Where are the type 2 AGNs?
arXiv:astro-ph/0001332
Abstract
Most of the energy of the X-ray background is contributed by sources with a hard X-ray spectrum, harder than the spectrum observed in nearby type 1 AGNs. The hard background contributors are conventionally identified with type 2 AGNs, obscured by circumnuclear matter both in the optical and in the soft X rays. However, preliminary results of identification programs seem to find systematically few type 2 AGNs in samples selected with obscuration insensitive criteria. We discuss this issue, and assess the various scenarios which are being proposed to solve the discrepancy.
To appear in the proceedings of the conference "Large Scale Structure in the X-ray Universe", Santorini, Greece, September 1999, 4 pages, 2 figures