... (ATCA)¹

The Australia Telescope Compact Array is part of the Australia Telescope National Facility (ATNF), a division of the Commonwealth Scientific and Industrial Research Organisation (CSIRO).

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... (VLA)²

The Very Large Array is a facility of The Very Large Array is a facility of the National Radio Astronomy Observatory (NRAO), which is operated by Associated Universities, Inc., under Cooperative agreement with the National Science Foundation.

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... absorption³

HI absorption studies are used in many other areas of astronomy, e.g., in Galactic work to determine distances for pulsars, HII regions, supernova remnants, etc., and spin temperatures of the interstellar medium (ISM). In extragalactic astronomy, HI and Lyman$\alpha$ absorption line measurements against bright quasars can help to uncover the amount and properties of the gas in the line of sight, often out to very large distances corresponding to the early stages of galaxy evolution.

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