Measurement of Substructure from the Kinematics of the GD-1 Stellar Stream
- 1Princeton University
- 2The Observatories of the Carnegie Institution for Science
- 3Flatiron Institute
Abstract
Stellar streams are sensitive tracers of low-mass dark matter subhalos and provide a means to test the cold dark matter (CDM) paradigm on small scales. In this work, we connect the intrinsic velocity dispersion of the GD-1 stream to the number density and internal structure of dark matter subhalos in the mass range 10 5 –10 9 M ⊙ . We measure the radial velocity dispersion of GD-1 based on 160 identified member stars across four different spectroscopic catalogs. We use repeat observations of the same stars to constrain binarity. We find that the stream's intrinsic radial velocity dispersion ranges from approximately 2–5 km s −1 across its length. The region of GD-1 with the highest velocity dispersion represents a 4 σ deviation from unperturbed stream models formed in a smooth Milky Way potential, which are substantially colder. We use perturbation theory to model the stream’s velocity dispersion as a function of dark matter subhalo population parameters, including the number of low-mass subhalos in the Milky Way, the dark matter half-mode mass, and the mass–concentration relation of subhalos. We find that the observed velocity dispersion can be explained by numerous impacts with low-mass dark matter subhalos or by a single impact with a very compact subhalo with M ≳ 10 8 M ⊙ . Our constraint on the fraction of mass in subhalos is f sub = 0.0 5 − 0.03 + 0.08 (68% confidence). In both scenarios, our model prefers subhalos that are more compact compared to CDM mass–size expectations. These results suggest a possible deviation from CDM at low subhalo masses.
Related
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- When Streams Curve Away: a Test of Dark Matter from Extragalactic Stellar Stream Populations
BibTeX
@article{nibauer2026measurement,
title = {{Measurement of Substructure from the Kinematics of the GD-1 Stellar Stream}},
author = {Jacob Nibauer and Ana Bonaca and Adrian M. Price-Whelan and David N. Spergel and Jenny E. Greene},
journal = {The Astrophysical Journal},
year = {2026},
month = jun,
doi = {10.3847/1538-4357/ae6776},
url = {https://doi.org/10.3847/1538-4357/ae6776},
note = {CC BY},
}
RIS
TY - JOUR
TI - Measurement of Substructure from the Kinematics of the GD-1 Stellar Stream
AU - Jacob Nibauer
AU - Ana Bonaca
AU - Adrian M. Price-Whelan
AU - David N. Spergel
AU - Jenny E. Greene
PY - 2026
DA - 2026/06/04
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/ae6776
UR - https://doi.org/10.3847/1538-4357/ae6776
AB - Stellar streams are sensitive tracers of low-mass dark matter subhalos and provide a means to test the cold dark matter (CDM) paradigm on small scales. In this work, we connect the intrinsic velocity dispersion of the GD-1 stream to the number density and internal structure of dark matter subhalos in the mass range 10 5 –10 9 M ⊙ . We measure the radial velocity dispersion of GD-1 based on 160 identified member stars across four different spectroscopic catalogs. We use repeat observations of the same stars to constrain binarity. We find that the stream's intrinsic radial velocity dispersion ranges from approximately 2–5 km s −1 across its length. The region of GD-1 with the highest velocity dispersion represents a 4 σ deviation from unperturbed stream models formed in a smooth Milky Way potential, which are substantially colder. We use perturbation theory to model the stream’s velocity dispersion as a function of dark matter subhalo population parameters, including the number of low-mass subhalos in the Milky Way, the dark matter half-mode mass, and the mass–concentration relation of subhalos. We find that the observed velocity dispersion can be explained by numerous impacts with low-mass dark matter subhalos or by a single impact with a very compact subhalo with M ≳ 10 8 M ⊙ . Our constraint on the fraction of mass in subhalos is f sub = 0.0 5 − 0.03 + 0.08 (68% confidence). In both scenarios, our model prefers subhalos that are more compact compared to CDM mass–size expectations. These results suggest a possible deviation from CDM at low subhalo masses.
SN - 0004-637X
SN - 1538-4357
ER -