Orientation of cosmic web filaments with respect to the underlying
  velocity field
  The large-scale structure of the Universe is characterised by a web-like
structure made of voids, sheets, filaments, and knots. The structure of this
so-called cosmic web is dictated by the local velocity shear tensor. In
particular, the local direction of a filament should be strongly aligned with
e3, the eigenvector associated with the smallest eigenvalue of the tensor. That
conjecture is tested here on the basis of a cosmological simulation. The cosmic
web delineated by the halo distribution is probed by a marked point process
with interactions (the Bisous model), detecting filaments directly from the
halo distribution (P-web). The detected P-web filaments are found to be
strongly aligned with the local e3: the alignment is within 30 degree for 80%
of the elements. This indicates that large-scale filaments defined purely from
the distribution of haloes carry more than just morphological information,
although the Bisous model does not make any prior assumption on the underlying
shear tensor. The P-web filaments are also compared to the structure revealed
from the velocity shear tensor itself (V-web). In the densest regions, the P-
and V-web filaments overlap well (90%), whereas in lower density regions, the
P-web filaments preferentially mark sheets in the V-web.
