{
  "abstract": "H I gas traces the large-scale structure and provides the primary fuel for star formation. High-$z$ protoclusters are ideal laboratories to study how H I gas is accreted and consumed during the formation of the most massive structures in the Universe. However, much remains unknown about the distribution and physical state of their H I gas. We examine a rare configuration in which a protocluster candidate is located in front of a quasar at $z=3.09$. Our spectroscopic campaign confirms a protocluster at $z=3.079$: however, no corresponding strong H I absorption is found in the background quasar spectrum. Instead, we serendipitously discover a prominent H I absorption feature at $z\\sim 3.01$, offset by $\\sim 60$ cMpc from the centre of the protocluster. Spanning an exceptionally broad velocity range of $\\sim 2000$ km s$^{-1}$ ($\\sim 40$ cMpc), this absorption is decoupled from the confirmed member galaxies. Detailed kinematic modelling reveals this absorption comprises five distinct components rather than a single cloud. Moreover, one of these components exhibits a super-solar metallicity ($[\\mathrm{O/H}] = +1.19^{+0.91}_{-0.78}$). We propose two physical scenarios for this unique system: (1) an additional, hidden massive protocluster along the line of sight, and/or (2) metal-rich outflows and metal-poor inflows driven by a single massive galaxy. The discovery highlights that while protoclusters are not universally associated with strong H I absorption, targeting the strong H I absorbers may serve as a beacon for uncovering massive, metal-rich protoclusters or complex gas kinematics in the early Universe.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.04349",
  "author_total": 15,
  "authors": [
    {
      "name": "Kentaro Koretomo"
    },
    {
      "name": "Nobunari Kashikawa"
    },
    {
      "name": "Toru Misawa"
    },
    {
      "name": "Jun Toshikawa"
    },
    {
      "name": "Yoshihiro Takeda"
    },
    {
      "name": "Hisakazu Uchiyama"
    },
    {
      "name": "Junya Arita"
    },
    {
      "name": "Shunta Shimizu"
    },
    {
      "name": "Ryo Emori"
    },
    {
      "name": "Kei Ito"
    },
    {
      "name": "Satoshi Kikuta"
    },
    {
      "name": "Mariko Kubo"
    },
    {
      "name": "Yoshiaki Ono"
    },
    {
      "name": "Marcin Sawicki"
    },
    {
      "name": "Rhythm Shimakawa"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/5zkrmyt3wjgm4.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.04349",
  "fulltext_url": null,
  "id": "5zkrmyt3wjgm4",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.04349",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.CO"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7211892934",
  "pdf_url": "https://arxiv.org/pdf/2609.04349",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/5zkrmyt3wjgm4.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:19:14Z",
      "native_id": "2609.04349",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.04349"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "H I Absorbers as Beacons of Hidden Structure at $z \\sim 3$: Multi-Component, Metal-Rich Absorption System near a Protocluster",
  "title_text": "H I Absorbers as Beacons of Hidden Structure at z ∼ 3: Multi-Component, Metal-Rich Absorption System near a Protocluster",
  "type": "preprint",
  "updated_at": "2026-10-30T12:19:14Z",
  "url": "https://research.draconitic.com/paper/5zkrmyt3wjgm4",
  "venue": "arXiv",
  "versions": []
}