Diagnosing the ISM of galaxies and energetic processes in a cosmological context

The evolution and formation of galaxies is one of the most interesting topics of research in astronomy. In this thesis, I focus on the interstellar medium (ISM) of galaxies and its energetic processes in a cosmological context. First, I dig into the ISM and its phases, which are the main point of interaction between the different gas components within a galaxy. Second, I look at the effects of intense star formation activity and the active galactic nuclei (AGN), which are crucial in the evolution of galaxies. I diagnose the ISM of galaxies using far-infrared (FIR) emission lines, which trace the cooling and heating of gas, to disentangle the ISM phases and analyse their dependence on other properties of the galaxies. Using cosmological simulations I reproduce the expected emissions from FIR lines at different cosmic times and estimate how the ISM phases change during the formation and evolution of galaxies. In addition, I examine the relationship between star-formation rates (SFR) and fractional AGN contributions in galaxies with different activity types to understand their importance in other observed physical parameters. Both SFR and AGN fractional contributions cause large differences in the ISM within a galaxy which are important for the accretion of mass into its supermassive black hole. The results of this thesis show that it is possible to use computational tools to understand the evolution of gas processes at different cosmic times and to estimate physical parameters that help to classify galaxies due to their energetic activity.