Abstract

When galaxies and stars began to form, they released ionizing radiation into the intergalactic medium which resulted in its reionization over the course of the first billion years. This ionizing radiation was dominated by massive stars. Reionization was inhomogeneous in space and time, reflecting the clustering of galaxies, and the inhomogeneous density field into which their radiation caused ionization fronts to propagate, resulting in different arrival times of those ionization fronts at different locations. The same massive stars that released this ionizing radiation also formed and released heavy elements when they exploded as supernovae, enriching the metal-free primordial gas both inside galaxies and outside them, by driving winds into the surrounding IGM. Just as reionization was inhomogeneous, so must the rise of metallicity during the EoR have been. The theory of this inhomogeneous rise of metallicity is, therefore, inseparable from the theory of reionization, and predicting its observable consequences requires us to model both processes, together, self-consistently. Towards this end, we have analyzed the results of the latest state-of-the-art radiation-hydro simulation of fully-coupled galaxy formation and reionization by The Cosmic Dawn (“CoDa”) Project, CoDa III, including its self-consistent tracking of the inhomogeneous rise of metallicity thru the end of the EoR and beyond, down to z = 4.6. We present these CoDa III results for the inhomogeneous evolution of metallicity in the universe. We quantify the global metal-enrichment process while comparing this to the global reionization history. We also study the statistics of the growth of metal-enriched bubbles and the "metallicity (free) gaps", an analogy of neutral hydrogen "dark gaps" in Lya forest observation, and suggest the metallicity gap statistics as a new observational diagnostic of the inhomogeneous rise of metallicity and reionization.