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W.B. Sparks, S.A. Baum, J. Biretta, F. Macchetto (Space Telescope Science Institute), A. Martel (Johns Hopkins University)
We have been using the solar-blind near-UV detector of STIS on HST to obtain high resolution UV images of nearby radio galaxies. The images are spectacular, showing the hot, old population of the host elliptical galaxy, weakly, and in addition extraordinarily prominent complex sources of emission. The contrast of the synchrotron jet of 3C66B over the host is dramatically enhanced compared to high resolution optical observations, and the UV synchrotron jet can be seen extending fully from the galaxy nucleus to the edge of the field of view. We present a quantitative measure of the radio/optical/UV spectral index. 3C317 is a source of strong, diffuse X-ray emission (a "cooling-flow"), and shows a very narrow, irregular filament of UV emission along the radio axis, which has no optical counterpart in its WFPC2 image. 3C236 presents a complex series of UV emitting knots close to the host nucleus also aligned along the radio jet axis. These may be regions of ongoing star formation triggered by the jet.
The low redshift UV images were obtained in part to serve as a comparison for the high redshift optical images of radio galaxies which show extraordinary morphologies and strong alignment between optical and radio structures. Those images are rest-frame UV, and we do not know whether the differences arise because of evolutionary effects or because of the different wavelengths of observation. With our UV images at low redshift, we aim to address this issue.
Acknowledgement: Based on observations with the NASA/ESA Hubble Space Telescope which is operated by AURA, Inc. under NASA contract NAS 5-26555 and by STScI grant GO-08275.01-97A.