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Dynamical streams in the local stellar halo

Dillamore, Adam M; Sanders, Jason L; Belokurov, Vasily; Zhang, Hanyuan; (2025) Dynamical streams in the local stellar halo. Monthly Notices of the Royal Astronomical Society , 541 (1) pp. 214-233. 10.1093/mnras/staf965. Green open access

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Abstract

Co-moving groups of stars (streams) are well known in the velocity space of the disc near the Sun. Many are thought to arise from resonances with the Galactic bar or spiral arms. In this work, we search for similar moving groups in the velocity space of the halo, at low angular momentum. From the asymmetry of the radial velocity distribution vR, we identify two inward-moving streams with vR < 0 and small |vφ|. These are projections of the ‘chevrons’ previously discovered in radial phase space (R, vR). A test particle simulation in a realistic Milky Way potential with a decelerating bar naturally produces analogues of these features, and they are observed across a wide range of metallicity. They are therefore very likely to be dynamical streams created by trapping in the bar’s resonances. Specifically, they occupy regions of phase space where orbits are trapped in the corotation and outer Lindblad resonances respectively. By tracing these streams across a range of radii in (R, vR) space, we fit resonant orbits to their tracks in a flexible potential with variable bar pattern speed. This allows us to simultaneously constrain the mass profile of the Milky Way for r 20 kpc and the pattern speed b. We estimate the mass enclosed within r = 20 kpc to be M20 = (2.17 ± 0.21) × 1011 M, and the pattern speed to be b = 31.9+1.8 −1.9 km s−1 kpc−1. Our fitted potential is in excellent agreement with previous results, while we favour a slightly slower pattern speed than most recent estimates.

Type: Article
Title: Dynamical streams in the local stellar halo
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staf965
Publisher version: https://doi.org/10.1093/mnras/staf965
Language: English
Additional information: Copyright © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Keywords: Galaxy: fundamental parameters, Galaxy: halo, Galaxy: kinematics and dynamics, Galaxy: structure
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10211220
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