Milliarcsecond Polarization Measurements of Compact Extragalactic Radio Sources

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AST 95-29228 PI: David Roberts Milliarcsecond Polarization Measurements of Compact Extragalactic Radio Sources Radio astronomy at centimeter wavelengths is used to study active galactic nuclei (AGN) on the very small scales. This is accomplished with Very Long Baseline Polarimetry, by which the linear polarization structure of compact radio sources may be determined on angular scales of milliarcseconds, corresponding to physical scales of light years at the distances of Active Galactic Nuclei (AGN). This high angular resolution allows changes in the structure of jets to be followed on moderate time scales (a year or less), and the polarimetry reveals the order and orientation of the magnetic field and allows study of the thermal particle environment around the heart of AGN. By observing at two or more wavelengths and using the Faraday effect, the emission line regions of AGN can be mapped out and interpreted in the framework of a model in which shock waves propagate in jets of highly relativistic plasma ejected from the active centers of AGN. The ultimate goal is to elaborate the mechanism that powers AGN, currently thought to be accretion onto massive black holes.