Angular momentum evolution can be predicted from cosmological initial conditions
Abstract
The angular momentum of dark matter haloes controls their spin magnitude and orientation, which in turn influences the galaxies therein. However, the process by which dark matter haloes acquire angular momentum is not fully understood; in particular, it is unclear whether angular momentum growth is stochastic. To address this question, we extend the genetic modification technique to allow control over the angular momentum of any region in the initial conditions. Using this technique to produce a sequence of modified simulations, we can then investigate whether changes to the angular momentum of a specified region in the evolved universe can be accurately predicted from changes in the initial conditions alone. We find that the angular momentum in regions with modified initial conditions can be predicted between 2 and 4 times more accurately than expected from applying tidal torque theory. This result is masked when analysing the angular momentum of haloes, because particles in the outskirts of haloes dominate the angular momentum budget. We conclude that the angular momentum of Lagrangian patches is highly predictable from the initial conditions, with apparent chaotic behaviour being driven by stochastic changes to the arbitrary boundary defining the halo.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2021
 DOI:
 10.1093/mnras/stab440
 arXiv:
 arXiv:2012.02201
 Bibcode:
 2021MNRAS.502.5480C
 Keywords:

 methods: numerical;
 galaxies: formation;
 galaxies: haloes;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 7 pages, 4 figures. Accepted for publication in MNRAS: 2021 February 3. Received 2021 January 30