  We use a combination of N-body simulations of the hierarchical clustering of
dark matter and semi-analytic modelling of the physics of galaxy formation to
probe the relationship between the galaxy distribution and the mass
distribution. The pairwise line-of-sight velocity dispersion of galaxies is
sensitive to the number of galaxies present in halos of different mass. The
galaxy velocity dispersion is ~40% lower than that of the dark matter and is in
reasonable agreement with the values measured in the Las Campanas redshift
survey by Jing et al. over two decades in pair separation. The origin of this
offset is statistical rather than dynamical, and depends upon the relative
efficiency of galaxy formation in dark matter halos of different mass. Although
the model galaxies and the dark matter have markedly different correlation
functions in real space, such biases conspire to cause the redshift space
correlation functions to be remarkably similar to each other. The predicted
redshift-space galaxy correlation function agrees well with observations. We
find no evidence in the model for a dependence of clustering strength on
intrinsic galaxy luminosity, unless extremely bright galaxies, two magnitudes
brighter than L*, are considered. However, there are significant differences
when model galaxies are selected either by morphology or by colour. Early type
or red galaxies show a much stronger clustering amplitude than late type or
blue galaxies, particularly on small scales, again in good agreement with
observations.

Astrophysics