Star Formation Efficiency and Class I Protostellar Timescales in ATLASGAL Dense Clumps

Star formation in galactic dense clumps is commonly interpreted using nearly uniform protostellar evolutionary timescales, yet the extent to which such assumptions obscure variations in star formation efficiency remains uncertain. Using 60 ATLASGAL dense clumps associated with MIPSGAL Class I protostars and NH3 velocity information, we show that compactness and dense-gas evolutionary state provide a stronger explanation of instantaneous and cumulative star formation behavior than adopting a universal Class I lifetime. By combining cumulative efficiencies with a dense-gas star formation calibration, we find that star formation proceeds with systematically mass- and density-dependent timescales, implying that a single evolutionary clock can significantly bias inferred efficiencies across the clump population. The lower-limit cumulative star formation efficiency is observed to increase with decreasing clump radius following Rcl−1.30±0.09, while no significant correlation is found with a Galactocentric radius. Upper- and lower-limit cumulative efficiencies exhibit a sublinear relation with slope 0.66±0.08, suggesting possible stellar initial mass function incompleteness. The dense-gas star formation timescale follows τSF,dense∝Mcl−0.77±0.04, with a median value of 0.54Myr. Assuming a relatively uniform timescale of 0.50Myr could overestimate and underestimate star formation rates in low-mass and massive clumps by factors of ∼32 and ∼25, respectively.