Signatures of the First Stars and Galaxies in the Local Group
Abstract: 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. This data provides simultaneous metallicities for stars across the footprint, deeper than previous work, 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 that preserves the first clear signature of element production by the first generation of stars within a primordial ultra-faint dwarf galaxy. I will contextualize this star's peculiar chemical abundance signature relative to analogous stars in the Milky Way and LMC, to comment on the mechanisms by which the first supernovae may have enriched this object. Finally, I will present some explorations of a large-scale metallicity map of the Milky Way.
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