The Fraction of Clumpy Galaxies in JADES Over $2<z<9$

Abstract

High-redshift galaxies exhibit compact regions of intense star formation, known as ``clumps,'' which are conspicuous in the rest-frame ultraviolet. Studying them can shed light on how they form and evolve and inform theoretical models of galaxy evolution. We examine the evolution of clumpy galaxies with redshift and stellar mass over $2<z<9$ with James Webb Space Telescope (JWST) imaging from the JWST Advanced Extragalactic Survey (JADES). Off-center clumps are detected in the rest-frame near-ultraviolet (NUV) using similar techniques to those in earlier studies based on Hubble Space Telescope (HST) images. This is done for a sample of 9,121 star-forming galaxies with stellar masses $\log \left(M_{\star }/M_{\odot }\right)\ge 8$. The fraction of clumpy galaxies, $f_{\mathrm{clumpy}}$, increases from $\sim 10\%$ at $z\sim 7.75$ to $\sim 70\%$ at $z\sim 2.75$ at $\log \left(M_{\star }/M_{\odot }\right)\ge 9$. Our $f_{\mathrm{clumpy}}$ values are generally higher at fixed redshift and increase faster with decreasing redshift than what studies based on HST data found, which we attribute largely to the higher sensitivity of JWST. $f_{\mathrm{clumpy}}$ correlates with stellar mass. Our $f_{\mathrm{clumpy}}$ measurements are compared with those from simulations as well as other observations. At low redshifts ($z\lesssim 5.75$) and intermediate-to-high stellar masses ($\log \left(M_{\star }/M_{\odot }\right)\ge 9$), our results suggest gas fragmentation due to violent disk instabilities to be the dominant mechanism for forming clumps. At high redshifts and intermediate stellar masses, compression of gas during mergers appears to dominate.

Accepted for publication in ApJ on 8 June 2026; 28 pages, 14 figures, 2 tables, and 2 short appendices; code to reproduce Fig. 9, a catalog of physical properties, and empirical PSFs can be found at https://doi.org/10.5281/zenodo.19444334; current version is in line with proofs