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Dissecting the phase space snail shell

Published online by Cambridge University Press:  14 May 2020

Zhao-Yu Li Open the ORCID record for Zhao-Yu Li [Opens in a new window]  and
Juntai Shen
Zhao-Yu Li
Affiliation:
Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong UniversityShanghai200240, China emails: lizy.astro@sjtu.edu.cn, jtshen@sjtu.edu.cn Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences 80 Nandan Road, Shanghai200030, China
Juntai Shen
Affiliation:
Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong UniversityShanghai200240, China emails: lizy.astro@sjtu.edu.cn, jtshen@sjtu.edu.cn Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences 80 Nandan Road, Shanghai200030, China College of Astronomy and Space Sciences, University of Chinese Academy of Sciences 19A Yuquan Road, Beijing100049, China
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Abstract

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The on-going phase mixing in the vertical direction of the Galactic disk has been discovered with the revolutionary Gaia DR2 data. It manifests itself as the snail shell in the Z–Vz phase space. To better understand the origin and properties of the phase mixing process, we study the phase-mixing signatures in moving groups (also known as the kinematic streams) with the Gaia DR2 data in the Galactic disk near the Solar circle. Interestingly, the phase space snail shell exists only in the main kinematic streams with |VR|≲ 50 km/s and |Vφ –VLSR|≲30 km/s, i.e., stars on dynamically “colder” orbits. Compared to the colder orbits, the hotter orbits may have phase-wrapped away already due to the much larger dynamical range in radial variation to facilitate faster phase mixing. These results help put tighter constraints on the vertical perturbation history of the Milky Way disk. To explain the lack of a well-defined snail shell in the hotter orbits, the disk should have been perturbed at least ∼400–500 Myr ago. Our results offer more support to the recent satellite-disk encounter scenario than the internal bar buckling perturbation scenario as the origin of the phase space mixing.

Keywords

Galaxy: diskGalaxy: kinematics and dynamicsGalaxy: structurestars: kinematics and dynamics
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S353: Galactic Dynamics in the Era of Large Surveys , June 2019 , pp. 10 - 12
Copyright
© International Astronomical Union 2020

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