Buder, SvenLind, KarinNess, Melissa K.Feuillet, DianeHorta, DannyMonty, StephanieBuck, TobiasNordlander, ThomasBland-Hawthorn, J.Casey, AndrewDe Silva, Gayandhi MD'Orazi, ValentinaFreeman, Kennethlin, janeSchlesinger, KatharineCiuca, IoanaTing, Yuan-Sen2024-04-082024-04-080035-8711http://hdl.handle.net/1885/316592Since 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.KL acknowledges funds from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 852977). TB acknowledges support from the European Research Council under ERC-CoG grant CRAGSMAN-646955. JK and TZ acknowledge financial support of the Slovenian Research Agency (research core funding No. P1-0188) and the European Space Agency (PRODEX Experiment Arrangement No. C4000127986). CK acknowledges funding from the UK Science and Technology Facility Council (STFC) through grants ST/R000905/1 and ST/V000632/1, and the Stromlo Distinguished Visitorship at the ANU. We thank Rohan Naidu for sharing the [Fe/H] values from Naidu et al. (2020). Hyperlink figures to code access are inspired by Rodrigo Luger.application/pdfen-AU© 2021 The authorshttp://creativecommons.org/licenses/by/4.0/Galaxy: abundancesGalaxy: formationGalaxy: haloGalaxy: kinematics and dynamics202210.1093/mnras/stab35042022-11-20