Subclustering in rich clusters of galaxies and their environs

Rich clusters of galaxies and their environs are studied by comparing high-resolution N-body simulations with observations, to examine whether the degree of subclustering in and around clusters is sensitive to the cosmogonic scenario which led to their formation. If it is, this sensitivity could be used to help constrain the allowable initial density fluctuations from which the presently observed large-scale structure of the universe might have arisen. Several new statistical methods for measuring the degree of subclustering are presented. The amount of substructure within the main bodies of rich clusters is found to be not very sensitive to the initial conditions. In general, the observed subclustering is much weaker than has sometimes been claimed and is in many cases no larger than that expected from random fluctuations. This suggests that most rich clusters are in a relaxed state at present. Virial and projected mass estimates are also consistent with most rich clusters having already relaxed. A more promising means for distinguishing between the different cosmogonic scenarios is found from statistical measurements of small-scale clustering in the regions immediately surrounding rich clusters in the simulations, which show significant dependence on the amount of small-scale power present in the initial fluctuation spectrum. This suggests that observational studies of the small-scale clustering of galaxies in the regions surrounding rich clusters and in the field may provide perhaps the most promising means yet for distinguishing between different cosmogonies.