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Measuring Galaxy Properties in the Cluster Abell 160

Craig Koontz
Ohio Northern University

We describe a procedure for building a catalog of photometric measurements of a large number of galaxies in the cluster of galaxies Abell 160. We have mosaiced this and about 20 other clusters in R (red) and V (yellow) bands using a CCD imager on the 1.3-meter McGraw-Hill telescope. This cluster is chosen as a test case because it is relatively nearby (z=0.045), x-ray data exist, and we have obtained spectroscopic redshifts for its brightest galaxies. We use the opensource software "WCStools" and "SExtractor" in our procedure to apply a world coordinate system to images, and to extract sources from images, respectively. We create software for merging catalogs in such a way as to avoid double counting, to reject cosmic rays, and to combine redundant measurements of galaxy properties. The properties include total magnitude, ellipticity, position angle, size (FWHM), and color (V-R). We investigate the efficacy of SExtractor at galaxy-star separation and find that it begins breaking down around R.0 magnitude. We attempt to separate cluster members from foreground and background galaxies using the color-magnitude relation and spectroscopic redshifts. In future work, we will investigate substructure (clumping) within clusters and its correlation with galaxy properties (especially color, size and morphology).

ONU Student Research Colloquium