PHANGS: constraining star formation time-scales using the spatial correlations of star clusters and giant molecular clouds

In the hierarchical view of star formation, giant molecular clouds (GMCs) undergo fragmentation to form small-scale structures made up of stars and star clusters. Here we study the connection between young star clusters and cold gas across a range of extragalactic environments by combining the high resolution (1 '') PHANGS-ALMA catalogue of GMCs with the star cluster catalogues from PHANGS-HST. The star clusters are spatially matched with the GMCs across a sample of 11 nearby star-forming galaxies with a range of galactic environments (centres, bars, spiral arms, etc.). We find that after 4 - 6 Myr the star clusters are no longer associated with any gas clouds. Additionally, we measure the autocorrelation of the star clusters and GMCs as well as their cross-correlation to quantify the fractal nature of hierarchical star formation. Young (<= 10 Myr) star clusters are more strongly autocorrelated on kpc and smaller spatial scales than the > 10 Myr stellar populations, indicating that the hierarchical structure dissolves over time.

Automated summary

The study reveals that after 4-6 million years, star clusters are no longer associated with any gas clouds. Moreover, the autocorrelation and cross-correlation of star clusters and GMCs are measured to quantify the fractal nature of hierarchical star formation. Young star clusters (<=10 million years) show stronger autocorrelation on kpc and smaller spatial scales compared to the >10 million-year-old stellar populations, indicating the dissolution of the hierarchical structure over time.