Polarization observations of 3C radio sources and galactic Faraday rotation

by Wright, William Edwin

Abstract (Summary)
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The linear polarization properties of 206 radio sources from the 3CR Catalogue have been measured--in most cases at 21, 18 and 6 cm. The observing scheme also allowed the establishement of upper limits for the degree of circular polarization. The Owens Valley Radio Observatory 90' interferometer was used for these observations, and it operated with the many advantages of a crossed-feed interference polarimeter over a single-dish system. With the use of all available data, the Faraday rotation measures of 354 radio sources, mostly extragalactic, have been computed with careful attention to ambiguities and uncertainties; a novel quality grading system has been employed. These rotation measures constitute a powerful probe of the magnetic field structure and electron density of the local spiral arm. If the electrons in the local regions of the galaxy form a disk 200 pc in thickness and 2 kpc in radius , then there is a uniform linear component of the galactic field in the direction 1 = 94[degress] [...] 3[degrees], b = -8[degrees] [...] 8[degrees] with a strength of n[subscript e]B = 0.12 electrons-cm[superscript -3]-[mu]guass, or B = 2.0 [mu]gauss for n[subscript e] = 0.06 cm[superscript]-3. Distributions of the differences between this model and the actual rotation measures show that regions of magnetic loops and field reversals or electron concentrations of 100 to 200 pc in size have values of n[subscript e]B two to three times that of the average linear field of the model, implying a high degree of disorder. Most of the very large rotation measures seem to be produced by small scale structure in the galaxy, although a very few may be intrinsic to the source. The linear field model compares well with hydrogen line Zeem splitting, pulsar dispersion and rotation measures, and other magnetic field data. The apparent discrepancy with field structures given by stellar polarization can be resolved by differences in the distributions of electrons and dust and by the large-scale loops and field reversals. Searches for correlations between rotation measure and source type, depolarization, or redhsift have all led to negative results. The upper limit for a uniform, linear component of the intergalactic magnetic field, based on the failure of the last correlation, is n[subscript e]B < 2 x 10[superscript -13] cm[superscript -3] gauss.
Bibliographical Information:

Advisor:George A. Seielstad

School:California Institute of Technology

School Location:USA - California

Source Type:Master's Thesis



Date of Publication:04/03/1973

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