Dynamical Equilibrium in the Molecular ISM in 28 Nearby Star-forming Galaxies
Jiayi Sun, Adam K. Leroy, Eve C. Ostriker, Annie Hughes, Erik Rosolowsky, Andreas Schruba, Eva Schinnerer, Guillermo A. Blanc, Christopher M. Faesi, J. M. Diederik Kruijssen, Sharon E. Meidt, Dyas Utomo, Frank Bigiel, Alberto D. Bolatto, Mélanie Chevance, I-Da Chiang, Daniel A. Dale, Éric Emsellem, Simon C. O. Glover, Kathryn Grasha, Jonathan D. Henshaw, Cinthya N. Herrera, María J. Jiménez-Donaire, Janice Lee, J. Pety, Miguel Querejeta, Toshiki Saito, Karin Sandström, A. Usero
Abstract
Abstract We compare the observed turbulent pressure in molecular gas, P turb , to the required pressure for the interstellar gas to stay in equilibrium in the gravitational potential of a galaxy, P DE . To do this, we combine arcsecond resolution CO data from PHANGS-ALMA with multiwavelength data that trace the atomic gas, stellar structure, and star formation rate (SFR) for 28 nearby star-forming galaxies. We find that P turb correlates with—but almost always exceeds—the estimated P DE on kiloparsec scales. This indicates that the molecular gas is overpressurized relative to the large-scale environment. We show that this overpressurization can be explained by the clumpy nature of molecular gas; a revised estimate of P DE on cloud scales, which accounts for molecular gas self-gravity, external gravity, and ambient pressure, agrees well with the observed P turb in galaxy disks. We also find that molecular gas with cloud-scale in our sample is more likely to be self-gravitating, whereas gas at lower pressure it appears more influenced by ambient pressure and/or external gravity. Furthermore, we show that the ratio between P turb and the observed SFR surface density, , is compatible with stellar feedback-driven momentum injection in most cases, while a subset of the regions may show evidence of turbulence driven by additional sources. The correlation between and kpc-scale P DE in galaxy disks is consistent with the expectation from self-regulated star formation models. Finally, we confirm the empirical correlation between molecular-to-atomic gas ratio and kpc-scale P DE reported in previous works.