The Formation of the Local Group Satellite Planes
Ed Shaya



It has recently been noted that the ~50 satellite galaxies in the Local Group are almost all in very thin planes. In particular, we identify most LG galaxies with just 3 planes, 2 near M31, and 1 near the MW. It has been conjectured that only a dissipative process, such as gas settling after a merger or tidal encounter, could have created such thin planes. However, if nearly all of the satellite galaxies in the Local Group were formed out of tidal debris, the Missing Satellite Problem would become a major crisis for the LCDM scenario. Instead, we are examining the conditions necessary for these planes to have formed using non-dissipative orbital dynamics. By combining the Numerical Action Method with a backwards integration from TRGB distances and redshifts, we solve for acceptable orbits for each LG galaxy. In particular, these orbits have early time peculiar velocities consistent with the gravity field at their z=4 positions. We make use of the newly determined proper motions of M31, M33, IC10, and LeoI, to develop a best overall model.