Galactic r-process enrichment by neutron star mergers in cosmological
  simulations of a Milky Way-mass galaxy
  We quantify the stellar abundances of neutron-rich r-process nuclei in
cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback
In Realistic Environments project. The galaxy is enriched with r-process
elements by binary neutron star (NS) mergers and with iron and other metals by
supernovae. These calculations include key hydrodynamic mixing processes not
present in standard semi-analytic chemical evolution models, such as galactic
winds and hydrodynamic flows associated with structure formation. We explore a
range of models for the rate and delay time of NS mergers, intended to roughly
bracket the wide range of models consistent with current observational
constraints. We show that NS mergers can produce [r-process/Fe] abundance
ratios and scatter that appear reasonably consistent with observational
constraints. At low metallicity, [Fe/H]<-2, we predict there is a wide range of
stellar r-process abundance ratios, with both supersolar and subsolar
abundances. Low-metallicity stars or stars that are outliers in their r-process
abundance ratios are, on average, formed at high redshift and located at large
galactocentric radius. Because NS mergers are rare, our results are not fully
converged with respect to resolution, particularly at low metallicity. However,
the uncertain rate and delay time distribution of NS mergers introduces an
uncertainty in the r-process abundances comparable to that due to finite
numerical resolution. Overall, our results are consistent with NS mergers being
the source of most of the r-process nuclei in the Universe.
