Biased galaxy formation in a universe dominated by cold dark matter

Abstract

The hypothesis that galaxies form from rare fluctuations in a universe dominated by cold, weakly interacting dark matter is shown to be in reasonable accord with most observed properties of the distribution of galaxies. The role of mass density fluctuations around the mean value on various mass scales is considered. The mass distribution of galaxies and the cluster multiplicity function are calculated for a model in which galaxy formation is biased by the assumption that galaxies form only at a redshift in excess of three. The fraction of gaseous matter that, at the epoch of galaxy formation, has not already collapsed on smaller scales is calculated. On scales which have turned around recently, gas infall to dark-matter potential wells is shown to result in observable diffuse X-ray emission. The galaxy distribution on these scales is found to be highly anisotropic, building up into large-scale filaments or pancakes.