tokens: We thank Dmitrii Barsukov, Serge Balashev and Aida Kirichenko for discussions. The work was supported by the Russian Science Foundation, grant 14-12-00316. For Fig. 6 we used the data from the VGPS survey conducted by the National Radio Astronomy Observatory (NRAO) instruments. NRAO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
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