The spatial evolution of star clusters in NGC 628 with JWST

We examine the spatial distribution of star clusters in NGC628 using the statistical tool INDICATE to quantify clustering tendencies. Our sample, based on Hubble Space Telescope and James Webb Space Telescope observations, is the most complete to date, spanning ages from 1 to >100 Myr. We find cluster spatial behaviour varies with galactic position, age, and mass. Most emerging young clusters are tightly spatially associated with each other, while fully emerged clusters are in ~1.5 times looser spatial associations, irrespective of age. Young Massive Clusters (YMCs ≥ 104 M⊙) tend to associate with lower-mass clusters but not strongly with other YMCs, implying that intense star formation regions produce a few YMCs alongside many lower-mass clusters rather than multiple YMCs together. Young concentrated clusters show a wide radial distribution in the galactic disc, which narrows with age; with concentrated clusters > 100Myr mostly residing between 2 and 6 kpc. This pattern may reflect either faster dispersal of isolated tight cluster spatial ‘structure’ in a lower gas density outer disc or gradual inside-out growth, with the formation of this structure shifting outwards over time. We also detect distinct spatial behaviours for clusters within 2 kpc, linked to the inner Lindblad resonance (≤1 kpc), nuclear ring (~0.5–1 kpc), and the start of spiral arms (~1.25–2 kpc), suggesting these regions exhibit strong radial motions that could hinder clusters from forming and remaining in tight concentrations. Our results highlight how spatially resolved studies of clusters can reveal the influence of galactic dynamics on star formation and cluster evolution.