The impact of inhomogeneous subgrid clumping on cosmic reionization – II. Modelling stochasticity

ABSTRACT Small-scale density fluctuations can significantly affect reionization, but are typically modelled quite crudely. Unresolved in numerical simulations and analytical calculations included using a gas clumping factor, assumed to be independent of the local environment. In Paper I, we presented an improved, density-dependent model for sub-grid clumping. Here, extend this empirical stochastic based on results from high-resolution which fully resolve all relevant fluctuations. Our reproduces well both mean density-clumping relation its scatter. We applied our model, along with one I deterministic create large-volume realizations field, used these radiative transfer cosmic reionization. show that simplistic delays reionization compared models, despite producing fewer recombinations overall. This is due very different spatial distribution clumping, resulting much higher photoionization rates latter cases. The produces smaller H ii regions throughout most those percolate faster at late times. It also causes significant delay 21-cm peak yields lower non-Gaussianity many bright pixels PDF distribution. shows relatively minor differences one, mostly concentrated around overlap, where it suppresses fluctuations, tail PDFs, noticeably more pixels.