  Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is
largely due to accretion onto supermassive black holes, integrated over cosmic
time. However, the characteristic hard spectrum of the XRB can only be
explained if most AGN spectra are heavily absorbed. The absorbed AGN will
suffer severe extinction and therefore, unlike classical QSOs, will not be
prominent at optical wavelengths. Most of the accretion power is being absorbed
by gas and dust and will have to be reradiated in the FIR/sub-mm band. AGN
could therefore contribute a substantial fraction to the recently discovered
cosmic FIR/sub-mm background. Here it is shown that a number of high-redshift
absorbed X-ray sources selected in the ROSAT Deep Survey of the Lockman Hole
have broad-band spectral energy distributions very similar to the local ULIRG
NGC6240, lending additional support to the background models for the obscured
universe.
