Co-formation of the disc and the stellar halo

By V. Belokurov, D. Erkal, N. Evans II, Sergey E. Koposov, A. Deason. 2018

575 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ef197fa7b9396afbe4162c87d421e51abe10541c

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In Astronomy and Astrophysics

Citations in the corpus

Evidence for an Intermediate-mass Milky Way from Gaia DR2 Halo Globular Cluster Motions (2018, background): “However, there have been recent claims that up to two thirds of the local stellar halo may have been deposited by the single encounter of a massive dwarf galaxy (e.g., Deason et al. 2013; Belokurov et al. 2018; Myeong et al. 2018).”
The Sausage Globular Clusters (2018, background): “Belokurov et al. (2018b) show that the velocity anisotropy parameter βMSTO is very extreme, βMSTO = 1− σ2vθ + σ 2 vϕ 2σ2vr ≈ 0.9, (1) Here, vϕ is the azimuthal velocity in the direction of the Milky Way’s rotation, vθ is increasing towards the Milky Way’s north pole and vr is the radial velocity in…”
Proper motions and dynamics of the Milky Way globular cluster system fromGaiaDR2 (2018, background): “At large galactocentric distances, the distribution becomes radially anisotropic, with the value of anisotropy parameter β ' 0.6 similar to that of the stellar halo (e.g., Deason et al. 2012; Kafle et al. 2014; Belokurov et al. 2018; Wegg et al. 2018, among others).”
The biggest splash (2019, methodology): “Myeong et al. (2019) present chemical and kinematic evidence for two (perhaps related) accretion events: the nearly radial GS merger (see Belokurov et al. 2018) and the highly retrograde Sequoia (see also Myeong et al. 2018a; Matsuno, Aoki & Suda 2019).”
Evidence from the H3 Survey That the Stellar Halo Is Entirely Comprised of Substructure (2020, methodology): “…more than half of the [Fe/H]<−1 stars in the local halo8 appear to originate from a single system, the accreted Gaia–Sausage–Enceladus (GSE) dwarf galaxy (e.g., Belokurov et al. 2018; Haywood et al. 2018; Helmi et al. 2018; Koppelman et al. 2018; Myeong et al. 2018b; Mackereth et al. 2019).”
Evidence for two early accretion events that built the Milky Way stellar halo (2019, methodology): “Also, we note that this suggested age range (9 Gyr to 11 Gyr) agrees very well with the suggested infall time of the Gaia Sausage itself.”
The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “This finding is supported by independent evidence from halo kine- 16 A small number of GCs with ages τ > 12.5 Gyr or galactocentric radii R < 5 kpc may still have an ex-situ origin, but we deliberately adopt conservative sample limits. matics (Belokurov et al. 2018; Deason et al. 2018a).”
In Disguise or Out of Reach: First Clues about In Situ and Accreted Stars in the Stellar Halo of the Milky Way from Gaia DR2 (2018, background): “Belokurov et al. (2018) find a strong orbital anisotropy for stars with metallicities above -1.7 and low anisotropy for stars below this limit.”