Details

Autor(en) / Beteiligte

• Donley, J. L
• Rieke, G. H
• Pérez-González, P. G
• Barro, G

Titel

Spitzer's Contribution to the AGN Population

Ist Teil von

• The Astrophysical journal, 2008-11, Vol.687 (1), p.111-132

Ort / Verlag

Chicago, IL: IOP Publishing

Erscheinungsjahr

2008

Quelle

EZB Electronic Journals Library

Beschreibungen/Notizen

• Infrared selection is a potentially powerful way to identify heavily obscured AGNs missed in even the deepest X-ray surveys. Using a 24 [mu]m- selected sample in GOODS-S, we test the reliability and completeness of three infrared AGN selection methods: (1) IRAC color-color selection, (2) IRAC power-law selection, and (3) IR-excess selection; we also evaluate a number of IR-excess approaches. We find that the vast majority of non-power-law IRAC color-selected AGN candidates in GOODS-S have colors consistent with those of star-forming galaxies. Contamination by star-forming galaxies is most prevalent at low 24 [mu]m flux densities ([image]100 [mu]Jy) and high redshifts, but the fraction of potential contaminants is still high ([image]50%) at 500 [mu]Jy, the highest flux density probed reliably by our survey. AGN candidates selected via a simple, physically motivated power-law criterion ('power-law galaxies,' or PLGs), however, appear to be reliable. We confirm that the IR-excess methods successfully identify a number of AGNs, but we also find that such samples may be significantly contaminated by star- forming galaxies. Adding only the secure Spitzer-selected PLG, color- selected, IR-excess, and radio/IR-selected AGN candidates to the deepest X- ray-selected AGN samples directly increases the number of known X-ray AGNs (84) by 54%-77%, and implies an increase to the number of 24 [mu]m-detected AGNs of 71%-94%. Finally, we show that the fraction of MIR sources dominated by an AGN decreases with decreasing MIR flux density, but only down to [image] [mu]Jy. Below this limit, the AGN fraction levels out, indicating that a nonnegligible fraction ([image]10%) of faint 24 [mu]m sources (the majority of which are missed in the X-ray) are powered not by star formation, but by the central engine. The fraction of all AGNs (regardless of their MIR properties) exceeds 15% at all 24 [mu]m flux densities.