Evidence of a population of dark subhalos from Gaia and Pan-STARRS observations of the GD-1 stream

TL;DR

This study uses Gaia and Pan-STARRS data to analyze the GD-1 stellar stream, providing evidence for a population of dark matter subhalos that cause observable perturbations, consistent with cold dark matter models.

Contribution

It presents the first observational evidence for dark subhalos in the Milky Way using stellar stream perturbations, aligning with cold dark matter predictions.

Findings

Dark subhalos with masses 10^7 to 10^9 solar masses cause stream perturbations.

Estimated subhalo abundance is about 40% of the standard cold dark matter prediction.

The mass fraction in subhalos is approximately 0.14%, consistent with hydrodynamical simulations.

Abstract

New data from the $\textit{Gaia}$ satellite, when combined with accurate photometry from the Pan-STARRS survey, allow us to accurately estimate the properties of the GD-1 stream. Here, we analyze the stellar density perturbations in the GD-1 stream and show that they cannot be due to known baryonic structures like giant molecular clouds, globular clusters, or the Milky Way's bar or spiral arms. A joint analysis of the GD-1 and Pal 5 streams instead requires a population of dark substructures with masses $\approx 10^{7}$ to $10^9 \ M_{\rm{\odot}}$. We infer a total abundance of dark subhalos normalised to standard cold dark matter $n_{\rm sub}/n_{\rm sub, CDM} = 0.4 ^{+0.3}_{-0.2}$ ($68 \%$), which corresponds to a mass fraction contained in the subhalos $f_{\rm{sub}} = 0.14 ^{+0.11}_{-0.07} \%$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.