Supernova-driven winds in simulated dwarf galaxies
  We investigate galactic winds driven by supernova (SN) explosions in an
isolated dwarf galaxy using high-resolution (particle mass $m_{\rm gas} = 1{\rm
M_\odot}$, number of neighbor $N_{\rm ngb} = 100$) smoothed-particle
hydrodynamics simulations that include non-equilibrium cooling and chemistry,
individual star formation, stellar feedback and metal enrichment. Clustered SNe
lead to the formation of superbubbles which break out of the disk and vent out
hot gas, launching the winds. We find much weaker winds than what cosmological
simulations typically adopt at this mass scale. At the virial radius, the
time-averaged loading factors of mass, momentum and energy are 3, 1 and 0.05,
respectively, and the metal enrichment factor is 1.5. Winds that escape the
halo consist of two populations that differ in their launching temperatures.
Hot gas acquires enough kinetic energy to escape when launched while warm gas
does not. However, warm gas can be further accelerated by the ram pressure of
the subsequently launched hot gas and eventually escape. The strong
interactions between different temperature phases highlight the caveat of
extrapolating properties of warm gas to large distances based on its local
conditions (e.g. the Bernoulli parameter). Our convergence study finds that
wind properties converge when the cooling masses of individual SNe are
resolved, which corresponds to $m_{\rm gas}=5 {\rm M_\odot}$ with an injection
mass of $500 {\rm M_\odot}$. The winds weaken dramatically once the SNe become
unresolved. We demonstrate that injecting the terminal momentum of SNe, a
popular sub-grid model in the literature, fails to capture SN winds
irrespective of the inclusion of residual thermal energy.
