Statistics of Substructures in Dark Matter Haloes
  We study the amount and distribution of dark matter substructures within dark
matter haloes, using a large set of high-resolution simulations ranging from
group size to cluster size haloes, and carried our within a cosmological model
consistent with WMAP 7-year data. In particular, we study how the measured
properties of subhaloes vary as a function of the parent halo mass, the
physical properties of the parent halo, and redshift. The fraction of halo mass
in substructures increases with increasing mass. There is, however, a very
large halo-to-halo scatter that can be explained only in part by a range of
halo physical properties, e.g. concentration. At given halo mass, less
concentrated haloes contain significantly larger fractions of mass in
substructures because of the reduced strength of tidal disruption. Most of the
substructure mass is located at the outskirts of the parent haloes, in
relatively few massive subhaloes. This mass segregation appears to become
stronger at increasing redshift, and should reflect into a more significant
mass segregation of the galaxy population at different cosmic epochs. When
haloes are accreted onto larger structures, their mass is significantly reduced
by tidal stripping. Haloes that are more massive at the time of accretion
(these should host more luminous galaxies) are brought closer to the centre on
shorter time-scales by dynamical friction, and therefore suffer of a more
significant stripping. The halo merger rate depends strongly on the environment
with substructure in more massive haloes suffering more important mergers than
their counterparts residing in less massive systems. This should translate into
a different morphological mix for haloes of different mass.
