arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1302.2744astro-ph.GAastro-ph.CO
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围绕Milky Way不同轨道矮星系的潮汐尾

Tidal tails of dwarf galaxies on different orbits around the Milky Way

Ewa L. Lokas, Grzegorz Gajda, Stelios Kazantzidis

摘要:

我们提出了一个现象学的描述周围的矮星系绕银河系的潮汐尾形成的属性。为此,我们使用无碰撞N体模拟的矮星最初由一个磁盘嵌入在NFW暗物质晕。这些矮星被放置在围绕银河系的七个轨道上,大小和偏心率不同,它们的演化被跟踪了10 Gyr。除了被充分研究的矮星主体的形态和动力学转变之外,潮汐剥离导致它们在暗物质和恒星中失去了相当大一部分质量,形成了明显的潮汐尾巴。我们专注于这样形成的潮汐尾巴的恒星成分的属性。我们首先讨论了恒星密度剖面中定义的过渡到潮汐尾的半径,剖面变得浅,并将它们与经典定义的潮汐半径。然后,我们计算的相对密度和速度的尾巴在几个断裂半径作为轨道相位的函数。接下来,我们测量尾巴相对于放置在银河系中心的观察者的方向。在近心点附近,尾巴只在短时间内垂直于这条视线。在大多数时间里,尾巴和这条视线之间的角度都很低,轨道平均中值都低于42度,即使是几乎圆形的轨道。对于更偏心的轨道,中值角通常较低,而最大相对密度较高。相对密度和尾部方向的综合效应表明,对于矮星系来说,在它们通过近心点后不久,它们应该是最容易被探测到的。

英文摘要:

We present a phenomenological description of the properties of tidal tails forming around dwarf galaxies orbiting the Milky Way. For this purpose we use collisionless N-body simulations of dwarfs initially composed of a disk embedded in an NFW dark matter halo. The dwarfs are placed on seven orbits around the Milky Way-like host, differing in size and eccentricity, and their evolution is followed for 10 Gyr. In addition to the well-studied morphological and dynamical transformation of the dwarf's main body, the tidal stripping causes them to lose a substantial fraction of mass both in dark matter and stars which form pronounced tidal tails. We focus on the properties of the stellar component of the tidal tails thus formed. We first discuss the break radii in the stellar density profile defining the transition to tidal tails as the radii where the profile becomes shallower and relate them to the classically defined tidal radii. We then calculate the relative density and velocity of the tails at a few break radii as a function of the orbital phase. Next, we measure the orientation of the tails with respect to an observer placed at the centre of the Milky Way. The tails are perpendicular to this line of sight only for a short period of time near the pericentre. For most of the time the angles between the tails and this line of sight are low, with orbit-averaged medians below 42 degrees for all, even the almost circular orbit. The median angle is typically lower while the maximum relative density higher for more eccentric orbits. The combined effects of relative density and orientation of the tails suggest that they should be easiest to detect for dwarf galaxies soon after their pericentre passage.

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