Exploring the relationship between X-ray binaries and compact star clusters (I): NGC 4490 and NGC 4214

Abstract

We conducted a study to investigate the relationship between X-ray binaries (XRBs) and compact star clusters in the nearby star-forming galaxies NGC 4490 and NGC 4214. By analyzing archival data from Chandra, we identified a total of 32 XRBs with X-ray luminosities Lx > 1036 erg s−1 in both galaxies. Utilizing data from HST/WFC3/UVIS, we presented a new catalog of 715 compact star clusters in NGC 4490 and identified 312 such clusters in NGC 4214. In the case of NGC 4490, 14 of the 17 XRBs are associated with clusters, whereas in NGC 4214 all 15 XRBs are connected to clusters within a radius of < 200 pc. Furthermore, among the XRBs in NGC 4490, 12 out of the 17 have optical counterparts. Similarly, in NGC4214, 11 out of the 15 XRBs exhibit optical counterparts. We have evidence for a substantial population of HMXBs associated with clusters, accounting for ∼ 70% and 40% of the detected XRBs in NGC 4490 and NGC 4214, respectively. HMXBs are often found near young, less massive clusters, while LMXBs are associated with older, more massive clusters in these galaxies. IMXBs in NGC 4214, on the other hand, tend to be close to young clusters, suggesting that their formation mechanism is more similar to HMXBs than to LMXBs.