The Low-mass Dwarf Host Galaxy of Nonrepeating FRB 20230708A

Abstract

We present Very Large Telescope/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by the Australian SKA Pathfinder observed through the “Fast and Unbiased FRB Host Galaxy (FURBY)” Large Programme at the European Southern Observatory, which imposes strict selection criteria on the included FRBs and their host galaxies to produce a homogeneous and well-defined sample. We describe the data reduction and analysis of these spectra and report their redshifts, line-emission fluxes, and derived host properties. From the present sample, this paper focuses on the faint host of FRB 20230708A (m R = 22.53 ± 0.02) identified at low redshift (z = 0.1050). This indicates an intrinsically very low-luminosity galaxy (L ≈ 108 L ⊙), making it the lowest-luminosity nonrepeating FRB host to date by a factor of ∼3 and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our spectral energy distribution fitting analysis reveals a low stellar mass (M * ≈ 108.0 M ⊙), low star formation rate (SFR ≈ 0.04M ⊙ yr−1), and very low metallicity(12 + log ( O / H) ∼ (8.0 − 8.3)), distinct from the more massive galaxies (log(M/M ⊙) ∼ 10) that are commonly identified for nonrepeating FRBs. Its discovery demonstrates that FRBs can arise in the faintest, metal-poor galaxies of the Universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high-z Universe where young, low-mass galaxies proliferate.