A Study of Globular Cluster Systems in the Shapley Supercluster Region with the Hubble Space Telescope
Barber DeGraaff, Regina Grace
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After a brief introduction to astronomy and topics related to this thesis, we present three projects directed towards expanding our understanding of globular cluster (GC) systems, or populations, in galaxies within clusters.We first present two-band Hubble Space Telescope imaging of the "transitional" S0 galaxy NGC 1533 in the Doradus group of galaxies. We study the globular cluster system of this galaxy in detail and estimate its distance using three different methods, two of which are based on mean properties of the galaxy's GCs.We next present an investigation of ultra-compact dwarfs (UCDs), which are dense stellar systems closely associated with GCs, in the giant elliptical galaxyESO325-G004. We find a significant sample of UCD candidates in the field of this galaxy; we discuss the implications of these results and possible follow-up strategies.The main part of the thesis is a survey of the globular cluster systems of 11 giant elliptical galaxies in clusters associated with the Shapley Supercluster, the largest mass concentration in the local universe and possibly a major source of the LocalGroup's ~630 km/s motion with respect to the cosmic microwave background radiation. The sample galaxies were imaged with the Advanced Camera for Surveys Wide Field Channel in the F814W bandpass and are in the redshift range z = 0.035 - 0.048. The radial density distributions and constraints on the total GC populations of these 11 galaxies are presented. We find substantial globular cluster systems in all the galaxies, with the specific frequencies being larger for more central galaxies. The most massive galaxies in our sample, ESO444-G046 at the center of the extremely rich cluster Abell 3558 and ESO383-G076 at the center of Abell 3571, may contain the largest GC populations studied to date. For one galaxy in our sample, ES0325-G004 additional multiband imaging was obtained. We analyze the color data and find that ESO325-G004 has a bimodal globular cluster color distribution with characteristics typical of most giant ellipticals, and we discuss new ideas about the underlying causes of such distributions.The final chapter provides a summary of the thesis and possible future work.