MAMMOTH-MOSFIRE: Environmental Effects on Galaxy Interstellar Medium at <i>z</i>  ∼ 2

Abstract The MAMMOTH-MOSFIRE program is a deep Keck/MOSFIRE K -band spectroscopic follow-up of emission-line galaxies identified in the MAMMOTH-Grism Hubble Space Telescope/wide-field camera 3 G141 slitless spectroscopic survey, targeting the core regions of the three most massive galaxy protoclusters at cosmic noon. To introduce this program, we present a comprehensive analysis of the [N II ] λ 6584, [S II ] λλ 6717,6731, and [O I ] λ 6300 Baldwin, Philips, and Terlevich (BPT) diagnostics for a unique sample of 43 protocluster member galaxies at z ∼ 2, investigating how the overdense environment influences their interstellar medium ionization conditions. We find that, similar to their field counterparts at z ∼ 2, protocluster galaxies exhibit a systematic offset in the [N II ] BPT diagram relative to the local star-forming sequence, but no such offset in the [S II ] BPT diagram. Notably, we detect significantly elevated [O I ]/H α ratios, which can be well reproduced by photoionization models incorporating both H II regions and low-velocity shocks ( v ∼ 200 km s −1 ). We caution that neglecting shock excitation can bias abundance measurements, leading to an overestimation of nitrogen enrichment. This provides a potential explanation for the long-standing puzzle of enhanced [N II ]/H α ratios observed in z ∼ 2 galaxies. We further suggest that these shocks are likely environmentally driven, e.g., by ram pressure stripping or tidal interactions, which requires future confirmation through direct observations of features such as stripped gas tails.

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Publication Details

Journal
The Astrophysical Journal
Published
2025-11-06
DOI
https://doi.org/10.3847/1538-4357/ae0649
Citations
1
Primary Topic
Galaxies: Formation, Evolution, Phenomena
Type
article
Field-Weighted Citation Impact
1.15
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article

MAMMOTH-MOSFIRE: Environmental Effects on Galaxy Interstellar Medium at z  ∼ 2

Fuyan Bian, Xianzhong Zheng, Mengting Ju, Harry I. Teplitz et al.
1 citations
The Astrophysical Journal
Galaxies: Formation, Evolution, Phenomena
1.15
article

MAMMOTH-MOSFIRE: Environmental Effects on Galaxy Interstellar Medium at z  ∼ 2

Fuyan Bian, Xianzhong Zheng, Mengting Ju, Harry I. Teplitz, Xiaohui Fan, Anahita Alavi, Tommaso Treu, Matthew A. Malkan, Hang Zhou, Zheng Cai, Sijia Li, Xin Wang, James Colbert, Alaina Henry, Zihao Li, Yiming Yang, Yifei Jin, Hu Zhan, Dong Dong Shi, Zheng Zheng
article en
1 citations

Abstract

Abstract The MAMMOTH-MOSFIRE program is a deep Keck/MOSFIRE K -band spectroscopic follow-up of emission-line galaxies identified in the MAMMOTH-Grism Hubble Space Telescope/wide-field camera 3 G141 slitless spectroscopic survey, targeting the core regions of the three most massive galaxy protoclusters at cosmic noon. To introduce this program, we present a comprehensive analysis of the [N II ] λ 6584, [S II ] λλ 6717,6731, and [O I ] λ 6300 Baldwin, Philips, and Terlevich (BPT) diagnostics for a unique sample of 43 protocluster member galaxies at z ∼ 2, investigating how the overdense environment influences their interstellar medium ionization conditions. We find that, similar to their field counterparts at z ∼ 2, protocluster galaxies exhibit a systematic offset in the [N II ] BPT diagram relative to the local star-forming sequence, but no such offset in the [S II ] BPT diagram. Notably, we detect significantly elevated [O I ]/H α ratios, which can be well reproduced by photoionization models incorporating both H II regions and low-velocity shocks ( v ∼ 200 km s −1 ). We caution that neglecting shock excitation can bias abundance measurements, leading to an overestimation of nitrogen enrichment. This provides a potential explanation for the long-standing puzzle of enhanced [N II ]/H α ratios observed in z ∼ 2 galaxies. We further suggest that these shocks are likely environmentally driven, e.g., by ram pressure stripping or tidal interactions, which requires future confirmation through direct observations of features such as stripped gas tails.

The Astrophysical JournalVol. 993(2)
California Institute of Technology (US), University of Copenhagen (DK), Space Telescope Science Institute (US), University of Arizona (US), University of California, Los Angeles (US), Anhui University of Science and Technology (CN), Xiamen University (CN), Chinese Academy of Sciences (CN), Peking University (CN), Beijing Normal University (CN), Purple Mountain Observatory (CN), Westlake University (CN), Kavli Institute for Theoretical Sciences (CN), European Southern Observatory (CL), National Astronomical Observatories (CN), University of Chinese Academy of Sciences (CN), Infrared Processing and Analysis Center (US), Tsinghua University (CN)
Openalex Percentile: Top 15%
Galaxies: Formation, Evolution, Phenomena
1.15
DOIOpen Access PDFOpenAlex
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