Magnetically Aligned Velocity Anisotropy in the Taurus Molecular Cloud

TL;DR

This study introduces a new method to analyze velocity anisotropy in molecular clouds, demonstrating its effectiveness on simulations and applying it to Taurus, revealing magnetic field alignment and strength consistent with strong MHD turbulence.

Contribution

A novel analysis technique for velocity anisotropy in molecular clouds is developed and validated using simulations, then applied to Taurus to infer magnetic field properties.

Findings

Velocity anisotropy aligns within 10° of magnetic field direction.

Estimated magnetic field strength agrees with other measurement methods.

Taurus cloud is magnetically subcritical, supporting strong MHD turbulence.

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 sub-field within the Taurus molecular cloud. Velocity anisotropy is identified that is aligned within 10 degrees 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, sub-critical, molecular gas substrate of the Taurus cloud.