Observational data on matter distribution on galactic and subgalactic scales seem to challenge the currently favored Cold Dark Matter model and possibly indicate the need for a WARM dark matter component. I will present high resolution numerical simulations for Warm Dark Matter (WDM) cosmologies to critically address the issue of WDM can and cannot do to solve/ameliorate problems on small scales. I will also show that on such scales the effects of ordinary matter (baryons) cannot be neglected and must be taken into account when extracting cosmological constraints on the nature of dark matter.

Max Planck Institute Heidelberg