  We present velocity statistics of galaxies and their biases inferred from the
statistics of the underlying dark matter using a cosmological hydrodynamic
simulation of galaxy formation in low-density and spatially flat cold dark
matter cosmogony. We find that the pairwise velocity dispersion (PVD) of all
galaxies is significantly lower than that of the dark matter particles, and
that the PVD of the young galaxies is lower than that of the old types, and
even of all galaxies together, especially at small separations. These results
are in reasonable agreement with the recent measurements of PVDs in the Las
Campanas redshift survey, the PSCz catalogue and the SDSS data. We also find
that the low PVD of young galaxies is due to the effects of dynamical friction
as well as the different spatial distribution. We also consider the mean infall
velocity and the POTENT density reconstruction that are often used to measure
the cosmological parameters, and investigate the effects of spatial bias and
dynamical friction. In our simulation, the mean infall velocity of young
galaxies is significantly lower than that of all the galaxies or of the old
galaxies, and the dynamical bias becomes important on scales less than 3Mpc/h.
The mass density field reconstructed from the velocity field of young galaxies
using the POTENT-style method suffers in accuracy both from the spatial bias
and the dynamical friction on the smoothing scale of R_s=8Mpc/h. On the other
hand, in the case of R_s=12Mpc/h, which is typically adopted in the actual
POTENT analysis, the density reconstruction based on various tracers of
galaxies is reasonably accurate.
