An optical search for distant galaxy clusters

Abstract

In this dissertation, a new catalogue of distant galaxy clusters is presented. Also presented are new results on the galaxy two-point angular correlation function and new data on galaxy number counts. These results are based on two deep I-band surveys of the sky, covering a total area of 13 square degrees and reaching a mean limiting magnitude of I = 22.5. The area imaged in the second survey, which covers 1.5 square degrees, was also imaged in V. These fields reach a mean V-band magnitude limit of 23.0. All the data were taken with the / / I camera on the A AT in conjunction a Thomson CCD. Reduction of the CCD data and the creation of an object catalogue for each / / I field are discussed in detail. From this data, galaxy number counts in V and I are determined. In /, the counts cover the magnitude interval from / = 16 to I = 22.5 and m atch very well the counts found at fainter limits. The theoretical counts for a few common cosmological models are fitted to the data. The model that agrees with the data best is one that includes a cosmological constant. Also presented are the colourmagnitude distributions for both stars and galaxies in both V — I and Bj — I . The galaxy two-point angular correlation function is also determined from the //1 data. The function is measured from / = 17 to / = 22.5 and is well described by a power law with an index near the canonical value of —0.8. The am plitude of the correlation function falls below that predicted by models that incorporate clustering evolution in a simple parametric way. Additionally, the area-averaged three and four point angular correlation functions are determined. The slope of these functions are respectively two and three times steeper than the slope of the two point function. The cell count distribution is calculated from the infinite hierarchy of correlation functions and then compared to that determined directly from the data. The methods by which distant clusters are found from the f/1 data are discussed. The cell count distribution is used to estim ate both the expected number of candidates with Abell Richness greater than or equal to zero and to calculate the expected red-shift distribution of such clusters. This distribution has a median near z = 0.5 The f/1 cluster catalogue contains 106 candidates; 96 of which are new candidates. At least half are expected to be poorer than Abell Richness zero. The red-shift of two cluster candidates is determined. Both clusters show significant contamination. In the appendix, the results of a search for halo white dwarfs are presented. It will be shown that white dwarfs are unlikely to contribute more than half the mass attributed to the Galaxy halo. Show more