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

点击翻译按钮获取中文摘要

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.