image: Four examples of recently quenched galaxies from the new study. These massive, distant galaxies are observed as they were around 9 billion years ago. Having recently ceased forming stars, they appear highly compact and show faint signs of disturbance, providing clues to the dramatic processes that abruptly shut down their star formation. The main image represents around 1 per cent of the full PRIMER-UDS survey field, observed using the James Webb Space Telescope.
Credit: David Maltby - University of Nottingham
Researchers have shed new light on why some distant galaxies suddenly stop forming stars.
An international team led by astronomers at the University of Nottingham used the James Webb Space Telescope to study a large sample of recently "quenched” galaxies in the distant Universe, observed around 9 billion years ago.
“This was the epoch of peak activity in the Universe, when many of the most massive galaxies we see today were formed,” said Professor Omar Almaini, who led the team behind the new study. "A long-standing problem has been to understand why these galaxies stop forming stars. With Webb we can see detail that was completely hidden before, allowing us to search for clues to what drives this dramatic transformation”.
The recently quenched galaxies were identified from their distinct spectral signatures, which allowed the team to pinpoint systems that had rapidly shut off their star formation. Deep images with Webb at different wavelengths then allow a detailed study of their structure and morphology.
“These galaxies look calm on the surface, but Webb allows us to see the subtle signs of past violence,” said lead author, Dr David Maltby. “The galaxies show clear signs of disturbance, telling us that something dramatic happened to them not long before their star formation shut down, most likely a merger with another galaxy.”
The exceptionally compact nature of these galaxies provides further evidence for their violent origins, as simulations show that collisions between gas-rich galaxies will typically produce very compact remnants. The newly observed signatures of disturbance add further weight to this merger hypothesis.
The team used data from the JWST PRIMER programme, led by Professor James Dunlop at The University of Edinburgh, combined with data from the Ultra-Deep Survey, led by Professor Omar Almaini at the University of Nottingham.
The paper has been published in the Monthly Notices of the Royal Astronomical Society.
Journal
Monthly Notices of the Royal Astronomical Society
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
The multiwavelength structure of post-starburst galaxies at 0.5 < 𝑧 < 3 with JWST PRIMER: compact morphologies and residual disturbances
Article Publication Date
1-Jul-2026