Dr. Anirudh Chiti (Stanford University)

The Milky Way's ancient, low-metallicity stars and its surrounding dwarf galaxies provide unique windows into early galaxy formation and the first episodes of element production. I will present new insights on these topics enabled by the DECam MAGIC survey, a 54-night NOIRLab survey program, that is imaging a quarter of the southern hemisphere with a metallicity-sensitive, narrow-band imaging filter covering the Ca II K line. These data provide simultaneous metallicities for stars across the footprint, several magnitudes deeper than existing metallicity-sensitive photometry, for systematic advances in low-metallicity, low surface brightness studies in the Milky Way and Magellanic Clouds (MCs). I will highlight two discoveries demonstrating this: (1) the detection of extended low-metallicity stellar populations around several dwarf galaxies, indicating the presence of extended dark matter halos or ongoing tidal disruption in these relic systems; (2) the detection and characterization of a star (with [Fe/H] < -4.6) that preserves the first clear signature of element production by Population III stars within a primordial ultra-faint dwarf galaxy. I will contextualize this star's chemical abundance signature relative to analogous stars in the Milky Way and LMC, to probe the mechanisms by which Population III supernovae may have enriched this object. Finally, I will present some explorations of a large-scale metallicity map of the Milky Way.