The spin and orientation of dark matter halos within cosmic filaments
  Clusters, filaments, sheets and voids are the building blocks of the cosmic
web. In this study, we present and compare two distinct algorithms for finding
cosmic filaments and sheets, a task which is far less well established than the
identification of dark matter halos or voids. One method is based on the
smoothed dark matter density field, the other uses the halo distributions
directly. We apply both techniques to one high resolution N-body simulation and
reconstruct the filamentary/sheet like network of the dark matter density
field. We focus on investigating the properties of the dark matter halos inside
these structures, in particular on the directions of their spins and the
orientation of their shapes with respect to the directions of the filaments and
sheets. We find that both the spin and the major axes of filament-halos with
masses <= 10^{13} M_sun/h are preferentially aligned with the direction of the
filaments. The spins and major axes of halos in sheets tend to lie parallel to
the sheets. There is an opposite mass dependence of the alignment strengths for
the spin (negative) and major (positive) axes, i.e. with increasing halo mass
the major axis tends to be more strongly aligned with the direction of the
filament whereas the alignment between halo spin and filament becomes weaker
with increasing halo mass. The alignment strengths as a function of distance to
the most massive node halo indicate that there is a transit large scale
environment impact: from the 2-D collapse phase of the filament to the 3-D
collapse phase of the cluster/node halo at small separation. Overall, the two
algorithms for filament/sheet identification investigated here agree well with
each other. The method based on halos alone can be easily adapted for use with
observational data sets.
