Ja n 19 98 Formation of Disk Galaxies : Feedback and the Angular Momentum problem

Tree-SPH, numerical simulations of disk galaxy formation in a cosmological context are presented. For the " passive " variant of such simulations, i.e. simulations not including the effects of stellar feedback processes, it is found that the resulting disk " galaxies " are far too small and specific angular momentum deficient, by about a factor of 8 in size and about a factor of 20 in specific angular momentum, compared to real disk galaxies. Two routes towards solving this disk galaxy size and angular momentum problem are discussed: 1) Stellar feedback processes in cold and dense, proto-galactic gas clouds and 2) Relatively early reheating and reionization of the Universe. Test simulations are presented, indicating that the first approach is a likely solution to the problem, whereas the second holds less promise, at least for large (Milky Way sized) disk galaxies.