Exploring the topology of hydrogen distribution in the early universe

Abstract

The topological distribution of neutral hydrogen (H i) during different stages of the Epoch of Reionization (EoR) can provide us a great wealth of information about the properties of the ionizing sources during this era. In this project, we have used an algorithm, SURFGEN2 on a suite of simulated H i 21-cm maps from the EoR to characterize the evolution of the shape and size of the largest ionized region in these maps. This specific method of characterizing any field is known as tracing the Largest Cluster Statistics (LCS). We perform a comparative study of the LCS of ionized regions for six different simulated reionization scenarios. Our study reveals that the shape of the LCS of ionized regions and hence their topology varies significantly in all six cases. Particularly the global neutral fraction at which percolation between all ionized regions occur is different for different reionization scenarios. Further, we find that LCS of ionized regions is a robust statistic that can differentiate between the fundamentally inside-out and outside-in reionization scenarios. The neutral fractions at which the percolation takes place for inside-out and outside-in reionization varies considerably from each other. The analysis done in this project is going to be particularly useful for analysing high resolution 21-cm tomographic maps of the EoR that the highly sensitive upcoming Square Kilometre Array promises to produce in future. These image analysis techniques can potentially be used to constrain the parameters of the EoR from such future 21-cm observations.