On The Nature of Variations in the Measured Star Formation Efficiency of Molecular Clouds

摘要: Measurements of the star formation efficiency (SFE) giant molecular clouds (GMCs) in Milky Way generally show a large scatter, which could be intrinsic or observational. We use magnetohydrodynamic simulations GMCs (including feedback) to forward-model relationship between true GMC SFE and observational proxies. that individual trace broad ranges observed throughout collapse, formation, disruption. Low measured SFEs (⁠≪1 per cent⁠) are ‘real’ but correspond early stages; ‘per-freefall’ where most stars actually form can much larger. Very high (⁠≫10 values often artificially enhanced by rapid gas dispersal. Simulations including stellar feedback reproduce GMC-scale SFEs, without produce 20× larger SFEs. Radiative dominates among mechanisms simulated. An anticorrelation with cloud mass is shown an artefact. also explore dense ‘clumps’ within (with their bulk properties agree well observations. Predicted clumps ∼2× than observed, possibly indicating physics other from massive (main-sequence) needed regulate collapse.