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We estimate the star formation efficiency per gravitational free fall time, $epsilon_{rm ff}$, from observations of nearby galaxies with resolution matched to the typical size of a Giant Molecular Cloud. This quantity, $epsilon_{rm ff}$, is theoretically important but so far has only been measured for Milky Way clouds or inferred indirectly in a few other galaxies. Using new, high resolution CO imaging from the PHANGS-ALMA survey, we estimate the gravitational free-fall time at 60 to 120 pc resolution, and contrast this with the local molecular gas depletion time to estimate $epsilon_{rm ff}$. Assuming a constant thickness of the molecular gas layer ($H = 100$ pc) across the whole sample, the median value of $epsilon_{rm ff}$ in our sample is $0.7%$. We find a mild scale-dependence, with higher $epsilon_{rm ff}$ measured at coarser resolution. Individual galaxies show different values of $epsilon_{rm ff}$, with the median $epsilon_{rm ff}$ ranging from $0.3%$ to $2.6%$. We find the highest $epsilon_{rm ff}$ in our lowest mass targets, reflecting both long free-fall times and short depletion times, though we caution that both measurements are subject to biases in low mass galaxies. We estimate the key systematic uncertainties, and show the dominant uncertainty to be the estimated line-of-sight depth through the molecular gas layer and the choice of star formation tracers.
Aims: The purpose of this work is to study the properties of the spatial distribution of the young population in three nearby galaxies in order to better understand the first stages of star formation. Methods: We used ACS/HST photometry and the pat
We study the relationship between the field star formation and cluster formation properties in a large sample of nearby dwarf galaxies. We use optical data from the Hubble Space Telescope and from ground-based telescopes to derive the ages and masses
On average molecular clouds convert only a small fraction epsilon_ff of their mass into stars per free-fall time, but differing star formation theories make contrasting claims for how this low mean efficiency is achieved. To test these theories, we n
We use Atacama Large Millimeter Array CO(3-2) observations in conjunction with optical observations from the Hubble Space Telescope to determine the ratio of stellar to gas mass for regions in the Antennae Galaxies. We adopt the term instantaneous ma
We examined radial variations in molecular-gas based star formation efficiency (SFE), which is defined as star formation rate per unit molecular gas mass, for 80 galaxies selected from the CO Multi-line Imaging of Nearby Galaxies project (Sorai et al