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.
Highlights
Molecular clouds host a significant fraction of the molecular gas mass in the interstellar medium (ISM), as well as all star formation activity in galaxies
We study 28 galaxies selected from the PHANGS-ALMA parent sample
For a sample of 28 nearby star-forming disk galaxies, we estimate the pressure needed to support the ISM against its own weight at a range of spatial scales, taking into account the combined gravity of all gas components and the stellar disk
Summary
Molecular clouds host a significant fraction of the molecular gas mass in the interstellar medium (ISM), as well as all star formation activity in galaxies. Understanding how the properties of molecular clouds change in response to the galactic environment is crucial for building a successful theory for star formation. Studies of giant molecular clouds (GMCs) in the Milky Way conjectured that they had “universal” properties, in the sense that all GMCs exist at the same surface density and follow the same size–linewidth scaling relation (e.g., Larson 1981; Solomon et al 1987). Subsequent observational studies have instead suggested that cloud properties may change systematically as a function of environment. In a careful reanalysis of the Solomon et al (1987) Milky Way clouds, Heyer et al (2009)
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