The growth of the nuclear black holes in submillimetre galaxies

We show that the ABC scenario we proposed for the co-evolution of spheroids and QSOs predicts accretion rates and masses of supermassive black holes in submillimetre galaxies in keeping with recent X-ray determinations. These masses are well below the local values as well as those predicted by alternative models. The observed column densities may be mostly due to interstellar medium in the galaxy. The contribution of the associated nuclear activity to the X-ray background is likely negligible, while they may contribute a sizeable fraction of similar to 10 per cent to hard X-ray cumulative counts at the faintest observed fluxes.