Simulating Supersonic Turbulence in Galaxy Outflows
  We present three-dimensional, adaptive mesh simulations of dwarf galaxy out-
flows driven by supersonic turbulence. Here we develop a subgrid model to track
not only the thermal and bulk velocities of the gas, but also its turbulent
velocities and length scales. This allows us to deposit energy from supernovae
directly into supersonic turbulence, which acts on scales much larger than a
particle mean free path, but much smaller than resolved large-scale flows.
Unlike previous approaches, we are able to simulate a starbursting galaxy
modeled after NGC 1569, with realistic radiative cooling throughout the
simulation. Pockets of hot, diffuse gas around individual OB associations sweep
up thick shells of material that persist for long times due to the cooling
instability. The overlapping of high-pressure, rarefied regions leads to a
collective central outflow that escapes the galaxy by eating away at the
exterior gas through turbulent mixing, rather than gathering it into a thin,
unstable shell. Supersonic, turbulent gas naturally avoids dense regions where
turbulence decays quickly and cooling times are short, and this further
enhances density contrasts throughout the galaxy- leading to a complex, chaotic
distribution of bubbles, loops and filaments as observed in NGC 1569 and other
outflowing starbursts.
