Constraints on dark matter in clusters & galaxies from the shapes of X-ray images

Abstract

We summarize an ongoing program to use the shapes of X‐ray images of clusters and galaxies to gain information about the dark matter contained in those systems. Studies of five Abell clusters and one early type galaxy are briefly described (another is reported elsewhere in this volume). In each of these systems, the stellar distribution appears very flattened. For the clusters, the X‐ray also appear flattened, but less than expected if light traces mass. For the galaxy, the X‐ray contours are flatter at larger radii than expected if light traces mass. This is ‘‘geometrical evidence’’ for dark matter in both clusters and early type galaxies. Detailed modeling constrains the quantity and distribution of the dark matter. Full details can be found in several published papers.