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The mass of the Milky Way out to 100 kpc using halo stars

Deason, Alis J and Erkal, Denis and Belokurov, Vasily and Fattahi, Azadeh and Gómez, Facundo A and Grand, Robert J J and Pakmor, Rüdiger and Xue, Xiang-Xiang and Liu, Chao and Yang, Chengqun and Zhang, Lan and Zhao, Gang (2021) 'The mass of the Milky Way out to 100 kpc using halo stars.', Monthly notices of the Royal Astronomical Society, 501 (4). pp. 5964-5972.


We use a distribution function analysis to estimate the mass of the Milky Way (MW) out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the vast majority (⁠∼98 per cent⁠) have 6D phase-space information. We pay particular attention to systematic effects, such as the dynamical influence of the Large Magellanic Cloud (LMC), and the effect of unrelaxed substructure. The LMC biases the (pre-LMC infall) halo mass estimates towards higher values, while realistic stellar haloes from cosmological simulations tend to underestimate the true halo mass. After applying our method to the MW data, we find a mass within 100 kpc of M (<100 kpc) = 6.07 ± 0.29 (stat.) ± 1.21 (sys.) × 1011 M⊙. For this estimate, we have approximately corrected for the reflex motion induced by the LMC using the Erkal et al. model, which assumes a rigid potential for the LMC and MW. Furthermore, stars that likely belong to the Sagittarius stream are removed, and we include a 5 per cent systematic bias, and a 20 per cent systematic uncertainty based on our tests with cosmological simulations. Assuming the mass–concentration relation for Navarro–Frenk–White haloes, our mass estimate favours a total (pre-LMC infall) MW mass of M200c = 1.01 ± 0.24 × 1012 M⊙, or (post-LMC infall) mass of M200c = 1.16 ± 0.24 × 1012 M⊙ when a 1.5 × 1011 M⊙ mass of a rigid LMC is included.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:21 December 2020
Date deposited:02 July 2021
Date of first online publication:28 December 2020
Date first made open access:02 July 2021

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