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Relative distribution of cosmic rays and magnetic fields

Lookup NU author(s): Amit Seta, Professor Anvar ShukurovORCiD, Dr Toby Wood, Professor Paul BushbyORCiD, Andrew Snodin



This is the authors' accepted manuscript of an article that has been published in its final definitive form by Oxford University Press, 2018.

For re-use rights please refer to the publisher's terms and conditions.


Synchrotron radiation from cosmic rays is a key observational probe of the galactic magneticfield. Interpreting synchrotron emission data requires knowledge of the cosmic ray number density, which is often assumed to be in energy equipartition (or otherwise tightly correlated) with the magnetic field energy. However, there is no compelling observational or theoretical reason to expect such tight correlation to hold across all scales. We use test particle simulations, tracing the propagation of charged particles (protons) through a random magnetic field, to study the cosmic ray distribution at scales comparable to the correlation scale of the turbulent flow in the interstellar medium (approx 100 pc in spiral galaxies). In these simulations, we find that there is no spatial correlation between the cosmic ray number density and the magnetic field energy density. In fact, their distributions are approximately statistically independent. We find that low-energy cosmic rays can become trapped between magnetic mirrors, whose location depends more on the structure of the field lines than on the field strength.

Publication metadata

Author(s): Seta A, Shukurov A, Wood TS, Bushby PJ, Snodin AP

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2018

Volume: 473

Issue: 4

Pages: 4544-4557

Print publication date: 01/02/2018

Online publication date: 09/10/2017

Acceptance date: 04/10/2017

Date deposited: 10/10/2017

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press


DOI: 10.1093/mnras/stx2606


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