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[21.06] The nature of the sources of the X-ray and infrared backgrounds

A. Comastri (Osservatorio Astronomico Bologna), F. Fiore (Osservatorio Astronomico Roma), C. Vignali (Osservatorio Astronomico Bologna), F. La Franca (Dipartimento di Fisica, Univ. Roma Tre), M. Brusa (Osservatorio Astronomico Bologna)

We present optical, infrared and radio follow-up observations of the hard X--ray selected sources discovered by BeppoSAX and Chandra surveys. The multiwavelength data indicate that at least half of the X--ray sources are ``intermediate'' AGN, i.e. type 1.8-1.9 AGN, ``red" quasars, and even a few broad line, blue continuum quasars, all obscured in X-rays by columns of the order of 10^22-23.5 cm^-2, but showing a wide dispersion in their optical extinction properties. Intriguingly, we also find a few X--ray bright optically dull galaxies. We discuss how our findings can help in discriminating among competing scenarios for the synthesis of the hard X--ray background. The present data are also used to compute the contribution of the hard X--ray sources to the far--infrared background.

This work is supported by the MURST grant Cofin 98--02--32 and by the ASI contract ASI--ARS--99--75.