HST observations of Cygnus A: circumnuclear effects of a powerful jet ?

Abstract

We present 340nm continuum and [OII] line images of the nuclear region of the radio galaxy Cygnus A at 0".1 resolution. At this high resolution the northwestern of the two nuclear components is resolved into two separate, line emitting subcomponents, and the radio jet points accurately between them. This suggests that the radio jet has blasted a path through emission-line clouds, and that the emission line clouds, having cooled after the passage of the shock, are being photoionized by a (presumably hidden) central source or by the shock itself. We confirm previous detections of a small component at a location corresponding to the radio nuclear position and discuss the evidence for a possible bifurcation of the emission region on the unseen "counterjet" side.