Unveiling Obscured Accretion in the Chandra Deep Field–South

Abstract

We make use of deep HST, VLT, Spitzer, and Chandra data on the Chandra Deep Field-South to constrain the number of Compton-thick AGNs in this field. We show that sources with high 24 μm-to-optical flux ratios and red colors form a distinct source population, and that their infrared luminosity is dominated by AGN emission. Analysis of the X-ray properties of these extreme sources shows that most of them (80% ± 15%) are indeed likely to be highly obscured, Compton-thick AGNs. The number of infrared-selected, Compton-thick AGNs with 5.8 μm luminosity higher than 10 44.2 ergs s _1 turns out to be similar to that of X-ray-selected, unobscured, and moderately obscured AGNs with 2-10 keV luminosity higher than 10 43 ergs s -1 in the redshift bin 1.2-2.6. This "factor of 2" source population is exactly what is needed to solve the discrepancies between model predictions and X-ray AGN selection. © 2008. The American Astronomical Society. All rights reserved.