The stellar IMF from Isothermal MHD Turbulence

TL;DR

This study uses high-resolution simulations of isothermal MHD turbulence to demonstrate that turbulent fragmentation alone can reproduce the observed stellar initial mass function across a wide range of stellar masses.

Contribution

The paper provides the first comprehensive numerical validation that isothermal MHD turbulence can fully explain the origin of the stellar IMF without feedback.

Findings

Simulations produce an IMF matching observations from brown dwarfs to massive stars.

The IMF results are numerically converged and robust across different physical parameters.

The initial time evolution of the IMF supports the turbulent fragmentation model.

Abstract

We address the turbulent fragmentation scenario for the origin of the stellar initial mass function (IMF), using a large set of numerical simulations of randomly driven supersonic MHD turbulence. The turbulent fragmentation model successfully predicts the main features of the observed stellar IMF assuming an isothermal equation of state without any stellar feedback. As a test of the model, we focus on the case of a magnetized isothermal gas, neglecting stellar feedback, while pursuing a large dynamic range in both space and timescales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 pc region within a typical Galactic molecular cloud, with a mass of 3000 Msun and an rms velocity 10 times the isothermal sound speed and 5 times the average Alfven velocity, in agreement with observations. We achieve a maximum resolution of 50 au and a maximum duration of star formation of 4.0 Myr, forming up to a thousand sink particles whose mass distribution closely matches the observed stellar IMF. A large set of medium-size simulations is used to test the sink particle algorithm, while larger simulations are used to test the numerical convergence of the IMF and the dependence of the IMF turnover on physical parameters predicted by the turbulent fragmentation model. We find a clear trend toward numerical convergence and strong support for the model predictions, including the initial time evolution of the IMF. We conclude that the physics of isothermal MHD turbulence is sufficient to explain the origin of the IMF.