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

Sharma, Sanjib and Hayden, Michael R. and Bland-Hawthorn, Joss and Stello, Dennis and Buder, Sven and Zinn, Joel C. and Kallinger, Thomas and Asplund, Martin and De Silva, Gayandhi M. and D'Orazi, Valentina and Freeman, Ken and Kos, Janez and Lewis, Geraint F. and Lin, Jane and Lind, Karin and Martell, Sarah and Simpson, Jeffrey D. and Wittenmyer, Rob A. and Zucker, Daniel B. and Zwitter, Tomaz and Chen, Boquan and Cotar, Klemen and Esdaile, James and Hon, Marc and Horner, Jonathan and Huber, Daniel and Kafle, Prajwal R. and Khanna, Shourya and Ting, Yuan-Sen and Nataf, David M. and Nordlander, Thomas and Mohd Saadon, Mohd Hafiz and Tepper-Garcia, Thor and Tinney, C. G. and Traven, Gregor and Watson, Fred and Wright, Duncan and Wyse, Rosemary F. G. (2021) Fundamental relations for the velocity dispersion of stars in the Milky Way. Monthly Notices of the Royal Astronomical Society, 506 (2). pp. 1761-1776. ISSN 0035-8711, DOI

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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 vertical bar z vertical bar, 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 sigma(z) and sigma(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 sigma(z) increases (implying flaring in the outer disc) while sigma(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 vertical bar z vertical bar. The same set of relations that work in the solar neighbourhood also work for stars between 3 < R/kpc < 20. Finally, the high-alpha/Fe] stars follow the same relations as the low-alpha/Fe] stars.

Item Type: Article
Funders: Senior Fellowship (University of Sydney), Australian Research Council [FL140100278] [FT1400147], Alexander von Humboldt Foundation
Uncontrolled Keywords: Galaxy: disc; Galaxy: evolution; Galaxy: formation; Galaxy: kinematics and dynamics
Subjects: Q Science > QB Astronomy
Divisions: Academy of Islamic Studies > Dept of Fiqh & Usul
Depositing User: Ms Zaharah Ramly
Date Deposited: 01 Jun 2022 06:51
Last Modified: 01 Jun 2022 06:51

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