The Northern Sky Optical Cluster Survey. I. Detection of galaxy clusters in DPOSS

The Northern Sky Optical Cluster Survey is a project to create an objective catalog of galaxy clusters over the entire high-Galactic-latitude northern sky with well-understood selection criteria. We use the object catalogs generated from the Digitized Second Palomar Sky Survey as the basis for this survey. We apply a color criterion to select against field galaxies and use a simple adaptive kernel technique to create galaxy density maps, combined with the bootstrap technique, to make significance maps from which density peaks are selected. This survey attempts to eliminate some of the subjective criteria and assumptions of past surveys, including detection by eye and assumed luminosity functions and cluster profiles as in the Palomar Distant Cluster Survey. We also use more information (especially colors) than the most similar recent survey, the APM. This paper presents the details of our cluster-detection technique, as well as some initial results for two small areas totaling similar to 60 deg(2). We find a mean surface density of similar to 1.5 clusters deg(-2), consistent with the detection of richness class 0 and higher clusters to z similar to 0.3. In addition, we demonstrate an effective photometric redshift estimator for our clusters.