NoSOCS in SDSS - I. Sample definition and comparison of mass estimates

Abstract

We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster properties of the systems first detected within Digitized Second Palomar Observatory Sky Survey. With the high-quality photometry of SDSS, we derived new photometric redshifts and estimated richness and optical luminosity. For a subset of low-redshift (z≤ 0.1) clusters, we have used SDSS spectroscopic data to identify groups in redshift space in the region of each cluster, complemented with massive systems from the literature to assure the continuous mass sampling. A method to remove interlopers is applied, and a virial analysis is performed resulting in the estimates of velocity dispersion, mass and a physical radius for each low-z system. We discuss the choice of maximum radius and luminosity range in the dynamical analysis, showing that a spectroscopic survey must be complete to at least M*+ 1 if one wishes to obtain accurate and unbiased estimates of velocity dispersion and mass. We have measured X-ray luminosity for all clusters using archival data from ROSAT All Sky Survey. For a smaller subset (21 clusters), we selected temperature measures from the literature and estimated mass from the M−TX relation, finding that they show good agreement with the virial estimate. However, these two mass estimates tend to disagree with the caustic results. We measured the presence of substructure in all clusters of the sample and found that clusters with substructure have virial masses higher than those derived from TX. This trend is not seen when comparing the caustic and X-ray masses. That happens because the caustic mass is estimated directly from the mass profile, so it is less affected by substructure.