土卫二盖亚经历了至少两次环绕银河系的证据*

Ása Skúladóttir, Heitor Ernandes, Diane K. Feuillet, Alice Mori, Sofia Feltzing, Romain E. R. Lucchesi and Paola Di Matteo
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引用次数: 0

摘要

最近的重大突破之一是发现了银河系历史上最后一次重大合并。大约10年前,盖亚星系恩塞拉多斯(Gaia Enceladus)的质量估计为银河系的10%,落入了我们银河系的潜力,带来了大量的恒星,可以通过它们独特的化学和运动学特征来识别。长期以来,模拟预测,在最终完全分散之前,这种大小的星系应该经历几次穿过银河系的圆盘。我们首次提出观测证据来支持这一观点。我们确定了从盖亚土卫二吸积的两个亚群:(1)今天具有大运动学能量的恒星,它们起源于盖亚土卫二的郊区,并在早期的通道中被吸积;(2)动能较低的恒星在后来的通道中被吸积,起源于盖亚土卫二的内部。通过使用高精度的化学丰度,关键是包括新的铝测量,我们表明,在所有观察到的丰度比([Fe/H], [Al/Fe], [Mg/Fe]和[Mg/Ba])中,与低能恒星相比,高能恒星显示出来自盖亚土卫二化学演化较少的外部区域的证据。因此我们得出结论,土卫二盖亚在与我们银河系的主体合并之前经历了几次穿越。这一发现对我们对这一事件的理解具有广泛的意义,并巩固了盖亚土卫二作为研究星系合并和分层星系形成的非凡细节的基准。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Evidence of Gaia Enceladus Experiencing at Least Two Passages around the Milky Way *
One of the major recent breakthroughs has been the discovery of the last major merger to happen in the history of the Milky Way. Around 10 Gyr ago, the galaxy Gaia Enceladus with an estimated ∼10% of the Milky Way mass, fell into the potential of our Galaxy, bringing a large amount of stars that can be identified through their unique chemical and kinematic signatures. Simulations have long predicted that a galaxy of this size should experience several passages through the disk of the Milky Way before eventually being fully dispersed. For the first time, we present observational evidence to support this. We identify two subpopulations accreted from Gaia Enceladus: (1) stars that today have large kinematic energy, which originated from the outskirts of Gaia Enceladus and were accreted during early passages; (2) stars with low kinetic energy accreted at later passages, originating from the inner parts of Gaia Enceladus. Through the use of high-precision chemical abundances, crucially including new aluminum measurements, we show that in all observed abundance ratios ([Fe/H], [Al/Fe], [Mg/Fe], and [Mg/Ba]), stars with high energy show evidence of coming from a less chemically evolved outer region of Gaia Enceladus, compared to the stars with low energy. We therefore conclude that Gaia Enceladus experienced several passages before merging with the main body of our Galaxy. This discovery has wide implications for our understanding of this event and consolidates Gaia Enceladus as a benchmark for studying galaxy mergers and hierarchical galaxy formation in extraordinary detail.
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