Feedback and Galaxy Dynamics: A Study of Turbulence and Star Formation in 34 Galaxies Using the PHANGS Survey

The correlation between interstellar turbulent speed and local star formation rate surface density, Sigma SFR, is studied using CO observations in the PHANGS survey. The local velocity dispersion of molecular gas, sigma, increases with Sigma SFR, but the virial parameter, alpha vir, is about constant, suggesting the molecular gas remains self-gravitating. The correlation arises because sigma depends on the molecular surface density, Sigma mol, and object cloud mass, M mol, with the usual molecular cloud correlations, while Sigma SFR increases with both of these quantities because of a nearly constant star formation efficiency for CO. Pressure fluctuations with Delta Sigma SFR are also examined. Azimuthal variations of molecular pressure, Delta P mol, have a weaker correlation with Delta Sigma SFR than expected from the power-law correlation between the total quantities, suggesting slightly enhanced star formation rate (SFR) efficiency per molecule in spiral arms. Dynamical equilibrium pressure and SFR correlate well for the whole sample, as P DE proportional to Sigma SFR 1.3 , which is steeper than in other studies. The azimuthal fluctuations, Delta P DE(Delta Sigma SFR), follow the total correlation P DE(Sigma SFR) closely, hinting that some of this correlation may be a precursor to star formation, rather than a reaction. Galactic dynamical processes correlate linearly such that Sigma SFR proportional to ( Sigma gas R ) 1.0 +/- 0.3 for total gas surface density Sigma gas and galactic dynamical rates, R, equal to kappa, A, or Omega, representing epicyclic frequency, shear rate A, and orbit rate Omega. These results suggest important roles for both feedback and galactic dynamics.