Self-similarity of the mass distribution in rich galaxy clusters up to z∼1 tracked with weak lensing

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti 93/3, I-40129 Bologna, Italy
² INFN, Sezione di Bologna, viale Berti Pichat 6/2, I-40127 Bologna, Italy

^⋆ Corresponding author: mauro.sereno@inaf.it

Received: 31 January 2025
Accepted: 18 March 2025

Abstract

In the standard theory of growth of nonbaryonic dark matter, cosmic structures form hierarchically and self-similarly from smaller clumps. The assembly merger tree extends from the linear perturbations in the early Universe to highly non-linear structures at late times. Gravity is the driving force, and self-similarity should inform cosmic haloes. However, it is unclear whether the apparent anomalies at non-linear scales are due to baryonic or new physics. I show that the mass distribution of rich haloes evolved self-similarly at least since the Universe was 5.7 Gyr old. Using gravitational weak lensing, I constrained the mass profiles of galaxy clusters with M_200c ≳ 2 × 10¹⁴ M_⊙ that were optically detected in the HSC-SSP survey in the redshift range 0.2 ≤ z < 1.0. The cluster self-similarity confirms the standard theory of growth in the non-linear regime. Clusters are still growing, but neither violent mergers nor matter slowly falling in from the cosmic web disrupt the self-similarity, which is in place well before the halo formation time. Dark matter growth can fit the fossil cosmic microwave background as well as young, very massive haloes. Next-generation survey searches at scales in clusters in which self-similarity breaks might pose a new challenge to dark matter.