EAGLE-Auriga: effects of different subgrid models on the baryon cycle
  around Milky Way-mass galaxies
  Modern hydrodynamical simulations reproduce many properties of the real
universe. These simulations model various physical processes, but many of these
are included using `subgrid models' due to resolution limits. Although
different subgrid models have been successful in modelling the effects of
supernovae (SNe) feedback on galactic properties, it remains unclear if, and by
how much, these differing implementations affect observable halo gas
properties. In this work, we use `zoom-in' cosmological initial conditions of
two volumes selected to resemble the Local Group (LG) evolved with both the
Auriga and EAGLE galaxy formation models. While the subgrid physics models in
both simulations reproduce realistic stellar components of $L^\star$ galaxies,
they exhibit different gas properties. Namely, Auriga predicts that the Milky
Way (MW) is almost baryonically closed, whereas EAGLE suggests that only half
of the expected baryons reside within the halo. Furthermore, EAGLE predicts
that this baryon deficiency extends to the LG, ($r \leq 1 \mathrm{~Mpc}$). The
baryon deficiency in EAGLE is likely due to SNe feedback at high redshift,
which generates halo-wide outflows, with high covering fractions and radial
velocities, which both eject baryons and significantly impede cosmic gas
accretion. Conversely, in Auriga, gas accretion is almost unaffected by
feedback. These differences appear to be the result of the different energy
injection methods from SNe to gas. Our results suggest that both quasar
absorption lines and fast radio burst dispersion measures could constrain these
two regimes with future observations.
