Stars from GAIA and APOGEE data

Based on high-quality APOGEE DR17 and Gaia DR3 data for 1742 red giants stars within 5 kpc of the Sun and not rotating with the Galactic disc (V_phi_<100km/s), we use the nonlinear technique of unsupervised analysis t-SNE to detect coherent structures in the space of ten chemical-abundance ratios: [Fe/H], [O/Fe], [Mg/Fe], [Si/Fe], [Ca/Fe], [C/Fe], [N/Fe], [Al/Fe], [Mn/Fe], and [Ni/Fe]. Additionally, we obtain orbital parameters for each star using the non-axisymmetric gravitational potential GravPot16.

Seven structures are detected, including the Splash, Gaia-Sausage-Enceladus (GSE), the high-alpha heated-disc population, N-C-O peculiar stars, and inner disk-like stars, plus two other groups that did not match anything previously reported in the literature, here named Galileo 5 and Galileo 6 (G5 and G6). These two groups overlap with Splash in [Fe/H], G5 being lower metallicity than G6, both between GSE and Splash in the [Mg/Mn] versus [Al/Fe] plane, G5 in the alpha -rich in-situ locus, and G6 on the border of the alpha-poor in-situ one; nonetheless their low [Ni/Fe] hints to a possible ex-situ origin.