Distribution of velocity gradient orientations: Mapping magnetization
  with the Velocity Gradient Technique
  Recent developments of the Velocity Gradient Technique (VGT) show that the
velocity gradients provide a reliable tracing of magnetic field direction in
turbulent plasmas. In this paper, we explore the ability of velocity gradients
to measure the magnetization of interstellar medium. We demonstrate that the
distribution of velocity gradient orientations provides a reliable estimation
of the magnetization of the media. In particular, we determine the relation
between Alfvenic Mach number $M_A$ in the range of $M_A \in [0.2,1.7]$ and
properties of the velocity gradient distribution, namely, with the dispersion
of velocity gradient orientation as well as with the peak to base ratio of the
amplitudes. We apply our technique for a selected GALFA-HI region and find the
results consistent with the expected behavior of $M_A$. Using 3D MHD
simulations we successfully compare the results with our new measure of
magnetization that is based on the dispersion of starlight polarization. We
demonstrate that, combined with the velocity dispersion along the line of sight
direction, our technique is capable to delivering the magnetic field strength.
The new technique opens a way to measure magnetization using other gradient
measures such as synchrotron intensity gradients (SIGs) and synchrotron
polarization gradients (SPGs).
