High-precision astrometric data from space observatories, such as the Hubble Space Telescope (HST) and Gaia, are revolutionizing our ability to study the Local Group. 6D phase space measurements (3-dimensional position and velocity) now make it possible to rewind the clock and trace the orbital histories of nearly half of all Local Group satellites to their cosmic origins in the early Universe. These new datasets pave the way for a revised model of the Local Group’s dynamical history and its current dark matter content. In this talk, I will focus on the Magellanic Clouds and M33, the most massive satellite galaxies orbiting around the MW and M31, respectively. These massive satellites are nearly 10% as massive as their host galaxies and LCDM simulations predict that they too host a population of “ultra-faint” satellite galaxies, i.e. a satellites of satellites hierarchy. I will juxtapose these two satellite systems and discuss ongoing efforts to characterize satellites of the Magellanic Clouds and future efforts for finding M33 satellites. Together, these two systems provide a direct test for LCDM predictions at the low mass end and act as a benchmark for next generation studies of analogous galaxies beyond the Local Group in the era of Roman, JWST, and LSST.
