Resolving shocks and filaments in galaxy formation simulations: effects
  on gas properties and star formation in the circumgalactic medium
  There is an emerging consensus that large amounts of gas do not shock heat in
the circumgalactic medium (CGM) of massive galaxies, but instead pierce deep
into haloes from the cosmic web via filaments. To better resolve this process
numerically, we have developed a novel `shock refinement' scheme within the
moving mesh code AREPO that adaptively improves resolution around shocks
on-the-fly in galaxy formation simulations. We apply this to a massive
$\sim10^{12}$ M$_\odot$ halo at $z=6$ using the successful FABLE model,
increasing the mass resolution by a factor of 512. With better refinement there
are significantly more dense, metal-poor and fast-moving filaments and clumps
flowing into the halo, leading to a more multiphase CGM. We find a $\sim50$ per
cent boost in cool-dense gas mass and a 25 per cent increase in inflowing mass
flux. Better resolved accretion shocks cause turbulence to increase
dramatically, leading to a doubling in the halo's non-thermal pressure support.
Despite much higher thermalisation at shocks with higher resolution, increased
cooling rates suppress the thermal energy of the halo. In contrast, the faster
and denser filaments cause a significant jump in the bulk kinetic energy of
cool-dense gas, while in the hot phase turbulent energy increases by up to
$\sim150$ per cent. Moreover, HI covering fractions within the CGM increase by
up to 60 per cent. Consequently star formation is spread more widely and we
predict a population of metal-poor stars forming within primordial filaments
that deep JWST observations may be able to probe.
