The impact and response of minihalos and the interhalo medium on cosmic reionization
Abstract
An ionization front (Ifront) that propagates through an inhomogeneous medium is slowed down by selfshielding and recombinations. We perform cosmological radiation hydrodynamics simulations of the Ifront propagation during the epoch of cosmic reionization. The simulations resolve gas in minihalos (halo mass $10^4\lesssim M_h[{\rm M}_\odot]\lesssim 10^8)$ that could dominate recombinations, in a computational volume that is large enough to sample the abundance of such halos. The numerical resolution is sufficient (gas particle mass $\sim 20{\rm M}_\odot$, spatial resolution $< 0.1\;{\rm ckpc}$) to allow accurate modelling of the hydrodynamic response of gas to photoheating. We quantify the photoevaporation time of minihalos as a function of $M_h$ and its dependence on the photoionization rate, $\Gamma_{12}$, and the redshift of reionization, $z_i$. The recombination rate can be enhanced over that of a uniform medium by a factor $\sim 1020$ early on. The peak value increases with $\Gamma_{12}$ and decreases with $z_i$, due to the enhanced contribution from minihalos. The clumping factor, $c_r$, decreases to a factor of a few at $\sim 100\;{\rm Myr}$ after the passage of the Ifront when the minihalos have been photoevaporated; this asymptotic value depends only weakly on $\Gamma_{12}$. Recombinations increase the required number of photons per baryon to reionize the Universe by 20100 per cent, with the higher value occurring when $\Gamma_{12}$ is high and $z_i$ is low. We complement the numerical simulations with simple analytical models for the evaporation rate and the inverse Strömgren layer. The study also demonstrates the proficiency and potential of SPHM1RT to address astrophysical problems in highresolution cosmological simulations.
 Publication:

arXiv eprints
 Pub Date:
 May 2023
 DOI:
 10.48550/arXiv.2305.04959
 arXiv:
 arXiv:2305.04959
 Bibcode:
 2023arXiv230504959K
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 34 pages, 34 figures