Dynamical evolution of high velocity clouds in the intergalactic medium

¹ Institut für Astronomie und Astrophysik der Universität München, Scheinerstraße 1, 81679 München, Germany
² Centre of Interdisciplinary Plasma Science, Garching, Germany
³ Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ The Australia Telescope National Facility, CSIRO, PO Box 76, Epping NSW 1710, Australia

Corresponding author: C. Konz, konz@usm.uni-muenchen.de

Received: 5 February 2002
Accepted: 6 June 2002

Abstract

observations of high-velocity clouds (HVCs) indicate, that they are interacting with their ambient medium. Even clouds located in the very outer Galactic halo or the intergalactic space seem to interact with their ambient medium. In this paper, we investigate the dynamical evolution of high velocity neutral gas clouds moving through a hot magnetized ambient plasma by means of two-dimensional magnetohydrodynamic plasma-neutral gas simulations. This situation is representative for the fast moving dense neutral gas cloudlets in the Magellanic Stream as well as for high velocity clouds in general. The question on the dynamical and thermal stabilization of a cold dense neutral cloud in a hot thin ambient halo plasma is numerically investigated. The simulations show the formation of a comet-like head-tail structure combined with a magnetic barrier of increased field strength which exerts a stabilizing pressure on the cloud and hinders hot plasma from diffusing into the cloud. The simulations can explain both the survival times in the intergalactic medium and the existence of head-tail high velocity clouds.