Tracing Thamnos: Chemical Clues to a Very Metal-Poor Galactic Immigrant

Xie et al. investigate two retrograde stellar groups, Rg8 and Rg9, using high-resolution spectroscopy and find them chemically identical across all measured elements. Their shared very metal-poor population and lack of an α-knee indicate origin in a low-mass dwarf galaxy. The groups strongly overlap with the known Thamnos substructure, suggesting all three trace the same ancient accretion event in the Milky Way’s halo.