M31东北陆架红巨星支星的运动学和金属丰度
Kinematics and Metallicity of Red Giant Branch Stars in the Northeast Shelf of M31
摘要：
我们获得了556颗红巨星分支星的Keck/DEIMOS光谱，它们分布在M31东北（NE）架上的4个光谱场，横跨$13-31$投影的kpc。我们提出了一个完整的楔形图案的第一次检测在空间中的投影M31中心的径向距离与视线速度为这个功能，其中包括返回流组件的货架。这种楔形图案同意在径向合并形成的潮汐壳的预期，并提供了强有力的证据，有利于预测的巨型恒星流（GSS）的形成模型中，东北货架起源于第二轨道包裹的潮汐碎片。观察到的同心楔形图案的东北，西（W），东南（SE）货架证实了这种解释独立的模型。我们没有检测到一个完整的祖核心，有利于GSS形成模型中的祖完全中断在NE货架区域的运动学签名。大陆架的光度金属丰度分布意味着它主要是潮汐物质，而不是相位混合的恒星晕或磁盘。金属丰度分布（[Fe/H] $_{\rm phot}$ = $-0.42$ $\pm$ $0.01$）也与GSS相匹配，因此与W和SE陆架相匹配，进一步支持潮汐特征之间的直接物理关联。
英文摘要：
We obtained Keck/DEIMOS spectra of 556 individual red giant branch stars in 4 spectroscopic fields spanning $13-31$ projected kpc along the Northeast (NE) shelf of M31. We present the first detection of a complete wedge pattern in the space of projected M31-centric radial distance versus line-of-sight velocity for this feature, which includes the returning stream component of the shelf. This wedge pattern agrees with expectations of a tidal shell formed in a radial merger and provides strong evidence in favor of predictions of Giant Stellar Stream (GSS) formation models in which the NE shelf originates from the second orbital wrap of the tidal debris. The observed concentric wedge patterns of the NE, West (W), and Southeast (SE) shelves corroborate this interpretation independently of the models. We do not detect a kinematical signature in the NE shelf region corresponding to an intact progenitor core, favoring GSS formation models in which the progenitor is completely disrupted. The shelf's photometric metallicity distribution implies that it is dominated by tidal material, as opposed to the phase-mixed stellar halo or the disk. The metallicity distribution ([Fe/H]$_{\rm phot}$ = $-0.42$ $\pm$ $0.01$) also matches the GSS, and consequently the W and SE shelves, further supporting a direct physical association between the tidal features.
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