The Local Void: for or against LCDM?
  The emptiness of the Local Void has been put forward as a serious challenge
to the current standard paradigm of structure formation in LCDM. We use a high
resolution cosmological N-body simulation, the Millennium-II run, combined with
a sophisticated semi-analytic galaxy formation model, to explore statistically
whether the local void is allowed within our current knowledge of galaxy
formation in LCDM. We find that about 15 percent of the Local Group analogue
systems (11 of 77) in our simulation are associated with nearby low density
regions having size and 'emptiness' similar to those of the observed Local
Void. This suggests that, rather than a crisis of the LCDM, the emptiness of
the Local Void is indeed a success of the standard LCDM theory. The paucity of
faint galaxies in such voids results from a combination of two factors: a lower
amplitude of the halo mass function in the voids than in the field, and a lower
galaxy formation efficiency in void haloes due to halo assembly bias effects.
While the former is the dominated factor, the later also plays a sizable role.
The halo assembly bias effect results in a stellar mass fraction 25 percent
lower for void galaxies when compared to field galaxies with the same halo
mass.
