MOJAVE: Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments. II. First-Epoch 15 GHz Circular Polarization Results

We report first-epoch circular polarization results for 133 active galacticnuclei in the MOJAVE program to monitor the structure and polarization of aflux limited sample of extra-galactic radio jets with the VLBA at 15 GHz. Wefound strong circular polarization ($\geq 0.3$%) in approximately 15% of oursample. The circular polarization was usually associated with jet cores;however, we did find a few strong jet components to be circularly polarized.The levels of circular polarization were typically in the range of $0.3-0.5$%of the local Stokes-$I$. We found no strong correlations between fractionalcircular polarization of jet cores and source type, redshift, EGRET detections,linear polarization, or other observed parsec-scale jet properties. There weredifferences between the circular-to-linear polarization ratios of two nearbygalaxies versus more distant quasars and BL Lac objects. We suggest this isbecause the more distant sources either have (1) less depolarization of theirlinear polarization, and/or (2) poorer effective linear resolution andtherefore their VLBA cores apparently contain a larger amount of linearlypolarized jet emission. The jet of 3C 84 shows a complex circular polarizationstructure, similar to observations by Homan & Wardle five years earlier;however, much of the circular polarization seems to have moved, consistent witha proper motion of 0.06$c$. The jet of 3C 273 also has several circularlypolarized components, and we find their fractional circular polarizationdecreases with distance from the core.Comment: 24 pages, accepted to appear in Astronomical Journa