STRUCTURE AND POPULATION OF THE ANDROMEDA STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY
STRUCTURE AND POPULATION OF THE ANDROMEDA STELLAR HALO FROM A SUBARU/SUPRIME-CAM SURVEY
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DOI：
10.1088/0004-637x/708/2/1168
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发表时间：
2009-08
期刊：
影响因子：
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通讯作者：
Mikito Tanaka;M. Chiba;Y. Komiyama;P. Guhathakurta;J. Kalirai;M. Iye
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文献类型：
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作者：
Mikito Tanaka;M. Chiba;Y. Komiyama;P. Guhathakurta;J. Kalirai;M. Iye
本文利用斯巴鲁望远镜上的Suprime-Cam对最近的巨型螺旋星系仙女座星系（M31）的恒星晕进行了光度测量。一个详细的分析VI色星等图的解决恒星人口被用来测量的属性，如视线距离，表面亮度，金属丰度和年龄。这些被用来分离和表征M31晕的不同组成部分：（1）巨大的南方流（GSS）;（2）其他几个子结构;和（3）光滑晕。首先，GSS的特征是一个宽的红巨星分支（RGB）和一个富金属/中等年龄的红团（RC）。RGB尖端的I星等表明，在距离M31中心R = 30 kpc的投影半径处，到观测到的GSS场的距离为（m-M）0 = 24.73 ± 0.11（883 ± 45 kpc）。通过与理论等时线的比较，GSS显示出高金属丰度，峰值为[Fe/H]<$−0.5，平均值（中位数）为−0.7（−0.6）。结合RC的光度，我们估计它的恒星群体的平均年龄为108 Gyr。其前身星系的质量可能在107- 109 M之间。其次，我们研究了M31的晕子结构沿着西北/东南短轴到R = 100 kpc和西南长轴区域在R = 60 kpc。我们证实了Ibata等人报道的东南晕中的两个亚结构，并在西北晕中发现了两个过密亚结构。我们研究了这四个子结构以及包括西大陆架在内的其他结构的性质，发现这些系统之间恒星种群的差异，从而表明每个系统都有不同的起源。我们的统计分析暗示，M31晕作为一个整体可能包含至少16个子结构，每个子结构都有不同的起源，所以它的外晕至少经历了这么多的吸积事件，涉及质量为107- 109 M的矮卫星，因为红移为z = 1。第三，我们研究了一个基本的，光滑的，扩展的晕组件的属性，R>100 kpc。我们发现这个光滑晕的表面密度可以拟合为尺度半径为17 kpc的Hernquist模型或Σ（R）‡ R-2.17±0.15的幂律分布。与相对平滑的晕密度分布相反，它的金属丰度分布似乎是空间上不均匀的，随着半径的非单调变化，这表明晕人口没有足够的时间来动态均匀的吸积人口。对M31晕形成的进一步影响进行了讨论。
We present a photometric survey of the stellar halo of the nearest giant spiral galaxy, Andromeda (M31), using Suprime-Cam on the Subaru Telescope. A detailed analysis of VI color–magnitude diagrams of the resolved stellar population is used to measure properties such as line-of-sight distance, surface brightness, metallicity, and age. These are used to isolate and characterize different components of the M31 halo: (1) the giant southern stream (GSS); (2) several other substructures; and (3) the smooth halo. First, the GSS is characterized by a broad red giant branch (RGB) and a metal-rich/intermediate-age red clump (RC). The I magnitude of the well-defined tip of the RGB suggests that the distance to the observed GSS field is (m − M)0 = 24.73 ± 0.11 (883 ± 45 kpc) at a projected radius of R ∼ 30 kpc from M31's center. The GSS shows a high metallicity peaked at [Fe/H]≳−0.5 with a mean (median) of −0.7 (−0.6), estimated via comparison with theoretical isochrones. Combined with the luminosity of the RC, we estimate the mean age of its stellar population to be ∼8 Gyr. The mass of its progenitor galaxy is likely in the range of 107–109M☉. Second, we study M31's halo substructure along the northwest/southeast minor axis out to R ∼ 100 kpc and the southwest major-axis region at R ∼ 60 kpc. We confirm two substructures in the southeast halo reported by Ibata et al. and discover two overdense substructures in the northwest halo. We investigate the properties of these four substructures as well as other structures including the western shelf and find that differences in stellar populations among these systems, thereby suggesting each has a different origin. Our statistical analysis implies that the M31 halo as a whole may contain at least 16 substructures, each with a different origin, so its outer halo has experienced at least this many accretion events involving dwarf satellites with mass 107–109M☉ since a redshift of z ∼ 1. Third, we investigate the properties of an underlying, smooth, and extended halo component out to R>100 kpc. We find that the surface density of this smooth halo can be fitted to a Hernquist model of scale radius ∼17 kpc or a power-law profile with Σ(R) ∝ R−2.17±0.15. In contrast to the relative smoothness of the halo density profile, its metallicity distribution appears to be spatially non-uniform with non-monotonic variations with radius, suggesting that the halo population has not had sufficient time to dynamically homogenize the accreted populations. Further implications for the formation of the M31 halo are discussed.