{
  "abstract": "JWST has extended the search for accreting black holes into the high-redshift, low-mass regime. We report a low-mass black hole candidate in MARTA 3887, a clumpy, metal-poor galaxy at $z=3.7694$, combining deep JWST/NIRSpec spectroscopy, HST and JWST imaging, and archival VLT/MUSE data. We detect a broad H$α$ component with $L_{\\rm Hα,b}=2.35\\times10^{41}$ erg s$^{-1}$ and FWHM $=1270^{+260}_{-250}$ km s$^{-1}$, with no [O III] counterpart of comparable width. Under a broad-line-region interpretation, virial calibrations give $\\log(M_{\\rm BH}/M_\\odot)=6.52^{+0.18}_{-0.23}$ and $λ_{\\rm Edd}=0.07$, or up to 0.38 for alternative calibrations. The host comprises at least three compact clumps, with $\\log(M_\\star/M_\\odot)=8.16^{+0.09}_{-0.10}$. If stellar photoionization dominates the narrow lines, the gas is highly ionized and metal poor, with $12+\\log({\\rm O/H})=7.68\\pm0.04$ ($\\simeq0.10\\,Z_\\odot$). The inferred $M_{\\rm BH}/M_\\star=2.3\\%$ lies about 2 dex above the extrapolated local relation, suggesting that black-hole growth has outpaced the assembly of the observed host. If growth began only when the first 10% of the observed stellar mass had formed ($t_{10}=92$ Myr ago), a $10^2\\,M_\\odot$ seed would require a lifetime-mean Eddington ratio $\\simeq5.7$; earlier growth or a more massive, e.g. direct-collapse, seed would allow sub-Eddington mean accretion. MUSE reveals extended Ly$α$ emission ($\\simeq6.5$-6.9 proper kpc), offset by $+64^{+10}_{-8}$ km s$^{-1}$ from systemic, with a provisional escape fraction of $\\simeq0.44$. Together with a Mg II doublet ratio close to the optically thin limit and a high [O III]/[O II] ratio, this makes MARTA 3887 a laboratory to study black-hole growth, stellar assembly, and ionizing-photon escape jointly.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2611.00199",
  "author_total": 23,
  "authors": [
    {
      "name": "Mirko Curti"
    },
    {
      "name": "Bianca Moreschini"
    },
    {
      "name": "Elisa Cataldi"
    },
    {
      "name": "Francesco Belfiore"
    },
    {
      "name": "Ivan Delvecchio"
    },
    {
      "name": "Alessandro Marconi"
    },
    {
      "name": "Filippo Mannucci"
    },
    {
      "name": "Elena Bertola"
    },
    {
      "name": "Giovanni Cresci"
    },
    {
      "name": "Anna Feltre"
    },
    {
      "name": "Roberto Maiolino"
    },
    {
      "name": "Francesca Pozzi"
    },
    {
      "name": "Letizia Scaloni"
    },
    {
      "name": "Alberto Traina"
    },
    {
      "name": "Caterina Bracci"
    },
    {
      "name": "Stefano Carniani"
    },
    {
      "name": "Carlotta Gruppioni"
    },
    {
      "name": "Giacomo Venturi"
    },
    {
      "name": "Magda Arnaboldi"
    },
    {
      "name": "Meriem Behiri"
    },
    {
      "name": "Michele Ginolfi"
    },
    {
      "name": "Mahsa Kohandel"
    },
    {
      "name": "Livia Vallini"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/14k34ts3xrtcv.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2611.00199",
  "fulltext_url": null,
  "id": "14k34ts3xrtcv",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2611.00199",
  "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.GA"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2611.00199",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-01",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/14k34ts3xrtcv.ris",
  "sources": [
    {
      "first_seen": "2026-11-03T12:20:59Z",
      "native_id": "2611.00199",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2611.00199"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "MARTA: A \"little\" black hole hidden in a clumpy, metal-poor galaxy at z~3.8",
  "title_text": "MARTA: A \"little\" black hole hidden in a clumpy, metal-poor galaxy at z~3.8",
  "type": "preprint",
  "updated_at": "2026-11-05T15:20:18Z",
  "url": "https://research.draconitic.com/paper/14k34ts3xrtcv",
  "venue": "arXiv",
  "versions": []
}