The Smith Cloud and its dark matter halo: survival of a Galactic disc passage
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Type of Work10 pages
journal articles preprints
Citation of Original PublicationMatthew Nichols, Nestor Mirabal, Oscar Agertz, Felix J. Lockman and Joss Bland-Hawthorn, The Smith Cloud and its dark matter halo: survival of a Galactic disc passage, Monthly Notices of the Royal Astronomical Society, Volume 442, Issue 4,Pages 2883–2891 (2014), https://doi.org/10.1093/mnras/stu1028
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This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society.
Under conservative assumptions about the Galaxy, the derived velocity of the Smith Cloud indicates that it will have undergone at least one passage of the Galactic disc. Using hydrodynamic simulations, we examine the present-day structure of the Smith Cloud and find that a dark matter supported cloud is able to reproduce the observed present-day neutral hydrogen mass, column density distribution and morphology. In this case, the dark matter halo becomes elongated owing to the tidal interaction with the Galactic disc. Clouds in models neglecting dark matter confinement are destroyed upon disc passage, unless the initial cloud mass is well in excess of what is observed today. We then determine integrated flux upper limits to the gamma-ray emission around such a hypothesized dark matter core in the Smith Cloud. No statistically significant core or extended gamma-ray emission are detected down to a 95 per cent confidence level upper limit of 1.4 × 10⁻¹⁰ ph cm⁻² s⁻¹ in the 1–300 GeV energy range. For the derived distance of 12.4 kpc, the Fermi upper limits set the first tentative constraints on the dark matter cross-sections annihilating into τ+τ− and bb¯ for a high-velocity cloud.