Nonequilibrium Temperature Evolution Of Ionization Fronts During The Epoch Of Reionization
ASTROPHYSICAL JOURNAL(2021)
摘要
The epoch of reionization (EoR) marks the end of the Cosmic Dawn and the beginning of large-scale structure formation in the universe. The impulsive ionization fronts (I-fronts) heat and ionize the gas within the reionization bubbles in the intergalactic medium (IGM). The temperature during this process is a key yet uncertain ingredient in current models. Typically, reionization simulations assume that all baryonic species are in instantaneous thermal equilibrium with each other during the passage of an I-front. Here we present a new model of the temperature evolution for the ionization front by studying nonequilibrium effects. In particular, we include the energy transfer between major baryon species (e(-), H.I, H.II, He.I, and He.II) and investigate their impacts on the post-ionization front temperature T-re. For a better step-size control when solving the stiff equations, we implement an implicit method and construct an energy transfer rate matrix. We find that the assumption of equilibration is valid for a nonrelativistic ionization front (speed less than 10(9) cm s(-1)), but deviations from equilibrium occur for faster fronts. The post-front temperature T-re is lower by up to 19.7% (at 3 x 10(9) cm.s(-1)) or 30.8% (at 1010 cm.s-1) relative to the equilibrium case.
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关键词
Reionization, Intergalactic medium, Cosmology, Plasma physics
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