Stellar Spiral Structures in Triaxial Dark Matter Haloes
  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.
