The stability of stellar disks in Milky-Way sized dark matter halos

TL;DR

This study uses high-resolution simulations to analyze the stability and evolution of stellar disks within Milky Way-sized dark matter halos, revealing effects of halo triaxiality and substructure interactions on disk tumbling and heating.

Contribution

It introduces an improved methodology for inserting live stellar disks into dark matter simulations and systematically studies their dynamical evolution in realistic Milky Way-like halos.

Findings

Disks experience about 40° tumbling from z=1 to z=0 over 6 Gyr.

Halo triaxiality causes significant disk tumbling, independent of galaxy structure.

Disks reduce central subhalo abundance by a factor of two due to gravitational shocks.

Abstract

We employ an improved methodology to insert live stellar disks into high-resolution dark matter simulations of Milky Way sized halos, allowing us to investigate the fate of thin stellar disks in the tumultuous environment of cold dark matter structures. We study a set of eight different halos, drawn from the Aquarius simulation project, in which stellar disks are adiabatically grown with a prescribed structure, and then allowed to self-consistently evolve. The initial velocity distribution is set-up in very good equilibrium with the help of the GALIC code. We find that the residual triaxiality of the halos leads to significant disk tumbling, qualitatively confirming earlier work. We show that the disk turning motion is unaffected by structural properties of the galaxies such as the presence or absence of a bulge or bar. In typical Milky Way sized dark matter halos, we expect an average turning of the disks by about 40 degrees between z=1 and z=0, over the coarse of 6 Gyr. We also investigate the impact of the disks on substructures, and conversely, the disk heating rate caused by the dark matter halo substructures. The presence of disks reduces the central subhalo abundance by a about a factor of two, due to an increased evaporation rate by gravitational shocks from disk passages. We find that substructures are important for heating the outer parts of stellar disks but do not appear to significantly affect their inner parts.