Discy dwarf disruption and the shape of the Galactic halo

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Gibbons, SLJ 
Erkal, D 
Evans, NW 

The shape of the Galactic dark halo can, in principle, be inferred through modelling of stellar tidal streams in the Milky Way halo. The brightest and the longest of these, the Sagittarius stream, reaches out to large Galactocentric distances and hence can deliver the tightest constraints on the Galaxy's potential. In this contribution, we revisit the idea that the Sagittarius Stream was formed from a rotating progenitor. We demonstrate that the angle between the disk's angular momentum and the progenitor's orbital angular momentum does not remain constant throughout the disruption. Instead, it undergoes a dramatic evolution caused, in part, by the changes in the progenitor's moment of inertia tensor. We show that, even in a spherical potential, the streams produced as a result of a disky dwarf disruption appear to be "precessing". Yet, this debris plane evolution is illusory as it is solely caused by the swaying and wobbling of the progenitor's disk. Stream plane precession is therefore not an unambiguous indicator of asphericity of the dark halo.

Galaxy: halo, Galaxy: kinematics and dynamics
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Monthly Notices of the Royal Astronomical Society: Letters
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Oxford University Press (OUP)
Science and Technology Facilities Council (ST/N000927/1)
SG thanks Michael Alexander for a thorough proofreading of the manuscript and acknowledges the Science and Technology Facilities Council (STFC) for the award of a studentship. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement no. 308024