| One of the best targets to study galaxy interactions and evolution is the M81 group of galaxies. The presence of
compact radio sources in M81 (nucleus) and M82 (H2O masers) offer the unique oppertunity to measure the relative
motions between the two galaxies. Furthermore, by including background continuum sources, one can measure the
transversal motions of the two galaxies relative to the Milky Way. We propose a first epoch of phase-referencing
observations of the known H2O maser sources in M82 and background continuum sources to the nucleus of M81. If
this observation is successful we will request similar observations roughly yearly. Based on our experience of similar
observations of water masers in M33, we expect to reach an astrometric accuracy of 1-2 æas yr-1 in 5 years. This
corresponds to an uncertainty of 15-30 km s-1 at a distance of 3.5 Mpc, enough to measure relative motions of
galaxies which are typically a few 100 km s-1 (the relative radial velocity between the two galaxies is 237 km s-1).
This project will provide a measure of three dimensional relative motions for targets outside the Local Group and is
hence a necessary next step towards a better kinematic model of the M81 group. |
