The GALAH survey: chemodynamics of the solar neighbourhood

Michael R. Hayden*, Joss Bland-Hawthorn, Sanjib Sharma, Ken Freeman, Janez Kos, Sven Buder, Borja Anguiano, Martin Asplund, Boquan Chen, Gayandhi M. De Silva, Shourya Khanna, Jane Lin, Jonathan Horner, Sarah Martell, Yuan-Sen Ting, Rosemary Wyse, Daniel Zucker, Tomaz Zwitter

*Corresponding author for this work

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    We present the chemodynamic structure of the solar neighbourhood using 55 652 stars within a 500 pc volume around the Sun observed by GALAH and with astrometric parameters from Gaia DR2. We measure the velocity dispersion for all three components (vertical, radial, and tangential) and find that it varies smoothly with [Fe/H] and [α/Fe] for each component. The vertical component is especially clean, with σvz increasing from a low of 10 km s-1 at solar [α/Fe] and [Fe/H] to a high of more than 50 km s-1 for more metal-poor and [α/Fe] enhanced populations. We find no evidence of a large decrease in the velocity dispersion of the highest [α/Fe] populations as claimed in surveys prior to Gaia DR2. The eccentricity distribution for local stars varies most strongly as a function of [α/Fe], where stars with [α/Fe] < 0.1 dex having generally circular orbits (e < 0.15), while the median eccentricity increases rapidly for more [α/Fe] enhanced stellar populations up to e ∼ 0.35. These [α/Fe] enhanced populations have guiding radii consistent with origins in the inner Galaxy. Of the stars with metallicities much higher than the local interstellar medium ([Fe/H] > 0.1 dex), we find that the majority have e < 0.2 and are likely observed in the solar neighbourhood through churning/migration rather than blurring effects, as the epicyclic motion for these stars is not large enough to reach the radii at which they were likely born based on their metallicity.
    Original languageEnglish
    Pages (from-to)2952-2964
    Number of pages13
    JournalMonthly Notices of the Royal Astronomical Society
    Issue number2
    Publication statusPublished - 1 Apr 2020

    Bibliographical note

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 2, April 2020, Pages 2952–2964, Copyright 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


    • Galaxy: abundances
    • Galaxy: kinematics and dynamics
    • Galaxy: stellar content
    • Galaxy: structure


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