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Space Distribution and Motion of the Local HI Gas

Published online by Cambridge University Press:  30 March 2016

H. Weaver
H. Weaver*
Affiliation:
Dept. of Astronomy and Radio Astronomy Laboratory, University of California, Berkeley, Calif, U.S.A.

Extract

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In a Joint Discussion devoted to the ages and kinematics of the local stars, inclusion of a paper on the local gas may seem anomalous. There is, however, strong justification for considering such a topic. Newly formed stars retain many properties of the gas from which they originated. To understand the spatial and kinematic properties of local young stars, we must understand the spatial distribution and the kinematics of the local gas from which they were formed.

A cloud within the interstellar gas can collapse gravitationally if its mass, density, and temperature satisfy the Jeans Criterion. Collapse is favored by low temperature and high density.

Various investigators have pointed out that in the Lin Spiral Density Wave Theory a shock must occur on the inner edge of a spiral arm. Such a shock compresses the gas and hence promotes cloud formation with subsequent gravitational collapse to form stars. Shu and several collaborators have shown that such a shock is very effective in triggering cloud formation in a two-phase interstellar medium of the type discussed by Field et al. (1969), and it is widely believed that this is the principal step in the process of forming stars.

Type
Joint Discussions
Information
Highlights of Astronomy , Volume 3: Highlights of Astronomy. As presented at the XVth General Assembly of the IAU, 1973 , 1974 , pp. 423 - 440
Copyright
Copyright © Reidel 1974

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