We report on the first SCUBA detection of a Type 2 QSO at z=3.660 in the Chandra Deep Field South .
This source is X-ray absorbed , shows only narrow emission lines in the optical spectrum and is detected in the sub-mm : it is the ideal candidate in an evolution scheme for AGN ( e.g .
Fabian ( 1999 ) ; Page et al .
( 2004 ) ) of an early phase corresponding to the main growth of the host galaxy and formation of the central black hole .
The overall photometry ( from the radio to the X-ray energy band ) of this source is well reproduced by the spectral energy distribution ( SED ) of NGC 6240 , while it is incompatible with the spectrum of a Type 1 QSO ( 3C273 ) or a starburst galaxy ( Arp 220 ) .
Its sub-mm ( 850 \mu m ) to X-ray ( 2 keV ) spectral slope ( \alpha _ { SX } ) is close to the predicted value for a Compton-thick AGN in which only 1 \% of the nuclear emission emerges through scattering .
Using the observed flux at 850 \mu m we have derived a SFR=550–680 M _ { \odot } /yr and an estimate of the dust mass , M _ { dust } = 4.2 \times 10 ^ { 8 } M _ { \odot } .