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Dissecting the phase space snail shell

Published online by Cambridge University Press:  14 May 2020

Zhao-Yu Li
Affiliation:
Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong UniversityShanghai200240, China emails: [email protected], [email protected] 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: [email protected], [email protected] 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 ZVz 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 |VφVLSR|≲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.

Type
Contributed Papers
Copyright
© International Astronomical Union 2020

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