Wiley, Astronomical Notes, 12(324), p. 109-112, 2003
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The high redshift sub-mm sources discovered by SCUBA are widely believed to represent the dust-enshrouded formation of massive elliptical galaxies. Given the strong evidence for a link between the formation of the spheroid and the growth of the central black hole, one might expect to see a luminous quasar at the nucleus of every SCUBA source. Somewhat surprisingly, however, only a very small fraction (~5%) are detected by Chandra with quasar luminosities. In this paper I discuss some of the implications of these results and discuss the accumulating evidence that sub-mm sources and quasars may represent different stages in the evolutionary sequence of a massive proto-spheroid.