Identifying luminous active galactic nuclei in deep surveys: Revised IRAC selection criteria

J. L. Donley, A. M. Koekemoer, M. Brusa, P. Capak, C. N. Cardamone, F. Civano, O. Ilbert, Christopher D Impey, J. S. Kartaltepe, T. Miyaji, M. Salvato, D. B. Sanders, J. R. Trump, G. Zamorani

Research output: Contribution to journalArticle

312 Citations (Scopus)

Abstract

Spitzer/IRAC selection is a powerful tool for identifying luminous active galactic nuclei (AGNs). For deep IRAC data, however, the AGN selection wedges currently in use are heavily contaminated by star-forming galaxies, especially at high redshift. Using the large samples of luminous AGNs and high-redshift star-forming galaxies in COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys. The new IRAC criteria are designed to be both highly complete and reliable, and incorporate the best aspects of the current AGN selection wedges and of infrared power-law selection while excluding high-redshift star-forming galaxies selected via the BzK, distant red galaxy, Lyman-break galaxy, and submillimeter galaxy criteria. At QSO luminosities of log L 2-10 keV(ergs-1)≥44, the new IRAC criteria recover 75% of the hard X-ray and IRAC-detected XMM-COSMOS sample, yet only 38% of the IRAC AGN candidates have X-ray counterparts, a fraction that rises to 52% in regions with Chandra exposures of 50-160ks. X-ray stacking of the individually X-ray non-detected AGN candidates leads to a hard X-ray signal indicative of heavily obscured to mildly Compton-thick obscuration (log N H (cm-2) = 23.5 0.4). While IRAC selection recovers a substantial fraction of luminous unobscured and obscured AGNs, it is incomplete to low-luminosity and host-dominated AGNs.

Original languageEnglish (US)
Article number142
JournalAstrophysical Journal
Volume748
Issue number2
DOIs
StatePublished - Apr 1 2012

Fingerprint

active galactic nuclei
galaxies
x rays
stars
wedges
luminosity
stacking
erg
power law
occultation
XMM-Newton telescope
quasars
COSMOS

Keywords

  • galaxies: active
  • infrared: galaxies
  • X-rays: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Donley, J. L., Koekemoer, A. M., Brusa, M., Capak, P., Cardamone, C. N., Civano, F., ... Zamorani, G. (2012). Identifying luminous active galactic nuclei in deep surveys: Revised IRAC selection criteria. Astrophysical Journal, 748(2), [142]. https://doi.org/10.1088/0004-637X/748/2/142

Identifying luminous active galactic nuclei in deep surveys : Revised IRAC selection criteria. / Donley, J. L.; Koekemoer, A. M.; Brusa, M.; Capak, P.; Cardamone, C. N.; Civano, F.; Ilbert, O.; Impey, Christopher D; Kartaltepe, J. S.; Miyaji, T.; Salvato, M.; Sanders, D. B.; Trump, J. R.; Zamorani, G.

In: Astrophysical Journal, Vol. 748, No. 2, 142, 01.04.2012.

Research output: Contribution to journalArticle

Donley, JL, Koekemoer, AM, Brusa, M, Capak, P, Cardamone, CN, Civano, F, Ilbert, O, Impey, CD, Kartaltepe, JS, Miyaji, T, Salvato, M, Sanders, DB, Trump, JR & Zamorani, G 2012, 'Identifying luminous active galactic nuclei in deep surveys: Revised IRAC selection criteria', Astrophysical Journal, vol. 748, no. 2, 142. https://doi.org/10.1088/0004-637X/748/2/142
Donley, J. L. ; Koekemoer, A. M. ; Brusa, M. ; Capak, P. ; Cardamone, C. N. ; Civano, F. ; Ilbert, O. ; Impey, Christopher D ; Kartaltepe, J. S. ; Miyaji, T. ; Salvato, M. ; Sanders, D. B. ; Trump, J. R. ; Zamorani, G. / Identifying luminous active galactic nuclei in deep surveys : Revised IRAC selection criteria. In: Astrophysical Journal. 2012 ; Vol. 748, No. 2.
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abstract = "Spitzer/IRAC selection is a powerful tool for identifying luminous active galactic nuclei (AGNs). For deep IRAC data, however, the AGN selection wedges currently in use are heavily contaminated by star-forming galaxies, especially at high redshift. Using the large samples of luminous AGNs and high-redshift star-forming galaxies in COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys. The new IRAC criteria are designed to be both highly complete and reliable, and incorporate the best aspects of the current AGN selection wedges and of infrared power-law selection while excluding high-redshift star-forming galaxies selected via the BzK, distant red galaxy, Lyman-break galaxy, and submillimeter galaxy criteria. At QSO luminosities of log L 2-10 keV(ergs-1)≥44, the new IRAC criteria recover 75{\%} of the hard X-ray and IRAC-detected XMM-COSMOS sample, yet only 38{\%} of the IRAC AGN candidates have X-ray counterparts, a fraction that rises to 52{\%} in regions with Chandra exposures of 50-160ks. X-ray stacking of the individually X-ray non-detected AGN candidates leads to a hard X-ray signal indicative of heavily obscured to mildly Compton-thick obscuration (log N H (cm-2) = 23.5 0.4). While IRAC selection recovers a substantial fraction of luminous unobscured and obscured AGNs, it is incomplete to low-luminosity and host-dominated AGNs.",
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