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The power of coordinate transformations in dynamical interpretations of Galactic structure

Hunt, JAS; Johnston, KV; Pettitt, AR; Cunningham, EC; Kawata, D; Hogg, DW; (2020) The power of coordinate transformations in dynamical interpretations of Galactic structure. Monthly Notices of the Royal Astronomical Society , 497 (1) pp. 818-828. 10.1093/mnras/staa1987. (In press). Green open access

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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 x¯ and ¯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 that 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.

Type: Article
Title: The power of coordinate transformations in dynamical interpretations of Galactic structure
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/staa1987
Publisher version: https://doi.org/10.1093/mnras/staa1987
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: disc – Galaxy: fundamental parameters – Galaxy: kinematics and dynamics – Galaxy: structure – solar neighbourhood
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/10106673
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