# Milky Way Halo Vibrations and Incommensurate Stream Velocities

## TL;DR

This paper investigates the oscillations of Milky Way-like dark matter halos and their impact on stellar stream velocities, providing insights into dark matter properties through simulation and observational comparisons.

## Contribution

It introduces an n-body simulation of a Milky Way-like halo to analyze halo oscillations and their effects on stellar stream velocities, linking these to dark matter characteristics.

## Key findings

- Stellar streams exhibit exponential distribution of perpendicular velocities (~10-20 km/s).
- Halo quadrupole fluctuations can explain observed tangential velocities.
- Velocity measurements can constrain dark matter self-interaction cross-section.

## Abstract

Collisionless dark matter galactic halos are expected to exhibit damped oscillations as a result of ongoing late time accretion. An n-body model of the cosmological assembly of a Milky Way-like halo is used to quantify the time dependence of its gravitational field. The simulation contains stellar streams whose incommensurate perpendicular velocities are found to have an approximately exponential distribution with a scale of 10-20\kms, depending on how the stars are selected, comparable to those reported for the Orphan stream. The fluctuations in the quadrupole moment of the dark matter halo are sufficient to largely explain the tangential velocities. If velocity measurements of a larger sample of Milky Way streams finds (or does not find) the expected distribution of transverse velocities it will lead to limits on the cross-section of self-interacting dark matter, in which kinetic viscosity can damp the oscillations more rapidly than the mixing processes of collisionless dark matter alone.