Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998pasj...50..547k&link_type=abstract
Publications of the Astronomical Society of Japan, v.50, p.547-558.
Astronomy and Astrophysics
Astronomy
1
Galaxies: Formation, Hydrodynamics, Numerical Methods
Scientific paper
The star-formation activity in protogalactic disks is regulated by the fragmentation process of self-gravitating gas disks formed by the collapse in dark halo potentials. In order to study this process, we numerically simulated the dynamical evolution of rotating gas clouds in external potentials. The fragmentation was found to occur only in the limited area of the parameter space defined by the initial ratios of the thermal and rotational energies to the gravitational energy. A linear instability analysis has been applied to rotating equilibrium disks resulting from the initial clouds. We found that the critical condition for the growth of axisymmetric perturbations nicely explains the fragmentation boundary found in the simulation results. The generalized fragmentation condition derived by the linear instability analysis consists of two criteria: the ``Q-value'' criterion, which requires existence of at least one unstable perturbation, and the ``wavelength'' criterion, which states that the wavelength of the most unstable perturbation is less than the radial scale length of the disk. The second criterion includes the first one automatically when the external gravitational field is absent, whereas the two criteria combine to control fragmentation process in the external potential.
Hanami Hitoshi
Kawata Daisuke
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