Observations of magnetic fields in diffuse clouds

Details Observations of magnetic fields in diffuse clouds Observations of magnetic fields in diffuse clouds

Mar 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...442..177m&link_type=abstract

The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 442, no. 1, p. 177-185

Astronomy and Astrophysics

Astrophysics

42

H I Regions, Interstellar Gas, Interstellar Magnetic Fields, Line Of Sight, Molecular Clouds, Radio Observation, Turbulence, Flux Density, Magnetic Flux, Magnetohydrodynamic Waves, Radio Spectra, Spectrum Analysis, Zeeman Effect

Scientific paper

We report 32 statistically significant measurements of the line-of-sight component of the magnetic field strength, Bz, in four diffuse clouds, via the Zeeman effect in the 21 cm line of H I. The region near Magnani, Blitz, and Mundy 1985 (MBM) 27-30 in the Ursa Major complex has Bz greater than 4 micro-G throughout a filamentary region 15 pc long, with significant structure on scales as small as 1.6 pc. The greatest field strength measured in this cloud is 19 +/- 2 micro-G, greater than in most diffuse clouds by a factor approximately 2. Comparison of measurements with different telescopes suggests that the field strength at the map peak may be significantly greater than 19 micro-G on scales smaller than 1.6 pc. The magnetic and kinetic energy densities M and K in this cloud are comparable, within a factor 2 of 2 x 10-11ergs/cu cm, and greater than the gravitational energy density by a factor approximately 500. Among the four clouds surveyed, six positions where CO emission is a local maximim have essentially the same mean line-of-sight field strength, Bz approximately = 8 micro-G, as do four positions where CO emission is too weak to be detected. The similarity of M and K in the diffuse clouds discussed here, as well as in denser, self-gravitating clouds, suggests strong coupling between magnetic fields and gas motions in some interstellar clouds, independent of their self-gravity. This coupling probably arises from ion-neutral collisions, which allow propagation of MHD waves.

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