AMICO galaxy clusters in KiDS-1000: Cosmological constraints and mass calibration from counts and weak lensing

¹ Dipartimento di Fisica e Astronomia “Augusto Righi” – Alma Mater Studiorum Università di Bologna, Via Piero Gobetti 93/2, I-40129 Bologna, Italy
² INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, I-40129 Bologna, Italy
³ INFN – Sezione di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna, Italy
⁴ Zentrum für Astronomie, Universität Heidelberg, Philosophenweg 12, D-69120 Heidelberg, Germany
⁵ ITP, Universität Heidelberg, Philosophenweg 16, 69120 Heidelberg, Germany
⁶ INAF – Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, I-35122 Padova, Italy
⁷ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing, 44780 Bochum, Germany
⁸ Center for Theoretical Physics, Polish Academy of Sciences, al. Lotników 32/46, 02-668 Warsaw, Poland
⁹ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
¹⁰ INAF – Istituto di Radioastronomia, Via Piero Gobetti 101, 40129 Bologna, Italy
¹¹ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Av. Complutense 40, E-28040 Madrid, Spain
¹² Institute of Cosmology & Gravitation, Dennis Sciama Building, University of Portsmouth, Portsmouth PO1 3FX, United Kingdom
¹³ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, Napoli 80131, Italy

^⋆ Corresponding author: giorgio.lesci2@unibo.it

Received: 24 April 2025
Accepted: 26 August 2025

Abstract

Aims. We present the joint modelling of weak-lensing and count measurements of the galaxy clusters detected with the Adaptive Matched Identifier of Clustered Objects (AMICO) code, in the fourth data release of the Kilo Degree Survey (KiDS-1000). The analysed sample comprises approximately 8000 clusters that cover an effective area of 839 deg² and extend up to a redshift of z = 0.8. This modelling provides the first mass calibration of this cluster sample, as well as the first cosmological constraints derived from it.

Methods. We derived stacked cluster weak-lensing and count measurements in bins of redshift and intrinsic richness, λ^*. To define the background galaxy samples for the stacked profiles, we used a combination of selections based on photometric redshifts (photo-zs) and colours. Then, based on self-organising maps, we reconstructed the true redshift distributions of the background galaxy samples. In the joint modelling of weak lensing and counts, we accounted for the systematic uncertainties arising from impurities in the background and cluster samples, biases in the cluster z and λ^*, projection effects, halo orientation and miscentring, truncation of cluster halo mass distributions, matter correlated with cluster haloes, multiplicative shear bias, baryonic matter, geometric distortions in the lensing profiles, uncertainties in the theoretical halo mass function, and super-sample covariance. In addition, we employed a blinding strategy based on perturbing the cluster sample completeness.

Results. The improved statistics and photometry, along with the refined analysis compared to the previous KiDS data release, KiDS-DR3, led to a halving of the uncertainties on Ω_m and σ₈, as we obtained Ω_m = 0.218^+0.024_−0.021 and σ₈ = 0.86^+0.03_−0.03, despite a more extensive modelling of systematic uncertainties. The constraint on S₈ ≡ σ₈(Ω_m/0.3)^0.5, S₈ = 0.74^+0.03_−0.03, is in excellent agreement with recent cluster count and KiDS-1000 cosmic shear analyses, while it shows a 2.8σ tension with Planck cosmic microwave background results. The constraints on the log λ^* − log M₂₀₀ relation imply a mass precision of 8%, on average, which is an improvement of three percentage points compared to KiDS-DR3. In addition, the result on the intrinsic scatter of the log λ^* − log M₂₀₀ relation, σ_intr = 0.052^+0.023_−0.015, confirms that λ^* is an excellent mass proxy.