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Register a new userCollapse, connectivity, and galaxy populations in supercluster cocoons: the case of A2142
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Maret Einasto
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The largest galaxy systems in the cosmic web are superclusters, overdensity regions of galaxies, groups, clusters, and filaments. Low-density regions around superclusters are called basins of attraction or cocoons. In my talk I discuss the properties of galaxies, groups, and filaments in the A2142 supercluster and its cocoon at redshift $z approx 0.09$. Cocoon boundaries are determined by the lowest density regions around the supercluster. We analyse the structure, dynamical state, connectivity, and galaxy content of the supercluster, and its high density core with the cluster A2142. We show that the main body of the supercluster is collapsing, and long filaments which surround the supercluster are detached from it. Galaxies with very old stellar populations lie not only in the central parts of clusters and groups in the supercluster, but also in the poorest groups in the cocoon.
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We study the dynamical state and properties of galaxies and groups in the supercluster SClA2142 that has a collapsing core, to understand its possible formation and evolution. 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. The supercluster core has a radius of about $8 h^{-1}$Mpc and total mass $M_{mathrm{tot}} approx 2.3times~10^{15}h^{-1}M_odot$ 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 SClA2142 having the median stellar age $t > 8$Gyr. Recently quenched galaxies and active galactic nuclei (AGNs) are mostly located at virial radii or in merging regions of groups, and at clustercentric distances $D_c approx 6 h^{-1}$ Mpc. 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 SClA2142 are dynamically young. 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.
We present a study of the Corona Borealis (CB) supercluster. We determined the high-density cores of the CB and the richest galaxy clusters in them, and studied their dynamical state and galaxy content. We determined filaments in the supercluster to analyse the connectivity of clusters. We compared the mass distribution in the CB with predictions from the spherical collapse model and analysed the acceleration field in the CB. We found that at a radius $R_{mathrm{30}}$ around clusters in the CB (A2065, A2061, A2089, and Gr2064) (corresponding to the density contrast $Deltarho approx 30$), the galaxy distribution shows a minimum. The $R_{30}$ values for individual clusters lie in the range of $3 - 6$ $h^{-1}$ Mpc. The radii of the clusters (splashback radii) lie in the range of $R_{mathrm{cl}} approx 2 - 3$ $R_{mathrm{vir}}$. The projected phase space diagrams and the comparison with the spherical collapse model suggest that $R_{mathrm{30}}$ regions have passed turnaround and are collapsing. Galaxy content in clusters varies strongly. The cluster A2061 has the highest fraction of galaxies with old stellar populations, and A2065 has the highest fraction of galaxies with young stellar populations. The number of long filaments near clusters vary from one at A2089 to five at A2061. During the future evolution, the clusters in the main part of the CB may merge and form one of the largest bound systems in the nearby Universe. Another part of the CB, with the cluster Gr2064, will form a separate system. The structures with a current density contrast $Deltarho approx 30$ have passed turnaround and started to collapse at redshifts $z approx 0.3 - 0.4$. The comparison of the number and properties of the most massive collapsing supercluster cores from observations and simulations may serve as a test for cosmological models.
The formation and evolution of the cosmic web in which galaxy superclusters are the largest relatively isolated objects is governed by a gravitational attraction of dark matter and antigravity of dark energy (cosmological constant). We study the characteristic density contrasts in the spherical collapse model for several epochs in the supercluster evolution and their dynamical state. We analysed the density contrasts for the turnaround, future collapse and zero gravity in different LCDM models and applied them to study the dynamical state of the supercluster A2142 with an almost spherical main body. The analysis of the supercluster A2142 shows that its high-density core has already started to collapse. The zero-gravity line outlines the outer region of the main body of the supercluster. In the course of future evolution the supercluster may split into several collapsing systems. The various density contrasts presented in our study and applied to the supercluster A2142 offer a promising way to characterise the dynamical state and expected future evolution of galaxy superclusters.
We investigate the evolution of superclusters and supercluster cocoons (basins of attraction), and the influence of cosmological parameters to the evolution. We perform numerical simulations of the evolution of the cosmic web for different cosmological models: the LCDM model with a conventional value of the dark energy (DE) density, the open model OCDM with no DE, the standard SCDM model with no DE, and the Hyper-DE HCDM model with an enhanced DE density value. We find ensembles of superclusters of these models for five evolutionary stages, corresponding to the present epoch z = 0, and to redshifts z = 1, 3, 10, 30. We use diameters of the largest superclusters and the number of superclusters as percolation functions to describe properties of the ensemble of superclusters in the cosmic web. We analyse the size and mass distribution of superclusters in models and in real Sloan Digital Sky Survey (SDSS) based samples. In all models numbers and volumes of supercluster cocoons are independent on cosmological epochs. Supercluster masses increase with time, and geometrical sizes in comoving coordinates decrease with time, for all models. LCDM, OCDM and HCDM models have almost similar percolation parameters. This suggests that the essential parameter, which defines the evolution of superclusters, is the matter density. The DE density influences the growth of the amplitude of density perturbations, and the growth of masses of superclusters, albeit significantly less strongly. The HCDM model has the largest speed of the growth of the amplitude of density fluctuations, and the largest growth of supercluster masses during the evolution. Geometrical diameters and numbers of HCDM superclusters at high threshold densities are larger than for LCDM and OCDM superclusters. SCDM model has about two times more superclusters than other models; SCDM superclusters have smaller diameters and masses.
We study the distribution, masses, and dynamical properties of galaxy groups in the A2142 supercluster. 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 the regions of different global density, calculate their masses and mass-to-light ratios and analyse their dynamical state with several 1D and 3D statistics. We use the spherical collapse model to study the dynamical state of the supercluster. We show that in A2142 supercluster groups and clusters with at least ten member galaxies lie along an almost straight line forming a 50 Mpc/h long main body of the supercluster. The A2142 supercluster has a very high density core surrounded by lower-density outskirt regions. The total estimated mass of the supercluster is M_est = 6.2 10^{15}M_sun. More than a half of groups with at least ten member galaxies in the supercluster lie in the high-density core of the supercluster, centered at the rich X-ray cluster A2142. Most of the galaxy 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 cluster A2142 axis 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 reached the turnaround radius and started to collapse. A2142 supercluster with luminous, collapsing core and straight body is an unusual object among galaxy superclusters. In the course of the future evolution the supercluster may be split into several separate systems.
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