Prospects for radio weak lensing

Studies using LOFAR observations in the ELAIS-N1 field

Leiden Observatory, Leiden University, Einsteinweg 55, 2333 CC Leiden, The Netherlands

^⋆ Corresponding author: jliu@strw.leidenuniv.nl

Received: 10 March 2025
Accepted: 25 June 2025

Abstract

We carried 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 detected a cosmic shear correlation signal at a significance of ∼9σ over a region of ∼6.4 deg². For the radio dataset, we analysed 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 ∼2.7 arcmin⁻², its 6″ resolution limits the accuracy of shape measurements. 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 ∼2σ significance, however. In contrast, ILT observation of the field offers a superior 0.3″ resolution. By cross-matching HSC and ILT samples, we measured a position angle correlation of R_cos(2α) = 0.15 ± 0.02. This result highlights the ability of ILT 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 used 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 systematics, a shear correlation could be detected with moderate significance. Precise radio shear measurements and effective mitigation of point spread function systematics is required to achieve this.