The formation of galaxies

The basic framework for a successful theory of large-scale structure is provided by the cold dark matter hypothesis. It works surprisingly well, and has led to predictions, such as the clustering of gas and galaxies as a function of redshift, that have been observationally tested. However, with regard to galaxy formation, the model has made limited progress. Attempts have been made to incorporate analytical parametrisations of star formation and gas cooling into the numerical simulations. While these so-called semi-analytical models have had some success, little more emerges from the models than is inserted. A robust testing of parameters is not feasible. Star formation is a complex process that is poorly understood in our local vicinity. It is not surprising that we have failed to develop a satisfactory model of star formation in protogalaxies, where conditions are likely to be very different from those at the current epoch. Modelling of galaxy formation must include the complexities of star formation in a multiphase interstellar medium, well beyond the reach of current three-dimensional formulations, and incorporate the astrophysical uncertainties of stellar feedback processes as well as the physical uncertainties of compressible and possibly, magnetohydrodynamical, turbulence. (C) 2001 Elsevier Science BN. All rights reserved.