The evolution of high-density cores of the BOSS Great Wall superclusters

¹ Tartu Observatory, Tartu University, Observatooriumi 1, 61602 Tõravere, Estonia
e-mail: maret.einasto@ut.ee
² The National Library of Finland, Unioninkatu 36, University of Helsinki, 00014 Helsinki, Finland
³ Estonian Academy of Sciences, Kohtu 6, 10130 Tallinn, Estonia
⁴ ICRANet, Piazza della Repubblica 10, 65122 Pescara, Italy

Received: 17 December 2021
Accepted: 4 April 2022

Abstract

Context. High-density cores (HDCs) of galaxy superclusters that embed rich clusters and groups of galaxies are the earliest large objects to form in the cosmic web, and the largest objects that may collapse in the present or future.

Aims. We aim to study the dynamical state and possible evolution of the HDCs in the BOSS Great Wall (BGW) superclusters at redshift z ≈ 0.5 from the CMASS (constant mass) galaxy sample, based on the Baryon Oscillation Spectroscopic Survey (BOSS) in order to understand the growth and evolution of structures in the Universe.

Methods. We analysed the luminosity density distribution in the BGW superclusters to determine the HDCs in them. We derived the density contrast values for the spherical collapse model in a wide range of redshifts and used these values to study the dynamical state and possible evolution of the HDCs of the BGW superclusters. The masses of the HDCs were calculated using stellar masses of galaxies in them. We found the masses and radii of the turnaround and future collapse regions in the HDCs of the BGW superclusters and compared them with those of local superclusters.

Results. We determined eight HDCs in the BGW superclusters. The masses of their turnaround regions are in the range of M_T ≈ 0.4–3.3 × 10¹⁵ h⁻¹ M_⊙, and radii are in the range of R_T ≈ 3.5–7 h⁻¹ Mpc. The radii of their future collapse regions are in the range of R_FC ≈ 4–8 h⁻¹ Mpc. Distances between individual cores in superclusters are much larger: of the order of 25–35 h⁻¹ Mpc. The richness and sizes of the HDCs are comparable with those of the HDCs of the richest superclusters in the local Universe.

Conclusions. The BGW superclusters will probably evolve to several poorer superclusters with masses similar to those of the local superclusters. This may weaken the tension with the ΛCDM model, which does not predict a large number of very rich and large superclusters in our local cosmic neighbourhood, and explains why there are no superclusters as elongated as those in the BGW in the local Universe.