Simulating Neutron Star Mergers as r-process Sources in Ultra Faint
  Dwarf Galaxies
  To explain the high observed abundances of r-process elements in local ultra-
faint dwarf (UFD) galaxies, we perform cosmological zoom simulations that
include r-process production from neutron star mergers (NSMs). We model
star-formation stochastically and simulate two different halos with total
masses $\approx 10^8 M_{\odot}$ at z = 6. We find that the final distribution
of [Eu/H] vs. [Fe/H] is relatively insensitive to the energy by which the
r-process material is ejected into the interstellar medium, but strongly
sensitive to the environment in which the NSM event occurs. In one halo the NSM
event takes place at the center of the stellar distribution, leading to
high-levels of r-process enrichment such as seen in a local UFD, Reticulum II
(Ret II). In a second halo, the NSM event takes place outside of the densest
part of the galaxy, leading to a more extended r-process distribution. The
subsequent star formation occurs in an interstellar medium with shallow levels
of r-process enrichment which results in stars with low levels of [Eu/H]
compared to Ret II stars even when the maximum possible r-process mass is
assumed to be ejected. This suggests that the natal kicks of neutron stars may
also play an important role in determining the r-process abundances in UFD
galaxies, a topic that warrants further theoretical investigation.
