Stellar Spiral Structures in Triaxial Dark Matter Haloes

TL;DR

This study uses high-resolution simulations to explore how triaxial dark matter haloes influence spiral structures in stellar discs, revealing that halo shape changes can induce long-lasting grand-design spirals and warps.

Contribution

It demonstrates that non-adiabatic halo shape changes can trigger persistent grand-design spirals and warps, providing insights into the connection between halo shape and disc morphology.

Findings

Triaxial haloes induce long-lived grand-design spirals.

Spiral pattern speed matches the inner Lindblad resonance.

Halo shape influences spiral strength and disc warps.

Abstract

We employ very high resolution simulations of isolated Milky Way-like galaxies to study the effect of triaxial dark matter haloes on exponential stellar discs. Non-adiabatic halo shape changes can trigger two-armed grand-design spiral structures which extend all the way to the edge of the disc. Their pattern speed coincides with the inner Lindblad resonance indicating that they are kinematic density waves which can persist up to several Gyr. In dynamically cold discs, grand-design spirals are swing amplified and after a few Gyr can lead to the formation of (multi-armed) transient recurrent spirals. Stellar discs misaligned to the principal planes of the host triaxial halo develop characteristic integral shaped warps, but otherwise exhibit very similar spiral structures as aligned discs. For the grand-design spirals in our simulations, their strength dependence with radius is determined by the torque on the disc, suggesting that by studying grand-design spirals without bars it may be possible to set constraints on the tidal field and host dark matter halo shape.