The GALAH Survey: chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+DR3 and Gaia eDR3

Since the advent of Gala astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, Goia-Sausage-Enceladus (GSE), appears to be an early 'building block' given its virial mass > 1010 Mo at infall (z <^> 1-3). in order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3), To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low -o, abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] versus [Mg/Min] in GALAH+ DR3, We provide tables of our selections and report the chrono-chetnodynamical properties (age, chemistry, and dynamics), Through a previously reported clean dynamical selection of USE stars, including 30 < OR/ kpc km s-1 < 55, we can characterize an unprecedented 24 abundances of this structure with GALAH+ DR3. With our chemical selection we characterize the dynamical properties of the GSE, for example mean OR/ kpc kin s-1 = 26'914. We find only (29 + 1) per cent of the USE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way.O

Automated summary

With the use of Gala astrometry, a method has been developed to identify massive accreted systems in the Galaxy based on their unique dynamical signatures. In this study, the Goia-Sausage-Enceladus (GSE) system is identified as an early "building block" with a high virial mass. By analyzing the chemical properties of stars and applying Gaussian mixture models, the GSE component is successfully separated from the background stars. The findings provide valuable insights into the formation of the Milky Way.