The baryon cycle in modern cosmological hydrodynamical simulations

In recent years, cosmological hydrodynamical simulations have proven their utility as key interpretative tools in the study of galaxy formation and evolution. In this work, we present a comparative analysis of the baryon cycle in three publicly available, leading cosmological simulation suites: EAGLE, IllustrisTNG, and SIMBA. While these simulations broadly agree in terms of their predictions for the stellar mass content and star formation rates of galaxies at z ≈0, they achieve this result for markedly different reasons. In EAGLE and SIMBA, we demonstrate that at low halo masses (M200c ≲10 11.5 M ⊙), stellar feedback (SF)-driven outflows can reach far beyond the scale of the halo, extending up to 2-3 R200c. In contrast, in TNG, SF-driven outflows, while stronger at the scale of the interstellar medium, recycle within the circumgalactic medium (within R200c). We find that active galactic nucleus (AGN)-driven outflows in SIMBA are notably potent, reaching several times R200c even at halo masses up to M 200c ≈10 13.5 M ⊙. In both TNG and EAGLE, AGN feedback can eject gas beyond 200c at this mass scale, but seldom beyond 2-3 R200c. We find that the scale of feedback-driven outflows can be directly linked with the prevention of cosmological inflow, as well as the total baryon fraction of haloes within R200c. This work lays the foundation to develop targeted observational tests that can discriminate between feedback scenarios, and inform subgrid feedback models in the next generation of simulations.