The dark side of accretion: chasing type 2 QSOs

We propose to detect the Xray emission of a sample of five extreme QSOs,selected to be bright at midIR Spitzer and Radio (VLA) waveleghts but withfaint nearIR and optical counterparts. They could be the tip of the iceberg ofa population of heavily obscured AGN which may carry a large fraction ofaccretion and of the SMBH mass density at z>2. The proposed observations arecrucial to evaluate the fraction of the midinfrared selected type 2 QSOs whichwould have been selected also by Xray surveys, and to assess whether the midIRselection is truly more efficient in discovering the long sougth population ofhighz Compton thick AGN postulated in all AGN synthesis models for the CXB,with obvious important consequences for the estimates of the SMBH mass density. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]