Physics of dissipational galaxy formation
A number of arguments lead one to consider the possibility that the first massive galaxies were formed after redshift 10. The formation of galaxies at small redshifts can only have occurred if the formation process was dissipative. This paper is concerned with one theory of dissipative galaxy formation: the theory which arises from the supposition that a protogalactic cloud would not have fragmented very extensively during the first phase of its infall and thus that the collapse of the cloud would be halted by the formation of shock fronts around a caustic surface. Detailed calculations of the formation and evolution of these shock fronts yield values for the physical conditions of the protogalactic gas and the rate of radiation of galactic binding energy by such shocks. The adiabaticity or isothermality of these shock fronts is found to be dependent on the characteristic infall velocity and the surface density associated with the shock front but not on the shape of the initial density profile perpendicular to the incipient shock surfaces. Protogalaxies which recollapsed at high z are more likely to have generated isothermal shocks than ones which collapsed at low z. It is found that this binding energy release could make collapsing protogalactic clouds very high surface brightness objects. It appears that there is a scale radius approx.30 kpc associated with the collapse of the most massive galaxies and that it may be possible to explain the original inability of the material of galactic disks to fragment in terms of this scale radius. A similar theory of the origin of Magellanic irregulars, low surface brightness spheroidals, and dwarf ellipticals is suggested.
- Research Organization:
- Princeton University Observatory
- OSTI ID:
- 7097861
- Journal Information:
- Astrophys. J.; (United States), Vol. 215:2
- Country of Publication:
- United States
- Language:
- English
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