The impact of environment on the dynamical structure of satellite systems

We examine the effects of environment on the dynamical structure of satellite systems based on the Millennium II Simulation. Satellite haloes are defined as subhaloes within the virial radius of a host halo. The satellite sample is restricted to those subhaloes which showed a maximum circular velocity above 30 km s(-1) at the time of accretion. Host halo masses range from 10(11) to 10(14) h(-1)M(circle dot). We compute the satellites' average accretion redshift, z(acc), velocity dispersion, sigma, and velocity anisotropy parameter, beta, utilizing stacked satellite samples of equal-mass hosts at similar background densities. The main results are as follows. (1) On an average, satellites within hosts in high-density environments are accreted earlier (Delta(z) approximate to 0.1) compared to their counterparts at low densities. For host masses above 5 x 10(13) h(-1)M(circle dot) this trend weakens, and may reverse for higher hostmasses. (2) The velocity dispersion of satellites in low-density environments follows that of the host, i.e. no velocity bias is observed for host haloes at low densities independent of host mass. However, for low-mass hosts in high-density environments the velocity dispersion of the satellites can be up to similar to 30 per cent larger than that of the host halo, i.e. the satellites are dynamically hotter than their host haloes. (3) The anisotropy parameter depends on host mass and environment. Satellites of massive hosts show more radially biased velocity distributions. Moreover in low-density environments, satellites have more radially biased velocities (Delta beta greater than or similar to 0.1) as compared to their counterparts in high-density environments. We believe that our approach allows us to predict a similar behaviour for observed satellite galaxy systems.