Rest-frame 2−10 keV (hard band) X-ray luminosity L_X vs. hydrogen obscuring column N_H for X-ray sources in this study. The upper four panels shows sources in COSMOS, while the lower panels show sources from both GOODS fields combined. Each panel is for a different bin in redshift, increasing left to right. In the three higher redshift bins, the location of the X-ray sources from the lowest (0.2 < z < 0.5) bin are shown for reference as small red points, to clearly bring out the redshift trends in the sample. Sources with N_H consistent with only Galactic obscuration are shown as left-pointing arrows. The fiducial limit of L_X = 10⁴² erg s^-1 used to define a clean AGN sample (employed in Sect. 4.3) is shown by a dashed line. The nominal Compton thick regime of X-ray obscuration (N_H > 10²⁴ cm^-2) is shown as a shaded region in each panel.