http://arxiv.org/abs/2304.14171
The Epoch of Reionization (EoR) neutral Hydrogen (HI) 21-cm signal evolves significantly along the line-of-sight (LoS) due to the light-cone (LC) effect. It is important to accurately incorporate this in simulations in order to correctly interpret the signal. 21-cm LC simulations are typically produced by stitching together slices from a finite number $(N_{\rm RS})$ of ”reionization snapshot”, each corresponding to a different stage of reionization. In this paper, we have quantified the errors in the 21-cm LC simulation due to the finite value of $N_{\rm RS}$. We show that this can introduce large discontinuities $(> 200 \%)$ at the stitching boundaries when $N_{\rm RS}$ is small $(= 2,4)$ and the mean neutral fraction jumps by $\delta \bar{x}{\rm HI} = 0.2,0.1$ respectively at the stitching boundaries. This drops to $17 \%$ for $N{\rm RS} = 13$ where $\delta \bar{x}{\rm HI}=0.02$. We present and also validate a method for mitigating this error by increasing $N{\rm RS}$ without a proportional increase in the computational costs which are mainly incurred in generating the dark matter and halo density fields. Our method generates these fields only at a few redshifts, and interpolates them to generate reionization snapshots at closely spaced redshifts. We use this to generate 21-cm LC simulations with $N_{\rm RS} = 26,51,101$ and $201$, and show that the errors go down as $N_{\rm RS}^{-1}$.
S. Pramanick, R. Mondal and S. Bharadwaj
Fri, 28 Apr 23
2/68
Comments: 11 pages, 8 (+1 in the appendix) figures