Gravitational Lensing Effects by Galaxy Clusters on Ionised Bubble Size Distribution during the Epoch of Reionisation

TL;DR

This study investigates how gravitational lensing by galaxy clusters affects the size distribution of ionised bubbles during the Epoch of Reionisation, revealing significant increases in large bubble counts that impact future observations.

Contribution

It provides a quantitative analysis of lensing effects on ionised bubble size distribution using detailed simulations and models, highlighting systematic biases for SKA observations.

Findings

Lensing increases large bubble counts significantly.

Small bubble counts remain unaffected by lensing.

Lensing introduces systematic biases in BSD measurements.

Abstract

The statistical properties of ionisation structures during the Epoch of Reionisation (EoR) provide valuable insights into the formation of the first stars and galaxies. However, statistics such as size distributions of ionisation structures can be affected by gravitational lensing caused by foreground massive structures like galaxy clusters. Hence, to quantify the impacts of lensing by galaxy clusters on ionised Bubble Size Distribution (BSD), we conducted a series of multiple-lens-plane lensing simulations involving the light cones of clusters alongside source light cones based on various ionisation models. The deflector population is generated using the Monte Carlo method, guided by halo mass function and empirical scaling relations, while deflectors' mass profile is modelled using the Truncated Navarro-Frenk-White (TNFW) model. Source light cones are produced via a semi-numerical approach or directly sourced from the Evolution of 21 cm Structure (EOS) project. By employing the Mean Free Path method, we measure unlensed and lensed BSD to reveal the lensing impacts. Our results indicate that lensing effects increase the number of large bubbles while leaving the number of small bubbles unchanged across all source models we adopted. Specifically, for the EOS faint galaxies model, the number of R > 15 cMpc bubbles increases by 219% at z = 14; for the EOS bright galaxies model, the above number increases by 832% under the same circumstances. Above all, lensing introduces unavoidable systematics for BSD, which must be carefully taken into account for relevant studies in the Square Kilometre Array (SKA) era.