Detecting Obscured AGN in the Distant Universe with

We present the results of a Spitzer search for obscured AGN in the Chandra Deep Field-North, using both radio-excess and mid-infrared power-law selection. AGN selected via the former technique tend to lie at z ∼ 1, have SEDs dominated by the 1.6 μm stellar bump, and have Seyfert-like X-ray luminosities (when detected in the X-ray). In contrast, the IRAC (3.6-8.0 μm) power-law selected AGN lie at higher redshifts of z ∼ 2, and comprise a significant fraction of the most X-ray luminous AGN in the CDF-N. While there is almost no overlap in the AGN samples selected via these two methods, their X-ray detection fractions are very similar. Only 40% and 55% of the radio-excess and power-law samples are detected in the 2 Ms X-ray catalog, respectively. The majority of the AGN selected via both methods are consistent with being obscured (NH > 10 22 cm), but not Compton-thick (NH > 10 24 cm), although Compton-thick candidates exist in both samples. We place an upper limit of ≤ 82% (or ≤ 4 : 1) on the obscured fraction of the power-law sample, consistent with predictions from the cosmic X-ray background. The sources selected via the power-law criteria comprise a subset of AGN selected via other IRAC color-color cuts. While smaller in number than the color-selected samples in the deep fields, the powerlaw sample suffers from less contamination by star-forming galaxies.