  A recent comparison by Merritt et al. 2020 of simulated and observed Milky
Way-mass galaxies has identified a significant tension between the outskirts
($r>20\kpc$) of the stellar halos in simulated and observed galaxies. Using
observations from the Dragonfly telescope and simulated galaxies from the
Illustris-TNG100 project, Merritt et al. 2020 finds that the outskirts of
stellar halos in simulated galaxies have surface densities $1-2$ dex higher
than observed galaxies. In this paper, we compare two suites of 15 simulated
Milky Way-like galaxies, each drawn from the same initial conditions, simulated
with the same hydrodynamical code, but with two different models for feedback
from supernovae. We find that the MUGS simulations, which use an older
``delayed-cooling'' model for feedback, also produce too much stellar mass in
the outskirts of the halo, with median surface densities well above
observational constraints. The MUGS2 simulations, which instead use a new,
physically-motivated ``superbubble'' model for stellar feedback, have $1-2$ dex
lower outer stellar halo masses and surface densities. The MUGS2 simulations
generally match both the median surface density profile as well as the scatter
in stellar halo surface density profiles seen in observed stellar halos. We
conclude that there is no ``missing outskirts'' problem in cosmological
simulations, provided that supernova feedback is modelled in a way that allows
it to efficiently regulate star formation in the low-mass progenitor
environments of stellar halo outskirts.
