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Universität zu Köln

I. Physikalisches Institut

Theoretical Astrophysics Group

Master's Thesis

Driving Turbulence into
Dense Clouds

Author: Tim-Eric Rathjen
Supervisor: Prof. Dr. S. Walch-Gassner

Supersonic turbulence is thought to be one of the main driving forces behind the complex velocity and density structures of molecular clouds. Naturally the question arises, what are the sources and underlying mechanisms for those turbulent, super-thermal motions. One common porposition is that these turbulences are driven from outside the clouds, for example through supernovae. This is what I will investigate in this thesis.

I perform a set of (magneto-) hydrodynamic simulations of elongated, periodic boxes with a density gradient along one axes to mimic the transition from te warm interstellar medium to dense molecular clouds. Furthermore, I only inject energy into the diffuse part of the simulation domain, to see whether the supersonic turbulence can propagate through the medium and into the clouds. Lastly, I back up my findings by varying the inital conditions like increasing the injected driving energy, setting up different density structures, including fractal media, and establishing a magnetic field.

My main result is that the velocity dispersion in the dense gas stayssstrongly subsonic throughout the entire simulation (up to t = 20 Myr). The inclusion of fractal initial denisty strucures and magnetic fields incereases the velocity dispersion, but not significantly - the dense gas stays subsonic. My hypothesis is that supersonic turbulence is not established in the das gas by soley driving it from an external source.

November 2017