{
  "abstract": "We aim to constrain the oxygen abundance, the ionizing properties, and the spatial structure of LAP2, a strongly lensed (with a magnification $μ$~50) oxygen-deficient galaxy at z=4.2 behind the galaxy cluster Abell 2744. We present new JWST/NIRSpec IFU PRISM observations (~13.6 hr) of LAP2, which we combine with archival JWST/NIRCam imaging. LAP2 is intrinsically extremely faint (M_UV=-12.7) and has a low stellar mass (M~$10^5~M_\\odot$), comparable to that of massive star clusters. It consists of a compact core ($R_{eff}$~7 pc) embedded in a more diffuse emission (with $R_{eff}$~20 pc). Strong H$α$ emission (EW$_{\\rm rest}\\simeq880$ Å, $\\logξ_{\\rm ion}\\simeq25.3$), a blue UV slope ($β_{\\rm UV}\\simeq-2.5$, down to $\\simeq-3.1$ in the core), and a Balmer decrement consistent with no dust attenuation indicate a young ($\\lesssim10$ Myr), dust-free burst. [OIII]$λ$5007 is not detected in the integrated spectrum, implying [OIII]/H$β\\leq0.61$ ($3σ$) and, using an extrapolated strong-line calibration, $12+\\log({\\rm O/H})\\leq6.4$ ($\\lesssim0.5\\%\\,Z_\\odot$). This places LAP2 among the most metal-poor galaxies known. Faint [OIII] emission is, however, detected in the core (with $\\rm4σ$ significance), where we derive $12+\\log({\\rm O/H})\\simeq6.6$ ($\\sim1\\%\\,Z_\\odot$). This difference can be explained either by local self-enrichment, requiring only $\\rm \\sim0.2\\,M_\\odot$ of newly synthesized oxygen, or by a higher ionization parameter in the core. The upper limit on HeII$λ$1640 (EW$_{\\rm rest}<39$ Å, $3σ$) does not exclude a contribution from metal-free stars. LAP2 extends the census of spectroscopically confirmed EMPGs to star-cluster masses and to $M_{\\rm UV}\\approx-13$. Its location in a low-density region supports a scenario in which underdense environments preserve nearly pristine gas well after reionization.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.05487",
  "author_total": 16,
  "authors": [
    {
      "name": "M. Messa"
    },
    {
      "name": "E. Vanzella"
    },
    {
      "name": "S. Rojas-Ruiz"
    },
    {
      "name": "T. Treu"
    },
    {
      "name": "P. Bergamini"
    },
    {
      "name": "G. Di Rosa"
    },
    {
      "name": "M. Lombardi"
    },
    {
      "name": "P. Rosati"
    },
    {
      "name": "A. Zanella"
    },
    {
      "name": "A. Adamo"
    },
    {
      "name": "A. Bolamperti"
    },
    {
      "name": "F. Calura"
    },
    {
      "name": "M. Castellano"
    },
    {
      "name": "R. Gilli"
    },
    {
      "name": "C. Grillo"
    },
    {
      "name": "U. Meštrić"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7xsnv61jdhhms.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.05487",
  "fulltext_url": null,
  "id": "7xsnv61jdhhms",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.05487",
  "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.GA"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.05487",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-03",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7xsnv61jdhhms.ris",
  "sources": [
    {
      "first_seen": "2026-11-05T15:20:56Z",
      "native_id": "2611.05487",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.05487"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "A pocket of oxygen in a near-pristine galaxy at z=4.2: chemical inhomogeneity at 10-parsec scales in LAP2",
  "title_text": "A pocket of oxygen in a near-pristine galaxy at z=4.2: chemical inhomogeneity at 10-parsec scales in LAP2",
  "type": "preprint",
  "updated_at": "2026-11-09T00:20:18Z",
  "url": "https://research.draconitic.com/paper/7xsnv61jdhhms",
  "venue": "arXiv",
  "versions": []
}