Stellar mass spectrum within massive collapsing clumps

Lee, Yueh-Ning; Hennebelle, P.

doi:10.1051/0004-6361/201731522

Cited by 47 publications

(46 citation statements)

References 66 publications

(92 reference statements)

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“…While the global parameters of the initial conditions (α turb , M, M 0 ) affect the mass spectrum of sink particles, we find no significant difference between Sphere and Box runs (see Figure 5), despite the difference in initial cloud shape, turbu-lent driving, density and magnetic fields 3 . The insensitivity of the sink mass spectrum to the specifics of the initial conditions is similar to the findings of Bate (2009b) and Lee & Hennebelle (2018a).…”

Section: Effects Of Turbulent Driving and Boundary Conditions (Box Vssupporting

confidence: 77%

Can magnetized turbulence set the mass scale of stars?

Guszejnov

Grudić

Hopkins

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Abstract Understanding the evolution of self-gravitating, isothermal, magnetized gas is crucial for star formation, as these physical processes have been postulated to set the initial mass function (IMF). We present a suite of isothermal magnetohydrodynamic (MHD) simulations using the GIZMO code, that follow the formation of individual stars in giant molecular clouds (GMCs), spanning a range of Mach numbers found in observed GMCs ($\mathcal {M} \sim 10-50$). As in past works, the mean and median stellar masses are sensitive to numerical resolution, because they are sensitive to low-mass stars that contribute a vanishing fraction of the overall stellar mass. The mass-weighted median stellar mass M50 becomes insensitive to resolution once turbulent fragmentation is well-resolved. Without imposing Larson-like scaling laws, our simulations find $M_\mathrm{50} M_\mathrm{0} \mathcal {M}^{-3} \alpha _\mathrm{turb} \mathrm{SFE}^{1/3}$ for GMC mass M0, sonic Mach number $\mathcal {M}$, virial parameter αturb, and star formation efficiency SFE = M⋆/M0. This fit agrees well with previous IMF results from the RAMSES, ORION2, and SphNG codes. Although M50 has no significant dependence on the magnetic field strength at the cloud scale, MHD is necessary to prevent a fragmentation cascade that results in non-convergent stellar masses. For initial conditions and SFE similar to star-forming GMCs in our Galaxy, we predict M50 to be >20M⊙, an order of magnitude larger than observed (∼2M⊙), together with an excess of brown dwarfs. Moreover, M50 is sensitive to initial cloud properties and evolves strongly in time within a given cloud, predicting much larger IMF variations than are observationally allowed. We conclude that physics beyond MHD turbulence and gravity are necessary ingredients for the IMF.

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Section: Effects Of Turbulent Driving and Boundary Conditions (Box Vssupporting

confidence: 77%

Can magnetized turbulence set the mass scale of stars?

Guszejnov

Grudić

Hopkins

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…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.…”

Section: The Imf and Sfe Of Molecular Cloudsmentioning

confidence: 99%

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

Ricotti

Geen

2019

Monthly Notices of the Royal Astronomical Society

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We present radiation-magneto-hydrodynamic simulations of star formation in selfgravitating, turbulent molecular clouds, modeling the formation of individual massive stars, including their UV radiation feedback. The set of simulations have cloud masses between m gas = 10 3 M to 3 × 10 5 M and gas densities typical of clouds in the local universe (n gas ∼ 1.8 × 10 2 cm −3 ) and 10× and 100× denser, expected to exist in high-redshift galaxies. The main results are: i) The observed Salpeter power-law slope and normalisation of the stellar initial mass function at the high-mass end can be reproduced if we assume that each star-forming gas clump (sink particle) fragments into stars producing on average a maximum stellar mass about 40% of the mass of the sink particle, while the remaining 60% is distributed into smaller mass stars. Assuming that the sinks fragment according to a power-law mass function flatter than Salpeter, with log-slope 0.8, satisfy this empirical prescription. ii) The star formation law that best describes our set of simulation is dρ * /dt ∝ ρ 1.5 gas if n gas < n cri ≈ 10 3 cm −3 , and dρ * /dt ∝ ρ 2.5 gas otherwise. The duration of the star formation episode is roughly 6 cloud's sound crossing times (with c s = 10 km/s). iii) The total star formation efficiency in the cloud is f * = 2%(m gas /10 4 M ) 0.4 (1 + n gas /n cri ) 0.91 , for gas at solar metallicity, while for metallicity Z < 0.1 Z , based on our limited sample, f * is reduced by a factor of ∼ 5. iv) The most compact and massive clouds appear to form globular cluster progenitors, in the sense that star clusters remain gravitationally bound after the gas has been expelled.

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“…In the companion paper (Lee & Hennebelle 2018, hereafter Paper I), we conduct a systematic exploration of the initial conditions by varying the initial density and turbulence of the molecular cloud. The physics is greatly simplified at this stage because our goal is to identify the physical processes at play.…”

Section: Introductionmentioning

confidence: 99%

Stellar mass spectrum within massive collapsing clumps

Lee

Hennebelle

2018

A&A

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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.

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Stellar mass spectrum within massive collapsing clumps

Cited by 47 publications

References 66 publications

Can magnetized turbulence set the mass scale of stars?

Can magnetized turbulence set the mass scale of stars?

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

Stellar mass spectrum within massive collapsing clumps

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