SPECTRAL CONSTRAINTS ON SEYFERT-2 GALAXIES AS MAJOR CONTRIBUTORS TO THE HARD (3-100 KEV) X-RAY-BACKGROUND

It has been suggested that the flat spectrum of the X-ray background (XRB) above 3 keV and below approximately 15 keV could be explained by the superposition of absorbed sources at different redshifts. To explain the steepening of the XRB spectrum above approximately 15 keV, the intrinsic source spectrum should cut off at approximately 50-100 keV, as observed in NGC 4151 and galactic black hole candidates. Here, assuming that Seyfert 2 galaxies are Seyfert 1 galaxies obscured by intervening matter in the line of sight, as postulated by the unified model, and that they provide the major contribution to the XRB in the 3-100 keV energy range, we derive some constraints on their spectrum and evolution, and indicate, in view of future ASCA measurements, the use of iron spectral features as a test of the model.