AI 中文总结
本文更新银河系矮椭球星系J因子，发现Jeans分析的J因子变化会带来2-4倍截面约束不确定性，基于宇宙学的先验排除了对$b\bar{b}$的热遗迹湮灭截面低于约70 GeV的情况，且最高J因子的矮星系已被发现，未来超暗矮星系发现难显著增强约束。
AI 中文摘要
矮星系是搜寻暗物质湮灭或衰变信号的极佳目标。本文采用校准后的半解析模型及最新恒星运动学数据（见第一部分），更新了银河系矮椭球星系的天体物理J因子。我们通过将SatGen半解析卫星模型生成的子晕群体，以矮星系运动学确定的动力学质量或恒星质量为条件，推断39个矮星系J因子的概率分布；还采用包含不同程度SatGen信息的更新恒星运动学与先验，通过Jeans方程计算J因子。利用计算得到的J因子，我们重新处理了Fermi-LAT数据对湮灭截面的现有约束。主要结果是：采用Jeans分析计算的J因子的变化，会给推断的截面约束引入2至4倍的不确定性。我们认为，基于宇宙学的先验是合理选择，该先验排除了对$b\bar{b}$的热遗迹湮灭截面低于约70 GeV的情况；作为对比，更常用的先验（可能导致非物理晕参数）在95%置信水平下排除了低于130 GeV的质量。我们还表明，最高J因子的矮星系在空间上是延展的，在天球上约1度，这对许多Fermi数据分析采用的点源近似的有效性提出了挑战。最后，基于半解析模型和运动学数据，最高J因子的晕已被发现，这表明未来超暗矮星系的发现不太可能显著增强对湮灭暗物质的约束。
英文摘要
Dwarf galaxies provide excellent targets to search for signals of dark matter annihilation or decay. Using a calibrated semi-analytic model and the latest stellar kinematic data (presented in Part I), this paper updates the astrophysical J-factors for the Milky Way's dwarf spheroidal galaxies. We infer the probability distributions for the J-factors of 39 dwarfs by conditioning a population of subhalos, generated with the SatGen semi-analytic satellite model, on either a dwarf's kinematically determined dynamical mass or its stellar mass. We also compute the J-factors using the Jeans equation with updated stellar kinematics and priors that incorporate varying degrees of SatGen information. We use the computed J-factors to recast existing limits from Fermi-LAT data on the annihilation cross section. Our main result is that variations in the J-factors computed using the Jeans analysis introduce a factor of 2-4 uncertainty into the inferred limits on the cross section. We argue that a cosmologically informed prior is a motivated choice that excludes thermal relic annihilation cross sections to $b\bar{b}$ below about 70 GeV. For comparison, the more commonly used priors, which can lead to unphysical halo parameters, exclude masses below 130 GeV at 95% confidence level. We also show that the highest-J-factor dwarfs are spatially extended, approximately one degree on the sky, which challenges the validity of the point-source approximation adopted in many analyses of Fermi data. Finally, based on the semi-analytic model and the kinematic data, the highest J-factor halos have already been discovered, suggesting future ultra-faint discoveries are unlikely to substantially strengthen limits on annihilating dark matter.
Comments16+9 pages, 4+6 figures, video abstract at https://youtu.be/x9zNkN6XyAA
