The Zeeman effect in 21 centimeter line radiation - Methods and initial results

Details The Zeeman effect in 21 centimeter line radiation - Methods and initial results The Zeeman effect in 21 centimeter line radiation - Methods and initial results

Jan 1982

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982apj...252..179t&link_type=abstract

Astrophysical Journal, Part 1, vol. 252, Jan. 1, 1982, p. 179-192. NSF-supported research.

Astronomy and Astrophysics

Astronomy

90

Emission Spectra, H Lines, Interstellar Magnetic Fields, Neutral Gases, Radio Sources (Astronomy), Zeeman Effect, Absorption Spectra, Centimeter Waves, Data Reduction, H I Regions, Hydrogen, Interstellar Matter, Polarimeters

Scientific paper

The causes and remedies of instrumental circular polarization effects, which impose severe limitations on H I emission line Zeeman effect measurements, are investigated in the course of a search for the Zeeman effect in the 21 cm line of galactic neutral hydrogen. It is found that circular polarization does not have a serious effect at current levels of sensitivity, and upper limits to the line-of-sight field of between 4 and 10 microgauss are derived in eight H I emission regions. Because the field strengths derived for H I regions are low, and magnetic energy densities are smaller than energy densities associated with turbulent or other macroscopic motions, magnetic forces should not influence motions of the gas. The alignment of interstellar dust grains by the conventional mechanism is not possible in the H I regions studied, due to the weakness of the magnetic field. The actual existence of grain alignment in these regions calls for a different and more efficient mechanism.

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