Left: cumulative distribution functions (CDFs) of the IRDCs, expressing the fraction of mass at column densities higher than the abscissa value. The functions are normalized to unity at A_V = 7 mag. For comparison, the CDF of the Orion A molecular cloud from K09 is shown in the panel. The functions are normalized at their value at A_V = 7 mag. Right: the CDFs of the IRDCs and three nearby clouds from K09 (Orion A, Orion B, and the California Cloud, shown with dotted lines). The CDFs of the IRDCs were derived after smoothing and re-binning the IRDC column density data to the spatial resolution of the nearby clouds. Only the values in the range A_V = 7−30 mag were used in deriving the CDFs shown in the panel.