Unveiling Obscured Accretion in the Chandra Deep Field South

We make use of deep HST, VLT, Spitzer and Chandra data on the Chandra Deep Field South to constrain the number of Compton thick AGN in this field. We show that sources with high 24μm 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 5.8μm luminosity higher than 10 erg s turns out to be similar to that of X-ray selected, unobscured and moderately obscured AGNs with 2-10 keV luminosity higher than 10 erg s in the redshift bin 1.2-2.6. This “factor of 2” source population is exactly what it is needed to solve the discrepancies between model predictions and X-ray AGN selection. Subject headings: Active Galactic Nuclei