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

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 as the nodes, connected through the filaments. In this work, we investigate the position in the Cosmic Web of one of the most known and best studied clusters of galaxies, the Coma cluster. We make use of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) Main Galaxy Sample and of the Discrete Persistent Structure Extractor (DisPerSE ) to detect large scale filaments around the Coma cluster and we analyse the properties of the Cosmic Web. We study the network of filaments around Coma in a 75 Mpc radius region. 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 expected from numerical simulations. It is indeed connected to 3 secure filaments which connect Coma 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, as for example NGC4839. 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.

Characterising filaments in the SDSS volume from the galaxy distribution

“…(which can be identified with the centres of voids). While in the analyses described in Malavasi et al (2020), Tanimura et al (2020), and Bonjean et al (2020) we only focused on maxima, type 2 saddle points, and bifurcations and in the present catalog we only distribute filaments and disregard walls for the moment, type 1 saddle points, and minima (voids), these types of critical points are still included in the numbers given in Table 5 and are included in some of the distributions presented below to provide a complete overview of the properties of the catalogue. Red lines refer to a 3σ persistence threshold, and blue lines refer to a 5σ persistence threshold.…”

“…This quantity is called connectivity, and it is an important observable for the study of the cosmic web, of structure formation, and cosmology (see e.g. Codis et al 2018;Sarron et al 2019;Darragh Ford et al 2019;Malavasi et al 2020;Kraljic et al 2019). The connectivity of maxima scales with the density of the maxima, that is, with the mass of the clusters associated with the peaks of the density field, and it is usually a number in the range 0 ÷ 10.…”

“…This figure shows a cubic region of 50 Mpc a side, centred on the Coma cluster. This region was taken as an example both because it was the subject of the analysis of Malavasi et al (2020) and because it is a massive cluster with a very prominent distortion. The top left panel shows the galaxies from the Legacy MGS colour-coded according to their density as computed from the DTFE.…”

“…This paper presented the first published general-purpose catalogues of filaments derived in the SDSS with the DisPerSE method, used in the works Malavasi et al (2020), Tanimura et al (2020), Bonjean et al (2020), and how they have been derived. We provided a full investigation of the effect of the parameter choice for the DisPerSE algorithm on the skeleton reconstruction.…”

“…DisPerSE can work with sparse datasets or with distributions of galaxies in which the density of tracers changes dramatically within the sampled volume). The catalogues of filaments described here have been used in Malavasi et al (2020), Tanimura et al (2020), Bonjean et al (2020) and represent the first published general-purpose catalogues of filaments in the SDSS obtained with the DisPerSE method. We study the systematic uncertainties deriving from the DisPerSE method and the SDSS survey characteristics.…”