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Can magnetized turbulence set the mass scale of stars?

Guszejnov, Dávid and Grudić, Michael Y. and Hopkins, Philip F. and Offner, Stella S. R. and Faucher-Giguère, Claude-André (2020) Can magnetized turbulence set the mass scale of stars? Monthly Notices of the Royal Astronomical Society, 496 (4). pp. 5072-5088. ISSN 0035-8711.

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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 (⁠M∼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 M₅₀∝∼M₀M⁻³α_(turb)SFE^(1/3) for GMC mass M₀, sonic Mach number M⁠, virial parameter α_(turb), 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.

Item Type:Article
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URLURL TypeDescription Paper ItemData
Guszejnov, Dávid0000-0001-5541-3150
Grudić, Michael Y.0000-0002-1655-5604
Hopkins, Philip F.0000-0003-3729-1684
Offner, Stella S. R.0000-0003-1252-9916
Faucher-Giguère, Claude-André0000-0002-4900-6628
Additional Information:© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2020 June 25. Received 2020 May 15; in original form 2020 February 4. Published: 02 July 2020. The authors thank Mark Krumholz and Philip Mocz for useful discussions, and Aaron Lee, James Wurster, Cristoph Federrath, and Eve J. Lee for providing data for comparison. DG is supported by the Harlan J. Smith McDonald Observatory Postdoctoral Fellowship. MYG is supported by a CIERA Postdoctoral Fellowship. Support for PFH was provided by NSF Collaborative Research Grants 1715847 and 1911233, NSF CAREER grant 1455342, and NASA grants 80NSSC18K0562 and JPL 1589742. SSRO is supported by NSF Career Award AST-1650486 and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. CAFG is supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522; by NASA through grant 17-ATP17-0067; and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. This work used computational resources provided by XSEDE allocation AST-190018, the Frontera allocation FTA-Hopkins supported by NSF, NASA HEC allocation SMD-16-7592, and additional resources provided by the University of Texas at Austin and the Texas Advanced Computing Center (TACC; Data Availability: The data supporting the plots within this article are available on reasonable request to the corresponding authors. A public version of the GIZMO code is available at
Group:Astronomy Department, TAPIR
Funding AgencyGrant Number
Harlan J. Smith McDonald ObservatoryUNSPECIFIED
Northwestern UniversityUNSPECIFIED
Cottrell Scholar of Research CorporationUNSPECIFIED
Subject Keywords:MHD – turbulence – stars: formation – cosmology: theory
Issue or Number:4
Record Number:CaltechAUTHORS:20200310-083102875
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Official Citation:Dávid Guszejnov, Michael Y Grudić, Philip F Hopkins, Stella S R Offner, Claude-André Faucher-Giguère, Can magnetized turbulence set the mass scale of stars?, Monthly Notices of the Royal Astronomical Society, Volume 496, Issue 4, August 2020, Pages 5072–5088,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101811
Deposited By: Tony Diaz
Deposited On:10 Mar 2020 16:08
Last Modified:23 Oct 2020 15:48

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