The Gas–Star Formation Cycle in Nearby Star-forming Galaxies. II. Resolved Distributions of CO and Hα Emission for 49 PHANGS Galaxies
Hsi-An Pan, Hsi-An Pan, Eva Schinnerer, Annie Hughes, Adam K. Leroy, Brent Groves, Ashley T. Barnes, Francesco Belfiore, Frank Bigiel, Guillermo A. Blanc, Yixian Cao, Mélanie Chevance, Enrico Congiu, Daniel A. Dale, Cosima Eibensteiner, Éric Emsellem, Christopher M. Faesi, Simon C. O. Glover, Kathryn Grasha, Cinthya N. Herrera, I-Ting Ho, Ralf S. Klessen, J. M. Diederik Kruijssen, P. Lang, Daizhong Liu, Rebecca McElroy, Sharon E. Meidt, E. J. Murphy, J. Pety, Miguel Querejeta, Alessandro Razza, Erik Rosolowsky, Toshiki Saito, Francesco Santoro, Andreas Schruba, Jiayi Sun, Neven Tomičić, A. Usero, Dyas Utomo, Thomas G. Williams
Abstract
Abstract The relative distribution of molecular gas and star formation in galaxies gives insight into the physical processes and timescales of the cycle between gas and stars. In this work, we track the relative spatial configuration of CO and H α emission at high resolution in each of our galaxy targets and use these measurements to quantify the distributions of regions in different evolutionary stages of star formation: from molecular gas without star formation traced by H α to star-forming gas, and to H ii regions. The large sample, drawn from the Physics at High Angular resolution in Nearby GalaxieS ALMA and narrowband H α (PHANGS-ALMA and PHANGS-H α ) surveys, spans a wide range of stellar masses and morphological types, allowing us to investigate the dependencies of the gas‒star formation cycle on global galaxy properties. At a resolution of 150 pc, the incidence of regions in different stages shows a dependence on stellar mass and Hubble type of galaxies over the radial range probed. Massive and/or earlier-type galaxies in our sample exhibit a significant reservoir of molecular gas without star formation traced by H α , while lower-mass galaxies harbor substantial H ii regions that may have dispersed their birth clouds or formed from low-mass, more isolated clouds. Galactic structures add a further layer of complexity to the relative distribution of CO and H α emission. Trends between galaxy properties and distributions of gas traced by CO and H α are visible only when the observed spatial scale is ≪500 pc, reflecting the critical resolution requirement to distinguish stages of the star formation process.