{
  "abstract": "The Seyfert 1 galaxy H 0557–385 (z = 0.034) has long been classified as radio-quiet on the basis of its radio-to-optical flux ratio, yet its radio properties are physically inconsistent with this designation. We present a broadband (0.076–258.8 GHz) radio spectral analysis combining new Australia Telescope Compact Array (ATCA) observations with archival Murchison Widefield Array (MWA), Australian Square Kilometre Array Pathfinder (ASKAP) and Atacama Large Millimeter/submillimeter Array (ALMA) data. The spectrum requires a two-component model: a compact, self-absorbed component with a stratified gigahertz-peaked (GPS)/high-frequency-peaked (HFP) spectral shape (turnover at $9.4^{+0.6}_{-0.5}$ GHz), superposed on an extended, optically thin power-law lobe (αpl = −0.78) that dominates below ~1.6 GHz. The derived parameters — a source size of ~15 pc, an equipartition magnetic field of 2.8 mG, a synchrotron age of ≲ 1.8 × 103 yr, and a time-averaged jet power of ~5 × 1041–5 × 1044 erg s−1 — are characteristic of compact steep-spectrum and GPS young radio galaxies, not of canonical radio-quiet AGN. The two-component structure admits two interpretations that the present data cannot distinguish: the extended emission may be the growing lobe of a genuinely young, expanding radio galaxy, or relic plasma from an earlier episode of a transient or recurrent jet. Under either, H 0557–385 is better understood as an intermediate object: optically a Seyfert, but with the radio-physical properties of a newly ignited or recently re-triggered radio galaxy. It is therefore a candidate missing link between radio-quiet AGN and large-scale radio galaxies. Distinguishing these scenarios will require high-resolution imaging and multi-epoch monitoring.",
  "abstract_shown": true,
  "affiliations": [
    "School of Physics and Astronomy, University of Leicester , University Rd, Leicester LE1 7RH ,",
    "INAF/IASF Palermo , via Ugo La Malfa 153, I-90146 Palermo ,",
    "Montana State University Department of Physics, , P.O. Box 173840, Bozeman, MT 59717-3840 ,",
    "Centre for Space Research, North West University , Potchefstroom 2520 ,",
    "INAF–Istituto di Astrofisica e Planetologia Spaziali , Via Fosso del Cavaliere, 00133, Roma ,",
    "U.S. Naval Research Laboratory , 4555 Overlook Avenue Southwest, WA, DC 20375 ,",
    "Durham University Centre for Extragalactic Astronomy, Department of Physics, , South Road, Durham DH1 3LE ,",
    "Inter-University Centre for Astronomy and Astrophysics , Ganeshkhind, Pune 411007 ,"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 12,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "J Chauhan",
      "orcid": "0000-0003-0330-1901"
    },
    {
      "affs": [
        1
      ],
      "name": "T D Russell",
      "orcid": "0000-0001-6958-8891"
    },
    {
      "affs": [
        2
      ],
      "name": "A Lohfink"
    },
    {
      "affs": [
        3
      ],
      "name": "M Böttcher"
    },
    {
      "affs": [
        4
      ],
      "name": "F Panessa",
      "orcid": "0000-0003-0543-3617"
    },
    {
      "affs": [
        0
      ],
      "name": "R L C Starling"
    },
    {
      "affs": [
        5
      ],
      "name": "K Nyland"
    },
    {
      "affs": [
        6
      ],
      "name": "C Done"
    },
    {
      "affs": [
        7
      ],
      "name": "S Chattopadhyay",
      "orcid": "0009-0004-7264-3184"
    },
    {
      "affs": [
        7
      ],
      "name": "T Ghosh",
      "orcid": "0000-0002-3033-5843"
    },
    {
      "affs": [
        7
      ],
      "name": "R Misra",
      "orcid": "0000-0002-7609-2779"
    },
    {
      "affs": [
        1
      ],
      "name": "M Del Santo"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ca5ett9pcqn71.bib",
  "cited_by": 0,
  "doi": "10.1093/mnras/stag2102",
  "fulltext_url": null,
  "id": "ca5ett9pcqn71",
  "issns": [
    "0035-8711",
    "1365-2966"
  ],
  "landing_url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2102/9012720",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [],
  "openalex": null,
  "pdf_url": "https://academic.oup.com/mnras/advance-article-pdf/doi/10.1093/mnras/stag2102/73037068/stag2102.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-04",
  "publisher": "Oxford University Press (OUP)",
  "ris": "https://research.draconitic.com/paper/ca5ett9pcqn71.ris",
  "sources": [
    {
      "first_seen": "2026-11-05T00:20:45Z",
      "native_id": "10.1093/mnras/stag2102",
      "source": "crossref",
      "url": "https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2102/9012720"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
    }
  ],
  "title": "H 0557–385: A Candidate Missing Link Between Radio-Quiet Seyferts and Young Radio Galaxies",
  "title_text": "H 0557–385: A Candidate Missing Link Between Radio-Quiet Seyferts and Young Radio Galaxies",
  "type": "peer-reviewed",
  "updated_at": "2026-11-05T00:20:45Z",
  "url": "https://research.draconitic.com/paper/ca5ett9pcqn71",
  "venue": "Monthly Notices of the Royal Astronomical Society",
  "versions": []
}