AAS 201st Meeting, January, 2003
Session 42. Galaxies and Clusters
Poster, Tuesday, January 7, 2003, 9:20am-6:30pm, Exhibit Hall AB

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[42.01] Photometric Determination of r200 for SDSS Galaxy Clusters and Groups

S. M. Hansen (Chicago), T. A. McKay (Michigan), J. Annis (FNAL), A. Kimball (Michigan), E. S. Sheldon (Chicago), R. H. Wechsler (Michigan)

We use photometric data from the Sloan Digital Sky Survey to determine directly a size-richness relation for groups and clusters with a model-independent method. We determine the radius at which the space density of cluster members is overdense by a factor of 200, without assuming a model for the radial distribution of galaxies in clusters. Up to a bias factor, the number of galaxies traces the mass of the halos in which they are embedded, so this space-density-based r200 should reasonably reflect the characteristic radii of clusters. Here, we present our results for r200 as a function of cluster richness, compare these results with the relationship determined from theoretical models, and examine the radial behavior of the luminosity function and color distribution of cluster members as a function of cluster richness.

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