An Observational Method to Measure the Relative Fractions of Solenoidal and Compressible Modes in Interstellar Clouds

Abstract

We introduce a new method for observationally estimating the fraction of momentum density ($\rho \mathbf{v}$) power contained in solenoidal modes (for which $\nabla \cdot \rho \mathbf{v}=0$) in molecular clouds. The method is successfully tested with numerical simulations of supersonic turbulence that produce the full range of possible solenoidal/compressible fractions. At present the method assumes statistical isotropy, and does not account for anisotropies caused by (e.g.) magnetic fields. We also introduce a framework for statistically describing density--velocity correlations in turbulent clouds.

20 pages, 13 figures, accepted for publication in MNRAS

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• CHIMPS2: Survey description and ${}^{12}$CO emission in the Galactic Centre
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• Filaments and striations: anisotropies in observed, supersonic, highly-magnetised turbulent clouds
• On the effects of solenoidal and compressive turbulence in prestellar cores
• The relation between the true and observed fractal dimensions of turbulent clouds
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• Energy balance and Alfvén Mach numbers in compressible magnetohydrodynamic turbulence with a large-scale magnetic field
• The driving mode of shock-driven turbulence
• Probes of turbulent driving mechanisms in molecular clouds from fluctuations in synchrotron intensity
• Identification of molecular clouds in emission maps: a comparison between methods in the \ce{^{13}CO}/\ce{C^{18}O} ($J=3-2$) Heterodyne Inner Milky Way Plane Survey
• Solenoidal turbulent modes and star formation efficiency in Galactic-plane molecular clouds
• On the origin of compressive turbulence in protoclumps in high redshift disks
• Star formation in cloud cores -- simulations and observations of dense molecular cores and the formation of solar mass stars
• From 2D to 3D: Recovering Turbulent Density Dispersions from Noisy Data