AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 88. Large-Scale Structure Surveys
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southwest Exhibit Hall

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[88.09] A New Objective Catalog of Nearby Clusters

D.A. Bramel, R.C. Nichol, A.C. Pope (Carnegie Mellon Univ.)

We have created a matched-filter galaxy cluster detection algorithm for use on the photographic survey called the Edinburgh-Durham Southern Galaxy Catalogue (EDSGC). Through the extensive use of Monte Carlo simulations, the efficiency and accuracy of our algorithm has been measured. Also, variable cutoff thresholds were used for cluster discrimination, allowing optimal detection of clusters with specific characteristics (i.e. redshift & richness). It was found that the algorithm's efficiency was a function of position on the sky, which we attributed to variations in field galaxy density and projection effects due to the large scale structure in the universe. Once we had determined the thresholds and efficiency of the algorithm, we applied it to 100 square degrees of the EDSGC, and detected 151 unique clusters with at least 50 member galaxies. This is the largest area ever used for such an algorithm to date. An effective volume for this 100 square degree area was determine! d from our efficiency functions, and the density of rich optical clusters determined. It was found to be in good agreement with the density of clusters found in the Palomar Distant Cluster Survey (Postman et al. 1996).

In the future, this algorithm can be modified to take advantage of new, multi-color CCD survey data. In particular, we are improving the algorithm to take advantage of five-color photometric redshift estimates like those available from the Sloan Digital Sky Survey (SDSS). This will improve the detectability of the clusters and allow us to investigate new ways of determining the richness and mass of these optical clusters.

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