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N. Mortessagne, P. Pavloff, and . M. Vignolo-for-helpful-discussions, A. is grateful to P. Leboeuf who was very enthusiastic about the idea of superfluid motion of light. This work has been supported by the the Region PACA and the French government, through the UCA JEDI Investments in the Future project managed by the National Research Agency (ANR) with the reference number ANR- 15-IDEX-01, L. was funded by the Centre National de la Recherche Scientifique (CNRS), the ANR under Grant No. ANR-14-CE26-0032 LOVE, and the Université de Cergy-Pontoise
URL : https://hal.archives-ouvertes.fr/hal-00019649

C. M. Author, O. B. , and M. B. , performed the experiments and analyzed the data, developed the theory. All authors participated in the discussions and in writing the paper. Competing interests The authors declare no competing interests