An intensity map of hydrogen 21-cm emission at redshift z ≈ 0.8

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Abstract
Observations of 21-cm radio emission by neutral hydrogen at redshifts z ≈ 0.5 to ∼ 2.5 are expected to provide a sensitive probe of cosmic dark energy1,2. This is particularly true around the onset of acceleration at z ≈ 1, where traditional optical cosmology becomes very difficult because of the infrared opacity of the atmosphere. Hitherto, 21-cm emission has been detected3 only to z = 0.24. More distant galaxies generally are too faint for individual detections but it is possible to measure the aggregate emission from many unresolved galaxies in the ‘cosmic web’. Here we report a three-dimensional 21-cm intensity field at z = 0.53 to 1.12. We then co-add neutral-hydrogen (H i) emission from the volumes surrounding about 10,000 galaxies (from the DEEP2 optical galaxy redshift survey4). We detect the aggregate 21-cm glow at a significance of ∼ 4σ.

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