Kinematics in galactic tidal tails - A source of hypervelocity stars?
Kinematics in galactic tidal tails - A source of hypervelocity stars?
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DOI：
10.1051/0004-6361/201117474
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发表时间：
2011-10
影响因子：
6.5
通讯作者：
T. Piffl;Mary E. K. Williams;M. Steinmetz
中科院分区：
文献类型：
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作者：
T. Piffl;Mary E. K. Williams;M. Steinmetz
上下文最近对银河系恒星晕中具有异常高径向速度的恒星的观测引起了人们对所谓超高速恒星的新兴趣。传统上，人们认为这些恒星的速度只能来自与银河系中心超大质量黑洞的相互作用。有人认为，从分裂的卫星星系剥离出来的恒星可以达到类似的速度并离开银河系。目标。在这项工作中，我们详细研究了潮汐碎片星的运动学，以探讨新的情况下的影响和观察到的超高速恒星的样本可能部分发展出这样的星系碰撞的概率。方法.我们使用了一套N体模拟的卫星星系与其银河系类型的宿主星系相遇后，收集统计数据的属性剥离的恒星。我们特别研究了这个人口的轨道能量分布。结果我们量化的典型模式，在角和相位空间形成的碎片星。我们进一步发展了一个简单的剥离模型来预测剥离星的运动学。我们表明，在潮汐碎片的轨道能量的分布采取一种典型的形式，可以相当准确地描述了一个简单的功能。在此基础上，我们开发了一种方法，预测的能量分布，使我们能够评估的意义和影响的高速星在卫星潮汐碎片。结论.一般来说，卫星星系的潮汐碰撞会产生逃逸到星系内空间的恒星，即使卫星本身在一个束缚轨道上。决定潮汐碎片星星所能获得的最大能量反冲的主要参数是卫星的初始质量，只是在较低程度上是它的轨道。以这种方式产生的未束缚恒星群的主要贡献者是大质量卫星（Msat > 10 9 M�）。因此，我们预计银河系内恒星的金属丰度高于银河系幸存的卫星人口。然而，根据我们的研究结果，所观察到的HVS人口受到潮汐碎片星严重污染的概率似乎很低。
Context. Recent observations of stars with unusually high radial velocities in the Galactic stellar halo have raised new interest in so-called hypervelocity stars. Traditionally, it is assumed that the velocities of these stars could only come from an interaction with the supermassive black hole in the Galactic center. It was suggested that stars stripped off a disrupted satellite galaxy could reach similar velocities and leave the Galaxy. Aims. In this work we study the kinematics of tidal debris stars in detail to investigate the implications of the new scenario and the probability that the observed sample of hypervelocity stars could partly develop out of such a galaxy collision. Methods. We used a suite of N-body simulations following the encounter of a satellite galaxy with its Milky Way-type host galaxy to gather statistics on the properties of stripped-off stars. We study especially the orbital energy distribution of this population. Results. We quantify the typical pattern in angular and phase space formed by the debris stars. We further develop a simple stripping model to predict the kinematics of stripped-off stars. We show that the distribution of orbital energies in the tidal debris takes a typical form that can be described quite accurately by a simple function. Based on this we develop a method predicting the energy distribution that allows us to evaluate the significance and the implications of highvelocity stars in satellite tidal debris. Conclusions. Generally the tidal collisions of satellite galaxy produce stars that escape into intragalactic space even if the satellite itself is on a bound orbit. The main parameters determining the maximum energy kick a tidal debris star can get is the initial mass of the satellite and only to a lower extent its orbit. Main contributors to an unbound stellar population created in this way are massive satellites (Msat > 10 9 M� ). We thus expect intragalactic stars to have a metallicity higher than the surviving satellite population of the Milky Way. However, the probability that the observed HVS population is significantly contaminated by tidal debris stars appears low in light of our results.