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A Wide-Field Imaging Survey of Low-Redshift Galaxy Clusters

Wayne Alan Barkhouse

Doctor of Philosophy 2003
Graduate Department of Astronomy and Astrophysics, University of Toronto

This thesis presents the results from a comprehensive study of 26 low-redshift galaxy clusters in order to study the radial dependence of various cluster properties. The observations were acquired using the 8k mosaic camera on the 0.9-m KPNO telescope. This dataset was supplemented by 43 clusters from the survey of Lopez-Cruz (1997), and an additional two clusters from Brown (1997). Thus, a total sample of 71 clusters covering a redshift range from ~0.01 to 0.20 was available for analysis. The dynamical radius of each cluster (r200) was estimated from the photometric measurement of cluster richness (Bgc). The cluster galaxy color-magnitude relation (CMR) was used as a tool to minimize the inclusion of contaminating background galaxies by selecting galaxies relative to this relation. The luminosity function (LF) of individual and composite galaxy samples were constructed via the statistical subtraction of background galaxies. A robust method of comparing LFs for a variety of galaxy samples over a range of cluster-centric radius was presented. The general shape of the LFs were found to correlate with radius in the sense that the faint-end slope was generally steeper in the cluster outskirts. Color selection of galaxies into a red sequence and blue population indicates that the blue galaxies become fainter toward the cluster central region. This result supports the scenario that infalling field galaxies have their star formation truncated by some dynamical process. The construction of a non-parametric dwarf-to-giant ratio (DGR) and the blue-to-red galaxy ratio (BRR), allowed the investigation of the change in these parameters with various cluster properties to be conducted. The radial dependence of the DGR and BRR suggests that blue dwarf galaxies are tidally disrupted in the inner cluster environment or fade and turn red. The red, mainly nucleated, dwarf galaxies remain relatively unchanged with respect to cluster-centric radius, while giant blue galaxies have transformed into their red galaxy counterparts. These results provide support for the model proposed by Lopez-Cruz et al. (1997) to explain the formation of cD and Brightest Cluster Galaxy halos in which dwarf galaxies get tidally disrupted in the inner cluster region.

Reproduced with permission by Marlene Cummins library@astro.utoronto.ca