Tracing of magnetic fields with gradients: subsonic turbulence

The recent development of the velocity gradient technique shows the capability of the technique for tracing magnetic field morphology in diffuse interstellar gas and molecular clouds. In this paper, we perform a systematic numerical study of the performance of the velocity and synchrotron gradient for a wide range of magnetization in the subsonic environment. Addressing the studies of magnetic fields in atomic hydrogen, we also study the formation of velocity caustics in spectroscopic channel maps in the presence of thermal broadening. We show that the velocity caustics can be recovered when applied to the cold neutral medium and the gradient technique (GT) can reliably trace magnetic fields there. Finally, we discuss the changes in the anisotropy of observed structure functions when we apply to the analysis the procedures developed within the framework of GT studies.

Automated summary

The recent development of the velocity gradient technique has shown its capability in tracing magnetic field morphology in diffuse interstellar gas and molecular clouds. This paper systematically studies the performance of velocity and synchrotron gradient at various levels of magnetization in a subsonic environment. The formation of velocity caustics in spectroscopic channel maps in the presence of thermal broadening is also addressed, with the recovery of velocity caustics in the cold neutral medium and reliable magnetic field tracing using the gradient technique (GT). The changes in anisotropy of observed structure functions when applying GT analysis procedures are discussed.