Recent dynamical evidence indicates that supermassive black holes reside
at the center of most nearby galaxies. The available data (about 30 objects)
show a strong correlation (but with a large scatter) between bulge and black
hole mass [36],
with Mbh = 0.006 Mbulge as a
best-fit. The total mass density in spheroids today is 
bulge =
0.0036+0.0024-0.0017
[14], implying a
mean mass density of dead quasars
Noting that the observed energy density from all quasars is equal to the
emitted energy divided by the average quasar redshift
[59], the
total contribution to the EBL from accretion onto black holes is
where 
(7)
0.1
is the efficiency for transforming accreted rest-mass
energy into radiation (in units of 10%). A population of AGNs at (say)
z ~ 1 could then make a significant contribution to the FIR background
if dust-obscured accretion onto supermassive black holes is an efficient
process [20].