Using strong gravitational lensing to probe the post reionization \HI power spectrum

TL;DR

This paper explores using strong gravitational lensing by galaxy clusters to enhance the detection of the post-reionization ext{HI} 21-cm power spectrum, aiming to overcome foreground challenges in cosmological observations.

Contribution

It introduces a novel method leveraging strong gravitational lensing to amplify the ext{HI} signal, potentially improving detection prospects of the 21-cm power spectrum after reionization.

Findings

Strong lenses at lower redshifts can significantly boost the ext{HI} signal.

Lensing enhances the ext{HI} signal without amplifying foreground emissions.

The method's effectiveness depends on the lens model and cluster properties.

Abstract

Probing statistical distribution of the neutral hydrogen (\HI) using the redshifted 21-cm hyperfine-transition spectral line holds the key to understand the formation and evolution of the matter density in the universe. The two-point statistics of the \HI distribution can be estimated by measuring the power spectrum of the redshifted 21-cm signal using visibility correlation. A major challenge in this regard is that the expected signal is weak compared to the foreground contribution from the Galactic synchrotron emission and extragalactic point sources in the observing frequencies. In this work, we investigate the possibility of detecting the power spectrum of the redshifted 21-cm signal by using strong gravitational lensing of the galaxy clusters. This method has the advantage that it only enhances the \HI signal and not the diffuse galactic foreground. Based on four simple models of the cluster potentials we show that the strong lenses at relatively lower redshifts with more than one dark matter halo significantly enhances the 21-cm signal from the post reionization era. We discuss the merits and demerits of the method and the future studies required for further investigations.