Low velocity shock-cloud encounters I.

Horváth, András; Tóth, L. V.

doi:10.1007/bf00627346

Cited by 2 publications

(2 citation statements)

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“…In the latter case the vorticity is generated in a sheet at the model cloud surface, and this material is swept behind the cloud by the shock, resulting in comet-shaped clouds (or filaments with "heads"). Such structures are found even in simulations of low-velocity shock-cloud interactions (Horvath & Toth 1995).…”

Section: Comparison Of Induced Velocity Amplitudes With Observationsmentioning

confidence: 97%

“…Vanhala & Cameron (1998) presented three dimensional simulations, including a very detailed treatment of the cooling rates, that addressed the question of disruption versus gravitational instability, for relatively high shock speeds and relatively sharp-edged (Gaussian) clouds. Horvath & Toth (1995) presented two-dimensinal simulations of lower-velocity non-disruptive shock-cloud interactions. In all these simulations, at least for early times, the vorticity is present only as a sheet on the outside of the cloud.…”

Section: Previous Workmentioning

confidence: 99%

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The Galactic Shock Pump: A Source of Supersonic Internal Motions in the Cool Interstellar Medium

Kornreich

Scalo

2000

ApJ

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We propose that galactic shocks propagating through interstellar density fluctuations provide a mechanism for the intermittent replenishment, or "pumping," of the supersonic motions and internal density enhancements observed pervasively within cool atomic and molecular interstellar structures, without necessarily requiring the presence of self-gravity, magnetic fields, or young stars. The shocks are assumed to be due to a variety of galactic sources on a range of scales. An analytic result for the kinematic vorticity generated by a shock passing through a radially-stratified two-dimensional isobaric model cloud is derived, assuming that the Mach number is not so large that the cloud is disrupted, and neglecting the shock curvature and cloud distortion. Two-dimensional lattice gas hydrodynamic simulations at modest Mach numbers were used to verify the analytic result. The induced internal velocities are initially a significant fraction of the shock speed divided by the square root of the density contrast, accounting for both the observed linewidth amplitudes and the apparent cloud-to-cloud linewidth-density scaling.The linewidth-size relation could then be interpreted in terms of the well-known power spectrum of a system of shocks. The induced vortical energy should quickly be converted to compressible and MHD modes, and so would be difficult to observe directly, even though it would still be the power source for the other modes. The shockpump thus produces density structure without the necessity of any sort of instability. We argue that the shockpump should lead to nested shock-induced structures, providing a cascade mechanism for supersonic "turbulence" and a physical explanation for the fractal-like structure of the cool interstellar medium. The average time between shock exposures for an idealized cloud in our Galaxy is estimated and found to be small enough that the shockpump is capable of sustaining the supersonic motions against readjustment and dissipation, except for the smallest structures. This suggests an explanation of the roughly spatially uniform and nearly sonic linewidths in small "dense cores." We speculate that the avoidance of shock pumping may be necessary for a localized region to form stars, and that the inverse dependence of probability of avoidance on region size may be an important factor in determining the stellar initial mass function.

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Section: Comparison Of Induced Velocity Amplitudes With Observationsmentioning

confidence: 97%

Section: Previous Workmentioning

confidence: 99%