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

TL;DR

This study leverages JWST/NIRCam imaging together with ALMA 1.2 mm data to explore the stellar structures of DSFGs in the Spiderweb protocluster at z=2.16. It identifies 22 JWST-detected ALMA sources, including 10 spectroscopically confirmed protocluster members, and conducts both non-parametric and parametric morphologies to show that these DSFGs harbor extended stellar disks with large $R_e$ and disk-dominated rest-frame optical/NIR structures. The results reveal that these protocluster DSFGs are larger at fixed mass than coeval field DSFGs, with a size–mass relation suggesting accelerated growth in dense environments and a downsizing trend from UV to NIR. The findings imply a predominantly secular growth pathway driven by cold gas accretion along filaments, with potential bulge formation and AGN feedback as the galaxies move toward the cluster core, ultimately contributing to the assembly of massive ellipticals in local clusters.

Abstract

We present JWST/NIRCam imaging of dusty star-forming galaxies (DSFGs) detected by Atacama Large Millimeter/submillimeter Array (ALMA) in the Spiderweb protocluster at $z=2.16$. We identify 22 DSFGs detected by both ALMA and JWST, 10 of which are spectroscopically confirmed as protocluster members. This is the first systematic analysis of a statistical DSFG sample in $z\sim2$ protocluster environments using JWST/NIRCam data. Most of the DSFG members exhibit very red colors 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/Msun) = 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 center are more evolved and more strongly affected by AGN feedback and environmental effects, e.g., 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.

Figures (11)

• Figure 1: JWST color-composite (F410M/F182M/F115W for RGB) image of the Spiderweb protocluster. The 22 ALMA sources detected by JWST and the 8 undetected ones are marked with orange and white squares, respectively, with their IDs labeled nearby. The Spiderweb galaxy is marked as a star, which represents the center of the protocluster. The dashed circle shows the $r_{500}=229$ kpc derived from the recently detected Sunyaev–Zeldovich signal Mascolo2023.
• Figure 2: The signal-to-noise ratio distribution of the 30 ALMA sources within the JWST/NIRCam footprint. The 22 sources detected by JWST are indicated in blue, while the eight undetected sources are shown in gray.
• Figure 3: The gallery of ten protocluster members detected by both ALMA and JWST/NIRCam, with a cutout size of 4$\times$4 arcsec. The names of the four filters are shown in the first row. The ALMA 1.2 mm contours at [2$\sigma$, 3$\sigma$, 4$\sigma$] are overlaid on the F405N image in the fourth column for each source, with a blue bar showing a physical distance of 5 kpc. The RGB-composite (F410M/F182M/F115W) color images are shown in the fifth column. The source IDs are positioned in the lower-left corner of each group of panels, consistent with the numbering in Fig. \ref{['fig:fov_map']}.
• Figure 4: Rest-frame $UVJ$ (F410M, F182M, F115W) diagram of the nine JWST-detected DSFG members, marked with their IDs. The criteria to separate the quiescent and star-forming regions are adopted from Whitaker2011. The normal star-forming galaxies and quiescent galaxies at $z\sim2-3$ from JWST/CEERS and JADES surveys are shown with gray dots Ren2024.
• Figure 5: The Gini-$M_{20}$ diagram of nine DSFG members across three filters—F410M (red), F182M (green), and F115W (blue)—is presented. The medians of the field DSFG sample are depicted as orange and lime diamonds in the rest-frame optical and NIR bands Gillman2024. Three extremely dusty starburst at cosmic noon are also shown in magenta circles for a comparison Polletta2024.