Could the Fermi-LAT detect-rays from dark matter annihilation in the dwarf galaxies of the Local Group?
Could the Fermi-LAT detect-rays from dark matter annihilation in the dwarf galaxies of the Local Group?
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费米-LAT 能否探测到本星系群矮星系中暗物质湮灭产生的射线？
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发表时间：
2013
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通讯作者：
F. Bertola
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作者：
L. Pieri;A. Pizzella;E. Corsini;F. Bertola
上下文。探测来自暗物质(DM)湮灭的射线是费米大面积望远镜(以前称为GLAST)和切伦科夫望远镜的科学目标之一。目标。本文以邻近的矮小球状星系(DSph)为目标，采用天文观测和N体模拟得到的Dm密度分布，研究了这一发现的现实变化的存在性。我们还利用最近关于黑洞的存在和局部群(LG)矮星内部的亚晕种群的亮点来研究助推因子。方法：研究方法。我们用Fermi-LAT研究了四个距离最近且高度以DM为主的LG dSph星系，即Draco、Ursa Minor、Carina和Sextans中DM湮灭产生的射线通量的可探测性，对于这些星系，我们提供了最新的DM密度分布。我们假设DM是由最轻的超对称粒子(LSP)等弱相互作用的大质量粒子组成的，并计算了预期的射线通量，以便乐观地选择未知的潜在物理参数。然后，我们计算了由于DM团和中心超大质量黑洞的存在而产生的助推因子。最后，我们将我们的预测与费米-拉特灵敏度图进行了比较。结果。我们发现dSph星系在银河系光滑晕上方发光：例如，银河晕只在银河系中心上方小于2.3度的角度比Draco dSph亮。我们还发现，DM质量密度分布中的尖点或恒定密度核的存在不会对射线通量产生任何相关的影响，这是由于费米-LAT探测器的几何接受度与星系的距离幸运地结合在一起的缘故，而且中心黑洞或亚晕的存在也不会带来显著的增强。结论。我们的结论是，即使对于最乐观的粒子物理情景，在LG的dSph星系中，DM湮灭产生的射线通量也太低，无法用费米-LAT探测到。
Context. The detection of-rays from dark matter (DM) annihilation is among the scientific goals of the Fermi Large Area Telescope (formerly known as GLAST) and Cherenkov telescopes. Aims. In this paper we investigate the existence of realistic chan ces of such a discovery selecting some nearby dwarf spheroidal galaxies (dSph) as a target, and adopting the DM density profiles de rived from both astronomical observations and N-body simulations. We also make use of recent highlights about the presence of black holes and of a population of sub-subhalos inside the Local Group (LG) dwarfs for boost factor studies. Methods. We study the detectability with the Fermi-LAT of the -ray flux from DM annihilation in four of the nearest and highl y DM-dominated dSph galaxies of the LG, namely Draco, Ursa Minor, Carina, and Sextans, for which the state-of-art DM density profiles were available. We assume the DM is made of Weakly Int eracting Massive Particles such as the Lightest Supersymmetric Particle (LSP) and compute the expected-ray flux for optimistic choices of the unknown underlying pa rticle physics parameters. We then compute the boost factors due to the presence of DM clumps and of a central supermassive black hole. Finally, we compare our predictions with the Fermi-LAT sensitivity maps. Results. We find that the dSph galaxies shine above the Galactic smooth halo: e.g., the Galactic halo is brighter than the Draco dSph only for angles smaller than 2.3 degrees above the Galactic Center. We also find that the presence of a cusp or a constant den sity core in the DM mass density profile does not produce any releva nt effect in the -ray flux due to the fortunate combination of the geometrical acceptance of the Fermi-LAT detector and the distance of the galaxies and that no significant enhancement is given by the presence of a central black hole or a population of sub-su bhalos. Conclusions. We conclude that, even for the most optimistic scenario of particle physics, the -ray flux from DM annihilation in the dSph galaxies of the LG would be too low to be detected with the Fermi-LAT.