We place strong spectral constraints on an AGN synthesis model for the extragalactic X-ray background (XRB). It is strongly believed that the XRB is nearly entirely composed of unresolved discrete sources, with a major contribution being due to AGN . Here, we use the unified AGN model of Antonucci to construct spectral models for the XRB. The primary adjustable parameters of these models are photon spectral index of the sources, column density for Seyfert 2 sources, ratio of Seyfert 2's to Seyfert 1's, their luminosity evolution, and the local volume emissivity. The existence of iron K line emission in AGN should produce spectral features in the XRB with some of these models. The magnitude of these features depend on the typical AGN X-ray spectrum as well as on the cosmological evolution of AGN. Several models predict structure in the 1-3 keV range where ASCA has high sensitivity and spectral resolution. We use the ASCA XRB data from deep survey fields to test these models. The ASCA data show no sharp spectral features in the XRB. The allowed parameter space for acceptable AGN synthesis models is small, but consistent with independently derived AGN data. We find that the equivalent width of the iron K line from the typical AGN must be less than 320 eV. We can put lower limits on the AGN luminosity evolution index of about 2.5. Applying independently derived X-ray volume emissivity results and AGN spectral indices as additional constraints, we can predict number ratios of Seyfert 2 to Seyfert 1 galaxies which are close to unity. We can also predict source counts in various bandpasses as a function of flux.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 1995