What Sets the Star Formation Rate of Molecular Clouds? The Density Distribution as a Fingerprint of Compression and Expansion Rates

Understand

We use a suite of 3D simulations of star-forming molecular clouds, with and without stellar feedback, magnetic fields, and driven turbulence, to study the compression and expansion rates of the gas as functions of density.

• We show that, around the mean density, supersonic turbulence promotes rough equilibrium between the amounts of compressing and expanding gas, consistent with continuous gas cycling between high and low density states.
• We find that the inclusion of protostellar jets produces rapidly expanding and compressing low-density gas.
• We find that the gas mass flux peaks at the transition between the lognormal and power-law forms of the density probability distribution function (PDF).