The distribution of neutral hydrogen around high-redshift galaxies and
  quasars in the EAGLE simulation
  The observed high covering fractions of neutral hydrogen (HI) with column
densities above $\sim 10^{17} \rm{cm}^{-2}$ around Lyman-Break Galaxies (LBGs)
and bright quasars at redshifts z ~ 2-3 has been identified as a challenge for
simulations of galaxy formation. We use the EAGLE cosmological, hydrodynamical
simulation, which has been shown to reproduce a wide range of galaxy properties
and for which the subgrid feedback was calibrated without considering gas
properties, to study the distribution of HI around high-redshift galaxies. We
predict the covering fractions of strong HI absorbers ($N_{\rm{HI}} \gtrsim
10^{17} \rm{cm}^{-2}$) inside haloes to increase rapidly with redshift but to
depend only weakly on halo mass. For massive ($M_{200} \gtrsim 10^{12} {\rm
M_{\odot}}$) halos the covering fraction profiles are nearly scale-invariant
and we provide fitting functions that reproduce the simulation results. While
efficient feedback is required to increase the HI covering fractions to the
high observed values, the distribution of strong absorbers in and around halos
of a fixed mass is insensitive to factor of two variations in the strength of
the stellar feedback. In contrast, at fixed stellar mass the predicted HI
distribution is highly sensitive to the feedback efficiency. The fiducial EAGLE
simulation reproduces both the observed global column density distribution
function of HI and the observed radial covering fraction profiles of strong HI
absorbers around LBGs and bright quasars.
