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

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.

Accepted for publication in MNRAS Letters, 6 pages, 3 figures, 1 table

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• Neutral hydrogen lensing simulations in the Hubble Frontier Fields
• Deep Extragalactic VIsible Legacy Survey (DEVILS): DR1 Blended Spectra Search for Candidate Strong Gravitational Lenses
• HI in and behind the Hubble Frontier Field Clusters: A Deep MeerKAT Pilot Search out to $z\sim 0.5$
• Combined lensed estimator to probe the post reionization H I power spectrum
• ATCA detections of massive molecular gas reservoirs in dusty, high-z radio galaxies
• MeerKAT discovery of 164 compact radio rings toward the Galactic Plane
• Using strong gravitational lensing to probe the post reionization \HI power spectrum