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J. P. Leahy (U. Manchester/STScI), W. B. Sparks (STScI), N. J. F. Jackson (U. Manchester)
3C 293 is very unusual among radio galaxies in that it possesses a massive cold interstellar medium, visible in CO and optical line emission, HI absorption, and as a thick and complex dust lane. The galaxy is an excellent candidate for a merger between a massive elliptical and a late-type galaxy. It hosts a radio source displaying emission on several distinct scales, from an asymmetric outer structure 240 kpc across to a parsec-scale core. The radio structure is dominated by a distorted kiloparsec-scale double, clearly interacting strongly with the ISM. High resolution MERLIN images (Akujor et al. 1995) revealed a collimated jet on the eastern side.
We have discovered infrared and optical synchrotron emission from the jet. In the optical, the jet is mostly obscured by the dust lane, but it is clear in our new HST NICMOS images at 1.6, 1.8 and 2.0 microns. The outer jet knot (or hotspot) is very highly polarized at 2 microns, confirming the synchrotron mechanism. The jet consists of three bright knots nearly identical in relative separation and orientation to the brightest radio features in the jet. There is no sign of emission from the jet in the opposite lobe, despite the lower absorption on that side. The radio/IR spectral index steepens significantly with distance from the nucleus, as in 3C 273 and unlike M 87. The outer knot is visible (with hindsight) on the WFPC2 image obtained for the 3CR snapshot survey. We present the HST and new MERLIN radio images, and analyze the spectra of the jet knots in terms of synchrotron loss models.
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