Radio-Aligned Blue Lobes in the Nearby Radio Galaxy 3C 171

We have obtained U-band, I-band and X-ray images of the powerful, FR II, z=0.2384 radio galaxy, 3C 171, with the KPNO 4m telescope, the 2.5m Isaac Newton telescope, and the ROSAT High Resolution Imager. The U-band image shows lobe-like continuum features projected 11 arcsec in length straddling a bright, unresolved, central continuum source. At the redshift of 3C 171, the optical lobes have a linear extent of ~ 55 kpc (H_0=50 km s(-1) Mpc(-1) ; q_0=0). The radio jets and emission-line gas (Heckman \etal , 1984, ApJ, 286, 509) appear to be nearly coincident with the blue continuum lobes. Based on the I-band and X-ray images, 3C 171 does not appear to be associated with a rich cluster of galaxies, although we have not excluded its association with a poor cluster or group. These and other observations support the conclusion that strong radio-optical alignments can occur at low redshifts (zlae 0.2) in relatively isolated FR II radio galaxies, and in the cores of nearby rich clusters (zlae 0.1) along weaker, FR I radio sources (McNamara & O'Connell 1993, AJ, 105, 417; Sarazin et al. 1994, preprint). The mechanism for the blue lobe emission is not uniquely determined by the existing data. The morphologies of the radio and U-band emission are suggestive of either the scattering of collimated emission originating in the nucleus or light from young stars forming along the jet. If scattering is the mechanism then the absence of detectable X-ray emission may favor dust scattering rather than electron scattering. However, the V-band light is unpolarized, although a polarized component could be diluted to some degree by stellar continuum and emission lines (Tadhunter et al. 1992, MNRAS, 256, 53p). The lack of polarized emission (i.e. evidence for scattered light) together with the kinematic evidence for entrained gas along the lobes (Heckman \etal, 1984, ApJ, 286, 509) are consistent with radio-triggered star formation as the source of the optical lobe emission.