The ramp-up of interstellar medium enrichment at z>4

TL;DR

This paper reports the detection of fluorine in a high-redshift galaxy, revealing rapid chemical enrichment driven primarily by Wolf-Rayet stars, which constrains models of element production in early massive galaxies.

Contribution

It provides the first measurement of fluorine in a z>4 galaxy, demonstrating the quick ramp-up of chemical enrichment and identifying Wolf-Rayet stars as key contributors.

Findings

Detection of HF in a z=4.4 galaxy with high fluorine abundance

Evidence that Wolf-Rayet stars dominate early fluorine production

Rapid chemical enrichment during early galaxy formation

Abstract

Fluorine is one of the most interesting elements for nuclear and stellar astrophysics. Fluorine abundance was first measured for stars other than the Sun in 1992, then for a handful metal-poor stars, which are likely to have formed in the early Universe. The main production sites of fluorine are under debate and include asymptotic giant branch (AGB) stars, $\nu$-process in core-collapse supernovae, and Wolf-Rayet (WR) stars. Due to the difference in the mass and lifetime of progenitor stars, high redshift observations of fluorine can help constrain the mechanism of fluorine production in massive galaxies. Here, we report the detection of HF (S/N = 8) in absorption in a gravitationally lensed dusty star-forming galaxy at redshift z=4.4 with $N_{\rm HF}$/$N_{\rm{H_2}}$ as high as $\sim2\times10^{-9}$, indicating a very quick ramp-up of the chemical enrichment in this high-z galaxy. At z=4.4, AGB stars of a few solar masses are very unlikely to dominate the enrichment. Instead, we show that WR stars are required to produce the observed fluorine abundance at this time, with other production mechanisms becoming important at later times. These observations therefore provide an insight into the underlying processes driving the `ramp-up' phase of chemical enrichment alongside rapid stellar mass assembly in a young massive galaxy.