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arXiv · 1802.03414

Co-formation of the Galactic disc and the stellar halo

V. Belokurov·D. Erkal·N. W. Evans·S. E. Koposov·A. J. Deason
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Abstract

Using a large sample of Main Sequence stars with 7-D measurements supplied by Gaia and SDSS, we study the kinematic properties of the local (within ~10 kpc from the Sun) stellar halo. We demonstrate that the halo's velocity ellipsoid evolves strongly with metallicity. At the low [Fe/H] end, the orbital anisotropy (the amount of motion in the radial direction compared to the tangential one) is mildly radial with 0.2 -1.7 we measure extreme values of beta~0.9. Across the metallicity range considered, i.e. -3<[Fe/H]<-1, the stellar halo's spin is minimal, at the level of 20 10^10 Msun around the epoch of the Galactic disc formation, i.e. between 8 and 11 Gyr ago. The radical halo anisotropy is the result of the dramatic radialisation of the massive progenitor's orbit, amplified by the action of the growing disc.

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V. Belokurov, D. Erkal, N. W. Evans, S. E. Koposov, A. J. Deason. 2018-02-09. Co-formation of the Galactic disc and the stellar halo. https://doi.org/10.1093/mnras%2Fsty982

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