Do fragmentation and accretion affect the stellar initial mass function?

Abstract

ABSTRACT While the stellar initial mass function (IMF) appears to be close to universal within the Milky Way galaxy, it is strongly suspected to be different in the primordial universe, where molecular hydrogen cooling is less efficient and the gas temperature can be higher by a factor of 30. In between these extreme cases, the gas temperature varies depending on the environment, metallicity, and radiation background. In this paper we explore if changes of the gas temperature affect the IMF of the stars considering fragmentation and accretion. The fragmentation behaviour depends mostly on the Jeans mass at the turning point in the equation of state (EOS) where a transition occurs from an approximately isothermal to an adiabatic regime due to dust opacities. The Jeans mass at this transition in the EOS is always very similar, independent of the initial temperature, and therefore the initial mass of the fragments is very similar. Accretion on the other hand is strongly temperature dependent. We argue that the latter becomes the dominant process for star formation efficiencies above 5–7  per cent, increasing the average mass of the stars.