The Smith Cloud and its dark matter halo: Survival of a Galactic disc passage

Abstract

The current velocity of the Smith Cloud indicates that it has undergone at least one passage of the Galactic disc. Using hydrodynamic simulations we examine the present day structure of the Smith Cloud. We 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 hypothesised dark matter core in the Smith Cloud. No statistically significant core or extended gamma-ray emission are detected down to a 95% confidence level upper limit of $1.4\times 10^{-10}$ 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 ${\tau }^{+}{\tau }^{-}$ and $b\bar{b}$ for a high-velocity cloud.

10 pages, 8 figures. Submitted to MNRAS

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• Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint
• Mass, Morphing, Metallicities: The Evolution of Infalling High Velocity Clouds
• Exploring the Dust Content of Galactic Halos with Herschel III. NGC 891
• Discovery of two embedded clusters with WISE in the high Galactic latitude cloud HRK 81.4-77.8
• The Smith Cloud: surviving a high speed transit of the Galactic disc
• The Effect of Mixing on the Observed Metallicity of the Smith Cloud
• The role of the halo magnetic field on accretion through High-Velocity Clouds
• Simulating the impact of the Smith Cloud
• A Component of the Smith High Velocity Cloud Now Crossing the Galactic Plane