{
  "abstract": "We present Leviathan, a sub-millimetre galaxy (SMG) spectroscopically confirmed at $z=4.051$ with JWST/NIRSpec. Modelling 31 bands of photometry from the rest-frame ultraviolet to the millimetre, we find a stellar mass of $\\log(M_\\star/M_\\odot)=11.34^{+0.15}_{-0.22}$, making Leviathan one of the most massive spectroscopically confirmed galaxies at $z>4$, yet consistent with $Λ$CDM for a star-formation efficiency of approximately 20%. Although SMGs are often thought to be building the dense cores of compact quiescent galaxies, Leviathan is extended, with a rest-frame $0.9\\,μ\\mathrm{m}$ half-light radius of 4.3 kpc. Spatially resolved SED fitting gives a half-mass radius of $3.1\\pm0.4$ kpc, consistent with its size in rest-frame $1.5\\,μ\\mathrm{m}$ imaging. This is three times larger than quiescent galaxies of the same mass, but consistent with the size-mass relation of star-forming galaxies at $4<z<5$ extrapolated to $M_\\star=10^{11.3}M_\\odot$. Leviathan forms stars on the main sequence (approximately $400\\,M_\\odot\\,\\mathrm{yr}^{-1}$) with dust spread across its disc. Both its stellar mass and dust are more extended than those of $z\\approx3$ SMGs. Alongside GN20.2b, which has a similar mass and star-formation rate but is three times smaller, these show that massive dusty galaxies at $z\\approx4$ can have very different stellar structures, and that not all have their stellar mass concentrated in a compact core.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.27101",
  "author_total": 8,
  "authors": [
    {
      "name": "William M. Baker"
    },
    {
      "name": "Francesco Valentino"
    },
    {
      "name": "Jens Hjorth"
    },
    {
      "name": "Gabriel Brammer"
    },
    {
      "name": "Ugnė Dudzevičiūtė"
    },
    {
      "name": "Kei Ito"
    },
    {
      "name": "Antonio Pensabene"
    },
    {
      "name": "Pengpei Zhu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fdwwvt83efn5r.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.27101",
  "fulltext_url": null,
  "id": "fdwwvt83efn5r",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.27101",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.CO"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7223104818",
  "pdf_url": "https://arxiv.org/pdf/2610.27101",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-19",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fdwwvt83efn5r.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:04Z",
      "native_id": "2610.27101",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.27101"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.CO",
      "subfield": "cosmology"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "Leviathan: a very massive, extended sub-millimetre galaxy spectroscopically confirmed at $\\rm z = 4.05$",
  "title_text": "Leviathan: a very massive, extended sub-millimetre galaxy spectroscopically confirmed at z = 4.05",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:04Z",
  "url": "https://research.draconitic.com/paper/fdwwvt83efn5r",
  "venue": "arXiv",
  "versions": []
}