Discovery of Very Minor Merger-Induced Star-forming Clumps at z=3.33 with JWST

High-redshift galaxies often contain ''clumps:'' compact, about kpc-scale regions of intense star formation. These substructures make up significant fractions of the masses and star-formation rates of their host galaxies and are expected to affect the morphologies of their hosts, such as by building up bulges. Studying clumps can therefore inform theoretical models of galaxy evolution. Two main mechanisms have been proposed for their formation: gas fragmentation from disk instabilities and compression of gas during gravitational interactions with other galaxies. In the latter, only mergers with mass ratios greater than 1:10 have been considered. Here, we report James Webb Space Telescope spectroscopy and imaging of JADES 1034862, a galaxy at z spec = 3.33, which hosts a clump that formed during an interaction with a companion with a stellar mass that is about28 times lower than the host. From fits to the spectral energy distributions of the clump and the companion, it is found that both of their star-formation histories rose sharply in the most recent 100-300 Myr, during which the clump formed about10 7.2 M in stars and currently makes up about10% of the total star-formation rate of its host. Given the higher frequency of mergers with low mass ratios (<1:10) to those with higher ratios, we infer that a substantial fraction of high-redshift clumps could have formed through weak gravitational interactions.