The Milky Way Halo as a Lyman Limit System: A Sensitive FUSE Survey of Galactic HI

High and Intermediate Velocity Clouds (IVC/HVCs) trace the circumgalactic medium (CGM) of our own Galaxy, and represent a fuel source for future Galactic star formation. Here I will present results from the deepest-to-date HI survey of IVCs and HVCs from archival Far Ultraviolet Spectroscopic Explorer (FUSE) spectra. By performing Voigt-profile fitting simultaneously across the 12 Lyman series transitions visible to FUSE, we are able to probe column densities down to N(HI) ~ 10¹⁴ cm², a nearly 4 dex sensitivity improvement over 21 cm results. We find a near unity covering fraction of both IVCs and HVCs, and evidence for a net inflow of gas. Furthermore, we construct a column density distribution function (CDDF), which for the first time allows us to quantify the Galactic halo mass structure in a metal-independent fashion over 6 orders of magnitude in column density. I will discuss our findings in the context extragalactic surveys, with particular emphasis on the similarities between our Galactic Halo and Lyman Limit Systems observed at higher redshift.