Submillimeter surveys at high redshift

Deep submillimeter (submm) surveys offer an unobscured view of dust-enshrouded star formation or AGN activity at high redshifts. SCUBA observations above 2 mJy have resolved 20 - 30% of the far-infrared (FIR) background into discrete sources and have revealed the existence of a distant population of galaxies with properties similar to those of local ultraluminous infrared galaxies. A large fraction of the submm sources have extremely faint optical/near-infrared (NIR) counterparts and hence are inaccessible to optical spectroscopy. Millimetric redshift estimation places the submm population at z = 1 to 3. While the cumulative surface density of the submm sources is low, they are so luminous that if powered mainly by star formation, they dominate the high redshift star formation history. Recent combined SCUBA submm and Chandra hard X-ray studies suggest that the majority of the submm sources are star formers with only a small admixture of obscured AGN.