Pressure-Regulated, Feedback-Modulated Star Formation In Disk Galaxies

TL;DR

This paper develops and tests a theory that links star formation rates in galactic disks to the physical state of the interstellar medium, emphasizing the role of feedback and pressure regulation, supported by simulations and observations.

Contribution

The paper introduces the Pressure-Regulated, Feedback-Modulated (PRFM) theory, providing a quantitative framework for star formation regulation in galactic disks based on ISM pressure and feedback.

Findings

PRFM theory predicts a nearly linear relation between SFR and ISM weight.

Simulations confirm the predicted feedback yield of approximately 1000 km/s.

Results show excellent agreement between theory, simulations, and observations.

Abstract

The star formation rate (SFR) in galactic disks depends on both the quantity of available interstellar medium (ISM) gas and its physical state. Conversely, the ISM's physical state depends on the SFR, because the "feedback" energy and momentum injected by recently-formed massive stars is crucial to offsetting losses from turbulent dissipation and radiative cooling. The ISM's physical state also responds to the gravitational field that confines it, with increased weight driving higher pressure. In a quasi-steady state, it is expected that the mean total pressure of different thermal phases will match each other, that the component pressures and total pressure will satisfy thermal and dynamical equilibrium requirements, and that the SFR will adjust as needed to provide the requisite stellar radiation and supernova feedback. The pressure-regulated, feedback-modulated (PRFM) theory of the star-forming ISM formalizes these ideas, leading to a prediction that the SFR per unit area, Sigma_SFR, will scale nearly linearly with ISM weight W. In terms of large-scale gas surface density Sigma, stellar plus dark matter density rho_sd, and effective ISM velocity dispersion sigma_eff, an observable weight estimator is W~P_DE=pi G Sigma^2/2+Sigma(2G rho_sd)^{1/2} sigma_eff, and this is predicted to match the total midplane pressure P_tot. Using a suite of multiphase magnetohydrodynamic simulations run with the TIGRESS computational framework, we test the principles of the PRFM model and calibrate the total feedback yield Upsilon_tot = P_tot/Sigma_SFR ~ 1000 km/s, as well as its components. We compare results from TIGRESS to theory, previous numerical simulations, and observations, finding excellent agreement.