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 \ 4$\sigma$.
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