Global Properties of M31’s Stellar Halo from the SPLASH Survey. III. Measuring the Stellar Velocity Dispersion Profile
Global Properties of M31’s Stellar Halo from the SPLASH Survey. III. Measuring the Stellar Velocity Dispersion Profile
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DOI：
10.3847/1538-4357/aa9f26
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发表时间：
2017-11
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影响因子：
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通讯作者：
K. Gilbert;E. Tollerud;R. Beaton;P. Guhathakurta;J. Bullock;M. Chiba;J. Kalirai;E. Kirby;S. Majewski;Mikito Tanaka
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作者：
K. Gilbert;E. Tollerud;R. Beaton;P. Guhathakurta;J. Bullock;M. Chiba;J. Kalirai;E. Kirby;S. Majewski;Mikito Tanaka
我们展示了M31光晕中红巨星分支星的速度色散，这是通过模拟分布在M31恒星光晕中的50个视场中5000多颗恒星的视距速度分布得出的。该数据集是仙女座恒星光晕（SPLASH）调查的光谱和光度景观的一部分，覆盖了M31中心9到175公里的投影半径。银河系（MW）和M31的所有主要结构成分都被纳入高斯混合模型，包括所有先前在观测场中确定的M31潮汐碎片特征。根据一组经验光度和光谱诊断，单个恒星是M31或MW组成部分的概率作为先验概率包含在混合模型中。M31光晕中恒星的速度色散随着投射半径的变化而轻微减小，从最内层径向区（8.2 ~ 14.1 kpc）的108 km s−1到投射半径（~ 40 ~ 130 kpc）的80 ~ 90 km s−1，可以用斜率为- 0.12±0.05的幂律来参数化。所引用的幂律斜率的不确定性仅反映了方法的精度，尽管我们考虑的其他不确定性来源对总体误差预算的贡献可以忽略不计。
We present the velocity dispersion of red giant branch stars in M31’s halo, derived by modeling the line-of-sight velocity distribution of over 5000 stars in 50 fields spread throughout M31’s stellar halo. The data set was obtained as part of the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo (SPLASH) Survey, and covers projected radii of 9 to 175 kpc from M31’s center. All major structural components along the line of sight in both the Milky Way (MW) and M31 are incorporated in a Gaussian Mixture Model, including all previously identified M31 tidal debris features in the observed fields. The probability that an individual star is a constituent of M31 or the MW, based on a set of empirical photometric and spectroscopic diagnostics, is included as a prior probability in the mixture model. The velocity dispersion of stars in M31’s halo is found to decrease only mildly with projected radius, from 108 km s−1 in the innermost radial bin (8.2 to 14.1 kpc) to ∼80 to 90 km s−1 at projected radii of ∼40–130 kpc, and can be parameterized with a power law of slope −0.12 ± 0.05. The quoted uncertainty on the power-law slope reflects only the precision of the method, although other sources of uncertainty we consider contribute negligibly to the overall error budget.