Numerical Simulations of Galaxy Formation

An overview over the current status of modeling galaxies by means of numerical simulations is given. After a short description of how galaxies form in hierarchically clustering scenarios, success and failures of current simulations are demonstrated using three different applications: the morphology of present day galaxies; the appearance of high redshift galaxies; and the nature of the Ly-α forest and metal absorption lines. It is shown that current simulations can qualitatively account for many observed features of galaxies. However, the objects which form in these simulations suffer from a strong overcooling problem. Star formation and feedback processes are likely to be indispensable ingredients for a realistic description even of the most basic parameters of a galaxy. The progenitors of todays galaxies are expected to be highly irregular and concentrated, as supported by recent observations. Though they exhibit a velocity dispersion similar to present day L >∼ L ∗ galaxies, they may be much less massive. The filamentary distribution of the gas provides a natural explanation for Ly-α and metal absorption systems. Furthermore, numerical simulations can be used to avoid misinterpretations of observed data and are able to alleviate some apparent contradictions in the size estimates of Ly-α absorption systems.