  We employ a high-resolution dissipationless N-body simulation of a galaxy
cluster to investigate the impact of subhalo selection on the resulting
velocity distributions. Applying a lower limit on the present bound mass of
subhalos leads to high subhalo velocity dispersions compared to the diffuse
dark matter (positive velocity bias) and to a considerable deviation from a
Gaussian velocity distribution (kurtosis -0.6). However, if subhalos are
required to exceed a minimal mass before accretion onto the host, the velocity
bias becomes negligible and the velocity distribution is close to Gaussian
(kurtosis -0.15). Recently it has been shown that the latter criterion results
in subhalo samples that agree well with the observed number-density profiles of
galaxies in clusters. Therefore we argue that the velocity distributions of
galaxies in clusters are essentially un-biased. The comparison of the galaxy
velocity distribution and the sound speed, derived from scaling relations of
X-ray observations, results in an average Mach number of 1.24. Altogether 65%
of the galaxies move supersonically and 8% have Mach numbers larger than 2 with
respect to the intra cluster gas.
