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[10.07] Automated Galaxy Counts Toward X-ray-Selected Abell Clusters

K. Whitman (Cornell U), B.R. McNamara, A. Vikhlinin (Harvard-Smithsonian CfA)

We have measured the surface density of galaxies on R-band Digital Sky Survey images toward 18, redshift z<0.1, X-ray-selected Abell clusters. Our automated galaxy counts within 3 Mpc apertures agree well with Abell's counts for richness class 0--2 clusters. However, we find a smaller scatter in the X-ray luminosity--cluster richness relation using galaxy counts within smaller, 1.0--1.5 Mpc apertures compared to counts within the 3 Mpc Abell radius. We find that galaxy counts for distant clusters are likewise most accurate within \alt 1.5 Mpc apertures, where the ratio of cluster galaxies to background/foreground galaxies is maximal. An expanded sample of nearby clusters selected and analyzed similarly will provide a basis for comparing nearby and distant (i.e. z>0.5) X-ray clusters to study evolution.