Evidence for Population-dependent Vertical Motions and the Long-lived Nonsteady Lopsided Milky Way Warp

Li, Xiang; Wang, Hai-Feng; Luo, Yang-Ping; López-Corredoira, Martín; Ting, Yuan-Sen; Chrobáková, Žofia
Bibliographical reference

The Astrophysical Journal

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2
2023
Number of authors
6
IAC number of authors
1
Citations
7
Refereed citations
6
Description
We present a Galactic disk vertical velocity analysis using OB type stars (OB stars), red clump (RC) stars, and main-sequence turnoff (MSTO) stars with different average age populations crossmatched with LAMOST DR5 and Gaia DR3. We show that the vertical velocities of the three populations clearly vary with the Galactocentric distance (R) and the younger stellar population has a stronger increasing trend in general. The bending and breathing modes indicated by the vertical motions are dependent on the populations and vary with spatial locations. These vertical motions may be due to the Galactic warp, or minor mergers, or nonequilibrium of the disk. Assuming the warp is the dominant component, we find that the amplitude of the warp (γ, Z ω ) of OB stars (younger population) is larger than that of RC stars (medium population) and the latter is also larger than that for MSTO stars (older population), which is in agreement with other independent analyses of stellar density distribution, and supports that the warp is a long-lived, nonsteady structure and is time evolving. This conclusion is robust whether the line of nodes ϕ w is fixed or is a free parameter (with ϕ w being around 3°-8.°5 as the best fit). Furthermore, we find that the warp is lopsided with asymmetries along the azimuthal angle (ϕ).
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NGC 2808 Globular Cluster
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis