Hayden, MichaelBland-Hawthorn, J.Sharma, SFreeman, KennethKos, J.Buder, SvenAnguiano, BorjaAsplund, MartinChen, BoquanDe Silva, Gayandhi MKhanna, ShouryaLin, JaneHorner, Jonathan2022-07-012022-07-010035-8711http://hdl.handle.net/1885/268636We 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.This research was supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013. In addition to ASTRO3D, MRH received support from ARC DP grant no. DP160103747. TZ acknowledges financial support of the Slovenian Research Agency (research core funding no. P1-0188). JBH is supported by an Australian Laureate Fellowship from the ARC. SLM acknowledges support from the Australian Research Council through grant no. DP180101791.application/pdfen-AU© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyGalaxy: abundancesGalaxy: kinematics and dynamicsGalaxy: stellar contentGalaxy: structureThe GALAH survey: chemodynamics of the solar neighbourhood202010.1093/mnras/staa3352021-08-01