J1030 field radio heavily obscured AGN

We then selected sources with REX>8.5 as radio- excess AGNs; this corresponds to a 3{sigma} excess above the median value (REX~1). In this way, we find 145 radio-excess sources falling in the Chandra X-ray image footprint but without X-ray detection. From the deep X-ray upper limits, we estimated a lower limit to the obscuration of each radio- excess AGN, finding on average log(N_H_/m{cm^-2^)>23.7.

A CTK AGN scenario is also supported by the results of the X-ray stacking analysis performed on sources at z>1.5, which revealed X-ray luminosities and hardness ratios compatible with very highly obscured AGNs. Finally, we computed the number density of these radio-selected CTK AGNs. While at z~2 the radio number density agrees well with the CTK AGN predictions of different population synthesis models, at z~3 the radio selection returns a CTK AGN number density ~2-3 times larger than what is predicted by the CXB models and X-ray observations.

This result supports the effectiveness of radio emission in selecting the most obscured sources, unraveling a population of AGNs potentially missed by X-ray surveys at z>3; this paves the way to a synergistic use of the future radio and X-ray facilities such as the Square Kilometer Array Observatory (SKAO), NewAthena, and the Advanced X-ray Imager Satellite (AXIS).