Journal article
THE OBSCURED FRACTION OF ACTIVE GALACTIC NUCLEI IN THE XMM-COSMOS SURVEY: A SPECTRAL ENERGY DISTRIBUTION PERSPECTIVE
The Astrophysical journal, v 777(2), pp 1-28
10 Nov 2013
Abstract
The fraction of active galactic nucleus (AGN) luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type 1) AGNs, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We use this technique to estimate the obscured AGN fraction as a function of luminosity and redshift for 513 Type 1 AGNs from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18 band COSMOS photometry with a custom spectral energy distribution fitting code, which jointly models emission from hot dust in the AGN torus, from the accretion disk, and from the host galaxy. We find a relatively shallow decrease of the luminosity ratio as a function of L-bol, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGNs, our measurements require a torus height that increases with luminosity as h proportional to L-bol(0.3-0.4). Our obscured-fraction-luminosity relation agrees with determinations from Sloan Digital Sky Survey censuses of Type 1 and Type 2 quasars and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of the obscured fraction on 2-10 keV luminosity than previous determinations from X-ray surveys and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGNs. Our analysis shows no clear evidence for evolution of the obscured fraction with redshift.
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Details
- Title
- THE OBSCURED FRACTION OF ACTIVE GALACTIC NUCLEI IN THE XMM-COSMOS SURVEY: A SPECTRAL ENERGY DISTRIBUTION PERSPECTIVE
- Creators
- E. Lusso - University of ConcepciónJ. F. Hennawi - University of ConcepciónA. Comastri - University of ConcepciónG. Zamorani - University of ConcepciónG. T. Richards - University of ConcepciónC. Vignali - University of ConcepciónE. Treister - University of ConcepciónK. Schawinski - University of ConcepciónM. Salvato - Max Planck SocietyR. Gilli - University of Concepción
- Publication Details
- The Astrophysical journal, v 777(2), pp 1-28
- Publisher
- Iop Publishing Ltd
- Number of pages
- 28
- Grant note
- 1120061 / FONDECYT; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT); CONICYT FONDECYT Alexander von Humboldt Foundation at the Max-Planck-Institut fur Astronomie; Alexander von Humboldt Foundation PFB 06 / Center of Excellence in Astrophysics and Associated Technologies INAF-PRIN; Istituto Nazionale Astrofisica (INAF); Ministry of Education, Universities and Research (MIUR); Research Projects of National Relevance (PRIN) Alexander von Humboldt Foundation I/009/10/0 / ASI-INAF; Istituto Nazionale Astrofisica (INAF); Agenzia Spaziale Italiana (ASI) 175.A-0839 / ESO telescopes at the La Silla or Paranal Observatories ACT1101 / Anillo project; Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT); CONICYT PIA/ANILLOS
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Physics
- Web of Science ID
- WOS:000326218800005
- Scopus ID
- 2-s2.0-84886694637
- Other Identifier
- 991019168962904721
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- Collaboration types
- Domestic collaboration
- International collaboration
- Web of Science research areas
- Astronomy & Astrophysics