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, Σ _SFR , is studied using CO observations in the PHANGS survey. The local velocity dispersion of molecular gas, σ , increases with Σ _SFR , but the virial parameter, α _vir , is about constant, suggesting the molecular gas remains self-gravitating. The correlation arises because σ depends on the molecular surface density, Σ _mol , and object cloud mass, M _mol , with the usual molecular cloud correlations, while Σ _SFR increases with both of these quantities because of a nearly constant star formation efficiency for CO. Pressure fluctuations with ΔΣ _SFR are also examined. Azimuthal variations of molecular pressure, Δ P _mol , have a weaker correlation with ΔΣ _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 ${P}_{\mathrm{DE}}\propto {{\rm{\Sigma }}}_{\mathrm{SFR}}^{1.3}$ , which is steeper than in other studies. The azimuthal fluctuations, Δ P _DE (ΔΣ _SFR ), follow the total correlation P _DE (Σ _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 ${{\rm{\Sigma }}}_{\mathrm{SFR}}\propto {({{\rm{\Sigma }}}_{\mathrm{gas}}R)}^{1.0\pm 0.3}$ for total gas surface density Σ _gas and galactic dynamical rates, R , equal to κ , A , or Ω, representing epicyclic frequency, shear rate A , and orbit rate Ω. These results suggest important roles for both feedback and galactic dynamics.

Keywords

• Interstellar molecules
• Star formation
• Spiral arms
• Interstellar medium
• Giant molecular clouds
• Stellar feedback