Seeking Observable Imprints of Small-Scale Structure on the Properties
  of Dark Matter Haloes
  The characteristic prediction of the Cold Dark Matter (CDM) model of
cosmological structure formation is that the Universe should contain a wealth
of small-scale structure -- low-mass dark matter haloes and subhaloes. However,
galaxy formation is inefficient in their shallow potential wells and so we
expect these low-mass haloes and subhaloes to be dark. Can we tell the
difference between a Universe in which low-mass haloes are present but dark and
one in which they never formed, thereby providing a robust test of the CDM
model? We address this question using cosmological simulations to examine how
properties of low-mass haloes that are potentially accessible to observation,
such as their spatial clustering, rate of accretions and mergers onto massive
galaxies and the angular momentum content of massive galaxies, differ between a
LCDM model and dark matter models in which low-mass halo formation is
suppressed. Adopting an effective cut-off mass scale M_cut below which
small-scale power is suppressed in the initial conditions, we study dark matter
models in which M_cut varies between 5e9 Msol/h and 1e11 Msol/h, equivalent to
the host haloes of dwarf and low mass galaxies. Our results show that both the
clustering strength of low-mass haloes around galaxy-mass primaries and the
rate at which they merge with these primaries is sensitive to the assumed value
of M_cut; in contrast, suppressing low-mass halo formation has little influence
on the angular momentum content of galaxy-mass haloes -- it is the quiescence
or violence of a halo's assembly history that has a more marked effect.
However, we expect that measuring the effect on spatial clustering or the
merger rate is likely to be observationally difficult for realistic values of
M_cut, and so isolating the effect of this small-scale structure would appear
to be remarkably difficult to detect, at least in the present day Universe.
