Constraining the dark matter halos of the Milky Way and Andomeda by µ-arcsecond VLBI Astrometry

测量本星系群暗物质含量和分布的关键参数是其成员星系的固有运动向量。目前，光学望远镜对星系外固有运动的测量仅限于离银河系最近的伴星，而且至多只能提供一些边缘结果。另一方面，通过对明亮脉泽源的VLBI观测，我们最近能够探测到仙女座亚群的两个成员星系M33和1C 10的河外固有运动。这些测量构成了本建议的第一部分，加上这里提出的进一步研究，将提供一个决定性的工具来区分当地群体的不同演变模式。该项目的长期目标是建立一个完整的局部群的三维运动模型。通过测量M33相对两侧的三个H20脉泽源的相对固有运动，并将其与M33的倾角和旋转速度进行比较，测量到M33的几何距离，最终精度优于5%。这也将允许重新校准基于造父变星的星系外距离尺度。银河系的结构、动力学和暗物质含量是非常不确定的。螺旋臂的位置和数量是有争议的，目前文献中报道的圆旋转速度（Өo）在170和250 km s-1之间。关于银河系结构的大多数结论仅仅是基于位置和径向速度的测量。用阵。我们可以测量精确到10 μas的视差和从< 1 km s-1到≈10 kpc的距离的适当运动。作为这个提议的第二部分，我们计划进行观测，以定位银河系的旋臂，并约束星系旋转模型和银河系的引力势。观测还将测试螺旋密度波理论的预测，该理论对螺旋星系的形成和演化非常重要。

Key and still largely missing parameters for measuring the dark matter content and distribution of the Local Group are the proper motion vectors of its member galaxies. Currently, measurements of extragalactic proper motions by optical telescopes are limited to the most nearby companions of the Milky Way and have only provided marginal results, at best. On the other hand, by VLBI observations of bright maser sources, we have recently been able to detect extragalactic proper motions of two member galaxies of the Andromeda subgroup, M33 and 1C 10. These measurements comprising the first part of the present proposal, together with further research proposed here, will provide a decisive tool to distinguish between different models of the evolution of the Local Group. The long term goal of the project is to construct a full 3-D kinematic model of the Local Group. Also a geometric distance to M33 will be measured, ultimately to better than 5% accuracy by measuring the relative proper motions of three H20 maser sources on opposite sides of M33 and comparing them with the inclination and rotation speed of M33. This will allow also re-calibration of the extra-galactic distance scale based on Cepheids.The structure, dynamics, and the dark matter content of the Milky Way are very uncertain. The location and even the number of spiral arms is controversial, and values of the circular rotation speed (Өo) between 170 and 250 km s-1 are reported in the current literature. Most conclusions about the Galactic structure are based only on measurements of positions and radial velocities. Using VLBI. we can measure parallaxes accurate to 10 μas and proper motions to < 1 km s-1 out to distances of ≈ 10 kpc. As the second part of this proposal we plan to conduct observations that will locate the spiral arms of the Milky Way and constrain models of galactic rotation and the gravitational potential of the Milky Way. The observations will also test predictions made by spiral density wave theory, which is important for the formation and evolution of spiral galaxies in general.