Deep SCUBA surveys have uncovered a large population of ultra-luminous galaxies at z > 1 .
These sources are often assumed to be starburst galaxies , but there is growing evidence that a substantial fraction host an AGN ( i.e. , an accreting super-massive black hole ) .
We present here possibly the strongest evidence for this viewpoint to date : the combination of ultra-deep X-ray observations ( the 2 Ms Chandra Deep Field-North ) and deep optical spectroscopic data .
We argue that upward of 38 % of bright ( f _ { 850 \mu m } \geq 5 mJy ) SCUBA galaxies host an AGN , a fraction of which are obscured QSOs ( i.e. , L _ { X } > 3 \times 10 ^ { 44 } erg s ^ { -1 } ) .
However , using evidence from a variety of analyses , we argue that in almost all cases the AGNs are not bolometrically important ( i.e. , < 20 % ) .
Thus , star formation appears to dominate their bolometric output .
A substantial fraction of bright SCUBA galaxies show evidence for binary AGN activity .
Since these systems appear to be interacting and merging at optical/near-IR wavelengths , their super-massive black holes will eventually coalesce .