Optical Polarimetry of the Jets of Nearby Radio Galaxies. I. The Data

We present an overview of new HST imaging polarimetry of six nearby radiogalaxies with optical jets. These observations triple the number ofextragalactic jets with subarcsecond-resolution optical polarimetry. We discussthe polarization characteristics and optical morphology of each jet. We findevidence of high optical polarization, averaging 20%, but reaching upwards of$\sim 50%$ in some objects, confirming that the optical emission issynchrotron, and that the components of the magnetic fields perpendicular tothe line of sight are well ordered. We find a wide range of polarizationmorphologies, with each jet having a somewhat different relationship betweentotal intensity and polarized flux and the polarization position angle. We findtwo trends in all of these jets. First, jet ``edges'' are very often associatedwith high fractional optical polarizations, as also found in earlier radioobservations of these and other radio jets. In these regions, the magneticfield vectors appear to track the jet direction, even at bends, where we seeparticularly high fractional polarizations. This indicates a strong linkbetween the local magnetic field and jet dynamics. Second, optical flux maximumregions are usually well separated from maxima in fractional polarization andoften are associated with polarization minima. This trend is not found in radiodata and was found in our optical polarimetry of M87 with HST. However, unlikein M87, we do not find a general trend for near-90$^\circ$ rotations in theoptical polarization vectors near flux maxima. We discuss possibilities forinterpreting these trends, as well as implications for jet dynamics, magneticfield structure and particle acceleration.