Fundamental relations for the velocity dispersion of stars in the Milky Way

Author(s): Sanjib Sharma, Michael R. Hayden, Joss Bland-Hawthorn, Dennis Stello, Sven Buder, Thomas Kallinger
Abstract: We explore the fundamental relations governing the radial and vertical velocity dispersions of stars in the Milky Way, from combined studies of complementary surveys including GALAH, LAMOST, APOGEE, the NASA Kepler and K2 missions, and Gaia DR2. We find that different stellar samples, even though they target different tracer populations and employ a variety of age estimation techniques, follow the same set of fundamental relations. We provide the clearest evidence to date that, in addition to the well-known dependence on stellar age, the velocity dispersions of stars depend on orbital angular momentum L_z, metallicity, and height above the plane |z|, and are well described by a multiplicatively separable functional form. The dispersions have a power-law dependence on age with exponents of 0.441 ± 0.007 and 0.251 ± 0.006 for σ_z and σ_R, respectively, and the power law is valid even for the oldest stars. For the solar neighbourhood stars, the apparent break in the power law for older stars, as seen in previous studies, is due to the anticorrelation of L_z with age. The dispersions decrease with increasing L_z until we reach the Sun's orbital angular momentum, after which σ_z increases (implying flaring in the outer disc) while σ_R flattens. For a given age, the dispersions increase with decreasing metallicity, suggesting that the dispersions increase with birth radius. The dispersions also increase linearly with |z|. The same set of relations that work in the solar neighbourhood also work for stars between 3 < R/kpc < 20. Finally, the high-[α/Fe] stars follow the same relations as the low-[α/Fe] stars.
Organisation(s): Department of Astrophysics
External organisation(s): Max-Planck-Institut für Astronomie, Australian National University, ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), The University of Sydney, Aarhus University, University of New South Wales
Journal: Monthly Notices of the Royal Astronomical Society
Volume: 506
Pages: 1761-1776
No. of pages: 16
ISSN: 0035-8711
DOI: https://doi.org/10.1093/mnras/stab1086
Publication date: 09-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics, 103038 Space exploration
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/589c117f-9820-4282-918b-4a08ace33f52

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