A comprehensive catalogue of OB cluster candidates in M31 and their association with giant molecular clouds

ABSTRACT We present a new catalogue of 578 OB cluster (OBC) candidates in the Andromeda galaxy (M31), identified using a MeanShift-based algorithm on HST’s F275W-band imaging from the PHAT (Dalcanton et al. 2012) and PHAST (Chen et al. 2025) Hubble surveys. These clusters exhibit typical half-light radii of 1–2 pc and strong ultraviolet luminosities indicative of recent massive star formation. Spatial analysis reveals a pronounced north–south asymmetry: clusters in the northern disc show tight associations with giant molecular clouds (GMCs), while southern clusters appear more compact and luminous but less correlated with molecular gas. Two-point correlation functions demonstrate significant clustering of OBC candidates on scales 100 pc and a strong spatial association with GMCs, consistent with hierarchical star formation in dense gas-rich environments. These findings offer new constraints on the early evolution and feedback-driven dispersal of young stellar clusters across galactic discs.