Magnetohydrodynamic Models of Molecular Tornadoes

Abstract

Recent observations near the Galactic Centre have found several molecular filaments displaying striking helically-wound morphology, which are collectively known as "molecular tornadoes." We investigate the equilibrium structure of these molecular tornadoes by formulating a magnetohydrodynamic model of a rotating, helically magnetized filament. A special analytical solution is derived where centrifugal forces balance exactly with toroidal magnetic stress. From the physics of torsional Alfvén waves, we derive a constraint that links the toroidal flux-to-mass ratio and the pitch angle of the helical field to the rotation laws, which we find to be an important component in describing molecular tornado structure. The models are compared to the Ostriker solution for isothermal, non-magnetic, non-rotating filaments. We find that neither the analytic model nor the Alfvén wave model suffer from unphysical density inversions noted by other authors. A Monte Carlo exploration of our parameter space is constrained by observational measurements of the Pigtail Molecular Cloud (Pigtail), Double Helix Nebula (DHN), and Galactic Centre molecular Tornado (GCT). Observable properties such as the velocity dispersion, filament radius, linear mass, and surface pressure can be used to derive three dimensionless constraints for our dimensionless models of these three objects. A virial analysis of these constrained models is studied for these three molecular tornadoes. We find that self-gravity is relatively unimportant, whereas magnetic fields, and external pressure play a dominant role in the confinement and equilibrium radial structure of these objects.

arXiv comment26 pages, 9 figures, Accepted for publication in ApJ

References in corpus (8)

• Helical Fields and Filamentary Molecular Clouds
• The ISM in distant star-forming galaxies: Turbulent pressure, fragmentation and cloud scaling relations in a dense gas disk at z=2.3
• Helical Fields and Filamentary Molecular Clouds II - Axisymmetric Stability and Fragmentation
• Turbulence sets the initial conditions for star formation in high-pressure environments
• On the equilibrium of rotating filaments
• Discovery of possible molecular counterparts to the infrared Double Helix Nebula in the Galactic center
• Detailed molecular observations toward the Double Helix Nebula
• Discovery of the Pigtail Molecular Cloud in the Galactic Center

Cited by in corpus (2)

• Magnetized Filament Models for Diverging Plasma Lenses
• Investigating Extreme Scattering Events by Volumetric Ray-tracing