Overall, this picture is in good agreement with direct theoretical predictions of the black-hole growth of SMGs and quasars. What was the catalyst for the rapid black-hole and stellar growth seen in SMGs? Rest-frame ultraviolet images taken by the Hubble

predictions of the black-hole growth of SMGs and quasars. What was the catalyst for the rapid black-hole and stellar growth seen in SMGs? Rest-frame ultraviolet images taken by the Hubble Space Telescope have shown that a considerably larger fraction of SMGs are in major mergers (that is, the merging of two galaxies of comparable masses) than has been found in the coeval galaxy population. Hydrodynamical simulations have shown that major mergers can efficiently transport material towards the central regions of galaxies, providing an effective mechanism to trigger nuclear star formation and fuel the black hole. The result of these major mergers is thought to be massive spheroid-dominated galaxies. Ultra-deep X-ray observations of SMGs undergoing major mergers have shown that AGN activity can be ongoing in both galactic components. Presumably in these major-merger events the black holes will eventually coalesce, further increasing the mass of the black hole in the resultant galaxy. A