Clustered Supernovae Drive Powerful Galactic Winds After Super-Bubble
  Breakout
  We use three-dimensional hydrodynamic simulations of vertically stratified
patches of galactic discs to study how the spatio-temporal clustering of
supernovae (SNe) enhances the power of galactic winds. SNe that are randomly
distributed throughout a galactic disc drive inefficient galactic winds because
most supernova remnants lose their energy radiatively before breaking out of
the disc. Accounting for the fact that most star formation is clustered
alleviates this problem. Super-bubbles driven by the combined effects of
clustered SNe propagate rapidly enough to break out of galactic discs well
before the clusters' SNe stop going off. The radiative losses post-breakout are
reduced dramatically and a large fraction ($\gtrsim 0.2$) of the energy
released by SNe vents into the halo powering a strong galactic wind. These
energetic winds are capable of providing strong preventative feedback and eject
substantial mass from the galaxy with outflow rates on the order of the star
formation rate. The momentum flux in the wind is only of order that injected by
the SNe, because the hot gas vents before doing significant work on the
surroundings. We show that our conclusions hold for a range of galaxy
properties, both in the local Universe (e.g., M82) and at high redshift (e.g.,
$z \sim 2$ star forming galaxies). We further show that if the efficiency of
forming star clusters increases with increasing gas surface density, as
suggested by theoretical arguments, the condition for star cluster-driven
super-bubbles to break out of galactic discs corresponds to a threshold star
formation rate surface density for the onset of galactic winds $\sim 0.03$
M$_\odot$ yr$^{-1}$ kpc$^{-2}$, of order that observed.
