Search

The shape and the intensity of the 6.4 keV iron line bring unique information on the geometrical and physical properties of the supermassive black hole and the surrounding accreting gas at the very center of Active Galactic Nuclei. While there is convincing evidence of a relativistically broadened iron line in a few nearby bright objects, their properties at larger distances are basically unknown. We have searched for the presence of iron lines by fully exploiting Chandra observations in the deep fields. The line is clearly detected in the average spectra of about 250 sources stacked in several redshift bins over the range z=0.5-4.0. We discuss their average properties with particular emphasis on the presence and intensity of a broad component. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Hard X-ray surveys efficiently sample the obscured AGN population and in particular those with redder colors which would not be selected by UVX surveys. The discovery that a sizable fraction (~20%) of hard X-ray sources are also associated to extremely red objects (EROs) with optical to near-infrared colour R-K>5 is even more intriguing [1,2,1]. [ABSTRACT FROM AUTHOR]