Detecting the Figure Rotation of Dark Matter Halos with Tidal Streams

Understand

The dark matter halos that surround Milky Way-like galaxies in cosmological simulations are, to first order, triaxial.

• Nearly 30 years ago it was predicted that such triaxial dark matter halos should exhibit steady figure rotation or tumbling motions for durations of several gigayears.
• The angular frequency of figure rotation predicted by cosmological simulations is described by a log-normal distribution of pattern speed with a median value 0.15hkm/s/kpc (~ 0.15h rad/Gyr ~ 9h deg/Gyr) and a width of 0.83km/s/kpc.
• These pattern speeds are so small that they have generally been considered both unimportant and undetectable.