Cosmological simulations of the circumgalactic medium with 1 kpc
  resolution: enhanced HI column densities
  The circumgalactic medium (CGM), i.e. the gaseous haloes around galaxies, is
both the reservoir of gas that fuels galaxy growth and the repository of gas
expelled by galactic winds. Most cosmological, hydrodynamical simulations focus
their computational effort on the galaxies themselves and treat the CGM more
coarsely, which means small-scale structure cannot be resolved. We get around
this issue by running zoom-in simulations of a Milky Way-mass galaxy with
standard mass refinement and additional uniform spatial refinement within the
virial radius. This results in a detailed view of its gaseous halo at
unprecedented (1 kpc) uniform resolution with only a moderate increase in
computational time. The improved spatial resolution does not impact the central
galaxy or the average density of the CGM. However, it drastically changes the
radial profile of the neutral hydrogen column density, which is enhanced at
galactocentric radii larger than 40 kpc. The covering fraction of Lyman-Limit
Systems within 150 kpc is almost doubled. We therefore conclude that some of
the observational properties of the CGM are strongly resolution dependent.
Increasing the resolution in the CGM, without increasing the resolution of the
galaxies, is a promising and computationally efficient method to push the
boundaries of state-of-the-art simulations.
