Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2011-03-15
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
12 pages, 14 figures, to be published in the Astrophysical Journal
Scientific paper
We investigate the gravitational fragmentation of expanding shells driven by HII regions using the three-dimensional Lagrangian simulation codes based on the Riemann solver, called Godunov smoothed particle hydrodynamics. The ambient gas is assumed to be uniform. In order to attain high resolution to resolve the geometrically thin dense shell, we calculate not the whole but a part of the shell. We find that perturbations begin to grow earlier than the prediction of the linear analysis under the thin-shell approximation. The wavenumber of the most unstable mode is larger than that in the thin-shell linear analysis. The development of the gravitational instability is accompanied by the significant deformation of the contact discontinuity. These results are consistent with a linear analysis presented by Iwasaki et al. (2011) that have taken into account the density profile across the thickness and approximate shock and contact discontinuity boundary conditions. We derive useful analytic formulae for the fragment scale and the epoch when the gravitational instability begins to grow.
Inutsuka Shu-ichiro
Iwasaki Kazunari
Tsuribe Toru
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