CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey. I. Infall Patterns and Mass Profiles

We use the Fourth Data Release of the Sloan Digital Sky Survey to test theubiquity of infall patterns around galaxy clusters and measure cluster massprofiles to large radii. We match X-ray cluster catalogs with SDSS, search forinfall patterns, and compute mass profiles for a complete sample of X-rayselected clusters. Very clean infall patterns are apparent in most of theclusters, with the fraction decreasing with increasing redshift due toshallower sampling. All 72 clusters in a well-defined sample limited byredshift (ensuring good sampling) and X-ray flux (excluding superpositions)show infall patterns sufficient to apply the caustic technique. This sample isby far the largest sample of cluster mass profiles extending to large radii todate. Similar to CAIRNS, cluster infall patterns are better defined inobservations than in simulations. Further work is needed to determine thesource of this difference. We use the infall patterns to compute mass profilesfor 72 clusters and compare them to model profiles. Cluster scaling relationsusing caustic masses agree well with those using X-ray or virial massestimates, confirming the reliability of the caustic technique. We confirm theconclusion of CAIRNS that cluster infall regions are well fit by NFW andHernquist profiles and poorly fit by singular isothermal spheres. This muchlarger sample enables new comparisons of cluster properties with those insimulations. The shapes (specifically, NFW concentrations) of the mass profilesagree well with the predictions of simulations. The mass inside the turnaroundradius is on average 2.19$\pm$0.18 times that within the virial radius. Thisratio agrees well with recent predictions from simulations of the final massesof dark matter haloes.