The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data
Abstract
We investigate the metallicity dependence of the tilt of the velocity ellipsoid using more than 572,000 stars selected from GALAH and Gaia. We find that the tilt angles of disk stars can be well described by the relation α= α0 arctan(Z/R), and the α0 differ significantly among different disk populations, with α0 are 0.78 ± 0.05, 0.86 ± 0.07, and 0.77 ± 0.07 for the whole sample, the Low-[α/Fe] and the High-[α/Fe] populations, respectively. These results indicate that Galactic disk populations are globally tilted toward cylindrical alignment, implying that the gravitational potential of the Galactic baryonic disk plays a dominant role in shaping the kinematics of dynamically relaxed stars. Our detailed analysis further reveals a metallicity dependence of α0 for various populations, with the Low-[α/Fe] and the High-[α/Fe] populations are respectively α0 = 0.12 sin(3.72 [Fe/H] + 1.09) + 0.75 and α0 = 0.20 sin(2.99 [Fe/H] + 1.90) + 0.71. These results indicate that the metallicity dependence observed in the Low-[α/Fe] population may be primarily associated with resonances induced by the Galactic bar, while the behavior of the High-[α/Fe] population may also have been affected by additional dynamical and evolutionary processes, such as violent heating associated with mergers, accretion, and/or the formation of these stars in an environment shaped by mergers of gas-rich systems and/or a turbulent ISM.
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BibTeX
@misc{he2026tilt,
title = {{The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data}},
author = {Zhenzhen He and Ruilan Yang and Hui Li and Weixiang Sun},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15349},
eprint = {2610.15349},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15349},
}
RIS
TY - UNPB
TI - The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data
AU - Zhenzhen He
AU - Ruilan Yang
AU - Hui Li
AU - Weixiang Sun
PY - 2026
DA - 2026/10/11
PB - arXiv
DO - 10.48550/arxiv.2610.15349
UR - https://arxiv.org/abs/2610.15349
AB - We investigate the metallicity dependence of the tilt of the velocity ellipsoid using more than 572,000 stars selected from GALAH and Gaia. We find that the tilt angles of disk stars can be well described by the relation α= α_0 arctan(Z/R), and the α_0 differ significantly among different disk populations, with α_0 are 0.78 ± 0.05, 0.86 ± 0.07, and 0.77 ± 0.07 for the whole sample, the Low-[α/Fe] and the High-[α/Fe] populations, respectively. These results indicate that Galactic disk populations are globally tilted toward cylindrical alignment, implying that the gravitational potential of the Galactic baryonic disk plays a dominant role in shaping the kinematics of dynamically relaxed stars. Our detailed analysis further reveals a metallicity dependence of α_0 for various populations, with the Low-[α/Fe] and the High-[α/Fe] populations are respectively α_0 = 0.12 sin(3.72 [Fe/H] + 1.09) + 0.75 and α_0 = 0.20 sin(2.99 [Fe/H] + 1.90) + 0.71. These results indicate that the metallicity dependence observed in the Low-[α/Fe] population may be primarily associated with resonances induced by the Galactic bar, while the behavior of the High-[α/Fe] population may also have been affected by additional dynamical and evolutionary processes, such as violent heating associated with mergers, accretion, and/or the formation of these stars in an environment shaped by mergers of gas-rich systems and/or a turbulent ISM.
ER -