Title: Major Substructure in the M31 Outer Halo: Distances and Metallicities along the Giant Stellar Stream Show Chinese title

Title: M31外晕中的主要结构：巨星流上的距离和金属量

Abstract: We present a renewed look at M31's Giant Stellar Stream along with the nearby structures Stream C and Stream D, exploiting a new algorithm capable of fitting to the red giant branch (RGB) of a structure in both colour and magnitude space. Using this algorithm, we are able to generate probability distributions in distance, metallicity and RGB width for a series of subfields spanning these structures. Specifically, we confirm a distance gradient of approximately 20 kpc per degree along a 6 degree extension of the Giant Stellar Stream, with the farthest subfields from M31 lying ~ 120 kpc more distant than the inner-most subfields. Further, we find a metallicity that steadily increases from -0.7^{+0.1}_{-0.1} dex to -0.2^{+0.2}_{-0.1} dex along the inner half of the stream before steadily dropping to a value of -1.0^{+0.2}_{-0.2} dex at the farthest reaches of our coverage. The RGB width is found to increase rapidly from 0.4^{+0.1}_{-0.1} dex to 1.1^{+0.2}_{-0.1} dex in the inner portion of the stream before plateauing and decreasing marginally in the outer subfields of the stream. In addition, we estimate Stream C to lie at a distance between 794 and 862 kpc and Stream D between 758 kpc and 868 kpc. We estimate the median metallicity of Stream C to lie in the range -0.7 to -1.6 dex and a metallicity of -1.1^{+0.3}_{-0.2} dex for Stream D. RGB widths for the two structures are estimated to lie in the range 0.4 to 1.2 dex and 0.3 to 0.7 dex respectively. In total, measurements are obtained for 19 subfields along the Giant Stellar Stream, 4 along Stream C, 5 along Stream D and 3 general M31 spheroid fields for comparison. We thus provide a higher resolution coverage of the structures in these parameters than has previously been available in the literature. Show Chinese abstract

Abstract: 我们对M31的巨恒星流以及附近的结构Stream C和Stream D进行了新的研究，利用一种新算法，该算法能够在颜色和亮度空间中拟合结构的红巨星分支（RGB）。 使用此算法，我们能够为跨越这些结构的一系列子区域生成距离、金属含量和RGB宽度的概率分布。 具体而言，我们确认在巨恒星流6度延伸范围内，距离梯度约为每度20千秒差距，离M31最远的子区域比最内部的子区域大约远120千秒差距。 此外，我们发现金属含量沿着流的内半部分从-0.7^{+0.1}_{-0.1} dex稳步增加到-0.2^{+0.2}_{-0.1} dex，然后在我们覆盖范围的最远端稳定下降到-1.0^{+0.2}_{-0.2} dex的值。 RGB宽度被发现从0.4^{+0.1}_{-0.1} dex迅速增加到流内部区域的1.1^{+0.2}_{-0.1} dex，然后在流的外部子区域趋于平缓并略有减少。 此外，我们估计流C位于794到862 kpc的距离之间，流D位于758 kpc到868 kpc之间。 我们估计流C的中位金属量位于-0.7到-1.6 dex范围内，流D的金属量为-1.1^{+0.3}_{-0.2} dex。这两个结构的RGB宽度分别估计在0.4到1.2 dex和0.3到0.7 dex范围内。 总共在巨星流上获得了19个子区域的测量数据，流C上有4个，流D上有5个，以及3个一般的M31球状场用于比较。 因此，我们在这些参数上提供了比文献中之前可用的更高分辨率的覆盖。