Left: probability density function (PDF) of column density in the Ophiuchus molecular cloud and its subclouds L1688, L1689 and L1709, as derived from the high-resolution column density map at a resolution of 18′′2. (See Table 2 for the results of power-law fits to the high-column density tails of the PDF.) The PDF of L1688 shows an overdensity around , probably as a consequence of the Sco OB2 influence. Right: normalized cumulative mass fraction as function of column density for the Ophiuchus molecular cloud using the same column-density map as in the top figure. The dashed line represents the fiducial dividing line between dense star-forming gas and lower-density gas. In the various parts of the cloud, the vast majority of the gas is found at low column density (A_V ≤ 2).