Clumping factors of HII, HeII and HeIII

TL;DR

This paper investigates the evolution of clumping factors for hydrogen and helium ions during reionization using high-resolution simulations, highlighting their dependence on various simulation parameters.

Contribution

It provides the first detailed analysis of how clumping factors of HII, HeII, and HeIII evolve with redshift in high-resolution reionization simulations.

Findings

Clumping factors vary significantly with ionization level and redshift.

Definition and resolution impact the measured clumping factors.

Results inform more accurate reionization modeling in low-resolution simulations.

Abstract

Estimating the intergalactic medium ionization level of a region needs proper treatment of the reionization process for a large representative volume of the universe. The clumping factor, a parameter which accounts for the effect of recombinations in unresolved, small-scale structures, aids in achieving the required accuracy for the reionization history even in simulations with low spatial resolution. In this paper, we study for the first time the redshift evolution of clumping factors of different ionized species of H and He in a small but very high resolution simulation of the reionization process. We investigate the dependence of the value and redshift evolution of clumping factors on their definition, the ionization level of the gas, the grid resolution, box size and mean dimensionless density of the simulations.