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

Abstract

New data from the $\text{Gaia}$ 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 $10^9{M}_{\odot }$. We infer a total abundance of dark subhalos normalised to standard cold dark matter $n_{\mathrm{sub}}/n_{\mathrm{sub},\mathrm{CDM}}=0.4_{-0.2}^{+0.3}$ ($68\%$), which corresponds to a mass fraction contained in the subhalos $f_{\mathrm{sub}}=0.14_{-0.07}^{+0.11}\%$, compatible with the predictions of hydrodynamical simulation of cold dark matter with baryons.

20 pages, 14 figures. Also see companion paper : "Novel constraints on the particle nature of dark matter from stellar streams". Accepted in MNRAS. Modified main text slightly. Updated Appendix B and added a plot. Main results and conclusions remain unchanged