Astrophys. J., 861, L18-L18 (2018/July-2)
Star formation efficiency per free-fall time in nearby galaxies.
UTOMO D., SUN J., LEROY A.K., KRUIJSSEN J.M.D., SCHINNERER E., SCHRUBA A., BIGIEL F., BLANC G.A., CHEVANCE M., EMSELLEM E., HERRERA C., HYGATE A.P.S., KRECKEL K., OSTRIKER E.C., PETY J., QUEREJETA M., ROSOLOWSKY E., SANDSTROM K.M. and USERO A.
Abstract (from CDS):
We estimate the star formation efficiency per gravitational free-fall time, εff, from observations of nearby galaxies with resolution matched to the typical size of a giant molecular cloud. This quantity, εff, 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 Physics at High Angular Resolution in nearby Galaxies-Atacama Large Millimeter Array (PHANGS-ALMA) survey, we estimate the gravitational free-fall time at 60-120 pc resolution, and contrast this with the local molecular gas depletion time in order to estimate εff. Assuming a constant thickness of the molecular gas layer (H = 100 pc) across the whole sample, the median value of εff in our sample is 0.7%. We find a mild scale dependence, with higher εff measured at coarser resolution. Individual galaxies show different values of εff, with the median εff ranging from 0.3% to 2.6%. We find the highest εff 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 (LOS) depth through the molecular gas layer and the choice of star formation tracers.
© 2018. The American Astronomical Society. All rights reserved.
galaxies: ISM - galaxies: spiral - galaxies: star formation - ISM: molecules
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