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The 21cm neutral hydrogen (HI) spectral line can be detected from
galaxies in the nearby universe, but is too faint to detect from
individual galaxies at even moderate redshifts. However,
three-dimensional intensity mapping allows the study of large-scale
structure directly by detecting the aggregate emission from many
galaxies in a large volume. Li et al. report results from a neutral
hydrogen (HI) intensity mapping survey conducted with a Phased Array
Feed (PAF) on the Parkes telescope in 2016. The full survey was
designed to cover 380 square degrees over the redshift range 0.3 < z <
1 in four fields covered by the WiggleZ Dark Energy Survey. The image
above shows the Parkes PAF intensity mapping survey coverage (red),
overlaid on the WiggleZ dark energy survey footprint (blue).
The paper
reports the detection of a cross-correlation signal between the
HI intensity maps and the WiggleZ redshift data.
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