Prospects for radio weak lensing: studies using LOFAR observations in the ELAIS-N1 field

TL;DR

This study evaluates the potential of LOFAR radio observations for weak lensing measurements, comparing radio and optical data, and projecting future capabilities with increased observation time and improved resolution.

Contribution

It demonstrates the current limitations and future prospects of radio weak lensing using LOFAR and ILT data, highlighting the importance of resolution and depth for accurate shear measurements.

Findings

HSC optical data detects a 9σ cosmic shear signal.

LoTSS radio data's shape measurements are limited by resolution.

Simulated ILT data suggests possible shear detection with 3200 hours of observation.

Abstract

We carry out a shape and weak lensing analysis of Low Frequency Array (LOFAR) radio sources and Hyper Suprime-Cam (HSC) optical sources within the European Large Area Infrared Space Observatory Survey-North 1 (ELAIS-N1) field. Using HSC data alone, we detect a cosmic shear correlation signal at a significance of $\sim$$9\sigma$ over a $\sim$$6.4$ deg$^2$ region. For the radio dataset, we analyse observations from both the LOFAR Two Metre Sky Survey (LoTSS) and the International LOFAR Telescope (ILT). While LoTSS provides the deepest radio imaging of ELAIS-N1 with a central source density of $\sim$2.7 arcmin$^{-2}$, its $6^{\prime\prime}$ resolution limits the accuracy of shape measurements. But, using LoTSS-matched HSC sources, we show that accurate radio shape measurements would enable us to measure the amplitude of the shear correlation function at least at $\sim$2$\sigma$ significance. In contrast, ILT observation of the field offers a superior $0.3^{\prime\prime}$ resolution. By cross-matching HSC and ILT samples, we measure a position angle correlation of $R_{\cos(2\alpha)} = 0.15 \pm 0.02$. This result highlights ILT's ability to resolve extended and diffuse emission. The current ILT observations lack the required depth for robust weak lensing measurements. To assess the potential of ILT, we use simulated data with increased observation hours. Our analysis indicates that with 3200 hours of ILT observations or deeper data, and assuming that statistical errors dominate over systematics, a shear correlation could be detected with moderate significance. To achieve this will require precise radio shear measurements and effective mitigation of point spread function (PSF) systematics.