An infrared study of Centaurus A

We present J-, H- and K-band images and 0.9-2.51 mu m spectra of the nuclear regions of Centaurus A obtained with IRIS on the AAT. While the K-band image has a point source coincident with the nucleus, at H and J we identify diffuse structure extending to the northeast as a possible ionization cone. By considering the near-infrared colours, we show that the point-like K-band emission originates not from the nucleus itself, but from dust which has been shock-heated by nuclear outflows. A J - K image reveals a band of high extinction across the nucleus lying perpendicular to the radio jet axis, as suggested by previous authors. We model the detailed structure of this extinction image with a circumnuclear torus of diameter 240 +/- 20 pc, thickness 75 +/- 4 pc and tilt 80 degrees +/- 2 degrees to the line of sight, and with the torus and radio jet axes aligned.