Large Quasar Groups at Redshift ~ 2

Abstract

This project aims to use the large public databases that are now becoming available in
the Virtual Observatory. For my purpose two of the most important datasets for investigating Large Quasar Groups (LQGs) are the Sloan Digital Sky Survey (SDSS) and the 2dF Quasar Redshift Survey (2QZ). These have been used: to investigate stripe 82 of the SDSS; to discover large scale structures, specifically LQGs in the early universe; to investigate the expectation of finding LQGs at high redshift, and to investigate their properties in detail; to assess the compatibility of these structures with the concordance model in cosmology; to identify low redshift LQGs for investigation of the galaxy and cluster environments of quasars; to investigate whether correlations exist between LQGs and other cosmological sources, such as gamma ray bursters, the highest redshift quasars and radio galaxies catalogues; to probe the high-z LQGs with MgII absorbers from the Gemini data.

Using an algorithm for single-linkage hierarchical clustering, four LQGs have been found in the redshift range of 1.8 - 2.5. These four groups were tested for statistical significance using a convex hull approach, to calculate the overdensity. Each group was submitted to 1000 random simulations, no comparable structure was found from the random simulations. The algorithm was then applied to a greater redshift range of 0.6 -
2.5. The total number of groups found was 36, each group was tested for statistical significance using random simulations, each group found was to be real.
To improve the statistical findings of these four high redshift groups, MgII absorbers from the Zue & Maynard catalogue of absorbers was used to investigate any MgII absorbers that were in the area of the four high redshift groups. The results found that many of the MgII absorbers lie in the peripherals of the groups, however, a few MgII absorbers lie within the groups themselves.