Abstract
We present a catalog of 799 clusters of galaxies in the redshift range z est = 0.05-0.3 selected from ∼400 deg 2 of early Sloan Digital Sky Survey (SDSS) commissioning data along the celestial equator. The catalog is based on merging two independent selection methods - a color-magnitude red-sequence maxBCG technique (B), and a hybrid matched filter method (H). The BH catalog includes clusters with richness Λ ≥ 40 (matched filter) and N gal ≥ 13 (maxBCG), corresponding to typical velocity dispersion of σ v ≲400 km s -1 and mass (within 0.6 h -1 Mpc radius) ≲ 5 × 10 13 h -1 M ⊙ . This threshold is below Abell richness class 0 clusters. The average space density of these clusters is 2 × 10 -5 h 3 Mpc -3 . All NORAS X-ray clusters and 53 of the 58 Abell clusters in the survey region are detected in the catalog; the five additional Abell clusters are detected below the BH catalog cuts. The cluster richness function is determined and found to exhibit a steeply decreasing cluster abundance with increasing richness. We derive observational scaling relations between cluster richness and observed cluster luminosity and cluster velocity dispersion; these scaling relations provide important physical calibrations for the clusters. The catalog can be used for studies of individual clusters, for comparisons with other sources such as X-ray clusters and active galactic nuclei, and, with proper correction for the relevant selection functions, also for statistical analyses of clusters.