Issue |
A&A
Volume 508, Number 2, December III 2009
|
|
---|---|---|
Page(s) | 725 - 735 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/200912806 | |
Published online | 27 October 2009 |
Fragmentation of a dynamically condensing radiative layer
Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan e-mail: [iwasaki; tsuribe]@vega.ess.sci.osaka-u.ac.jp
Received:
1
July
2009
Accepted:
14
September
2009
In this paper,
the stability of a dynamically condensing radiative gas layer is investigated by linear
analysis.
Our own time-dependent, self-similar solutions describing a dynamical condensing
radiative gas layer are used as an unperturbed state.
We consider perturbations that are both perpendicular and parallel
to the direction of condensation.
The transverse wave number of the perturbation is defined by k.
For , it is found that the condensing gas layer is unstable. However,
the growth rate is too low to become nonlinear during dynamical condensation.
For k
0, in general,
perturbation equations for constant wave number cannot be reduced to
an eigenvalue problem
due to the unsteady unperturbed state.
Therefore, direct numerical integration of the perturbation equations is performed.
For comparison, an eigenvalue problem neglecting the time evolution
of the unperturbed state
is also solved and both results agree well.
The gas layer is unstable for all wave numbers, and the growth rate depends a little
on wave number.
The behaviour of the perturbation is specified by
at the centre, where
the cooling length,
, represents the length that a sound wave can travel
during the cooling time. For
≫ 1,
the perturbation grows isobarically.
For
≪ 1,
the perturbation grows because each part has a different collapse time without interaction.
Since the growth rate is sufficiently high, it is not long before the perturbations become nonlinear
during the dynamical condensation. Therefore, according to the linear analysis,
the cooling layer is expected to
split into fragments with various scales.
Key words: hydrodynamics / instabilities / ISM: kinematics and dynamics / ISM: structure / ISM: clouds
© ESO, 2009
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