Assembly bias and the dynamical structure of dark matter halos

TL;DR

This study uses the Millennium Simulation to analyze how various properties of dark matter halos, such as shape, spin, and velocity anisotropy, influence their clustering behavior, revealing complex dependencies and correlations.

Contribution

It provides a comprehensive analysis of assembly bias across multiple halo properties using consistent particle definitions, extending previous work with new insights into velocity structure correlations.

Findings

Spherical and high-spin halos cluster more strongly.

Oblate halos are more clustered than prolate ones.

Halos with weak velocity anisotropy are more clustered.

Abstract

Based on the Millennium Simulation we examine assembly bias for the halo properties: shape, triaxiality, concentration, spin, shape of the velocity ellipsoid and velocity anisotropy. For consistency we determine all these properties using the same set of particles, namely all gravitationally self-bound particles belonging to the most massive sub-structure of a given friends-of-friends halo. We confirm that near-spherical and high-spin halos show enhanced clustering. The opposite is true for strongly aspherical and low-spin halos. Further, below the typical collapse mass, M*, more concentrated halos show stronger clustering whereas less concentrated halos are less clustered which is reversed for masses above M*. Going beyond earlier work we show that: (1) oblate halos are more strongly clustered than prolate ones; (2) the dependence of clustering on the shape of the velocity ellipsoid coincides with that of the real-space shape, although the signal is stronger; (3) halos with weak velocity anisotropy are more clustered, whereas radially anisotropic halos are more weakly clustered; (4) for all highly clustered subsets we find systematically less radially biased velocity anisotropy profiles. These findings indicate that the velocity structure of halos is tightly correlated with environment.