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Resonance sweeping by a decelerating Galactic bar

Chiba, R; Friske, JKS; Schönrich, R; (2021) Resonance sweeping by a decelerating Galactic bar. Monthly Notices of the Royal Astronomical Society , 500 (4) pp. 4710-4729. 10.1093/mnras/staa3585. Green open access

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Abstract

We provide the first quantitative evidence for the deceleration of the Galactic bar from local stellar kinematics in agreement with dynamical friction by a typical dark matter halo. The kinematic response of the stellar disc to a decelerating bar is studied using secular perturbation theory and test particle simulations. We show that the velocity distribution at any point in the disc affected by a naturally slowing bar is qualitatively different from that perturbed by a steadily rotating bar with the same current pattern speed Ωp and amplitude. When the bar slows down, its resonances sweep through phase space, trapping, and dragging along a portion of previously free orbits. This enhances occupation on resonances, but also changes the distribution of stars within the resonance. Due to the accumulation of orbits near the boundary of the resonance, the decelerating bar model reproduces with its corotation resonance the offset and strength of the Hercules stream in the local vR-vφ plane and the double-peaked structure of mean vR in the Lz–φ plane. At resonances other than the corotation, resonant dragging by a slowing bar is associated with a continuing increase in radial action, leading to multiple resonance ridges in the action plane as identified in the Gaia data. This work shows models using a constant bar pattern speed likely lead to qualitatively wrong conclusions. Most importantly we provide a quantitative estimate of the current slowing rate of the bar Ω˙p=(−4.5±1.4)kms−1kpc−1Gyr−1 with additional systematic uncertainty arising from unmodelled impacts of e.g. spiral arms.

Type: Article
Title: Resonance sweeping by a decelerating Galactic bar
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staa3585
Publisher version: https://doi.org/10.1093/mnras/staa3585
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: methods: numerical, Galaxy: evolution, Galaxy: kinematics and dynamics
UCL classification: UCL
UCL > Provost and Vice Provost Offices
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/10118257
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