Environmental Effects of Dark Matter Halos: The Clustering-Substructure Relation of Group-Size Halos

Abstract

We estimate the two-point correlation function of dark matter halos, with masses ≥1013 h-1 M☉, that have or do not have significant substructure. The halos are identified with a friends-of-friends algorithm in a large ΛCDM simulation at two redshift snapshots (z = 0.0 and 1.0), while halo substructure is determined using an observationally driven method. We find in both epochs a clear and significant signal by which halos with substructure are more clustered than those with no substructure. This is true for all the considered halo mass ranges, although for the highest halo masses the signal is noisy and present only out to ~20 h-1 Mpc. There is also a smooth increase of the halo correlation length with increasing amplitude of the halo substructure. We also find that substructured halos are typically located in high-density large-scale environments, while the opposite is true for nonsubstructured halos. If the halos found in high-density regions have a relatively earlier formation time, as suggested by recent works, then they do indeed have more time to cluster than halos of a similar mass, which form later in the low-density regions. In such a case, one would have naively expected that the former (earlier formed) halos would typically be dynamically more relaxed than the latter (later formed). However, the higher merging and interaction rate, expected in high-density regions, could disrupt their relatively relaxed dynamical state and thus be the cause for the higher fraction of halos with substructure found in such regions.