Star formation in molecular clouds is intimately linked to their internal mass distribution .
We present an unprecedentedly detailed analysis of the column density structure of a high-mass , filamentary molecular cloud , namely IRDC G11.11-0.12 ( G11 ) .
We use two novel column density mapping techniques : high-resolution ( FWHM = 2 \arcsec , or \sim 0.035 pc ) dust extinction mapping in near- and mid-infrared , and dust emission mapping with the Herschel satellite .
These two completely independent techniques yield a strikingly good agreement , highlighting their complementarity and robustness .
We first analyze the dense gas mass fraction and linear mass density of G11 .
We show that G11 has a top heavy mass distribution and has a linear mass density ( M _ { \mathrm { l } } \sim 600 M _ { \odot } pc ^ { -1 } ) that greatly exceeds the critical value of a self-gravitating , non-turbulent cylinder .
These properties make G11 analogous to the Orion A cloud , despite its low star-forming activity .
This suggests that the amount of dense gas in molecular clouds is more closely connected to environmental parameters or global processes than to the star-forming efficiency of the cloud .
We then examine hierarchical fragmentation in G11 over a wide range of size-scales and densities .
We show that at scales 0.5 \mathrm { pc } \gtrsim l \gtrsim 8 pc , the fragmentation of G11 is in agreement with that of a self-gravitating cylinder .
At scales smaller than l \lesssim 0.5 pc , the results agree better with spherical Jeans ’ fragmentation .
One possible explanation for the change in fragmentation characteristics is the size-scale-dependent collapse time-scale that results from the finite size of real molecular clouds : at scales l \lesssim 0.5 pc , fragmentation becomes sufficiently rapid to be unaffected by global instabilities .