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Tree-ring structure of Galactic bar resonance

Chiba, R; Schönrich, R; (2021) Tree-ring structure of Galactic bar resonance. Monthly Notices of the Royal Astronomical Society , 505 (2) pp. 2412-2426. 10.1093/mnras/stab1094. Green open access

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Galaxy models have long predicted that galactic bars slow down by losing angular momentum to their postulated dark haloes. When the bar slows down, resonance sweeps radially outwards through the galactic disc while growing in volume, thereby sequentially capturing new stars at its surface/separatrix. Since trapped stars conserve their action of libration, which measures the relative distance to the resonance centre, the order of capturing is preserved: the surface of the resonance is dominated by stars captured recently at large radius, while the core of the resonance is occupied by stars trapped early at small radius. The slow down of the bar thus results in a rising mean metallicity of trapped stars from the surface towards the centre of the resonance as the Galaxy’s metallicity declines towards large radii. This argument, when applied to Solar neighbourhood stars, allows a novel precision measurement of the bar’s current pattern speed Ωp=35.5±0.8kms−1kpc−1⁠, placing the corotation radius at RCR=6.6±0.2kpc⁠. With this pattern speed, the corotation resonance precisely fits the Hercules stream in agreement with kinematics. Beyond corroborating the slow bar theory, this measurement manifests the deceleration of the bar of more than 24 per cent since its formation and thus the angular momentum transfer to the dark halo by dynamical friction. The measurement therefore supports the existence of a standard dark-matter halo rather than alternative models of gravity.

Type: Article
Title: Tree-ring structure of Galactic bar resonance
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stab1094
Publisher version: https://doi.org/10.1093/mnras/stab1094
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Galaxy: fundamental parameters, Galaxy: evolution, Galaxy: kinematics and dynamics
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 Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10127747
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