Nonlinear Dynamics of Ionization Fronts in HII Regions |
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Authors: | Akira Mizuta Jave O Kane Marc W Pound Bruce A Remington Dmitri D Ryutov Hideaki Takabe |
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Institution: | (1) Max-Planck-Institute für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany;(2) Lawrence Livermore National Laboratory, University of California, 7000 East Ave., Livermore, CA 94551, USA;(3) Department of Astronomy, University of Maryland, College Park, MD 20742, USA;(4) Institute of Laser Engineering, Osaka University, 2-6 Yamada Oka, Suita Osaka, 565-0871, Japan |
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Abstract: | Hydrodynamic instability of an accelerating ionization front (IF) is investigated with 2D hydrodynamic simulations, including
absorption of incident photoionizing photons, recombination in the HII region, and radiative molecular cooling. When the amplitude
of the perturbation is large enough, nonlinear dynamics of the IF triggered by the separation of the IF from the cloud surface
is observed. This causes the second harmonic of the imposed perturbation to appear on the cloud surfaces, whereas the perturbation
in density of ablated gas in the HII region remains largely single mode. This mismatch of modes between the IF and the density
perturbation in the HII region prevents the strong stabilization effect seen in the linear regime. Large growth of the perturbation
caused by Rayleigh-Taylor-like instability is observed late in time. |
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Keywords: | HII regions ISM: molecules ISM: kinematics and dynamics Hydrodynamics Instabilities Methods: numerical ISM individual object: M16 |
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