{
  "abstract": "Extreme emission metal-poor galaxies (EEMPGs) are excellent local laboratories for understanding the extreme physical conditions and ionizing radiation fields in the early Universe. However, the exact source of high-ionization emission lines in them, whether from intermediate-mass black holes (IMBHs), ultra-luminous X-ray sources (ULXs), or radiative shocks, remains debated. We characterize the fundamental properties and ionizing radiation field on metal-poor EEMPGs, aiming to identify the dominant sources of the highly ionizing photons that drive these lines. We selected a sample of 11 EEMPGs, among the most metal-poor galaxies with JWST/MIRI observations known so far (12+log(O/H) < 8.0, or Z/Z$_\\odot$ < 20%). Using optical and IR diagnostic diagrams for ions of both high and low ionization potential, we constrain the ionization source dominating their spectral features. We detect high-ionization lines, notably He II$λ$4686 in all galaxies and [Ne V] 14.3 $μ$m in 42% of a broader sample of local EEMPGs. The multi-wavelength diagnostic diagrams reveal that our EEMPGs are located in areas that normally are occupied by active galactic nuclei (AGNs) or between the star-formation and AGN sequences. Evaluating the energetics required to produce these lines, we find that radiative shocks and ULXs are not sufficient. Instead, our analysis suggests that a combination of sources with star-formation and a small contribution from an IMBH provide enough high-energy photon budget to explain the emission lines of ions with high-ionization potentials (> 54 eV). Our EEMPG sample, covering various properties, is ideal for studying the first galaxies. Their flux ratios of low- and high-ionization lines suggest stellar radiation as the likely ionization source, with a small contribution from an IMBH (4-8%). Pure shocks fail to explain the observed emission line ratios and ionizing photon budget.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.28329",
  "author_total": 14,
  "authors": [
    {
      "name": "C. Daoutis"
    },
    {
      "name": "V. Lebouteiller"
    },
    {
      "name": "D. Schaerer"
    },
    {
      "name": "I. Morel"
    },
    {
      "name": "O. Bait"
    },
    {
      "name": "S. Satyapal"
    },
    {
      "name": "S. Doan"
    },
    {
      "name": "B. Trahin"
    },
    {
      "name": "A. Gurpide"
    },
    {
      "name": "Y. Izotov"
    },
    {
      "name": "N. Guseva"
    },
    {
      "name": "L. Ramambason"
    },
    {
      "name": "A. Verhamme"
    },
    {
      "name": "SpeXion Team"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7g6jdcxqxqh3v.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.28329",
  "fulltext_url": null,
  "id": "7g6jdcxqxqh3v",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.28329",
  "language": "en",
  "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"
    ],
    [
      "hal",
      "0.phys"
    ],
    [
      "hal",
      "1.phys.astr"
    ],
    [
      "hal",
      "2.phys.astr.co"
    ],
    [
      "openalex",
      "3103|Galaxies: Formation, Evolution, Phenomena"
    ]
  ],
  "openalex": "W7214190388",
  "pdf_url": "https://arxiv.org/pdf/2609.28329",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-23",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7g6jdcxqxqh3v.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:56Z",
      "native_id": "2609.28329",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.28329"
    },
    {
      "first_seen": "2026-11-03T12:20:17Z",
      "native_id": "hal-05848406",
      "source": "hal",
      "url": "https://hal.science/hal-05848406v1"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "hal:2.phys.astr.co",
      "subfield": "cosmology"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "physics",
      "origin": "hal:0.phys",
      "subfield": "general"
    }
  ],
  "title": "Investigating the ionization mechanisms powering the extreme emission lines in metal-poor galaxies",
  "title_text": "Investigating the ionization mechanisms powering the extreme emission lines in metal-poor galaxies",
  "type": "preprint",
  "updated_at": "2026-11-04T12:20:48Z",
  "url": "https://research.draconitic.com/paper/7g6jdcxqxqh3v",
  "venue": "arXiv",
  "versions": []
}