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The Low Mass Dwarf Host Galaxy of Non-Repeating FRB 20230708A

August R. Muller, Alexa C. Gordon, Stuart D. Ryder, Alexandra G. Mannings, J. Xavier Prochaska, Keith W. Bannister, A. Bera, Shivani Bhandari, N. D. R. Bhat, Adam T. Deller, Wen-fai Fong, Marcin Glowacki, Vivek Gupta, J. N. Jahns-Schindler, C. W. James, Regina A. Jorgenson, Lachlan Marnoch, R. M. Shannon, Nicolas Tejos, P. A. Uttarkar, Yuanming Wang, Ziteng Wang

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 (ASKAP) observed through the ESO Large Programme "FURBY", 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 ($m_R = 22.53 \pm 0.02$) identified at low redshift ($z=0.1050$). This indicates an intrinsically very low-luminosity galaxy ($L \approx 10^8 L_\odot$), making it the lowest-luminosity non-repeating FRB host to date by a factor of $\sim 3$, and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our SED fitting analysis reveals a low stellar mass ($M_* \approx 10^{8.0} M_\odot$), low star formation rate (${\rm SFR} \approx 0.04 M_\odot \rm yr^{-1}$), and very low metallicity ($12+\log(\text{O}/\text{H})\sim(8.0-8.3)$), distinct from the more massive galaxies ($\log(M/M_\odot) \sim 10$) that are commonly identified for non-repeating FRBs. Its discovery demonstrates that FRBs can arise in among 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.

The Low Mass Dwarf Host Galaxy of Non-Repeating 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 (ASKAP) observed through the ESO Large Programme "FURBY", 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 () identified at low redshift (). This indicates an intrinsically very low-luminosity galaxy (), making it the lowest-luminosity non-repeating FRB host to date by a factor of , and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our SED fitting analysis reveals a low stellar mass (), low star formation rate (), and very low metallicity (), distinct from the more massive galaxies () that are commonly identified for non-repeating FRBs. Its discovery demonstrates that FRBs can arise in among 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- universe where young, low-mass galaxies proliferate.

Paper Structure

This paper contains 11 sections, 5 figures.

Table of Contents

  1. Introduction
  2. The FURBY Sample and Observations
  3. Characterizing the Host Galaxy and Environment of FRB 20230708A
  4. Emission Lines
  5. SED Modeling
  6. Luminosity Comparison
  7. Constraints on a Persistent Radio Source
  8. Discussion
  9. Acknowledgments
  10. FURBY Spectroscopic Data Release I
  11. Spectroscopic Observations

Figures (5)

  • Figure 1: VLT/FORS2 $R$-band image of the host galaxy associated with FRB 20230708A (center of image). The VLT/X-Shooter slit outline is shown in white, and the FRB localization ellipse is shown in black.
  • Figure 2: VLT/X-Shooter spectrum of the FRB 20230708A host galaxy showing prominent H$\alpha$, H$\beta$, [O$\;$], and [O$\;$] emission. There is a notable lack of clear [N$\;$] emission features. The pPXF gas emission (orange) and stellar continuum (red) best fits are shown. Spectral error is shown in blue.
  • Figure 3: A BPT classification diagram indicating the dominant ionization mechanisms of FRB host galaxies. Previously published FRB host galaxies (see Eftekhari2023) are shown in black; all hosts from the FURBY survey presented here are included in blue. The host galaxy of FRB 20230708A is emphasized in magenta. A background sample of all galaxies in the SDSS catalog is shown in gray.
  • Figure 4: The star formation history of FRB 20230708A. The increase in SFR towards present day suggests that this host is actively building up its mass.
  • Figure 5: Apparent magnitude versus redshift for all FRB hosts in Bhandari2023, Hewitt2024, Bhardwaj2025, andFRB_Repo with $P(O|x) > 0.9$ and a published $m_R$ or $m_r$ value. FURBY hosts are shown as stars (FRB 20230708A is labeled accordingly; all FURBYs correspond to non-repeating FRBs). Other public FRB host galaxies are shown in gray (shape depends on repeater status). The shaded region indicates the portion of parameter space excluded from FURBY due to the imposed magnitude cut. The Hewitt2024 host is shown as a limit at the published photometric $z_{\text{max}}$ as no spectroscopic redshift is available.