Temporal Evolution of the Radial Distribution of Milky Way Satellite Galaxies

Abstract

The Milky Way (MW) is surrounded by dozens of satellite galaxies, with six-dimensional (6D) phase-space information measured for over 80% of this population. The spatial distribution of these satellites is an essential probe of galaxy formation and for mapping the MW’s underlying dark matter distribution. Using measured 6D phase-space information of known MW satellites, we calculate orbital histories in a joint MW+LMC potential, including the gravitational influence of the LMC on all satellites and on the MW’s center of mass, and dynamical friction owing to both galaxies, to investigate the evolution of the MW’s cumulative radial profile. We conclude that radial profiles become more concentrated over time when we consider the LMC’s gravitational influence and the group infall of LMC-associated satellites. The MW’s radial distribution is consistently more concentrated at the present day and 1 and 2 Gyr ago compared to recent surveys of nearby MW-like systems. Compared to MW-mass hosts in cosmological, zoom-in simulations, we find the MW’s radial profile is also more concentrated than those of simulated counterparts; however, some overlap exists between simulation results and our analysis of the MW’s satellite distribution 2 Gyr ago, pre-LMC infall. Finally, we posit that radial profiles of simulated MW-mass analogs also hosting an LMC companion are likely to evolve similarly to our results, such that the accretion of a massive satellite along with its satellites will lead to a more concentrated radial profile as the massive satellite advances toward its host galaxy.