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arXiv 0907.4004astro-ph.GAastro-ph.CO
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星暴驱动的银河风:暗条的形成和发射过程

Starburst-Driven Galactic Winds: Filament Formation and Emission Processes

J. L. Cooper, G. V. Bicknell, R. S. Sutherland, J. Bland-Hawthorn

摘要:

我们对超音速风与非球形辐射云的相互作用进行了一系列三维模拟。这些模拟的动机是我们最近的三维模型的星暴驱动的星系风与不均匀的磁盘相互作用,这表明,一个光学发射灯丝可以形成由云的分裂和加速成超音速风。在这项研究中,我们考虑了两种不同的几何形状(分形和球形)的云的演变,并调查辐射冷却对云的生存的重要性。我们还进行了全面的分辨率研究,以确定假设的数值分辨率对结果的影响。我们发现云辐射热量的能力对其生存至关重要。当绝热云在短时间内被破坏时,辐射云通过开尔文-亥姆霍兹不稳定性被分解成许多小而密集的云团,这些云团被吸入气流中形成对流结构。破碎的程度在很大程度上取决于模拟的分辨率,随着开尔文-亥姆霍兹不稳定性得到更好的解决,所形成的云的数量会增加。然而,有一个明显的质量趋势,即在高分辨率下仍然存在碳纳米管结构。我们证实了在我们的全球模拟的恒星暴驱动的风中发现的H-α发射丝形成背后的机制。基于我们的分辨率研究,我们得出结论,加速气体云周围的弓形激波,以及它们之间的相互作用,是在这些银河尺度风中观察到的软X射线发射的主要来源。[删节]

英文摘要:

We have performed a series of three-dimensional simulations of the interaction of a supersonic wind with a non-spherical radiative cloud. These simulations are motivated by our recent three-dimensional model of a starburst-driven galactic wind interacting with an inhomogeneous disk, which show that an optically emitting filament can be formed by the break-up and acceleration of a cloud into a supersonic wind. In this study we consider the evolution of a cloud with two different geometries (fractal and spherical) and investigate the importance of radiative cooling on the cloud's survival. We have also undertaken a comprehensive resolution study in order to ascertain the effect of the assumed numerical resolution on the results. We find that the ability of the cloud to radiate heat is crucial for its survival. While an adiabatic cloud is destroyed over a short period of time, a radiative cloud is broken up via the Kelvin-Helmholtz instability into numerous small, dense cloudlets, which are drawn into the flow to form a filamentary structure. The degree of fragmentation is highly dependent on the resolution of the simulation, with the number of cloudlets formed increasing as the Kelvin-Helmholtz instability is better resolved. Nevertheless, there is a clear qualitative trend, with the filamentary structure still persistent at high resolution. We confirm the mechanism behind the formation of the H-alpha emitting filaments found in our global simulations of a starburst-driven wind. Based on our resolution study, we conclude that bow shocks around accelerated gas clouds, and their interaction, are the main source of the soft X-ray emission observed in these galactic-scale winds. [ABRIDGED]

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