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Interaction between the Galactic Disk and Halo Components

Published online by Cambridge University Press:  12 April 2016

Jeremiah P. Ostriker
Jeremiah P. Ostriker*
Affiliation:
Princeton University Observatory

Extract

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At least three component parts of the galaxy must be recognized. The Disk Component of the galaxy might be defined as follows. Spatially it is largely confined between the planes ± 1 kpc from the plane of symmetry. With regard to velocities, it is a cold subsystem in that the random motions within it (~ 20 km/s) are small compared to the systematic flow of rotational motion (~ 200 km/s). Finally, its composition is largely stellar with stars of all ages and masses being present. Few galaxies are known where the ratio of (gas/stellar) mass is > 10% (cf. Roberts 1975a), and the metal abundance is typically high with at most one percent of the stars having metallicity less than 1/4 that of the Sun (cf. Schmidt 1963). From this point of view the spiral parts are a relatively unimportant (in terms of mass and composition) sub-part of the disk system.

Type
Part IV: Kinematics and Dynamical Evolution of the Galaxy
Information
International Astronomical Union Colloquium , Volume 45: Chemical and Dynamical Evolution of our Galaxy , September 1977 , pp. 241 - 246
Copyright
Copyright © Geneva Observatory 1977

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