Interaction of supernova remnants with interstellar clouds
Final Report Abstract
The interaction of an interstellar cloud with a supernova shock wave is a potential triggering mechanism for the formation of gravitationally-bound gas aggregations within the crushed cloud. The longer-term evolution of shocked clouds were investigated by means of sophisticated, computationally expensive numerical simulations in three space dimensions, and its dependence on a pre-existing interstellar magnetic field were explored. The study represented the first 3D simulations which simultaneously combined magnetohydrodyamics with radiative cooling and anisotropic, i.e. magnetic-field-dependent, thermal conduction. As in many other studies on shock-cloud interactions the model was based on the small-cloud approximation where the incident shock is assumed planar and postshock conditions are steady. The simulations demonstrated that cold, dense gas condensations can be formed which remain relatively stable over time. Density enhancement factors measured against the initial cloud center density are in the range 10^2 − 10^4 . A substantial fraction of the cloud matter adopts a low gas temperature of ≈ 10 K. The observed split-up of the crushed cloud into condensations and their properties is moderately dependent on the strength and orientation relativ to the shock normal of an applied magnetic field with the notable exception of a weak (plasma-β of 10^3 ), perpendicular field. This run produced the highest densities with a compression factor in condensations of 10^4, even higher than values obtained in the non-magnetic situation. It is argued that this somewhat surprising result is likely an effect of anisotropic conduction with the magnetic field strength in this case being weak enough not to hinder ongoing compression and, on the other hand, being strong enough to thermally insulate condensations, thus preventing them from rapid evaporation. Analysis of the data has yielded, however, that none of the condensations found in the simulations is close to a state where it is gravitationally-bound.
Publications
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Radiative interaction of shocks with small interstellar clouds as a pre-stage to star formation, ApJ 766 (2013), 11
Johansson E.P.G., Ziegler U.
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Radiative interaction of shocks with small interstellar clouds as a pre-stage to star formation, in Numerical Modeling of Space Plasma Flows: ASTRONUM 2012, Eds. N.V. Pogorelov, E. Audit, G.P. Zank (Astronomical Society of the Pazific: San Francisco), 474 (2013), 72
Johansson E.P.G., Ziegler U.
