本地团在ΛCDM中的动态历史
Dynamical History of the Local Group in $Λ$CDM
AI总结：
研究通过模拟粒子轨迹确定本地团质量，发现ΛCDM模型无法解释观测到的径向速度偏差，可能由MW和M31的近距离飞越引起。
摘要：
银河系和仙女座星系的位置和速度测量了本地团内的引力场。我们通过模拟粒子轨迹，利用32个本地团星系的距离和径向速度测量来约束其质量。我们的模拟采用轴对称模型，考虑了仙女座A的引力影响。本地团总质量为4.33±0.37×10^12 M☉，其中0.14±0.07在银河系中。观测到的径向速度系统性地高于ΛCDM模型预测，最大偏差达110±13 km/s。MW和M31的近距离飞越可能是解释非卫星星系远离速度的原因之一。
英文摘要：
The positions and velocities of galaxies in the Local Group (LG) measure the gravitational field within it. This is mostly due to the Milky Way (MW) and Andromeda (M31). We constrain their masses using distance and radial velocity (RV) measurements of 32 LG galaxies. To do this, we follow the trajectories of many simulated particles starting on a pure Hubble flow at redshift 9. For each observed galaxy, we obtain a trajectory which today is at the same position. Its final velocity is the model prediction for the velocity of that galaxy. Unlike previous simulations based on spherical symmetry, ours are axisymmetric and include gravity from Centaurus A. We find the total LG mass is ${4.33^{+0.37}_{-0.32}\times{10}^{12}M_\odot}$, with $0.14 \pm 0.07$ of this being in the MW. We approximately account for IC 342, M81, the Great Attractor and the Large Magellanic Cloud. No plausible set of initial conditions yields a good match to the RVs of our sample of LG galaxies. Observed RVs systematically exceed those predicted by the best-fitting $Λ$CDM model, with a typical disagreement of ${45.1^{+7.0}_{-5.7}}$ km/s and a maximum of ${110 \pm 13}$ km/s for DDO 99. Interactions between LG dwarf galaxies can't easily explain this. One possibility is a past close flyby of the MW and M31. This arises in some modified gravity theories but not in $Λ$CDM. Gravitational slingshot encounters of material in the LG with either of these massive fast-moving galaxies could plausibly explain why some non-satellite LG galaxies are moving away from us even faster than a pure Hubble flow.
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