The outermost edges of the Milky Way halo from galaxy kinematics
  We measure for the first time the outermost edges of the Milky Way (MW) halo
in terms of the depletion and turnaround radii. The inner depletion radius,
$r_\mathrm{id}$, identified at the location of maximum infall velocity,
separates a growing halo from the draining environment, while the turnaround
radius, $r_\mathrm{ta}$, marks the outermost edge of infalling material towards
the halo, both of which are located well outside the virial radius. Using the
motions of nearby dwarf galaxies within $3\mathrm{Mpc}$, we obtain a marginal
detection of the infall zone around the MW with a maximum velocity of
$v_\mathrm{inf, max}=-46_{-39}^{+24}\mathrm{km s^{-1}}$. This enables us to
measure $r_\mathrm{id}=559\pm 107 \mathrm{kpc}$ and $r_\mathrm{ta}=839\pm 121
\mathrm{kpc}$. The measured depletion radius is about 1.5 times the MW virial
radius ($R_\mathrm{200m}$) measured from internal dynamics. Compared with halos
in the cosmological simulation Illustris TNG100, the factor 1.5 is consistent
with that of halos with similar masses and dynamical environments to the MW but
slightly smaller than typical values of Local Group analogs, potentially
indicating the unique evolution history of the MW. These measurements of halo
edges directly quantify the ongoing evolution of the MW outer halo and provide
constraints on the current dynamical state of the MW that are independent from
internal dynamics.
