2026A&A...706A...9Z

We present JWST/NIRCam imaging of dusty star-forming galaxies (DSFGs) detected by the Atacama Large Millimetre/submillimetre Array (ALMA) in the Spiderweb protocluster at z = 2.16. We identified 22 DSFGs detected by both ALMA and JWST, ten of which are spectroscopically confirmed as protocluster members. This is the first systematic analysis of a statistical DSFG sample in z ∼ 2 protocluster environments using JWST/NIRCam data. Most of the DSFG members exhibit red colours and reside in the dusty star-forming region of the rest-frame UVJ diagram, indicating strong dust obscuration. The Gini-M₂₀ diagram suggests that most DSFGs in this protocluster are late-type disks, with a significant fraction displaying clumpy and disturbed rest-frame UV/optical morphologies, but few showing clear merger signatures. The DSFG members exhibit relatively large stellar disks and effective radii with a median stellar mass of log(M/M_⊙) = 10.8 ± 0.3, placing them above coeval field DSFGs and typical protocluster galaxies in the size-mass relation at both rest-frame optical and near-infrared wavelengths. These sizes are comparable to those of more evolved field DSFGs at z ∼ 1 - 2, indicating accelerated structural growth in dense environments. Moreover, these DSFG members show a decreasing trend in stellar size from shorter to longer wavelengths, with a moderately steep slope comparable to coeval field DSFGs. These results may support an inside-out growth scenario for protocluster evolution, in which massive galaxies near the centre are more evolved and more strongly affected by active galactic nucleus feedback and environmental effects, for example, ram-pressure stripping. We propose that the cold gas accretion at the protocluster outskirts drives intense star formation and stellar disk growth in ALMA-detected DSFGs, which are expected to evolve into massive elliptical galaxies at later stages.