Tracing the formation of the Milky Way through ultra metal-poor stars
Tracing the formation of the Milky Way through ultra metal-poor stars
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DOI：
10.1093/mnras/stz043
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发表时间：
2018-11
影响因子：
4.8
通讯作者：
F. Sestito;N. Longeard;N. Martin;E. Starkenburg;M. Fouesneau;J. I. González Hernández-J.-I.-González Hernández-2124193234;A. Arentsen
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文献类型：
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作者：
F. Sestito;N. Longeard;N. Martin;E. Starkenburg;M. Fouesneau;J. I. González Hernández-J.-I.-González Hernández-2124193234;A. Arentsen
我们使用 Gaia DR2 天体测量和光度数据、已发布的径向速度和 MESA 模型来推断所有超贫金属恒星 ([Fe/H] 11 Gyr) 的距离、轨道、表面重力和有效温度，并且预计它们属于银河系晕，我们发现这 42 颗恒星（18 颗矮星和 24 颗巨星或亚巨星）目前距离太阳 20 kpc 以内，并且他们绘制了各种各样的轨道。这些恒星中的很大一部分仍然局限于光环的内部，很可能是在银河系历史的早期形成或吸积的，而其他恒星则具有更大的远心（> 30 kpc），暗示着矮星系后来的吸积。特别有趣的是，我们发现证据表明，所有已知 UMP 恒星中很大一部分（26％）都位于银河系平面 3 kpc 以内的顺行轨道上（J_z < 100 km s^{-1} kpc）。一种有趣的解释是，这些恒星属于原银河系的巨大组成部分，形成了银河系圆盘的主干。或者，它们可能在早期盘中形成并被动态加热，或者通过一个或多个吸积事件被带入银河系，其轨道在破坏之前被动态摩擦拖入平面。精致的盖亚 DR2 数据与对金属含量非常贫乏的天空的勘测相结合，开启了一个令人兴奋的时代，我们可以在其中追踪银河系的早期形成。
We use Gaia DR2 astrometric and photometric data, published radial velocities and MESA models to infer distances, orbits, surface gravities, and effective temperatures for all ultra metal-poor stars ([Fe/H] 11 Gyr) and that they are expected to belong to the Milky Way halo, we find that these 42 stars (18 dwarf stars and 24 giants or sub-giants) are currently within 20 kpc of the Sun and that they map a wide variety of orbits. A large fraction of those stars remains confined to the inner parts of the halo and was likely formed or accreted early on in the history of the Milky Way, while others have larger apocentres (> 30 kpc), hinting at later accretion from dwarf galaxies. Of particular interest, we find evidence that a significant fraction of all known UMP stars (26 per cent) are on prograde orbits confined within 3 kpc of the Milky Way plane (J_z < 100 km s^{-1} kpc). One intriguing interpretation is that these stars belonged to the massive building block(s) of the proto-Milky Way that formed the backbone of the Milky Way disc. Alternatively, they might have formed in the early disc and have been dynamically heated, or have been brought into the Milky Way by one or more accretion events whose orbit was dragged into the plane by dynamical friction before disruption. The combination of the exquisite Gaia DR2 data and surveys of the very metal-poor sky opens an exciting era in which we can trace the very early formation of the Milky Way.