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Register a new userThe Sloan Great Wall. Rich clusters
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We present the results of the study of the substructure and galaxy content of ten rich clusters of galaxies in three different superclusters of the Sloan Great Wall. We determine the substructure in clusters using the Mclust package from the R statistical environment and analyse their galaxy content. We analyse the distribution of the peculiar velocities of galaxies in clusters and calculate the peculiar velocity of the first ranked galaxy. We show that clusters in our sample have more than one component; in some clusters different components also have different galaxy content. We find that in some clusters with substructure the peculiar velocities of the first ranked galaxies are large. All clusters in our sample host luminous red galaxies. They can be found both in the central areas of clusters as well as in the outskirts, some of them have large peculiar velocities. About 1/3 of red galaxies in clusters are spirals. The scatter of colours of red ellipticals is in most clusters larger than that of red spirals. The presence of substructure in rich clusters, signs of possible mergers and infall, as well as the large peculiar velocities of the first ranked galaxies suggest that the clusters in our sample are not yet virialized. We present merger trees of dark matter haloes in an N-body simulation to demonstrate the formation of present-day dark matter haloes via multiple mergers during their evolution. In simulated dark matter haloes we find a substructure similar to that in observed clusters.
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We present the results of the study of the morphology and galaxy content of the Sloan Great Wall (SGW). We use the luminosity density field to determine superclusters in the SGW, and the fourth Minkowski functional V_3 and the morphological signature (the K_1-K_2 shapefinders curve) to show the different morphologies of the SGW, from a single filament to a multibranching, clumpy planar system. The richest supercluster in the SGW, SCl~126 and especially its core resemble a very rich filament, while another rich supercluster in the SGW, SCl~111, resembles a multispider - an assembly of high density regions connected by chains of galaxies. Using Minkowski functionals we study the substructure of individual galaxy populations determined by their color in these superclusters. We assess the statistical significance of the results with the halo model and smoothed bootstrap. We study the galaxy content and the properties of groups of galaxies in two richest superclusters of the SGW, paying special attention to bright red galaxies (BRGs) and to the first ranked galaxies in SGW groups. About 1/3 of BRGs are spirals. The scatter of colors of elliptical BRGs is smaller than that of spiral BRGs. About half of BRGs and of first ranked galaxies in groups have large peculiar velocities. Groups with elliptical BRGs as their first ranked galaxies populate superclusters more uniformly than the groups, which have a spiral BRG as its first ranked galaxy. The galaxy and group content of the core of the supercluster SCl~126 shows several differences in comparison with the outskirts of this supercluster and with the supercluster SCl~111. Our results suggest that the formation history and evolution of individual neighbour superclusters in the SGW has been different.
We use extreme value statistics to assess the significance of two of the most dramatic structures in the local Universe: the Shapley supercluster and the Sloan Great Wall. If we assume that Shapley (volume ~ 1.2 x 10^5 (Mpc/h)^3) evolved from an overdense region in the initial Gaussian fluctuation field, with currently popular choices for the background cosmological model and the shape and amplitude sigma8 of the initial power spectrum, we estimate that the total mass of the system is within 20 percent of 1.8 x 10^16 Msun/h. Extreme value statistics show that the existence of this massive concentration is not unexpected if the initial fluctuation field was Gaussian, provided there are no other similar objects within a sphere of radius 200 Mpc/h centred on our Galaxy. However, a similar analysis of the Sloan Great Wall, a more distant (z ~ 0.08) and extended concentration of structures (volume ~ 7.2 x 10^5 (Mpc/h)^3) suggests that it is more unusual. We estimate its total mass to be within 20 percent of 1.2 x 10^17 Msun/h; even if it is the densest such object of its volume within z=0.2, its existence is difficult to reconcile with Gaussian initial conditions if sigma8 < 0.9. This tension can be alleviated if this structure is the densest within the Hubble volume. Finally, we show how extreme value statistics can be used to address the likelihood that an object like Shapley exists in the same volume which contains the Great Wall, finding, again, that Shapley is not particularly unusual. It is straightforward to incorporate other models of the initial fluctuation field into our formalism.
In the cosmic web, galaxy superclusters or their high-density cores are the largest objects that may collapse at present or during the future evolution. We study the dynamical state and possible future evolution of galaxy superclusters from the Sloan Great Wall (SGW), the richest galaxy system in the nearby Universe. We calculated supercluster masses using dynamical masses of galaxy groups and stellar masses of galaxies. We employed normal mixture modelling to study the structure of rich SGW superclusters and search for components (cores) in superclusters. We analysed the radial mass distribution in the high-density cores of superclusters centred approximately at rich clusters and used the spherical collapse model to study their dynamical state. We found that the lower limit of the total mass of the SGW is approximately $M = 2.5times~10^{16}h^{-1}M_odot$. Different mass estimators of superclusters agree well, the main uncertainties in masses of superclusters come from missing groups and clusters. We detected three high-density cores in the richest SGW supercluster (SCl~027) and two in the second richest supercluster (SCl~019). They have masses of $1.2 - 5.9 times~10^{15}h^{-1}M_odot$ and sizes of up to $approx 60 h^{-1}$ Mpc. The high-density cores of superclusters are very elongated, flattened perpendicularly to the line of sight. The comparison of the radial mass distribution in the high-density cores with the predictions of spherical collapse model suggests that their central regions with radii smaller than $8 h^{-1}$Mpc and masses of up to $M = 2times~10^{15}h^{-1}M_odot$ may be collapsing. The rich SGW superclusters with their high-density cores represent dynamically evolving environments for studies of the properties of galaxies and galaxy systems.
We study the morphology, luminosity and mass of the superclusters from the BOSS Great Wall (BGW), a recently discovered very rich supercluster complex at the redshift $z = 0.47$. We have employed the Minkowski functionals to quantify supercluster morphology. We calculate supercluster luminosities and masses using two methods. Firstly, we used data about the luminosities and stellar masses of high stellar mass galaxies with $log(M_*/h^{-1}M_odot) geq 11.3$. Secondly, we applied a scaling relation that combines morphological and physical parameters of superclusters to obtain supercluster luminosities, and obtained supercluster masses using the mass-to-light ratios found for local rich superclusters. We find that the BGW superclusters are very elongated systems, with shape parameter values of less than $0.2$. This value is lower than that found for the most elongated local superclusters. The values of the fourth Minkowski functional $V_3$ for the richer BGW superclusters ($V_3 = 7$ and $10$) show that they have a complicated and rich inner structure. We identify two Planck SZ clusters in the BGW superclusters, one in the richest BGW supercluster, and another in one of the poor BGW superclusters. The luminosities of the BGW superclusters are in the range of $1 - 8times~10^{13}h^{-2}L_odot$, and masses in the range of $0.4 - 2.1times~10^{16}h^{-1}M_odot$. Supercluster luminosities and masses obtained with two methods agree well. We conclude that the BGW is a complex of massive, luminous and large superclusters with very elongated shape. The search and detailed study, including the morphology analysis of the richest superclusters and their complexes from observations and simulations can help us to understand formation and evolution of the cosmic web.
The Perseus-Pisces supercluster is known as one of the largest structures in the nearby Universe that has been charted by the galaxy and galaxy cluster distributions. For the latter mostly clusters from the Abell catalogue have been used. Here we take a new approach to a quantitative characterisation of the Perseus-Pisces supercluster using a statistically complete sample of X-ray luminous galaxy groups and clusters from our CLASSIX galaxy cluster redshift survey. We used a friends-of-friends technique to construct the supercluster membership. We also studied the structure of the Southern Great Wall, which merges with the Perseus-Pisces supercluster with a slightly increased friends-of-friends linking length. In this work we discuss the geometric structure of the superclusters, compare the X-ray luminosity distribution of the members with that of the surroundings, and provide an estimate of the supercluster mass. These results establish Perseus-Pisces as the largest superstructure in the Universe at redshifts z <= 0.03. With the new data this supercluster extends through the zone of avoidance, which has also been indicated by some studies of the galaxy distribution by means of HI observations. We investigated whether the shapes of the member groups and clusters in X-rays are aligned with the major axis of the supercluster. We find no evidence for a pronounced alignment, except for the ellipticities of Perseus and AWM7, which are aligned with the separation vector of the two systems and weakly with the supercluster.
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