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

Presentation #508.04 in the session “AGN and Quasars 5”.

Published onJan 11, 2021
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.


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