Article Summary #4

Probing the Evolution of Molecular Cloud Structure

J. Kainulainen, H. Beuther, T. Henning, and R. Plume, 2009, A&A 508, L35-L38
http://www.aanda.org.mutex.gmu.edu/index.php?option=article&access=standard&Itemid=129&url=/articles/aa/abs/2009/48/aa13605-09/aa13605-09.html

This paper focuses on describing the physical processes inside a molecular cloud, i.e. the way the material is distributed and arranged inside the cloud by calculating the probability distribution of densities in the cloud.

It is known that star formation occurs only in molecular clouds and their structure is very complex and easily affected by the motions created by supersonic turbulences, gas self-gravity and magnetic fields.

For their investigation Kainulainen et al. 2009 chose a sample of molecular clouds complexes within relatively close proximity. The method they used is called the near-infrared dust extinction map technique and with that they derived the extinction of the maps of nearby molecular clouds.

Their results show expected well-fitted log-normal functions at low column densities. Column densities can be derived by measuring the line emission of CO, emission from thermal dust, or from dust extinction. It appears that all clouds with active star formation have a strong excess of high column densities while all quiescent clouds show low excess of high energy clouds.

What they also noticed that the behavior is different at higher column densities where noticeable power law-like wings are present most of the time. These results support the theory that turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but in time gravity becomes predominant.

Thus, the role of the turbulences is important and mostly influences the molecular cloud formation during its early stages, almost to the point where it can be considered the triggering of the active star formation in these molecular clouds.