VLBI Observations of Symmetric Parsec-Scale Twin Jets in the Narrow-Angle-Tail Radio Galaxy NGC 1265 (3C 83.1B)

We present global VLBI observations of the nucleus of the narrow-angle–tail radio galaxy NGC 1265. We report the discovery of symmetric parsec-scale twin jets which are well aligned with the kiloparsec-scale jets. We also present an archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) image of the galaxy, showing an apparently almost edge-on dust disk within 10° of perpendicular to the jet axis. The jets in NGC 1265 are consistent with either (1) relativistic motion near the plane of the sky, (2) nonrelativistic motion, or (3) a "coaxial" structure with a nonrelativistic sheath surrounding a relativistic spine. A study of the properties of the nine large-scale sources known so far with twin parsec-scale jets suggest that these sources are more likely to be nonrelativistic or only mildly relativistic. We also suggest that at least some sources with symmetric parsec-scale jets have been decelerated on the parsec scale, possibly through interaction with ambient gas or the shock at the sonic radius of a cooling flow. Other sources may be reborn compact symmetric object-type sources propagating out of the galaxy's nuclear interstellar medium. Further proper-motion studies of this class of source are needed.