The incidence of obscuration in active galactic nuclei

A. Merloni, A. Bongiorno, M. Brusa, K. Iwasawa, V. Mainieri, B. Magnelli, M. Salvato, S. Berta, Nico Cappelluti, A. Comastri, F. Fiore, R. Gilli, A. Koekemoer, E. Le Floc'h, E. Lusso, D. Lutz, T. Miyaji, F. Pozzi, L. Riguccini, D. J. RosarioJ. Silverman, M. Symeonidis, E. Treister, C. Vignali, G. Zamorani

Research output: Contribution to journalArticle

117 Citations (Scopus)

Abstract

We study the incidence of nuclear obscuration on a complete sample of 1310 active galactic nuclei (AGN) selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMMCOSMOS survey, in the redshift range 0.3 < z < 3.5. We classify the AGN as obscured or unobscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70 per cent of the objects, and the remaining 30 per cent can be further subdivided into two distinct classes: at low luminosities X-ray unobscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at highluminosities broad-line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and unobscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.

Original languageEnglish (US)
Pages (from-to)3550-3567
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Volume437
Issue number4
DOIs
StatePublished - Feb 1 2014
Externally publishedYes

Fingerprint

occultation
active galactic nuclei
incidence
luminosity
x rays
dilution
dust
star formation rate
stellar mass
optical spectrum
galaxies
continuums
radiation

Keywords

  • Active - galaxies
  • catalogues - surveys - galaxies
  • Evolution - galaxies
  • Fundamental parameters.

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Merloni, A., Bongiorno, A., Brusa, M., Iwasawa, K., Mainieri, V., Magnelli, B., ... Zamorani, G. (2014). The incidence of obscuration in active galactic nuclei. Monthly Notices of the Royal Astronomical Society, 437(4), 3550-3567. https://doi.org/10.1093/mnras/stt2149

The incidence of obscuration in active galactic nuclei. / Merloni, A.; Bongiorno, A.; Brusa, M.; Iwasawa, K.; Mainieri, V.; Magnelli, B.; Salvato, M.; Berta, S.; Cappelluti, Nico; Comastri, A.; Fiore, F.; Gilli, R.; Koekemoer, A.; Le Floc'h, E.; Lusso, E.; Lutz, D.; Miyaji, T.; Pozzi, F.; Riguccini, L.; Rosario, D. J.; Silverman, J.; Symeonidis, M.; Treister, E.; Vignali, C.; Zamorani, G.

In: Monthly Notices of the Royal Astronomical Society, Vol. 437, No. 4, 01.02.2014, p. 3550-3567.

Research output: Contribution to journalArticle

Merloni, A, Bongiorno, A, Brusa, M, Iwasawa, K, Mainieri, V, Magnelli, B, Salvato, M, Berta, S, Cappelluti, N, Comastri, A, Fiore, F, Gilli, R, Koekemoer, A, Le Floc'h, E, Lusso, E, Lutz, D, Miyaji, T, Pozzi, F, Riguccini, L, Rosario, DJ, Silverman, J, Symeonidis, M, Treister, E, Vignali, C & Zamorani, G 2014, 'The incidence of obscuration in active galactic nuclei', Monthly Notices of the Royal Astronomical Society, vol. 437, no. 4, pp. 3550-3567. https://doi.org/10.1093/mnras/stt2149
Merloni A, Bongiorno A, Brusa M, Iwasawa K, Mainieri V, Magnelli B et al. The incidence of obscuration in active galactic nuclei. Monthly Notices of the Royal Astronomical Society. 2014 Feb 1;437(4):3550-3567. https://doi.org/10.1093/mnras/stt2149
Merloni, A. ; Bongiorno, A. ; Brusa, M. ; Iwasawa, K. ; Mainieri, V. ; Magnelli, B. ; Salvato, M. ; Berta, S. ; Cappelluti, Nico ; Comastri, A. ; Fiore, F. ; Gilli, R. ; Koekemoer, A. ; Le Floc'h, E. ; Lusso, E. ; Lutz, D. ; Miyaji, T. ; Pozzi, F. ; Riguccini, L. ; Rosario, D. J. ; Silverman, J. ; Symeonidis, M. ; Treister, E. ; Vignali, C. ; Zamorani, G. / The incidence of obscuration in active galactic nuclei. In: Monthly Notices of the Royal Astronomical Society. 2014 ; Vol. 437, No. 4. pp. 3550-3567.
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T1 - The incidence of obscuration in active galactic nuclei

AU - Merloni, A.

AU - Bongiorno, A.

AU - Brusa, M.

AU - Iwasawa, K.

AU - Mainieri, V.

AU - Magnelli, B.

AU - Salvato, M.

AU - Berta, S.

AU - Cappelluti, Nico

AU - Comastri, A.

AU - Fiore, F.

AU - Gilli, R.

AU - Koekemoer, A.

AU - Le Floc'h, E.

AU - Lusso, E.

AU - Lutz, D.

AU - Miyaji, T.

AU - Pozzi, F.

AU - Riguccini, L.

AU - Rosario, D. J.

AU - Silverman, J.

AU - Symeonidis, M.

AU - Treister, E.

AU - Vignali, C.

AU - Zamorani, G.

PY - 2014/2/1

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N2 - We study the incidence of nuclear obscuration on a complete sample of 1310 active galactic nuclei (AGN) selected on the basis of their rest-frame 2-10 keV X-ray flux from the XMMCOSMOS survey, in the redshift range 0.3 < z < 3.5. We classify the AGN as obscured or unobscured on the basis of either the optical spectral properties and the overall SED or the shape of the X-ray spectrum. The two classifications agree in about 70 per cent of the objects, and the remaining 30 per cent can be further subdivided into two distinct classes: at low luminosities X-ray unobscured AGN do not always show signs of broad lines or blue/UV continuum emission in their optical spectra, most likely due to galaxy dilution effects; at highluminosities broad-line AGN may have absorbed X-ray spectra, which hints at an increased incidence of small-scale (sub-parsec) dust-free obscuration. We confirm that the fraction of obscured AGN is a decreasing function of the intrinsic X-ray luminosity, while the incidence of absorption shows significant evolution only for the most luminous AGN, which appear to be more commonly obscured at higher redshift. We find no significant difference between the mean stellar masses and star formation rates of obscured and unobscured AGN hosts. We conclude that the physical state of the medium responsible for obscuration in AGN is complex and mainly determined by the radiation environment (nuclear luminosity) in a small region enclosed within the gravitational sphere of influence of the central black hole, but is largely insensitive to the wider scale galactic conditions.

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KW - catalogues - surveys - galaxies

KW - Evolution - galaxies

KW - Fundamental parameters.

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