Donley, J. L. and Koekemoer, A. M. and Brusa, M. and Capak, P. and Cardamone, C. N. and Civano, F. and Ilbert, O. and Impey, C. D. and Kartaltepe, J. S. and Miyaji, T. and Salvato, M. and Sanders, D. B. and Trump, J. R. and Zamorani, G. (2012) Identifying Luminous Active Galactic Nuclei in Deep Surveys: Revised IRAC Selection Criteria. Astrophysical Journal, 748 (2). Art. No. 142. ISSN 0004-637X. http://resolver.caltech.edu/CaltechAUTHORS:20120507-113750592
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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_(2-10keV)(erg s^(–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 50-160 ks. 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.
|Additional Information:||© 2012 American Astronomical Society. Received 2011 August 4; accepted 2012 January 18; published 2012 March 16. We thank Ranga Chary, Harry Ferguson, Joanna Kuraszkiewicz, Mark Lacy, Daniel Stern, Belinda Wilkes, Steve Willner, and the anonymous referee for helpful discussions and comments that improved this paper. J.L.D. is supported by the Giacconi Fellowship at STScI. This work is partially supported by CONACyT Apoyo 83564, DGAPA UNAM Grant PAPIIT IN110209, and NASA ADP Grant NNX07AT02G.|
|Subject Keywords:||galaxies: active; infrared: galaxies; X-rays: galaxies|
|Official Citation:||Identifying Luminous Active Galactic Nuclei in Deep Surveys: Revised IRAC Selection Criteria J. L. Donley et al. 2012 ApJ 748 142|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||08 May 2012 16:14|
|Last Modified:||06 Jul 2015 17:50|
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