REVIEW - ALMA Brings Molecular Gas in Galaxies Into Focus

Over its first few years of operation, ALMA has dramatically sharpened our view of cold gas in galaxies. I will review highlights from these first few years. These include resolving cold gas disks and outflows from centers of active galaxies, discovering forming star clusters in dwarf and starburst galaxies, and directly imaging the dense, star-forming gas in other galaxies. I will also give an overview of ALMA's first Large Program targeting nearby galaxies. PHANGS ALMA is carrying out the first high completeness, wide area survey of individual molecular clouds across the whole nearby galaxy population. Using CO 2-1 emission, this survey traces the structure and kinematics of gas at ~ 100 pc resolution across more than 80 nearby star forming galaxies. These observations reveal a highly structured medium in which the distribution and properties of cold gas clouds are closely coupled to the host galaxy and galactic environment. When the cold gas seen by ALMA is contrasted with signatures of high mass star formation, these same observations show a violent cycle of cloud collapse and feedback. Based on what ALMA has done so far, I will also call out some of the major questions for the next five years.