Strongly lensed neutral hydrogen emission: detection predictions with current and future radio interferometers

TL;DR

This paper predicts that current and future radio interferometers, especially the SKA, will detect strongly lensed neutral hydrogen emission at high redshifts, enabling new insights into early universe galaxies.

Contribution

It introduces a semi-analytic simulation combined with relativistic ray tracing to forecast high-redshift lensed HI detections with upcoming radio telescopes.

Findings

Wide-field SKA surveys will efficiently discover lensed HI systems at z > 2.

Lensed HI detection is facilitated by magnification, luminosity function steepness, and spectral isolation.

Existing facilities can target known lenses to probe high-redshift HI emission.

Abstract

Strong gravitational lensing provides some of the deepest views of the Universe, enabling studies of high-redshift galaxies only possible with next-generation facilities without the lensing phenomenon. To date, 21 cm radio emission from neutral hydrogen has only been detected directly out to z~0.2, limited by the sensitivity and instantaneous bandwidth of current radio telescopes. We discuss how current and future radio interferometers such as the Square Kilometre Array (SKA) will detect lensed HI emission in individual galaxies at high redshift. Our calculations rely on a semi-analytic galaxy simulation with realistic HI disks (by size, density profile and rotation), in a cosmological context, combined with general relativistic ray tracing. Wide-field, blind HI surveys with the SKA are predicted to be efficient at discovering lensed HI systems, increasingly so at z > 2. This will be enabled by the combination of the magnification boosts, the steepness of the HI luminosity function at the high-mass end, and the fact that the HI spectral line is relatively isolated in frequency. These surveys will simultaneously provide a new technique for foreground lens selection and yield the highest redshift HI emission detections. More near term (and existing) cm-wave facilities will push the high redshift HI envelope through targeted surveys of known lenses.