Computer Science
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........24k&link_type=abstract
Thesis (PhD). OULUN YLIOPISTO (FINLAND), Source DAI-C 61/02, p. 546, Summer 2000, 123 pages.
Computer Science
3
Scientific paper
In this thesis, as well as in the included publications, we have presented a local three-dimensional MHD model for the ISM, which incorporates large-scale shear due to galactic differential rotation, external gravitational potential arising form the stellar disk and a spherical halo, magnetic fields, turbulent forcing provided by supernova heating and radiative cooling of the ISM. This model has been used for investigating the structure and dynamics of a supernova regulated ISM, the general properties and dynamics of supernova driven interstellar turbulence, the role of supernovae in the disk-halo connection and for interstellar magnetic fields and dynamos. Supernovae were found to produce and maintain a multiphase structure in the ISM: in the simulated ISM warm and hot phases coexist in pressure equilibrium. Some cold, dense gas in cloudy and filamentary structures was formed in the regions of high supernova compression, indicating that supernova compression can act as a trigger for star formation. The turbulent forcing provided by supernovae is of a compressible nature; supernovae heat, accelerate and compress the ISM driving shock waves. In our calculations, however, 60-90% of the energy was found to be in the vortical mode of the velocity field throughout the simulation run. These results clearly indicate that supernova regulated flows are governed by vortical motions. To investigate the role of supernovae for interstellar magnetic fields and dynamos, we have monitored the evolution of a weak magnetic field in a supernova regulated flow. The initially weak magnetic field was rapidly amplified up to 1μG strength, and a random component was generated by supernova activity. A correlation between the mean azimuthal electromotive force and the mean azimuthal magnetic field, characteristic for αω dynamos, was established and maintained throughout the simulation run with α +/- 6 km s -1, the plus sign corresponding to the upper and the minus sign to the lower part of the disk. A weak mean radial field is also generated in the simulated ISM. In conclusion, we have found some evidence that a dynamo of the conventional form could be operating in our simulation.
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