Superclusters and the Void-High Density Region Correlations in the Sloan Digital Sky Survey

Abstract

The large-scale structure of the Universe comprising of galaxies and dark matter has a web-like geometry which is called the 'Cosmic Web'. Its main constituents are walls, filaments, clusters, and voids. The galaxy redshift surveys have shown that there are structures present on even larger scales than clusters and these are called the superclusters (clusters of galaxy clusters). Massive superclusters are the largest structures found in the Universe and they are rare. The properties of superclusters can be used to test various cosmological models while there are still unknowns how superclusters form and evolve.

In this thesis, we present the discovery of a massive, 200 Mpc (Megaparsecs) scale supercluster, the Saraswati, at redshift of 0.28. Saraswati is one of the most massive superclusters with at least 43 galaxy clusters and a total mass of ~ 2 x 10^16 M_sun (solar masses). We also present a catalog of superclusters, identified using the data on clusters, in the redshift range of 0.05 <= z <= 0.42. This is the largest catalog of superclusters (571 superclusters) in this redshift range having a range of masses and sizes with the most massive supercluster being at z ~ 0.12 containing 59 clusters within ~ 170 Mpc. Our new catalog of superclusters is useful for the statistical studies of their properties. With a goal to understand the relation between overdensities (dominated by dark matter) and under-densities (dominated by dark energy), we have extracted voids and high-density regions from the Sloan Digital Sky Survey. Using the Watershed and Voronoi tessellation methods, we measured their two-point correlation functions. This study has led to the understanding of the high correlation scales among voids and high-density regions and their physical inter-relationship.