EAGLE-Auriga: effects of different subgrid models on the baryon cycle around Milky Way-mass galaxies

TL;DR

This study compares how different subgrid models in hydrodynamical simulations affect the baryon content and gas properties of Milky Way-like galaxies, revealing significant differences driven by supernova feedback implementations.

Contribution

It demonstrates that subgrid physics models lead to divergent predictions of baryon distribution and gas dynamics in galaxy halos, highlighting the importance of feedback modeling.

Findings

Auriga predicts near baryon closure in MW halo, EAGLE predicts only half.

EAGLE shows high-redshift outflows eject baryons and hinder accretion.

Differences stem from distinct supernova energy injection methods.

Abstract

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.