Non-equilibrium temperature evolution of ionization fronts during the Epoch of Reionization. (arXiv:2007.02940v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Zeng_C/0/1/0/all/0/1">Chenxiao Zeng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hirata_C/0/1/0/all/0/1">Christopher M. Hirata</a>
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
non-equilibrium effects. In particular, we include the energy transfer between
major baryon species ($e^{-}$, HI, HII, HeI, and HeII) and investigate
their impacts on the post-ionization front temperature $T_{mathrm{re}}$. 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 low-speed ionization front
($lessapprox 10^9~mathrm{cm}/mathrm{s}$), but deviations from equilibrium
occur for faster fronts. The post-front temperature $T_{mathrm{re}}$ is lower
by up to 19.7% (at $3times 10^9$ cm/s) or 30.8% (at $10^{10}$ cm/s) relative
to the equilibrium case.
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
non-equilibrium effects. In particular, we include the energy transfer between
major baryon species ($e^{-}$, HI, HII, HeI, and HeII) and investigate
their impacts on the post-ionization front temperature $T_{mathrm{re}}$. 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 low-speed ionization front
($lessapprox 10^9~mathrm{cm}/mathrm{s}$), but deviations from equilibrium
occur for faster fronts. The post-front temperature $T_{mathrm{re}}$ is lower
by up to 19.7% (at $3times 10^9$ cm/s) or 30.8% (at $10^{10}$ cm/s) relative
to the equilibrium case.
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