Generation of Magnetic Fields in the Multi-phase ISM with Supernova-Driven Turbulence

摘要

Several lines of evidence suggest that protogalactic and galacticenvironments manage to grow magnetic field very rapidly. This makes thetheoretical problem of achieving rapid growth of magnetic fields in suchenvironments difficult. Following Balsara, Benjamin and Cox (2001), we showthat a multiphase ISM that is dominated by realistic energy inputs viasupernova explosions will naturally become a strongly turbulent medium withlarge positive and negative values of the fluid helicity. The resultantinterstellar turbulence seems to have some of the essential characteristics ofa fast dynamo. Magnetic field growth in such a turbulent dynamo is studied inthis paper. It is shown that the field undergoes a linear phase of evolutionwhere it has a time of growth that is comparable to the eddy turn-over time.Energetics, power spectra, statistics and structures of the turbulent dynamoare studied here. It is shown that despite the fact that the ISM is driven bycompressive motions, the kinetic energy in this high Mach number flow is mainlyconcentrated in solenoidal motions rather than compressive motions.