Feedback and galaxy dynamics: A study of turbulence and star formation in 34 galaxies using the PHANGS survey
Abstract
The correlation between interstellar turbulent speed and local star formation rate surface density, SigmaSFR, is studied using CO observations in the PHANGS survey. The local velocity dispersion of molecular gas, sigma, increases with SigmaSFR, but the virial parameter, alphavir, is about constant, suggesting the molecular gas remains self-gravitating. The correlation arises because sigma depends on the molecular surface density, Sigmamol, and object cloud mass, Mmol, with the usual molecular cloud correlations, while SigmaSFR increases with both of these quantities because of a nearly constant star formation efficiency for CO. Pressure fluctuations with Delta SigmaSFR are also examined. Azimuthal variations of molecular pressure, Delta Pmol, have a weaker correlation with Delta SigmaSFR than expected from the power-law correlation between the total quantities, suggesting slightly enhanced SFR efficiency per molecule in spiral arms. Dynamical equilibrium pressure and star formation rate correlate well for the whole sample, as PDE~SigmaSFR1.3, which is steeper than in other studies. The azimuthal fluctuations, Delta PDE(Delta SigmaSFR), follow the total correlation PDE(SigmaSFR) 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 SigmaSFR~(Sigmagas R)(1.00.3) for total gas surface density Sigmagas 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.
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