ORIGAMI: Delineating Halos using Phase-Space Folds

Understand

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.