X-ray absorption in distant type II QSOs

Aims. We present the results of the X-ray spectral analysis of an XMM-Newton-selected type II QSO sample with z >= 0.5 and 0.5-10 keV flux of 0.3-33 x 10(-14) erg/s/cm(2). The distribution of absorbing column densities in type II QSOs is investigated and the dependence of absorption on X-ray luminosity and redshift is studied. Methods. We inspected 51 spectroscopically classified type II QSO candidates from the XMM-Newton Marano field survey, the XMM-Newton-2dF wide angle survey (XWAS), and the AXIS survey to set-up a well-defined sample with secure optical type II identifications. Fourteen type II QSOs were classified and an X-ray spectral analysis performed. Since most of our sources have only similar to 40 X-ray counts (PN-detector), we carefully studied the fit results of the simulated X- ray spectra as a function of fit statistic and binning method. We determined that fitting the spectra with the Cash-statistic and a binning of minimum one count per bin recovers the input values of the simulated X- ray spectra best. Above 100 PN counts, the free fits of the spectrum's slope and absorbing hydrogen column density are reliable. Results. We find only moderate absorption (NH = (2-10) x 10(22) cm(-2)) and no obvious trends with redshift and intrinsic X- ray luminosity. In a few cases a Compton-thick absorber cannot be excluded. Two type II objects with no X- ray absorption were discovered. We find no evidence for an intrinsic separation between type II AGN and high X- ray luminosity type II QSO in terms of absorption. The stacked X- ray spectrum of our 14 type II QSOs shows no iron K alpha line. In contrast, the stack of the 8 type II AGN reveals a very prominent iron Ka line at an energy of similar to 6.6 keV and an EW similar to 2 keV.