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Description
We present the C4 Cluster Catalog, a new sample of 748 clusters of galaxies identified in the spectroscopic sample of the Second Data Release (DR2, 2004AJ....128..502A) of the Sloan Digital Sky Survey (SDSS). The C4 cluster-finding algorithm identifies clusters as overdensities in a seven-dimensional position and color space, thus minimizing projection effects that have plagued previous optical cluster selection. The present C4 catalog covers ~2600deg^2^ of sky and ranges in redshift from z=0.02 to 0.17. The mean cluster membership is 36 galaxies (with measured redshifts) brighter than r=17.7, but the catalog includes a range of systems, from groups containing 10 members to massive clusters with over 200 cluster members with measured redshifts. The catalog provides a large number of measured cluster properties including sky location, mean redshift, galaxy membership, summed r-band optical luminosity (L_r_), and velocity dispersion, as well as quantitative measures of substructure and the surrounding large-scale environment. We use new, multicolor mock SDSS galaxy catalogs, empirically constructed from the {Lambda}CDM Hubble Volume (HV) Sky Survey output, to investigate the sensitivity of the C4 catalog to the various algorithm parameters (detection threshold, choice of passbands, and search aperture), as well as to quantify the purity and completeness of the C4 cluster catalog.
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