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本身运动矢量，而这些参数在很大程度上仍然缺乏。目前，光学望远镜对银河系外自行的测量仅限于银河系最近的伴星，充其量只能提供微不足道的结果。另一方面，通过对明亮脉泽源的VLBI观测，我们最近已经能够探测到仙女座星系亚群M33和1C10的两个成员星系的河外自行。这些测量组成了本提议的第一部分，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局部群演化的不同模型。该项目的长期目标是建立一个完整的本地群的3-D运动学模型。此外，还将测量到M33的几何距离，通过测量M33相对两侧的三个H20脉泽源的相对自行，并将它们与M33的倾角和旋转速度进行比较，最终获得比5%更好的精度。这也将允许重新校准基于造父变星的银河系外距离尺度。银河系的结构、动力学和暗物质含量非常不确定。螺旋臂的位置和数目存在争议，目前文献中报道的圆周转速(Өo)在170250公里S-1之间。大多数关于银河系结构的结论只是基于对位置和径向速度的测量。使用VLBI。我们可以精确地测量视差到10μ，自行测量到&lt；1公里S-1到≈10kpc的距离。作为这项提议的第二部分，我们计划进行观测，以定位银河系的旋臂，并约束星系自转和银河系引力势的模型。这些观测还将检验螺旋密度波理论的预测，该理论对于螺旋星系的形成和演化总体上是重要的。

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.