Dynamics of pairwise motions in the Cosmic Web
  We present results of analysis of the dark matter (DM) pairwise velocity
statistics in different Cosmic Web environments. We use the DM velocity and
density field from the Millennium 2 simulation together with the NEXUS+
algorithm to segment the simulation volume into voxels uniquely identifying one
of the four possible environments: nodes, filaments, walls or cosmic voids. We
show that the PDFs of the mean infall velocities $v_{12}$ as well as its
spatial dependence together with the perpendicular and parallel velocity
dispersions bear a significant signal of the large-scale structure environment
in which DM particle pairs are embedded. The pairwise flows are notably colder
and have smaller mean magnitude in wall and voids, when compared to much denser
environments of filaments and nodes. We discuss on our results, indicating that
they are consistent with a simple theoretical predictions for pairwise motions
as induced by gravitational instability mechanism. Our results indicate that
the Cosmic Web elements are coherent dynamical entities rather than just
temporal geometrical associations. In addition it should be possible to
observationally test various Cosmic Web finding algorithms by segmenting
available peculiar velocity data and studying resulting pairwise velocity
statistics
