Southern voids : structure and cosmological implications

Master Thesis


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University of Cape Town

A review of standard cosmology theory and observational results is presented. The main tool for investigating large-scale structure in this thesis is a visually compiled void catalogue. Void selection effects that cause the detected distribution of voids to differ from the true distribution are discussed and suggestions are made for how to correct for these effects in the catalogue. The geometrical distribution of voids is then studied by dividing the void catalogue into two parts - wall voids and non-wall voids. The wall voids are smaller with typical radii of around 150 km s-¹ whereas non-wall voids have a mean radius of approximately 1150 km s-¹. The non-wall, and therefore, the larger voids are distributed isotropically and their correlation function is found to correspond roughly to that of Abell clusters, thus suggesting a link between the two structures. A relation between the velocity dispersions of clusters and the void radii is found using a spherical collapse model for structure formation. The ratio of these two quantities is used to put constraints on the cosmic density parameter 0 and observational data indicate that the universe is open.

Bibliography: pages 107-113.