Dissecting the Evolution of Dark Matter Subhaloes in the Bolshoi
  Simulation
  We present a comprehensive analysis of the evolution of dark matter subhaloes
in the cosmological Bolshoi simulation. We identify a complete set of 12 unique
evolution channels by which subhaloes evolve in between simulation outputs, and
study their relative importance and demographics. We show that instantaneous
masses and maximum circular velocities of individual subhaloes are extremely
noisy, despite the use of a sophisticated, phase-space-based halo finder. We
also show that subhaloes experience frequent penetrating encounters with other
subhaloes (on average about one per dynamical time), and that subhaloes whose
apo-center lies outside the virial radius of their host (the 'ejected' or
'backsplash' haloes) experience tidal forces that modify their orbits. This
results in an average fractional subhalo exchange rate among host haloes of
roughly 0.01 per Gyr (at the present time). In addition, we show that there are
three distinct disruption channels; one in which subhaloes drop below the mass
resolution limit of the simulation, one in which subhaloes merge with their
host halo largely driven by dynamical friction, and one in which subhaloes
abruptly disintegrate. We estimate that roughly 80 percent of all subhalo
disruption in the Bolshoi simulation is numerical, rather than physical. This
over-merging is a serious road-block for the use of numerical simulations to
interpret small scale clustering, or for any other study that is sensitive to
the detailed demographics of dark matter substructure.
