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Colloquium - The First Large Absorption Survey in HI: A history of cold gas in the Universe

Submitter: James Allison
Description: The First Large Absorption Survey in HI with the Australian SKA Pathfinder (ASKAP) will provide a unique perspective on the cool (< 1000 K) gas that fuels star formation and black hole growth in galaxies throughout cosmic history. By detecting the HI 21-cm line in absorption towards distant radio-loud active galactic nuclei (AGN), we will use ASKAP to construct a census of neutral gas in intervening galaxies over the past 8 billion years. I will discuss a recent paper in which I proposed a method for measuring the fraction of cold-phase atomic hydrogen using a statistical approach based on the number of expected detections. I will also present early science results from ASKAP, which have successfully demonstrated the feasibility of carrying out such an all-sky survey.

The image shows how the density of high-column density HI systems vary as a function of redshift, including early ASKAP science results from 21-cm line absorption with ASKAP. The ASKAP FLASH survey will provide strong constraints on both the abundance and physical conditions of HI in galaxies at redshifts currently only achievable with space-borne telescopes.
Copyright: Colloquium
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