The clumpy fraction of galaxies at z=1-9 with JADES: evidence for a mass-dependent transition in clump origin

We measure the fraction of clumpy galaxies (f clumpy) over the redshift range z=1-9 and stellar masses 10(M/ M) at least 8 using JWST/NIRCam imaging from JADES. We define clumps as compact off-centre surface-brightness peaks with characteristic sizes of a few hundred parsecs, and develop a dendrogram-based clump-finding method with astrodendro to identify them directly in rest-frame UV, blue, and optical images. Clump-detection completeness is quantified through injection-recovery simulations, which we use to define (M, z)-dependent 50 per cent completeness-limited f clumpy, alongside a probability-weighted completeness-corrected statistic for comparison. For the full sample, the blue and optical f clumpy reach about55 per cent at z about1-2 and decline to 5 per cent by z about8-9, while the UV fraction remains higher at about12 per cent. At z about1-2, f clumpy increases strongly with stellar mass, from about35 per cent in the lowest-mass bin to about85 per cent at 10(M/ M) at least10. Most clumpy galaxies host only one or two robustly detected off-centre clumps, while higher-multiplicity systems occur preferentially in massive, strongly star-forming galaxies at low to intermediate redshift. Comparison with major merger rates suggests that mergers could account for a substantial fraction of low-mass (10(M/ M)<8.5), high-redshift clumpy galaxies, while the observed fractions in more massive systems (10(M/ M)>9) require an additional in situ clump-formation channel. Our results are consistent with a transition from merger-dominated clumpy morphologies at early times and low stellar masses to an increasing contribution from in situ clump-formation channels, such as disc instabilities, in more massive systems.