Low-α metal-rich stars with sausage kinematics in the LAMOST survey: Are they from the Gaia-Sausage-

• 作 者: Gang Zhao Yuqin Chen
• 机 构: CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sci
• 出 处: 中国科学：物理学 力学 天文学（英文版）
• 发表日期: 2021年3期
• 关键词: Galactic halo spiral arms and Galactic disk chemical composition and chemical ev

We search for metal-rich Sausage-kinematic (MRSK) stars with[Fe/H]＞-0.8 and-100 ＜ Vφ ＜ 50 km/s in LAMOST DR5 in order to investigate the influence of the Gaia-Sausage-Enceladus (GSE) merger event on the Galactic disk.For the first time,we find a group of low-α MRSK stars,and classify it as a metal-rich tail of the GSE galaxy based on the chemical and kinematical properties.This group has slightly larger Rapo,Zmax and Etot distributions than a previously-reported high-α group.Its low-α ratio does not allow for an origin resulting from the splash process of the GSE merger event,as is proposed to explain the high-α group.A hydrodynamical simulation by Amarante et al.provides a promising solution,in which the GSE galaxy is a clumpy Milky-Way analogue that develops a bimodal disk chemistry.This scenario explains the existence of MRSK stars with both high-α and low-α ratios found in this work.It is further supported by another new feature that a clump of MRSK stars is located at Zmax=3-5 kpc,which corresponds to the widely adopted disk-halo transition at |Z| ～ 4 kpc.We suggest that a pile-up of MRSK stars at Zmax contributes significantly to this disk-halo transition,an interesting imprint left by the GSE merger event.These results also provide an important implication on the connection between the GSE and the Virgo Radial Merger.