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GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

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Michał Hanasz, Dominik Wóltański and Kacper Kowalik

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We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.


Keywords

cosmic rays; galaxies: ISM; galaxies: magnetic fields; ISM: magnetic fields; MHD


PACS

98.38.Am Physical properties (abundances, electron density, magnetic fields, scintillation, scattering, kinematics, dynamics, turbulence, etc.)

95.75.-z Observation and data reduction techniques; computer modeling and simulation

98.35.Hj Spiral arms and galactic disk

98.70.Sa Cosmic rays (including sources, origin, acceleration, and interactions)

98.35.Ac Origin, formation, evolution, age, and star formation

98.38.Mz Supernova remnants

Subjects

Astrophysics and astroparticles

Dates

Issue 1 (2009 November 20)

Received 2009 July 2, accepted for publication 2009 October 19

Published 2009 November 4



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