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The Z Velocity Dispersion of Outer H I Disks

Published online by Cambridge University Press:  25 May 2016

John M. Dickey
John M. Dickey*
Affiliation:
University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA

Abstract

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The velocity dispersion of the interstellar gas measured perpendicular to the disk in face-on spiral galaxies shows a remarkable consistency. Typically the width of the velocity distribution decreases monotonically with increasing galactic radius through the luminous, stellar disk; but in the outer disk where there is gas but no stars the velocity dispersion is συ ≃ 7 km s−1 with a scatter of 2 km s–1 at most from one position to another and from one galaxy to another. Trying to understand this number raises questions about the thermal state of the H I in outer, gaseous disks. The most important issue is to understand the dominant heating and cooling processes for the atomic gas.

Type
Chapter 6: How are we to Understand the Large Scale Structure of the ISM?
Information
Symposium - International Astronomical Union , Volume 169: Unsolved Problems of the Milky Way , 1996 , pp. 489 - 495
Copyright
Copyright © Kluwer 1996 

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