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 H α , H β , [O iii ] λλ 4959,5007, [N ii ] λλ 6548,6583, and [S ii ] λ 6716 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 H α emission line is (0.06 ± 0.01) M ⊙ yr −1 , and the spectral energy distribution fitting suggests the lower limit of the SFR(UV) is 0.09 M ⊙ yr −1 . The stellar mass is (4.0 ± 1.8) × 10 8 M ⊙ , making the specific SFR <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">log</mml:mi> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">sSFR</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi>α</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>9.17</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.07</mml:mn> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">yr</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . The line ratios indicate an upper limit of a metallicity of 12 + log 10 ([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 H α -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.