Galaxy Formation: the Fragmentation Problem.

Abstract

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galaxy Formation: the Fragmentation Problem. Michie, Richard W. Abstract This study of fragmentation uses the moment technique reported previously (Astron. J. 70, 327, 1965), and includes the following physics: (a) a nonlinear, nonhomologous fluid flow, (b) the full radiation of energy modified by the self-absorption of the Lyman lines and continua, (c) the (2s- 1s) two photon emission, (d) the conduction of heat into or out of the fragment, and (e) the tidal force exerted on the nonspherical fragment by the surrounding gas in the cloud. In one example, a cloud forms from a small perturbation in an expanding universe and initially shares the cosmic motion. The gas temperature at the start is l0~ 0K. Before the outer parts of the cloud cool very much and begin to collapse it is shown that a perturbation can grow, even if it initially shares the motion of the surrounding (cloud) gas. This example can lead to a cluster of galaxies. A second example illustrates the fragmentation of gas clouds when a cloud is in a state of free fall and is developing a large central concentration. In both examples, as the fragment grows, it loses pressure support and starts to move inward toward the center faster than the surrounding (cloud) gas. The role of the opacity and the tidal force is to delay the growth of fragments and to help determine the mass spectrum. The nonhomologous collapse is of first importance for the tidal force affects the outer parts of the fragment, and when the fragment develops some central concentration the tidal force becomes much less important. The opacity always delays the collapse by maintaining the internal pressure forces for a long time, and the fragmentation studies made so far indicate the thermal instability is of little or no importance due to the lengthened cooling time scales. Publication: The Astronomical Journal Pub Date: 1965 DOI: 10.1086/109630 Bibcode: 1965AJ.....70R.685M full text sources ADS |