Gamma-ray probe of the QSO's obscured evolution

The idea that substantial absorption in AGN could be a definite characteristic of the early phases of QSO evolution was invoked to explain the submillimeter observations of X-ray absorbed AGN at z~1 to z~3, that have shown strong emission at 850 mkm. This strong emission is a signature of the copious star formation. In AGN evolution model, the main obscured growth phase of the QSO coincides with formation of the host galaxy spheroid, the completion of which indicates the beginning of the luminous, unobscured phase of the QSO's evolution. The verification of this model at redshifts up to z~6 appears possible via application of the gamma-ray resonant absorption method.