Formation of a Nuclear Star Cluster through a Merger Event in the Low-surface-brightness Galaxy AGC 223218

Abstract We present the properties of a nuclear star cluster (NSC) in the low-surface-brightness galaxy AGC 223218. The disk of the galaxy can be modeled using two Sérsic components with distinct central positions: one representing the inner bright disk and the other corresponding to the extended outer disk. We estimate the stellar masses of the NSC and the host galaxy using two methods: spectral energy distribution (SED) fitting and mass-to-light versus color relations (MLCRs). The stellar mass ratio of the NSC to AGC 223218 is 0.094 based on the SED method and 0.072 using MLCRs. The NSC presents a younger stellar population and a lower [Fe/H] value than the host, as determined from Sloan Digital Sky Survey (SDSS) and LAMOST spectra analysis using pPXF fitting. AGC 223218 is located at the boundary between the Seyfert and star-forming regions in the [S II ]-Baldwin–Phillips–Terlevich (BPT) diagram, whereas in the [N II ]-BPT diagram, it falls in the track of star-forming SDSS galaxies. This suggests the presence of strong shocks in AGC 223218. We propose that the NSC in AGC 223218 may have formed as a result of a merger event. Furthermore, the observed X-ray luminosity of AGC 223218 with eROSITA is 2 orders of magnitude higher than the expected X-ray luminosity from X-ray binaries, suggesting the presence of an intermediate-mass black hole (IMBH) in the NSC. To account for the observed X-ray luminosity, we estimate the IMBH accretion rate to be approximately 0.001.