Fluorine Evolution in the Galactic Halo

Abstract

The chemical evolution of fluorine is still a matter of debate in Galactic archaeology, especially at low metallicities, where it is particularly challenging to obtain the corresponding chemical abundances from observations. We present here the first detailed theoretical study of the chemical evolution of fluorine at low metallicity by means of a stochastic chemical evolution model for the Galactic halo, in light of the most recent data for fluorine, which further pushed observations to lower metallicities down to [Fe/H]$\sim$-4 dex, more than a factor of 10 lower in metallicity than previous detections. We employ a state-of-the-art stochastic chemical evolution model to follow the evolution in the Galactic halo, which has been shown to reproduce well the main observables in this Galactic component and the abundance patterns of CNO and neutron-capture elements, and we implement nucleosynthesis prescriptions for fluorine, focusing on the chemical evolution of this element. By comparing recent observations with model predictions, we confirm the importance of rotating massive stars at low metallicities to explain both the [F/Fe] vs [Fe/H] and [F/O] vs [O/H] diagrams. In particular, we showed that we can reach high [F/Fe]$\sim$2 dex at [Fe/H]$\sim$-4 dex, in agreement with recent observations at the lowest metallicity. With a stochastic chemical evolution model for the Galactic halo, we confirm the importance of rotating massive stars as fluorine producers, as hinted by previous studies using chemical evolution models for the Galactic disc. We also expect an important production of F at high redshift, in agreement with recent detections of supersolar N by JWST. Further data for fluorine at low metallicities and also at high redshift would be needed to put further constraints on the chemical evolution of fluorine and be compared to our theoretical predictions.