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R.T. Zavala (National Radio Astronomy Observatory, New Mexico State University), G.B. Taylor (National Radio Astronomy Observatory)
Multifrequency polarimetry with the VLBA can reveal the distribution of Faraday Rotation Measures (RM) within the central parsecs of radio galaxies. The RM is produced by the magnetic field strength along the line of sight weighted by the electron density. Using the electron density established through spectral line diagnostics a magnetic field strength and topology can be estimated within a few parsecs of the central engines of these AGN.
We present high-resolution (sub-milliarcsecond) Faraday Rotation Measure observations of the radio galaxies M87, 3C\,111, 3C\,120, and J2022+616. M87 has no detectable polarized emission in the core. However, within a projected distance from the core of ~ 1.2 pc RMs of -3000 to -4000 rad m-2 are seen. Likewise, 3C\,111 lacks polarized emission from the core but shows a detectable RM within a projected distance of 5 pc from the core. The RMs in 3C\,111 display a gradient which changes from -200 to -700 rad m-2 towards the core. Both M87 and 3C\,111 have less than 0.5 percent polarization in their central regions. The weak to nonexistent polarized emission in the cores, and detectable polarized emission and Faraday Rotation in the jets of these radio galaxies, appears consistent with the expectations for radio galaxies from unified schemes.
R.T.Z. gratefully acknowledges support from a pre-doctoral research appointment at NRAO and from the New Mexico Alliance for Graduate Education and the Professiorate through NSF grant HRD-0086701.
The author(s) of this abstract have provided an email address for comments about the abstract: rzavala@nrao.edu