In disk galaxies ranging from our own Milky Way to high-redshift systems, star formation takes place in very cold, dense cores, but draws on a much larger reservoir of neutral atomic and molecular gas. Recent surveys have spatially resolved both nearby and high-redshift disks to establish increasingly precise empirical correlations among gas, old stars, and the star formation rate (SFR). Traditional single power law Kennicutt-Schmidt relations have been refined to reveal three star-forming regimes for disks that extend over more than six orders of magnitude in SFR. In all regimes, gas depletion timescales far exceed both global and local dynamical times. To understand these empirical relations, it is necessary to consider the physical state of the ISM, which is strongly coupled to recent star formation through the feedback from massive stars -- including copious UV radiation and powerful supernova blasts. This energetic feedback can lead to a state of self-regulated star formation. Using multiphase numerical simulations, we show that following the driving and dissipation of turbulence in the warm/cold ISM, and resolving scales down to pc in normal disks and 0.1 pc in starbursts, is necessary to follow the detailed processes controlling SFRs. Intriguingly, equilibrium-state SFRs and ISM properties can also be captured with simple models in which pressure powered by feedback balances gravitational confinement of the warm/cold gas. Both numerical simulations and equilibrium models agree with observations, and demonstrate the importance of accurately modeling feedback in order to understand galactic SFRs.
Followed by wine and cheese in Pupin 1402.