Like a spider in its web: a study of the large-scale structure around the Coma cluster

Nicola Malavasi,Nabila Aghanim,Victor Bonjean,Marian Douspis,Hideki Tanimura

doi:10.1051/0004-6361/201936629

Abstract

The Cosmic Web is a complex network of filaments, walls, and voids that represent the largest structures in the Universe. In this network, which is the direct result of structure formation, galaxy clusters occupy central positions that form the nodes and these are connected by filaments. In this work, we investigate the position in the Cosmic Web of one of the most well-known and best-studied clusters of galaxies, the Coma cluster. We make use of the Sloan Digital Sky Survey Data Release 7 Main Galaxy Sample and of the Discrete Persistent Structure Extractor to detect large-scale filaments around the Coma cluster and analyse the properties of the Cosmic Web. We study the network of filaments around Coma in a region of 75 Mpc in radius. We find that the Coma cluster has a median connectivity of 2.5, in agreement with measurements from clusters of similar mass in the literature as well as with what is expected from numerical simulations. Coma is indeed connected to three secure filaments which connect it to Abell 1367 and to several other clusters in the field. The location of these filaments in the vicinity of Coma is consistent with features detected in the X-ray, as well as the likely direction of infall of galaxies, such as for example NGC 4839. The overall picture that emerges of the Coma cluster is that of a highly connected structure occupying a central position as a dense node of the Cosmic Web. We also find a tentative detection, at 2.1σ significance, of the filaments in the SZ signal.

Highlights

The spatial distribution of galaxies in the Universe is far from uniform at the megaparsec scale
In the same figure we show with a different colour the filaments directly connected to a critical point within the virial radius of Coma and those directly connected to the critical points at the end of the first generation filaments and not within the Coma virial radius (“second generation filaments”)
Looking in more detail at the properties of the three secure filaments detected here, where they connect to the Coma cluster, we find a very good agreement with the position of known features of the cluster emerging from X-ray, SZ, and optical analyses in the literature

Summary

Introduction

The spatial distribution of galaxies in the Universe is far from uniform at the megaparsec scale. Smaller, lower-mass galaxy associations can be found inside the filaments and are referred to as knots This configuration of matter arises from the process of structure formation driven by gravitational collapse: following the initial density anisotropies whose imprint is visible in the cosmic microwave background (CMB, e.g. Planck Collaboration I 2016), matter departs from under-dense regions which become voids, flows inside walls to the filaments which are located at the intersections, and flows inside filaments to reach clusters. It is in this evolving environment that galaxies are formed and that complex interactions with the gaseous phase present in these structures take place

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Methods

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Discussion

Conclusion