The Pristine Survey – VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime
The Pristine Survey – VIII. The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime
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DOI：
10.1093/mnras/stz3619
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发表时间：
2020-01
影响因子：
4.8
通讯作者：
K. Youakim;E. Starkenburg;N. Martin;G. Matijevič;D. Aguado;C. A. Prieto;C. A. Prieto;A. Arentsen;P. Bonifacio;R. Carlberg;J. I. G. Hernández;J. I. G. Hernández;V. Hill;G. Kordopatis;C. Lardo;Julio F. Navarro;P. Jablonka;P. Jablonka;R. S. Janssen;F. Sestito;G. Thomas;K. Venn
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文献类型：
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作者：
K. Youakim;E. Starkenburg;N. Martin;G. Matijevič;D. Aguado;C. A. Prieto;C. A. Prieto;A. Arentsen;P. Bonifacio;R. Carlberg;J. I. G. Hernández;J. I. G. Hernández;V. Hill;G. Kordopatis;C. Lardo;Julio F. Navarro;P. Jablonka;P. Jablonka;R. S. Janssen;F. Sestito;G. Thomas;K. Venn
原始巡天使用窄带光度测定法精确获得金属丰度，精确到金属极贫的区域（[Fe/H] < -3），目前在$\sim 2~500\, \mathrm{deg}^2$的天空区域有超过400万颗fgk型恒星。我们集中分析了$\sim 80~000$主序关闭星的一个子样本，其日心距离在6 ～ 20kpc之间，我们认为这是内晕的一个代表性样本。得到的金属丰度分布函数（MDF）在[Fe/H] = -1.6处有峰值，在金属丰度-3.4 < [Fe/H] < -2.5处斜率为$\Delta$ (LogN)/ $\Delta[Fe/H] = 1.0 \pm 0.1$。这与这个范围内的一个简单的闭盒化学富集模型非常吻合，但比以前文献中提出的光谱MDFs要浅，这表明在内晕中可能有比以前报道的更大比例的金属贫乏恒星。我们在低纬度场中心方向的金属丰度空间中发现了Monoceros/TriAnd/ACS/EBS/A13结构，并讨论了内晕由单个大型合并事件主导的可能性，但目前的数据无法有力地支持或反驳这一观点。最后，根据场星的MDF，我们估计银河系晕中预期的金属丰度较低的球状星团的数量为[Fe/H] < -2.5的为5.4,[Fe/H] < -3的为1.5，这表明银河系中缺乏低金属丰度的球状星团并不仅仅是由于统计欠采样。
The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ([Fe/H] < -3), and currently consists of over 4 million FGK-type stars over a sky area of $\sim 2~500\, \mathrm{deg}^2$. We focus our analysis on a subsample of $\sim 80~000$ main sequence turnoff stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at [Fe/H] = -1.6, and a slope of $\Delta$(LogN)/$\Delta[Fe/H] = 1.0 \pm 0.1$ in the metallicity range of -3.4 < [Fe/H] < -2.5. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low latitude field in the anticenter direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for [Fe/H] < -2.5 and 1.5 for [Fe/H] < -3, suggesting that the lack of low metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.