Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V
Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-faint Satellites Grus II, Tucana IV, and Tucana V
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DOI：
10.3847/1538-4357/ab7ccb
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
J. Simon;T. Li;D. Erkal;A. Pace;A. Pace;A. Drlica-Wagner;A. Drlica-Wagner;D. James;J. Marsh
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文献类型：
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作者：
J. Simon;T. Li;D. Erkal;A. Pace;A. Pace;A. Drlica-Wagner;A. Drlica-Wagner;D. James;J. Marsh
我们提出了麦哲伦/IMACS光谱最近发现的三个超微弱的银河系卫星，鹤II，杜鹃IV，杜鹃V。我们测量系统的速度，和为三个对象，分别。它们巨大的相对速度表明，尽管它们在物理上非常接近，但这些卫星并不相关。我们确定的Tuc IV的速度分散，但我们不能解决其他两个系统的速度分散。对于Gru II，我们对σ < 1.9的离散度设置了上限（90%置信度），而对于Tuc V，我们没有获得任何有用的限值。所有三颗卫星都有金属丰度低于，但没有一颗卫星有可检测的金属丰度分布。我们根据盖亚天体测量学确定每个卫星的自行，并计算它们绕银河系的轨道。Gru II在一个紧密束缚的轨道上，近心点为kpc，轨道偏心率为。Tuc V可能有一个超过100 kpc的远心点，可能是第一次接近银河系。图克四号目前的轨道与格鲁二号相似，近心点为千秒差距，离心率为千秒差距。然而，对图克四号位置的后向积分表明，它在1亿2000万年前以4千秒差距的撞击参数与大麦哲伦星云相撞，使其轨道偏转，并可能改变其内部运动学。根据它们的大小、质量和金属丰度，我们将格鲁II和图克IV归类为可能的矮星系，但图克V的性质仍然不确定。
We present Magellan/IMACS spectroscopy of three recently discovered ultra-faint Milky Way satellites, Grus II, Tucana IV, and Tucana V. We measure systemic velocities of , , and for the three objects, respectively. Their large relative velocities demonstrate that the satellites are unrelated despite their close physical proximity. We determine a velocity dispersion for Tuc IV of , but we cannot resolve the velocity dispersions of the other two systems. For Gru II, we place an upper limit (90% confidence) on the dispersion of σ < 1.9 , and for Tuc V, we do not obtain any useful limits. All three satellites have metallicities below , but none has a detectable metallicity spread. We determine proper motions for each satellite based on Gaia astrometry and compute their orbits around the Milky Way. Gru II is on a tightly bound orbit with a pericenter of kpc and orbital eccentricity of . Tuc V likely has an apocenter beyond 100 kpc and could be approaching the Milky Way for the first time. The current orbit of Tuc IV is similar to that of Gru II, with a pericenter of kpc and an eccentricity of . However, a backward integration of the position of Tuc IV demonstrates that it collided with the Large Magellanic Cloud at an impact parameter of 4 kpc ∼120 Myr ago, deflecting its trajectory and possibly altering its internal kinematics. Based on their sizes, masses, and metallicities, we classify Gru II and Tuc IV as likely dwarf galaxies, but the nature of Tuc V remains uncertain.