RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION

By Mark R. Krumholz, Richard Klein, C. McKee. 2012

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We report a series of simulations of the formation of a star cluster similar to the Orion Nebula Cluster (ONC), including both radiative transfer and protostellar outflows, and starting from both smooth and self-consistently turbulent initial conditions. Each simulation forms >150 stars and brown dwarfs, yielding a stellar mass distribution that ranges from <0.1 M☉ to >10 M☉. We show that a simulation that begins with self-consistently turbulent density and velocity fields embedded in a larger turbulent volume, and that includes protostellar outflows, produces an initial mass function (IMF) that is consistent both with that of the ONC and the Galactic field, at least within the statistical power provided by the number of stars formed in our simulations. This is the first simulation published to date that reproduces the observed IMF in a cluster large enough to contain massive stars, and where the peak of the mass function is determined by a fully self-consistent calculation of gas thermodynamics rather than a hand-imposed equation of state. This simulation also produces a star formation rate that, while still somewhat too high, is much closer to observed values than if we omit either the larger turbulent volume or the outflows. Moreover, we show that the combination of outflows, self-consistently turbulent initial conditions, and turbulence continually fed by motions on scales larger than that of the protocluster yields an IMF that is in agreement with observations and invariant with time, resolving the “overheating” problem in which simulations without these features have an IMF peak that shifts to progressively higher masses over time as more and more of the gas is heated, inconsistent with the observed invariance of the IMF. The simulation that matches the observed IMF also qualitatively reproduces the observed trend of stellar multiplicity strongly increasing with mass. We show that this simulation produces massive stars from distinct massive cores whose properties are consistent with those of observed massive cores. However, the stars formed in these cores also undergo dynamical interactions as they accrete that naturally produce Trapezium-like hierarchical multiple systems of massive stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/a902d2a93a0c7cdc71d4012848bb8ae008b16c5d

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Citations in the corpus

SOUTHERN MASSIVE STARS AT HIGH ANGULAR RESOLUTION: OBSERVATIONAL CAMPAIGN AND COMPANION DETECTION (2014, result): “The high accretion rates, which promote binary formation in disks, are consistent with those observed (Klaassen et al. 2012), and those seen in high-resolution radiation hydrodynamic models (Krumholz et al. 2012).”
Global collapse of molecular clouds as a formation mechanism for the most massive stars (2013, background): “This is few free-fall times longer than the typical timescale over which simulations modelling the evolution of massive star-forming clouds evolve (e.g. Smith et al. 2009; Krumholz et al. 2012).”
Before the first supernova: combined effects of H II regions and winds on molecular clouds (2014, unknown): “…focussed on single feedback mechanisms and the most popular choice has been HIIRs (e.g Dale et al. 2005; Peters et al. 2010; Vázquez-Semadeni et al. 2010) or jets (e.g Li & Nakamura 2006; Wang et al. 2010; Hansen et al. 2012; Krumholz et al. 2012), although there has also been interest in winds.”
STELLAR POPULATIONS IN THE CENTRAL 0.5 pc OF THE GALAXY. II. THE INITIAL MASS FUNCTION (2013, result): “Star formation theories do not yet predict an analytic functional form for the MF, CSF, and q distributions and how they vary with primary mass; however, simulations are beginning to produce distributions that are in rough agreement with observations (Bate 2012; Krumholz et al. 2012).”
On the diversity and statistical properties of protostellar discs (2018, background): “S R ] 2 3 Ja n tems and resolve discs reasonably well (e.g. to au scales), or those that study the formation of many protostars in molecular clouds but do not resolve most protostellar discs (e.g. Klessen et al. 1998; Bonnell & Bate 2002; Krumholz et al. 2012).”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, methodology): “(2) Krumholz et al. (2007) and Krumholz et al. (2012a) collect a large sample of observations, including both resolved regions of galaxies and entire galaxies, and conclude that all the data are consistent with a universal value ff ∼ 0.01.”
ramses-rt: radiation hydrodynamics in the cosmological context (2013, background): “Radiative feedback effects also appear to be relevant in lower redshift galaxies, and likely have a considerable impact on the initial mass function of stellar populations (Krumholz et al. 2012).”
The VAST Survey - III. The multiplicity of A-type stars within 75 pc (2013, background): “…1996; Bate & Bonnell 1997; Kratter et al. 2010; Stamatellos et al. 2011) and the results of large numerical simulations of star formation within stellar clusters (e.g. Sterzik & Durisen 2003; Moeckel & Bate 2010; Bate 2012; Krumholz et al. 2012) require large-scale surveys for empirical comparison.”
Inefficient star formation through turbulence, magnetic fields and feedback (2015, background): “The extragalactic data of disc (D) and starburst (SB) galaxies at low and high redshift were compiled in Krumholz et al. (2012a, 2013), and summarized and extended by the Small Magellanic Cloud (SMC) in Federrath (2013b).”
On the fraction of star formation occurring in bound stellar clusters (2012, methodology): “A more realistic treatment of feedback (see e.g. Wang et al. 2010; Krumholz et al. 2012) may work in two ways.”