The Northern Sky Optical Cluster Survey. I. Detection of Galaxy Clusters in DPOSS

Abstract

The Northern Sky Optical Cluster Survey is a project to create an objective\ncatalog of galaxy clusters over the entire high-galactic-latitude Northern sky,\nwith well understood selection criteria. We use the object catalogs generated\nfrom the Digitized Second Palomar Sky Survey (DPOSS, Djorgovski et al. 1999) as\nthe basis for this survey. We apply a color criterion to select against field\ngalaxies, and use a simple adaptive kernel technique to create galaxy density\nmaps, combined with the bootstrap technique to make significance maps, from\nwhich density peaks are selected. This survey attempts to eliminate some of the\nsubjective criteria and assumptions of past surveys, including detection by eye\n(Abell 1958, ACO 1989) and assumed luminosity functions and cluster profiles\n(PDCS, Postman et al. 1995). We also utilize more information (especially\ncolors) than the most similar recent survey, the APM (Dalton et al. 1992). This\npaper presents the details of our cluster detection technique, as well as some\ninitial results for two small areas totaling ~60 square degrees. We find a mean\nsurface density of ~1.5 clusters per square degree, consistent with the\ndetection of richness class 0 and higher clusters to z~0.3. In addition, we\ndemonstrate an effective photometric redshift estimator for our clusters.\n