The birth of cosmic complexity
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In this thesis, we construct custom built sub-grid models for the first and second generation of stars, the so-called Population III and II (Pop III/II). Implementing them in the state of the art hydrodynamical/N-body code GIZMO, we explore the legacy left by star formation processes in the first billion years of the Universe. With this powerful tool, we are able to create a virtual universe in a computational box with which we can study, in detail, the processes of star and galaxy formation. This technique is well suited to investigate epochs in cosmic history which are currently still beyond the reach of existing telescopes. More specifically, we examine how Pop III stars, which form from primordial, metal-free gas, leave behind a legacy of metal enrichment, thus setting the stage for the observable second generation of stars and first galaxies. They also begin the process of creating the basic chemical building blocks, the elements beyond H and He, for everything we know. We have found that Pop III star formation continues at a high rate down to ~750 million years after the Big Bang. While we find that Pop III dominated galaxies are likely to remain beyond our view, the inferred high rate of star formation could lead to the detection of the theorized pair-instability supernova (PISN), thought to be the consequence of the death of high mass Pop III stars. We also find that the metal enrichment provided by the death of Pop III stars is insufficient to significantly redden the spectrum from the first galaxies, but that it is critical to determining where and when the second generation of stars forms. Finally, we are able to quantify the number density of galaxies with specific brightness to determine that the number of galaxies at low luminosities assumes a near-plateau value. This is in contrast to the current paradigm, where it is assumed that this number will continue to grow along a power-law track. With the launch of the next generation James Webb Space Telescope (JWST) on the horizon, this thesis provides key constraints for future frontier observations.