Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud

Abstract

Velocity anisotropy induced by MHD turbulence is investigated using computational simulations and molecular line observations of the Taurus molecular cloud. A new analysis method is presented to evaluate the degree and angle of velocity anisotropy using spectroscopic imaging data of interstellar clouds. The efficacy of this method is demonstrated on model observations derived from three-dimensional velocity and density fields from the set of numerical MHD simulations that span a range of magnetic field strengths. The analysis is applied to 12CO J = 1–0 imaging of a subfield within the Taurus molecular cloud. Velocity anisotropy is identified that is aligned within ~10° of the mean local magnetic field direction derived from optical polarization measurements. Estimated values of the field strength based on velocity anisotropy are consistent with results from other methods. When combined with new column density measurements for Taurus, our magnetic field strength estimate indicates that the envelope of the cloud is magnetically subcritical. These observations favor strong MHD turbulence within the low-density, subcritical, molecular gas substrate of the Taurus cloud.