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

TL;DR

This paper investigates how the array synthesized beam affects the interpretation of 21-cm cosmology maps during reionization, highlighting biases introduced in the Largest Cluster Statistics analysis for upcoming SKA1-Low observations.

Contribution

It demonstrates the impact of the array beam on LCS analysis of 21-cm signals and emphasizes the need for denser uv-coverage for unbiased reionization studies.

Findings

Bias in LCS estimation due to array beam effects.

Shift of percolation transition point to later reionization stages.

Recommendation for denser uv-coverage for accurate analysis.

Abstract

We analyse the evolution of the largest ionized region using the topological and morphological evolution of the redshifted 21-cm signal coming from the neutral hydrogen distribution during the different stages of reionization. For this analysis, we use the "Largest Cluster Statistics" - LCS. We mainly study the impact of the array synthesized beam on the LCS analysis of the 21-cm signal considering the upcoming low-frequency Square Kilometer Array (SKA1-Low) observations using a realistic simulation for such observation based on the 21cmE2E-pipeline using OSKAR. We find that bias in LCS estimation is introduced in synthetic observations due to the array beam. This in turn shifts the apparent percolation transition point towards the later stages of reionization. The biased estimates of LCS, occurring due to the effect of the lower resolution (lack of longer baselines) and the telescope synthesized beam will lead to a biased interpretation of the reionization history. This is important to note while interpreting any future 21-cm signal images from upcoming or future telescopes like the SKA, HERA, etc. We conclude that one may need denser $uv$-coverage at longer baselines for a better deconvolution of the array synthesized beam from the 21-cm images and a relatively unbiased estimate of LCS from such images.