Cold dark matter, the structure of galactic haloes and the origin of the Hubble sequence

Abstract

A popular theory for galaxy formation holds that the Universe is dominated by exotic particles such as axions, photinos or gravitinos (collectively known as cold dark matter, CDM)1-3. This hypothesis can reconcile the aesthetically pleasing idea of a flat universe with the standard theory of primordial nucleosynthesis and with upper limits on anisotropies in the cosmic microwave background4-6. The resulting model is consistent with the observed dynamics of galaxy clustering only if galaxy formation is biased towards high-density regions7,8. We have shown that such a biased model successfully matches the distribution of galaxies on megaparsec (Mpc) scales9. If it is to be viable, it must also account for the structure of individual galaxies and their haloes. Here we describe a simulation of a flat CDM universe which can resolve structures of comparable scale to the luminous parts of galaxies. We find that such a universe produces objects with the abundance and characteristic properties inferred for galaxy haloes. Our results imply that merging plays an important part in galaxy formation and suggest a possible explanation for the Hubble sequence. © 1985 Nature Publishing Group.