Gamma-ray background anisotropy from Galactic dark matter substructure
Gamma-ray background anisotropy from Galactic dark matter substructure
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DOI：
10.1103/physrevd.80.023520
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发表时间：
2009-03
影响因子：
5
通讯作者：
S. Ando
中科院分区：
文献类型：
--
作者：
S. Ando
银河系亚结构中的暗物质湮灭将在漫射伽马射线背景的全天空图上留下特征角度特征。我们研究由次晕引起的伽马射线背景各向异性，并讨论费米伽马射线太空望远镜的可探测性。与依赖于模拟全天图的早期工作相比，我们推导了解析公式，可以在给定子晕参数（例如质量函数）和伽马射线光度的径向剖面的情况下直接计算角功率谱。作为我们的基准次晕模型，我们采用 M^(-1.9) 质谱、向银河中心抑制的次晕径向分布以及由其平滑分量主导的每个次晕的光度分布。我们发现，对于对应于 theta<~5° 的多极状态，角功率谱由类噪声项主导，并由于相关子晕的内部结构而受到抑制。如果质谱向下延伸到地球质量尺度，那么如果子晕对伽马射线背景的贡献大于约 20%，则将在约 10° 角尺度的费米各向异性中检测到子晕。另一方面，如果最小质量约为 10^4M[sun]，则检测的相关角尺度约为 1°，各向异性检测要求次晕对伽马射线背景强度的贡献仅为约 4%。这些可以通过适度提高粒子物理参数来实现。我们还发现，各向异性分析可能是比单独检测更灵敏的子晕探针。我们还研究了对模型参数的依赖性，我们对所有研究的模型得出了类似的结论。当分析费米数据并根据子晕模型解释所获得的角功率谱时，解析方法应该非常有用。
Dark matter annihilation in Galactic substructure will imprint characteristic angular signatures on the all-sky map of the diffuse gamma-ray background. We study the gamma-ray background anisotropy due to the subhalos and discuss detectability at the Fermi Gamma-ray Space Telescope. In contrast to earlier work that relies on simulated all-sky maps, we derive analytic formulae that enable to directly compute the angular power spectrum, given parameters of subhalos such as mass function, and radial profile of gamma-ray luminosity. As our fiducial subhalo models, we adopt M^(-1.9) mass spectrum, subhalos radial distribution suppressed toward the Galactic center, and luminosity profile of each subhalo dominated by its smooth component. We find that, for multipole regime corresponding to theta<~5°, the angular power spectrum is dominated by a noiselike term, with suppression due to internal structure of relevant subhalos. If the mass spectrum extends down to Earth-mass scale, then the subhalos would be detected in the anisotropy with Fermi at angular scales of ~10°, if their contribution to the gamma-ray background is larger than ~20%. If the minimum mass is around 10^4M[sun], on the other hand, the relevant angular scale for detection is ~1°, and the anisotropy detection requires that the subhalo contribution to the gamma-ray background intensity is only ~4%. These can be achieved with a modest boost for particle-physics parameters. We also find that the anisotropy analysis could be a more sensitive probe for the subhalos than individual detection. We also study dependence on model parameters, where we reach the similar conclusions for all the models investigated. The analytic approach should be very useful when Fermi data are analyzed, and the obtained angular power spectrum is interpreted in terms of subhalo models.