Star Stream Velocity Distributions in CDM and WDM Galactic Halos

TL;DR

This paper investigates how dark matter subhalos influence stellar stream velocities in galactic halos, revealing non-Gaussian velocity features that depend on the dark matter model, with implications for constraining dark matter properties.

Contribution

It models the velocity distributions in stellar streams within WDM and CDM halos, providing a new method to distinguish dark matter types through velocity measurements.

Findings

Velocity distributions are well modeled by a Gaussian plus exponential.

Exponential wings increase with subhalo mass and differ between WDM and CDM.

Stream velocity measurements can potentially constrain dark matter properties.

Abstract

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 $\approx 10^{6-7} M_\odot$. The distribution of random velocities in long, thin, streams is measured in simulated Milky Way-like halos that develop in representative WDM and CDM cosmologies. The radial velocity distributions are well modeled as the sum of a Gaussian and an exponential. The resulting MCMC fits find Gaussian cores of 1-2 km/sec and exponential wings that increase from 3 km/sec for 5.5 keV WDM, 4 km/sec for 7 keV WDM, to 6 km/sec for a CDM halo. The observational prospects to use stream measurements to constrain the nature of galactic dark matter are discussed.