A spatially resolved view of Fast Radio Burst host metallicities with Integral-field Spectroscopy

Magnetars are the leading candidate progenitors of fast radio bursts (FRBs); if they dominate, any metallicity preference for magnetar formation should be reflected at the FRB site within the host galaxy.

To test this, the team used Integral Field Unit (IFU) spectroscopy to spatially resolve gas-phase metallicity in five FRB host galaxies—FRB 20240210A, FRB 20240312D, FRB 20250227A, FRB 20211127I, and FRB 20250316A—all at z < 0.05. They derived metallicities via the O3N2 index. The first four hosts were observed with the newly commissioned Large Lenslet Array Magellan Spectrograph (LLAMAS) IFU on the Magellan Telescopes, while archival Keck/KCWI data were used for FRB 20250316A.

They find ISM metallicity variations of at least 0.3 dex within individual hosts for the majority of the sample, with median host metallicities spanning 12 + log(O/H) ≈ 8.5–8.7. At the burst sites, four have metallicities of 12 + log(O/H) ≈ 8.5–8.9, while the fifth lies below 8.5.

These results reveal substantial metallicity variations among FRB host galaxies and within the local environments of the bursts. Consequently, long-slit-based global estimates of host galaxy metallicity do not always represent the true burst-site distributions. The authors advocate for IFU follow-up of larger host samples to provide FRB-site-relevant observational constraints on metallicity preferences for FRB occurrence.