arXiv 1302.03022013-02astro-ph.GA

Milky Way卫星星系中的双星群体：来自船底座、天炉座、玉夫座和六分仪座矮球状星系多历元数据的约束

Binary populations in Milky Way satellite galaxies: constraints from multi-epoch data in the Carina, Fornax, Sculptor and Sextans dwarf spheroidal galaxies

Quinn E. Minor

备注：: 20 pages, 12 figures; accepted for publication in ApJ
DOI：: 10.1088/0004-637X/779/2/116

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摘要：

我们引入了多历元恒星视线速度的似然分析来约束矮球状星系的双星分数和双星周期分布。这种方法适用于多时代的数据，从麦哲伦/MMFS调查的船底座，天炉座，玉夫座和六分仪dSph星系后，应用模型的测量误差，占二进制轨道运动。我们发现，天炉座，雕刻家，六分仪dSphs是一致的，有二进制人口类似的银河系领域的二进制在68%的置信限内，而船底座dSphs是显着不足的二进制周期小于10年。如果船底座的周期分布与银河场的周期分布相同，它的最佳拟合双星分数为0.14^{+0.28}_{-0.05}，并且在90%的置信水平下被限制为小于0.5;因此它不太可能拥有与银河场相同的双星数。相比之下，所有四个星系合并样本的最佳拟合双星分数为0.46^{+0.13}_{-0.09}，与银河系场双星的结果一致。更一般地说，我们推断概率分布在二进制分数，平均轨道周期，和分散的周期为每个星系的样本。展望未来的调查，我们表明，允许的参数空间的二进制分数和dSphs的周期分布参数将显着缩小一个大的多历元调查。然而，参数之间存在简并性，除非测量误差在~0.1 km/s或更小的量级，否则不太可能被打破，目前只能通过高分辨率光谱仪实现。

英文摘要：

We introduce a likelihood analysis of multi-epoch stellar line-of-sight velocities to constrain the binary fractions and binary period distributions of dwarf spheroidal galaxies. This method is applied to multi-epoch data from the Magellan/MMFS survey of the Carina, Fornax, Sculptor and Sextans dSph galaxies, after applying a model for the measurement errors that accounts for binary orbital motion. We find that the Fornax, Sculptor, and Sextans dSphs are consistent with having binary populations similar to that of Milky Way field binaries to within 68% confidence limits, whereas the Carina dSph is remarkably deficient in binaries with periods less than ~10 years. If Carina is assumed to have a period distribution identical to that of the Milky Way field, its best-fit binary fraction is 0.14^{+0.28}_{-0.05}, and is constrained to be less than 0.5 at the 90% confidence level; thus it is unlikely to host a binary population identical to that of the Milky Way field. By contrast, the best-fit binary fraction of the combined sample of all four galaxies is 0.46^{+0.13}_{-0.09}, consistent with that of Milky Way field binaries. More generally, we infer probability distributions in binary fraction, mean orbital period, and dispersion of periods for each galaxy in the sample. Looking ahead to future surveys, we show that the allowed parameter space of binary fraction and period distribution parameters in dSphs will be narrowed significantly by a large multi-epoch survey. However, there is a degeneracy between the parameters that is unlikely to be broken unless the measurement error is of order ~0.1 km/s or smaller, presently attainable only by a high-resolution spectrograph.

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