Mapping the Ancient Milky Way and its Relic Dwarf Galaxies

Abstract

In the first billion years after the Big Bang, the first stars and galaxies began transforming the dark, primitive universe into the rich, complex one that we observe today. These primitive objects thus govern crucial, foundational rungs in our understanding of how the universe came to be. However, little is directly known of their properties since their large distances render direct, detailed observations difficult.

Fortunately, the Milky Way hosts populations of ancient, “metal-poor" stars and satellite dwarf galaxies that function as nearby time capsules for investigations of early star formation, galaxy formation, and chemical evolution. The study of these objects is known as Galactic Archaeology, and has led to significant advances in our understanding of the first stars, supernovae, and galaxies. However, the most primitive, metal-poor stars are rare, and the difficulty of discovering them continues to bottleneck this promising approach.

In this thesis, I present several pioneering studies of the ancient stellar populations in the Milky Way including (1) a large-scale mapping of low-metallicity stars in the Galaxy, (2) first insights into the early evolution of carbon in several satellite dwarf galaxies and implications on the early assembly of the Milky Way, and (3) a detection of an extended “halo" of stars around a tiny (∼3000 stars) relic galaxy; the first direct evidence that primitive galaxies formed in massive, extended dark matter halos, and that even the tiniest galaxies may have had an early merger history. These discoveries were enabled by my development of novel imaging analyses that has led to nearly an order of magnitude improvement in the efficiency of identifying the most metal-poor stars relative to traditional spectroscopic techniques. Such analyses will be readily scalable with upcoming surveys (e.g., LSST) for the next generation of Galactic Archaeology studies.