Tracing of Magnetic field with gradients: Sub-Sonic Turbulence

Recent development of the velocity gradient technique shows the {\toreferee capability} of the technique in the way of tracing magnetic fields morphology in diffuse interstellar gas and molecular clouds. In this paper, we perform the numerical systemic study of the performance of velocity and synchrotron gradient for a wide range of magnetization in the sub-sonic environment. Addressing the studies of magnetic field in atomic hydrogen, we also study the formation of velocity caustics in the spectroscopic channel maps in the presence of the thermal broadening. We show that the velocity caustics can be recovered when applied to the Cold Neutral Medium (CNM) and the Gradient Technique (GT) can reliably trace magnetic fields there. Finally, we discuss the changes of the anisotropy of observed structure functions when we apply to the analysis the procedures developed within the framework of GT studies.