The oldest and most metal-poor stars in the APOSTLE Local Group simulations.
The oldest and most metal-poor stars in the APOSTLE Local Group simulations.
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DOI：
10.1093/mnras/stw2873
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发表时间：
2016-09
影响因子：
4.8
通讯作者：
E. Starkenburg;K. Oman;J. Navarro;R. Crain;Azadeh Fattahi;C. Frenk;Till Sawala;J. Schaye
中科院分区：
文献类型：
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作者：
E. Starkenburg;K. Oman;J. Navarro;R. Crain;Azadeh Fattahi;C. Frenk;Till Sawala;J. Schaye
我们研究了银河系大小的星系中最古老和最贫金属的恒星种群的空间分布，使用模拟本地环境（APOSTLE）的宇宙学流体动力学模拟的本地组的项目。与早期的工作一致，我们发现在最古老的恒星（tform < 0.8 Gyr）和大多数贫金属恒星（[Fe/H]<-2.5）中有很强的径向梯度，两者都向外增加。大多数贫金属恒星形成的时间较长;其中一半形成于z = 5.3之后，最后10%形成于z = 2.8之后。贫金属恒星群的年龄也显示出随环境的显著变化;它们中的很大一部分在星系的中心区域是老的，在一些个别的矮星系中甚至更高，从矮星系到矮星系有大量的分散。我们调查的依赖这些结果的假设金属混合。总的来说，属于最古老和最贫金属的恒星中有一半以上位于太阳圈之外。有些违反直觉，我们发现，矮星系的大部分贫金属恒星是非常古老的系统，贫金属恒星相对罕见，但存在大量的老年人口。我们的研究结果为解释旨在寻找银河系中最早和最原始的恒星组成部分的调查结果提供了指导。
We examine the spatial distribution of the oldest and most metal-poor stellar populations of Milky Way-sized galaxies using the A Project Of Simulating The Local Environment (APOSTLE) cosmological hydrodynamical simulations of the Local Group. In agreement with earlier work, we find strong radial gradients in the fraction of the oldest (tform < 0.8 Gyr) and most metal-poor ([Fe/H]<−2.5) stars, both of which increase outwards. The most metalpoor stars form over an extended period of time; half of them form after z = 5.3, and the last 10 per cent after z = 2.8. The age of the metal-poor stellar population also shows significant variation with environment; a high fraction of them are old in the galaxy’s central regions and an even higher fraction in some individual dwarf galaxies, with substantial scatter from dwarf to dwarf. We investigate the dependence of these results on the assumptions made for metal mixing. Overall, over half of the stars that belong to both the oldest and most metal-poor population are found outside the solar circle. Somewhat counter-intuitively, we find that dwarf galaxies with a large fraction of metal-poor stars that are very old are systems where metalpoor stars are relatively rare, but where a substantial old population is present. Our results provide guidance for interpreting the results of surveys designed to hunt for the earliest and most pristine stellar component of our Milky Way.