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arXiv 1209.6052astro-ph.COastro-ph.GA
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太菲星系UGC 12914/5的动力学模型

A dynamical model for the Taffy galaxies UGC 12914/5

B. Vollmer, J. Braine, M. Soida

备注：
30 pages, 27 figures, accepted for publication in A&A
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摘要：

Taffy系统的两个富含气体的星系UGC 12914/15的壮观正面碰撞为我们提供了一个独特的机会来研究直接ISM-ISM碰撞的后果。为了解释现有的多波长观测，我们对包括粘性粒子成分的Taffy系统进行了动力学模拟。为了比较HI和CO观测的模拟快照，我们假设气体的分子分数取决于气体体积密度的平方根。为了比较我们的模拟与观测的极化无线电连续辐射，我们计算了我们的模拟的三维大尺度磁场的演变。为此，求解了动力学模型中包含时变气体速度场的诱导方程。模拟结果再现了原始星系UGC 12914的恒星分布、突出的HI和CO气体桥、桥区CO和HI辐射的偏移、平行于桥区的桥等速度矢量、桥区HI双线轮廓、桥区的大线宽等（~200 km/s）、桥区的高场强、大尺度规则磁场、平行于桥的投影磁场矢量和桥区强的总功率无线电连续辐射。次级模型星系的恒星分布比观测到的更受扰动。我们的模拟使用初始对称的气体盘，没有再现所观察到的失真的HI信封的Taffy系统。该模型允许我们在三维中定义桥区域。我们估计桥气体的总质量（HI，温暖和寒冷的H2）为5至6 × 10^9 M_sun，分子分数M_H2/M_HI约为1（省略）。

英文摘要：

The spectacular head-on collision of the two gas-rich galaxies of the Taffy system, UGC 12914/15, gives us a unique opportunity to study the consequences of a direct ISM-ISM collision. To interpret existing multi-wavelength observations, we made dynamical simulations of the Taffy system including a sticky particle component. To compare simulation snapshots to HI and CO observations, we assume that the molecular fraction of the gas depends on the square root of the gas volume density. For the comparison of our simulations with observations of polarized radio continuum emission, we calculated the evolution of the 3D large-scale magnetic field for our simulations. The induction equations including the time-dependent gas-velocity fields from the dynamical model were solved for this purpose. Our simulations reproduce the stellar distribution of the primary galaxy, UGC 12914, the prominent HI and CO gas bridge, the offset between the CO and HI emission in the bridge, the bridge isovelocity vectors parallel to the bridge, the HI double-line profiles in the bridge region, the large line-widths (~200 km/s) in the bridge region, the high field strength of the bridge large-scale regular magnetic field, the projected magnetic field vectors parallel to the bridge and the strong total power radio continuum emission from the bridge. The stellar distribution of the secondary model galaxy is more perturbed than observed. The observed distortion of the HI envelope of the Taffy system is not reproduced by our simulations which use initially symmetric gas disks. The model allows us to define the bridge region in three dimensions. We estimate the total bridge gas mass (HI, warm and cold H2) to be 5 to 6 10^9 M_sun, with a molecular fraction M_H2/M_HI of about unity (abrigded).

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