Supercluster A2142 and collapse in action: infalling and merging groups and galaxy transformations

Context. Superclusters with collapsing cores represent dynamically evolving environments for galaxies, galaxy groups, and clusters.Aims. We study the dynamical state and properties of galaxies and groups in the supercluster SCl A2142 that has a collapsing core, to understand its possible formation and evolution.Methods. We find the substructure of galaxy groups using normal mixture modelling. We have used the projected phase space (PPS) diagram, spherical collapse model, clustercentric distances, and magnitude gap between the brightest galaxies in groups to study the dynamical state of groups and to analyse group and galaxy properties. We compared the alignments of groups and their brightest galaxies with the supercluster axis.Results. The supercluster core has a radius of about 8h−1Mpc and total massMtot≈ 2.3 × 1015h−1M⊙and is collapsing. Galaxies in groups on the supercluster axis have older stellar populations than off-axis groups, with median stellar ages 4 − 6 and < 4 Gyr, correspondingly. The cluster A2142 and the group Gr8 both host galaxies with the oldest stellar populations among groups in SCl A2142 having the median stellar aget> 8 Gyr. Recently quenched galaxies and active galactic nuclei (AGNs) are mostly located at virial radii or in merging regions of groups, and at clustercentric distancesDc≈ 6h−1Mpc. The most elongated groups lie along the supercluster axis and are aligned with it. Magnitude gaps between the brightest galaxies of groups are less than one magnitude, suggesting that groups in SCl A2142 are dynamically young.Conclusions. The collapsing core of the supercluster, infall of galaxies and groups, and possible merging groups, which affect galaxy properties and may trigger the activity of AGNs, show how the whole supercluster is evolving.