Observations of magnetic fields in diffuse clouds

Abstract

view Abstract Citations (51) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of Magnetic Fields in Diffuse Clouds Myers, P. C. ; Goodman, A. A. ; Gusten, R. ; Heiles, C. Abstract 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. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175433 Bibcode: 1995ApJ...442..177M Keywords: 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; Astronomy; ISM: CLOUDS; ISM: MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS: MHD; RADIO LINES: ISM full text sources ADS | data products SIMBAD (8)