Interaction between collisionless galactic discs and nonaxissymmetric dark matter haloes

TL;DR

This study uses large-scale N-body simulations to explore how non-axisymmetric dark matter haloes influence the formation of spiral structures and the shape evolution of stellar galactic discs.

Contribution

It demonstrates that non-axisymmetric haloes can induce long-lasting spiral patterns without significant heating and offers a method to infer halo shape from disc velocity fields.

Findings

Non-axisymmetric haloes generate persistent spiral patterns.

Spiral arms form without significant dynamical heating.

Velocity field analysis reveals halo triaxiality.

Abstract

Using $N$-body simulations ($N\sim 10^6 - 10^7$), we examine how a non-axisymmetric dark halo affects the dynamical evolution of the structure in collisionless (stellar) discs. We demonstrate how the model parameters such as mass of the halo, initial conditions in the disc and the halo axes ratio affect morphology and kinematics of the stellar discs. We show that a non-axisymmetric halo can generate a large-scale spiral density pattern in the embedded stellar disc. The pattern is observed in the disc for many periods of its revolution, even if the disc is gravitationally over-stable. The growth of the spiral arms is not accompanied by significant dynamical heating of the disc, irrelevant to its initial parameters. We also investigate transformation of the dark halo's shape driven by the long-lived spiral pattern in the disc . We show that the analysis of the velocity field in the stellar disc and in the spiral pattern gives us a possibility to figure out the spatial orientation of the triaxial-shaped dark halo and to measure the triaxiality.