Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...725..466c&link_type=abstract
The Astrophysical Journal, Volume 725, Issue 1, pp. 466-479 (2010).
Astronomy and Astrophysics
Astronomy
31
Ism: Magnetic Fields, Polarization, Stars: Formation
Scientific paper
The only direct measurements of interstellar magnetic field strengths depend on the Zeeman effect, which samples the line-of-sight component Bz of the magnetic vector. In this paper, we use a Bayesian approach to analyze the observed probability density function (PDF) of Bz from Zeeman surveys of H I, OH, and CN spectral lines in order to infer a density-dependent stochastic model of the total field strength B in diffuse and molecular clouds. We find that at n < 300 cm-3 (in the diffuse interstellar medium sampled by H I lines), B does not scale with density. This suggests that diffuse clouds are assembled by flows along magnetic field lines, which would increase the density but not the magnetic field strength. We further find strong evidence for B in molecular clouds being randomly distributed between very small values and a maximum that scales with volume density n as B vprop n 0.65 for n>300 cm-3, with an uncertainty at the 50% level in the power-law exponent of about ±0.05. This break-point density could be interpreted as the average density at which parsec-scale clouds become self-gravitating. Both the uniform PDF of total field strengths and the scaling with density suggest that magnetic fields in molecular clouds are often too weak to dominate the star formation process. The stochasticity of the total field strength B implies that many fields are so weak that the mass/flux ratio in many clouds must be significantly supercritical. A two-thirds power law comes from isotropic contraction of gas too weakly magnetized for the magnetic field to affect the morphology of the collapse. On the other hand, our study does not rule out some clouds having strong magnetic fields with critical mass/flux ratios.
Crutcher Richard M.
Falgarone Edith
Heiles Carl
Troland Thomas H.
Wandelt Benjamin
No associations
LandOfFree
Magnetic Fields in Interstellar Clouds from Zeeman Observations: Inference of Total Field Strengths by Bayesian Analysis does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Magnetic Fields in Interstellar Clouds from Zeeman Observations: Inference of Total Field Strengths by Bayesian Analysis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic Fields in Interstellar Clouds from Zeeman Observations: Inference of Total Field Strengths by Bayesian Analysis will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1478654