No Metallicity Preference in Fast Radio Burst Host Galaxies

TL;DR

This study analyzes the metallicity of 31 FRB host galaxies, finding no preference for metallicity and suggesting FRB progenitors can form across a wide range of environments, including low-metallicity, high-redshift galaxies.

Contribution

It provides the largest uniform sample analysis of FRB host metallicities, showing they span a broad range and are consistent with star-forming galaxy relations, indicating metallicity insensitivity.

Findings

FRB hosts show wide metallicity range.

No lower metallicity bound for FRB progenitors.

Possible metallicity offset related to galaxy interactions.

Abstract

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of unknown origin, and studying their host galaxies could offer clues to constrain progenitor models. Among host properties, gas-phase metallicity is a key factor influencing stellar evolution and transient productions. We analyze the largest uniformly selected sample of FRB host galaxies, measuring oxygen abundances (12+log(O/H)=8.04-8.85) for 31 hosts at redshifts z=0.04-0.98, using consistent emission-line diagnostics. Using a volume-limited subsample, we compare the distributions of stellar mass, star formation rate (SFR), and metallicity to a control sample of star-forming galaxies selected by the same criteria. We find that FRB host galaxies span a wide metallicity range and are broadly consistent with the SFR-weighted mass-metallicity relation of star-forming galaxies. We find no clear lower metallicity bound, suggesting that FRB progenitors can form in any metallicity environment through channels largely insensitive to metal abundance. Encouragingly, this implies FRBs can arise even in low-metallicity, high-redshift galaxies, supporting their potential as probes of matter distribution across cosmic time. Additionally, we find marginal ($\sim$2$\sigma$) evidence for a -0.09\pm0.04 dex metallicity offset from the fundamental metallicity relation. Despite model uncertainties, if real, this offset likely reflects suppressed SFRs at fixed mass and metallicity rather than metal deficiency. Similar offsets are observed in local post-merger galaxies and may reflect a post-starburst phase following galaxy interactions. Such systems may host FRB progenitors formed during the starburst that produce FRBs after a 100-500 Myr delay, broadly consistent with observed delay-time distributions, although further data are needed to confirm this interpretation.