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Through large spectroscopic surveys providing chemistry for > 10^6 stars, and Gaia mapping >10^9 stars in the Galaxy, we have learned that the inner stellar halo is dominated by the accretion of Gaia Enceladus. With the richness of data at hand, there are a myriad of ways these accreted stars have been selected: from kinematics, to dynamics, to even chemistry. In this work, we explore these different selections and their effects on the inferred progenitor properties using APOGEE DR17 and Gaia data. Specifically, we investigate the selections made in eccentricity, E-Lz, Vphi-Vr, Jr-Lz, and [Mg/Mn] vs [Al/Fe] and quantify the overlap between and contamination in each selection method. To ultimately understand their efficacy, we apply similar selections in Milky Way like galaxies with a known Gaia Enceladus progenitor in the AURIGA hydrodynamical simulations and similarly infer progenitor properties. Through this, we are able to understand which selection is best to recover true Gaia Enceladus stars in terms of completeness and purity, how much contamination from other accretion events and from in-situ population is present depending on the method, and ultimately which selection is best for inferring Gaia Enceladus mass. |
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