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Astron. Astrophys. 320, 746-756 (1997)

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Dissipation of magnetic fields in the Galactic halo

Dedicated to Professor Karl Schindler on the occasion of his 65th birthday

F. Zimmer 1, H. Lesch 2 and G.T. Birk 2

1 Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
2 Institut für Astronomie und Astrophysik der Universität München, Scheinerstraße 1, D-81679 München, Germany

Received 27 June 1996 / Accepted 4 October 1996

Abstract

This paper shows that magnetic reconnection could be an important heating process in cosmic gases. In any volume where magnetized plasmas collide, the dissipation of magnetic energy via reconnection seems to be unavoidable. Since most cosmic plasmas are highly conductive, the magnetic field lines are transported with the gas and no dissipation occurs for the most part of the volume. This ideal frozen-in property of the magnetic field is broken in small volumes if field gradients with different field polarity appear, in which localized dissipative effects, e.g. anomalous resistivity, become important. On the base of X-ray measurements exhibiting a clear connection of infalling high-velocity clouds (HVC) with ROSAT "hotspots" we perform resistive magnetohydrodynamic simulations to investigate the capabilities of magnetic dissipation as a major heating process in the interaction zone of the cloud with the halo. The main result is that in the physical environment of a galactic halo heating by externally driven magnetic reconnection cannot be suppressed by thermal conduction and/or radiative cooling. Thus, the gas reaches the maximum temperature given by the magnetic field pressure in the interaction zone of the HVC with the galactic halo.

Key words: MHD – methods: numerical – Galaxy: halo – ISM: magnetic fields – ISM: clouds

Send offprint requests to: F. Zimmer

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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