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 halos are defined as
sub--halos within the virial radius of a host halo. The satellite sample is
restricted to those sub--halos which showed a maximum circular velocity above
30 km/s at the time of accretion. Host halo masses range from 10^11 to 10^14
Msol/h. We compute the satellites' average accretion redshift, z_acc, velocity
dispersion, sigma, and velocity anisotropy parameter, beta, utilising stacked
satellite samples of equal mass hosts at similar background densities. The main
results are: (1) On average satellites within hosts in high density
environments are accreted earlier (Delta z~ 0.1$) compared to their
counterparts at low densities. For host masses above 5 times10^13 Msol/h this
trend weakens and may reverse for higher host masses; (2) The velocity
dispersion of satellites in low density environments follows that of the host,
i.e. no velocity bias is observed for host halos 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 ~30% larger than that of the
host halo, i.e. the satellites are dynamically hotter than their host halos.
(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 > 0.1) compared to their counterparts in high density environments. We
believe that our approach allows to predict a similar behaviour for observed
satellite galaxy systems.
