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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 [42], with Mbh = 0.006 Mbulge as a best-fit. The total mass density in spheroids today is Omegabulge = 0.0036+0.0024-0.0017 [18], implying a mean mass density of dead quasars

Equation 6 (6)

Noting that the observed energy density from all quasars is equal to the emitted energy divided by the average quasar redshift [63], the total contribution to the EBL from accretion onto black holes is

Equation 7 (7)

where eta0.1 is the efficiency for transforming accreted rest-mass energy into radiation (in units of 10%). A population of AGNs at (say) z ~ 1.5 could then make a significant contribution to the FIR background if dust-obscured accretion onto supermassive black holes is an efficient process [24], [15]. It is interesting to note in this context that a population of AGNs with strong intrinsic absorption (Type II quasars) is actually invoked in many current models for the X-ray background [37], [9].