Thermal instability revisited

Abstract

Field's linear analysis of thermal instability is repeated using methods related to Whitham's theory of wave hierarchies, which brings out the physically relevant parameters in a much clearer way than in the original analysis. It is also used for the stability of non-equilibrium states and we show that for gas cooling behind a shock, the usual analysis is only quantitatively valid for shocks that are just able to trigger a transition to the cold phase. A magnetic field can readily be included and we show that this does not change the stability criteria. By considering steady shock solutions, we show that almost all plausible initial conditions lead to a magnetically dominated state on the unstable part of the equilibrium curve. These results are used to analyse numerical calculations of perturbed steady shock solutions and of shocks interacting with a warm cloud.

17 pages, 15 figures

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• Cooling and Instabilities in Colliding Flows
• Shocks in the warm neutral medium I -- Theoretical model
• Shocking interactions of supernova remnants with atomic and molecular clouds -- the interplay between shocks, thermal instability and gravity in the large cloud regime
• Striations, integrals, hourglasses and collapse -- thermal instability driven magnetic simulations of molecular clouds
• An origin of narrow extended structure in the interstellar medium: an interstellar contrail created by a fast-moving massive object
• Shocks in the warm neutral medium II -- Origin of neutral carbon at high pressure
• Effect of optically thin cooling curves on condensation formation: Case study using thermal instability
• Thermal instability and multiphase dynamics in the ISM with polybaric pressure effects