In this talk I will present the long-standing quest for obscured Active Galactic Nuclei (AGN) using multi-wavelength methods and their importance in the reconstruction of the black hole accretion rate density across cosmic time.
In particular, I will highlight some recent results from X-ray surveys and pointed observations, coupled with those coming from the complementary selection of heavily obscured AGN in the mid-IR and optical bands. This multi-band observing strategy has pushed the search for obscured AGN and provided clues to the AGN-galaxy co-evolution scenario up to very high redshift (z~5).
Artistic view of the innermost regions around a supermassive black hole. Credit: NASA/CXC/M. Weiss.