The role of the turbulence driving mode for the Initial Mass Function

TL;DR

This study uses magnetohydrodynamical simulations to investigate how different turbulence driving modes influence the initial mass function of stars, revealing that compressive driving produces more low-mass stars and affects multiplicity and angular momentum.

Contribution

It provides the first detailed comparison of the effects of compressive versus solenoidal turbulence driving modes on the stellar initial mass function in star formation simulations.

Findings

Compressive turbulence driving results in a higher fraction of low-mass stars.

The median stellar mass is lower by a factor of ~1.5 in compressive driving.

Turbulence mode influences multiplicity fraction and angular momentum of protostars.

Abstract

Turbulence is a critical ingredient for star formation, yet its role for the initial mass function (IMF) is not fully understood. Here we perform magnetohydrodynamical (MHD) simulations of star cluster formation including gravity, turbulence, magnetic fields, stellar heating and outflow feedback to study the influence of the mode of turbulence driving on IMF. We find that simulations that employ purely compressive turbulence driving (COMP) produce a higher fraction of low-mass stars as compared to simulations that use purely solenoidal driving (SOL). The characteristic (median) mass of the sink particle (protostellar) distribution for COMP is shifted to lower masses by a factor of ~ 1.5 compared to SOL. Our simulation IMFs capture the important features of the observed IMF form. We find that turbulence-regulated theories of the IMF match our simulation IMFs reasonably well in the high-mass and low-mass range, but underestimate the number of very low-mass stars, which form towards the later stages of our simulations and stop accreting due to dynamical interactions. Our simulations show that for both COMP and SOL, the multiplicity fraction is an increasing function of the primary mass, although the multiplicity fraction in COMP is higher than that of SOL for any primary mass range. We find that binary mass ratio distribution is independent of the turbulence driving mode. The average specific angular momentum of the sink particles in SOL is a factor of 2 higher than that for COMP. Overall, we conclude that the turbulence driving mode plays a significant role in shaping the IMF.