Unbound Particles in Dark Matter Halos

TL;DR

This study tracks dark matter particles over cosmic time to understand which become unbound from halos, revealing that energy calculations poorly predict unbinding and that unbound fractions vary with halo radius and redshift.

Contribution

It provides a novel analysis of unbound dark matter particles using long-term simulations, challenging traditional energy-based predictions and exploring implications for cosmology.

Findings

Energy sum poorly predicts unbound particles.

Unbound fraction increases at halo edges.

Unbound fraction decreases at higher redshifts.

Abstract

We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches for intergalactic supernovae.