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Fig. 2.


Two extreme cases in which XZ provides the correct redshift. Left panel: unbinned X-ray source and background region counts for R65, a heavily obscured AGN (log NH ≃ 24.4 cm−2) with a relatively low number of source counts. The counts are plotted in a horizontal line to show their energy in the observed frame. While the background count rate is nearly independent of energy, source counts clearly cluster at 4 keV. Assuming that feature corresponds to the rest-frame 6.4 keV Fe Kα feature, we can compute the corresponding redshift z = 6.4 keV/Eobs−1 to the energy (top axis). We find z = 0.69, which is consistent with the optically derived spectroscopic redshift. Right panel: binned X-ray spectrum of source R4, a mildly obscured AGN with a high number of counts. The green curve is the best fit, yielding log NH ≃ 22.6 cm−2 and Γ ∼ 1.9 and finds the spectroscopic redshift z = 0.31 (see Fig. 3). The black curve shows the fit if the redshift is fixed to z = 2, which does not follow the data points as well.

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