ORIGAMI: Delineating Halos using Phase-Space Folds

TL;DR

ORIGAMI is a novel method for identifying cosmic structures in simulations by detecting phase-space folds, offering a dynamical, density-independent way to delineate halos, filaments, walls, and voids.

Contribution

The paper introduces ORIGAMI, a phase-space fold-based approach for structure identification that improves upon traditional density-based methods in cosmological simulations.

Findings

ORIGAMI halos are larger and more diffuse than FOF halos.

The method effectively distinguishes different cosmic structures based on shell-crossing.

Global properties of ORIGAMI halos align with other algorithms.

Abstract

We present the ORIGAMI method of identifying structures, particularly halos, in cosmological N-body simulations. Structure formation can be thought of as the folding of an initially flat three-dimensional manifold in six-dimensional phase space. ORIGAMI finds the outer folds that delineate these structures. Halo particles are identified as those that have undergone shell-crossing along 3 orthogonal axes, providing a dynamical definition of halo regions that is independent of density. ORIGAMI also identifies other morphological structures: particles that have undergone shell-crossing along 2, 1, or 0 orthogonal axes correspond to filaments, walls, and voids respectively. We compare this method to a standard Friends-of-Friends halo-finding algorithm and find that ORIGAMI halos are somewhat larger, more diffuse, and less spherical, though the global properties of ORIGAMI halos are in good agreement with other modern halo-finding algorithms.