Journal Article

Numerical simulations of shocks encountering clumpy regions

R. Alūzas, J. M. Pittard, T. W. Hartquist, S. A. E. G. Falle and R. Langton

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 3, pages 2212-2227
Published in print September 2012 | ISSN: 0035-8711
Published online September 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21598.x
Numerical simulations of shocks encountering clumpy regions

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Abstract

We present numerical simulations of the adiabatic interaction of a shock with a clumpy region containing many individual clouds. Our work incorporates a sub-grid turbulence model which for the first time makes this investigation feasible. We vary the Mach number of the shock, the density contrast of the clouds and the ratio of total cloud mass to intercloud mass within the clumpy region. Cloud material becomes incorporated into the flow. This ‘mass loading’ reduces the Mach number of the shock and leads to the formation of a dense shell. In cases in which the mass loading is sufficient the flow slows enough that the shock degenerates into a wave. The interaction evolves through up to four stages: initially the shock decelerates; then its speed is nearly constant; next the shock accelerates as it leaves the clumpy region; finally, it moves at a constant speed close to its initial speed. Turbulence is generated in the post-shock flow as the shock sweeps through the clumpy region. Clouds exposed to turbulence can be destroyed more rapidly than a similar cloud in an ‘isolated’ environment. The lifetime of a downstream cloud decreases with increasing cloud-to-intercloud mass ratio. We briefly discuss the significance of these results for starburst superwinds and galaxy evolution.

Keywords: hydrodynamics; shock waves; turbulence; ISM: clouds; ISM: kinematics and dynamics; galaxies: starburst

Journal Article.  9518 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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