Absolute and relative ZGR23 extinction in dust-free regions. Panel (a): Histogram of the ZGR23 extinctions in dust-free regions translated to A_V. The mean extinction in dust-free regions based on Planck is shown as a vertical green line, and the cutoff value translated to A_V for our definition of dust-free is shown in red. Panel (b): Same as panel (a) but the extinctions are scaled by their accompanying uncertainties. A truncated standard normal distribution and a standard normal distribution are plotted on top. Both ordinates are logarithmic.