Bursty star formation feedback and cooling outflows
  We study how outflows of gas launched from a central galaxy undergoing
repeated starbursts propagate through the circumgalactic medium (CGM), using
the simulation code RAMSES. We assume that the outflow from the disk can be
modelled as a rapidly moving bubble of hot gas at $\mathrm{\sim1\;kpc}$ above
disk, then ask what happens as it moves out further into the halo around the
galaxy on $\mathrm{\sim 100\;kpc}$ scales. To do this we run 60 two-dimensional
simulations scanning over parameters of the outflow. Each of these is repeated
with and without radiative cooling, assuming a primordial gas composition to
give a lower bound on the importance of cooling. In a large fraction of
radiative-cooling cases we are able to form rapidly outflowing cool gas from in
situ cooling of the flow. We show that the amount of cool gas formed depends
strongly on the 'burstiness' of energy injection; sharper, stronger bursts
typically lead to a larger fraction of cool gas forming in the outflow. The
abundance ratio of ions in the CGM may therefore change in response to the
detailed historical pattern of star formation. For instance, outflows generated
by star formation with short, intense bursts contain up to 60 per cent of their
gas mass at temperatures $<5 \times 10^4\,\mathrm{K}$; for near-continuous star
formation the figure is $\lesssim$ 5 per cent. Further study of cosmological
simulations, and of idealised simulations with e.g., metal-cooling, magnetic
fields and/or thermal conduction, will help to understand the precise signature
of bursty outflows on observed ion abundances.
