Metallicity-Suppressed Collapsars Cannot be the Dominant r-Process
  Source in the Milky Way
  We develop a high-performance analytical model of Galactic Chemical
Evolution, which accounts for delay time distributions and lock-up of stellar
yields in a thermal-phased ISM. The model is capable of searching, for the
first time, through the high-dimensional parameter space associated with the
r-process enrichment of the Milky Way by its possible sources: Neutron Star
Mergers and Collapsar events. Their differing formation mechanisms give these
two processes different time dependencies, a property which has frequently been
used to argue in favour of collapsars as the dominant r-process source.
However, we show that even with large degrees of freedom in the allowed
thermal, structural, and chemical properties of the galaxy, large regions of
parameter space are in strong tension with the data. In particular, whilst we
are able to find models in which neutron star mergers produce the majority of
r-process material, the data rule out all models with dominant collapsar
yields. With no other identified source, we conclude that Neutron Star Mergers
must be the dominant contributors to the modern Milky Way r-process budget.
