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The local high-velocity tail and the Galactic escape speed

Deason, AJ, Fattahi, A, Belokurov, V, Wyn Evans, N, Grand, RJJ, Marinacci, F and Pakmor, R (2019) The local high-velocity tail and the Galactic escape speed. Monthly Notices of the Royal Astronomical Society, 485 (3). pp. 3514-3526. ISSN 0035-8711

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We model the fastest moving (vtot > 300 km s−1) local (D 3 kpc) halo stars using cosmological simulations and six-dimensional Gaia data. Our approach is to use our knowledge of the assembly history and phase-space distribution of halo stars to constrain the form of the high-velocity tail of the stellar halo. Using simple analytical models and cosmological simulations, we find that the shape of the high-velocity tail is strongly dependent on the velocity anisotropy and number density profile of the halo stars - highly eccentric orbits and/or shallow density profiles have more extended high-velocity tails. The halo stars in the solar vicinity are known to have a strongly radial velocity anisotropy, and it has recently been shown the origin of these highly eccentric orbits is the early accretion of a massive (Mstar ∼ 109 M☉) dwarf satellite. We use this knowledge to construct a prior on the shape of the high-velocity tail. Moreover, we use the simulations to define an appropriate outer boundary of 2r200, beyond which stars can escape. After applying our methodology to the Gaia data, we find a local (r0 = 8.3 kpc) escape speed of vesc(r0) = 528+−2425 km s−1. We use our measurement of the escape velocity to estimate the total Milky Way mass, and dark halo concentration: M200,tot = 1.00+−003124 × 1012 M☉, c200 = 10.9+−4343. Our estimated mass agrees with recent results in the literature that seem to be converging on a Milky Way mass of M200,tot ∼ 1012 M☉.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2019 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 19 Apr 2023 11:43
Last Modified: 19 Apr 2023 11:43
DOI or ID number: 10.1093/mnras/stz623
URI: https://researchonline.ljmu.ac.uk/id/eprint/19328
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