Fragmentation of Isothermal Sheet-Like Clouds. II : Full Nonlinear Numerical Simulations

概要

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The fragmentational instability of an infinite isothermal gas layer, extending infinitely in the x- and y-direction, is investigated by means of three-dimensional numerical simulations. The nonlinear growth of perturbations with the initial wave pattern, cos(k_xx)×cos(k_yy), is calculated for various values of the wave numbers k_x and k_y. For unstable modes, the fragmentation of a layer and the subsequent collapse of fragments are simulated. It is found that, if the ratio, K_y/K_x, is in the range, 0.8-1.2,each fragment collapses almost axisymmetrically without flattening along the z-axis. However, if the ratio is greater than 1.2 or less than 0.8, each fragment becomes more and more slender as it collapses and finally a thin filament is formed. We also calculate the growth of random perturbations and confirm that a large number of filaments are formed. As a results of the computations, we construct a scenario of fragmentation and subequent evolution of a sheet-like cloud such that most of the fragments become finally thin filaments and re-fragment. This scenario explains why filamentary structures often appear in interstellar clouds observed. We also find that the mass function of the final fragments is expressed in the form, N∝m^<-2>, where N and m are the number and mass, respectively.
理論物理学刊行会の論文
1987-12-25