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Wednesday 12 Dec 2018[Seminar] Filaments, feedback and forming the Rosette - MHD simulation of cloud formation by the thermal instability and consequent massive star feedback

Dr Chris Wareing - University of Leeds

4th Floor, Physics Building 14:00-15:00

The AMR magnetohydrodynamic code, MG, has been used to perform 3D MHD simulations of the formation of a molecular cloud through the action of the thermal instability, with self-gravity and magnetic fields. Two initial diffuse atomic conditions have been investigated: 1) a 100 pc-diameter 17,500 solar mass spherical cloud; and 2) a 200 pc-diameter 135,000 solar mass spherical cloud. For both initial conditions, the hydrodynamic case of no magnetic field and the magnetic case of magnetic/thermal pressure equivalence (plasma beta=1) have been considered, with further investigations into the evolution of the clouds in the presence of galactic shear. A range of structures form with molecular cloud densities. In particular, the hydrodynamic case leads to the formation of a clumpy spherical molecular cloud, until shear is introduced, which extends the structure into a thick corrugated sheet-like cloud, eventually collapsing into a thin sheet. The magnetic case sees material ‘trace a flow’ along the magnetic field lines and form an initially thick, but at late times thin, corrugated sheet-like cloud perpendicular to the magnetic field. In projection, the cloud appears remarkably filamentary, with striations parallel to the fieldlines. The introduction of galactic shear triggers high-density thermal condensations at earlier times, accelerating the evolution of the molecular cloud and in the magnetic case, a large inclination to the magnetic field away from the perpendicular cloud formed in non-shear case. Striations remain aligned to the field. At high resolution, examinations of the collapse of individual clumps, their collisions and their evolution towards star-forming cores have been performed. Into these structures, mechanical stellar feedback in the form of winds from single and multiple massive stars ranging from 15 to 120 solar masses and their consequent supernovae have been considered. The dynamic and thermal evolution of the molecular material during feedback reveals key information about the survival of the molecular cloud. Finally, a demonstration that the striking structure of the Rosette Nebula can be understood in terms of these feedback models is presented with supporting evidence from Planck-based magnetic field observations and Gaia-based proper motions of the stars in the central cluster.

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