James Webb Space Telescope images from JADES reveal a strong mass dependence in the fraction of galaxies with bright off-centre clumps. A new preprint compares ultraviolet, blue and optical structures across a wide redshift range. The results point to different mixtures of merger-related and locally formed clumps in different galaxy populations.
A new arXiv preprint uses the James Webb Space Telescope’s JADES deep extragalactic survey to count galaxies containing compact, bright structures away from their centres. These clumps have characteristic sizes of a few hundred parsecs. The sample’s stellar-mass floor is 100 million solar masses. Its redshift range extends from 1 to 9.[1]
The team searched ultraviolet, blue and optical images in the galaxies’ own reference frames. It inserted simulated structures and checked their recovery to measure missed detections. Around redshifts 1–2, the clumpy fraction rose from approximately 35 percent in the lowest-mass group to approximately 85 percent among the most massive. In most clumpy galaxies, robust detection was limited to one or two structures away from the centre.[1]
In the full sample, blue and optical clumpy fractions reached approximately 55 percent around redshifts 1–2. At redshifts 8–9, they fell below about 5 percent, while the ultraviolet fraction remained around 12 percent.[1]
Comparison with major-merger rates points to an important role for mergers in low-mass, distant systems. For galaxies with greater stellar mass, the authors also point to locally formed clumps, potentially linked to disc instabilities. The population comparison does not trace each individual clump’s origin.[1]
