Unveiling obscured accretion in the Chandra Deep Field South

We make use of deep HST, VLT, Spitzer, and Chandra data on the Chandra Deep FieldYSouth to constrain the number of Compton-thick AGNs in this field. We show that sources with high 24 mYtoYoptical 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 m luminosity higher than 1044.2 ergs s1 turns out to be similar to that of X-ray-selected, unobscured, and moderately obscured AGNs with 2Y10 keV luminosity higher than 1043 ergs s1 in the redshift bin 1.2Y2.6. This ‘‘factor of 2’’ source population is exactly what is needed to solve the discrepancies between model predictions and X-ray AGN selection