We present a new backward evolution model for galaxies and AGNs in theinfrared (IR). What is new in this model is the separate study of theevolutionary properties of the different IR populations (i.e. spiral galaxies,starburst galaxies, low-luminosity AGNs, "unobscured" type 1 AGNs and"obscured" type 2 AGNs) defined through a detailed analysis of the spectralenergy distributions (SEDs) of large samples of IR selected sources. Theevolutionary parameters have been constrained by means of all the availableobservables from surveys in the mid- and far-IR (source counts, redshift andluminosity distributions, luminosity functions). By decomposing the SEDsrepresentative of the three AGN classes into three distinct components (astellar component emitting most of its power in the optical/near-IR, an AGNcomponent due to hot dust heated by the central black hole peaking in themid-IR, and a starburst component dominating the far-IR spectrum) we havedisentangled the AGN contribution to the monochromatic and total IR luminosityemitted by the different populations considered in our model from that due tostar-formation activity. We have then obtained an estimate of the total IRluminosity density (and star-formation density - SFD - produced by IR galaxies)and the first ever estimate of the black hole mass accretion density (BHAR)from the IR. The derived evolution of the BHAR is in agreement with estimatesfrom X-rays, though the BHAR values we derive from IR are slightly higher thanthe X-ray ones. Finally, we have simulated source counts, redshiftdistributions and SFD and BHAR that we expect to obtain with the futurecosmological Surveys in the mid-/far-IR that will be performed with JWST-MIRIand SPICA-SAFARI.
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