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Co-formation of the disc and the stellar halo

Belokurov, V, Erkal, Denis, Evans, NW, Koposov, SE and Deason, AJ (2018) Co-formation of the disc and the stellar halo Monthly Notices of the Royal Astronomical Society, 478 (1). pp. 611-619.

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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 < β < 0.4. However, for stars with [Fe/H]> −1.7 we measure extreme values of β ∼ 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 < v¯θ(kms−1 ) < 30. Using a suite of cosmological zoom-in simulations of halo formation, we deduce that the observed acute anisotropy is inconsistent with the continuous accretion of dwarf satellites. Instead, we argue, the stellar debris in the inner halo were deposited in a major accretion event by a satellite with Mvir > 1010M⊙ 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.

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Physics
Authors :
Belokurov, V
Evans, NW
Koposov, SE
Deason, AJ
Date : 2 June 2018
Funders : FP7; STFC
DOI : 10.1093/mnras/sty982
Copyright Disclaimer : © 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (
Uncontrolled Keywords : Milky Way – galaxies: dwarf – galaxies: structure – Local Group – stars
Depositing User : Melanie Hughes
Date Deposited : 03 Oct 2018 15:22
Last Modified : 11 Dec 2018 11:24

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