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由于棒的形成而导致的晕三轴度的损失

Loss of halo triaxiality due to bar formation

Rubens E. G. Machado, E. Athanassoula

备注：
20 pages, 26 figures, accepted for publication in MNRAS
发表信息：
2010MNRAS.406.2386M
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摘要：

宇宙学N体模拟表明星系的暗物质晕一般是三轴的。然而，重子盘的存在被认为改变了晕的形状。在这里，我们的目标是研究酒吧的形成是如何影响晕三轴性，以及如何，反过来，酒吧的存在影响晕的形状。我们进行了一组无碰撞N体模拟盘星系与三轴暗物质晕，使用椭圆盘作为初始条件。我们研究模型的不同的晕三轴，并在没有酒吧形成的情况下，调查的晕形状的行为，我们运行的模型与不同的磁盘质量，晕浓度，磁盘速度分散和模型的磁盘形状保持人工轴对称。我们发现，引入一个巨大的磁盘的原因晕三轴性被部分稀释。一旦圆盘完全长大，一个强大的恒星棒在仍然是非轴对称的晕内发展，导致它失去剩余的非轴对称性。在三轴晕的初始条件是这样的酒吧不形成，晕是能够保持三轴和圆化其形状的平面上的磁盘是有限的磁盘增长的时期。我们的结论是，部分循环的光环是由于光盘的增长，但部分必须归因于酒吧的形成。我们发现，最初的圆盘响应过度的三轴电位，并成为高度拉长。它们也比最初的椭圆盘失去更多的角动量，从而形成更强的杆。正因为如此，他们的酒吧在他们的光环上引起的循环也更快。我们还分析了晕的垂直形状，并观察到它们的垂直方向仍然相当大，这意味着晕成为近似扁圆的模拟结束。[删节]

英文摘要：

Cosmological N-body simulations indicate that the dark matter haloes of galaxies should be generally triaxial. Yet, the presence of a baryonic disc is believed to alter the shape of the haloes. Here we aim to study how bar formation is affected by halo triaxiality and how, in turn, the presence of the bar influences the shape of the halo. We perform a set of collisionless N-body simulations of disc galaxies with triaxial dark matter haloes, using elliptical discs as initial conditions. We study models of different halo triaxialities and, to investigate the behaviour of the halo shape in the absence of bar formation, we run models with different disc masses, halo concentrations, disc velocity dispersions and also models where the disc shape is kept artificially axisymmetric. We find that the introduction of a massive disc causes the halo triaxiality to be partially diluted. Once the disc is fully grown, a strong stellar bar develops within the halo that is still non-axisymmetric, causing it to lose its remaining non-axisymmetry. In triaxial haloes in which the initial conditions are such that a bar does not form, the halo is able to remain triaxial and the circularisation of its shape on the plane of the disc is limited to the period of disc growth. We conclude that part of the circularisation of the halo is due to disc growth, but part must be attributed to the formation of a bar. We find that initially circular discs respond excessively to the triaxial potential and become highly elongated. They also lose more angular momentum than the initially elliptical discs and thus form stronger bars. Because of that, the circularisation that their bars induce on their haloes is also more rapid. We also analyse halo vertical shapes and observe that their vertical flattenings remain considerable, meaning that the haloes become approximately oblate by the end of the simulations. [abridged]

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