{
  "abstract": "We report the discovery of a galaxy protocluster candidate (dubbed MACS0416-OD-z8p5) at a spectroscopic redshift of z ∼ 8.47, dating back to ∼550 Myr after the Big Bang. The observations are part of the JWST Cycle 3 Treasury Program Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (or SAPPHIRES) using NIRCam grism observations. Using wide-field slitless spectroscopy (WFSS) obtained in the MACS0416 parallel field, we robustly confirm nine galaxies at z spec ∼ 8.47 via emission-line detections of [O iii ] 5008 Å (with >5 σ ) and tentatively confirm one additional galaxy (at ∼3 σ ). This discovery represents the highest-redshift spectroscopically confirmed galaxy overdensity known to date and is ∼6–8 times more dense than the average number density of galaxies at the same redshift. Furthermore, a galaxy hosting a low-mass active galactic nucleus (a “little red dot”) is found as a member, suggesting that black hole growth may already be underway in dense environments at early cosmic times. This finding of a massive dark matter halo hosting a galaxy overdensity at z ∼ 8.5 is surprising given that our survey covered only a small, random field ( 16.5 arcmin 2 ) as part of a pure-parallel observation. Comparison with cosmological simulations shows that the likelihood of finding such a large-scale structure is <5% under the current galaxy formation scenario and within the observed survey volume. Our results demonstrate the power of WFSS observations for building complete samples of line-emitting galaxies and suggest an important role for overdensities in enhancing galaxy formation by funneling large-scale gas supplies into small cosmological volumes.",
  "abstract_shown": true,
  "affiliations": [
    "Chiba University",
    "University of Arizona",
    "Tsinghua University",
    "Center for Astrophysics ∣ Harvard & Smithsonian",
    "Space Telescope Science Institute (STScI)",
    "The Johns Hopkins University",
    "University of Oxford",
    "University of Cambridge",
    "The University of Tokyo",
    "National Astronomical Observatory of Japan",
    "SOKENDAI (The Graduate University for Advanced Studies)",
    "University of Tokyo",
    "University College London",
    "University of Michigan"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 22,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Yoshinobu Fudamoto",
      "orcid": "0000-0001-7440-8832"
    },
    {
      "affs": [
        1
      ],
      "name": "Jakob M. Helton",
      "orcid": "0000-0003-4337-6211"
    },
    {
      "affs": [
        2,
        1
      ],
      "name": "Xiaojing Lin",
      "orcid": "0000-0001-6052-4234"
    },
    {
      "affs": [
        3
      ],
      "name": "Fengwu Sun",
      "orcid": "0000-0002-4622-6617"
    },
    {
      "affs": [
        1
      ],
      "name": "Peter Behroozi",
      "orcid": "0000-0002-2517-6446"
    },
    {
      "affs": [
        3,
        4,
        5
      ],
      "name": "Tiger Yu-Yang Hsiao",
      "orcid": "0000-0003-4512-8705"
    },
    {
      "affs": [
        1
      ],
      "name": "Eiichi Egami",
      "orcid": "0000-0003-1344-9475"
    },
    {
      "affs": [
        6
      ],
      "name": "Andrew J. Bunker",
      "orcid": "0000-0002-8651-9879"
    },
    {
      "affs": [
        7
      ],
      "name": "Francesco D’Eugenio",
      "orcid": "0000-0003-2388-8172"
    },
    {
      "affs": [
        8
      ],
      "name": "Yuichi Harikane",
      "orcid": "0000-0002-6047-430X"
    },
    {
      "affs": [
        9,
        10,
        8,
        11
      ],
      "name": "Masami Ouchi",
      "orcid": "0000-0002-1049-6658"
    },
    {
      "affs": [
        1
      ],
      "name": "Yichen Liu",
      "orcid": "0000-0003-4247-0169"
    },
    {
      "affs": [
        1
      ],
      "name": "Weizhe Liu",
      "orcid": "0000-0003-3762-7344"
    },
    {
      "affs": [
        12,
        7
      ],
      "name": "R. Maiolino",
      "orcid": "0000-0002-4985-3819"
    },
    {
      "affs": [
        1
      ],
      "name": "Zhiyuan Ji",
      "orcid": "0000-0001-7673-2257"
    },
    {
      "affs": [
        1
      ],
      "name": "Xiangyu Jin",
      "orcid": "0000-0002-5768-738X"
    },
    {
      "affs": [
        1
      ],
      "name": "Wei Leong Tee",
      "orcid": "0000-0003-0747-1780"
    },
    {
      "affs": [
        13
      ],
      "name": "Feige Wang",
      "orcid": "0000-0002-7633-431X"
    },
    {
      "affs": [
        1
      ],
      "name": "Christopher N. A. Willmer",
      "orcid": "0000-0001-9262-9997"
    },
    {
      "affs": [
        8
      ],
      "name": "Yi Xu",
      "orcid": "0000-0002-5768-8235"
    },
    {
      "affs": [
        13
      ],
      "name": "Jinyi Yang",
      "orcid": "0000-0001-5287-4242"
    },
    {
      "affs": [
        1
      ],
      "name": "Yongda Zhu",
      "orcid": "0000-0003-3307-7525"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ba9enpm5ehp9f.bib",
  "cited_by": 20,
  "doi": "10.3847/1538-4357/ae743f",
  "fulltext_url": null,
  "id": "ba9enpm5ehp9f",
  "issns": [
    "0004-637X",
    "1538-4357"
  ],
  "landing_url": "https://doi.org/10.3847/1538-4357/ae743f",
  "language": "en",
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae743f/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-04",
  "publisher": "IOP Publishing",
  "ris": "https://research.draconitic.com/paper/ba9enpm5ehp9f.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T13:21:02Z",
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      "url": "https://doi.org/10.3847/1538-4357/ae743f"
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  "subjects": [
    {
      "field": "astronomy",
      "origin": "openalex:3103|Galaxies: Formation, Evolution, Phenomena",
      "subfield": "galaxies"
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  ],
  "title": "SAPPHIRES: A Galaxy Overdensity in the Heart of Cosmic Reionization at z = 8.47",
  "title_text": "SAPPHIRES: A Galaxy Overdensity in the Heart of Cosmic Reionization at z = 8.47",
  "type": "peer-reviewed",
  "updated_at": "2026-11-08T13:20:39Z",
  "url": "https://research.draconitic.com/paper/ba9enpm5ehp9f",
  "venue": "The Astrophysical Journal",
  "versions": []
}