Detection of HI 21 cm emission from a strongly lensed galaxy at z~1.3

TL;DR

This study reports the first successful detection of HI 21 cm emission from a galaxy at redshift ~1.3, leveraging gravitational lensing and upgraded radio telescope technology to explore cosmic neutral gas evolution.

Contribution

It demonstrates the feasibility of detecting high-redshift HI emission in lensed galaxies using current radio telescopes, opening new avenues for cosmic gas studies.

Findings

First 5σ HI detection at z~1.3 in emission from an individual galaxy.

HI mass nearly twice the galaxy's stellar mass, indicating extended gas structure.

High magnification due to lensing allows detailed study of distant galaxy's gas.

Abstract

We report the first $5\sigma$ detection of HI 21 cm emission from a star-forming galaxy at redshift $z\sim1.3$ (nearly 9 billion years ago) using upgraded Giant Metrewave Radio Telescope (uGMRT). This is the highest redshift HI detection in emission from an individual galaxy to date. The emission is strongly boosted by the gravitational lens, an early type elliptical galaxy, at redshift $z \sim 0.13$. The measured HI mass of the galaxy is $\rm M_{HI} = (0.90 \pm 0.14 \pm 0.05) \times 10^{10}M_{\odot}$, which is almost twice the inferred stellar mass of the galaxy, indicating an extended structure of the HI gas inside the galaxy. By fitting two-dimensional Gaussian to the HI signal at the peak of the spectral line, we find the source to be marginally resolved with the position angle consistent with the emission being tangential to the critical curve of the lens mass distribution. This indicates that the solid angle of the approaching HI line flux comes very close to the inner lens caustic and results in very high magnification. These results, for the first time, demonstrate the feasibility of observing high redshift HI in a lensed system with a modest amount of telescope time and open up exciting new possibilities for probing the cosmic evolution of neutral gas with existing and upcoming low-frequency radio telescopes in the near future.