The Cosmic V-Web
  The network of filaments with embedded clusters surrounding voids seen in
maps derived from redshift surveys and reproduced in simulations has been
referred to as the cosmic web. A complementary description is provided by
considering the shear in the velocity field of galaxies. The eigenvalues of the
shear provide information on whether a region is collapsing in three
dimensions, the condition for a knot, expanding in three-dimensions, the
condition for a void, or in the intermediate condition of a filament or sheet.
The structures that are quantitatively defined by the eigenvalues can be
approximated by iso-contours that provide a visual representation of the cosmic
velocity (V) web. The current application is based on radial peculiar
velocities from the Cosmicflows-2 collection of distances. The
three-dimensional velocity field is constructed using the Wiener filter
methodology in the linear approximation. Eigenvalues of the velocity shear are
calculated at each point on a grid. Here, knots and filaments are visualized
across a local domain of diameter ~0.1c.
