1202.4699 (Sami Dib et al.)

The Lesser Role of Shear in Star Formation: Insight from the Galactic Ring Survey    [PDF]

Sami Dib, George Helou

We analyse the role played by shear in regulating star formation in the Galaxy on the scale of individual molecular clouds. The clouds are selected from the $^{13}$CO $J=1-0$ line of the Galactic Ring Survey. We estimate the shear parameter which is the ratio of a critical surface density for the clouds to be disrupted by shear to their actual surface density. We find that for almost all molecular clouds considered in the sample, there is no evidence that shear is playing a significant role in opposing the effects of self-gravity. Furthermore, we find that the shear parameter of the clouds does not depend on their position in the Galaxy, which implies that shear can not explain the radial profiles of the Galactic star formation rates. We also find that for gravitationally bound clouds, higher shear parameters do not imply lower masses nor that the shear parameter correlates with the clouds level of fragmentation. Our results suggest that shear is playing only a minor role in affecting the rates at which gravitationally bound molecular clouds convert their gas into dense cores and thereafter into stars.

View original: http://arxiv.org/abs/1202.4699