The Infall of Gas onto the Galactic Disk

Ongoing accretion of low-metallicity gas onto the disk is a natural prediction of semi-analytical Galactic chemical evolution models. This star formation fuel ameliorates the overproduction of metal-poor Gand K-dwarfs in the solar neighbourhood which otherwise plague socalled “closed-box” models of Galaxy evolution. Do High-Velocity Clouds (HVCs) represent the source of this necessary fuel? We know that HVCs provide an important clue as to the processes governing galaxy formation and evolution what is less clear is whether their role lies more closely aligned with cosmology (as relics of the Local Group’s formation) or star formation (as tidal debris from nearby disrupted dwarfs, or the waste byproducts of disk supernova-driven winds). I provide a summary of recent speculations as to the origins of HVCs, and highlight several future projects which will lead to a deeper understanding of the role they play in galaxy evolution.