{
  "id": "1811.03631",
  "version": "v1",
  "published": "2018-11-08T19:00:03.000Z",
  "updated": "2018-11-08T19:00:03.000Z",
  "title": "The Spur and the Gap in GD-1: Dynamical evidence for a dark substructure in the Milky Way halo",
  "authors": [
    "Ana Bonaca",
    "David W. Hogg",
    "Adrian M. Price-Whelan",
    "Charlie Conroy"
  ],
  "comment": "submitted to ApJ",
  "categories": [
    "astro-ph.GA",
    "astro-ph.CO",
    "hep-ph"
  ],
  "abstract": "We present a model for the interaction of the GD-1 stellar stream with a massive perturber that naturally explains many of the observed stream features, including a gap and an off-stream spur of stars. The model involves an impulse by a fast encounter, after which the stream grows a loop of stars at different orbital energies. At specific viewing angles, this loop appears offset from the stream track. The configuration-space observations are sensitive to the mass, age, impact parameter, and total velocity of the encounter, and future velocity observations will constrain the full velocity vector of the perturber. A quantitative comparison of the spur and gap features prefers models where the perturber is in the mass range of $10^6\\,\\rm M_\\odot$ to $10^8\\,\\rm M_\\odot$. Orbit integrations back in time show that the stream encounter could not have been caused by any known globular cluster or dwarf galaxy, and mass, size and impact-parameter arguments show that it could not have been caused by a molecular cloud in the Milky Way disk. The most plausible explanation for the gap-and-spur structure is an encounter with a dark matter substructure, like those predicted to populate galactic halos in $\\Lambda$CDM cosmology. However, the expected densities of $\\Lambda$CDM subhalos in this mass range and in this part of the Milky Way are $2-3\\,\\sigma$ lower than the inferred high density of the GD-1 perturber. This observation opens up the possibility that detailed observations of streams could measure the mass spectrum of dark-matter substructures and even identify individual substructures and their orbits in the Galactic halo.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-11-08T19:00:03.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "milky way halo",
      "dark substructure",
      "dynamical evidence",
      "mass range",
      "gap features prefers models"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}