Dependence of unresolved 6.4 keV Fe line equivalent width on the average luminosity (left) and the average redshift (right) of the subsamples (first row of Table 3). Squares: L − z subsamples; circles: redshift subsamples; triangles: luminosity subsamples. We represent upper limits by a down-pointing arrow. Each set of points with the same symbol are statistically independent, but not between the symbols.