Turbulence and magnetic fields in elliptical galaxies

Abstract

We discuss the physical nature of turbulence and interstellar magnetic fields in the X-ray haloes of elliptical galaxies. The turbulent velocity field is represented by two components, acoustic turbulence driven by type I supernovae and vortical turbulence whose energy source is the stellar motion with respect to the interstellar gas. The typical velocity of the sound-wave turbulence is 60 km s-1 and the scale is 350 pc. For the vortical turbulence, these are 3 km s-1 and 3pc, respectively; the latter velocity field is expected to be rather inhomogeneous. The turbulent motions drive a dynamo generating, within a galactocentric distance of 10 kpc, random magnetic fields whose strength is about 14 μG at the centre and decreases to 1 μG at radius 10 kpc; the correlation scale is the same as that of the acoustic turbulence, i.e. a few hundred parsecs. The magnetic fields produce spatial fluctuations in the Faraday rotation measure whose amplitude is 30 and 300 rad m-2, for observations with linear resolution 1 kpc and 0.1 kpc, respectively.