The richest clusters in the Coma and Leo superclusters: Properties and evolution

¹ Tartu Observatory, University of Tartu, Observatooriumi 1, 61602 Tõravere, Estonia
² Tuorla Observatory, Department of Physics and Astronomy, University of Turku, 20014 Turku, Finland
³ Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
⁴ Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA
⁵ ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy

^⋆ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 19 June 2025
Accepted: 18 September 2025

Abstract

Context. Superclusters of galaxies represent dynamically active environments in which galaxies and their systems form and evolve.

Aims. We study the substructure, connectivity, and galaxy content of galaxy clusters A1656 and A1367 in the Coma supercluster and of A1185 in the Leo supercluster with the aim of understanding the evolution of clusters from turnaround to virialisation, and the evolution of whole superclusters.

Methods. We used data from the Sloan Digital Sky Survey DR10 MAIN galaxy sample and from DESI cluster catalogues. The projected phase space diagram and the distribution of mass were used to identify regions of various infall stages (early and late infall, and regions of ongoing infall, i.e. regions of influence), their characteristic radii, embedded mass, and density contrasts in order to study the evolution of clusters with the spherical collapse model. We determined the substructure of clusters using normal mixture modelling and their connectivity by counting filaments in the cluster’s regions of influence. We analysed galaxy content in clusters and in their environment and derived scaling relations between cluster masses.

Results. All three clusters have a substructure with two to five components and up to six filaments connected to them. The radii of regions of influence are R_inf ≈ 4 h⁻¹ Mpc, and the density contrast at their borders is Δρ_inf ≈ 50 − 60. The scaling relations between the masses of clusters have a very small scatter. The galaxy content of the clusters and of their regions of influence vary from cluster to cluster. In high-density regions (superclusters), the percentage of quiescent galaxies is higher than in low-density regions between superclusters, where approximately one-fourth of the galaxies are still quiescent.

Conclusions. The collapse of the regions of influence of clusters started at redshifts z ≈ 0.4 − 0.5. Clusters will be virialised approximately in ≈3.3 Gyrs. Clusters in superclusters will not merge, and their present-day turnaround regions will be virialised in ≈10 Gyrs. The large variety of properties of clusters suggests that they have followed different paths during evolution.