Magnetic Fields in Dark Cloud Cores: Arecibo OH Zeeman Observations

By T. Troland, R. Crutcher. 2008

184 citations recorded by the source corpus.

We have carried out an extensive survey of magnetic field strengths toward dark cloud cores in order to test ambipolar-diffusion-driven and turbulence-driven models of star formation. The survey involved ~500 hr of observing with the Arecibo telescope in order to make sensitive OH Zeeman observations toward 34 dark cloud cores. Nine new probable detections were achieved at the 2.5 σ level; the certainty of the detections varies from solid to marginal, so we discuss each probable detection separately. However, our analysis includes all the measurements and does not depend on whether each position has a detection or just a sensitive measurement. Rather, the analysis establishes mean (or median) values over the set of observed cores for relevant astrophysical quantities. The results are that the mass-to-flux ratio is supercritical by ~2, and that the ratio of turbulent to magnetic energies is also ~2. These results are compatible with both models of star formation. However, these OH Zeeman observations do establish for the first time on a statistically sound basis the energetic importance of magnetic fields in dark cloud cores at densities of order 103–104 cm−3, and they lay the foundation for further observations that could provide a more definitive test.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/8e81bd6e7081884b03c67088e0b9212ae6c5454c

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Citations in the corpus

Disk formation during collapse of magnetized protostellar cores (2009, result): “This result is very difficult to explain without a magnetic field, but agrees at least qualitatively with our conclusion if the source is sufficiently magnetized (Troland & Crutcher 2008).”
RADIATION MAGNETOHYDRODYNAMIC SIMULATIONS OF PROTOSTELLAR COLLAPSE: PROTOSTELLAR CORE FORMATION (2012, background): “…transport angular momentum very efficiently and modify the structure of the accretion flow significantly, and observations suggest that molecular clouds are considerably magnetized (Heiles & Crutcher 2005; Girart et al. 2006; Falgarone et al. 2008; Troland & Crutcher 2008; Crutcher et al. 2009).”
THE STAR FORMATION RATE OF SUPERSONIC MAGNETOHYDRODYNAMIC TURBULENCE (2009, methodology): “The compilation of OH and CN Zeeman measurements by Troland & Crutcher (2008) and Falgarone et al. (2008) give an average value of β = 0.39, independent of density (the value is the same in the two samples, even if the mean gas density of the CN cores is approximately two orders of magnitude larger…”
THE EFFECTS OF RADIATIVE TRANSFER ON LOW-MASS STAR FORMATION (2009, background): “Observations by Troland & Crutcher (2008) suggest that the energy contributed by magnetic fields on core scales is subdominant to the gravitational and turbulent energies.”
Magnetically Regulated Star Formation in Three Dimensions: The Case of the Taurus Molecular Cloud Complex (2008, methodology): “The magnetic field strength has been measured for three dense cores in Taurus through OH Zeeman measurements using Arecibo telescope (Troland & Crutcher 2008).”
NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION (2011, background): “The most comprehensive measurements of the magnetic field strength in dense cores of low-mass star formation come from Troland & Crutcher (2008).”
Our astrochemical heritage (2012, background): “Stars like our Sun form in slowly rotating and collapsing magnetized dense cloud cores (e.g., Goodman et al. 1993; Troland and Crutcher 2008).”
THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES (2010, background): “(18) The total mean strength of the line–of–sight magnetic field (Blos) measured in molecular clouds (n ∼ 10 3–104 cm3) is ∼10–20µG (Crutcher 1999; Troland & Crutcher 2008).”
DIRECT NUMERICAL SIMULATION OF RADIATION PRESSURE-DRIVEN TURBULENCE AND WINDS IN STAR CLUSTERS AND GALACTIC DISKS (2012, background): “…Zeeman and polarization observations indicate that there are ordered magnetic fields in rough equipartition with turbulence (Crutcher 1999; Troland & Crutcher 2008; Chapman et al. 2011; Li & Henning 2011; however see Padoan et al. 2004 for a contrasting view), in which case magnetic…”
Magnetic Fields of Nondegenerate Stars (2009, background): “Actual Zeeman detections are obtained in only about 2 dozen clouds (Crutcher1999; Troland & Crutcher 2008).”