The most massive star clusters in molecular clouds: Insights from the integrated cloud-wide initial mass function (ICIMF) theory

The combination of the high-resolution ALMA, JWST and HST observations provides unprecedented insights into the connection between individual molecular clouds and their internal stellar populations in nearby galaxies. The molecular clouds in five nearby galaxies were identified based on the integrated intensity maps of CO (2$-$1) emission from ALMA observations. We used the JWST 21 $μ$m data to estimate the star formation rate (SFR) surface density of the clouds and calculate the masses of the embedded stellar populations in the clouds. After matching the star cluster and stellar association catalogs derived from the HST observations with the identified molecular clouds, we found clear correlations between the physical parameters of molecular clouds and their internal stellar populations. Based on the masses of the total stellar populations and their corresponding clouds, we obtained a typical value of the cloud-scale star formation efficiency (SFE), $\approx$1.4\%. The mass of the most massive cluster ($M_{\rm cluster, max}$) in a cloud is positively proportional to the mass ($M_{\rm cloud}$), the column density, the SFR sand the SFR surface density of the cloud. The observed $M_{\rm cluster, max}$-$M_{\rm cloud}$ relation can be interpreted theoretically on the basis of the integrated cloud-wide IMF (ICIMF) theory, which provides a quantitative framework for understanding the correlations between molecular clouds and their internal stellar populations.