Stellar mass spectrum within massive collapsing clumps

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.

On the origin of the peak of the stellar initial mass function: exploring the tidal screening theory

“…Using the lognormal distribution of the density fluctuations inside our turbulent box, we could estimate the probability of finding a collapsing clump of a certain density and at a certain distance from the central core. This is precisely what Lee & Hennebelle (2018b) and Hennebelle et al (2019) did in their earlier, albeit recent study using an analytical approach, providing also an analytical estimate of the tidal mass. In this paper, instead of adopting a probabilistic approach, we used the actual gas density field in the simulation to compute the tidal mass.…”

“…Many authors have since repeated and improved Larson's numerical experiments, but the mass of the first Larson core M 1LC is still found to be of the order 0.02 M and has proven to be very robust against variations in the equation of state and the properties of the surrounding envelop (e.g. Vaytet et al 2013;Krumholz 2017;Bhandare et al 2018;Lee & Hennebelle 2018b). When the second Larson core forms, it accretes the leftovers of the first Larson core on a very short timescale.…”

“…This makes the first Larson core a very robust candidate for explaining why the characteristic mass of the IMF would remain constant in different environments. In a recent series of papers, Lee & Hennebelle (2018b proposed to explain the characteristic mass of the IMF by tidal forces caused by the first Larson core and its envelope, preventing the formation of new cores in their surroundings. This allows the central core to gather all the mass available in this tidally screened reservoir, without sharing it with the other cores that would have collapsed otherwise.…”

System initial mass function of the 25 Ori group from planetary-mass objects to intermediate/high-mass stars

“…These comparisons indicate that the 25 Ori system IMF is similar to that of a diversity of stellar clusters, which supports the idea that the shape of the IMF is largely insensitive to environmental properties, as predicted by the models from Bonnell et al (2006), Elmegreen et al (2008) and Lee & Hennebelle (2018).…”

Simulating star clusters across cosmic time – I. Initial mass function, star formation rates, and efficiencies

“…Gavagnin et al (2017) have lower mass resolution but capture more massive stars that emit significant quantities of ionising radiation, arguing that this alters the high mass end of the IMF. In the absence of radiation and cooling, Lee & Hennebelle (2018a) and Lee & Hennebelle (2018b) study the early formation of protostellar Larson cores, and find that the choice of equation of state (eos) has a strong influence on the peak of the IMF. In general, these works are relatively successful at reproducing not only the IMF but also stellar multiplicity and separation.…”