JWST reveals extended stellar disks for ALMA-bright dusty star-forming galaxies in the Spiderweb protocluster

¹ Purple Mountain Observatory, Chinese Academy of Sciences 10 Yuanhua Road Nanjing 210023, China
² School of Astronomy and Space Science, University of Science and Technology of China Hefei Anhui 230026, China
³ Instituto de Astrofísica de Canarias (IAC) E-38205 La Laguna Tenerife, Spain
⁴ Universidad de La Laguna, Dpto. Astrofísica E-38206 La Laguna Tenerife, Spain
⁵ National Astronomical Observatory of Japan 2-21-1 Osawa Mitaka Tokyo 181-8588, Japan
⁶ Graduate University for Advanced Studies (SOKENDAI) 2-21-1 Osawa Mitaka Tokyo 181-8588, Japan
⁷ Tsung-Dao Lee Institute and State Key Laboratory of Dark Matter Physics, Shanghai Jiao Tong University Shanghai 201210, China
⁸ INAF–Osservatorio Astronomico di Capodimonte Salita Moiariello 16 80131 Napoli, Italy
⁹ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1, Yoshinodai Chuou-ku Sagamihara Kanagawa 252-5210, Japan
¹⁰ European Southern Observatory Karl–Schwarzschild–Straße 2 D-85748 Garching bei München, Germany
¹¹ Institute de Physique du Globe de Paris, 5 Rue Jussieu Paris, France
¹² CEA-Saclay, IRFU, DAp, AIM 91191 Gif-sur-Yvette, France
¹³ National Radio Astronomy Observatory 520 Edgemont Road Charlottesville VA 22903, USA
¹⁴ Cosmic Dawn Center (DAWN), Denmark
¹⁵ DTU Space, Technical University of Denmark Elektrovej 327 DK-2800 Kgs. Lyngby, Denmark
¹⁶ Astronomical Institute, Tohoku University, 6-3 Aramaki Aoba-ku Sendai 980-8578, Japan
¹⁷ Université Lyon 1, ENS de Lyon, CNRS UMR5574, Centre de Recherche Astrophysique de Lyon F-69230 Saint-Genis-Laval, France
¹⁸ Astronomical Observatory Institute, Faculty of Physics and Astronomy, Adam Mickiewicz University ul. Słoneczna 36 60-286 Poznań, Poland
¹⁹ Centro de Astrobiología (CAB), CSIC-INTA Ctra. de Ajalvir km 4 Torrejón de Ardoz E-28850 Madrid, Spain

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Received: 26 July 2025
Accepted: 4 December 2025

Abstract

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.