The effects of dynamical substructure on Milky Way mass estimates from the high-velocity tail of the local stellar halo

Grand, Robert JJ; Deason, Alis J; White, Simon DM; Simpson, Christine M; Gómez, Facundo A; Marinacci, Federico; Pakmor, Rüdiger

Abstract

We investigate the impact of dynamical streams and substructure on estimates of the local escape speed and total mass of Milky-Way-mass galaxies from modelling the high-velocity tail of local halo stars. We use a suite of high-resolution magnetohydrodynamical cosmological zoom-in simulations that resolve phase space substructure in local volumes around solar-like positions. We show that phase space structure varies significantly between positions in individual galaxies and across the suite. Substructure populates the high-velocity tail unevenly and leads to discrepancies in the mass estimates. We show that a combination of streams, sample noise, and truncation of the high-velocity tail below the escape speed leads to a distribution of mass estimates with a median that falls below the true value by ∼20 per cent ∼20 per cent ⁠, and a spread of a factor of 2 across the suite. Correcting for these biases, we derive a revised value for the Milky Way mass presented in Deason et al. of 1.29 +0.37 −0.47 × 10 12 M ⊙ 1.29−0.47+0.37×1012M⊙ ⁠.

Citation

Grand, R. J., Deason, A. J., White, S. D., Simpson, C. M., Gómez, F. A., Marinacci, F., & Pakmor, R. (2019). The effects of dynamical substructure on Milky Way mass estimates from the high-velocity tail of the local stellar halo. Monthly Notices of the Royal Astronomical Society: Letters, 487(1), L72-L76. https://doi.org/10.1093/mnrasl/slz092

• Journal Article Type: Article
• Acceptance Date: Jun 3, 2019
• Online Publication Date: Jun 18, 2019
• Publication Date: Jul 31, 2019
• Deposit Date: Sep 13, 2019
• Publicly Available Date: Sep 13, 2019
• Journal: Monthly Notices of the Royal Astronomical Society: Letters
• Electronic ISSN: 1745-3933
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 487
• Issue: 1
• Pages: L72-L76
• DOI: https://doi.org/10.1093/mnrasl/slz092
• Public URL: https://durham-repository.worktribe.com/output/1322083