UNIONS: The impact of systematic errors on weak-lensing peak counts^⋆

¹ Observatoire de Paris, Université PSL, 61 avenue de l’Observatoire, 75014 Paris, France
e-mail: emma.aycoberry@iap.fr
² Université Paris-Saclay, Université Paris-Cité, CEA, CNRS, Astrophysique, Instrumentation et Modélisation Paris-Saclay, 91191 Gif-sur-Yvette, France
³ Institut d’Astrophysique de Paris, UMR 7095, CNRS & Sorbonne Université, 98 bis boulevard Arago, 75014 Paris, France
⁴ Institute for Particle Physics and Astrophysics, Department of Physics, ETH Zürich, Wolfgang Pauli Strasse 27, 8093 Zürich, Switzerland
⁵ Université de Paris, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
⁶ Laboratoire d’Astrophysique de Marseille, Aix-Marseille Univ., CNRS, CNES, 13388 Marseille Cedex 13, France
⁷ Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada
⁸ Waterloo Centre for Astrophysics, Waterloo, ON N2L 3G1, Canada
⁹ Perimeter Institute for Theoretical Physics, 31 Caroline St. N., Waterloo, ON N2L 2Y5, Canada

Received: 29 April 2022
Accepted: 28 October 2022

Abstract

Context. The Ultraviolet Near-Infrared Optical Northern Survey (UNIONS) is an ongoing deep photometric multiband survey of the northern sky. As part of UNIONS, the Canada-France Imaging Survey (CFIS) provides r-band data, which we use to study weak-lensing peak counts for cosmological inference.

Aims. We assess systematic effects for weak-lensing peak counts and their impact on cosmological parameters for the UNIONS survey. In particular, we present results on local calibration, metacalibration shear bias, baryonic feedback, the source galaxy redshift estimate, intrinsic alignment, and cluster member dilution.

Methods. For each uncertainty and systematic effect, we describe our mitigation scheme and the impact on cosmological parameter constraints. We obtain constraints on cosmological parameters from Monte Carlo Markov chains using CFIS data and MassiveNuS N-body simulations as a model for peak counts statistics.

Results. Depending on the calibration (local versus global, and the inclusion or not of the residual multiplicative shear bias), the mean matter density parameter, Ω_m, can shift by up to −0.024 (−0.5σ). We also see that including baryonic corrections can shift Ω_m by +0.027 (+0.5σ) with respect to the dark-matter-only simulations. Reducing the impact of the intrinsic alignment and cluster member dilution through signal-to-noise cuts leads to larger constraints. Finally, with a mean redshift uncertainty of Δz̄ = 0.03, we see that the shift in Ω_m (+0.001, which corresponds to +0.02σ) is not significant.

Conclusions. This paper investigates, for the first time with UNIONS weak-lensing data and peak counts, the impact of systematic effects. The value of Ω_m is the most impacted and can shift by up to ∼0.03, which corresponds to 0.5σ depending on the choices for each systematics. We expect constraints to become more reliable with future (larger) data catalogs, for which the current pipeline will provide a starting point. The code used to obtain the results is available on GitHub.