不对称战争：M31及其卫星
Asymmetric Warfare: M31 and its Satellites
摘要：
对M31晕的光度测量生动地说明了等级星系形成造成的残骸。M31的几颗卫星被M31的潮汐场破坏，其中包括M33和And I，而其他潮汐结构则是已经被摧毁的卫星的尸体。M31的卫星在多大程度上给它留下了战争的伤疤是未知的;要回答这个问题，我们需要精确的轨道和扰动物的质量。我在这里集中在M31的150 kpc长的巨大的南流（GSS）作为一个例子，这些可以确定，即使在没有一个可见的祖先。将N体模型与光度和光谱数据进行比较，我发现这个流是由大约750 Myr前的一次近距离通过导致一个大型卫星星系的分裂造成的。GSS与M31光环中的其他几个碎片结构相连。贝叶斯抽样的模拟估计的原始质量为log（Mstar/Msun）= 9.5 +- 0.2，表明它是直到最近最大的本星系群之一。流模型将M31的晕质量限定为（1.8+-0.5 x10 ^{12} Msun.虽然这些小的不确定性忽略了几个重要的自由度，但即使使用更完整的模型，它们也可能保持良好。未来对M31卫星和星流的研究将提供对M31质量的独立限制，并揭示M31及其晕组成的共同历史。
英文摘要：
Photometric surveys of M31's halo vividly illustrate the wreckage caused by hierarchical galaxy formation. Several of M31's satellites are being disrupted by M31's tidal field, among them M33 and And I, while other tidal structures are the corpses of satellites already destroyed. The extent to which M31's satellites have left battle scars upon it is unknown; to answer this we need accurate orbits and masses of the perturbers. I focus here on M31's 150-kpc-long Giant Southern Stream (GSS) as an example of how these can be determined even in the absence of a visible progenitor. Comparing N-body models to photometric and spectroscopic data, I find this stream resulted from the disruption of a large satellite galaxy by a close passage about 750 Myr ago. The GSS is connected to several other debris structures in M31's halo. Bayesian sampling of the simulations estimates the progenitor's initial mass as log(Mstar/Msun) = 9.5 +- 0.2, showing it was one of the most massive Local Group galaxies until quite recently. The stream model constrains M31's halo mass to be (1.8+-0.5)x10^{12} Msun. While these small uncertainties neglect several important degrees of freedom, they are likely to remain good even with a more complete model. Future work on M31's satellites and streams will provide independent constraints on M31's mass, and reveal the shared history of M31 and its halo components.
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