Retainment of r-process material in dwarf galaxies

TL;DR

This paper investigates how well dwarf galaxies retain r-process elements from energetic explosions, finding high retention unless the explosions are extremely energetic or the galaxy has lost much of its gas.

Contribution

It provides estimates of r-process element retention in dwarf galaxies and models their abundance distribution, linking observations to galaxy evolution and nucleosynthesis.

Findings

Retention fraction is approximately 0.9 under typical conditions.

Estimated r-process mass per event aligns with previous studies.

About 7% of UFDs are predicted to show r-process enrichment.

Abstract

The synthesis of $r$-process elements is known to involve extremely energetic explosions. At the same time, recent observations find significant $r$-process enrichment even in extremely small ultra-faint dwarf (UFD) galaxies. This raises the question of retainment of those elements within their hosts. We estimate the retainment fraction and find that it is large $\sim 0.9$, unless the $r$-process event is very energetic ($\gtrsim 10^{52}$erg) and / or the host has lost a large fraction of its gas prior to the event. We estimate the $r$-process mass per event and rate as implied by abundances in UFDs, taking into account imperfect retainment and different models of UFD evolution. The results are consistent with previous estimates (Beniamini et al. 2016) and with the constraints from the recently detected macronova accompanying a neutron star merger (GW170817). We also estimate the distribution of abundances predicted by these models. We find that $\sim 0.07$ of UFDs should have $r$-process enrichment. The results are consistent with both the mean values and the fluctuations of [Eu/Fe] in galactic metal poor stars, supporting the possibility that UFDs are the main 'building blocks' of the galactic halo population.