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Characteristics of the diffuse interstellar medium

Published online by Cambridge University Press:  03 August 2017

D. P. Cox
D. P. Cox*
Affiliation:
Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706, U.S.A.

Abstract

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There have been several recent changes in perspective on the diffuse interstellar environment, including recognition of a thick disk of warm gas, cosmic rays, and magnetic field. In addition, evidence for a pervasive hot phase driven by supernova disruption has weakened to the point that a quasihomogeneous warm intercloud gas may occupy most of the interstellar volume at midplane, with individual bubbles created by supernovae and OB associations occupying perhaps 10 and 20 per cent respectively. The bubble population is sufficient to explain the high stage ions (0 VI, N V, C IV, perhaps Si IV) found in the disk, though possibly not those found at higher z. The estimated midplane pressure has increased, leaving the thermal pressure inside clouds almost negligible. The reduced porosity of the medium, its greater thickness, and its larger pressure all act to suppress fountain activity, either arising from the disk generally, or from the blowout of superbubbles. Finally, there appears to be a peculiar coincidence between the cloud heating mechanism and the activity determining the interstellar pressure.

Type
Large Scale Structure
Information
Symposium - International Astronomical Union , Volume 147: Fragmentation of Molecular Clouds and Star Formation , 1991 , pp. 3 - 10
Copyright
Copyright © Kluwer 1991 

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