Intensity Mapping of Neutral Hydrogen in Cosmology
Summary
The intensity mapping of neutral hydrogen employs measurement of the unresolved 21 cm emission across wide areas of the sky to trace the large-scale distribution of matter. Rather than detecting individual galaxies, this technique records fluctuations in the aggregate brightness temperature of H i gas as a function of frequency, yielding three-dimensional tomographic maps. By capturing the redshifted 21 cm line from the post-reionisation era to the present day, intensity mapping enables reconstruction of the matter power spectrum on ultra-large scales. It provides independent measurements of baryon acoustic oscillations and the growth rate of cosmic structure, thereby constraining dark energy, neutrino masses and modifications to gravity. The rapid survey speed and sensitivity to low surface-brightness emission complement optical and spectroscopic galaxy surveys, while forthcoming instruments such as the Square Kilometre Array will enhance sensitivity, sky coverage and redshift reach. Successful cosmological inference demands robust foreground mitigation and precise calibration strategies to isolate the faint H i signal from bright Galactic and extragalactic contaminants.
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Intensity Mapping of Neutral Hydrogen in Cosmology publication trend
The graph below shows the total number of articles in intensity mapping of neutral hydrogen in cosmology across all publications each year (not limited to Nature Index journals).
Technical terms
Neutral Hydrogen (H i): Atomic hydrogen in its ground state, traced via the 21 cm hyperfine transition.
21 centimetre line: Radio emission at a rest frequency of 1.420 GHz arising from the spin-flip transition of neutral hydrogen, redshifted by cosmic expansion.
Intensity Mapping: A survey technique that measures the integrated emission from unresolved sources to map large-scale structure without detecting individual objects.
Power Spectrum: The statistical measure of fluctuation amplitude as a function of spatial scale, used to characterise matter clustering.
Foreground Contamination: Bright Galactic and extragalactic radio emission that must be modelled and removed to reveal the faint cosmological H i signal.
References
- FAST Drift Scan Survey for Hi Intensity Mapping: I. Preliminary Data Analysis. The Astrophysical Journal (2023).
- The foreground transfer function for H i intensity mapping signal reconstruction: MeerKLASS and precision cosmology applications. Monthly Notices of the Royal Astronomical Society (2023).
- H i intensity mapping with MeerKAT: power spectrum detection in cross-correlation with WiggleZ galaxies. Monthly Notices of the Royal Astronomical Society (2022).
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