Unusual A2142 supercluster with a collapsing core: distribution of light and mass

¹ Tartu Observatory, Observatooriumi 1, 61602 Tõravere, Estonia
e-mail: maret.einasto@to.ee
² Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
³ Institute of Physics, University of Tartu, Ravila 14c, 51010 Tartu, Estonia
⁴ Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
⁵ School of Physics, Korea Institute for Advanced Study, 85 Hoegiro, Dong-Dae-Mun-Gu, 130-722 Seoul, Korea
⁶ ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy

Received: 24 April 2015
Accepted: 27 May 2015

Abstract

Context. Superclusters of galaxies can be used to test cosmological models of the formation and evolution of the largest structures in the cosmic web, and of galaxy and cluster evolution in superclusters.

Aims. We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster.

Methods. We analyse the global luminosity density distribution in the supercluster and divide the supercluster into the high-density core and the low-density outskirts regions. We find galaxy groups and filaments in these regions, calculate their masses and mass-to-light ratios and analyse their dynamical state with 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster.

Results. In the A2142 supercluster rich groups and clusters lie along an almost straight line forming the 50h^-1 Mpc long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirts. The total estimated mass of the supercluster is M_est = 6.2 × 10¹⁵ M_⊙. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centred at the X-ray cluster A2142. Most of the groups in the core region are multimodal. In the outskirts of the supercluster, the number of groups is larger than in the core, and groups are poorer. The orientation of the axis of the cluster A2142 follows the orientations of its X-ray substructures and radio halo, and is aligned along the supercluster axis. The high-density core of the supercluster with the global density D8 ≥ 17 and perhaps with D8 ≥ 13 may have started to collapse.

Conclusions. A2142 supercluster with collapsing core and straight body, is an unusual object among superclusters. In the course of the future evolution, the supercluster may split into several systems.