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arXiv 2001.04988astro-ph.GA
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原始调查VIII:Milky Way晕到极贫金属区的金属丰度分布函数

The Pristine survey VIII: The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime

K. Youakim, E. Starkenburg, N. F. Martin, G. Matijevic, D. S. Aguado, C. Allende Prieto, A. Arentsen, P. Bonifacio, R. G. Carlberg, J. I. González Hernández, V.… 展开作者

K. Youakim, E. Starkenburg, N. F. Martin, G. Matijevic, D. S. Aguado, C. Allende Prieto, A. Arentsen, P. Bonifacio, R. G. Carlberg, J. I. González Hernández, V. Hill, G. Kordopatis, C. Lardo, J. F. Navarro, P. Jablonka, R. Sánchez Janssen, F. Sestito, G. F. Thomas

摘要:

原始巡天使用窄带测光法来获得精确的金属丰度,精确到极贫金属区([Fe/H] < -3),目前在$\sim 2~500\, \mathrm{deg}^2$的天空区域内有超过400万颗FGK型恒星。我们把我们的分析集中在一个子样本的$\sim 80~000$主序星关闭与日心距离6和20千秒差距之间,我们采取的是一个有代表性的样本的内晕。得到的金属丰度分布函数(Imax)在[Fe/H] =-1.6处具有峰值,并且$Δ$(LogN)/ $Δ[Fe/H] = 1.0 \pm 0.1$的斜率在-3.4 < [Fe/H] <-2.5的金属丰度范围内。这与一个简单的闭盒化学富集模型在这个范围内,但比以前的光谱MDF在文献中提出的浅,这表明可能有一个更大的比例贫金属恒星的内晕比以前报道。我们确定了Monoceros/TriAnd/ACS/EBS/A13结构的金属丰度空间在低纬领域的反中心方向,并讨论了内晕是由一个单一的,大的合并事件,但不能有力地支持或反驳这一想法与现有的数据。最后,基于场星的数量,我们估计银河系晕中贫金属球状星团的数量在[Fe/H] < -2.5时为5.4,在[Fe/H] <-3时为1.5,这表明银河系中缺乏低金属丰度球状星团不仅仅是由于统计欠采样。

英文摘要:

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 $Δ$(LogN)/$Δ[Fe/H] = 1.0 \pm 0.1$ 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.

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