Galactic outflow rates in the EAGLE simulations
  We present measurements of galactic outflow rates from the EAGLE suite of
cosmological simulations. We find that gas is removed from the interstellar
medium (ISM) of central galaxies with a dimensionless mass loading factor that
scales approximately with circular velocity as $V_{\mathrm{c}}^{-3/2}$ in the
low-mass regime where stellar feedback dominates. Feedback from active galactic
nuclei (AGN) causes an upturn in the mass loading for halo masses $> 10^{12} \,
\mathrm{M_\odot}$. We find that more gas outflows through the halo virial
radius than is removed from the ISM of galaxies, particularly at low redshift,
implying substantial mass loading within the circum-galactic medium (CGM).
Outflow velocities span a wide range at a given halo mass/redshift, and on
average increase positively with redshift and halo mass up to $M_{200} \sim
10^{12} \, \mathrm{M_\odot}$. Outflows exhibit a bimodal flow pattern on
circum-galactic scales, aligned with the galactic minor axis. We present a
number of like-for-like comparisons to outflow rates from other recent
cosmological hydrodynamical simulations, and show that comparing the
propagation of galactic winds as a function of radius reveals substantial
discrepancies between different models. Relative to some other simulations,
EAGLE favours a scenario for stellar feedback where agreement with the galaxy
stellar mass function is achieved by removing smaller amounts of gas from the
ISM, but with galactic winds that then propagate and entrain ambient gas out to
larger radii.
