Bridging Theory and Observation: Synthetic Far-infrared Insights into Star Formation Efficiency
Abstract
The star formation efficiency per free-fall time (εff) quantifies how efficiently giant molecular clouds (GMCs) convert gas into stars and is often observed to be orders of magnitude lower than expected for free-fall collapse. Observers typically estimate εff by mapping far-infrared (FIR) dust emission to infer gas surface densities (Σgas) and counting embedded protostars, assuming simplified lifetimes and masses. Using the fiducial STARFORGE radiation-magnetohydrodynamics simulation of an Mcl = 2×104 M⊙ GMC that self-consistently models star cluster formation and stellar feedback, we generate synthetic FIR observations and apply the same methodologies used in GMC surveys to investigate this discrepancy. We present the first εff−Σgas analysis in a fully feedback-regulated GMC simulation that resolves the formation of stellar systems. Our synthetic measurements reproduce the low observationally inferred efficiencies, showing that feedback-regulated star formation naturally produces εff ∼ 1−3% without requiring extreme initial conditions. We also find that εff varies strongly over a GMC's lifetime, suggesting that much of the observed scatter reflects evolutionary sampling rather than intrinsic cloud-to-cloud differences. Finally, by comparing observational and simulation definitions, we show that methodological assumptions introduce systematic biases, with a transition near log Σgas ≈ 2.3 M⊙ pc−2 that depends on resolution. Above this threshold, the smoothing of dense structure increases both the inferred free-fall time and enclosed gas, with the latter dominating and suppressing εff. Below the threshold, the discrepancies are primarily driven by star formation rate assumptions.
Versions
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BibTeX
@misc{escamilla2026bridging,
title = {{Bridging Theory and Observation: Synthetic Far-infrared Insights into Star Formation Efficiency}},
author = {Alexander Escamilla and Michael Y. Grudić and Anna L. Rosen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12729},
eprint = {2610.12729},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12729},
}
RIS
TY - UNPB
TI - Bridging Theory and Observation: Synthetic Far-infrared Insights into Star Formation Efficiency
AU - Alexander Escamilla
AU - Michael Y. Grudić
AU - Anna L. Rosen
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12729
UR - https://arxiv.org/abs/2610.12729
AB - The star formation efficiency per free-fall time (ε_ff) quantifies how efficiently giant molecular clouds (GMCs) convert gas into stars and is often observed to be orders of magnitude lower than expected for free-fall collapse. Observers typically estimate ε_ff by mapping far-infrared (FIR) dust emission to infer gas surface densities (Σ_gas) and counting embedded protostars, assuming simplified lifetimes and masses. Using the fiducial STARFORGE radiation-magnetohydrodynamics simulation of an M_cl = 2×10^4 M_⊙ GMC that self-consistently models star cluster formation and stellar feedback, we generate synthetic FIR observations and apply the same methodologies used in GMC surveys to investigate this discrepancy. We present the first ε_ff−Σ_gas analysis in a fully feedback-regulated GMC simulation that resolves the formation of stellar systems. Our synthetic measurements reproduce the low observationally inferred efficiencies, showing that feedback-regulated star formation naturally produces ε_ff ∼ 1−3% without requiring extreme initial conditions. We also find that ε_ff varies strongly over a GMC's lifetime, suggesting that much of the observed scatter reflects evolutionary sampling rather than intrinsic cloud-to-cloud differences. Finally, by comparing observational and simulation definitions, we show that methodological assumptions introduce systematic biases, with a transition near log Σ_gas ≈ 2.3 M_⊙ pc^−2 that depends on resolution. Above this threshold, the smoothing of dense structure increases both the inferred free-fall time and enclosed gas, with the latter dominating and suppressing ε_ff. Below the threshold, the discrepancies are primarily driven by star formation rate assumptions.
ER -