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Published July 20, 2013 | Published
Journal Article Open

Star Formation on Subkiloparsec Scale Triggered by Non-linear Processes in Nearby Spiral Galaxies


We report a super-linear correlation for the star formation law based on new CO(J = 1-0) data from the CARMA and NOBEYAMA Nearby-galaxies (CANON) CO survey. The sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined with the star formation rate surface density traced by Hα and 24 μm images, CO(J = 1-0) data provide a super-linear slope of N = 1.3. The slope becomes even steeper (N = 1.8) when the diffuse stellar and dust background emission is subtracted from the Hα and 24 μm images. In contrast to the recent results with CO(J = 2-1) that found a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO(J = 2-1) is likely enhanced in the regions with higher star formation and does not linearly trace the molecular gas mass. In addition, the diffuse emission contaminates the SFE measurement most in regions where the star formation rate is law. These two effects can flatten the power-law correlation and produce the apparent linear slope. The super-linear slope from the CO(J = 1-0) analysis indicates that star formation is enhanced by non-linear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions.

Additional Information

© 2013 The American Astronomical Society. Received 2013 March 28; accepted 2013 June 23; published 2013 July 10. We are grateful to the referee for constructive comments to improve this Letter. We thank to Frank Bigiel, Rahul Shetty, and Junichi Baba for discussions, Yasutaka Kurono for helping us to combine our CO(J = 1–0) data, and James Barrett for helpful comments on the English. We also thank the SINGS team, the NRO staff for NRO45 observations, and the CARMA staff for CARMA observations. Support for CARMA construction was derived from the Gordon and Betty Moore Foundation, the Kenneth T. and Eileen L. Norris Foundation, the James S. McDonnell Foundation, the Associates of the California Institute of Technology, the University of Chicago, the states of California, Illinois, and Maryland, and the National Science Foundation. Ongoing CARMA development and operations are supported by the National Science Foundation under a cooperative agreement and by the CARMA partner universities. This research was partially supported by Hayakawa Yukio Foundation. J.K. acknowledges support from the NSF through grant AST-1211680.

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