{
  "abstract": "The ionisation balance in molecular clouds is regulated by several ionising sources, including cosmic rays, X-rays, and ultraviolet radiation. Their relative importance depends on the local physical conditions and on the shielding column density. We compute the contribution of the large-scale diffuse X-ray radiation field to the ionisation in molecular clouds in the absence of strong local X-ray sources, such as young stars. Our goal is to quantify its significance relative to the Galactic cosmic rays. Using measurements of diffuse X-ray emission from the first eROSITA all-sky survey, we estimate the depth-dependent X-ray ionisation rate in molecular clouds across different Galactic environments. We consider both the observed diffuse field and a deabsorbed field obtained by correcting for foreground Galactic attenuation using HI4PI line-of-sight column densities in a pixel-by-pixel framework. Diffuse Galactic X-rays are unlikely to dominate the ionisation balance in well-shielded molecular gas ($N_{\\mathrm{H}} > 5 \\times 10^{21} \\mathrm{cm^{-2}}$), where cosmic rays remain the primary ionising agent. At low column densities, the deabsorbed diffuse X-ray field produces ionisation rate of $ζ_X \\sim 10^{-18}\\mathrm{s^{-1}}$ at $N_{\\mathrm H} \\sim 10^{19}\\mathrm{cm^{-2}}$, remaining below the lower end of Galactic cosmic ray ionisation rate ($\\sim 10^{-17} \\mathrm{s^{-1}}$). The X-ray contribution decreases rapidly with increasing shielding, falling to $ζ_{X}\\sim10^{-19}\\mathrm{s^{-1}}$ by $N_{\\rm H}\\sim10^{21}\\mathrm{cm^{-2}}$ and to $ζ_X \\sim5\\times10^{-21}\\mathrm{s^{-1}}$ by $N_{\\rm H}\\sim10^{22}\\mathrm{cm^{-2}}$. Diffuse X-ray may therefore contribute to the thermal and chemical structure of low-extinction material and should be considered when interpreting ionisation tracers in diffuse or cloud-envelope environments.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.02648",
  "author_total": 8,
  "authors": [
    {
      "name": "E. I. Makarenko"
    },
    {
      "name": "A. V. Ivlev"
    },
    {
      "name": "S. Bialy"
    },
    {
      "name": "X. Zheng"
    },
    {
      "name": "B. A. L. Gaches"
    },
    {
      "name": "P. Caselli"
    },
    {
      "name": "M. Padovani"
    },
    {
      "name": "M. C. H. Yeung"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/d653w0x9d798e.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.02648",
  "fulltext_url": null,
  "id": "d653w0x9d798e",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.02648",
  "language": null,
  "licence": "CC-BY-NC-ND-4.0",
  "licence_label": "CC BY-NC-ND 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.02648",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-02",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/d653w0x9d798e.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:18:16Z",
      "native_id": "2609.02648",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.02648"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Can diffuse X-rays be important in driving photoionisation in molecular clouds?",
  "title_text": "Can diffuse X-rays be important in driving photoionisation in molecular clouds?",
  "type": "preprint",
  "updated_at": "2026-10-30T12:18:16Z",
  "url": "https://research.draconitic.com/paper/d653w0x9d798e",
  "venue": "arXiv",
  "versions": []
}