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Title: The dynamics of massive starless cores with ALMA

How do stars that are more massive than the Sun form, and thus how is the stellar initial mass function (IMF) established? Such intermediate- and high-mass stars may be born from relatively massive pre-stellar gas cores, which are more massive than the thermal Jeans mass. The turbulent core accretion model invokes such cores as being in approximate virial equilibrium and in approximate pressure equilibrium with their surrounding clump medium. Their internal pressure is provided by a combination of turbulence and magnetic fields. Alternatively, the competitive accretion model requires strongly sub-virial initial conditions that then lead to extensive fragmentation to the thermal Jeans scale, with intermediate- and high-mass stars later forming by competitive Bondi-Hoyle accretion. To test these models, we have identified four prime examples of massive (∼100 M {sub ☉}) clumps from mid-infrared extinction mapping of infrared dark clouds. Fontani et al. found high deuteration fractions of N{sub 2}H{sup +} in these objects, which are consistent with them being starless. Here we present ALMA observations of these four clumps that probe the N{sub 2}D{sup +} (3-2) line at 2.''3 resolution. We find six N{sub 2}D{sup +} cores and determine their dynamical state. Their observed velocity dispersions and sizes are broadlymore » consistent with the predictions of the turbulent core model of self-gravitating, magnetized (with Alfvén Mach number m{sub A} ∼ 1) and virialized cores that are bounded by the high pressures of their surrounding clumps. However, in the most massive cores, with masses up to ∼60 M {sub ☉}, our results suggest that moderately enhanced magnetic fields (so that m{sub A} ≅ 0.3) may be needed for the structures to be in virial and pressure equilibrium. Magnetically regulated core formation may thus be important in controlling the formation of massive cores, inhibiting their fragmentation, and thus helping to establish the stellar IMF.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4]
  1. Departments of Astronomy and Physics, University of Florida, Gainesville, FL 32611 (United States)
  2. Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)
  3. School of Physics and Astronomy, The University of Leeds, Leeds LS2 9JT (United Kingdom)
  4. INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze (Italy)
Publication Date:
OSTI Identifier:
22348479
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALFVEN WAVES; APPROXIMATIONS; DEUTERATION; DISPERSIONS; DUSTS; EQUILIBRIUM; FORECASTING; FRAGMENTATION; MACH NUMBER; MAGNETIC FIELDS; MASS; RESOLUTION; SUN; TURBULENCE