Relative distributions of cosmic ray electrons and magnetic fields in the ISM

We calculate the relative magnitudes of the fluctuations in total synchrotron intensity in the interstellar medium, both from observations and from theory under various assumptions about the correlation or anticorrelation between cosmic rays and interstellar magnetic fields. The results are inconsistent with local energy equipartition between cosmic rays and magnetic fields. The distribution of cosmic rays must be rather uniform at scales of order 1 kpc, whereas interstellar magnetic fields vary at much smaller scales.