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The ecosystem of a galaxy is driven by the balance between outflows from the star-forming disk and infall due to interactions with nearby galaxies and the surrounding intergalactic medium. In the case of the Milky Way, the number of stars being born has long been at odds with the detected hydrogen fuel in the halo, raising the important question of where the Milky Way predominantly gets its gas and its relationship to the surrounding halo. I will present my work using the Parkes Galactic All Sky Survey in HI to catalogue and study anomalous velocity hydrogen in the Galactic halo. As part of this work, we combined our data with a sensitive northern-sky survey to reveal a halo hidden from the view of most large-scale surveys, changing our understanding of the neutral gaseous halo. We are currently following up this result with SWISH, a deep sightline survey using Parkes. While the 21cm emission line is a powerful tracer of neutral atomic hydrogen (HI) in nearby galaxies like the Milky Way, it is too weak to be observable in the distant universe with current telescopes. In contrast, 21cm absorption can be observed in individual galaxies over a wide range in redshift and provides insight into the cosmic evolution of gas content in galaxies. As part of the First Large Absorption Survey in HI (FLASH), we aim to study neutral gas across the Universe to z = 1, in order to understand the relationship between supermassive black holes and the gas reservoir of their host galaxies. I will give an overview of FLASH and the observations carried out with ASKAP so far, my specific focus on the relationship between soft X-ray absorption and HI absorption near the cores of active galaxies and our future work as part of the SEAFOG radio/X-ray collaboration. |
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