Simple Yet Powerful: Hot Galactic Outflows Driven by Supernovae
  Supernovae (SNe) drive multiphase galactic outflows, impacting galaxy
formation; however, cosmological simulations mostly use \textit{ad hoc}
feedback models for outflows, making outflow-related predictions from first
principles problematic. Recent small-box simulations resolve individual SNe
remnants in the interstellar medium (ISM), naturally driving outflows and
permitting a determination of the wind loading factors of energy $\eta_E$, mass
$\eta_m$, and metals $\eta_Z$. In this Letter, we compile small-box results,
and find consensus that the hot outflows are much more powerful than the cool
outflows: (i) hot outflows generally dominate the energy flux, and (ii) their
specific energy $e_{s,h}$ is 10-1000 times higher than cool outflows. Moreover,
the properties of hot outflows are remarkably simple: $e_{s,h} \propto
\eta_{E,h}/\eta_{m,h}$ is almost invariant over four orders of magnitude of
star formation surface density. Also, we find tentatively that
$\eta_{E,h}/\eta_{Z,h} \sim$ 0.5. If corroborated by more simulation data,
these correlations reduce the three hot phase loading factors into one.
Finally, this one parameter is closely related to whether the ISM has a
"breakout" condition. The narrow range of \esh\ indicates that hot outflows
cannot escape dark matter halos with log $M_{\rm{halo}}\ [M_\odot] \gtrsim 12$.
This mass is also where the galaxy mass-metallicity relation reaches its
plateau, implying a deep connection between \textit{hot} outflows and galaxy
formation. We argue that hot outflows should be included explicitly in
cosmological simulations and (semi-)analytic modeling of galaxy formation.
