Velocity Dispersion of the GD-1 Stellar Stream

TL;DR

This study measures the velocity dispersion of the GD-1 stellar stream, revealing evidence of dynamical heating and suggesting an accreted origin from a dwarf galaxy with a cored dark matter profile.

Contribution

First measurement of GD-1's velocity dispersion across a large span, indicating dynamical heating and supporting its origin from an accreted dwarf galaxy.

Findings

Velocity dispersion of 2.3 km/s in GD-1 stream.

Constant velocity dispersion over 15 degrees.

Evidence of dynamical heating in GD-1.

Abstract

Tidally dissolved globular clusters form thin stellar streams that preserve a historical record of their past evolution. We report a radial velocity dispersion of $2.3\pm0.3\,\textrm{km}\,\textrm{s}^{-1}$ in the GD-1 stellar stream using a sample of 43 spectroscopically confirmed members. The GD-1 velocity dispersion is constant over the surveyed $\approx15^\circ$ span of the stream. We also measured velocity dispersion in the spur adjacent to the main GD-1 stream, and found a similar value at the tip of the spur. Surprisingly, the region of the spur closer to the stream appears dynamically colder than the main stream. An unperturbed model of the GD-1 stream has a velocity dispersion of $\approx0.6\,\textrm{km}\,\textrm{s}^{-1}$, indicating that GD-1 has undergone dynamical heating. Stellar streams arising from globular clusters, which prior to their arrival in the Milky Way, orbited a dwarf galaxy with a cored density profile are expected to have experienced the amount of heating required to match the velocity dispersion observed in GD-1. This suggests that GD-1 has been accreted and that imprints of its original host galaxy, including the inner slope of its dark-matter halo, remain observable in the stream today.