We use FIRE-2 zoom simulations of Milky Way size disk galaxies to derive easy-to-use relationships between the observed circular speed of the Galaxy at the Solar location, v _c, and dark matter properties of relevance for direct detection experiments: the dark matter density, the dark matter velocity dispersion, and the speed distribution of dark matter particles near the Solar location. We find that both the local dark matter density and 3D velocity dispersion follow tight power laws with v _c. Using this relation together with the observed circular speed of the Milky Way at the Solar radius, we infer the local dark matter density and velocity dispersion near the Sun to be ρ = 0.42±0.06 GeV cm^-3 and ^σ _3D = 280⁺¹⁹ _-18 km s^-1. We also find that the distribution of dark matter particle speeds is well-described by a modified Maxwellian with two shape parameters, both of which correlate with the observed v _c. We use that modified Maxwellian to predict the speed distribution of dark matter near the Sun and find that it peaks at a most probable speed of 257 km s^-1 and begins to truncate sharply above 470 km s^-1. This peak speed is somewhat higher than expected from the standard halo model, and the truncation occurs well below the formal escape speed to infinity, with fewer very-high-speed particles than assumed in the standard halo model.

中文翻译：

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滑入DM：仅使用星系的局部圆周速度确定局部暗物质密度和速度分布


我们使用 FIRE-2 对银河系大小的盘状星系进行变焦模拟，得出在太阳位置观测到的星系圆周速度之间的易于使用的关系， v _c ，以及与直接探测实验相关的暗物质特性：暗物质密度、暗物质速度色散以及太阳位置附近暗物质粒子的速度分布。我们发现局部暗物质密度和 3D 速度色散都遵循严格的幂律v _c .利用这种关系以及观测到的银河系在太阳半径处的圆周速度，我们推断太阳附近的局部暗物质密度和速度色散为ρ = 0.42±0.06 GeV cm ^-3且^σ _3D = 280 ⁺¹⁹ _-18 km s ^-1 。我们还发现，暗物质粒子速度的分布可以通过具有两个形状参数的修正麦克斯韦方程很好地描述，这两个参数都与观测到的相关。 v _c .我们使用修改后的麦克斯韦方程来预测太阳附近暗物质的速度分布，发现其最可能速度为 257 km s ^-1达到峰值，并在 470 km s ^-1以上开始急剧截断。该峰值速度略高于标准光晕模型的预期，并且截断发生在远低于正式逃逸速度至无穷大的情况下，超高速粒子比标准光晕模型中假设的要少。