Star Formation, Stellar Feedback, and the Ecology of Galaxies

I will discuss the evolution of molecular gas and subsequent star formation/feedback across the entire disk of the barred spiral galaxy M83. I will show an analysis of the ALMA CO J=1-0 and 2-1 line maps, which have x10 higher sensitivity (10^4Msun) and x2-3 higher resolution (40pc) than the target sensitivity and resolution of PHANGS. The CO 2-1/1-0 ratio map clearly shows the large-scale variations of gas physical conditions as a function of galactic structures. The density and temperature of the bulk gas systematically increase by a factor of 2-3 from the interarm regions to the bar and spiral arms. This gas evolution occurs even without (massive) star formation and is likely controlled by large-scale galactic dynamics. HII regions appear as a consequence of this evolution, and their feedback appears to push the gas density and temperature even higher. However, the impacts of the feedback is localized to their vicinity, and therefore, it role is limited in the galaxy-scale gas evolution. A similar evolutionary sequence is seen in an analysis of molecular clouds. Low-mass, unbound clouds without star formation are abundant in the interarm regions. They become more massive and bounds in the bar and spiral arms and form stars. These results suggest that both stellar feedback and galactic dynamics should be considered as the energy sources for ISM evolution, star formation, and galaxy evolution (Koda et al. submitted). M83 is the closest morphological analog of the Milky Way at the very close distance (4.5 Mpc), and thus, is an important prototype of MW-type galaxies. The similar evolutionary trends are also being confirmed in other spiral galaxies in our on-going ALMA survey.