Magnetic field alignment in low-mass molecular clouds: the role of turbulence and density of the clouds

Abstract

ABSTRACT In this work, we report the role of turbulence (measured by the $^{12}\mathrm{ CO}$ linewidth, $\Delta V$) on the offset between the orientation of local magnetic field in the low-density regions of dark clouds ($\theta ^{\mathrm{ env}}_\mathrm{ B}$) and the position angle of the Galactic Plane (GP; $\theta _{\mathrm{ GP}}$) in 15 low-mass isolated molecular clouds. We find a dependency of $\Delta V$ on offset, ($\theta _{\mathrm{ off}} =|\theta ^{\mathrm{ env}}_\mathrm{ B}-\theta _{\mathrm{ GP}}|$), represented by a second-order polynomial equation, $\theta _{\mathrm{ off}}=(3.328 \pm 1.187) {\Delta V}^2 - (0.991 \pm 5.541) {\Delta V} + (4.767 \pm 5.309)$. In regions where the majority of low turbulence is observed, characterized by $\Delta V \ \lt\ 3.1 \ \mathrm{ km\,s}^{-1}$, the envelope magnetic fields closely align with the orientation of the GP ($\theta _{\mathrm{ off}}\ \lt\ 20^\circ$). Conversely, in areas exhibiting high turbulence with $\Delta V \ \gt\ 3.1 \ \mathrm{ km\,s}^{-1}$ (for clouds CB130 and CB188), the envelope magnetic field tends to misalign with the GP ($\theta _{\mathrm{ off}}\ \gt\ 50^\circ$). This suggests that turbulence could be one of the important factors influencing the alignment of the local magnetic field with the GP. We have also explored the potential link between gas density of clouds ($\rho$) and turbulence ($\Delta V$) for the first time, utilizing data from 10 isolated clouds. This analysis suggests a possible correlation, with the observed trend quantified as, $\Delta V \propto \rho ^{-0.19}$.