The Contribution of Quasars to the Far-Infrared Background

Abstract

Recent observational results obtained with the Submillimeter Common-User Bolometric Array, COBE, and the Infrared Space Observatory have greatly improved our knowledge of the infrared and submillimeter background radiation. These limits become constraining given the realization that most active galactic nuclei (AGNs) are heavily obscured and must reradiate strongly in the IR/submillimeter wavelengths. Here we predict the contribution of AGNs to the IR/submillimeter background, starting from measurements of the hard X-ray background. We show that an application of what we know of AGN spectral energy distributions and the IR background requires that a significant fraction of the 10-150 μm background comes from AGNs. This conclusion can be avoided only if obscured AGNs are intrinsically brighter in the X-rays (with respect to the optical-UV) than unobscured AGNs, which is contrary to "unified schemes" for AGNs, or if they have a dust-to-gas ratio much lower (≤0.1) than Galactic. We show that these results are rather robust and not strongly dependent on the details of the modeling.