Institute for Advanced Study Astrophysics Seminar

ABSTRACT: Recent surveys have established increasingly precise correlations between star formation rates (SFRs) and the gas, stellar, and dark matter contents of galaxies. Outer galactic disks are dominated by atomic gas and have steep Kennicutt-Schmidt (KS) relations. Mid-disks are dominated by molecular gas and have nearly linear KS relations. Starburst regions (in ULIRGs and high-z galaxies) are molecule-dominated and have steep KS relations. Recent data also confirm a pervasive inefficiency of gas consumption: for all regimes, the gas supply divided by the local dynamical time far exceeds the SFR. To understand these empirical relations, it is crucial to consider the ISM physics at scales small compared to the disk thickness, and the demands imposed by rapid gas cooling and dissipation of turbulence. Recently, we have developed theoretical models in which feedback from massive stars self-regulates SFRs, subject to local environmental conditions including the stellar and dark matter gravitational potentials. In equilibrium, the SFR adjusts until ISM heating balances cooling, total pressure balances gravity, and turbulent driving balances dissipation. These models are in remarkably good agreement with observations in all three regimes of star formation, and have been confirmed and calibrated using multiphase numerical hydrodynamic simulations. From this perspective, it is the high efficiency of massive-star feedback -- stellar UV and expanding SN remnants replenish thermal and turbulent energy in less than a dynamical time -- that enables low gas consumption and sustained star formation in disk galaxies.