Draft:First Large Absorption Survey in HI

The First Large Absorption Survey in HI (FLASH) is a large survey project conducted with CSIRO's Australian Square Kilometre Array Pathfinder telescope. FLASH was first proposed in 2011 by Elaine Sadler^[1]. Following the successful completion of the FLASH Pilot Survey^[2], the main survey started in 2021 and was completed in 2026, making it the first of the eight ASKAP Survey Science Projects to be completed^[3], ahead of the scheduled completion date of 2030. However, the data are not yet fully analyzed.

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• Comment: can you find some secondary sources? Astropedian (talk) 15:44, 14 April 2026 (UTC)

The aim of FLASH is to observe clouds of neutral hydrogen in absorption between the Earth and distant radio galaxies. The clouds, which might either be associated with the radio galaxies, or lie along the line of sight by chance, absorb radio waves at the hydrogen line absorption wavelength of 21 cm, but because of their great distance from Earth, they are redshifted to much longer wavelengths. Several hundred clouds are expected to be detected, which would enable studies of the evolution of galaxies, and provide an estimate of the density of hydrogen over cosmic time. The redshift range covered by FLASH is important because it is a period of the history of the Universe, between four and eight billion years ago, over which we have very little information^[4]