Early Emergence of Environmental Effects: Accelerated Galaxy Assembly in a z=2.96 Protocluster in the COSMOS Field
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| Format: | Preprint |
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2026
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| _version_ | 1866917499539292160 |
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| author | Li, Shuaiyi Cai, Zheng Wu, Yunjing Yu, Fujiang Lin, Xiaojing Men, Jingyang Wei, Xiaoyang |
| author_facet | Li, Shuaiyi Cai, Zheng Wu, Yunjing Yu, Fujiang Lin, Xiaojing Men, Jingyang Wei, Xiaoyang |
| contents | The redshift range z=2-4 marks a critical transition in large scale structure formation, where the dynamically unrelaxed progenitors of local massive clusters undergo rapid stellar mass assembly. We report the discovery and physical characterization of a highly significant protocluster, PC J1001+0214, at z=2.96 within the COSMOS field. Leveraging the multi-wavelength COSMOS2025 catalog with exceptional photometric precision in conjunction with JWST/NIRCam wide-field slitless spectroscopy (WFSS) from the COSMOS-3D program, we robustly identify a cosmic overdensity with $δ=2.66$. The structure comprises 131 member galaxies, including 21 spectroscopically confirmed members (identified primarily via He I $\lambda10830$ emission) and 110 high-fidelity photometric members. A comparative analysis against a mass-complete coeval field sample reveals a statistically significant +0.2 dex shift in the stellar mass distribution of protocluster members, signaling accelerated mass assembly in the dense environment by $z\sim3$. While the protocluster population broadly follows the star-forming main sequence, low-to-intermediate mass galaxies ($\log_{10}(M_{*}/M_{\odot})\le9.7$) exhibit a measurable star formation rate (SFR) enhancement of +0.11 to +0.15 dex. Crucially, the quiescent fraction remains extremely low and indistinguishable from the field sample, implying that environmental quenching mechanisms have not yet become dominant. Furthermore, a preliminary size-mass analysis hints at elevated morphological compactness among protocluster members at fixed stellar mass. These results suggest that PC J1001+0214 represents a growth-dominated protocluster phase in which environmental effects are already detectable, primarily through accelerated stellar mass assembly and ongoing growth rather than through strong quenching. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_15712 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Early Emergence of Environmental Effects: Accelerated Galaxy Assembly in a z=2.96 Protocluster in the COSMOS Field Li, Shuaiyi Cai, Zheng Wu, Yunjing Yu, Fujiang Lin, Xiaojing Men, Jingyang Wei, Xiaoyang Astrophysics of Galaxies The redshift range z=2-4 marks a critical transition in large scale structure formation, where the dynamically unrelaxed progenitors of local massive clusters undergo rapid stellar mass assembly. We report the discovery and physical characterization of a highly significant protocluster, PC J1001+0214, at z=2.96 within the COSMOS field. Leveraging the multi-wavelength COSMOS2025 catalog with exceptional photometric precision in conjunction with JWST/NIRCam wide-field slitless spectroscopy (WFSS) from the COSMOS-3D program, we robustly identify a cosmic overdensity with $δ=2.66$. The structure comprises 131 member galaxies, including 21 spectroscopically confirmed members (identified primarily via He I $\lambda10830$ emission) and 110 high-fidelity photometric members. A comparative analysis against a mass-complete coeval field sample reveals a statistically significant +0.2 dex shift in the stellar mass distribution of protocluster members, signaling accelerated mass assembly in the dense environment by $z\sim3$. While the protocluster population broadly follows the star-forming main sequence, low-to-intermediate mass galaxies ($\log_{10}(M_{*}/M_{\odot})\le9.7$) exhibit a measurable star formation rate (SFR) enhancement of +0.11 to +0.15 dex. Crucially, the quiescent fraction remains extremely low and indistinguishable from the field sample, implying that environmental quenching mechanisms have not yet become dominant. Furthermore, a preliminary size-mass analysis hints at elevated morphological compactness among protocluster members at fixed stellar mass. These results suggest that PC J1001+0214 represents a growth-dominated protocluster phase in which environmental effects are already detectable, primarily through accelerated stellar mass assembly and ongoing growth rather than through strong quenching. |
| title | Early Emergence of Environmental Effects: Accelerated Galaxy Assembly in a z=2.96 Protocluster in the COSMOS Field |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.15712 |