Tensor anisotropy as a tracer of cosmic voids
  We present a new method to find voids in cosmological simulations based on
the tidal and the velocity shear tensors definitions of the cosmic web. We use
the fractional anisotropy (FA) computed from the eigenvalues of each web scheme
as a void tracer. We identify voids using a watershed transform based on the
local minima of the FA field without making any assumption on the shape or
structure of the voids. We test the method on the Bolshoi simulation and report
on the abundance and radial averaged profiles for the density, velocity and
fractional anisotropy. We find that voids in the velocity shear web are smaller
than voids in the tidal web, with a particular overabundance of very small
voids in the inner region of filaments/sheets. We classify voids as
subcompensated/overcompansated depending on the absence/presence of an
overdense matter ridge in their density profile, finding that close to $65\%$
and $35\%$ of the total population are classified into each category,
respectively. Finally, we find evidence for the existence of universal profiles
from the radially averaged profiles for density, velocity and fractional
anisotropy. This requires that the radial coordinate is normalized to the
effective radius of each void. Put together, all these results show that the FA
is a reliable tracer for voids, which can be used in complementarity to other
existing methods and tracers.
