Measuring the Star Formation Efficiency of Molecular Clouds in the Small Magellanic Cloud

The star formation efficiency per gravitational free-fall time (SFE/t_ff) describes the ability of molecular clouds to convert their gas into stars. Theoretical predictions for this critical parameter vary widely, but it is observationally difficult to accurately measure due to the need for a cloud-scale tracer of star formation. Observations of solar-mass pre-main sequence stars in the low-A(V) environment of the nearby Small Magellanic Cloud provide one of the best opportunities to obtain such a tracer, and thereby measure SFE/t_ff when combined with CO mapping of molecular clouds. We propose using ACS and WFC3 to image a gas-rich sample of molecular clouds in the SW Bar of the SMC at optical and near-IR wavelengths to identify a robust sample of pre-MS stars. These clouds have been characterized with ALMA observations, making them ideal targets for studying SFE/t_ff. Our proposed observations will provide a critical bridge between Milky Way and extragalactic studies of star formation efficiency---a cornerstone in our knowledge of star formation scaling laws throughout the Universe.