CAIRNS: The Cluster and Infall Region Nearby Survey. I. Redshifts and Mass Profiles

The CAIRNS (Cluster And Infall Region Nearby Survey) project is aspectroscopic survey of the infall regions surrounding eight nearby, rich,X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new orremeasured) within \sim 5-10 Mpc of the centers of the clusters, making it thelargest study of the infall regions of clusters. We determine clustermembership and the mass profiles of the clusters based on the phase spacedistribution of the galaxies. All of the clusters display decreasing velocitydispersion profiles. The mass profiles are fit well by functional forms basedon numerical simulations but exclude an isothermal sphere. Specifically, NFWand Hernquist models provide good descriptions of cluster mass profiles totheir turnaround radii. Our sample shows that the predicted infall pattern isubiquitous in rich, X-ray luminous clusters over a large mass range. Thecaustic mass estimates are in excellent agreement with independent X-rayestimates at small radii and with virial estimates at intermediate radii. Themean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the meanratio of the caustic mass to the virial mass (when corrected for the surfacepressure term) is 0.93\pm0.07. We further demonstrate that the caustictechnique provides reasonable mass estimates even in merging clusters.Comment: 54 pages, 18 figures, to appear in The Astronomical Journa