The Host Galaxy of the Hyperactive Repeating FRB 20240114A: Behind a Galaxy Cluster

Abstract

We report on the optical spectroscopic observations of the host galaxy of the hyperactive repeating fast radio burst (FRB) FRB 20240114A. The host galaxy is a dwarf galaxy at a redshift of z = 0.1306 ± 0.0002. With a rest-frame coverage of 4300-7900 Å, we have detected Hα, Hβ, [O iii] λλ4959,5007, [N ii]λλ6548,6583, and [S ii] λ6716 emission lines. The emission line ratios suggest that the ionization in the host galaxy is dominated by star formation. The star formation rate (SFR) derived from the Hα emission line is (0.06 ± 0.01) M<inf>⊙</inf> yr⁻¹, and the spectral energy distribution fitting suggests the lower limit of the SFR(UV) is 0.09 M<inf>⊙</inf> yr⁻¹. The stellar mass is (4.0 ± 1.8) × 10⁸ M<inf>⊙</inf>, making the specific SFR log sSFR ( Hα ) = − 9.17 ± 0.07 yr⁻¹. The line ratios indicate an upper limit of a metallicity of 12 + log<inf>10</inf>([O/H]) ∼ 8.5. As the nearest dwarf host galaxy with a repeating FRB, the activity of FRB 20240114A and the properties of this host galaxy closely resemble those of FRB 20121102A and FRB 20190520B. The Hα-traced dispersion measure provided by the ionized gas of the host galaxy has a moderate contribution of ∼200 pc cm⁻³, assuming a warm ionized gas. We found that the distributions of the stellar mass versus SFR are significantly different between repeating and one-off FRBs, as determined by the MANOVA test with p = 0.0116.