Hydrodynamics of the hot component of the Galactic halo. II - Radiative and dynamical instabilities

Details Hydrodynamics of the hot component of the Galactic halo. II - Radiative and dynamical instabilities Hydrodynamics of the hot component of the Galactic halo. II - Radiative and dynamical instabilities

Aug 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...395..475f&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 395, no. 2, Aug. 20, 1992, p. 475-483.

Astronomy and Astrophysics

Astrophysics

9

Galactic Halos, H I Regions, Hydrodynamic Equations, Interstellar Gas, Magnetohydrodynamic Stability, Milky Way Galaxy, Boundary Conditions, Iue, Thermal Instability

Scientific paper

The role that hydrodynamical instabilities may play in the formation mechanism of H I high-velocity clouds (HVCs) in the Galactic halo is studied taking into account the effects of both convection and thermal conduction. The linearized MHD equations are solved numerically in order to analyze the behavior of small perturbations applied to different equilibrium configurations whose relevance in a Galactic halo context has been discussed in a previous paper (Einaudi and Ferrara). The conditions for the growth of a condensation mode, often invoked to explain the origin of HVCs, and its spatial profile are derived. It is shown that, for the range of parameters appropriate to the hot disk gas generated by multisupernova explosions, thermal instability is strongly inhibited by spatial gradients in the background flow. It is argued that HVCs can hardly form as a result of a thermal instability in a hot Galactic flow. A nonradiative but rather 'dynamical' instability may develop whose growth rate is maximum when parameters close to those determining a transonic solution for the flow are adopted; transonic solutions themselves are found to be stable. Some discussion is devoted to the possibility that this 'dynamical' instability may be connected with the onset of a thermal supersonic Galactic wind.

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