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4rd of September 2020
HI intensity mapping with a PAF on Parkes
by Li et al.
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 initial results presented by Li et al. target a narrow redshift range of 0.73 < z < 0.78 where the effect of radio frequency interference (RFI) was less problematic. The image above shows the the rms noise level in the gridded data cubes for each field over the frequency range considered in the paper. The frequency channels in red were masked as they were affected by RFI. The frequency channels in blue correspond to the final data cube. The paper reports the detection of a cross-correlation signal between the HI intensity maps and WiggleZ redshift data. A future Parkes cryogenic PAF is expected to detect the cross-correlation signal with higher accuracy than previously possible and allow measurement of the cosmic HI density up to redshifts of ~1.

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