The Relationship Between X-Ray Binaries and Compact Star Clusters in NGC 2403, NGC 4303 and NGC 1672

Abstract This study investigates the identification X-ray binary systems (XRBs) and their association with nearby compact star clusters in the galaxies NGC 2403, NGC 4303, and NGC 1672. Using data from the Hubble Space Telescope (HST)/ACS/Wide Field Camera (WFC) and HST/WFC3/UVIS, we compiled a catalog of compact star clusters, identifying 541 in NGC 2403, 934 in NGC 4303, and 543 in NGC 1672. Archival Chandra data revealed 79 XRBs within the HST field of view across these galaxies. Optical counterparts were detected within an error radius at 2 σ confidence levels for 26 of the 31 XRBs in NGC 2403, 15 of the 25 in NGC 4303, and 10 of the 23 in NGC 1672. We find that 66% of XRBs are associated with star clusters, with a fraction (49%) of high-mass XRBs (HMXBs) linked to young, compact clusters located within 200 pc in all three galaxies. Notably, in NGC 4303, five HMXBs are found within young clusters, while one low-mass XRB is located in an old cluster. Intermediate-mass XRBs (IMXBs) comprise about 45% of the XRB population in NGC 2403 and are predominantly found in the vicinity of young compact star clusters. A similar pattern is observed in the nearby galaxy NGC 4214, suggesting that the formation mechanisms of IMXBs may be more closely related to those of HMXBs.