Galaxy subgroups in galaxy clusters
  Galaxies which fall into clusters as part of the same infall halo can retain
correlations due to their shared origin. N-body simulations are used to study
properties of such galaxy subgroups within clusters, including their richnesses
and prevalence. The sizes, densities and velocity dispersions of all subgroups
with >= 8 galaxies are found and compared to those of the host clusters. The
largest galaxy subgroup provides a preferred direction in the cluster and is
compared to other preferred directions in the cluster. Scatter in cluster mass
measurements (via five observables), along ~ 96 lines of sight, is compared to
the relation of the line of sight to this preferred direction: scatter in
cluster velocity dispersion measurements show the strongest correlation. The
Dressler-Shectman test (Dressler & Shectman 1988), is applied to these
clusters, to see whether the substructure it identifies is related to these
subgroups. The results for any specific line of sight seem noisy; however,
clusters with large subgroups tend to have a higher fraction of lines of sight
where the test detects substructure.
