Hot-dust-poor type 1 active galactic nuclei in the COSMOS survey

Heng Hao, Martin Elvis, Francesca Civano, Giorgio Lanzuisi, Marcella Brusa, Elisabeta Lusso, Gianni Zamorani, Andrea Comastri, Angela Bongiorno, Chris D. Impey, Anton M. Koekemoer, Emeric Le Floc'h, Mara Salvato, David Sanders, Jonathan R. Trump, Cristian Vignali

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


We report a sizable class of type 1 active galactic nuclei (AGNs) with unusually weak near-infrared (1-3μm) emission in the XMM-COSMOS type 1 AGN sample. The fraction of these "hot-dust-poor" AGNs increases with redshift from 6%at lowredshift (z < 2) to 20% at moderate high redshift (2 < z < 3.5). There is no clear trend of the fraction with other parameters: bolometric luminosity, Eddington ratio, black hole mass, and X-ray luminosity. The 3μm emission relative to the 1μmemission is a factor of 2-4 smaller than the typical Elvis et al.AGNspectral energy distribution (SED), which indicates a "torus" covering factor of 2%-29%, a factor of 3-40 smaller than required by unified models. The weak hot dust emission seems to expose an extension of the accretion disk continuum in some of the source SEDs. We estimate the outer edge of their accretion disks to lie at (0.3-2.0) × 104 Schwarzschild radii, ∼10-23 times the gravitational stability radii. Formation scenarios for these sources are discussed.

Original languageEnglish (US)
Pages (from-to)L59-L63
JournalAstrophysical Journal Letters
Issue number1 PART 2
StatePublished - Nov 20 2010


  • Galaxies: evolution
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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