  Observations of the interstellar medium are key to deciphering the physical
processes regulating star formation in galaxies. However, observational
uncertainties and detection limits can bias the interpretation unless carefully
modeled. Here I re-analyze star formation rates and gas masses of a
representative sample of nearby galaxies with the help of multi-dimensional
Bayesian modeling. Typical star forming galaxies are found to lie in a 'star
forming plane' largely independent of their stellar mass. Their star formation
activity is tightly correlated with the molecular and total gas content, while
variations of the molecular-gas-to-star conversion efficiency are shown to be
significantly smaller than previously reported. These data-driven findings
suggest that physical processes that modify the overall galactic gas content,
such as gas accretion and outflows, regulate the star formation activity in
typical nearby galaxies, while a change in efficiency triggered by, e.g.,
galaxy mergers or gas instabilities, may boost the activity of starbursts.
