SDSS superclusters: morphology and galaxy content

We compare the galaxy populations in superclusters of different morphology in the nearby Universe (180 < d < 270 Mpc) to see whether the inner structure and overall morphology of superclusters are important in shaping galaxy properties in superclusters. Supercluster morphology has been found with Minkowski functionals. We analyse the probability density distributions of colours, morphological types, stellar masses, star formation rates (SFR) of galaxies, and the peculiar velocities of the main galaxies in groups in superclusters of filament and spider types, and in the field. We show that the fraction of red, early-type, low SFR galaxies in filament-type superclusters is higher than in spider-type superclusters; in low-density global environments their fraction is lower than in superclusters. In all environments the fraction of red, high stellar mass, and low SFR galaxies in rich groups is higher than in poor groups. In superclusters of spider morphology red, high SFR galaxies have higher stellar masses than in filament-type superclusters. Groups of equal richness host galaxies with larger stellar masses, a larger fraction of early-type and red galaxies, and a higher fraction of low SFR galaxies, if they are located in superclusters of filament morphology. The peculiar velocities of the main galaxies in groups from superclusters of filament morphology are higher than in those of spider morphology. Groups with higher peculiar velocities of their main galaxies in filament-type superclusters are located in higher density environment than those with low peculiar velocities. There are significant differences between galaxy populations of the individual richest superclusters. Therefore both local (group) and global (supercluster) environments and even supercluster morphology play an important role in the formation and evolution of galaxies.Comment: Comments: 14 pages, 11 figures, accepted for publication in Astronomy and Astrophysic

SDSS DR7 superclusters. Principal component analysis

We apply the principal component analysis and Spearman's correlation test to study the properties of superclusters drawn from the SDSS DR7. We analyse possible selection effects in the supercluster catalogue, study the physical and morphological properties of superclusters, find their possible subsets, and determine scaling relations for superclusters. We show that the parameters of superclusters do not correlate with their distance. The correlations between the physical and morphological properties of superclusters are strong. Superclusters can be divided into two populations according to their total luminosity. High-luminosity superclusters form two sets, more elongated systems with the shape parameter K_1/K_2 0.5. The first two principal components account for more than 90% of the variance in the supercluster parameters and define the fundamental plane, which characterises the physical and morphological properties of superclusters. We use principal component analysis to derive scaling relations for superclusters, in which we combine the physical and morphological parameters of superclusters. Structure formation simulations for different cosmologies, and more data about the local and high redshift superclusters are needed to understand better the evolution and the properties of superclusters.Comment: 13 pages, 10 figures, accepted for publication in Astronomy and Astrophysic

Shell-like structures in our cosmic neighbourhood

Context. Signatures of the processes in the early Universe are imprinted in the cosmic web. Some of them may define shell-like structures characterised by typical scales. Examples of such structures are shell-like systems of galaxies, which are interpreted as a signatures of the baryon acoustic oscillations.Aims. We search for shell-like structures in the distribution of nearby rich clusters of galaxies drawn from the SDSS DR8.Methods. We calculated the distance distributions between rich clusters of galaxies and groups and clusters of various richness, searched for the maxima in the distance distributions and selected candidates of shell-like structures. We analysed the space distribution of groups and clusters that form shell walls.Results. We find six possible candidates of shell-like structures, in which galaxy clusters have the maximum in their distance distribution to other galaxy groups and clusters at a distance of about 120-130 h(-1) Mpc. Another, less probable maximum is found at a distance of about 240 h(-1) Mpc. The rich galaxy cluster A1795, which is the central cluster of the Bootes supercluster, has the highest maximum in the distance distribution of all other surrounding groups and clusters in our rich cluster sample. It lies at a distance of about 120 h(-1) Mpc. The structures of galaxy systems that cause this maximum form an almost complete shell of galaxy groups, clusters, and superclusters. The richest systems in the nearby universe, the Sloan Great Wall, the Corona Borealis supercluster, and the UrsaMajor supercluster, are among them. The probability that we obtain maxima like this from random distributions is lower than 0.001.Conclusions. Our results confirm that shell-like structures can be found in the distribution of nearby galaxies and their systems. The radii of the possible shells are larger than expected for a baryonic acoustic oscillations (BAO) shell (approximate to 109 h(-1) Mpc versus approximate to 120-130 h(-1) Mpc), and they are determined by very rich galaxy clusters and superclusters. In contrast, BAO shells are barely seen in the galaxy distribution. We discuss possible consequences of these differences