Statistical selection of high-redshift, neutral-hydrogen-rich, lensed galaxies with the Square Kilometre Array

TL;DR

This paper proposes a statistical method to select high-redshift, HI-rich, lensed galaxies using the SKA, which could improve detection efficiency and enable detailed studies of galaxy evolution and dark matter properties.

Contribution

It introduces a flux density criterion based on HI mass function distortion to identify lensed HI sources in future SKA surveys, enhancing detection efficiency.

Findings

Potential to detect 0.1–10 lensed HI galaxies per square degree up to z≈3.

Selection method achieves about 50% efficiency without additional data.

Combining SKA-MID with LSST data can significantly improve high-redshift galaxy studies.

Abstract

Deep wide spectral line surveys with the Square Kilometre Array (SKA) will expand the cosmic frontiers of neutral atomic hydrogen (HI) in galaxies. However, at cosmologically significant redshifts ($z \gtrsim 0.5$), detections will typically be spatially unresolved and limited to the highest mass systems. Gravitational lensing could potentially alleviate these limitations, enabling lower mass systems to be studied at higher redshift and spatially resolved dynamical studies of some HI discs. Additionally, lensed HI systems would select foreground dark matter haloes using a different, more extended baryonic tracer compared to other lens surveys. This may result in a wider selected range of foreground dark matter halo properties, such as the concentration parameter. This paper uses the distortion of the observed HI mass function (HIMF) produced by strong gravitational lensing to find a flux density criterion for selecting lensed HI sources in future SKA-Mid spectral line surveys. This selection approach could yield lensed HI source densities in the range of $\sim 0.1$--$10$ galaxies per square degree out to a redshift of $z \simeq 3$ covered by SKA-MID Band 1. Although the sample sizes are modest, even with the proposed SKA-Mid surveys, the selection approach is straightforward and should have a 50% efficiency without any additional information, such as low-impact-factor or lower-redshift massive galaxies. The efficiency of selecting high-redshift, neutral-hydrogen-rich, lensed galaxies should then be greatly enhanced by using SKA-MID data in concert with the Vera C. Rubin Large Survey of Space and Time.