The gas and dust cycle in the first galaxies

Investigating the evolution of high-redshift galaxies is a crucial field of research in modern astronomy. In fact, distant galaxies offer us a glimpse back into cosmic history of our Universe, allowing us to study the early stages of structure formation and evolution. In this thesis, I explore the intricate landscape of high-redshift galaxy evolution, focusing on the physical properties of z > 4 galaxies and their interaction with the surrounding environment. During the last decades, our understanding of the primordial Universe has been revolutionized thanks to technological advancements and the availability of advanced instrumentation such as HST, ALMA, and, more recently, JWST. In particular, the combination of multi-band observations from the above facilities has provided us with a more comprehensive picture of the evolution of high-redshift galaxies, not only allowing us to study in detail their physical integrated properties, but also their star formation and interaction with the surrounding environment. In fact, galaxies can be considered as complex ecosystems whose evolution is governed by interplay of physical mechanisms involving both their Interstellar and Circumgalactic Media. Key processes such as the accretion of external cold gas, star formation, chemical enrichment, gas recycling in the ISM and the ejection of processed material through starburst/quasar-driven outflows constitute the building blocks of the so called "baryon cycle" governing the evolution of galaxies. On the other hand, models and simulations are of paramount importance to lead our interpretation of the observations from telescopes. In fact, cosmological simulations play a pivotal role in helping us understating the aforementioned baryon cycle, its role in galaxy evolution and the properties of our Universe at different epochs. In this thesis, I employ both observations and simulations, highlighting their interplay in exploring and interpreting the primordial Universe. Generally, simulations have assisted us in predicting potential scenarios of galaxy evolution by reproducing various feedback mechanisms and by interpreting observational data. Conversely, observations have been of vital importance for validating our models and providing evidence of the phenomena characterising the early Universe. Through this research work, I aim at contributing to the understanding of high-redshift galaxy evolution, providing new insights into the fundamental processes that have shaped the primordial Universe and influenced its evolution to the present day.