We study the probability distribution function ( PDF ) of mass surface densities , \Sigma , of infrared dark cloud ( IRDC ) G028.37+00.07 and its surrounding giant molecular cloud .
This PDF constrains the physical processes , such as turbulence , magnetic fields and self-gravity , that are expected to be controlling cloud structure and star formation activity .
The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 parsecs , making it one of the most massive , dense molecular structures known and is thus a potential site for the formation of a “ super star cluster. ” We study \Sigma in two ways .
First , we use a combination of NIR and MIR extinction maps that are able to probe the bulk of the cloud structure up to \Sigma \sim 1 \ > { g\ > cm ^ { -2 } } \ > ( A _ { V } \simeq 200 mag ) .
Second , we study the FIR and sub-mm dust continuum emission from the cloud utilizing Herschel PACS and SPIRE images and paying careful attention to the effects of foreground and background contamination .
We find that the PDFs from both methods , applied over a \sim 20 ^ { \prime } ( 30 pc ) -sized region that contains \simeq 1.5 \times 10 ^ { 5 } \ > M _ { \odot } and encloses a minimum closed contour with \Sigma \simeq 0.013 \ > { g\ > cm ^ { -2 } } \ > ( A _ { V } \simeq 3 mag ) , shows a log-normal shape with the peak measured at \Sigma \simeq 0.021 \ > { g\ > cm ^ { -2 } } \ > ( A _ { V } \simeq 4.7 mag ) .
There is tentative evidence for the presence of a high- \Sigma power law tail that contains from \sim 3 \% to 8 % of the mass of the cloud material .
We discuss the implications of these results for the physical processes occurring in this cloud .