SPLASH巡天：仙女座巨大南流的光谱图像
The SPLASH Survey: A Spectroscopic Portrait of Andromeda's Giant Southern Stream
摘要：
巨大的南流（GSS）是M31恒星晕中最显著的潮汐碎片特征。GSS由一个相对富含金属、表面亮度高的“核心”和一个金属丰度较低、表面亮度较低的“外壳”组成。“我们在M31的GSS附近的六个区域和流C上的一个区域中呈现了红巨星的Keck/DEIMOS光谱，这是M31 SE短轴上R=60 kpc的弧形特征。这里介绍了与全球卫星系统有关的几项调查结果和测量结果。我们提出了最深的GSS核心的运动学检测的日期（R=17千秒差距）。这一区域还包含了第二个运动学冷分量的延续，这一冷分量最初出现在R=21 kpc的GSS核心区域。的GSS和第二个组件在合并的数据集的速度梯度是平行的径向范围为7千秒差距，这表明可能的分歧线的视线速度的GSS星。我们还提出了第一次运动学检测GSS包络的子结构。使用运动学确定的样品，我们表明，信封碎片有一个~0.7德克斯较低的平均光度金属丰度和可能更高的固有速度色散比GSS核心。在M31 dSph卫星And I的区域中也发现了GSS;该区域中的GSS具有与GSS核心相同的金属丰度分布。我们确认存在两个运动学冷组件流C，并测量的内在速度分散度~10和~4公里/秒。这一对GSS核心和包层中恒星的运动学（平均速度、内禀速度色散）和化学性质的汇编，加上已公布的表面亮度测量和广域恒星计数图，将改善对这颗矮卫星前身的轨道和内部结构的限制。
英文摘要：
The giant southern stream (GSS) is the most prominent tidal debris feature in M31's stellar halo. The GSS is composed of a relatively metal-rich, high surface-brightness "core" and a lower metallicity, lower surface brightness "envelope." We present Keck/DEIMOS spectroscopy of red giant stars in six fields in the vicinity of M31's GSS and one field on Stream C, an arc-like feature on M31's SE minor axis at R=60 kpc. Several GSS-related findings and measurements are presented here. We present the innermost kinematical detection of the GSS core to date (R=17 kpc). This field also contains the continuation of a second kinematically cold component originally seen in a GSS core field at R=21 kpc. The velocity gradients of the GSS and the second component in the combined data set are parallel over a radial range of 7 kpc, suggesting a possible bifurcation in the line-of-sight velocities of GSS stars. We also present the first kinematical detection of substructure in the GSS envelope. Using kinematically identified samples, we show that the envelope debris has a ~0.7 dex lower mean photometric metallicity and possibly higher intrinsic velocity dispersion than the GSS core. The GSS is also identified in the field of the M31 dSph satellite And I; the GSS in this field has a metallicity distribution identical to that of the GSS core. We confirm the presence of two kinematically cold components in Stream C, and measure intrinsic velocity dispersions of ~10 and ~4 km/s. This compilation of the kinematical (mean velocity, intrinsic velocity dispersion) and chemical properties of stars in the GSS core and envelope, coupled with published surface brightness measurements and wide-area star-count maps, will improve constraints on the orbit and internal structure of the dwarf satellite progenitor.
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