The ancient stellar populations of the Milky Way and its surrounding dwarf galaxies are a window on the earliest stages of galaxy formation and element production. Their most ancient, lowest metallicity stars are plausibly directly enriched by the first stars, and the Milky Way’s ultra-faint dwarf galaxies (UFDs) are the products of early galaxy formation on the smallest scales. Recent, metallicity-sensitive imaging techniques have dramatically increased the efficiency of identifying such stars, with transformational potential for this field. I will present three results highlighting this: (1) the detection of an extended population of stars around several UFDs, highlighting the Tucana II UFD, indicating that several of these relic galaxies may host extended halos; (2) the detailed chemical abundances of stars in the outskirts of Tucana II, along with a framework that ties such studies to their possible formation mechanisms; and (3) the detection and detailed chemical characterization of a [Fe/H] < -4.0 star in the Large Magellanic Cloud (LMC)—nearly two orders of magnitude more metal-poor than any such studied LMC star, plausibly preserving the chemical yields of an extragalactic first star. I will conclude by introducing a new Dark Energy Camera survey that will chemically map a quarter of the southern sky with a metallicity-sensitive, narrow-band CaHK filter down to the proper motion limit of Gaia. This survey will unlock new discovery space in the low metallicity, low surface brightness regime of the Milky Way and dramatically increase the sample of low metallicity stars, providing direct insights on the products of the first stars.
Yale Astronomy Colloquium - Anirudh Chiti
Thursday, October 12, 2023 - 2:30pm
University of Chicago
Uncovering the ancient Milky Way
Kline Tower 13th floor, Room 1327 A & B New Haven, CT 06511