Angular Momentum Evolution in Dark Matter Halos

TL;DR

This study uses high-resolution simulations to show that dark matter halos experience significant angular momentum variation over cosmic time, challenging assumptions in galaxy formation models.

Contribution

It reveals that angular momentum in dark matter halos is not conserved and varies due to external torques, impacting the accuracy of adiabatic contraction models.

Findings

Angular momentum varies by factors of a few over the Universe's age.

External torques are the primary cause of angular momentum changes.

Implications for the accuracy of galaxy evolution models.

Abstract

We have analyzed high resolution N-body simulations of dark matter halos, focusing specifically on the evolution of angular momentum. We find that not only is individual particle angular momentum not conserved, but the angular momentum of radial shells also varies over the age of the Universe by up to factors of a few. We find that torques from external structure are the most likely cause for this distribution shift. Since the model of adiabatic contraction that is often applied to model the effects of galaxy evolution on the dark-matter density profile in a halo assumes angular momentum conservation, this variation implies that there is a fundamental limit on the possible accuracy of the adiabatic contraction model in modeling the response of DM halos to the growth of galaxies.