The Angular Momentum Problem in Cosmological Simulations of Disk Galaxy Formation

TL;DR

This study investigates the angular momentum loss in cosmological disk galaxy simulations, finding feedback processes crucial for realistic galaxy formation and that resolution alone cannot solve the problem.

Contribution

It demonstrates that feedback mechanisms, especially supernova feedback, are essential to mitigate angular momentum loss in galaxy simulations, beyond just increasing numerical resolution.

Findings

Angular momentum loss is resolution-independent and linked to dynamical friction.

Star formation alone does not affect angular momentum loss.

Supernova feedback reduces angular momentum loss by suppressing early star formation.

Abstract

We conduct a systematic study of the angular momentum problem in numerical simulations of disk galaxy formation. We investigate the role of numerical resolution using a semi-cosmological setup which combines an efficient use of the number of particles in an isolated halo while preserving the hierarchical build-up of the disk through the merging of clumps. We perform the same simulation varying the resolution over 4 orders of magnitude. Independent on the level of resolution, the loss of angular momentum stays the same and can be tied to dynamical friction during the build-up phase. This is confirmed in a cosmological simulation. We also perform simulations including star formation and star formation and supernova feedback. While the former has no influence on the angular momentum problem, the latter reduces the loss to a level potentially in agreement with observations. This is achieved through a suppression of early star formation and therefore the formation of a large, slowly rotating bulge. We conclude that feedback is a critical component to achieve realistic disk galaxies in cosmological simulations. Numerical resolution is important, but by itself not capable of solving the angular momentum problem.