tokens: z sample imply the presence of a puffed-up torus in the low- N H NLRGs, suggesting that L / L Edd extends to lower values than those in the high- z sample. 7.2. <italic>N</italic><sub>H</sub> Distribution The distributions of the intrinsic N H in the medium- and high- z 3CRR samples are presented in Figure 17 . The high- z sample (on the right) shows a bimodal distribution, where quasars have N H 10 22.5 cm −2 , consistent with low obscuration at face-on inclination angles, while the NLRGs show N H > 10 22.5 cm −2 , implying higher obscuration at higher inclination angles, consistent with unification schemes. There are two quasars with moderate column densities (10 22.5 N H /cm −2 10 23 ) and hard HRs (0 HR 0.5) in this sample. In the medium- z sample, the distributions of quasars and NLRGs overlap. Although the quasars show N H 10 22.5 cm −2 , similar to quasars at high redshifts, the NLRGs have a much broader range of column densities that extend to lower, quasar-like values in the low- N H NLRGs. These NLRGs possibly have low L / L Edd , which allows clouds with low column density to form in the vicinity of the central engine (Section 6.3 ). Such low L / L Edd NLRGs are missing from the high- z sample. Figure 17. Histograms of the X-ray equivalent intrinsic hydrogen column density N H for the medium- z 3CRR sample (left) and the high- z 3CRR sample (Wilkes et al. 2013 ; right). Quasars are shown in blue and NLRGs in red. Upper limits, mostly for quasars with no evidence for intrinsic absorption, are indicated by arrows. CT NLRGs in the medium- z sample with no measurement of N H due to low S/N are indicated by an underlined 3C identification. Note the low- N H (≤10 22 cm −2 ) NLRGs in the medium- z sample that are not present in the high- z sample. Although a simple unification model was sufficient to explain the X-ray data and the bimodal N H distribution in the high- z sample, this is not the case in the medium- z sample. An additional parameter, a range of L / L Edd , is required to explain the large range of N H in NLRGs seen at intermediate inclination angles, skimming the edge of the torus or accretion disk atmosphere/wind. As a result, the broad range of L / L Edd smears the N H distribution for NLRGs, removing the bimodality that was found in the high- z sample. Turning this argument around, because the unification model was sufficient for the high- z 3CRR sample, producing a bimodal and narrow N H distribution, the L / L Edd ratio must have a narrower range and higher values compared to the medium- z sample, allowing orientation effects to dominate the properties of the high- z sample. To test this hypothesis, we compiled spectra of the high- z 3CRR quasars (from the SDSS archive; Barthel et al. 1990 ; M. Vestergaard D. Stern 2021, private communication) and measured the black hole masses from the widths of the C iv and Mg ii emission lines. The masses (measured in 12 out of 20 high- z quasars) are in the range of M BH = 10 7.7 to
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