The Relation Between Halo Shape, Velocity Dispersion and Formation Time
  We use dark matter haloes identified in the MareNostrum Universe and galaxy
groups identified in the Sloan Data Release 7 galaxy catalogue, to study the
relation between halo shape and halo dynamics, parametrizing out the mass of
the systems. A strong shape-dynamics, independent of mass, correlation is
present in the simulation data, which we find it to be due to different halo
formation times. Early formation time haloes are, at the present epoch, more
spherical and have higher velocity dispersions than late forming-time haloes.
The halo shape-dynamics correlation, albeit weaker, survives the projection in
2D (ie., among projected shape and 1-D velocity dispersion). A similar
shape-dynamics correlation, independent of mass, is also found in the SDSS DR7
groups of galaxies and in order to investigate its cause we have tested and
used, as a proxy of the group formation time, a concentration parameter. We
have found, as in the case of the simulated haloes, that less concentrated
groups, corresponding to late formation times, have lower velocity dispersions
and higher elongations than groups with higher values of concentration,
corresponding to early formation times.
