No Metallicity Preference in Fast Radio Burst Host Galaxies

Shotaro Yamasaki^1*, Tetsuya Hashimoto¹, Haruka Kusakabe², Tomotsugu Goto³

¹Physics Department, NCHU, Taichung, Taiwan
²Department of General Systems Studies, University of Tokyo, Tokyo, Japan
³Institute of Astronomy, NTHU, Hsinchu, Taiwan

* Presenter:Shotaro Yamasaki, email:shotaro.s.yamasaki@gmail.com

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 various host properties, gas-phase metallicity is a key factor influencing stellar evolution and the production of transients. To date, most FRB host studies have examined the distributions of stellar mass and star formation rate (SFR), without directly measuring metallicity in a statistically significant sample. In this study, we present the first systematic analysis of gas-phase metallicities for a large, uniformly selected sample of FRB host galaxies. We measured oxygen abundances (12+log(O/H) = 8.04–8.84) for 40 hosts using consistent emission-line diagnostics. Using a volume-limited subsample, we compare the distributions of stellar mass, SFR, and metallicity to a control sample of star-forming galaxies matched in the same selection criteria. We find that FRB host galaxies span a wide range in metallicity and are broadly consistent with the SFR-weighted mass–metallicity relation of the star-forming galaxy population. We find no clear lower bound on metallicity, suggesting that FRB progenitors can form in any metallicity environment through channels largely insensitive to chemical abundance. Encouragingly, this implies FRBs can form even in low-metallicity, high-redshift galaxies, supporting their potential as probes of matter distribution across cosmic time. Additionally, we find marginal (∼2σ) evidence for a −0.09 ± 0.04 dex metallicity offset from the fundamental metallicity relation, likely due to suppressed SFRs at fixed mass and metallicity rather than metal deficiency. This offset resembles that observed in local post-merger galaxies, and may reflect a post-starburst phase following galaxy interactions. In this picture, FRB progenitors formed during the starburst would produce FRBs after a 100–500 Myr delay. Such a delay is consistent with observed delay-time distributions, favoring progenitors formed through binary evolution channels over core-collapse supernovae as the dominant origins.　

Keywords: Fast Radio Bursts, Galaxies, Metallicity