Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...518..748g&link_type=abstract
The Astrophysical Journal, Volume 518, Issue 2, pp. 748-759.
Astronomy and Astrophysics
Astronomy
21
Ism: Bubbles, Ism: Clouds, Instabilities, Magnetohydrodynamics: Mhd, Stars: Supernovae: General, Turbulence
Scientific paper
In this paper, we study the role of superbubbles in the evolution of the large-scale interstellar medium, within the context of numerical simulations that incorporate most of the relevant physical parameters. Our previous model has been completed by the addition of supernova (SN) explosions and the effect on the gravitational potential of the density stratification in the direction perpendicular to the Galactic disk, and by the inclusion of the three velocity and magnetic-field components in the Galactic midplane dynamics. The explosions of many Type II SNe in dense clouds lead to the creation of a hot ( K) and tenuous (n~10^-3) phase that expands in the intercloud medium, creating supershells that fragment under the effect of magnetohydrodynamical instabilities. One conspicuous effect is the formation of dense, roundish clouds in regions where the magnetic field, aligned perpendicular to the direction of the expansion, undergoes a strong bending and where the Lorentz force is thus directed inward. The magnetic-field component perpendicular to the Galactic plane contributes significantly to the pressure inside the shells, thus opposing their collapse. This model, which has a very limited number of ad hoc assumptions, also allows us to monitor the star formation (SF) cycle and to study its dependence on the environmental parameters. The rate of SN explosions per unit surface, which is not imposed but is determined by the dynamics, is consistent with recent estimates in the solar neighborhood. We also find that the presence of superbubbles leads to a more intermittent cycle and a globally increased SF rate. When the strength of the uniform component of the magnetic field increases, the SF rate increases, while the size of individual bubbles decreases, resulting in a more complex influence on the hot gas filling factor. The latter can reach 20% for isolated bubbles, but on average it does not exceeds a few percent.
Gazol-Patiño Adriana
Passot Thierry
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