2025/11/12 by Yuri Oku, Renyue Cen, Oku, Yuri +1
Physics and Astronomy · #astro-ph.CO
paper · pdf · doi:10.48550/arxiv.2511.09364
The recombination clumping factor, C, is a key parameter in modeling cosmic reionization, but its value is sensitive to the definition of the Intergalactic Medium (IGM). We investigate the clumping factor using the Gamer-2 adaptive mesh refinement cosmological hydrodynamical simulation code. We introduce a new, physically-motivated definition of the IGM based on the effective transmission factor of ionizing photons. We perform large-scale simulations with varying intensities of the uniform ultraviolet background, and we find that our physically-defined clumping factor is slightly lower than, yet comparable to, the values derived from traditional overdensity thresholds, within a factor of two. At z=6, we obtain a clumping factor of C ∼ 3, consistent with previous studies, indicting that the clumping factor is robust to numerical resolution, box size, and the definition of the IGM. Our zoom-in simulations further show that supernova feedback has two competing effects on reionization; it enhances recombination by increasing the density of ionized gas, while facilitating ionization by heating gas and reducing the neutral fraction. However, these effects are limited to the scales of ∼ 100 kpc and do not significantly alter the global clumping factor.