Galaxy Formation, Cold Dark Matter Substructure, and GLAST

Many of today's "observables" within the Milky Way and nearby galaxies relate to events occurring at early cosmic epochs. It is a clear, unique prediction of LCDM that galaxies are embedded in massive, extended dark matter halos teeming with self-bound substructure or "subhalos." I will discuss how the amount and spatial distribution of subhalos around their host provide unique information and clues on the galaxy assembly process during and after the reionization era, and on the nature of the dark matter. While most dark matter subhalos in the Milky Way appear to have no optically luminous counterparts, the substructure population has been shown to be detectable via flux ratio anomalies in strong gravitational lenses, through its effects on stellar streams, or via gamma-rays from dark matter annihilation in their cores. Surviving nearby subhalos are among the brightest sources of annihilation radiation and could be observed by GLAST.