UNIONS-3500 Weak Lensing: III. 2D Cosmological Constraints in Configuration Space

TL;DR

This paper presents the first cosmological constraints from the UNIONS-3500 weak lensing galaxy catalogue using 2D cosmic shear analysis, achieving results consistent with Planck CMB measurements.

Contribution

It introduces a novel 2D cosmic shear analysis pipeline applied to the largest deep northern sky survey, demonstrating robust cosmological constraints.

Findings

Constraints on S_8 = 0.831^{+0.067}_{-0.078} consistent with Planck.

Robustness of results against analysis choices and systematic effects.

Demonstrates UNIONS' capability for competitive cosmological measurements.

Abstract

We present the first cosmological constraints from the cosmic shear analysis of the UNIONS-3500 weak lensing galaxy catalogue in configuration space. The Ultraviolet Near Infrared Optical Northern Survey (UNIONS) is the largest and deepest photometric survey of the northern hemisphere to date, with the UNIONS-3500 catalogue using high-quality $r$-band imaging across 3500 deg2 of the sky. We perform a 2D cosmic shear analysis with a single tomographic bin, using the two-point correlation function (2PCF) statistic. Assuming a flat LCDM model, we obtain constraints on the clustering amplitude of S_8 = 0.831^{+0.067}_{-0.078}, which is consistent with constraints from Planck CMB measurements and precedent cosmic shear results within 1sigma. We outline the construction of our cosmological inference pipeline, including the estimation of the source redshift distribution, shear calibration, and covariance matrix, and describe methodologies for the mitigation of systematic effects arising from PSF systematics and B-modes. We demonstrate that our results are robust to variations in analysis choices, including scale cuts, prior ranges, and nonlinear modelling. This paper is part of a coordinated release which collectively demonstrates the maturity and readiness of UNIONS to deliver competitive cosmological results, positioning it as a key stepping stone towards the forthcoming era of Stage IV weak lensing experiments.