In galactic disks, star formation rates (SFRs) are related to the gas content by empirical Kennicutt-Schmidt (KS) laws. Recent ~ kpc resolution surveys have shown that these laws take on different scaling behavior in outer disks, mid disks, and inner disks. In addition, in some regions there are also strong correlations of SFRs with the old stellar disk. In all regimes, star formation is observationally considered to be highly inefficient, in the sense that gas mass depletion timescales far exceed both global and local dynamical timescales. I will argue that when viewed from the perspective of energy and momentum production rather than mass consumption, star formation is instead highly efficient, and that observed SFR scalings (and normalization) are a consequence of ISM self-regulation mediated by energy feedback from massive stars. This feedback includes radiative heating to balance ISM cooling, and turbulent driving (primarily by supernovae, for the atomic ISM) to balance dissipation. Simple equilibrium models, also including vertical force balance of the total ISM pressure with the weight of the ISM, yield remarkably good agreement with observations in all three regimes of star formation. High-resolution numerical simulations of the turbulent, multiphase ISM have confirmed and calibrated these results.
Received Feb 13, 2013