Galaxies grow through both internal and external processes. In about 10% of nearby red galaxies with little star formation, gas and stars are counter-rotating, demonstrating the importance of external gas acquisition in these galaxies. However, systematic studies of such phenomena in blue, star-forming galaxies are rare, leaving uncertain the role of external gas acquisition in driving evolution of blue galaxies. Here, based on new measurements with integral field spectroscopy of a large representative galaxy sample, we find an appreciable fraction of counter-rotators among blue galaxies (9 out of 489 galaxies). The central regions of blue counter-rotators show younger stellar populations and more intense, ongoing star formation than their outer parts, indicating ongoing growth of the central regions. The result offers observational evidence that the acquisition of external gas in blue galaxies is possible; the interaction with pre-existing gas funnels the gas into nuclear regions (< 1 kpc) to form new stars.

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Published in Nature Communications, v. 7, article no. 13269, p. 1-9.

© The Author(s) 2016

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Due to the large number of authors, only the first 30 and the authors affiliated with the University of Kentucky are listed in the author section above. For the complete list of authors, please download this article.

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Funding Information

Y.M.C. acknowledges support from NSFC grant 11573013, 11133001, the Natural Science Foundation of Jiangsu Province grant BK20131263, the Opening Project of Key Laboratory of Computational Astrophysics, National Astronomical Observatories, Chinese Academy of Sciences. Y.S. acknowledges support from NSFC grant 11373021, the CAS Pilot-b grant no. XDB09000000 and Jiangsu Scientific Committee grant BK20150014. C.A.T. acknowledges support from National Science Foundation of the United States grant no. 1412287. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah.

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The data supporting the findings of this study are avail- able through SDSS Data Release Thirteen which can be downloaded from http://www.sdss.org/dr13/manga/.

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