Turbulence and Magnetic Field Alignment in Small Molecular Clouds: The Role of Cloud Size, Mass, and Density

Abstract

In this study, we investigate the relationship between turbulence (ΔV) and different physical parameters in 22 isolated small molecular clouds and their cores, extending the analysis to a hierarchical scenario from core to cloud. Using 12CO line width as a tracer of turbulence, we find that ΔV correlates with both cloud size and mass, following and . Further, the surface density of the clouds (Σcl) influences the ΔV–Lcl relation, with . This indicates that gravitational energy drives turbulence in clouds, indicating possible virial equilibrium. We observe that Lcl correlates with Mcl and volume gas density of the cloud (ρcl), implying nearly constant Σcl across the clouds. In cloud cores, C18O line-width data show complex behavior, with no direct correlation between ΔV and core size (Lco). However, a positive correlation emerges when the surface density of the core is included in Lco. Notably, the relation between volume gas density (ρco) and core size (Lco) deviates from constant core surface density. Our analysis reveals that turbulent pressure increases with gravitational pressure to maintain global equilibrium. Finally, on the core-to-cloud scale, physical relationships remain continuous, reflecting the interconnected nature of clouds and cores. Extending our previous work, where we demonstrated a nonlinear dependence of turbulence on the alignment of the local magnetic field in molecular clouds with the Galactic plane, we now compare observations with a theoretical model based on kinetic theory. Our result confirms that higher turbulence causes greater magnetic misalignment consistent with the derived second-order polynomial relationship.