The formation and evolution of the Milky Way from the accretion of high-velocity clouds

We review the arguments that the HVCs are extragalactic and represent the leftover building blocks of the Local Group. The primary evidence comes from the lack of interaction of a large HVC with the Galactic disk, the mean velocity and velocity dispersion of the HVC ensemble and simulations that reproduce the spatial distribution and kinematics of the HVCs, The HVCs are shown to be inconsistent with either a Galactic origin, such as a Galactic fountain, or tidal debris from:an interaction: with a Milky Way satellite. We also discuss recent independent evidence in favor of a Local Group origin and review the: predictions of our model. We speculate that the HVCs are local analogues of the Ly alpha absorbers, and that the Milky Way may have an X-ray halo.