  We present a synthesis model of the X-ray background based on the
cross-correlation between mid-infrared and X-ray surveys, where the
distribution of type 2 sources is assumed to follow that of luminous infrared
galaxies while type 1 sources are traced by the observed ROSAT distribution.
The best fits to both the X-ray number counts and background spectrum require
at least some density evolution. We explore a limited range of parameter space
for the evolutionary variables of the type 2 luminosity function. Matching the
redshift distribution to that observed in deep Chandra and XMM fields, we find
weak residuals as a signature of Fe emission from sources in a relatively
peaked range of redshift. This extends the recent work of Franceschini et al.,
and emphasizes the possible correlation between obscured AGN and star-forming
activity.
