DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions

TL;DR

This paper introduces a new parameter-free method called DIVE, based on Delaunay Triangulation, to identify cosmic voids from discrete matter tracers, revealing two main void types with distinct properties and environments.

Contribution

The paper presents a novel Delaunay Triangulation-based void finder that efficiently characterizes cosmic voids and their environments from galaxy survey data.

Findings

Two main types of DT voids identified with different responses to distortions.

Large DT voids are in expanding regions, while their haloes are in collapsing regions.

Bias differences between small and large DT void populations.

Abstract

We present a novel parameter-free cosmological void finder (\textsc{dive}, Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which efficiently computes the empty spheres constrained by a discrete set of tracers. We define the spheres as DT voids, and describe their properties, including an universal density profile together with an intrinsic scatter. We apply this technique on 100 halo catalogues with volumes of 2.5\,$h^{-1}$Gpc side each, with a bias and number density similar to the BOSS CMASS Luminous Red Galaxies, performed with the \textsc{patchy} code. Our results show that there are two main species of DT voids, which can be characterised by the radius: they have different responses to halo redshift space distortions, to number density of tracers, and reside in different dark matter environments. Based on dynamical arguments using the tidal field tensor, we demonstrate that large DT voids are hosted in expanding regions, whereas the haloes used to construct them reside in collapsing ones. Our approach is therefore able to efficiently determine the troughs of the density field from galaxy surveys, and can be used to study their clustering. We further study the power spectra of DT voids, and find that the bias of the two populations are different, demonstrating that the small DT voids are essentially tracers of groups of haloes.