The galaxy population in cold and warm dark matter cosmologies
  We use a pair of high resolution N-body simulations implementing two dark
matter models, namely the standard cold dark matter (CDM) cosmogony and a warm
dark matter (WDM) alternative where the dark matter particle is a 1.5keV
thermal relic. We combine these simulations with the GALFORM semi-analytical
galaxy formation model in order to explore differences between the resulting
galaxy populations. We use GALFORM model variants for CDM and WDM that result
in the same z=0 galaxy stellar mass function by construction. We find that most
of the studied galaxy properties have the same values in these two models,
indicating that both dark matter scenarios match current observational data
equally well. Even in under-dense regions, where discrepancies in structure
formation between CDM and WDM are expected to be most pronounced, the galaxy
properties are only slightly different. The only significant difference in the
local universe we find is in the galaxy populations of "Local Volumes", regions
of radius 1 to 8Mpc around simulated Milky Way analogues. In such regions our
WDM model provides a better match to observed local galaxy number counts and is
five times more likely than the CDM model to predict sub-regions within them
that are as empty as the observed Local Void. Thus, a highly complete census of
the Local Volume and future surveys of void regions could provide constraints
on the nature of dark matter.
