The outer edges of the Milky Way halo from the motion of nearby galaxies

We present the first measurements of the outermost edges of the Milky Way (MW) halo in terms of the depletion and turnaround radii. The inner depletion radius, r_id, identified at the maximum infall location separates a growing halo from the draining environment, while the turnaround radius, r_ta, marks the outermost edge of infalling material towards the halo, both of which are located well outside the virial radius. Using the motion of nearby dwarf galaxies within 3 Mpc, we obtain a marginal detection of the infall zone around the MW which enables us to measure r_id=559±107 kpc and r_ta=839±121 kpc. According to the previous estimate of MW virial mass and the scaled density profile of MW analogs in the cosmological hydrodynamical simulation Illustris TNG100, the total masses of the MW enclosed within these edges are estimated to be M(r_id) = (2.0_-0.3^+0.4) × 10¹² Msun and M(r_ta) = (2.8_-0.6^+1.0) × 10¹² Msun respectively. These measurements of halo edges directly quantify the ongoing evolution of the MW outer halo and provide independent constraints on the current dynamical state and mass content of the MW.