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QuaStar: A first look at the Milky Way’s Hidden CGM

Published onJun 01, 2020
QuaStar: A first look at the Milky Way’s Hidden CGM

The Milky Way's circumgalactic medium (CGM) is both the best studied galactic ecosystem and the most biased. Hundreds of sightlines toward quasars have been observed with ultraviolet spectrographs revealing numerous absorption lines across a large range of ions surrounding our Galaxy. While many high-velocity absorbers have been discovered, low-velocity absorbers are occluded by the ISM. Observations of neutral gas have shown that low-velocity halo clouds exist, and simulations show that about half of the Galactic CGM may be obscured at low velocity. QuaStar, our Cycle 26 Large HST/COS program, seeks to solve this problem and reveal the unbiased CGM for the first time. By observing absorption lines towards halo stars near lines of sight with archival COS QSO spectra, we can inspect the absorption caused by the CGM alone in the difference. We will present early results from the program, and provide the first unbiased glimpse of our CGM.

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