SQUARE_BRACKET_OPENNe VSQUARE_BRACKET_CLOSE-selected heavily obscured QSOs at the epoch of the X-ray background

Despite extensive searches over a wide wavelength range, the population ofheavily obscured, Comptonthick AGN still remains elusive. In particular, athigh redshifts and luminosities only a few Comptonthick objects have beendiscovered. We propose a pilot program of moderately deep XMM exposures (40 to80 ksec each) to observe 3 luminous QSOs at zvirgul1, which is the epoch where thebulk of the missing.. Xray background is expected to be produced. These QSOsare likely to suffer from heavy obscuration. The targets have been selected fromthe SDSS DR5 based on their strong NeV3427A emission. The proposedobservations will unambiguously determine their obscuration degree. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]