Gravitational Lensing of Cosmological 21cm Emission

TL;DR

This paper explores the potential of using 21cm intensity mapping with the SKA to measure weak gravitational lensing at high redshifts, offering a new way to probe the universe's expansion and gravity.

Contribution

It demonstrates the feasibility of measuring the lensing power spectrum with SKA, analyzes the dependence on HI density and telescope parameters, and applies the method to dark energy models.

Findings

SKA-Mid can measure lensing evolution at z~2-3.

Higher HI density improves signal-to-noise ratio.

Application to dark energy models shows potential to distinguish them.

Abstract

We investigate the feasibility of measuring weak gravitational lensing using 21cm intensity mapping with special emphasis on the performance of the planned Square Kilometre Array (SKA). We find that the current design for SKA-Mid should be able to measure the evolution of the lensing power spectrum at z~2-3 using this technique. This will be a probe of the expansion history of the universe and gravity at a unique range in redshift. The signal-to-noise is found to be highly dependent on evolution of the neutral hydrogen fraction in the universe with a higher HI density resulting in stronger signal. With realistic models for this, SKA Phase 1 should be capable of measuring the lensing power spectrum and its evolution. The signal-to-noise's dependence on the area and diameter of the telescope array is quantified. We further demonstrate the applications of this technique by applying it to two specific coupled dark energy models that would be difficult to observationally distinguish without information from this range of redshift. We also investigate measuring the lensing signal with 21cm emission from the Epoch of Reionization (EoR) using SKA-Low and find that it is unlikely to constrain cosmological parameters because of the small survey size, but could provide a map of the dark matter within a small region of the sky.