4.4. Active galaxies and X-ray sources

An important category of objects that could be associated with submm galaxies are accreting AGN. As discussed in Sections 2.8 and 3.2.4, the overlap between Chandra and SCUBA galaxies does not appear to be very great - at about the 10% level. However, the gravitational energy released when forming the supermassive black holes in the centers of galactic bulges (Magorrian et al., 1998) is likely to be only a few times less than the energy released by stellar nucleosynthesis over the lifetime of the stars in the bulge, and so a case remains for the existence of both a significant population of Compton-thick AGN submm sources with no detectable X-ray emission at energies less than 10 keV, and for hot dusty AGN detectable in the mid- and far-IR but not the submm wavebands (Wilman et al., 2000; Blain and Phillips, 2002).