  A high density of massive dark objects (MDOs), probably supermassive black
holes, in the centres of nearby galaxies has been inferred from recent
observations. There are various indications that much of the accretion
responsible for producing these objects took place in dust-enshrouded active
galactic nuclei (AGNs). If so, then measurements of the intensity of background
radiation and the source counts in the far-infrared and submillimetre wavebands
constrain the temperature of dust in these AGNs. An additional constraint comes
from the hard X-ray background, if this is produced by accretion. One
possibility is that the dust shrouds surrounding the accreting AGNs are cold,
about 30 K. In this event, the dusty AGNs could be some subset of the
population of luminous distant sources discovered at 850 microns using the
SCUBA array on the JCMT, as proposed by Almaini et al. (1999). An alternative
is that the dust shrouds surrounding the accreting AGNs are much hotter (> 60
K). These values are closer to the dust temperatures of a number of
well-studied low-redshift ultraluminous galaxies that are thought to derive
their power from accretion. If the local MDO density is close to the maximum
permitted, then cold sources cannot produce this density without the
submillimetre background being overproduced if they accrete at high radiative
efficiency, and thus a hot population is required. If the dust-enshrouded
accretion occurred at similar redshifts to that taking place in unobscured
optical quasars, then a significant fraction of the far-infrared background
radiation measured by COBE at 140 microns, but very little of the
submilllimetre background at 850 microns, may have been produced by hot
dust-enshrouded AGNs which may have already been seen in recent X-ray surveys.
