Cosmological Small-Scale Structure: The Formation of The First Stars, Galaxies, and Globular Clusters.

Abstract

Though the majority of stars now live in large, massive galaxies, understanding the origins of all galaxies ab initio requires fully comprehensive modeling of cosmological small-scale structure. In this thesis, I present a theoretical study of galaxy formation that focuses on low-mass halos. These halos are the sites for the formation of the first stars and galaxies at high redshift, and they also they play a role in forming massive globular clusters in the outskirts of the Milky Way.

I develop a physical model for Population III star formation and feedback, and implemented it into the Eulerian hydrodynamic Adaptive Refinement Tree (ART) code. With this code, I designed, performed, and analyzed a suite of cosmological simulations that resolve the formation of the first stars and galaxies. I quantify the extent of the dynamical signatures Population III stars can impart on their host galaxies, and derive a characteristic mass threshold, 3 million solar masses, above which Population III stellar feedback is no longer dynamically significant over significant cosmic timescales.

I measure the duration of time for which Population III stars are the dominant drivers of feedback in the universe. Due to the inhomogeneous and patchy enrichment of the intergalactic medium, I find Population III stars can continue forming in some environments well after the end of the cosmic dark ages. However, in individual galaxies that are sufficiently massive, Population II star formation takes over soon after the efficient enrichment by a single pair-instability supernova. Globally, Population II is dominant at cosmic epochs later than redshift (z ~ 15).

Finally, I construct a semi-analytical model for globular cluster formation in hierarchical cosmology, and use it to demonstrate a plausible scenario for the formation of the Milky Way’s globular cluster system. My model is successful in matching both the metallicity and mass distributions of galactic globular clusters. In particular, the bimodal nature of the metallicity distribution is for the first time explained by the single mechanism of the merging of protogalaxies.