Cosmic ray driven dynamo in spiral galaxies

Abstract

We investigate galactic magnetic field generation by means of direct simulations of magnetized ISM composed of ionized gas, magnetic fields and cosmic rays. We consider galactic disk of interstellar matter rotating under timedependent galactic gravitational potential due to stars and dark matter particles forming disk, bulge and halo. The seed field is assumed to be of stellar origin and is considered to be supplied by supernovae remnants. As a result of underlying CRdriven dynamo process magnetic field is amplified up to the equipartition level. In the present model we note magnetic field reversals and further temporal changes of magnetic field polarity. We find the strongest magnetic field between spiral arms, which is aligned with the arms. In the presence of a galaxy companion galactic magnetic field evolution proceeds analogously until the merger event, after which magnetic field is disordered. For the simple comparison with real observed galaxies we make synthetic maps of synchrotron emission and show similarities to magnetic field structures observed in spiral galaxies such as NGC 6946.