Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aspc..365..162i&link_type=abstract
SINS - Small Ionized and Neutral Structures in the Diffuse Interstellar Medium ASP Conference Series, Vol. 365, Proceedings of t
Astronomy and Astrophysics
Astronomy
2
Scientific paper
We illustrate two recent studies on the dynamics of a multi-phase interstellar medium. The first is the result of two- and three-dimensional numerical simulations for the non-linear development of simple thermal instability incorporating physical viscosity. No external forcing is used in order to isolate the effects of various processes responsible for long-lasting turbulent motion. We measure the average amplitude of turbulent motion as a function of various physical parameters. In general, the amplitude increases when we increase the ratio of the computational domain length to the cooling length ( the product of the cooling time and the sound speed). The amplitude of the turbulent velocity also increases when we reduce the Prandtl number (the non-dimensional ratio of kinetic viscosity to thermal conduction). This shows that thermal conduction plays an important role in maintaining turbulent motions against viscous dissipation. Secondly we follow the time-evolution of a magnetized multi-phase medium produced by thermal instability. This is done by decreasing the external radiative heating rate to simulate the growth of the cloud toward a larger cloud with higher column density. We find that multi-phase (i.e.high density contrast) structure persists even after the temperature of the warm phase substantially decreases. The spatial distribution of the ratio of magnetic pressure to gas pressure is highly non-uniform in the resultant structure; thus a large gas pressure gradient is partially maintained by the magnetic force. In order to understand the evolution of the ISM, we emphasize the importance of theoretical studies of the physical property of this magnetically multi-phase medium.
Inutsuka Shu-ichiro
Koyama Hiroshi
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