# Stellar mass spectrum within massive collapsing clumps III. Effects of temperature and magnetic field

## TL;DR

This study investigates how temperature and magnetic fields influence the stellar mass spectrum during star formation, finding that the peak is mainly determined by high-density physics rather than diffuse gas properties or magnetic effects.

## Contribution

It demonstrates that the stellar initial mass function's peak is primarily set by high-density thermodynamics, with magnetic fields playing a secondary role.

## Key findings

- The shape of the stellar mass spectrum is insensitive to the diffuse gas EOS.
- Magnetic fields slightly alter the mass spectrum only at extreme strengths.
- The IMF peak is mainly determined by high-density adiabatic physics, not the Jeans mass at lower densities.

## Abstract

The stellar mass spectrum is an important property of the stellar cluster and a fundamental quantity to understand our Universe. The fragmentation of diffuse molecular cloud into stars is subject to physical processes such as gravity, turbulence, thermal pressure, and magnetic field. The final mass of a star is believed to be a combined outcome of a virially unstable reservoir and subsequent accretion. We aim to clarify the roles of different supporting energies, notably the thermal pressure and the magnetic field, in determining the stellar mass. Following previous studies by Lee & Hennebelle (2018a,b), we perform a series of numerical experiments of stellar cluster formation inside an isolated molecular clump. By changing the effective equation of state (EOS) of the diffuse gas (that is to say gas whose density is below the critical density at which dust becomes opaque to its radiation) and the strength of the magnetic field, we investigate whether any characteristic mass is introduced into the fragmentation processes. The EOS of the diffuse gas, including the bulk temperature and the polytropic index, does not affect significantly the shape of the stellar mass spectrum. The presence of magnetic field slightly modifies the shape of the mass spectrum only when extreme values are applied. This study confirms that the peak of the IMF is primarily determined by the adiabatic high-density end of the EOS that mimics the radiation inside the high-density gas. Furthermore, the shape of the mass spectrum is mostly sensitive to the density PDF, and the magnetic field has likely only a secondary role. In particular, we stress that the Jeans mass at the mean cloud density and at the critical density are not responsible of setting the peak.