Resonance sweeping by a decelerating Galactic bar

Chiba, Rimpei; Friske, Jennifer K S; Schönrich, Ralph

doi:10.1093/mnras/staa3585

Cited by 64 publications

(38 citation statements)

References 66 publications

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“…We demonstrated that the most intense migration appears at the epoch of the bar formation, which is followed by a rapid decrease in its pattern speed and migration of the bar resonances. We note that signatures of the bar deceleration have been potentially found in the Milky Way, by studying local stellar kinematics (Chiba et al 2019), thus making our proposed scenario particularly suitable for the Milky Way. Therefore, we suggest that the age of the youngest high-metallicity stars ([Fe/H] > 0.2−0.3) on nearly circular orbits in the solar vicinity should correspond to the age of the Milky Way bar.…”

Section: Discussionmentioning

confidence: 86%

Escapees from the bar resonances

Khoperskov

Matteo

Haywood

et al. 2020

A&A

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Understanding radial migration is a crucial point for building relevant chemical and dynamical evolution models of the Milky Way disk. In this paper we analyze a high-resolution N-body simulation of a Milky Way-type galaxy to study the role that the slowing down of a stellar bar has in generating migration from the inner to the outer disk. Stellar particles are trapped by the main resonances (corotation and outer Lindblad resonance, OLR) which then propagate outward across the disk due to the bar slowing down. Once the bar strength reaches its maximum amplitude, some of the stars delivered to the outer disk escape the resonances and some of them settle on nearly circular orbits. The number of escaped stars gradually increases, also due to the decrease in the bar strength when the boxy/peanut bulge forms. We show that this mechanism is not limited to stars on nearly circular orbits; stars initially on more eccentric orbits can also be transferred outward (out to the OLR location) and can end up on nearly circular orbits. Therefore, the propagation of the bar resonances outward can induce the circularization of the orbits of some of the migrating stars. The mechanism investigated in this paper can explain the presence of metal-rich stars at the solar vicinity and more generally in the outer Galactic disk. Our dynamical model predicts that up to 3% of stars between corotation and the OLR can be formed in the innermost region of the Milky Way. The epoch of the Milky Way bar formation can be potentially constrained by analyzing the age distribution of the most metal-rich stars at the solar vicinity.

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Section: Discussionmentioning

confidence: 86%

Escapees from the bar resonances

Khoperskov

Matteo

Haywood

et al. 2020

A&A

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“…Moreover, it is well known that spiral modes in simulations can be transient, remaining stationary for only a few rotations (Sellwood & Carlberg 2014), and the response of the disc should be different during the period of rising or declining amplitude. The same can be true for the bar, whose amplitude and pattern speed can also grow or vary with time (e.g., Chiba et al 2021;Hilmi et al 2020).…”

Section: Introductionmentioning

confidence: 88%

Perturbed distribution functions with accurate action estimates for the Galactic disc

Kazwini

Agobert

Siebert

et al. 2022

A&A

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In the Gaia era, understanding the effects of the perturbations of the Galactic disc is of major importance in the context of dynamical modelling. In this theoretical paper we extend previous work in which, making use of the epicyclic approximation, the linearized Boltzmann equation had been used to explicitly compute, away from resonances, the perturbed distribution function of a Galactic thin-disc population in the presence of a non-axisymmetric perturbation of constant amplitude. Here we improve this theoretical framework in two distinct ways in the new code that we present. First, we use better estimates for the action-angle variables away from quasi-circular orbits, computed from the AGAMA software, and we present an efficient routine to numerically re-express any perturbing potential in these coordinates with a typical accuracy at the per cent level. The use of more accurate action estimates allows us to identify resonances such as the outer 1:1 bar resonance at higher azimuthal velocities than the outer Lindblad resonance, and to extend our previous theoretical results well above the Galactic plane, where we explicitly show how they differ from the epicyclic approximation. In particular, the displacement of resonances in velocity space as a function of height can in principle constrain the 3D structure of the Galactic potential. Second, we allow the perturbation to be time dependent, thereby allowing us to model the effect of transient spiral arms or a growing bar. The theoretical framework and tools presented here will be useful for a thorough analytical dynamical modelling of the complex velocity distribution of disc stars as measured by past and upcoming Gaia data releases.

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“…However, even a few km s −1 , e.g. the current level of uncertainty, is enough to make it unclear which feature in the Solar neighbourhood kinematics arises from which resonance, and if the bar is slowing, then multiple features can be explained by the resonant sweeping of a single resonance (Chiba, Friske & Schönrich 2019).…”

Section: Introductionmentioning

confidence: 99%

The power of coordinate transformations in dynamical interpretations of Galactic structure

Hunt

Johnston

Pettitt

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Abstract Gaia DR2 has provided an unprecedented wealth of information about the positions and motions of stars in our Galaxy, and has highlighted the degree of disequilibria in the disc. As we collect data over a wider area of the disc it becomes increasingly appealing to start analysing stellar actions and angles, which specifically label orbit space, instead of their current phase space location. Conceptually, while $\bar{x}$ and $\bar{v}$ tell us about the potential and local interactions, grouping in action puts together stars that have similar frequencies and hence similar responses to dynamical effects occurring over several orbits. Grouping in actions and angles refines this further to isolate stars which are travelling together through space and hence have shared histories. Mixing these coordinate systems can confuse the interpretation. For example, it has been suggested that by moving stars to their guiding radius, the Milky Way spiral structure is visible as ridge-like overdensities in the Gaia data (Khoperskov et al. 2020). However, in this work, we show that these features are in fact the known kinematic moving groups, both in the Lz − φ and the vR − vφ planes. Using simulations we show how this distinction will become even more important as we move to a global view of the Milky Way. As an example, we show that the radial velocity wave seen in the Galactic disc in Gaia and APOGEE should become stronger in the action-angle frame, and that it can be reproduced by transient spiral structure.

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Resonance sweeping by a decelerating Galactic bar

Cited by 64 publications

References 66 publications

Escapees from the bar resonances

Escapees from the bar resonances

Perturbed distribution functions with accurate action estimates for the Galactic disc

The power of coordinate transformations in dynamical interpretations of Galactic structure

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