The Stellar IMF from Isothermal MHD Turbulence
StarPlan/NBI, Copenhagen, DK
|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 time scales covering the full spectrum of stellar masses from brown dwarfs to massive stars. Our simulations represent a generic 4 parsec region within a typical Galactic molecular cloud (MC), with a mass of 3,000 Msol, an rms velocity ten times the isothermal sound speed and five 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 match 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 towards 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.
|Caption: (A) Column density as a function of time. Red circles mark stars with m < 0.5 Msol, brown triangles are stars with 0.5 Msol < M < 1.5 Msol, while orange squares indicate stars with M > 1.5 Msol. (B) IMF as a function of the virial parameter. (C) IMF as a function of molecular cloud age.
P. Padoan, ES
A. Nordlund, DK
Suggested Session: Star formation "laws" and IMF