Analysis of realistic HI 21-cm maps from Epoch of Reionization using Largest Cluster Statistics (LCS)

Abstract

Using the topological and morphological evolution of neutral hydrogen distribution during the different stages of the Epoch of Reionization (EoR), we try to reveal the nature of the ionizing sources and the astrophysical processes in the Intergalactic Medium (IGM) during this period by studying the evolution of the largest ionized region (via the Largest Cluster Statistics - LCS). We show that It can identify the difference between two distinct reionization scenarios - inside-out and outside-in, even when realistic observational conditions are taken into account i.e. the simulated HI 21cm maps are initially translated to a lower resolution, then corrupted with a simulated Gaussian noise having an RMS value of $\sim 3mK$ in line with the future SKA1-low observations. Afterwards, the effect of the beam was simulated and incorporated into the maps, and then the images are analyzed via LCS. Additionally, we use Shapefinders (SFs) to investigate the morphology of ionized volumes as they change in different reionization models. We observed that the greatest ionized volume abruptly expands solely in terms of its third SF after percolation while the first two SFs stay almost constant. Ergo, when approaching percolation, the ionized hydrogen in these circumstances becomes very filamentary, with a characteristic cross-section’ that differs between source models.