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

TL;DR

This study investigates the properties, substructure, and evolution of galaxy clusters in the Coma and Leo superclusters, revealing their diverse evolutionary paths and the timing of their virialization processes.

Contribution

It provides a detailed analysis of cluster substructure, connectivity, and galaxy content using SDSS and DESI data, highlighting differences in their evolutionary stages.

Findings

Clusters have multiple substructures and filaments.

Regions of influence have radii around 4 Mpc with specific density contrasts.

Clusters will virialize in approximately 3.3 Gyr, while supercluster regions take about 10 Gyr.

Abstract

We study the substructure, connectivity, and galaxy content of galaxy clusters A1656 and 1367 in the Coma supercluster and of A1185 in the Leo supercluster with the aim of understanding the evolution of clusters from turnaround to virialisation. We used data from the SDSS 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, analysed galaxy content of clusters, and derived scaling relations between cluster masses. 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 $R_\mathrm{inf} \approx 4$ Mpc, and the density contrast at their borders is $\Delta\rho_{inf} \approx 50 - 60$. 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 superclusters the percentage of quiescent galaxies is higher than in low-density regions between superclusters. The collapse of the regions of influence of clusters started at redshifts $z \approx 0.4 - 0.5$. Clusters will be virialised in $\approx 3.3$ Gyrs. Clusters in superclusters will not merge, and their present-day turnaround regions will be virialised in $\approx 10$ Gyrs. The large variety of properties of clusters suggests that they have followed different paths during evolution.