We compare the observed turbulent pressure in molecular gas, $P_\mathrm{ turb}$, to the required pressure for the interstellar gas to stay in equilibrium in the gravitational potential of a galaxy, $P_\mathrm{ DE}$. 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 $P_\mathrm{ turb}$ correlates with, but almost always exceeds the estimated $P_\mathrm{ DE}$ 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 $P_\mathrm{ DE}$ on cloud scales, which accounts for molecular gas self-gravity, external gravity, and ambient pressure, agrees well with the observed $P_\mathrm{ turb}$ in galaxy disks. We also find that molecular gas with cloud-scale ${ P_\mathrm{ turb}}\approx{ P_\mathrm{ DE}}\gtrsim{ 10^5\,k_\mathrm{ B}\,\mathrm{ K\,cm^{ -3}}}$ 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 $P_\mathrm{ turb}$ and the observed SFR surface density, $\Sigma_\mathrm{ SFR}$, 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 $\Sigma_\mathrm{ SFR}$ and kpc-scale $P_\mathrm{ DE}$ 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 $P_\mathrm{ DE}$ reported in previous works.
Categories: astro-ph.GA