The Jet and Circumnuclear Environment of 3C 293

Abstract

We present new HST NIR polarimetry, broadband and narrowband imaging, and MERLIN 4.5 GHz multifrequency synthesis radio imaging of 3C 293, a unique radio galaxy whose host is an obvious merger remnant, in an exceptionally underdense region of space. We have discovered NIR, optical, and UV synchrotron emission from the jet. In the optical, the jet is mostly obscured by a dust lane, but three knots are clear in our HST NICMOS images at 1.6 and 2.0 μm, clearly aligning with features in the radio. The outer jet knot is highly polarized (~15%) at 2 μm, confirming the synchrotron emission mechanism. The radio-IR spectral index steepens significantly with distance from the nucleus, as in 3C 273 and in contrast to M87. The inner knot is visible (with hindsight) on the WFPC2 and STIS images obtained for the earlier 3CR HST snapshot surveys. There is no [Fe II] emission seen associated with the jet, constraining the role of shock-induced ionization by the jet. Overall there is a strong implication that the NIR jet emission is indeed synchrotron. From our NIR images, the core of the galaxy is clearly identifiable with the main feature in the western extension of the radio ``jet'' image, although no unresolved AGN component is identifiable even at K band, consistent with an FR II-like nucleus obscured by an optically thick torus. The galaxy appears to have a single nucleus, with any multiple nuclei falling within the central <~100 pc.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555.

Based on observations with MERLIN, a national facility operated by the University of Manchester on behalf of PPARC in the UK.