Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient
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DOI：
10.1093/mnras/sty2033
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发表时间：
2018-04
影响因子：
4.8
通讯作者：
I. Minchev;F. Anders;A. Recio-Blanco;C. Chiappini;P. Laverny;A. Queiroz;Matthias Steinmetz;
中科院分区：
文献类型：
--
作者：
I. Minchev;F. Anders;A. Recio-Blanco;C. Chiappini;P. Laverny;A. Queiroz;Matthias Steinmetz;
我们提出了一个半经验的，很大程度上独立于模型的方法来估计银河系的诞生半径，r_出生，银河系盘星。该技术依赖于合理的假设，即在星际介质（ISM）中存在的大部分磁盘寿命的负径向金属丰度梯度。根据观测导出的年龄和[Fe/H]，不需要运动学信息，将恒星投影回它们的出生位置。应用我们的方法对AMBRE：HARPS和HARPS-GTO局部样本，我们表明，我们可以约束ISM金属丰度演化与银河系半径和宇宙时间，[Fe/H]_ISM（r，t），通过要求一个物理上有意义的r_出生分布。我们发现，这些数据与ISM径向金属丰度梯度一致，该梯度随时间变化，从盘形成开始时的~-0.15 dex/kpc，到现在的测量值（-0.07 dex/kpc）。本文给出了单胎种群的几种化学运动学关系。一个值得注意的结果是，运动学上最热的恒星可能是在本地或在外盘中诞生的，这与单年龄种群的嵌套耀斑和宇宙学模拟的预测一致。这种现象也可以在观测到的年龄-速度色散关系中看到，因为它的上边界由出生在较大半径的恒星所主导。我们还发现，局部年龄-金属丰度关系（AMR）的平坦性是单出生人口的AMR叠加的结果，每个都有一个明确的负斜率。太阳的诞生半径估计为7.3 +-0.6 kpc，而目前银河系的半径为8 kpc。
We present a semi-empirical, largely model-independent approach for estimating Galactic birth radii, r_birth, for Milky Way disk stars. The technique relies on the justifiable assumption that a negative radial metallicity gradient in the interstellar medium (ISM) existed for most of the disk lifetime. Stars are projected back to their birth positions according to the observationally derived age and [Fe/H] with no kinematical information required. Applying our approach to the AMBRE:HARPS and HARPS-GTO local samples, we show that we can constrain the ISM metallicity evolution with Galactic radius and cosmic time, [Fe/H]_ISM(r, t), by requiring a physically meaningful r_birth distribution. We find that the data are consistent with an ISM radial metallicity gradient that flattens with time from ~-0.15 dex/kpc at the beginning of disk formation, to its measured present-day value (-0.07 dex/kpc). We present several chemo-kinematical relations in terms of mono-r_birth populations. One remarkable result is that the kinematically hottest stars would have been born locally or in the outer disk, consistent with thick disk formation from the nested flares of mono-age populations and predictions from cosmological simulations. This phenomenon can be also seen in the observed age-velocity dispersion relation, in that its upper boundary is dominated by stars born at larger radii. We also find that the flatness of the local age-metallicity relation (AMR) is the result of the superposition of the AMRs of mono-r_birth populations, each with a well-defined negative slope. The solar birth radius is estimated to be 7.3+-0.6 kpc, for a current Galactocentric radius of 8 kpc.