Gravitational lensing of 21 cm H  <scp>i</scp> signal: detection prospects at <i>z</i> ∼ 1 with the uGMRT in galaxy cluster lenses

Abstract The atomic hydrogen H i content of galaxies is intimately related to star formation and galaxy evolution through the baryon cycle, which involves processes such as accretion, feedback, outflows, and gas recycling. While probing the H i gas over cosmic time has improved our understanding, direct H i detection with the redshifted 21 cm line is essentially limited to z ≲ 0.42. Detections beyond this redshift are based on stacking to obtain average H i mass of galaxy populations. Gravitational lensing by the cluster lenses enhances the H i signal and can extend the redshift limit further. In this work, we describe simulations of H i lensing in cluster lenses. We explore the feasibility of detecting strongly lensed H i emission from background galaxies using known 50 cluster lenses within the uGMRT sky coverage. We demonstrate that certain clusters offer a strong likelihood of H i detection. We also investigate how strong lensing distorts the H i spectral lines. The shape of the H i signal in these lensing models provides useful information and can be used in optimising signal extraction in blind and targeted H i surveys. We find that blind detection of H i signal from galaxies in the redshift range up to 1.58 requires more than a few hundred hours of observations of individual clusters with the uGMRT. Detecting H i emission in galaxies with strong optical lensing seems promising, with a 5σ detection potential in less than 50 hours for Abell 370 and 75 hours for Abell 1703 using the uGMRT.