MeerKAT measures large-scale clustering of cosmic hydrogen

The MeerKLASS Collaboration, working with data from the South African MeerKAT radio telescope, has reported its first measurement of the large-scale clustering of neutral hydrogen in the distant Universe, according to sarao.ac.za. sarao.ac.za The distribution of the gas follows the structure of the cosmic web. The paper has been accepted for publication in Monthly Notices of the Royal Astronomical Society. sarao.ac.za

Mapping this structure on the largest scales has been a goal of cosmology for decades. The team describes the result as the product of a decade of preparation and work by researchers in seven countries on three continents. sarao.ac.za

21-cm intensity mapping with MeerKAT

The measurement uses 21-cm intensity mapping. The technique combines hydrogen emission from many galaxies within large patches of sky and captures the collective pattern even when individual galaxies cannot be distinguished. sarao.ac.za In principle it allows a large 3D map of the Universe to be built.

The team analysed MeerKAT observations across approximately 250 square degrees of sky, roughly the area of 1250 full moons. The detected signal originated about 4.5 billion years ago, when the Universe was a little older than 9 billion years. sarao.ac.za

The survey relied on a new observing mode. Instead of combining its 64 dishes into a single interferometer, the team operated each dish as an independent telescope, trading angular resolution for survey speed. This produced many independent maps from different dishes and observing times. Real cosmic structure recurs across them, while differing instrumental effects are suppressed. sarao.ac.za

Foregrounds, systematics and next steps

The main difficulty was removing astrophysical foreground emission around 10,000 times stronger than the hydrogen signal. The analysis built 4 independent datasets to minimise observational effects and contamination, and measured the clustering as a function of scale through the power spectrum. The signal stands more than six times above the statistical noise, with a signal-to-noise ratio of 6.2. sarao.ac.za

"This is a milestone in establishing 21-cm intensity mapping as a novel tool for cosmology," said Prof. Mário Santos of the University of the Western Cape, Principal Investigator of MeerKLASS. sarao.ac.za

Since 2023 the collaboration has continued collecting data at lower radio frequencies, which correspond to hydrogen emission from even more distant past times. MeerKLASS expects eventually to map a volume of the Universe over a thousand times larger than the one used for this detection. According to the team, this would allow study of the growth of cosmic structure and the expansion of the Universe, and help test models of gravity and dark energy. sarao.ac.za

MeerKAT telescope maps neutral hydrogen clustering over 250 square degrees at signal-to-noise 6.2

21-cm intensity mapping with MeerKAT

Foregrounds, systematics and next steps

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