Introduction

V² is a software package for finding voids based on the ZOBOV (ZOnes Bordering On Voidness) algorithm by Neyrinck (2008), which uses the gradient of the volume of adjacent voronoi cells to flow multiple cells into larger void regions. Voids can be found both in observational surveys and simulations with periodic boundary conditions.

VAST contains the package, as well as an example script for automatically running all steps of the algorithm. To import the main void-finding class of V²:

from vast.vsquared import zobov

Voronoi tesselation

V² first produces a Voronoi tessellation of the catalog of large-scale tracers, and the volumes of the Voronoi cells are used to identify local density minima.

Zones

Zones are then built from density minima in the distribution of the Voronoi cells using a watershed transform, where each cell is linked to its least dense neighbor.

Defining the voids

Finally, voids are formed from these by identifying low-density boundaries between adjacent zones and using them to grow unions of weakly divided zones. This list of voids is then typically pruned to remove void candidates unlikely to be true voids. V² includes several of the different void-pruning methods that exist, including methods from other ZOBOV implementations such as VIDE and REVOLVER.

Citation

Please cite Neyrinck (2008) when using this algorithm.