January
2026
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2026ApJ...997...95Y
Authors
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Yang, Yiming
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Wang, Xin
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He, Xianlong
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Tsai, Chao-Wei
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Cai, Zheng
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Li, Zihao
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Malkan, Matthew A.
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Shi, Dong Dong
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Alavi, Anahita
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Bian, Fuyan
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Colbert, James
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Fan, Xiaohui
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Henry, Alaina L.
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Teplitz, Harry I.
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Zheng, Xian Zhong
Abstract
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We present one of the first measurements of the mass─metallicity relation (MZR) in multiple massive protoclusters at cosmic noon, using Hubble Space Telescope (HST) G141 slitless spectroscopy from the MAMMOTH-Grism survey. We identify 63 protocluster member galaxies across three overdense structures at z = 2─3 with robust detections of [O III], Hβ, and [O II] emission. The sample spans gas-phase metallicities of 12+log(O/H)=8.2−8.6 , dust-corrected Hβ-based star formation rates (SFRs) of 10─250 M⊙ yr−1, and stellar masses of M* ∼ 109.4─1010.5 M⊙, derived via spectral energy distribution fitting using deep HST and ground-based photometry. We stack spectra in five M* bins to obtain average metallicities and SFRs. Relative to field galaxies at similar redshifts, protocluster members show elevated SFRs at M* < 1010.25 M⊙ and a systematically shallower MZR: 12+log(O/H) =(6.96 ± 0.13) + (0.143 ± 0.017) ×log(M*/M⊙) . We detect a mass-dependent environmental offset: massive protocluster galaxies are metal-poor compared to field counterparts of similar mass, whereas lower-mass systems exhibit comparable or mildly enhanced metallicities. This trend is consistent with a scenario where cold-mode accretion dilutes the interstellar medium (ISM) across the full mass range, while efficient recycling of feedback-driven outflows preferentially enriches the ISM in low-mass galaxies. Finally, we assess the dependence of metallicity offsets on local overdensity and find no significant trend, likely reflecting the survey's bias toward protocluster cores.
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