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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 multi-wavelength data that traces 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 over-pressurized relative to the large- scale environment. We show that this over-pressurization 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 P_turb≈P_DE≳10⁵k_BKcm⁻³ in our sample is more likely to be self-gravitating, whereas gas at lower pressure 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, Σ_SFR, 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 Σ_SFR 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.