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


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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Figure 1: Spectra of DEEP2 Field-4.
Figure 2: The cross-correlation between the DEEP2 density field and GBT H  i brightness temperature.


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We are grateful to the GBT support staff, in particular T. Minter and P. Ruffle, for their help with the observation. We thank K. Blagrave, O. Doré, P. McDonald, J. Sievers, K. Sigurdson and R. Yen for discussions. We acknowledge financial support by NSERC, NSF and NRAO. The NRAO is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc.

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T.-C.C. and U.-L.P. analysed and interpreted the data. K.B. conducted the remote observations. J.B.P. was in charge of manuscript preparation. All authors were present at the telescope for the on-site observations and contributed to the writing of the manuscript and Supplementary Information.

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Correspondence to Tzu-Ching Chang.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Information comprising Observation details, Radio Frequency Interference (RFI) Removal, Calibration, Foreground (Continuum) Removal, Cross Correlation, Auto Correlation, Error Estimation and Null Tests, Adjustment for 21-cm signal loss, Volume and Mass Scales and Supplementary References. (PDF 221 kb)

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Chang, TC., Pen, UL., Bandura, K. et al. An intensity map of hydrogen 21-cm emission at redshift z ≈ 0.8. Nature 466, 463–465 (2010).

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