The Principal Investigator and his collaborators will investigate a promising alternative to popular cold dark matter models of galaxy formation, a model in which the medium around low-mass halos is preheated by the formation of pancakes (sheet-like cosmic structures). Cold dark matter models in general predict too many low-mass dark matter halos compared to the observed number density of galaxies. A preliminary analysis suggests that the formation of massive pancakes may precede that of low-mass halos and heat the intergalactic medium, and demonstrates that such a process can have a significant effect on the number of dwarf galaxies. N-body simulations and analytical models will be used to study in detail the relationship between halo progenitors and the pancakes within which the halos form. Full hydrodynamical simulations will be carried out to quantify directly preheating by gravitational pancaking and its effect on gas accretion into galaxy halos. The results will provide new avenues for interpreting observations from major observational programs, both ground- and space based. The proposed projects also provide multidisciplinary training opportunities for graduate students, and help promote public interest in programs supported by the National Science Foundation and other funding agencies.
