2024ApJ...975..135C

The dark matter subhalos orbiting in a galactic halo perturb the orbits of stars in thin stellar streams. Over time, the random velocities in the streams develop non-Gaussian wings. The rate of velocity increase is approximately a random walk at a rate proportional to the number of subhalos, primarily those in the mass range ≈10^6–7M_⊙. The distribution of random velocities in long streams is measured in simulated Milky Way-like halos that develop in representative warm dark matter (WDM) and cold dark matter (CDM) cosmologies. The radial velocity distributions are well modeled as the sum of a Gaussian and an exponential. The resulting Markov Chain Monte Carlo fits find Gaussian cores of 1-2 km s^–1 and exponential wings that increase from 3 km s^–1 for 5.5 keV WDM, 4 km s^–1 for 7 keV WDM, to 6 km s^–1 for a CDM halo. The observational prospects to use stream measurements to constrain the nature of galactic dark matter are discussed.