Why Are Only High-Redshift Obscured AGN Bright Submillimeter Sources?

The bulk of the QSO luminosity density was produced at 1<z<3, and with 0.5-2 keV luminosities close to the break of the X-ray luminosity function [6,5]. We have used sensitive submillimetre (submm) observations [8,9,12] (using SCUBA at the JCMT) to show that the submm luminosities of unabsorbed and absorbed broad line QSO in those intervals are radically different (>3σ): only 1 out of 20 unabsorbed QSO has been detected, while 8 out of 19 absorbed QSOs have been detected, all of them are ULIRGs at z>1.5 (see Fig. 1). Furthermore, there is a significant correlation between the far infrared luminosity LFIR and the redshift of the absorbed QSOs. The FIR emission of these objects is due to dust heated by starbursts, rather than reprocessed QSO emission [8,12]. The implied star formation rates (SFR) are >1000 M⊙/y, sufficient to build a substantial fraction of a galaxy spheroid in only a few 100 Myr.