THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK
THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK
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DOI：
10.1088/0004-637x/753/2/148
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发表时间：
2012-07-10
影响因子：
4.9
通讯作者：
Lee, Young Sun
中科院分区：
文献类型：
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作者：
Bovy, Jo;Rix, Hans-Walter;Lee, Young Sun
银河星系的星盘的空间、运动学和元素丰度结构都很复杂，很难用当地的光谱学或全球光度学数据来分析。在这里，我们开发并应用了一种严格的密度建模方法用于银河系光谱调查，该方法可以在[alpha/Fe]和[Fe/H]的窄箱中调查恒星子种群的全球空间结构，使用来自SDSS/SEGUE的23，767颗G型矮星，其有效地采样了5 kpc < R-GC < 12 kpc和0.3kpc小于或接近于垂直条Z垂直条小于或接近于3 kpc。我们拟合模型的数量密度的每个这样的（[α/Fe]和[Fe/H]）单丰度组件，适当占复杂的光谱SEGUE采样的底层恒星人口，以及金属丰度和颜色分布的样品。我们发现，每个单丰度亚种群有一个简单的空间结构，可以描述为一个单一的指数在垂直和径向方向上，不断增加的标度高度（约200秒差距至1千秒差距）和减少的标度长度（>4.5千秒差距至2千秒差距）为越来越老的亚种群，如其较低的金属丰度和[α/Fe]增强。具有最大尺度高度的丰度选择子分量具有最短尺度长度与纯几何“厚-薄盘”分解形成鲜明对比。在某种程度上，[α/Fe]是一个足够的代理年龄，我们的研究结果直接表明，较老的磁盘子人口更集中，这意味着由内而外形成的星系盘。事实上，最大的尺度高度子分量集中在银河系的中心，这几乎是通过内部演化来解释盘的垂直结构的必然结果。是否简单的空间结构的单丰度子组件和显着的年龄之间的相关性，规模的长度和规模的高度可以合理地解释卫星吸积或其他外部加热还有待观察。
The spatial, kinematic, and elemental-abundance structure of the MilkyWay's stellar disk is complex, and has been difficult to dissect with local spectroscopic or global photometric data. Here, we develop and apply a rigorous density modeling approach for Galactic spectroscopic surveys that enables investigation of the global spatial structure of stellar sub-populations in narrow bins of [alpha/Fe] and [Fe/H], using 23,767 G-type dwarfs from SDSS/SEGUE, which effectively sample 5 kpc < R-GC < 12 kpc and 0.3 kpc less than or similar to vertical bar Z vertical bar less than or similar to 3 kpc. We fit models for the number density of each such ([alpha/Fe] and [Fe/H]) mono-abundance component, properly accounting for the complex spectroscopic SEGUE sampling of the underlying stellar population, as well as for the metallicity and color distributions of the samples. We find that each mono-abundance sub-population has a simple spatial structure that can be described by a single exponential in both the vertical and radial directions, with continuously increasing scale heights (approximate to 200 pc to 1 kpc) and decreasing scale lengths (>4.5 kpc to 2 kpc) for increasingly older sub-populations, as indicated by their lower metallicities and [alpha/Fe] enhancements. That the abundance-selected sub-components with the largest scale heights have the shortest scale lengths is in sharp contrast with purely geometric "thick-thin disk" decompositions. To the extent that [alpha/Fe] is an adequate proxy for age, our results directly show that older disk sub-populations are more centrally concentrated, which implies inside-out formation of galactic disks. The fact that the largest scale-height sub-components are most centrally concentrated in the Milky Way is an almost inevitable consequence of explaining the vertical structure of the disk through internal evolution. Whether the simple spatial structure of the mono-abundance sub-components and the striking correlations between age, scale length, and scale height can be plausibly explained by satellite accretion or other external heating remains to be seen.