Dependence of the dynamical properties of light-cone simulation dark
  matter halos on their environment
  Aims: We study the dependence of the dynamical properties of dark matter
halos on their environment in a whole-sky $\Lambda$CDM light-cone simulation
extending to $z\sim 0.65$. The properties of interest are halo shape
(parametrized by its principal axes), spin and virialisation status, the
alignment of halo spin and shape, as well as the shape-shape and spin-spin
alignments among halo neighbours. Methods: We define the halo environment using
the notion of halo isolation status determined by the distance to its nearest
neighbor. This defines a maximum spherical region around each halo devoid of
other halos, above the catalog threshold mass. We consider as 'close halo
pairs', the pairs that are separated by a distance lower than a specific
threshold. In order to decontaminate our results from the known dependence of
halo dynamical properties on mass, we use a random sampling procedure in order
to compare properties of similar halo abundance distributions. Results: (a) We
find a strong dependence of halo properties on their environment, confirming
that isolated halos are more aspherical and more prolate with lower spin
values. (b) Correlations between halo properties exist and are mostly
independent of halo environment. (c) Halo spins are aligned with the minor
axis, regardless of halo shape. (d) Close halo neighbors have their major axes
statistically aligned, while they show a slight but statistically significant
preference for anti-parallel spin directions. The latter result is enhanced for
the case of close halo pairs in low-density environments. Furthermore, we find
a preference of the spin vectors to be oriented perpendicular to the line
connecting such close halo pairs.
