloud surface density / mass and velocity dispersion correlate strongly with the local average gas abundance, stellar mass distribution, and strength of star formation activity. By comparing molecular gas turbulent pressure to the the kpc-scale average ISM pressure expected from vertical hydrostatic equilibrium, we find that molecular gas is over-pressurized (by a factor of ∼3) relative to its ambient environment. Self-gravity appears to govern cloud-scale molecular gas dynamics over a wide pressure range, whereas stellar gravity and ambientpressure only become important in low density / pressure environment. The observed relations betweenISM pressure and SFR surface density agree well with predictions from the self-regulated star forming disk model.