South Africa’s MeerKAT telescope detects neutral hydrogen in galaxies more than 4 billion light-years away — and tests a key law of galaxy dynamics
(Left) Images of the HI emission centred on the optical galaxies shown on the Right panels.
The Central panels show the emission line associated with atomic hydrogen which has been redshifted, due to the expansion of the Universe, to the frequencies shown on the horizontal axes.
An international team using the MeerKAT radio telescope, operated by the National Research Foundation’s South African Radio Astronomy Observatory (SARAO), has detected neutral hydrogen gas in individual galaxies more than 4 billion light-years away.
They identified 11 galaxies containing a faint 21-cm “signal” of hydrogen, including one at a redshift of z = 0.3841—the most distant interferometric detection of its kind. The findings also provide the first-ever test of a key law of galaxy dynamics traced by neutral hydrogen (HI), the baryonic Tully–Fisher relation (bTFR), at these distances.
“This is really exciting as it really paves the way to trace the dark matter in galaxies over a significant fraction of cosmic time ,” said Professor Matt Jarvis (University of Oxford / University of the Western Cape), lead author of the study. “MeerKAT has once again shown it is the world’s premier telescope for exploring the distant hydrogen universe.”
Why it matters
- Historic milestone: First interferometric detections of hydrogen from individual galaxies this far back in cosmic history.
- Future science: The result previews the transformational discoveries expected from the Square Kilometre Array (SKA), now under construction in South Africa and Australia.
About the study
The detections come from the MIGHTEE-H I survey, which used precise galaxy positions from the Dark Energy Spectroscopic Instrument (DESI) to guide MeerKAT’s observations. Instead of a blind search, astronomers targeted known galaxies in the COSMOS field, dramatically boosting detection success.
Paper
“MIGHTEE-H I: The direct detection of neutral hydrogen in galaxies at z>0.25”
M. J. Jarvis, M. N. Tudorache, I. Heywood, A. A. Ponomareva, … O. I. Wong (2025). Preprint on arXiv.2506.11935.
Link here
https://arxiv.org/pdf/2506.11935
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