MHD Turbulence within Molecular Clouds
Presented by Mark Heyer
University of Massachusetts, Amherst
Thursday, August 20, 2015
4:00 P.M. in 169-336
Turbulence within star forming regions of the Milky Way is generally inferred from supersonic velocity dispersions measured in the line profiles of molecular line emission, most notably, the millimeter rotational transitions of 12CO and 13CO. Our ability to measure and quantify turbulent motions in molecular clouds has been enhanced in recent years. First, heterodyne focal plane arrays at millimeter wavelengths on moderate to large telescopes enable wide-field spectroscopic imaging of molecular line emission. Second, analysis tools have been developed to exploit the velocity information resident within the produced data cubes.
In my presentation, I will review these efforts with attention towards the velocity spectrum of turbulence within well-resolved molecular clouds. These results are extended to the cloud-to-cloud integrated size-line width relationship. A fundamental plane for molecular clouds emerges from the near universality of the turbulence in molecular clouds and the equipartition between gravitational and turbulent kinetic energy densities.
While the size-line width relationships offer insights to phenomenological descriptions of turbulence, these do not identify the physical origin of cloud motions within molecular clouds. I will present recent 1-mm and 3-mm imaging of CO lines in the low column density (Av ~ 1) envelope of the Taurus cloud that reveals wave-like motions of molecular gas responsible for the observed striae aligned along the local magnetic field direction. Many of the observed features can be explained by the propagation of magnetosonic waves across the cloud.
JPL Contact: Paul Goldsmith (3-0518)