Magnetic fields in shocked regions: Very large array observations of H 2O masers

A. P. Sarma, T. H. Troland, R. M. Crutcher, D. A. Roberts

Research output: Contribution to journalArticlepeer-review


We present VLA observations of the Zeeman effect in 22 GHz H2O masers in several high-mass star-forming regions. These masers are believed to arise from collisional pumping in postshock environments. Therefore, the Zeeman effect data provide the most direct measurements of magnetic field strengths in high-density (n ≳ 108 cm-3) postshock gas, where the field energy determines other physical conditions. Our observations yield significant magnetic field detections in W3 IRS 5, W3(OH), W49 N, and OH 43.8-0.1. In these sources, we detect line-of-sight field strengths ranging from 13 to 49 mG. For some regions, the detected fields provide a 2-3 point sampling of the magnetic field, indicating the nature of field variations on arcsecond scales. These field strengths are consistent with a shock-driven maser model having relatively low speed (20 km s-1), C-type shocks. We examine the balance between magnetic field energy and turbulent kinetic energy in the masing regions. These energies appear close to equilibrium.

Original languageEnglish (US)
Pages (from-to)928-937
Number of pages10
JournalAstrophysical Journal
Issue number2 I
StatePublished - Dec 1 2002


  • ISM: clouds
  • ISM: magnetic fields
  • Masers
  • Polarization
  • Radio lines: ISM
  • Shock waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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