Observations of large-scale structure in the Universe from the Edinburgh/Durham Southern Galaxy Catalogue
Nichol, Robert Clive
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The study of the large-scale structure in the universe places tight constraints on theories of galaxy formation. On scales greater than 10/i- 1Mpc, the conditions in the early universe should still be imprinted on the large-scale structure we see today. However, these studies have been hampered by the lack of a reliable, homogeneous catalogue of galaxies and clusters of galaxies over a large area of the sky. Previous catalogues have been built from visual scans of photographic plates (e.g. the Lick galaxy catalogue and the Abell cluster catalogue) and many authors believe the large-scale structure seen in these catalogues is an artifact of the subjective manner in which they were constructed.This thesis is concerned with the scientific analysis of the Edinburgh/Durham Southern Galaxy Catalogue (EDSGC), the Edinburgh/Durham Cluster Catalogue (EDCC) and the Edinburgh/Milano (EM) cluster redshift survey. The first of these databases was objectively constructed from COSMOS scans of 60 UK Schmidt Illa-J survey plates and contains 1.5 million galaxies covering over 1500 degrees square of the sky centred at the South Galactic Pole. The EDSGC is therefore, ideal for studying the large-scale structure in the universe free from the criticisms levelled at previous catalogues.The other two databases were constructed from the EDSGC and are described in detail in this thesis. The EDCC was constructed from the EDSGC using a peak-finding algorithm to locate the galaxy over densities, followed by a pseudo-Abell style analysis to classify the clusters. In total, 737 groups or clusters were detected and the EDCC was found to be complete to a limiting magnitude of m10(6J) = 18.75 (z = 0.13). When compared to the Abell catalogue over the EDCC area, over 80% of the Abell clusters were found in the EDCC to the completeness limits of both the catalogues. However, only 50% of the EDCC clusters, to the respective completeness limits, were found. The EM survey was constructed from the EDCC and consists of 103 cluster redshifts, each with an average of 10 galaxy redshift measurements. Over 70% of the clusters were found to have some level of interloper contamination and ~ 10% of the clusters were defined as spurious. These figures are much higher than previously thought. From the EM survey, a 90% redshift complete sample of cluster was selected using an Abell radius of 1.0/i- 1Mpc.The distribution of galaxies and clusters seen in the EDSGC and the EM survey were investigated using the two—point correlation function. The angular galaxy correlation function was calculated for the whole EDSGC and was found to have significantly more power on angular scale greater than 5 degrees than the canonical value derived from the Lick galaxy catalogue. The EDSGC angular correlation function is inconsistent (3cr at 5 degrees) with the popular model of biased Cold Dark Matter galaxy formation and is a major constraint on the theory. The spatial cluster correlation function of the EM 90% redshift complete sample of clusters was computed and was found to have less power on all scales compared to correlation functions computed from the Abell catalogue. On investigating the radial and transverse components of the EM correlation function separately, it was observed to be isotropic on scales of less than 30 h~ Mpc. By comparison, correlation functions computed from the Abell catalogue show strong anisotropies in the redshift direction which suggests that the catalogue is contaminated by projection effects. The EM cluster correlation function is consistent with predictions from CDM models of galaxy formation and has removed one of the last conflicting observations with this theory.The new observations presented in this thesis show that our previous knowledge of the large-scale structure in the universe was biased because of systematic errors in prior object catalogues. Presently, no single theory of galaxy formation can explain these new observations.