arXiv 0906.53482009-06-30astro-ph.GAastro-ph.CO

Milky Way的暗盘

The Dark Disk of the Milky Way

Chris W. Purcell, James S. Bullock, Manoj Kaplinghat

备注：: 11 pages, 6 figures, 1 table; submitted to ApJ
发表信息：: Astrophys.J.703:2275-2284,2009
DOI：: 10.1088/0004-637X/703/2/2275

摘要：

大量的卫星吸积到早期的星系盘上，会导致暗物质沉积在与星系共同旋转的盘状结构中。这种现象对暗物质探测实验有潜在的戏剧性后果。我们利用集中的，高分辨率的模拟吸积事件到磁盘被设计成银河系类似物，并比较由此产生的磁盘的银河系的厚盘的形态和运动学特性，以括号的范围内的同向旋转吸积暗物质。我们发现银河系的合并历史与LCDM预期的中值相比一定是异常平静的，因此它的暗盘一定相对较小：太阳附近的吸积暗盘物质的部分约为宿主晕密度的20%或更小，而太阳附近的同向旋转暗物质部分，定义为以小于50 km/s的旋转速度滞后移动的粒子，与标准光晕模型相比，增强了约30%或更少。这样的暗盘可能主要有助于直接检测实验的低能量（对于质量为100 GeV的暗物质粒子为keV量级）核反冲事件率，但它不会显著改变检测的可能性。这些暗盘提供了弱相互作用的大质量粒子暗物质模型的可检验的预测，应该在与实验数据的详细比较中加以考虑。我们的研究结果表明，银河系的暗盘可能为间接探测实验提供了可探测的信号，在银河系中心方向上贡献了大约25%的暗物质自湮灭信号，使信号具有明显的扁圆形态。

英文摘要：

Massive satellite accretions onto early galactic disks can lead to the deposition of dark matter in disk-like configurations that co-rotate with the galaxy. This phenomenon has potentially dramatic consequences for dark matter detection experiments. We utilize focused, high-resolution simulations of accretion events onto disks designed to be Galaxy analogues, and compare the resultant disks to the morphological and kinematic properties of the Milky Way's thick disk in order to bracket the range of co-rotating accreted dark matter. We find that the Milky Way's merger history must have been unusually quiescent compared to median LCDM expectations and therefore its dark disk must be relatively small: the fraction of accreted dark disk material near the Sun is about 20% of the host halo density or smaller and the co-rotating dark matter fraction near the Sun, defined as particles moving with a rotational velocity lag less than 50 km/s, is enhanced by about 30% or less compared to a standard halo model. Such a dark disk could contribute dominantly to the low energy (of order keV for a dark matter particle with mass 100 GeV) nuclear recoil event rate of direct dectection experiments, but it will not change the likelihood of detection significantly. These dark disks provide testable predictions of weakly-interacting massive particle dark matter models and should be considered in detailed comparisons to experimental data. Our findings suggest that the dark disk of the Milky Way may provide a detectable signal for indirect detection experiments, contributing up to about 25% of the dark matter self-annihilation signal in the direction of the center of the Galaxy, lending the signal a noticeably oblate morphology.

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英文摘要：

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