The first known measurements of atomic hydrogen emissions from a group of galaxies at an average redshift of one is reported in Nature this week. The observations, made by the upgraded Giant Metrewave Radio Telescope in India, could help in our understanding of star formation in galaxies.
Star formation involves gas infall onto galaxies to form atomic hydrogen, which is then converted into its molecular state (H2) before being used in the formation of stars. Atomic hydrogen has been detected from galaxies up to a redshift of 0.4, but it has so far been impossible to measure for galaxies at higher redshifts with existing telescopes. Redshift, a measure of how much the wavelength of light from astronomical objects increases as they move farther away, can be used to measure distances to galaxies. The lack of measurements from more distant galaxies limits our understanding of galaxy evolution.
Aditya Chowdhury, Nissim Kanekar and colleagues conducted a search for atomic hydrogen emissions from 7,653 star-forming galaxies at redshifts of 0.74–1.45. They found that the average total mass of atomic hydrogen was comparable to — and possibly larger than — the average mass of stars, providing plenty of fuel for star formation. When estimating the star-formation rate, they found that the mass of atomic hydrogen observed could fuel star formation for only 1–2 billion years more. This suggests that gas infall onto galaxies at a redshift of one may have been insufficient to sustain high star-formation rates.
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