Obscured accreting black holes at high redshift
  A significant fraction of the accreting black holes powering high redshift AGN are obscured by large columns of dust and gas. For this reason, luminous type 2 quasars can be efficiently discovered combining hard X-ray and near-infrared observations. We will briefly discuss the most recent results. 
A. Comastri, F. Fiore, C. Vignali, M. Brusa, F. Civano