Abstract

Heavily obscured AGN represent a fundamental phase in the MBH -galaxy coevolution scenario. They are expected to constitute a major fraction of the whole AGN population, in particular at high-z, but their statistics and evolution across cosmic time are still highly uncertain. A promising way to select most obscured AGN is through radio emission, which is largely unaffected by obscuration and can be used as a proxy for nuclear activity. In this talk, I will present a detailed investigation of the effectiveness of radio selection to discover heavily obscured AGN , I will compare their radio and X-ray detectability, and present predictions for current and future radio surveys. Our results show that, while X-ray selection is generally more effective in detecting unobscured AGN , radio selection is significantly more effective in detecting the most heavily obscured, Compton-thick AGN . Thousands of Compton-thick nuclei are indeed expected to hide among the sources of popular radio catalogs, escaping any detection in the corresponding X-ray observations. I will finally present expectations for the number of AGN to be detected by the continuum surveys of the Square Kilometer Array Observatory (SKAO). SKAO is expected to detect more than 2000 AGN at z>6, and even some tens at z>10: half of them Compton-thick.