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P.A.A. Lopes (CIT, ON), R.R. Gal, S.G. Djorgovski (CIT), R.R. de Carvalho (IAG-USP), S.C. Odewahn (ASU)
We present a study of substructure in clusters of galaxies, with the largest sample of clusters used for this purpose to date. The data set consists of 356 Abell clusters in the redshift range 0.02 < z < 0.30. Our goal is to examine the evolution of substructure in this redshift range, if any is present, and to relate the changes in galaxy populations (e.g., the Butcher-Oemler effect) to the cluster morphology, at a given redshift and cluster richness. This should provide further insights in our understanding of cluster assembly and the evolution of galaxy populations in them.
All of the sample clusters have been imaged as part of the Palomar Abell Cluster Optical Survey (PACOS) at the Palomar Observatory 60-inch telescope, in Gunn gri bands, as a part of the DPOSS photometric calibration project. These CCD images (FOV ~ 13 arcmin square) are supplemented with DPOSS (photographic plate based) galaxy catalogs, which do not reach as deep, but do cover a much larger area. Spectroscopic redshfts exist for many clusters, and good photometric redshift estimates for all of them.
A color selection criterion is used to exclude probable field galaxies. We then use the adaptive kernel technique to create surface density maps for each cluster field. The presence of substructure in the clusters is indicated by density peaks in these maps, and statistically quantified in different ways.
In the future we also plan to correlate our galaxy density maps with x-ray images of the clusters.