Discovery of a Disrupting Open Cluster Far into the Milky Way Halo: A Recent Star Formation Event in the Leading Arm of the Magellanic Stream?
Discovery of a Disrupting Open Cluster Far into the Milky Way Halo: A Recent Star Formation Event in the Leading Arm of the Magellanic Stream?
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DOI：
10.3847/1538-4357/ab4bdd
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发表时间：
2018-11
期刊：
影响因子：
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通讯作者：
A. Price-Whelan;D. Nidever;Yumi Choi;E. Schlafly;T. Morton;Sergey E. Koposov;V. Belokurov
中科院分区：
文献类型：
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作者：
A. Price-Whelan;D. Nidever;Yumi Choi;E. Schlafly;T. Morton;Sergey E. Koposov;V. Belokurov
我们报告了在日心距离上发现的一个年轻的低质量贫金属星协，它位于银河系晕的深处。在目前的银河中心位置，星协（在天空上）靠近麦哲伦云系统发出的气流的前缘，但位于大麦哲伦云中心的MW盘的另一侧。如果星团与流中的H i气体共位，我们直接测量到麦哲伦流的前臂的距离。测量的距离是不一致的麦哲伦流模型预测，不考虑冲压压力和气体与MW磁盘的相互作用。该星团的估计年龄与最后一次通过银河系中平面的主导臂气体的时间是一致的，因此我们推测这一星星形成事件是由其最后一次磁盘中平面通道触发的。这个想法的大部分细节仍然是一个谜：麦哲伦流具有低柱密度，大半径的MW盘具有低气体密度，并且主导臂和MW气体的相对速度很大。无论它是如何形成的，在MW晕中发现一个年轻的恒星团为研究提供了一个有趣的机会。这个星团是单独用盖亚天体测量和测光发现的，但后续的DECam测光对测量其性质至关重要。
We report the discovery of a young ( ), low-mass ( ), metal-poor ( ) stellar association at a heliocentric distance , placing it far into the Milky Way (MW) halo. At its present Galactocentric position , the association is (on the sky) near the leading arm of the gas stream emanating from the Magellanic Cloud system, but is located from the Large Magellanic Cloud center on the other side of the MW disk. If the cluster is colocated with H i gas in the stream, we directly measure the distance to the leading arm of the Magellanic stream. The measured distance is inconsistent with Magellanic stream model predictions that do not account for ram pressure and gas interaction with the MW disk. The estimated age of the cluster is consistent with the time of last passage of the leading arm gas through the Galactic midplane; we therefore speculate that this star formation event was triggered by its last disk midplane passage. Most details of this idea remain a puzzle: the Magellanic stream has low column density, the MW disk at large radii has low gas density, and the relative velocity of the leading arm and MW gas is large. However it formed, the discovery of a young stellar cluster in the MW halo presents an interesting opportunity for study. This cluster was discovered with Gaia astrometry and photometry alone, but follow-up DECam photometry was crucial for measuring its properties.