仙女座和三角座的晕：action星系形成的全景
The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
摘要：
我们提出了一个深测光调查的M31，进行了CFHT和INT，覆盖内50千秒差距的星系，南象限到150千秒差距，并延伸到M33。这是第一次对这个星系最外层区域进行系统的全景研究。我们探测到几个流和其他大尺度结构，以及两个新的矮星系：和XV和XVI。短轴上亚结构的发现，以及0.5 < R < 1.3之间的光分布遵循指数"扩展盘“的事实，对于阐明以前研究中报告的混合和有时相互矛盾的结果特别重要。在亚结构下面是一个微弱的、贫金属的、光滑的、极度延伸的晕，延伸到至少150千秒差距。M31中的平滑晕成分的轮廓可以用赫恩奎斯特模型来拟合，该模型的巨大尺度半径约为55 kpc，几乎是理论预测的4倍。或者，指数为-1.91 +/-0.11的幂律可以拟合到曲线。这个结构的总光度与银河系的晕相似。这个巨大、光滑、潜在的光环让人想起经典的整体模型，完全出乎现代星系形成模型的意料。M33还具有扩展的贫金属晕成分，这也可以用尺度半径约为55 kpc的Hernquist模型拟合。这些扩展的缓慢减少的晕将为进一步的建模提供挑战和强约束。[删节]
英文摘要：
We present a deep photometric survey of M31, conducted with the CFHT and INT, covering the inner 50 kpc of the galaxy, the Southern quadrant out to 150 kpc, and extending to M33. This is the first systematic panoramic study of this very outermost region of galaxies. We detect several streams and other large-scale structures, and two new dwarf galaxies: And XV and XVI. The discovery of substructure on the minor axis, together with the fact that the light profile between 0.5 < R < 1.3 follows the exponential ``extended disk'', is particularly important in shedding light on the mixed and sometimes conflicting results reported in previous studies. Underlying the substructures lies a faint, metal-poor, smooth and extremely extended halo, reaching out to at least 150 kpc. The smooth halo component in M31 has a profile that can be fit with a Hernquist model of immense scale radius ~55 kpc, almost a factor of 4 larger than theoretical predictions. Alternatively a power-law with exponent -1.91 +/- 0.11 can be fit to the profile. The total luminosity of this structure is similar to that of the halo of the Milky Way. This vast, smooth, underlying halo is reminiscent of a classical monolithic model and completely unexpected from modern galaxy formation models. M33 is also found to have an extended metal-poor halo component, which can be fit with a Hernquist model also of scale radius ~55 kpc. These extended slowly-decreasing halos will provide a challenge and strong constraints for further modeling. [Abridged]
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