From fueling to quenching star formation across cosmic time

Investigating the mechanisms that regulate star formation (SF) across cosmic time is a complex issue. Most of our knowledge of the cosmic SF history at z > 3 relies on UV surveys, which could miss SF obscured by dust. IR/mm-selections of galaxies are thus a crucial tool for unveiling the total amount of SF. In addition, active galactic nuclei (AGN) are considered to play a crucial role in galaxy evolution. According to models, AGN could be decisive in suppressing SF in massive galaxies. Despite this, some theories predict that AGN could also trigger SF inside outflows. These two mechanisms have been named as “negative” and “positive” AGN feedback and their study is crucial to understand what regulates SF inside galaxies. The aim of this thesis is to investigate the processes that fuel and suppress SF across cosmic time. On one side, we focused on the study of cold gas in the early Universe. We derived the first [C II] luminosity function at z~5 from a mm-selection of galaxies. By using [C II] as a SF rate indicator, we measured the cosmic SF rate density at z~5, which shows a possible excess compared to previous estimates. On the other side, we studied the impact of negative and positive AGN feedback on SF. First, we investigated negative feedback in a massive galaxy at z~2, which will possibly evolve into a passive galaxy. Then, we studied positive feedback in a sample of 70 nearby star-forming galaxies by using UV spectroscopy. We detected in several objects blueshifted stellar absorption, which could be indicative of young stars formed inside outflows. Despite the uncertainties affecting our analysis, studying cold gas and AGN feedback represents a powerful approach to constrain the processes that feed and quench SF across cosmic time.