State of the Art Chemodynamical Simulations of the First Metals in the Universe

We live in a Universe filled with an infinite variety of shapes and structures: stars, planets, mountains, clouds, oceans, flowers,—and humans, to name a few. One fascinating truth connects them all: everything is made from the same basic building blocks — atoms. These atoms, composed of subatomic particles, interact to form molecules, the foundation of life as we know it. Yet, perhaps even more remarkable is that many of the atoms within us were forged billions of years ago in the hearts of ancient stars. This thesis is dedicated to understanding the origin of these first elements and how they came to be distributed throughout the cosmos. To trace the origin of the elements, we must understand how galaxies became chemically enriched in the early Universe. This process, known as chemical enrichment, depends on a complex combination of physical mechanisms, such as stellar nucleosynthesis, gas inflows and outflows, star formation, and most importantly, feedback from stars and active galactic nuclei (AGNs). Among these, stellar feedback, which refers to the energy released from supernova explosions at the end of their lives, remains one of the most uncertain processes in galaxy formation theory. In the first part of this thesis, I focus on constraining its role by implementing and comparing four supernova feedback models: thermal, stochastic, kinetic, and mechanical in state-of-the-art cosmological hydrodynamical simulations. To test these models, we use two key observational diagnostics: the mass–metallicity relation (MZR) and metallicity gradients, for both stars and gas, across a wide range of galaxy masses and redshifts. These chemical signatures act as fossil records of how efficiently galaxies formed stars, retained metals, and redistributed them over cosmic time. Our analysis shows that mechanical feedback best reproduces the observed MZR and metallicity gradients within galaxies up to redshift � = 5, providing the most realistic balance between star formation regulation and metal retention. Having constrained stellar feedback using recent observations, we return to our core question: how were the first elements produced? Observational data from the James Webb Space Telescope (JWST) has revealed surprisingly high elemental abundance ratios in some of the earliest observed galaxies, patterns that were not expected to appear so early in cosmic history. These findings challenge existing theories and raise important questions about the nature of the first stars and galaxies. Several hypotheses have been proposed to explain these enhanced ratios, including enrichment by very massive stars or massive rotating Wolf-Rayet (WR) stars. To address this, we take the novel step of simulating these scenarios in a fully cosmological context. For the first time, we implement nucleosynthetic yields from rotating Population III stars, specifically, WR stars up to 120 M⊙, faint supernovae, and rotating Pair-Instability Supernovae (PISNe) up to 300 M⊙. These yields are incorporated self-consistently into our simulations to study their impact on the chemical evolution of early galaxies. My results suggest that rotating WR stars are the most likely source of the enhanced nitrogen and other elemental abundances seen in high-redshift galaxies such as GN-z11. This thesis offers a new perspective on the chemical evolution of the Universe by combining detailed feedback modeling with early Universe nucleosynthesis in a cosmological framework. From constraining feedback models using present-day and high-redshift observations, to exploring the fingerprints of the first stars, this work brings us closer to understanding how the elements that make up our world — and ourselves—came into being.