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Title:
On the fragmentation of cosmic gas clouds. I - The formation of galaxies and the first generation of stars
Authors:
Silk, J.
Publication:
Astrophysical Journal, Part 1, vol. 211, Feb. 1, 1977, p. 638-648. (ApJ Homepage)
Publication Date:
02/1977
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
FRAGMENTATION, GALACTIC EVOLUTION, IONIZED GASES, STELLAR EVOLUTION, COOLING, ELLIPTICAL GALAXIES, GALACTIC STRUCTURE, HEAVY ELEMENTS, HYDROGEN CLOUDS, STELLAR MASS
Comment:
A&AA ID. AAA019.158.009
DOI:
10.1086/154972
Bibliographic Code:
1977ApJ...211..638S

Abstract

The formation of galaxies is studied in the context of the fragmentation of massive diffuse ionized gas clouds. A semiquantitative discussion of the role of cooling indicates that there is a characteristic mass of a galaxy (of the order of 500 billion solar masses) which can fragment out of an ionized medium of density not exceeding 10 to the -25th power g/cu cm, whereas more massive galaxies attain a characteristic radius of the order of 60 kpc. The relationship between binding energy and mass is investigated for spheroidal galaxies. The role of H2 and Ly-alpha cooling in the fragmentation of primordial gas clouds is evaluated, and relatively qualitative arguments indicate that the first stars have masses of at least 0.3 solar mass with a characteristic mass of approximately 20 solar masses. When the average heavy-element abundance by mass exceeds about 0.00001, heavy-element cooling prevails over Ly-alpha cooling, and subsequent fragmentation forms second-generation stars of low characteristic mass.

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