暗物质间接探测中的球形牛
Spherical Cows in Dark Matter Indirect Detection
摘要：
暗物质（DM）晕长期以来一直被认为是三轴的，但在研究可能的湮灭和衰变信号时，它们通常被视为近似球形。在这项工作中，我们研究了潜在的DM湮灭和衰变的间接检测信号的不对称性，利用大量的统计数据的流体动力学模拟插图。我们仔细研究的重子上的球度的湮灭和衰变信号的情况下，观察者是在8.5千秒差距从中心的晕（例如在银河系的晕的情况下），和一个观察者位于良好的晕外。在银河信号的情况下，我们发现，湮灭和衰变信号预计是相当对称的，轴比非常不同于1发生很少。在河外信号的情况下，虽然衰减信号仍然优先球形，湮灭信号的轴比有一个更平坦的分布，与细长的配置文件经常出现。许多这些拉长的剖面是由于大的subhalos和/或最近的合并。与银河系的伽马射线辐射和星团的X射线图相比，我们发现伽马射线背景看起来比来自绝大多数晕的预期DM信号更少球形/更细长，并且银河系的伽马射线过剩看起来非常球形，而X射线数据将难以单独通过伸长率/球度测量与DM信号区分开。
英文摘要：
Dark matter (DM) halos have long been known to be triaxial, but in studies of possible annihilation and decay signals they are often treated as approximately spherical. In this work, we examine the asymmetry of potential indirect detection signals of DM annihilation and decay, exploiting the large statistics of the hydrodynamic simulation Illustris. We carefully investigate the effects of the baryons on the sphericity of annihilation and decay signals for both the case where the observer is at 8.5 kpc from the center of the halo (exemplified in the case of Milky Way-like halos), and for an observer situated well outside the halo. In the case of Galactic signals, we find that both annihilation and decay signals are expected to be quite symmetric, with axis ratios very different from 1 occurring rarely. In the case of extragalactic signals, while decay signals are still preferentially spherical, the axis ratio for annihilation signals has a much flatter distribution, with elongated profiles appearing frequently. Many of these elongated profiles are due to large subhalos and/or recent mergers. Comparing to gamma-ray emission from the Milky Way and X-ray maps of clusters, we find that the gamma-ray background appears less spherical/more elongated than the expected DM signal from the large majority of halos, and the Galactic gamma ray excess appears very spherical, while the X- ray data would be difficult to distinguish from a DM signal by elongation/sphericity measurements alone.
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