Bars in Cuspy Dark Halos

TL;DR

This study investigates the formation and evolution of galactic bars within cuspy dark matter halos using high-resolution simulations, revealing the importance of resonances and showing that bar formation does not erase the density cusp.

Contribution

It provides the first convergence study of bar instability in cuspy halos across a wide range of simulation resolutions, highlighting the role of resonances in angular momentum transfer.

Findings

Most dynamical features converge for halos with over 10 million particles.

Bar formation does not destroy the dark matter density cusp.

Resonant angular momentum transfer is crucial in bar evolution.

Abstract

We examine the bar instability in models with an exponential disk and a cuspy NFW-like dark matter (DM) halo inspired by cosmological simulations. Bar evolution is studied as a function of numerical resolution in a sequence of models spanning 10K to 100M DM particles - including a multi-mass model with an effective resolution of 10G. The goal is to find convergence in dynamical behaviour. We characterize the bar growth, the buckling instability, pattern speed decay through resonant transfer of angular momentum, and possible destruction of the DM halo cusp. Overall, most characteristics converge in behaviour in detail for halos containing more than 10M particles. Notably, the formation of the bar does not destroy the density cusp in this case. These higher resolution simulations clearly illustrate the importance of discrete resonances in transporting angular momentum from the bar to the halo.