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 20240114A. The host galaxy is a dwarf galaxy at a redshift of $z=0.1306\pm 0.0002$. With a rest-frame coverage of 4300-7900 Ã , we have detected H$\hat{\mathrm{I}}\pm$, H${\hat{\mathrm{I}}}^2$, [O III]$\hat{I}»\hat{I}»$4959,5007, [N II]$\hat{I}»\hat{I}»$6548,6583, and [S II]$\hat{I}»$6716 emission lines. The emission line ratios suggest that the ionization in the host galaxy is dominated by star formation. The star formation rate (SFR) derived from the H$\hat{\mathrm{I}}\pm$ emission line is $(0.06\pm 0.01){\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, and the SED fitting suggests the lower limit of the SFR(UV) is $0.09{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$. The stellar mass is $(4.0\pm 1.8)\times 10^8{\mathrm{M}}_{\odot }$, making the specific star formation rate $\log \mathrm{sSFR}(\mathrm{H}\hat{\mathrm{I}}\pm )=-9.8\pm 0.2\mathrm{y}{\mathrm{r}}^{-1}$. The line ratios indicate an upper limit of a metallicity of $12+\mathrm{lo}{\mathrm{g}}_{10}([O/H])\sim 8.5$. 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$\hat{\mathrm{I}}\pm$-traced dispersion measure (DM) provided by the ionized gas of the host galaxy has a moderate contribution of $\sim 200\mathrm{pc}\mathrm{c}{\mathrm{m}}^{-3}$, 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 $p=0.0116$.

Accepted by ApJL