Extracting information from the exteriors of dark matter halos

While significant amounts of time has been spent studying dark matter halos, the environment around halos and the impact this environment has on structures that pass through it has not been investigated in nearly as much detail. In this thesis we perform several different studies all related to extracting information from the exteriors of dark matter halos. We study subhalos in clusters and the region outside of their virial radii, finding that there is additional matter correlated with recently accreted subhalos. We also find that recently accreted subhalos have stronger correlations with other subhalos than subhalos accreted long ago. We argue that this could distinguish between different theories of what causes star formation to be quenched in high-density environments like clusters. We also demonstrate that the caustic feature seen in the density profile of the exteriors of clusters is indeed related to the splashback radius. In addition, we investigate the possibility of observing matter that has been stripped by tidal interactions as galaxies enter clusters. We find that we can indeed detect tidal tails when using full 3D data but cannot do so when we only have access to projected data. Finally, we study the impact that future accretion has on galaxy-sized halos located near cluster-sized halos. We find that there is indeed a drop in the accretion rate of future subhalos even outside of the virial radius of the cluster, but the exact radius where this drop begins is sensitive to the smoothing scale we use for the local density