A Joint Model of the X-ray And Infrared Extragalactic Backgrounds: I.
  Model Construction And First Results
  We present an extragalactic population model of the cosmic background light
to interpret the rich high-quality survey data in the X-ray and IR bands. The
model incorporates star-formation and supermassive black hole (SMBH) accretion
in a co-evolution scenario to fit simultaneously 617 data points of number
counts, redshift distributions and local luminosity functions (LFs) with 19
free parameters. The model has four main components, the total IR LF, the SMBH
accretion energy fraction in the IR band, the star-formation SED and the
unobscured SMBH SED extinguished with a HI column density distribution. As a
result of the observational uncertainties about the star-formation and SMBH
SEDs, we present several variants of the model. The best-fit reduced chi^2
reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed
by cosmic variances or caveats associated with data. Compared to previous
models, the unique result of this model is to constrain the SMBH energy
fraction in the IR band that is found to increase with the IR luminosity but
decrease with redshift up to z ~ 1.5; this result is separately verified using
aromatic feature equivalent width data. The joint modelling of X-ray and mid-IR
data allows for improved constraints on the obscured AGN, especially the
Compton-thick AGN population. All variants of the model require that
Compton-thick AGN fractions decrease with the SMBH luminosity but increase with
redshift while the type-1 AGN fraction has the reverse trend.
