{
  "abstract": "Massive galaxies are expected to host extended halos of hot gas that contain a substantial fraction of their baryons and feedback energy. X-ray observations probe the dense, X-ray-bright component of this circumgalactic medium (CGM), while the thermal Sunyaev-Zel'dovich (SZ) effect is also sensitive to lower-density gas through its integrated thermal pressure. We present the first spatially resolved joint X-ray and SZ analysis of a massive isolated disk galaxy, using deep XMM-Newton observations of NGC 4594 from the X-raying the Accretion Reservoir Transferred to the ATmosphere Orbiting a Massive Spiral (XART-ATOMS) program, together with multiple independent Planck-based SZ reconstructions. The measured SZ signal in the inner halo appears to exceed the value predicted from the X-ray-derived gas properties, even after accounting for major systematic uncertainties. Our preferred interpretation is that an additional lower-density CGM component contributes little to the observed soft X-ray emission but carries substantial thermal pressure. Under a simple two-phase model in approximate pressure equilibrium, the most probable X-ray-to-SZ ratio implies that the detected X-ray-emitting gas occupies only a small fraction of the halo volume, with a characteristic filling factor of f_X ~ (4-6)x10^-3 near r~50 kpc. Such a small filling factor implies that single-phase X-ray analyses can underestimate the baryon mass contained in the hot CGM by a factor of ~2.5, while the thermal energy content of the CGM is underestimated by about one order of magnitude. The non-detection of the additional component in the X-ray spectra requires it to be very hot and/or spatially extended, so weak in the soft X-ray emissions. These results favor the presence of a \"hidden\" X-ray-faint hotter halo component, while alternative interpretations, including a nonthermal contribution, are not excluded.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": "Journal reference: J.-T. Li, et al., 2026, ApJ, 1009, 72",
  "arxiv": "2609.18006",
  "author_total": 5,
  "authors": [
    {
      "name": "Jiang-Tao Li"
    },
    {
      "name": "Rui Huang"
    },
    {
      "name": "Joel N. Bregman"
    },
    {
      "name": "Q. Daniel Wang"
    },
    {
      "name": "Cameron Pratt"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3aftyxdvhrxsh.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.18006",
  "fulltext_url": null,
  "id": "3aftyxdvhrxsh",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.18006",
  "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"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.18006",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-16",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3aftyxdvhrxsh.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:22:01Z",
      "native_id": "2609.18006",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.18006"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "A Possible Hidden Hot Halo Component Revealed by Joint X-ray and Sunyaev--Zel'dovich Observations",
  "title_text": "A Possible Hidden Hot Halo Component Revealed by Joint X-ray and Sunyaev--Zel'dovich Observations",
  "type": "preprint",
  "updated_at": "2026-10-30T12:22:01Z",
  "url": "https://research.draconitic.com/paper/3aftyxdvhrxsh",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.3847/1538-4357/ae883f",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}