A Radio Survey for Linear and Circular Polarization in Low-Luminosity Active Galactic Nuclei

We conducted a Very Large Array survey of eleven low luminosity activegalactic nuclei for linear and circular polarization at 8.4 GHz. We detectedcircular polarization in one source (M81*) and linear polarization in 3sources. Sensitivity limits were ~0.1% for both modes of polarization in 9 of11 sources. The detections confirm the importance of nonthermal emission inLLAGN. However, detection rates for circular and linear polarization are lowerfor these sources than for more powerful AGN. Fractional linear polarization indetected sources is also lower than in more powerful AGN. The weak linearpolarization in the survey sources indicates their overall similarity to SgrA*. Confusion with thermal sources, depolarization and weaker, less extendedjets may contribute to these differences. We detect a rotation measure >~ 7 x10^4 rad m^-2 for NGC 4579. This may arise from magnetized plasma in theaccretion, outflow or interstellar regions. Inverted spectra are present inboth M81* and Sagittarius A* and absent from all sources in which circularpolarization is not detected. This suggests that optical depth effects areimportant in the creation of circular polarization.Comment: 12 pages, 2 figures, accepted for publication in ApJ