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Published October 20, 2012 | Published
Journal Article Open

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

Abstract

We analyze 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. For each cloud, we estimate the shear parameter which describes the ability of density perturbations to grow within the cloud. We find that for almost all molecular clouds considered, there is no evidence that shear is playing a significant role in opposing the effects of self-gravity. We also find that the shear parameter of the clouds does not depend on their position in the Galaxy. Furthermore, we find no correlations between the shear parameter of the clouds with several indicators of their star formation activity. No significant correlation is found between the shear parameter and the star formation efficiency of the clouds which is measured using the ratio of the massive young stellar objects luminosities, measured in the Red MSX survey, to the cloud mass. There are also no significant correlations between the shear parameter and the fraction of their mass that is found in denser clumps which is a proxy for their clump formation efficiency, nor with their level of fragmentation expressed in the number of clumps per unit mass. Our results strongly suggest that shear is playing only a minor role in affecting the rates and efficiencies at which molecular clouds convert their gas into dense cores and thereafter into stars.

Additional Information

© 2012 American Astronomical Society. Received 2012 January 31; accepted 2012 August 31; published 2012 October 8. We are very grateful to the referee for a thoughtful report which helped us improve both the content of the paper and the presentation of the results. We also thank Samuel Boissier and Ruixiang Chang for useful discussions. S.D. acknowledges support from the Science and Technology Facilities Council (STFC) grant ST/H00307X/1 and a Santander Mobility Award. T.J.T.M. is supported in part by STFC grant ST/001847/1. This publication makes use of molecular line data from the Boston University-FCRAO Galactic Ring Survey (GRS). The GRS is a joint project of Boston University and Five College Radio Astronomy Observatory, funded by the National Science Foundation under grants AST-9800334, AST-0098562, and AST-0100793. This paper made use of information from the RedMSX Source survey database at www.ast.leeds.ac.uk/RMS which was constructed with support from the STFC. Partial support for this work was provided by NASA through the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology.

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August 22, 2023
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