VLA Zeeman observations of W3

D. A. Roberts, R. M. Crutcher, T. H. Troland, W. M. Goss

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47 Scopus citations


The Zeeman effect has been observed in the 1420 MHz line of H I using the Very Large Array. The line-of-sight magnetic field (Blos) in the W3 complex has been determined independently in the two velocity components at -38 and -46 km s-1 with a resolution of ∼25″ and an rms noise of 3 mJy beam-1. The field reversal across the W3 core in the -38 km s-1 component reported by Troland et al. (1989) has been confirmed with the field varying from -120 μG in the northeast to +220 μG in the southwest. This reversal has been modeled as an hourglass magnetic field with a peak strength of ∼1 mG created by the collapse of the parent molecular cloud. Within the uncertainties of the model, the flux-to-mass ratio appears to be near the magnetically critical value. A second reversal is observed in the large, ringlike H II region to the south of the core, associated with the optical H II region NGC 896. Blos changes from +40 μG in the middle of NGC 896 to -40 μG in the southern portion of NGC 896. The large-scale structure of Blos is consistent with an originally uniform held that has been pinched into an hourglass shape near the core and which has been distorted by the expansion of the H II region NGC 896 to the south of the core. In the velocity component at -46 km s-1, there is a uniform field of ∼ +40 μG, except for a ridge of enhanced Blos (∼ + 30 μG) across the center of the source. There appears to be a correspondence between the ridge of enhanced Blos and enhanced optical depth previously observed in the same area.

Original languageEnglish
Pages (from-to)675-683
Number of pages9
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 1 1993


  • ISM: individual (W3)
  • ISM: magnetic fields
  • Radio lines: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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