论文标题
银河系和仙女座的极为贫穷的恒星在哪里？ TNG50的期望
Where are the extremely metal-poor stars in the Milky Way and Andromeda? Expectations from TNG50
论文作者
论文摘要
我们在TNG50模拟中分析了198银河系（MW）/m31类的星系，分析了198银河系/m31的星系中极为贫穷的星（EMP，[fe/h] $ <-3 $）的位置。除卫星外，每个系统都分为四个运动学定义的形态学恒星成分，即基于恒星圆形和半乳房中心距离，即凸出，冷盘，温暖的磁盘和恒星光环（带有卫星（带有恒星质量$ \ ge 5 \ ge 5 \ ge 5 \ times10^6 \，m_，m_，m_，m_ \ odot $）。根据TNG50和所有模拟系统，主要银河系和卫星的恒星光环呈现出EMP的最高频率（最大的$ M _ {\ Mathrm {emp，comp}} $ - to- $ m _ {\ $ m _ {\ mathrm {tot，comp}} $ Stellar质量比例，因此是最高的。在低质量中，这种频率比高质量卫星大。此外，TNG50预测，主要星系的恒星光环始终托管，因此贡献了系统的大多数EMP。也就是说，它的EMP与系统中的所有EMP的质量比最高（最大的$ M _ {\ Mathrm {emp，comp}} $ - to- $ m_ \ $ m_ \ mathrm {emp}（<300 \ 300 \ m mathrm {kpc}）$）。但是，值得注意的是，我们还发现，TNG50中的33 MW/M31样星系具有冷盘，其贡献超过10％，每个EMP质量贡献了10％以上，每个磁盘都有$ \ gtrsim 10^{6.5-7} \，M_ \ odot，M_ \ odot y odot y odot odot odot odot odot odot。这些定性陈述不取决于EMP恒星的确切定义，即所采用的金属性阈值。这项工作的结果为EMP恒星的位置提供了从空间和运动学角度以及空前数量良好的良好溶解的MW/M31样系统的理论预测。
We analyse the location of extremely metal-poor stars (EMPs, [Fe/H]$ < -3$) in 198 Milky Way (MW)/M31-like galaxies at $z=0$ in the TNG50 simulation. Each system is divided into four kinematically-defined morphological stellar components based on stellar circularity and galactocentric distance, namely bulge, cold disk, warm disk, and stellar halo, in addition to satellites (with stellar mass $\ge 5\times10^6\,M_\odot$). According to TNG50 and across all simulated systems, the stellar halo of the main galaxy and satellites present the highest frequency of EMPs (largest $M_{\mathrm{EMP, comp}}$-to-$M_{\mathrm{tot, comp}}$ stellar mass ratio), and thus the highest chances of finding them. Such frequency is larger in lower-mass than high-mass satellites. Moreover, TNG50 predicts that the stellar halo of the main galaxy always hosts and thus contributes the majority of the EMPs of the system. Namely, it has the highest mass ratio of EMPs in it to all the EMPs in the system (largest $M_{\mathrm{EMP, comp}}$-to-$M_\mathrm{EMP} (<300\mathrm{kpc})$). However, notably, we also find that 33 MW/M31-like galaxies in TNG50 have cold disks that contribute more than 10 per cent to the total EMP mass, each with $\gtrsim 10^{6.5-7}\, M_\odot$ of EMPs in cold circular orbits. These qualitative statements do not depend on the precise definition of EMP stars, i.e. on the adopted metallicity threshold. The results of this work provide a theoretical prediction for the location of EMP stars from both a spatial and kinematic perspective and across an unprecedented number of well-resolved MW/M31-like systems.
