The star formation history of the Sagittarius stream
The star formation history of the Sagittarius stream
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DOI：
10.1093/mnras/stv946
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发表时间：
2015-05
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影响因子：
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通讯作者：
T. D. Boer;V. Belokurov;Sergey E. Koposov
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文献类型：
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作者：
T. D. Boer;V. Belokurov;Sergey E. Koposov
我们提出了第一个详细的定量研究的人马座（Sgr）流的条纹82区域内的恒星种群，使用从斯隆数字巡天（SDSS）的光度和光谱观测。星星的形成历史（SFH）分别为明亮和暗淡的Sgr流，以确定是否两个组件组成的类似的恒星人口的混合或有不同的起源。最佳拟合SFH解决方案的特点是一个定义明确，在年龄金属丰度空间的紧密序列，表明星星形成发生在一个良好的混合，均匀富集介质。星星的形成率在5-7 Gyr的年龄急剧下降，可能与MW吸积Sgr有关。最后，Sgr序列显示年龄-金属丰度空间在11- 1 - 3 Gyr之间的斜率变化与Sgr α-元素拐点一致，表明Ia型超新星在星星形成开始后开始对丰度模式~1-3 Gyr做出贡献。两个流的结果与从亲本Sgr群体混合物中提取的结果一致，但在不同的时期。亮流的SFH从古老的贫金属种群开始，扩展到[Fe/H]~-0.7，峰值在~7和11 Gyr。微弱的SFH采样了Sgr序列中更古老、更贫金属的部分，在远古时代达到峰值，大多数恒星的[Fe/H] 9 Gyr。因此，我们主张赞成这样一种情况，即微弱的流由i）早些时候剥离的物质组成，ii）从Sgr矮星的外围剥离的物质。
We present the first detailed quantitative study of the stellar populations of the Sagittarius (Sgr) streams within the Stripe 82 region, using photometric and spectroscopic observations from the Sloan Digital Sky Survey (SDSS). The star formation history (SFH) is determined separately for the bright and faint Sgr streams, to establish whether both components consist of a similar stellar population mix or have a distinct origin. Best fit SFH solutions are characterised by a well-defined, tight sequence in age-metallicity space, indicating that star formation occurred within a well-mixed, homogeneously enriched medium. Star formation rates dropped sharply at an age of ~5-7 Gyr, possibly related to the accretion of Sgr by the MW. Finally, the Sgr sequence displays a change of slope in age-metallicity space at an age between 11-13 Gyr consistent with the Sgr alpha-element knee, indicating that supernovae type Ia started contributing to the abundance pattern ~1-3 Gyr after the start of star formation. Results for both streams are consistent with being drawn from the parent Sgr population mix, but at different epochs. The SFH of the bright stream starts from old, metal-poor populations and extends to a metallicity of [Fe/H]~-0.7, with peaks at ~7 and 11 Gyr. The faint SFH samples the older, more metal-poor part of the Sgr sequence, with a peak at ancient ages and stars mostly with [Fe/H] 9 Gyr. Therefore, we argue in favour of a scenario where the faint stream consists of material stripped i) earlier, and ii) from the outskirts of the Sgr dwarf.