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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

Diverse Metallicities in Protoclusters at z ~ 3.4 detected by Deep Learning

  • Yoshihiro Takeda1
  • Nobunari Kashikawa2,3
  • Kei Ito4,5
  • Jun Toshikawa6,7
  • Mariko Kubo7,8
  • Rieko Momose9,10
  • Yongming Liang10,11
  • Takehiro Yoshioka2
  • Junya Arita2
  • Hiroki Hoshi2
  • Shunta Shimizu2
  • Hisakazu Uchiyama10,12
3 more authors
  • Satoshi Kikuta2
  • Ryo Emori2
  • Kentaro Koretomo2
12 affiliations
  1. 1The University of Tokyo Department of Astronomy, School of Science, , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 ,
  2. 2School of Science, The University of Tokyo Department of Astronomy, , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 ,
  3. 3Center for the Early Universe, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 ,
  4. 4Cosmic Dawn Center (DAWN) , Copenhagen ,
  5. 5DTU Space, Technical University of Denmark , Elektrovej 327, DK2800 Kgs. Lyngby ,
  6. 6Nishi-Harima Astronomical Observatory, Center for Astronomy, University of Hyogo , Sayo, Hyogo 679-5313 ,
  7. 7Astronomical Institute, Tohoku University , Aoba-ku, Sendai 980-8578 ,
  8. 8School of Science, Kwansei Gakuin University Department of Physics and Astronomy, , 1 Gakuen Uegahara, Sanda, Hyogo 669-1330 ,
  9. 9Observatories of the Carnegie Institution for Science , 813 Santa Barbara Street, Pasadena, CA 91101 ,
  10. 10National Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588 ,
  11. 11Institute for Cosmic Ray Research, The University of Tokyo , Kashiwa, Chiba 277-8582 ,
  12. 12Faculty of Science and Engineering, Hosei University Department of Advanced Sciences, , 3-7-2 Kajino-cho, Koganei, Tokyo 184-8584 ,
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Abstract

We present spectroscopic follow-up observations with Subaru/MOIRCS of four protocluster candidate regions identified by the deep-learning model PCFNet. In three candidate regions, we confirm four protoclusters at z = 3.316, 3.403, 3.408 and 3.425, exhibiting galaxy density peaks over five times the uniform distribution. The detection rate of confirmed members aligns with PCFNet’s predictions, underscoring its effectiveness. Analysis of spectral energy distributions (SEDs), incorporating up to ten photometric bands (uu*grizyJHK), reveals that protocluster members lie on the star-formation main sequence. The masses of the most massive halos in the protoclusters are estimated from the most massive stellar mass of the member galaxies, yielding log Mhalo/M⊙ = 12.4–12.8, which are consistent with those at this redshift predicted by cosmological simulations and are comparable to those of the progenitors of typical local clusters (Mhaloz=0∼ 1014M⊙). Using the Voronoi Tessellation Monte Carlo technique based on the probability of protocluster membership from PCFNet, we find that our protoclusters exhibit a significantly higher SFRD than the cosmic SFRD at z ~ 3.4. Based on the [O iii]/Hβ emission line ratio, two protoclusters show marginally (1.4–2σ) higher average metallicities than the field, while the other protoclusters are statistically consistent with the field. These diverse metallicities highlight the environmental impact within protoclusters detected by PCFNet, likely reflecting the complex opposing interplay between metal-rich gas recycling and metal-poor gas inflow, which may depend on the surrounding environment of each protocluster. This work demonstrates PCFNet’s capability to unveil diverse samples of high-redshift protoclusters, paving the way for a more comprehensive understanding of their role in galaxy evolution.

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Cite

BibTeXRIS
BibTeX
@article{takeda2026diverse,
  title = {{Diverse Metallicities in Protoclusters at z ~ 3.4 detected by Deep Learning}},
  author = {Yoshihiro Takeda and Nobunari Kashikawa and Kei Ito and Jun Toshikawa and Mariko Kubo and Rieko Momose and Yongming Liang and Takehiro Yoshioka and Junya Arita and Hiroki Hoshi and Shunta Shimizu and Hisakazu Uchiyama and Satoshi Kikuta and Ryo Emori and Kentaro Koretomo},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = nov,
  doi = {10.1093/mnras/stag2110},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2110/9017892},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Diverse Metallicities in Protoclusters at z ~ 3.4 detected by Deep Learning
AU  - Yoshihiro Takeda
AU  - Nobunari Kashikawa
AU  - Kei Ito
AU  - Jun Toshikawa
AU  - Mariko Kubo
AU  - Rieko Momose
AU  - Yongming Liang
AU  - Takehiro Yoshioka
AU  - Junya Arita
AU  - Hiroki Hoshi
AU  - Shunta Shimizu
AU  - Hisakazu Uchiyama
AU  - Satoshi Kikuta
AU  - Ryo Emori
AU  - Kentaro Koretomo
PY  - 2026
DA  - 2026/11/06
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag2110
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2110/9017892
AB  - We present spectroscopic follow-up observations with Subaru/MOIRCS of four protocluster candidate regions identified by the deep-learning model PCFNet. In three candidate regions, we confirm four protoclusters at z = 3.316, 3.403, 3.408 and 3.425, exhibiting galaxy density peaks over five times the uniform distribution. The detection rate of confirmed members aligns with PCFNet’s predictions, underscoring its effectiveness. Analysis of spectral energy distributions (SEDs), incorporating up to ten photometric bands (uu*grizyJHK), reveals that protocluster members lie on the star-formation main sequence. The masses of the most massive halos in the protoclusters are estimated from the most massive stellar mass of the member galaxies, yielding log Mhalo/M⊙ = 12.4–12.8, which are consistent with those at this redshift predicted by cosmological simulations and are comparable to those of the progenitors of typical local clusters (M_halo^z=0∼ 10^14M_⊙). Using the Voronoi Tessellation Monte Carlo technique based on the probability of protocluster membership from PCFNet, we find that our protoclusters exhibit a significantly higher SFRD than the cosmic SFRD at z ~ 3.4. Based on the [O iii]/Hβ emission line ratio, two protoclusters show marginally (1.4–2σ) higher average metallicities than the field, while the other protoclusters are statistically consistent with the field. These diverse metallicities highlight the environmental impact within protoclusters detected by PCFNet, likely reflecting the complex opposing interplay between metal-rich gas recycling and metal-poor gas inflow, which may depend on the surrounding environment of each protocluster. This work demonstrates PCFNet’s capability to unveil diverse samples of high-redshift protoclusters, paving the way for a more comprehensive understanding of their role in galaxy evolution.
SN  - 0035-8711
SN  - 1365-2966
ER  -