Abstract
Context. Understanding the origin of the initial mass function (IMF) of stars is a major problem for the star formation process and beyond. Aim. We investigate the dependence of the peak of the IMF on the physics of the so-called first Larson core, which corresponds to the point where the dust becomes opaque to its own radiation. Methods. We performed numerical simulations of collapsing clouds of 1000 M⊙ for various gas equations of state (eos), paying great attention to the numerical resolution and convergence. The initial conditions of these numerical experiments are varied in the companion paper. We also develop analytical models that we compare to our numerical results. Results. When an isothermal eos is used, we show that the peak of the IMF shifts to lower masses with improved numerical resolution. When an adiabatic eos is employed, numerical convergence is obtained. The peak position varies with the eos, and using an analytical model to infer the mass of the first Larson core, we find that the peak position is about ten times its value. By analyzing the stability of nonlinear density fluctuations in the vicinity of a point mass and then summing over a reasonable density distribution, we find that tidal forces exert a strong stabilizing effect and likely lead to a preferential mass several times higher than that of the first Larson core. Conclusions. We propose that in a sufficiently massive and cold cloud, the peak of the IMF is determined by the thermodynamics of the high-density adiabatic gas as well as the stabilizing influence of tidal forces. The resulting characteristic mass is about ten times the mass of the first Larson core, which altogether leads to a few tenths of solar masses. Since these processes are not related to the large-scale physical conditions and to the environment, our results suggest a possible explanation for the apparent universality of the peak of the IMF.
Highlights
Star formation is believed to have major consequences on the structure of our Universe
We develop an analytical model that accounts for the factor, on the order of ten, between the mass of the first Larson core and the peak of the stellar distribution obtained from numerical simulations
As we show below, that the peak of the stellar distribution is proportional to the mass of the first Larson core, ML, these calculations can be used to interpret the results obtained from the numerical simulations
Summary
Star formation is believed to have major consequences on the structure of our Universe. At relatively high densities ( 105 cm−3), the shape of the stellar distribution, including the peak position and the high-mass end slope, becomes no longer dependent on the global density of the parent molecular cloud. This means that some physical mechanisms are operating at local scales and do not depend on the large ones, such as the collapsing clump itself. The origin of a characteristic mass in our simulations is not obvious and needs to be elucidated For this purpose, we perform in this paper a series of simulations with initial conditions identical to those in Paper I, while altering the gas equation of state (eos).
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