Cosmic - ray driven dynamo in the interstellar medium of irregular galaxies

Context. Irregular galaxies usually are smaller and less massive when compared to the spiral, S0 and elliptical counterparts. The radio observations show that the magnetic field in irregular galaxies is present and its value reaches the same level as in spiral galaxies. However the conditions in the medium of irregular galaxy are very unfavorable for amplification of the magnetic field due to slow rotation and low shearing rate. Aims. We investigate the cosmic ray driven dynamo in the interstellar medium of irregular galaxy. We study its efficiency under the conditions of slow rotation and a weak shearing. The star formation is also taken into account in our model and is parametrized by frequency of explosions and modulations of activity. Methods. The numerical model includes magnetohydrodynamical dynamo driven by cosmic rays injected into the interstellar medium through randomly exploding supernovae. Essential elements such as: vertical gravity of the disk, differential rotation in a local approximation – shearing box, and resistivity leading to magnetic reconnection are included in the model as well. Results. We find that even slow galactic rotation with a low shearing rate gives an amplification of the magnetic field and that the fast rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.