The Baryon Budget of Galaxies across the First Billion Years
Umberto Maio, C\'eline P\'eroux

TL;DR
This study uses advanced simulations to comprehensively analyze the distribution and evolution of baryonic matter in early galaxies across cosmic time, linking gas phases with galaxy properties.
Contribution
It provides a detailed, phase-resolved census of baryons in early galaxies, including new insights into gas phases, stellar return fractions, and their dependencies on galaxy characteristics.
Findings
Cosmic gas is mostly cold before reionisation and warm dominates later.
Stellar return fractions are about 0.15-0.20, lower than commonly assumed.
Gas-to-star fractions decline with galaxy mass, with star formation efficiencies of a few percent.
Abstract
We provide a complete census of the baryons in early galaxies to investigate the phases in which gas and stars reside, their corresponding budgets, depletion times, and stellar return fraction as a function of redshift and stellar age. We use the ColdSIM hydrodynamical time-dependent non-equilibrium chemistry simulations and perform a detailed analysis of the cold, warm, hot, and stellar phases for both bound structures (galaxies/CGM) and the diffuse IGM. We investigate in depth the cold HI and H2 components, explicitly computed in our simulations, and their relations with host mass, SFR, metallicity and depletion times. We also provide observational insights and discuss the implications for stellar mass functions, PopIII star formation and changes in the IMF. We find that cosmic gas prior to reionisation is mostly cold, while at later epochs the warm phase becomes dominant due to…
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