Abstract:
Magnetic fields are a dynamically important component of the turbulent interstellar medium (ISM) of star-forming galaxies. These magnetic fields are due to a dynamo action, which is a process of converting turbulent kinetic energy to magnetic energy. A dynamo that acts at scales less than the turbulent driving scale is known as the turbulent dynamo. The ISM is a multiphase medium and observations suggests that the properties of magnetic fields differ with the phase. Here, we aim to study how the properties of the turbulent dynamo depend on the phase. We simulate the non-isothermal turbulent dynamo in a two-phase medium (most previous work assumes an isothermal gas). We show that the warm phase is transsonic and the cold phase is supersonic. We find that the growth rate of magnetic fields in the exponentially growing stage is similar in both the phases. We compute the terms responsible for amplification and destruction of vorticity and show that in both phases vorticity is amplified due to turbulent motions, further amplified by the baroclinic term in the warm phase, and destroyed by the term for viscous interactions in the presence of logarithmic density gradients in the cold phase. We find that the final ratio of magnetic to turbulent kinetic energy is lower in the cold phase due to a stronger Lorentz force. We show that the non-isothermal turbulent dynamo is significantly different from its isothermal counterpart and this demonstrates the need for studying the turbulent dynamo in a multiphase medium.
Further details: https://ui.adsabs.harvard.edu/abs/2022MNRAS.514..957S/abstract
Density, temperature, velocity, and magnetic field structures in compressively (left) and solenoidally (right) driven turbulence in the two phase ISM.