| This thesis presents a detailed study of infall regions surrounding nearby galaxy clusters, the largest and most thorough such study to date. I show how large numbers of redshifts around clusters may be used to estimate the mass profile both within and beyond the virial radius.; I study Abell 576 with over a thousand redshifts and wide-field, CCD photometry. I compare the relative distributions of galaxies, light, and matter. Surprisingly, the mass-to-light ratio decreases with radius, suggesting that light is less clustered than the matter.; Next, I show that Abell 2199 contains bound, infalling groups. These groups contain many member galaxies and extended X-ray emission, showing that they are bound systems. Many of the groups are aligned along one axis, suggesting that the large-scale structure around A2199 is filamentary.; I compute the mass-to-light profile throughout the infall region of the Coma cluster in near-infrared wavelengths. Near-infrared light is an excellent tracer of stellar mass and is insensitive to dust extinction in our Galaxy and in other galaxies. The mass-to-light profile is quite flat, indicating that the matter is no less concentrated than the light. Systematic effects may mask a slight decrease in the mass-to-light profile. These results place strong constraints on variations in star formation efficiency with environment.; I then investigate the dynamics of A2199 and its environment. The caustics show that the mass of the A2199 supercluster is sufficiently large that many, but not all, of the bound groups are infalling.; Chapter 6 discusses the Cluster And Infall Region Nearby Survey (CAIRNS). This survey includes 15665 redshifts in the infall regions of eight rich, nearby X-ray luminous clusters. This survey demonstrates that the caustic infall pattern is ubiquitous in rich, nearby, X-ray luminous clusters. The resulting mass profiles agree well with models based on numerical simulations. As expected for such mass profiles, the velocity dispersion decreases with radius. Surprisingly, extrapolating a simple model of the mass profile produces velocity dispersion profiles very similar to those observed to the turnaround radii, even though these galaxies are not expected to be in equilibrium. X-ray mass estimates agree very well with the caustic mass profiles, as do virial mass estimates when corrected for the surface pressure term. |
