The Cosmic Baryon Cycle in IllustrisTNG: Flows of Mass, Energy, and Metals

Abstract We measure and analyze the inflows and outflows of mass, energy, and metals through the interstellar medium (ISM) and circumgalactic medium (CGM) of galaxies in the TNG100 simulation. We identify the dominant feedback mechanism in bins of halo virial mass and redshift by computing the integrated energy input from supernovae (SNe) and the “kinetic” and “thermal” modes of active galactic nucleus (AGN) feedback. We measure all quantities in a shell at the virial radius (“halo scale”) and one chosen to be approximately at the interface of the CGM and the ISM (“ISM scale”). At z ≳ 2, we find that galaxies have strong net positive inflows on halo scales, and weaker but still net positive inflows on ISM scales. At later times, partially due to the onset of kinetic AGN feedback in massive halos, inflows and outflows nearly balance one another, leading to the familiar effects of the slowdown of galaxy growth and the onset of quenching. Halos dominated by SN feedback show only weak evidence of preventative feedback on halo scales, and we see excess ISM-scale accretion indicative of rapid gas recycling. Wind mass loadings decrease with increasing halo mass, and with increasing redshift, while energy loadings are nearly independent of both mass and redshift. The detailed measurements of these mass, metal, and energy inflow and outflow rates on galaxy and halo scales can be used to guide empirical and semianalytic models, and provide deeper insight into how galaxy growth and quenching are regulated in the IllustrisTNG simulations.