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… Click to show full abstract
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 σ _{v_z} 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), 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.
               
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