The impact of rare events on the chemical enrichment in dwarf galaxies

In the environments where the abundance of heavy elements is low, rare events are expected to impact the chemical enrichment. Dwarf galaxies have small masses, low average metallicities and in general low star formation rates, and thus investigating the chemical enrichment provides understanding on the impact of each source of elements on the chemical abundance. Using a chemical evolution model in which the rarity is introduced, we investigate the impact of rare events on the chemical enrichment for Local Group dwarf galaxies. In the model, the occurrence of individual sources of elements is estimated with the star formation history derived by the colour-magnitude diagram. The abundance ratios of trans-iron elements to iron predicted by the model show the oscillation at the lowest metallicities because of the r-process events. In the case of a galaxy of a lower mass, the oscillation caused by neutron star mergers is also seen at higher metallicities, which suggests that the rarity can be important in lower-mass systems. Regarding the source of the chemical enrichment, we observe that the r-process sites seem to contribute more to the production of trans-iron elements at low metallicities, but massive stars of different rotating velocities also contribute to create part of the dispersion of the abundance ratios through the s-process. Both observational and theoretical data, including nucleosynthesis calculations and the chemical abundance of metal-poor stars, are needed to obtain deeper insights into the sources of the chemical enrichment at low metallicities.

Automated summary

In environments with low abundance of heavy elements, rare events are expected to have a significant impact on chemical enrichment. This study investigates the chemical enrichment in dwarf galaxies of the Local Group, which have low masses, average metallicities, and star formation rates, by introducing a chemical evolution model that takes rarity into account. The model predicts oscillation in the abundance ratios of trans-iron elements to iron at low metallicities due to r-process events, and also suggests that rarity can play an important role in lower-mass systems, with oscillation caused by neutron star mergers even at higher metallicities. Both r-process sites and massive stars with different rotating velocities contribute to the chemical enrichment, and further insight into the sources of chemical enrichment at low metallicities requires observational and theoretical data, including nucleosynthesis calculations and the chemical abundance of metal-poor stars.