Distinguishing reionization models using the largest cluster statistics of the 21-cm maps

Abstract

The evolution of topology and morphology of ionized or neutral hydrogen during different stages of the Epoch of Reionization (EoR) have the potential to provide us a great amount of information about the properties of the ionizing sources during this era. We compare a variety of reionization source models in terms of the geometrical properties of the ionized regions. We show that the percolation transition in the ionized hydrogen, as studied by tracing the evolution of the Largest Cluster Statistics (LCS), is a robust statistic that can distinguish the fundamentally different scenarios — inside-out and outside-in reionization. Particularly, the global neutral fraction at the onset of percolation is significantly higher for the inside-out scenario as compared to that for the outside-in reionization. In complementary to percolation analysis, we explore the shape and morphology of the ionized regions as they evolve in different reionization models in terms of the Shapefinders (SFs) that are ratios of the Minkowski functionals (MFs). The shape distribution can readily discern the reionization scenario with extreme non-uniform recombination in the IGM, such as the clumping model. In the rest of the reionization models, the largest ionized region abruptly grows only in terms of its third SF — 'length' — during percolation while the first two SFs — 'thickness' and 'breadth' — almost remain stable. Thus the ionized hydrogen in these scenarios becomes highly filamentary near percolation and exhibit a 'characteristic cross-section' that varies among the source models. Therefore, the geometrical studies based on SFs, together with the percolation analysis can shed light on the reionization sources.

Interpreting the HI 21-cm cosmology maps through Largest Cluster Statistics -- I: Impact of the synthetic SKA1-Low observations

“…In the previous work in [80] and in the initial portion of this paper, we consider the same simulations as [40]. In [40], the 𝑁-body simulations were performed with the 𝐶𝑈𝐵𝐸 𝑃 3 𝑀 code [93], which is based on the earlier algorithm PMFAST, as part of the PRACE4LOFAR project (PRACE projects 2012061089 and 2014102339) [?…”

“…Minimum halo mass (𝑀 ℎ 𝑚𝑖𝑛 ) that was considered here is 2.02 × 10 9 𝑀 . For this simulation, we use the Fiducial model of reionization as mentioned in [80].…”

“…The simulation volume for this realization is 143.36 Mpc in comoving length along each side of the cube. In this simulation as well, we use the Fiducial model as mentioned in [80].…”

“…In the context of this work, we identify the percolation transition when the largest ionized region stretches from one end of the simulation volume to the other end and it becomes formally infinitely extended due to periodic boundary conditions. In this particular work, which is a follow-up of [69,80], we follow the largest ionized region (LIR) with the progress of reionization. For our study we use a novel statistic called the "Largest Cluster Statistic" (LCS) [103][104][105] to track the percolation process and it is From the above definition it can be stated that, LCS essentially denotes the ratio of the largest ionized volume to the total ionized volume.…”

“…They use a novel statistic named the "Largest Cluster Statistics (LCS)" along with Shapefinders to draw this conclusion. Pathak et al [80] have taken this tool a step further and have distinguished the different major reionization scenarios (inside-out and outside-in) through the same analysis.…”