Column density PDFs of a nearby star-forming cloud (Taurus, red histogram) from K09 and one IRDC of this study (Cloud A, blue histogram). In K09, the different parts of the PDFs are referred to as “log-normal” and a “tail” (or, a “power-law)”. The ranges of these two components are indicated in the figure with red arrows. The red dashed line shows a log-normal fit to the “log-normal” part of the PDF. The blue dashed line that shows a log-normal fit to the IRDC data results to a clearly wider log-normal function than those discussed by K09. As the figure indicates, the log-normals we fit to IRDC data are relatively close in their shape to the “power-law tails” discussed by K09 in the range A_V = 7−25 mag.