Key points are not available for this paper at this time.
We present a catalog of 799 clusters of galaxies in the redshift range zₑst = 0. 05 - 0. 3 selected from ~400 deg² of early 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 >= 40 (Matched-Filter) and Ngal >= 13 (maxBCG), corresponding to typical velocity dispersion of ᵥ >~ 400 km s^-1 and mass (within 0. 6 h^-1) Mpc radius) >~ 5*10^{13 h^-1 Mₛun. This threshold is below Abell richness class 0 clusters. The average space density of these clusters is 2*10^-5 h³ Mpc^-3. All NORAS X-ray clusters and 53 of the 58 Abell clusters in the survey region are detected in the catalog; the 5 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 AGNs, and, with proper correction for the relevant selection functions, also for statistical analyses of clusters.
Bahcall et al. (Tue,) studied this question.