Gas processes in galaxy formation

This work consists of two parts. The first part investigates the effect of an assumption in Nulsen and Fabians semi-analytical model for galaxy formation. They assume that star formation in low mass systems is regulated by supernova explosions which shut it off by expelling the rest of the gas from the galaxy. The sensitivity of the model to their assumption that this happens when the energy released by supernovae exactly equals the binding energy of the remaining gas is tested here. It is found that the outcomes of the model are insensitive to this assumption, with the exception of the ratio of elliptical to spiral galaxies, which is also sensitive to a number of other model parameters. It is concluded that their assumption has a relatively minor influence on the results of their model