{
  "abstract": "We present a spectro-photometric analysis of RUBIES-EGS-9809, a broad-line AGN host at z=5.7 with a Balmer break and a dominant point source. The source is dust reddened ($A_V>$3 mag), shows hot- and cold-dust emission, and is X-ray Compton thick, with X-ray-to-bolometric ratio consistent with luminous AGN. The large $A_V$ agrees with strong NaI absorption (EW=17$\\pm 2 Å$), possibly from a neutral-gas outflow (3 $σ$), while broad [O III] traces an ionized outflow, suggesting AGN feedback may be affecting the host. We estimate a stellar mass log(M*/M$_\\odot$)=10.7$\\pm$0.3, Lbol$\\sim4\\times10^{46}$ erg s$^{-1}$ , and black-hole mass log(M$_{BH}/M_\\odot)\\sim8.1$ (subject to large systematics). The resolved Balmer break (0.1 arcsec, 0.6 kpc) is consistent with a stellar origin, implying the galaxy is already old in stars while still heavily obscured. This shows that massive galaxies can host evolved stellar populations during their compact, dust-obscured phase, consistent with formation in an earlier dusty starburst. SED modelling suggests a declining SFR, but low-resolution spectroscopy alone cannot constrain the recent SFR, so we treat the source as a strong quenching candidate rather than a secure post-starburst system. Because quenching follows the decline in SFR, star-formation-driven outflows are disfavoured, leaving AGN feedback as a plausible driver. We speculate that such rapid feedback ($\\sim$100 Myr timescale) may precipitate quenching while the post-quenching phase stays dust-enshrouded, concealing the UV-bright quenched phase that would otherwise be easily detected, if dust free. By the time dust clears, the UV-luminous stars may have already dwindled, leaving a classic dust-free quiescent galaxy. This 'dusty path' to quiescence may explain the lack of intermediate-age quenched progenitors (ages 50-100 Myr) linking dusty starbursts to massive quiescent systems at z=3-7.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.07825",
  "author_total": 15,
  "authors": [
    {
      "name": "Francesco D'Eugenio"
    },
    {
      "name": "Matilde Brazzini"
    },
    {
      "name": "Roberto Maiolino"
    },
    {
      "name": "Elena Bertola"
    },
    {
      "name": "Stefano Carniani"
    },
    {
      "name": "Xihan Ji"
    },
    {
      "name": "Ignas Juodžbalis"
    },
    {
      "name": "Yixiao Liu"
    },
    {
      "name": "Minjung Park"
    },
    {
      "name": "Eleonora Parlanti"
    },
    {
      "name": "Robert G. Pascalau"
    },
    {
      "name": "Gabriele Pezzulli"
    },
    {
      "name": "Jan Scholtz"
    },
    {
      "name": "Sandro Tacchella"
    },
    {
      "name": "Stefano Zibetti"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/2gx74amb55w52.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.07825",
  "fulltext_url": null,
  "id": "2gx74amb55w52",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.07825",
  "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/2609.07825",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-07",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/2gx74amb55w52.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.07825",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.07825"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    }
  ],
  "title": "A Dusty Quenching-candidate AGN host at z=5.7: massive quiescent galaxies may quench already during the dust-obscured phase",
  "title_text": "A Dusty Quenching-candidate AGN host at z=5.7: massive quiescent galaxies may quench already during the dust-obscured phase",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/2gx74amb55w52",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.33232/001c.170057",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}