Figure 16: Stacked background-subtracted Chandra counts as a function of rest-frame energy, for sources with and in the 4 Msec CDF-S field (filled circles; [75]). The cyan dashed lines (stars) show the simulated spectra for the high-mass X-ray binary (HMXB) population normalized using the relation between star-formation rate and X-ray luminosity [76]. The blue dashed lines (open squares) show simulated thermal spectra corresponding to a black body with  keV. An absorbed AGN spectrum, given by a power law with and a fixed  cm−2, is shown by the red dashed lines (open circles). In addition, a scattered AGN component, characterized by a 1% reflection of the underlying unobscured power law, is shown by the green dashed lines (open triangles). The resulting summed spectrum (black solid lines) is in very good agreement with the observed counts. The strong detection in the stacked spectrum at  keV confirms the presence of a significant number of heavily obscured AGN in these IR-excess objects [75].